JP2003007345A - Lithium secondary battery - Google Patents

Abstract

(57) [Problem] To improve the safety against overcharge of a lithium secondary battery using a lithium nickel composite oxide as a positive electrode active material. SOLUTION: A lithium secondary battery comprising a lithium secondary battery element 1 containing a lithium nickel composite oxide as a positive electrode active material and housed in cases 2 and 3. The specific surface area of the lithium nickel composite oxide is 0.1 to 10 m ² / g, and the surface area capacity ratio S / C which is the ratio of the battery surface area S (cm ² ) to the battery capacity C (mAh) is 0.05 to 5

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery in which a battery element using a lithium nickel composite oxide as a positive electrode active material is housed in a case. The present invention relates to a lithium secondary battery with improved safety during overcharge.

[0002]

2. Description of the Related Art A lithium secondary battery having a high energy density which has been developed in recent years (in this specification, "lithium secondary battery" may be simply referred to as "secondary battery" or "battery"). However, because of its high energy density, ensuring safety, especially safety against overcharging, is important. The reason is as follows.

That is, when charging a lithium secondary battery,
When a current or voltage higher than a predetermined value is applied or a capacity higher than a predetermined value is charged for some reason, the lithium secondary battery is overcharged. As a result, the positive electrode active material or the negative electrode active material, which is a material forming the lithium secondary battery, becomes chemically unstable, or an internal short circuit between the electrodes occurs, which causes the battery temperature. There is a high possibility that an excessive rise in In fact, in a lithium secondary battery, when it is in an overcharged state, gas may be generated due to decomposition of an electrolytic solution or the like. This gas generation not only makes the battery liable to burst, leaks, etc., but if this state continues, the battery temperature may eventually rise excessively, and the battery may ignite or explode.

For this reason, various studies have heretofore been made on measures for preventing overcharge, and the following measures have been proposed. An electronic circuit (safety circuit) attached to the outside of the battery controls the charging current when the battery becomes dangerous in an overcharged state. A method of shutting off the charging current by using the gas generated by the decomposition of the electrolyte during overcharging to increase the internal pressure of the battery and mechanically operating the safety valve. Utilizing the melting of the separator due to the temperature rise of the battery,
A method of blocking the charging current by closing the pores of the separator. By adding an organic additive having an oxidation potential that is nobler than the positive electrode potential at full charge to the electrolytic solution, when the positive electrode potential rises in an overcharged state, an oxidation reaction of the organic additive is caused to cause overcharge. Method to control the runaway reaction in the battery at the time.

By the way, as a technique for improving the structure of secondary batteries, in recent years, a flat case is constructed by using a lightweight exterior material such as a laminate film in which resin layers are provided on both sides of a gas barrier layer. Batteries of the type in which a battery element having a positive electrode and a negative electrode inside is sealed have been developed in the field of lithium secondary batteries. Since such a battery uses a lightweight film as an exterior material, the battery can be made lighter and smaller than a battery using a conventional metal case, and the case configuration is simple. Therefore, it is advantageous in terms of cost.

Among the secondary batteries, particularly as a technique for improving the material side of lithium secondary batteries, lithium nickel composite oxides such as lithium nickel oxide having a layered structure of LiNiO ₂ as a basic composition have been conventionally used as lithium secondary batteries. It is attracting attention as a high-capacity material that replaces LiCoO ₂ that has been used as a positive electrode active material for secondary batteries.

[0007]

Among the means for ensuring the safety of the battery at the time of overcharging mentioned above,
The control method using a safety circuit and the mechanical current cutoff method using a safety valve have the problems that the cost of the battery rises and restrictions on the design of the battery occur because the electronic circuit and the safety valve must be mounted on the battery. . In particular, in the battery of the type in which the battery element is hermetically sealed in the flat plate case using the above-mentioned laminate film, the above-mentioned safety circuit and safety valve are difficult to attach because the laminate film has a variable shape.

Further, in the above-mentioned method of melting the separator to cut off the charging current, since the runaway reaction at the time of overcharging is rapid, the melting of the separator cannot be done in time, and the safety at the time of overcharging is sufficient. In some cases, it cannot be secured. Further, from the viewpoint of liquid retention, when a gel electrolyte that is a non-fluidic electrolyte is used as the electrolyte of the lithium secondary battery, the gel electrolyte impregnated in the pores of the separator inhibits pore clogging due to melting of the separator. Therefore, the cutoff of the charging current may be incomplete. In addition, in the method of controlling the runaway reaction in the battery during overcharge by adding the overcharge inhibitor such as the organic additives mentioned above to the electrolytic solution, the overcharge prevention that is not directly involved in the charging and discharging of ordinary batteries is prevented. The addition of the agent to the electrolytic solution may adversely affect the battery performance other than the overcharge characteristics. Further, gas is generated as a result of the oxidation reaction of the overcharge inhibitor during overcharge, and there is concern that the generated gas may corrode the equipment used or leak toxic gas such as organic gas.

In this way, as a safety measure during overcharge,
No fully satisfactory technology has yet been provided. on the other hand,
In a lithium secondary battery using a lithium nickel composite oxide, which is attracting attention as a high-capacity positive electrode active material for a lithium secondary battery, the surface of the lithium nickel composite oxide existing in a particle state in the positive electrode has high reactivity. As a result, there is a tendency that the safety and the like at the time of overcharge are relatively reduced.

Therefore, in a lithium secondary battery using a lithium nickel composite oxide as a positive electrode active material, it is desired to develop a more reliable safety measure during overcharge.

Furthermore, in recent years, as a lithium secondary battery has been used as a power source for devices carried by humans such as mobile phones, higher safety has been demanded of the battery. Further, there is a demand for cost reduction by simplifying a safety valve or a safety circuit, and it is strongly desired to improve the intrinsic safety of the lithium secondary battery itself.

The present invention has been made in view of the above conventional circumstances, and an object thereof is a lithium secondary battery using a lithium nickel composite oxide as a positive electrode active material, which is further improved in safety against overcharge. It is to provide a lithium secondary battery.

[0013]

Means for Solving the Problems As a result of intensive studies for achieving the above object, the present inventors have made the assumption that a lithium nickel composite oxide having a specific specific surface area is used, and in this case, lithium The present invention has been completed by finding that the safety during overcharge is improved by setting the value of the surface area per capacity of the secondary battery within a predetermined range. That is, the gist of the present invention is a lithium secondary battery in which a lithium secondary battery element containing a lithium nickel composite oxide containing lithium and nickel as a positive electrode active material is housed in a case. Has a specific surface area of 0.1 to 10 m ² / g, and a battery surface area S (c
m ² ) and the battery capacity C (mAh), which is a lithium secondary battery having a surface area capacity ratio S / C of 0.05 to 5.

The battery surface area (S) and battery capacity (C) in the present invention are as defined below.

[Battery surface area (S)] The battery surface area S means the surface area on the outside of the case that houses the battery element. That is, for example, when a laminate film in which a gas barrier layer and a resin layer are laminated is used as the case, it indicates the surface area of the laminate film, and when a metal case is used as the case, it indicates the surface area of the metal portion. .

In the battery case, not all the parts thereof contribute to heat dissipation, and for example, the joining piece portion at the peripheral portion of the exterior material, which will be described later, contributes little to heat dissipation. However, in a battery, the ratio of such a joint piece to the total surface area is generally small. Therefore, the surface area of the entire outside of the case is used as the battery surface area S, which is used as a criterion for the safety during overcharge. be able to.

[Battery capacity (C)] Battery capacity is 4.2 V
It is the maximum capacity that can be taken out when discharged from 3 to 3.0V. Specifically, 10 from a fully charged state of 4.2V
It is the discharge capacity obtained when discharging to 3.0 V at a current value such that the time becomes 3.0 V.

The full charge state of the battery is usually 4.2.
Constant current charging at 1 CmA until reaching V, then 1
Change in charging current value Ic over time: dIc / dt is 1
It can be obtained by performing constant voltage charging at 4.2V until it becomes within 0%. The constant voltage charging will be described in more detail. When the charging current at time (t) is XmA, when the charging current after 1 hour (t + 1 hour) becomes larger than 0.9XmA, charging is performed. Will end.

As mentioned above, the lithium nickel composite oxide exists in the form of particles in the positive electrode. And, this particulate lithium-nickel composite oxide (in the present invention, the particulate lithium-nickel composite oxide may be simply referred to as lithium-nickel composite oxide) has high reactivity on the particle surface, As a result, it has been said that there is a problem in safety during overcharge. Therefore, in order to improve safety during overcharge, it has been considered that it is better to reduce the specific surface area of the lithium nickel composite oxide as much as possible to suppress the reactivity during overcharge. On the other hand, reducing the specific surface area of the lithium nickel composite oxide tends to deteriorate battery characteristics such as charge / discharge characteristics (rate characteristics) at high current values. The problem derived from the specific surface area has been one of the causes of impeding the practical use of lithium secondary batteries using a lithium nickel composite oxide.

In the present invention, the lithium nickel composite oxide is completely different from the conventional technical idea in which the specific surface area of such a lithium nickel composite oxide is reduced to lower the reactivity during overcharge. On the contrary, the high surface reactivity of is used to secure the safety of the lithium secondary battery itself during overcharge.

That is, when a reaction occurs on the surface of the lithium-nickel composite oxide during overcharge, the surface of the lithium-nickel composite oxide changes from its original state and is deactivated. When the surface of the lithium-nickel composite oxide is deactivated in this way, the portion of the non-deactivated lithium-nickel composite oxide existing inside the lithium-nickel composite oxide becomes inactive without causing a decomposition reaction. , Runaway reaction does not occur. Therefore, the reaction on the surface of the lithium nickel composite oxide is suppressed along with the deactivation on the surface of the lithium nickel composite oxide, and the inactive lithium nickel composite oxide portion existing inside the particles increases. Therefore, the lithium secondary battery is in a safe state. In this case, the deactivated portion has a reduced reactivity and does not participate in the runaway reaction, so that the more the deactivated portion, the higher the safety of the battery. Since the deactivation of the lithium-nickel composite oxide proceeds by the reaction on the surface of the particulate lithium-nickel composite oxide, the deactivation of the lithium-nickel composite oxide with a larger specific surface area is different from the conventional idea. Since the ratio of the portion to be charged increases, the battery is likely to shift to a safer state.

However, reaction heat is generated due to deactivation of the surface of the lithium nickel composite oxide. For this reason,
If the rate of generation of this reaction heat becomes too fast, the rise in battery temperature due to the above-mentioned reaction heat will become large, causing a runaway reaction during overcharge. In the present invention, even when the reaction heat is large, the surface area of the entire lithium secondary battery is relatively large with respect to the capacity of the lithium secondary battery, so that heat dissipation of the reaction heat is promoted. Therefore, the runaway reaction of the battery can be suppressed.

That is, in the present invention, by using the lithium nickel composite oxide having a specific surface area, the lithium nickel composite oxide is positively deactivated at the time of overcharge, and the lithium secondary battery is quickly and safely protected. By setting the ratio of the surface area to the capacity of the lithium secondary battery while maintaining the above state, the heat of reaction generated by the deactivation is efficiently released, and the safety of the lithium secondary battery during overcharging is further ensured. It can be secured.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION A lithium secondary battery according to the present invention is a lithium secondary battery in which a lithium secondary battery element having a lithium nickel composite oxide containing lithium and nickel as a positive electrode active material is housed in a case. In the battery, the specific surface area of the lithium nickel composite oxide is 0.1 to 10 m ² /
g, and the battery surface area S (cm ² ) and the battery capacity C
Surface area capacity ratio S / C, which is the ratio with (mAh), is 0.05
~ 5.

By using such a lithium secondary battery, the surface of the lithium-nickel composite oxide is positively deactivated while keeping the temperature rise at the time of overcharge low, and the battery is surely brought into a safe state. You will be able to.

In the present invention, if the specific surface area of the lithium nickel composite oxide is too large, the battery capacity will decrease. In addition, the increase in viscosity when made into a coating causes difficulties in the manufacturing process. If it is too small, the battery performance such as rate characteristics and cycle characteristics tends to be deteriorated. Therefore, the specific surface area is 0.1 m ² / g or more, preferably 0.5
m ² / g or more, more preferably 1 m ² / g or more,
On the other hand, 10 m ² / g or less, preferably 5 m ² / g or less,
It is more preferably 3 m ² / g or less. By setting the specific surface area within the above range, it is possible to positively cause deactivation on the surface of the lithium-nickel composite oxide during overcharge, while maintaining good battery performance, workability during manufacturing, and the like.
The specific surface area is measured according to the BET method.

In the present invention, a lithium nickel composite oxide is used as the positive electrode active material.

The lithium-nickel composite oxide is an oxide containing at least lithium, nickel and oxygen. The lithium nickel composite oxide has a large current capacity per unit weight, and is a very useful positive electrode material from the viewpoint of high capacity. As the lithium nickel composite oxide,
LiNi having a layered structure such as α-NaCrO ₂ structure
A lithium nickel composite oxide such as O ₂ is preferred.
As a specific composition, for example, LiNiO ₂ , Li ₂ N
Examples thereof include iO ₂ and LiNiO ₄ , and preferably LiNiO ₂ .

The lithium-nickel composite oxide according to the present invention may have a lithium site or a part of the nickel site replaced with another element. By performing such element substitution, the stability of the crystal structure is improved, the diffusion of Li is facilitated, and the discharge characteristics, capacity characteristics, high temperature characteristics, and overcharge characteristics can be improved. In particular, the lithium nickel composite oxide is preferably one in which some of the sites occupied by Ni are replaced with an element other than Ni. By substituting a part of the Ni site with another element, the stability of the crystal structure can be improved, and a part of the Ni element moves repeatedly to the Li site during repeated charge / discharge, resulting in a capacity decrease. Since it is suppressed, the cycle characteristics are also improved. Furthermore, by substituting a part of the Ni site with an element other than Ni, the runaway reaction of the lithium-nickel composite oxide when the temperature of the battery rises is suppressed, resulting in an improvement in safety.

The elements to be substituted (hereinafter referred to as "substitution elements") are F, P, S, Al, Ti, V, Cr,
Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, G
One or two or more of a, Zr and the like can be mentioned, preferably Al, Cr, Fe, Co, Li, Ni, Mg and Ga, and more preferably Co and Al. Part of Ni element is C
By substituting with o or Al, the effect of improving cycle characteristics and safety becomes large. Of course, the Ni site and the Li site may be substituted with two or more other elements.

The substitution ratio by the substituting element is usually 2.5 mol% or more, preferably 5 mol% or more of the base element, and usually 50 mol% or less, preferably 30 mol% or less of the base element. , And more preferably 20 mol%
It is the following. If this substitution ratio is too small, the effect of improving the characteristics such as cycle characteristics may not be sufficient, and if it is too large, the battery capacity may decrease.

The lithium-nickel composite oxide may have a small amount of oxygen deficiency and nonstoichiometry. Further, part of the oxygen site may be replaced with sulfur or a halogen element.

In the present invention, a particularly preferable lithium nickel composite oxide is represented by the general formula Li _α Ni _X Co _Y Al _Z.
It is represented by O ₂ . That is, a lithium nickel composite oxide in which a part of the Ni site is replaced with Co and / or Al is particularly preferable. When a part of the Ni site is replaced with Co, the crystal structure is stabilized, and as a result, cycle characteristics can be improved. There is also an advantage that manufacturing control becomes easy. Further, when a part of the Ni site is replaced with Al, the crystal structure is stabilized as in the case where Co is replaced with Co. By substituting with Al, the effect of stabilizing the crystal structure becomes higher than that of Co, but the degree of capacity decrease becomes large. Formula Li _α Ni _X Co _Y Al _Z in alpha, X, Y, normal range for Z, preferred range,
More preferable ranges are as follows (provided that X + Y
+ Z is 0.9 to 1.1, preferably 1. ).

[0034]

[Table 1]

The average secondary particle size of the lithium nickel composite oxide is usually 0.1 μm or more, preferably 0.2 μm.
m or more, more preferably 0.3 μm or more, most preferably 0.5 μm or more, usually 300 μm or less, preferably 100 μm or less, more preferably 50 μm or less, most preferably 20 μm or less. If this average particle size is too small, the cycle deterioration of the battery may become large, and if it is too large, the internal resistance of the battery may become large, and it may be difficult to output power.

In the present invention, as the positive electrode active material, other positive electrode active material may be used in combination with such a lithium nickel composite oxide. Examples of the combination method include mixing of independent particles, coexistence in agglomerated particles, and multi-layered particles having one core as a core and the other as a coating. Among these, a mixture of independent particles and a multilayer structure particle are particularly preferable. From the viewpoint of capacity, the mixing ratio is preferably such that the proportion of the lithium nickel composite oxide is 50% by weight or more of the whole positive electrode active material.

Positive used in combination with lithium nickel composite oxide
As the active material, transition metal oxide, lithium nickel
Complex oxides of lithium and transition metals other than complex oxides,
Examples include various inorganic compounds such as transition metal sulfides. here
As the transition metal, Fe, Co, Ni, Mn, etc. are used.
To be As the transition metal oxide, specifically, Mn
O, V₂ O_Five , V₆ O₁₃, TiO₂ Such as powder
You can In addition, other than lithium nickel composite oxide
As the composite oxide of lithium and transition metal,
Is a lithium cobalt composite oxide, lithium manganese composite oxide
Powders such as compound oxides can be mentioned. Furthermore, the transition
As the metal sulfide, specifically, TiS ₂ , FeS,
MoS₂ And the like. A combination of these
The material was partially elementally substituted to improve its properties.
It may be one. In addition, polyaniline, poly pillow
, Polyacene, disulfide compounds, polysulfi
Organic compounds such as dope compounds and N-fluoropyridinium salts
It is also possible to use a thing. These inorganic compounds, organized
You may mix and use a compound.

The particle size of the positive electrode active material used in combination with the lithium nickel composite oxide is usually 1 to 30 μm, preferably 1 to 10 μm. If the particle size is too large or too small, battery characteristics such as rate characteristics and cycle characteristics tend to deteriorate.

Of these positive electrode active materials, the preferred one is
It is a composite oxide of lithium and a transition metal other than the lithium nickel composite oxide, and specifically, a lithium cobalt composite oxide such as LiCoO ₂ or a lithium manganese composite oxide such as LiMn ₂ O ₄ .

It is more preferable to use a lithium cobalt composite oxide as the positive electrode active material used together with the lithium nickel composite oxide. Lithium-cobalt composite oxide is a highly safe material, although its capacity is inferior to that of lithium-nickel composite oxide. Therefore, by using it together with lithium-nickel composite oxide, the battery capacity and safety during overcharge can be improved. You will be able to maintain a good balance.

The lithium-cobalt composite oxide is a useful positive electrode active material excellent in rate characteristics because it has a flat discharge curve. Examples of the lithium-cobalt composite oxide include LiCoO ₂ having a layered structure. The lithium-cobalt composite oxide may be one in which some of the sites occupied by Co are replaced with an element other than Co. By substituting the Co site with another element, the cycle characteristics and rate characteristics of the battery may be improved. When substituting part of the site occupied by Co with an element other than Co, the substituting elements include Al, Ti, V, and C.
r, Mn, Fe, Li, Ni, Cu, Zn, Mg, G
a, Zr, Sn, Sb, Ge and the like, and preferably Al, Cr, Fe, Li, Ni, Mg, Ga, Zr, S.
n, Sb, Ge, more preferably Al, Mg, Zr, S
n. The Co site may be substituted with two or more other elements.

When substituting the Co site with the substituting element, the proportion thereof is usually 0.03 mol% or more, preferably 0.05 mol% or more of the Co element, and usually 3% of the Co element.
It is 0 mol% or less, preferably 20 mol% or less. If the substitution ratio is too small, the stability of the crystal structure may not be sufficiently improved, and if it is too large, the capacity of the battery may decrease.

The lithium-cobalt composite oxide is usually represented by LiCoO ₂ as a basic composition before charging,
As described above, part of the Co site may be replaced with another element. In the above composition formula, a small amount of oxygen deficiency,
It may have indefiniteness, and a part of the oxygen site may be replaced with sulfur or a halogen element. Furthermore, in the above composition formula, the amount of lithium can be made excessive or insufficient.

Specific surface area of lithium cobalt composite oxide
Is usually 0.01 m^Two/ G or more, preferably 0.1 m^Two
/ G or more, more preferably 0.4 m^Two/ G or more,
Also usually 10m^Two/ G or less, preferably 5.0 m^Two/ G
Below, more preferably 2.0 m ^Two/ G or less. Ratio table
If the area is too small, the rate characteristics will deteriorate, and in some cases
May lead to a decrease in capacity, and if it is too large, it may be
It causes unfavorable reactions and deteriorates cycle characteristics.
Sometimes. The specific surface area is measured according to the BET method.

The average particle size of the lithium cobalt composite oxide is usually 0.1 μm or more, preferably 0.2 μm or more,
More preferably 0.3 μm or more, most preferably 0.
5 μm or more, usually 300 μm or less, preferably 1
The thickness is 00 μm or less, more preferably 50 μm or less, and most preferably 20 μm or less. If the average particle size is too small, the cycle deterioration of the battery may be large, or a safety problem may occur. If the average particle size is too large, the internal resistance of the battery may be large and the output may be difficult to output.

Materials other than the positive electrode active material that form the positive electrode and other materials that form the lithium secondary battery will be described later.

In the present invention, the ratio S / C between the battery surface area S and the battery capacity C of the lithium secondary battery is controlled within a predetermined range. That is, if the S / C is too small, a sufficient amount of heat cannot be obtained with respect to the generation of reaction heat due to the deactivation of the surface of the lithium nickel composite oxide, and the safety at the time of overcharging is reduced. On the other hand, if the S / C is too large, the energy density capacity of the battery decreases. Therefore, the surface area capacity ratio S / C is
0.05 or more, preferably 0.1 or more, particularly preferably 0.2 or more, while 5 or less, preferably 2 or less, more preferably 1.7 or less, particularly preferably 1 or less, most preferably 0.85. Below. If the surface area capacity ratio S / C is controlled within the above range, the safety at the time of overcharging can be ensured without lowering the energy density capacity of the battery.

Battery capacity C of the lithium secondary battery of the present invention
Is usually 1 mAh or more, preferably 10 mAh or more,
On the other hand, it is usually 10 Ah or less, preferably 2000 mAh or less, more preferably 1200 mAh or less, further preferably 1000 mAh or less, particularly preferably 500 mAh.
It is the following. If the battery capacity C is too small, the usability of the lithium secondary battery in actual use becomes poor. On the other hand, if the battery capacity C is too large, overcharging may not be able to be suppressed depending on the case when the current is unevenly distributed due to the influence of electrode variations and the like. Further, when the capacity is large, the degree of danger (for example, the degree of explosion or ignition) in the event of a runaway increases due to the large capacity. However, basically, there is no particular limitation on the battery capacity C, and even when the battery capacity C is large, the safety at the time of overcharging can be sufficiently ensured by increasing the battery surface area S. That is, in the present invention, since the ratio of the battery surface area S that contributes to heat dissipation with respect to the battery capacity C is specified, it is effective for a lithium secondary battery of any battery capacity C.

Particularly preferable in the lithium secondary battery of the present invention is that the lithium secondary battery has a battery capacity C suitable for use in a portable electric device in which safety is particularly important.

Battery surface area S of the lithium secondary battery of the present invention
Is set within a range of a predetermined surface area capacity ratio S / C with respect to the battery capacity C of the lithium secondary battery. The battery surface area S is usually 1 cm ² or more, preferably 10 cm
² or more, whereas generally 10000 cm ² or less, preferably 1000 cm ² or less, more preferably 200 cm ² or less, more preferably 100 cm ² or less, particularly preferably 60cm ² or less. When the battery surface area S is within the above range, heat dissipation can be sufficiently ensured in practical use, which is preferable.

Next, the materials constituting the positive electrode other than the positive electrode active material and the other materials constituting the lithium secondary battery will be described using the preferred embodiment of the lithium secondary battery of the present invention.

First, a specific structure of the lithium secondary battery of the present invention will be described with reference to FIGS.

FIG. 1 is an exploded perspective view of a battery according to an embodiment, FIG. 2 is a cross-sectional view of a main part of this battery, FIG. 3 is a schematic perspective view of a battery element, and FIGS. 4 and 5 are perspective views of the battery. Is. For convenience of explanation, the battery shown in FIG. 1 is shown upside down in FIGS. 4 and 5.

The lithium secondary battery has a lithium secondary battery element (which may be simply referred to as a “battery element” in this specification) 1 accommodated in a recess (accommodation portion 3b) of the exterior material 3 and then the exterior. The exterior material 3 is covered with the material 2, and the peripheral portions 2a and 3a of the exterior materials 2 and 3 are joined by vacuum sealing. A case in which the exterior material 2 and the exterior material 3 are joined together forms a case for housing the battery element 1.

As shown in FIG. 1, the exterior material 2 has a flat plate shape. The exterior material 3 is a shallow lidless box shape having a housing portion 3b formed of a rectangular box-shaped recess and a peripheral edge portion 3a protruding outward in a flange shape from four peripheral edges of the housing portion 3b.

As shown in FIG. 3, the battery element 1 is a stack of a plurality of unit battery elements. The tab 4a or 4b is pulled out from this unit battery element. The tabs 4a from the positive electrode are bundled (that is, superposed on each other), and the positive electrode lead 21 is joined to form a positive electrode terminal portion. The tabs 4b from the negative electrode are also bundled, and the negative electrode lead 21 is joined to form the negative electrode terminal portion.

The battery element 1 is accommodated in the accommodating portion 3b of the exterior material 3, and the exterior material 2 is covered. The pair of leads 21 extending from the battery element 1 are drawn to the outside through the mating surfaces of the peripheral portions 2a and 3a of one side of the exterior materials 2 and 3, respectively. After that, in a reduced pressure (preferably vacuum) atmosphere, the four peripheral edges 2a, 3a of the outer packaging materials 2, 3 are airtightly joined together by a method such as thermocompression bonding, and the battery element 1 is enclosed in the outer packaging materials 2, 3. To be done.

By joining the peripheral edge portions 2a and 3a to each other, a case composed of the exterior materials 2 and 3 is formed. Figure 4
As shown in FIG. 3, this case has a side wall portion 4B ₁ and an upper bottom portion 4B.
₂ and a lower bottom portion (not shown) that encloses the battery element 1 and has a substantially rectangular parallelepiped encapsulation portion 4B, and joining piece portions 4A and 4A in which the peripheral portions 2a and 3a of the exterior material are joined together. ，
It has 4F and 4G.

In the state shown in FIG. 4, the joining piece portions 4A, 4A, 4F and 4G project outward from the side wall portion 4B ₁ of the encapsulating portion 4B enclosing the battery element 1. . Therefore, as shown in FIG. 5, among these joining piece portions, the joining piece portions 4A, 4A, and 4G are the side wall portions 4 of the encapsulating portion 4B.
Bent along the B _1, and fixed fastened to the side wall portion 4B ₁ of the encapsulated portion 4B by an adhesive or an adhesive tape (not shown) or the like.

In the present invention, the joining piece portion 4
The ratio of A, 4A, 4F, 4G in the battery surface area S is
It is usually 1% or more and 50% or less, preferably 30% or less, and more preferably 15% or less. If this ratio is too large, the capacity of the battery tends to decrease, and if it is too small, gas may penetrate into the case and the hermeticity of the case may deteriorate.

In FIG. 1, the exterior materials 2 and 3 are separate bodies, but in the present invention, the exterior materials 2 and 3 may be integrally formed as shown in FIG. In FIG. 6, one side of the exterior material 3 and one side of the exterior material 2 are connected to each other, and the exterior material 2 has a lid shape that is connected to the exterior material 3 in a bendable manner. The concave portion of the housing portion 3b is formed from one side where the exterior materials 2 and 3 are continuous,
This one side has the same structure as the joining piece portion except that the joining piece portion is not formed. And what joined these exterior materials 2 and 3 becomes a case which stores battery element 1.

1 and 6, the exterior material 3 having the accommodation portion 3b and the flat exterior material 2 are shown, but in the present invention, as shown in FIG. 7, each is a shallow box-shaped accommodation portion. 6b, 7b
And the peripheral edge portion 6 protruding from the four peripheral edges of the accommodating portions 6b and 7b.
The battery element 1 may be encapsulated by the exterior materials 6 and 7 having a and 7a. In FIG. 7, the exterior materials 6 and 7 are integrally formed, but they may be separate bodies as in the case of FIG. And what joined these exterior materials 6 and 7 becomes a case which stores battery element 1.

In the present invention, as shown in FIG. 8, the battery element 1 is interposed between the two flat sheet-like exterior materials 8A and 8B, and the peripheral edge portion 8a of the exterior material 8A and the exterior material are arranged as shown in FIG. 8B
The battery element 1 may be enclosed by joining it to the peripheral edge portion 8b. In this case, a case in which the exterior material 8A and the exterior material 8B are joined together becomes a case for housing the battery element 1.

As shown in FIG. 5, in this embodiment, since the bent joint piece portion is arranged along the encapsulation portion and fixed with an adhesive or an adhesive tape, the battery High side strength and rigidity. Of course, it is also prevented that the bent joint piece part separates from the envelope part. Also, since the side surface of the battery has high strength and rigidity, even if a side surface is impacted,
Peeling of the active material is prevented.

The battery of the present invention also has a structure as shown in FIG.
One long sheet-shaped exterior material 9 is wrapped with the leads 21 being drawn out so as to be wound around the battery element, and both ends 9A and 9B of the exterior material 9 are overlapped and folded back. 9C may be fixed with an adhesive or an adhesive tape.
Then, by fixing the folded-back portion 9C, a case made of the exterior material 9 is formed.

In any of the batteries described above, a high moisture permeation-preventing effect can be obtained by using a laminated film in which a gas barrier layer and a resin layer are directly laminated without an adhesive layer as an exterior material used for a case. Can
The battery performance of the internal non-aqueous battery element can be stably maintained for a long period of time.

In any structure, the ratio of the area of the joining piece or the folded portion of the battery case is usually 1% or more and 50% or less, preferably 30%, with respect to the battery surface area S for the above-mentioned reason. It is preferably 20% or less, more preferably 20% or less, and particularly preferably 15% or less. In addition, below, the area ratio of the joining piece of a case with respect to the battery surface area S may be called "joining piece area ratio."

Next, the structure of the lithium secondary battery element will be described with reference to FIGS.

FIG. 11 shows a preferred example of the unit battery element of this lithium secondary battery element. This unit cell element includes a positive electrode current collector 22, a positive electrode active material layer 23, a spacer (electrolyte layer) 24, a negative electrode active material layer 25, and a negative electrode current collector 2.
6 is laminated.

In a preferred embodiment of the present invention, a plurality of unit battery elements shown in FIG. 11 are laminated to form a lithium secondary battery element.
Alternately, a unit cell element in a forward posture (Fig. 11) in which the positive electrode is on the upper side and a negative electrode is in the lower side and a unit cell element in a reverse posture (not shown) in which the positive electrode is on the lower side and the negative electrode is on the upper side To stack. That is, the unit battery elements adjacent in the stacking direction are stacked so that the same poles (that is, positive electrodes and negative electrodes) face each other.

A positive electrode tab 4a extends from the positive electrode collector 22 of this unit battery element, and a negative electrode tab 4b extends from the negative electrode collector 26.

Instead of the unit cell element in which the positive electrode active material layer, the spacer and the negative electrode active material layer are laminated between the positive electrode current collector and the negative electrode current collector as shown in FIG. 11, as shown in FIG. A positive electrode 31 and a negative electrode 32 are prepared by stacking a positive electrode active material layer 31a or a negative electrode active material layer 32a on both surfaces of the current collector 35a or the negative electrode current collector 35b as a core material.
And the negative electrode 32 as shown in FIG. 13 with a spacer (electrolyte layer) 33.
Alternatively, they may be alternately laminated to form a unit battery element. In this case, the combination of the pair of positive electrode 31 and negative electrode 32 (strictly speaking, from the center in the thickness direction of the current collector 35a of the positive electrode 31 to the center in the thickness direction of the current collector 35b of the negative electrode 32) is the unit cell element. Equivalent to.

Various metals such as aluminum, nickel and SUS can be used as the positive electrode current collectors 35a and 22, but aluminum is preferable.

On the other hand, as the negative electrode current collectors 35b and 26,
Various metals such as copper, nickel and SUS can be used, but copper is preferable.

A positive electrode current collector and a negative electrode current collector (in this specification, the “positive electrode current collector” and the “negative electrode current collector” may be simply referred to as “current collector”). The thickness is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and is usually 30 μm or less, preferably 25 μm or less, more preferably 20 μm or less. The thinner the current collector, the more preferable from the viewpoint of volume energy density and weight energy density. However, if the current collector is too thin, handling tends to be difficult in terms of strength and the like. The current collector may have a plate shape like a normal metal foil or a mesh shape like a punching metal. The surface of the current collector can be roughened if necessary.

The positive electrode active material layer and the negative electrode active material layer (in this specification, the “positive electrode active material layer” and the “negative electrode active material layer” may be simply referred to as “active material layer”). Each contains a positive electrode active material or a negative electrode active material (in this specification, the “positive electrode active material” and the “negative electrode active material” may be simply referred to as “active material”). Examples of other materials contained in the active material layer include a binder and a conductive material.

The positive electrode active material is as described above.

As the active material that can be used for the negative electrode, in addition to lithium metal, various compounds capable of inserting and extracting lithium can be used. Specific examples include lithium metal; lithium alloys such as lithium-aluminum alloys, lithium-bismuth-cadmium alloys and lithium-tin-cadmium alloys; carbon materials such as graphite and coke. Further, oxides of silicon, tin, zinc, manganese, iron, nickel and the like, and lead sulfate can also be used. When a lithium metal or a lithium alloy is used, dendrites are likely to be generated during charging and the safety particularly during overcharging tends to be lowered, and therefore carbon materials such as graphite and coke are preferable. The average particle size of the negative electrode active material is usually 1 to 50 μm, preferably 15 to 30 μm in terms of battery characteristics such as initial efficiency, rate characteristics and cycle characteristics.

A binder is preferably used to bind the positive electrode active material and the negative electrode active material onto the current collector. The binder to be used needs to be stable with respect to the electrolytic solution and the like, and weather resistance, chemical resistance, heat resistance, flame resistance, etc. are desired. As the binder, inorganic compounds such as silicate and glass, and various resins mainly composed of polymers can be used. As the resin, for example,
Alkane-based polymers such as polyethylene, polypropylene and poly-1,1-dimethylethylene; unsaturated polymers such as polybutadiene and polyisoprene; polymers having rings such as polystyrene, polymethylstyrene, polyvinylpyridine and poly-N-vinylpyrrolidone (Meth) acrylic polymers such as polymethylmethacrylate, polyethylmethacrylate, polybutylmethacrylate, polymethylacrylate, polyethylacrylate, polyacrylic acid, polymethacrylic acid, and polyacrylamide;
Fluorine-based resins such as polyvinyl fluoride, polyvinylidene fluoride and polytetrafluoroethylene; CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide; polyvinyl alcohol-based polymers such as polyvinyl acetate and polyvinyl alcohol; polyvinyl chloride and poly A halogen-containing polymer such as vinylidene chloride; a conductive polymer such as polyaniline can be used. Further, a mixture of the above polymers, a modified product, a derivative, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer and the like can also be used. The molecular weight of these resins is preferably 10,000 to 3,000,000, more preferably 100,000 to 1,000,000. If the molecular weight is smaller than this range, the strength of the active material layer is lowered, and if it is too large, the viscosity tends to be high, which makes it difficult to form an electrode.

The blending amount of the binder with respect to 100 parts by weight of the active material is preferably 0.1 to 30 parts by weight, more preferably 1 to 20 parts by weight. If the amount of the binder is too small, the strength of the electrode may decrease, and if it is too large, the capacity tends to decrease and the ionic conductivity tends to decrease.

In the positive electrode active material layer and the negative electrode active material layer, if necessary, an additive such as a conductive material and a reinforcing material exhibiting various functions, a powder, a filler and the like may be added.

The conductive material is not particularly limited as long as it can be mixed with the above active material in an appropriate amount to impart conductivity, but usually, carbon powder such as acetylene black, carbon black or graphite, and various metals. Fiber, foil, etc. may be mentioned. DBP oil absorption of carbon powder conductive material is 1
20cc / 100g or more is preferable, especially 150cc /
100 g or more is preferable because it holds the electrolytic solution. As additives, trifluoropropylene carbonate, vinylene carbonate, 1,6-dioxaspiro [4,4] nonane-2,7-dione, 12-crown-
4-ether or the like can be used to improve the stability and life of the battery. As a reinforcing material, various inorganic materials,
Organic spherical or fibrous fillers can be used.

As a method for forming the active material layer on the current collector, for example, a powdery active material is mixed with a binder in a solvent, and a dispersion coating is formed by a ball mill, a sand mill, a biaxial kneader or the like. Is preferably applied on a current collector and dried. In this case, the type of solvent used is not particularly limited as long as it is inert to the electrode material and can dissolve the binder, and for example, commonly used inorganic or organic solvents such as N-methylpyrrolidone. Can also be used. After application, the active material layer may be subjected to a consolidation treatment. Here, the volume fraction of the binder in the active material layer can be controlled by controlling the composition of the coating material, the drying conditions, the compaction conditions, and the like.

The active material layer can also be formed by pressing or spraying the active material on the current collector in a state in which the active material is mixed with a binder and heated to be softened. Further, the active material layer can be formed by firing the active material alone on the current collector.

The film thickness of the active material layers of the positive electrode and the negative electrode is preferably thick from the viewpoint of increasing the capacity and thin from the viewpoint of improving the rate characteristics. The thickness of the active material layer is usually 20 μm or more, preferably 30 μm or more, more preferably 50 μm or more, and most preferably 8 μm or more.
It is 0 μm or more. The thickness of the active material layer is usually 200 μm
The following is preferably 150 μm or less.

Prior to the formation of the active material layer, an undercoat primer layer may be provided between the active material layer and the current collector, if necessary, in order to improve the adhesion between the active material layer and the current collector.

When the undercoat primer layer is provided, examples of the composition thereof include a resin to which conductive particles such as carbon black, graphite and metal powder are added, and a conductive organic conjugated resin. Preferably, carbon black or graphite that can also function as an active material may be used for the conductive particles. As the resin, it is preferable to use polyaniline, polypyrrole, polyacene, a disulfide compound, a polysulfide compound, or the like, which can function as an active material, because the capacity is not reduced.
In the case of a composition whose main component is a resin to which conductive particles are added,
The ratio of the resin to the conductive particles is 1 to 300% by weight,
In particular, it is preferably 5 to 100% by weight. If the amount of the resin is less than this range, the coating film strength is reduced, and peeling may occur during the process when the battery is used. If the amount is too large, the conductivity is decreased and the battery characteristics tend to be deteriorated. .
The thickness of the undercoat primer layer is usually 0.05 to
The thickness is 10 μm, preferably 0.1 to 1 μm. If this film thickness is too thin, coating becomes difficult and it becomes difficult to ensure uniformity. If the film thickness is too thick, the volumetric capacity of the battery will be unnecessarily reduced, which is not preferable.

The spacers (electrolyte layers) 33 and 24 are usually impregnated with various electrolytes such as a fluid electrolyte, a non-fluid electrolyte such as a gel electrolyte or a completely solid electrolyte. The electrolyte is impregnated not only in the spacer but also in the positive electrode active material layer and the negative electrode active material layer. When the spacer, the positive electrode active material layer, and the negative electrode active material layer are sufficiently impregnated with the electrolyte, diffusion of lithium ions is promoted and battery performance is improved.

As the electrolyte, an electrolyte solution is used in view of the characteristics of the battery.
Alternatively, it is preferable to use a gel electrolyte among the non-fluidic electrolytes, and it is preferable to use the non-fluidic electrolyte for safety.

In the present invention, the electrolyte is preferably a non-fluidic electrolyte. When a non-fluidic electrolyte is used, the electrolyte does not flow out of the unit cell element during overcharge, the battery easily accumulates heat without impairing heat transfer, and thus the present invention promotes heat dissipation during overcharge. The effect of is maximized. In addition, since it is unlikely that the surface layer of the deactivated lithium nickel composite oxide will be dissolved, it is unlikely that a highly reactive surface will appear continuously, and the surface of the lithium nickel composite oxide will be positively activated during overcharge. The effect of the present invention of deactivating is certainly exhibited. In addition, when a non-fluidic electrolyte is used, liquid leakage can be more effectively prevented with respect to a battery using a conventional electrolytic solution, so there is an advantage of using a case having shape variability such as a laminate film described later. You can make the most of it.

On the other hand, an electrolytic solution obtained by dissolving a lithium salt in a non-aqueous solvent has a high fluidity and generally tends to have an excellent ion conductivity as compared with a non-fluidic electrolyte. Therefore, it is preferable to use an electrolyte containing an electrolytic solution in terms of improving ionic conductivity.

The electrolytic solution used as the electrolyte is usually prepared by dissolving a lithium salt, which is a supporting electrolyte, in a non-aqueous solvent.
As the non-aqueous solvent, a solvent having a relatively high dielectric constant is preferably used. Specifically, cyclic carbonates such as ethylene carbonate and propylene carbonate, acyclic carbonates such as dimethyl carbonate, diethyl carbonate and ethylmethyl carbonate, ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane and diphenyl ether, and γ-butyrolactone. Such as lactones, sulfur compounds such as sulfolane,
Examples thereof include nitriles such as acetonitrile. From the viewpoint of battery characteristics such as cycle characteristics, rate characteristics, and safety, cyclic carbonates and / or lactones are preferable.

In the present invention, as the solvent of the electrolytic solution,
Preferably, a non-aqueous solvent having a boiling point of 150 ° C. or higher at normal pressure (hereinafter sometimes referred to as “high-boiling point solvent”) is used. Here, “boiling point is X ° C. or higher” means that the vapor pressure does not exceed 1 atm even when heated from room temperature to X ° C. under a pressure of 1 atm. That is, when heating from room temperature to 150 ° C. under a pressure of 1 atm, the vapor pressure is always 1 a
It is preferable to use a non-aqueous solvent having a tm or less. As a result, higher cycle characteristics can be obtained, and the safety of the battery can be improved. For example, when using a low boiling point solvent consisting of a solvent such as dimethyl carbonate, diethyl carbonate, dimethoxyethane, the evaporation of the solvent causes bubbles between the active material and the solvent to reduce the impregnation state of the electrolytic solution, Non-uniformity of
The cycle characteristics tend to deteriorate. Further, by using the high boiling point solvent, it is possible to suppress the shape change (deformation) of the battery under high temperature or the like, the volatilization and leakage of the electrolytic solution, even when the battery element is housed in the shape variable case. .
As such a high boiling point solvent, propylene carbonate, ethylene carbonate, butylene carbonate, γ
-Butyrolactone and the like can be mentioned. Among such high boiling point solvents, preferred are propylene carbonate, ethylene carbonate and γ-butyrolactone. In this case, the boiling point is defined with respect to the whole solvent used. That is, when using a plurality of non-aqueous solvents, it does not mean that the boiling points of the individual solvents are 150 ° C. or higher, but that the boiling points of all the mixed solvents are 150 ° C. or higher. Further, the non-aqueous solvent preferably has a viscosity of 1 mPa · s or more.

Among these non-aqueous solvents, it is particularly preferable to use a solvent containing propylene carbonate in the present invention. That is, since propylene carbonate has a high boiling point, it is safe and hard to coagulate, and has good low-temperature characteristics. On the other hand, since propylene carbonate has secondary carbon, it is easily oxidized on the surface of the lithium nickel composite oxide. Therefore, the deactivation of the lithium-nickel composite oxide is likely to proceed, so that the effect of the present invention is more remarkable when propylene carbonate is used.

As a lithium salt as a supporting electrolyte to be dissolved in a non-aqueous solvent such as propylene carbonate, L
_{iPF 6, LiAsF 6, LiSbF 6} , LiBF 4,
LiClO ₄ , LiI, LiBr, LiCl, LiAl
Cl, LiHF ₂ , LiSCN, LiSO ₃ CF _{2 and the} like can be mentioned, and among these, LiPF ₆ , LiCl in particular.
O ₄ is preferred.

The concentration of these supporting electrolytes in the electrolytic solution is preferably 0.5 to 2.5 mol / L.

A gel electrolyte, which is a kind of non-fluid electrolyte, can be formed from such an electrolytic solution and a gel-forming polymer. The gel electrolyte is usually formed by holding the electrolytic solution with a polymer. The gel electrolyte is a particularly preferable electrolyte in the present invention because it can impart the same level of ionic conductivity as the electrolytic solution and makes the electrolyte non-fluidized.

The concentration of the polymer in the gel electrolyte with respect to the electrolytic solution depends on the molecular weight of the polymer used,
It is usually 0.1 to 30% by weight. If this concentration is too low, it becomes difficult to form a gel, and the retention of the electrolytic solution decreases, which may cause problems of fluidity and liquid leakage. On the other hand, if the concentration is too high, the viscosity becomes too high, which causes difficulty in the process, and the proportion of the electrolytic solution tends to decrease, the ionic conductivity tends to decrease, and battery characteristics such as rate characteristics tend to deteriorate. As the polymer holding the electrolyte, a poly (meth) acrylate polymer, an alkylene oxide polymer having an alkylene oxide unit, a fluorine-based polymer such as polyvinylidene fluoride or vinylidene fluoride-hexafluoropropylene copolymer Examples thereof include various polymers having a function of gelling an electrolytic solution.

As a method of forming a gel electrolyte, a method of non-fluidizing an electrolyte paint in which a polymer is dissolved in an electrolyte solution in advance, or a cross-linking reaction of an electrolyte paint containing a polymerizable gelling agent in the electrolyte solution If necessary, a material and a manufacturing method such as a method of forming a non-fluidic electrolyte can be adopted.

When the gel electrolyte is formed by a method in which a coating solution containing a polymerizable gelling agent in an electrolytic solution is subjected to a crosslinking reaction, the polymer is treated by a polymerization treatment such as ultraviolet curing or heat curing. A coating material is prepared by adding a component serving as a monomer to be formed to the electrolytic solution as a polymerizable gelling agent.

Examples of the polymerizable gelling agent include those having an unsaturated double bond such as an acryloyl group, a methacryloyl group, a vinyl group and an allyl group. In particular,
For example, acrylic acid, methyl acrylate, ethyl acrylate, ethoxyethyl acrylate, methoxyethyl acrylate, ethoxyethoxyethyl acrylate, polyethylene glycol monoacrylate, ethoxyethyl methacrylate, methoxyethyl methacrylate, ethoxyethoxyethyl methacrylate, polyethylene glycol monomethacrylate, N , N-diethylaminoethyl acrylate, N, N-dimethylaminoethyl acrylate, glycidyl acrylate, allyl acrylate, acrylonitrile, N-vinylpyrrolidone, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol acrylate, polyethylene glycol diacrylate, diethylene glycol Methacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polyalkylene glycol diacrylate, polyalkylene glycol dimethacrylate, trimethylolpropane alkoxylate triacrylate, pentaerythritol alkoxylate triacrylate, pentaerythritol alkoxylate Examples thereof include tetraacrylate and ditrimethylolpropane alkoxylate tetraacrylate. These may be used alone or in combination of two or more. Of these, diacrylates and triacrylates containing a plurality of ethylene oxide groups are particularly preferred.

The content of the polymerizable gelling agent in the electrolytic solution is not particularly limited, but is preferably 1% by weight or more. When the content is low, the efficiency of polymer formation decreases, and it becomes difficult to make the electrolyte non-fluidizable. On the other hand, if the amount is too large, the amount of unreacted monomer remains and the operability as an electrolyte coating deteriorates. Therefore, the amount is usually 30% by weight or less.

When the gel electrolyte is formed by a method of non-fluidizing an electrolyte paint containing a polymer in advance, a polymer that dissolves in an electrolytic solution at high temperature and forms a gel electrolyte at room temperature is used as a polymer. Preference is given to using. That is, the polymer dissolved in the electrolytic solution at high temperature is brought to room temperature to form a gel electrolyte. The temperature at high temperature is usually 50 to 200 ° C., preferably 100.
~ 160 ° C. If this melting temperature is too low, the stability of the gel electrolyte is reduced. If the melting temperature is too high, decomposition of electrolyte components, polymers, etc. may occur. As a non-fluidizing method, it is preferable to leave the electrolytic solution at room temperature, but it is also possible to perform forced cooling.

Polymers which can be used in this method include, for example, polymers having a ring such as polyvinyl pyridine and poly-N-vinylpyrrolidone; polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate. , (Meth) acrylic derivative polymers such as poly (ethyl acrylate), polyacrylic acid, polymethacrylic acid, polyacrylamide; Fluorine-based resins such as polyvinyl fluoride and polyvinylidene fluoride; CN groups such as polyacrylonitrile and polyvinylidene cyanide Polymers containing; polyvinyl alcohol-based polymers such as polyvinyl acetate and polyvinyl alcohol; halogen-containing polymers such as polyvinyl chloride and polyvinylidene chloride. Of these, polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, or modified products thereof are preferably used. It is also possible to use a mixture of the above polymers, a modified product, a derivative, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer and the like. The weight average molecular weight of these polymers is preferably in the range of 10,000 to 5,000,000. When the molecular weight is small, it becomes difficult to form a gel, and when the molecular weight is large, the viscosity becomes too high and the handling becomes difficult.

Among the methods for forming these gel electrolytes, a method in which an electrolyte coating containing a polymerizable gelling agent in an electrolytic solution is subjected to a cross-linking reaction to form a non-fluid electrolyte, and adhesion between electrodes is improved. It is preferable because it is improved and the effect of the present invention becomes particularly remarkable.

If necessary, various additives can be added to the electrolyte in order to improve the performance of the battery. The additive that exerts such a function is not particularly limited, but trifluoropropylene carbonate,
1,6-dioxaspiro [4,4] nonane-2,7-dione, 12-crown-4-ether, vinylene carbonate, catechol carbonate, dimethyl sulfone,
Propane sultone, sulfolene, sulfolane, succinic anhydride and the like can be mentioned.

In the present invention, the compound represented by the following general formula (1) is preferably present in the lithium secondary battery element. A1-X-A2 (1)

In the above formula (1), X is an element belonging to Group 6 of the periodic table, preferably oxygen or sulfur, and more preferably oxygen. A1 and A2 each independently represent a group having an aromatic ring such as a phenyl group, a naphthyl group and an anthryl group. A phenyl group and a naphthyl group are preferable, and a phenyl group is more preferable. In this case, a part of hydrogen atoms of the aromatic ring is a chain, branched or cyclic alkyl group, chain, branched or cyclic alkenyl group, aryl group, heterocyclic group, alkoxy group, aryloxy group,
It may be substituted with a substituent such as a heterocyclic oxy group or a halogen atom. Here, in a linear, branched or cyclic alkyl group, a linear, branched or cyclic alkenyl group, aryl group, heterocyclic group, alkoxy group, aryloxy group or heterocyclic oxy group which can be used as a substituent The number of carbon atoms is preferably 15 or less, more preferably 10 or less, and most preferably 5 or less. Further, hydrogen bonded to the above-mentioned chain, branched or cyclic alkyl group, chain, branched or cyclic alkenyl group, aryl group, heterocyclic group, alkoxy group, aryloxy group and heterocyclic oxy group. Atoms may be replaced by halogen atoms.

Specific examples of the substituent include a chain, branched or cyclic alkyl group such as a methyl group, an ethyl group and n-
Propyl group, i-propyl group, n-butyl group, sec-
Examples thereof include a butyl group, a t-butyl group, an n-pentyl group, an n-hexyl group, a cyclopropyl group, a cyclobutyl group, a cyclopentyl group and a cyclohexyl group. Examples of the chain, branched or cyclic alkenyl group which can be used as the substituent include a vinyl group, a propenyl group, a butenyl group and a hexenyl group. further,
Examples of the aryl group that can be used as the substituent include a phenyl group and a naphthyl group. Further, as the heterocyclic group that can be used as a substituent, a pyridyl group,
Thiazolyl group, benzothiazolyl group, oxazolyl group,
Examples thereof include a benzoxazolyl group and a benzofuranyl group. Furthermore, examples of the alkoxy group that can be used as the substituent include a methoxy group, an ethoxy group, an n-propoxy group, an i-propoxy group, and an n-butoxy group. Furthermore, examples of the aryloxy group that can be used as the substituent include a phenoxy group and a naphthyloxy group. Furthermore, examples of the heterocyclic oxy group that can be used as the substituent include a pyridyloxy group, a furyloxy group, a thiazolyloxy group and the like. Further, examples of the halogen atom that can be used as the substituent include fluorine, chlorine, bromine and the like.

A1 and A2 may be bonded to each other to form a ring. That is, A1 and A2 are bonded to each other through the element X, and apart from this bond, A1 and A2
And are bonded directly or through one or more atoms,
As a whole, a ring containing the element X can be formed.

The boiling point of the compound represented by the general formula (1) at atmospheric pressure is usually 100 ° C. or higher, preferably 120 ° C. or higher, more preferably 150 ° C. or higher. When the boiling point is low, the pressure inside the deformable case increases due to vaporization, and the battery is likely to swell and deform. In particular, since swelling is likely to occur in a high temperature environment or during overcharging, the boiling point is preferably as high as possible in order to secure the high temperature storage characteristics of the battery and safety against overcharging. However, since it is practically difficult to obtain a compound having a too high boiling point, the boiling point is usually 30
It is 0 ° C or lower.

Specific examples of the compound represented by the general formula (1) include phenyl ether, naphthyl ether, diphenyl sulfide, bis (p-tolyl) ether, bis (p-tolyl) sulfide and bis (p-fluorophenyl). ) Ether, bis (p-fluorophenyl) sulfide, bis (p-chlorophenyl) ether, diphenoxybenzene, dibenzofuran, 1,4-dibenzodioxane, xanthene and the like. Among these, phenyl ether, diphenyl sulfide and dibenzofuran are particularly preferable, and phenyl ether is most preferable. Of course, the compound represented by the general formula (1) can be used in combination of plural kinds.

By allowing the compound represented by the general formula (1) to be present in the lithium secondary battery element, the impregnating property of the battery electrolyte and the cycle characteristics can be improved. Although its action is not clear, it is because the above compound is a compound having an aromatic group and having high hydrophobicity, and therefore generally has a high affinity for a member (electrode, spacer, etc.) of a battery having hydrophobicity. Conceivable. On the other hand, if the hydrophobicity is too high, the affinity with an electrolyte having a high hydrophilicity may be generally inferior. However, since the compound has an appropriate hydrophilicity because it has a Group 6 element, depending on the balance between the two, It is estimated that such effects will occur.

The compound represented by the general formula (1) is preferably contained in the electrolyte of the lithium secondary battery element. In this case, when the above compound is uniformly present in the electrolyte, the impregnation property of the electrolyte and the cycle characteristics are further improved. For example, when an electrolyte containing an electrolyte solution obtained by dissolving a lithium salt in a non-aqueous solvent is used, if the compound that dissolves in the electrolyte solution used is used as the compound, the compound is used with respect to the electrolyte. And become evenly distributed.

The amount of the compound represented by the general formula (1) present in the lithium secondary battery element is appropriately selected depending on the kind of the compound and the required properties, but the larger the amount is. The cycle characteristics tend to improve. However, even if the amount of abundance is too large, no significant improvement in cycle characteristics is observed, which may adversely affect other battery characteristics. Further, when the existing amount is small, the cycle characteristics tend to deteriorate. The amount of the compound represented by the general formula (1) is usually 15% by weight or less, preferably 11% by weight or less, more preferably 1% by weight based on the weight of the electrolytic solution.
0 wt% or less, more preferably 8 wt% or less, particularly preferably 7.6 wt% or less, most preferably 7.5 wt% or less, and usually 1 wt% or more, preferably 2 wt% or more, More preferably 4 wt% or more, further preferably 5.5 wt% or more, most preferably 6 wt% or more.

Here, the weight of the electrolytic solution is an amount including the weight of the above compound. That is, when the electrolytic solution is composed of a lithium salt, a non-aqueous solvent and the compound represented by the general formula (1), the total weight of the respective components is the weight of the electrolytic solution.

When an electrolyte containing an electrolytic solution prepared by dissolving a lithium salt in a non-aqueous solvent is used, the most preferable amount is more than 5% by weight and 7.5% by weight based on the weight of the electrolytic solution. % Or less by weight.

The electrolyte layer is usually formed by impregnating a spacer made of a porous sheet with an electrolyte. The spacer is a porous film provided between the positive electrode and the negative electrode, and isolates them and supports the electrolyte layer. Examples of the material for the spacer include polyolefins such as polyethylene and polypropylene, polyolefins in which some or all of hydrogen atoms thereof are substituted with fluorine atoms, and polymers such as polyacrylonitrile and polyaramid. Preferred are polyolefins and fluorine-substituted polyolefins. Specific examples include polyethylene, polypropylene, polytetrafluoroethylene, polyvinylidene fluoride and the like. It may be a copolymer containing monomer units of these polymers or a mixture of polymers. The spacer may be a stretched film formed by uniaxial stretching or biaxial stretching, or may be a non-woven fabric. Spacer film thickness is usually 1
It is not more than 00 μm, preferably not more than 50 μm, more preferably not more than 30 μm, most preferably not more than 20 μm. If the film thickness is too thick, the rate characteristics and the volume energy density of the battery tend to decrease. If it is too thin,
Cutting tends to be difficult due to insufficient rigidity, and short circuits are likely to occur, so it is usually 5 μm or more, preferably 7 μm.
m or more, and more preferably 8 μm or more. The porosity of the spacer is usually 45 to 90%, preferably 45 to 75.
%. If the porosity is too large, the mechanical strength will be insufficient,
If it is too small, the rate characteristic of the battery tends to deteriorate.

The planar shape of the electrode is arbitrary and can be a quadrangle, a circle, a polygon, or the like.

As shown in FIGS. 11 and 13, the current collectors 22, 26 or 35a, 35b are normally provided with tabs 4 for connecting leads.
a and 4b are arranged in series. When the electrode has a rectangular shape, a tab 4a protruding from the positive electrode current collector is usually formed near one side of one side of the electrode as shown in FIG. 2, and the tab 4b of the negative electrode current collector is near the other side. Form.

It is effective to stack a plurality of battery elements in order to increase the capacity of the battery. At this time, the tabs 4a and 4b from each battery element are usually arranged in the thickness direction. The positive electrode and the negative electrode are connected to form a terminal portion. As a result, a large capacity battery element 1 can be obtained.

As shown in FIG. 2, the tabs 4a and 4b are
Leads 21 made of flaky metal are joined. As a result, the lead 21 and the positive and negative electrodes of the battery element are electrically coupled. Connection between tabs 4a and 4b and tab 4
The a and 4b can be connected to the lead 21 by resistance welding such as spot welding, ultrasonic welding or laser welding.

In the present invention, it is preferable to use an annealed metal as at least one of the positive electrode lead 21 and the negative electrode lead 21 and preferably both of them. As a result, not only the strength but also the bending durability can be made excellent.

Generally, aluminum, copper, nickel, SUS or the like can be used as the kind of metal used for the leads. The preferred material for the positive electrode lead is aluminum. A preferable material for the negative electrode lead is copper.

The thickness of the lead 21 is usually 1 μm or more, preferably 10 μm or more, more preferably 20 μm or more,
Most preferably, it is 40 μm or more. If it is too thin, the mechanical strength of the lead such as tensile strength tends to be insufficient. The thickness of the lead is usually 1000 μm or less, preferably 500 μm or less, more preferably 100 μm or less. If it is too thick, the bending durability tends to deteriorate, and sealing of the battery element by the case tends to become difficult. The advantage of using an annealed metal for the leads is more pronounced as the leads are thicker.

The width of the lead is usually 1 mm or more and 20 mm or less, particularly 1 mm or more and 10 mm or less, and the exposed length of the lead to the outside is usually 1 mm or more and 50 mm or less.

In the present invention, it is preferable that the exterior material used in the case for accommodating the lithium secondary battery element has shape changeability. A shape-variable exterior material not only makes it easy to create batteries of various shapes, but also adds a function to strengthen the bonding between the electrodes of the battery elements when the exterior material is sealed under vacuum. As a result, battery characteristics such as cycle characteristics can be improved.
The thickness of the outer casing is not only preferable because the thinner the volume energy density and the weight energy density of the battery are, but also the strength itself is relatively low and the battery easily swells when overcharged. Is especially noticeable. The thickness of the exterior material is usually 0.2 mm or less, preferably 0.15 mm or less. However, if it is too thin, the lack of strength will be noticeable and it will be easier for moisture and the like to permeate.
It is usually 0.01 mm or more, preferably 0.02 mm or more.

As the material of the exterior material, aluminum, nickel-plated iron, metal such as copper, synthetic resin or the like can be used. A laminate film having a gas barrier layer and a resin layer is preferable, and a laminate film having a resin layer on both sides of the gas barrier layer is preferable.
Such a laminated film has high gas barrier properties, high shape variability, and thinness. As a result, it is possible to reduce the thickness and weight of the exterior material, and to improve the capacity per volume of the battery.
Further, when such a laminate film having low rigidity is used, the battery is likely to swell and burst during overcharge, and thus the effect of the present invention of improving safety during overcharge is more significantly exhibited. To be done.

Materials for the gas barrier layer used for the laminate film include aluminum, iron, copper, nickel,
Metals such as titanium, molybdenum, and gold, alloys such as stainless steel and Hastelloy, and metal oxides such as silicon oxide and aluminum oxide can be used. Aluminum is preferable because it is lightweight and excellent in workability.

As the resin used for the resin layer, various synthetic resins such as thermoplastics, thermoplastic elastomers, thermosetting resins and plastic alloys can be used. Fillers such as fillers may be mixed with these resins.

As a concrete structure of the laminate film, as shown in FIG. 14A, a laminate of a metal layer (gas barrier layer) 40 and a synthetic resin layer 41 can be used. 14B, a more preferable laminated film is provided with a synthetic resin layer 41 for functioning as an outer protective layer on the outer peripheral surface of a metal layer (gas barrier layer) 40, and is corroded by an electrolyte on the inner side surface. A three-layer structure in which a synthetic resin layer 42 that functions as an inner protective layer for preventing contact between the gas barrier layer and the battery element and protecting the gas barrier layer is laminated.

In this case, the resin used for the outer protective layer is
Resins having excellent chemical resistance and mechanical strength such as polyethylene, polypropylene, modified polyolefins, ionomers, amorphous polyolefins, polyethylene terephthalate and polyamides are preferable.

As the resin for the inner protective layer, a chemically resistant synthetic resin is used, and examples thereof include polyethylene, polypropylene, modified polyolefin, ionomer, ethylene-
A vinyl acetate copolymer or the like can be used.

The laminated film is shown in FIG.
As shown in (C), a metal layer (gas barrier layer) 40, a protective layer-forming synthetic resin layer 41, and a corrosion-resistant layer-forming synthetic resin layer 42.
An adhesive layer 43 may be provided between them. Furthermore, in order to adhere the exterior materials to each other, an adhesive layer made of a resin such as polyethylene or polypropylene that can be welded can be provided on the innermost surface of the composite material.

The thickness of such a laminated film is
Usually 10 to 1000 μm, preferably 50 to 200 μm
Is. If the thickness is too thin, the strength will be poor, and if it is too thick, the workability will be poor.

In the present invention, a laminated film having a structure of resin layer / metal foil / resin layer sandwiching a metal foil between them is particularly preferable from the viewpoint of ensuring heat dissipation. In this case, the thickness of the resin layer is 10 to 100 μm. The thickness of the metal foil is 10 to 10
It is preferably 0 μm.

In order to form a case-shaped exterior material from such a laminated film, the periphery of the film-like body may be fusion-bonded, and the sheet-like body may be vacuum-formed, pressure-formed, press-formed, or the like. You may draw by. It can also be molded by injection molding a synthetic resin. When injection molding is used, a gas barrier layer such as a metal foil is usually formed by sputtering or the like.

[0138] To form the accommodating portion formed of the concave portion in the exterior material, drawing processing or the like can be performed.

The thickness of the lithium secondary battery of the present invention is usually 0.1 mm or more, 0.2 mm or more, more preferably 0.4 mm or more, while it is usually 10 mm or less, preferably 4 mm or less, more preferably 3 mm. It is 0.5 mm or less, particularly preferably 3 mm or less. If the lithium secondary battery is too thick, the heat dissipation efficiency will decrease. Further, since heat transfer takes time, heat storage in the central portion may proceed too much. If it is too thin, the capacity will decrease.

The electrical equipment in which the lithium secondary battery of the present invention is used as a power source is not particularly limited. Examples of the electric device include a laptop computer, a pen input personal computer, a mobile personal computer, an electronic book player, a mobile phone, a cordless phone handset, a pager, a handy terminal, a mobile fax, a mobile copy, a mobile printer, a headphone stereo, a video movie, a liquid crystal display. TV, handy cleaner, portable CD, mini disk, electric shaver, transceiver, electronic organizer, calculator, memory card, portable tape recorder, radio,
Examples include backup power supplies, motors, lighting equipment, toys, game machines, road conditioners, watches, strobes, cameras, medical equipment (pacemakers, hearing aids, shoulder massagers, etc.) and the like.

Of these various electric devices, it is preferable to use the lithium secondary battery of the present invention as a power source.
It is an electric device such as a mobile phone, a watch, and a mobile personal computer that can be carried around by a person. Since it is desired that such an electric device has particularly high safety, the effect of using the present invention becomes remarkable.

[0142]

The present invention will be described in more detail with reference to the following examples and comparative examples. However, the present invention is not limited to the following examples, and may be appropriately modified within the scope of the invention. It can be carried out.

In the following, "parts" in the composition means "parts by weight".

Example 1 [Production of Positive Electrode] Lithium-nickel composite oxide (Li _α Ni _X Co _Y Al _Z O ₂ (α = 1.02, X =
0.82, Y = 0.15, Z = 0.03)) (specific surface area 0.4 m ² / g, average secondary particle size 10 μm) 90 parts, acetylene black 5 parts, polyvinylidene fluoride 5 parts and N
80 parts of -methyl-2-pyrrolidone was kneaded with a kneader for 2 hours to obtain a positive electrode coating material 1.

Next, the positive electrode coating material 1 was applied onto an aluminum current collector base material having a thickness of 20 μm by an extrusion type die coating and dried, and the active material was bound to the current collector by a binder to form a porous material. A positive electrode active material layer made of a film was formed, then, after consolidation using a roll press (calender), the electrode portion was cut into a size of 3 cm × 5 cm to obtain a positive electrode 1. The thickness of the formed positive electrode active material layer is 55.
μm.

[Production of Negative Electrode] Graphite (Average particle size: 1
5 μm) 90 parts, polyvinylidene fluoride 10 parts and N-
Negative electrode paint 1 was obtained by kneading 100 parts of methyl-2-pyrrolidone for 2 hours with a kneader.

Next, the negative electrode coating material 1 was applied onto a copper current collector substrate having a thickness of 20 μm by extrusion type die coating and dried, and the active material was bound by a binder to the porous film. A negative electrode active material layer consisting of was formed, then, after consolidation using a roll press (calender), the electrode portion was cut into 3 cm × 5 cm to obtain a negative electrode 1.
The thickness of the formed negative electrode active material layer is 60 μm.

[Production of Electrolyte Paint] 1M LiPF
Mixed solution of ethylene carbonate and propylene carbonate containing ₆ (volume ratio; ethylene carbonate:
Propylene carbonate = 1: 1) 925 parts, tetraethylene glycol diacrylate 44 parts, polyethylene oxide triacrylate 22 parts, polymerization initiator 2 parts and additive (succinic anhydride) 9 parts are mixed and stirred to dissolve, and electrolyte coating 1 And

[Battery Preparation and Overcharge Test] The positive electrode 1 and the negative electrode 1 were coated with the electrolyte paint 1, and a polyethylene porous film (thickness: 15 μm) dipped in the electrolyte paint 1 was sandwiched between them to form a laminate. The electrolyte was non-fluidized by heating at 90 ° C. for 10 minutes to prepare a flat unit battery element having a positive electrode, a negative electrode, and a non-fluidizable electrolyte as shown in FIG.

A lead for taking out a current was connected to the terminal portion of the obtained unit battery element. Then, inside the aluminum layer (thickness 40 μm), the polypropylene layer (thickness 40 μm)
8) and (m) are housed in a facing film of a laminate film having a polyamide layer (thickness of 25 μm) and a thickness of about 100 μm, a long side of 6.5 cm, and a short piece of 4 cm, and vacuum-sealed as shown in FIGS. A lithium secondary battery was obtained.
The battery capacity C of the flat battery A thus created is 32 m.
The battery surface area S was 52.4 cm ² , the joint piece area ratio was 26%, the battery thickness was 0.36 mm, and the surface area capacity ratio S / C was 1.63.

Here, the discharge capacity C was measured as follows. That is, the battery A was charged at a constant current of 1 C (32 mA) to 4.2 V, and then at 4.2 V until the change in the charging current value within 1 hour was within 10%. Fully charged. And
The battery capacity was obtained by discharging from 4.2 V to 3.0 V at a current value such that it becomes 3.0 V in 10 hours.
The method for measuring the discharge capacity is the same in Examples 2 to 7 and Comparative Example 1 below.

An overcharge test was conducted on this flat battery A.

In the overcharge test, the upper limit voltage is set to 10V,
120C at constant current of 3C (96mA) from discharged state
Charged for a minute. As a result, no smoking or ignition of the battery was observed in the overcharged state, and it was confirmed that the flat battery A is a highly safe battery that can withstand the overcharge of 3C.

Example 2 A flat battery B was prepared in the same manner as in Example 1 except that two sets of the unit battery elements prepared in Example 1 were laminated and the terminals were collectively connected to the leads.

The battery capacity C of the flat battery B is 64 mAh.
Yes, battery surface area S is 52.4 cm ^Two, Joint piece area ratio
Is 26%, the battery thickness is 0.52 mm, and the surface area capacity ratio
The S / C was 0.82.

An overcharge test was conducted on this flat battery B.

In the overcharge test, the upper limit voltage is set to 10V,
The battery is discharged at a constant current of 3 C (192 mA) for 12
It was charged for 0 minutes. As a result, no smoke or ignition of the battery was observed in the overcharged state, and it was confirmed that the flat battery B is a highly safe battery that can withstand the overcharge of 3C.

Example 3 In Example 1, the size of the positive electrode and the negative electrode was 5.2 cm ×
The thickness was changed to 3.3 cm, which were designated as positive electrode 2 and negative electrode 2, respectively. A unit battery element was prepared in the same manner as in Example 1 except that the positive electrode 2 and the negative electrode 2 were used, 20 sets of this unit battery element were stacked, and the terminal portions were collectively connected to the leads. A laminated film similar to that used in Example 1 was formed in advance as an exterior material by facing molding as shown in FIG. A flat plate battery C was prepared in the same manner as in Example 1 except for this.

The battery capacity C of the flat battery C is 730 mAh.
The battery surface area S was 55.6 cm ² , the joint piece area ratio was 14.8%, the battery thickness was 3.3 mm, and the surface area capacity ratio S / C was 0.076.

An overcharge test was conducted on this flat battery C.

In the overcharge test, the upper limit voltage is set to 10V,
1 at 3C (2190mA) constant current from discharged battery
It was charged for 20 minutes. As a result, no smoking or ignition of the battery was observed in the overcharged state, and the flat battery C was 3C.
It was confirmed that the battery is highly safe and can withstand overcharging.

Example 4 Instead of the lithium nickel composite oxide in Example 1, a lithium nickel composite oxide (Li _α Ni _X Co _{Y Y) was used.}
Al _Z O ₂ (α = 1.05, X = 0.82, Y = 0.1
5, Z = 0.03)) (specific surface area 1.1 m ² / g, average secondary particle size 10 μm), except that the positive electrode coating material 2 was manufactured in the same manner, and the same positive electrode coating material 2 was used. Positive electrode 3
Was prepared, and a flat battery D was prepared in the same manner as in Example 1 except that this positive electrode 3 was used as a unit battery element.

The battery capacity of this flat battery D is 31 mAh.
The battery surface area S was 52.4 cm ² , the joint piece area ratio was 26%, the battery thickness was 0.35 mm, and the surface area capacity ratio S / C was 1.68.

An overcharge test was conducted on the flat battery D.

In the overcharge test, the upper limit voltage is set to 10V,
The battery is discharged from the discharged state at a constant current of 3 C (93 mA) for 120
Charged for a minute. As a result, no smoking or ignition of the battery was observed in the overcharged state, and it was confirmed that the flat battery D is a highly safe battery that can withstand the overcharge of 3C.

Example 5 In Example 1, the lithium nickel composite oxide was replaced by a lithium nickel composite oxide (Li _α Ni _X Co _Y Al _Z).
O ₂ (α = 1.01, X = 0.80, Y = 0.15, Z
= 0.05)) (specific surface area 0.8 m ² / g, average secondary particle size 8 μm) and lithium cobalt oxide (LiCoO ₂ ) (specific surface area 0.5 m ² / g, average secondary particle size 5 μm) Instead, a positive electrode coating material 3 was prepared in the same manner except that the lithium nickel composite oxide: lithium cobalt oxide = 7: 3 (weight ratio) was used as a mixture. In the same manner as in Example 3, except that the thicknesses of the positive electrode active material layer and the negative electrode active material layer were adjusted so that the ratio between the positive electrode charging capacity and the negative electrode capacity in Example 3 was adjusted, the sizes of the positive electrode and the negative electrode were adjusted. 2 unit battery elements of 5.2 cm x 3.3 cm
A flat battery E was prepared by stacking 0 batteries.

The battery capacity C of this flat battery E is 700 m.
The battery surface area S was 55.4 cm ² , the joint piece area ratio was 14.9%, the battery thickness was 3.2 mm, and the surface area capacity ratio S / C was 0.079.

An overcharge test was conducted on this flat battery E.

In the overcharge test, the upper limit voltage is set to 10V,
1 at constant current of 3C (2100mA) from discharged battery
It was charged for 20 minutes. As a result, no smoking or ignition of the battery was observed in the overcharged state, and the flat battery E was 3C
It was confirmed that the battery is highly safe and can withstand overcharging.

Comparative Example 1 A flat battery F was prepared in the same manner as in Example 3 except that 40 unit battery elements were laminated.

The battery capacity C of the flat battery F is 1460 mA.
h, the battery surface area S was 61.2 cm ² , the joint piece area ratio was 13.5%, the battery thickness was 6.4 mm, and the surface area capacity ratio S / C was 0.042.

An overcharge test was conducted on this flat battery F.

In the overcharge test, the upper limit voltage is set to 10V,
The battery was discharged at a constant current of 3 C (4380 mA) for a maximum of 120 minutes. As a result, test start 3
The battery ignited after 0 minutes.

The above results are summarized in Table 2.

[0175]

[Table 2]

From Table 2, it is understood that the lithium secondary battery of the present invention has high safety during overcharge.

Example 6 [Production of Positive Electrode] In Example 1, the lithium nickel composite oxide was replaced by a lithium nickel composite oxide (Li _α Ni
_X Co _Y Al _Z O ₂ (α = 1.05, X = 0.82, Y
= 0.15, Z = 0.03)) (specific surface area 0.5 m ² /
g, average secondary particle size 7 μm) and lithium cobalt oxide (Li
CoO ₂ ) (specific surface area 0.5 m ² / g, average secondary particle size 5
μm), 64.4 parts of the lithium nickel composite oxide, and 27.6 of the lithium cobalt oxide.
Part, acetylene black 4 parts, polyvinylidene fluoride 4
A positive electrode coating material 4 was prepared in the same manner as in Example 1 except that the components were mixed at a ratio of parts (weight ratio).

Next, the positive electrode coating material 4 was applied onto an aluminum current collector base material having a thickness of 15 μm by extrusion type die coating and dried, and the active material was bound to the current collector by a binder to form a porous material. A positive electrode active material layer made of a film was formed, and then, after consolidation using a roll press (calender), the electrode portion was cut into a size of 3.2 cm × 5.2 cm to obtain a positive electrode 4. The thickness of the formed positive electrode active material layer is 53.5 μm.

[Production of Negative Electrode] Graphite (average particle size 1
5 μm) 91.8 parts, polyvinylidene fluoride 8.2 parts and N-methyl-2-pyrrolidone 100 parts were kneaded with a kneader for 2 hours to obtain a negative electrode coating material 2.

Next, the negative electrode coating material 2 was applied onto a copper current collector base material having a thickness of 8 μm by an extrusion type die coating and dried, and a porous film in which an active material was bound on the current collector by a binder. Forming a negative electrode active material layer consisting of
Then, after consolidation using a roll press (calendar),
The electrode portion was cut into a piece of 3.3 cm × 5.25 cm to obtain a negative electrode 4. The thickness of the formed negative electrode active material layer is 62.5 μm.

[Manufacture of Electrolyte Paint] 1M Concentration of LiPF
Mixed solution of ethylene carbonate and propylene carbonate containing ₆ (volume ratio; ethylene carbonate:
Propylene carbonate = 1: 1) 921 parts, phenyl ether 30 parts, tetraethylene glycol diacrylate 47 parts, polyethylene oxide triacrylate 2
3 parts, 10 parts of dimethyl sulfone, 5 parts of a surfactant, 2 parts of a polymerization initiator and 9 parts of an additive (succinic anhydride) were mixed and stirred to prepare an electrolyte paint 2.

[Battery Preparation and Overcharge Test] The positive electrode 4 and the negative electrode 2 were coated with the electrolyte coating 2, and a polyethylene porous film (thickness: 9 μm) dipped in the electrolyte coating 2 was sandwiched between them for lamination. The electrolyte was non-fluidized by heating at 90 ° C. for 10 minutes to prepare a flat unit battery element having a positive electrode, a negative electrode, and a non-fluidizable electrolyte as shown in FIG.

Then, in the same manner as in Example 3, 22 unit battery elements were laminated, the terminal portions of the obtained unit battery elements were put together, and a lead for taking out a current was connected to this. Then, a polypropylene layer (thickness 40 μm) inside the aluminum layer (thickness 40 μm) and a polyamide layer (thickness 25 μm) on the outside, a laminate film having a thickness of about 110 μm, a long side of 6.1 cm, and a short piece of 4 cm is formed by facing. After being housed in the material, it was vacuum-sealed to obtain a flat lithium secondary battery G as shown in FIGS. The battery capacity C of the flat battery G thus created is 850 mAh, the battery surface area S is 55.0 cm ² , the joint piece area ratio is 20%, the battery thickness is 3.78 mm, and the surface area capacity ratio S is
/ C was 0.065.

An overcharge test was conducted on this flat plate battery G.

In the overcharge test, the upper limit voltage is set to 10V,
The battery was charged from the discharged state for 120 minutes at a constant current equivalent to 1.8 C (1440 mA). As a result, no smoking or ignition of the battery was observed in the overcharged state, and it was confirmed that this flat plate battery G is a highly safe battery capable of withstanding overcharge equivalent to 1.8C.

Example 7 [Production of Positive Electrode] In Example 1, the lithium nickel composite oxide was replaced by a lithium nickel composite oxide (Li _α Ni
_X Co _Y Al _Z O ₂ (α = 1.05, X = 0.82, Y
= 0.15, Z = 0.03)) (specific surface area 0.5 m ² /
g, average secondary particle size 7 μm) and lithium cobalt oxide (Li
CoO ₂ ) (specific surface area 0.5 m ² / g, average secondary particle size 5
Example 1 except that 63 parts of lithium nickel composite oxide, 27 parts of lithium cobalt oxide, 5 parts of acetylene black, and 5 parts of polyvinylidene fluoride (weight ratio) were mixed. A positive electrode coating material 5 was prepared in the same manner as in.

Next, the positive electrode coating material 5 was applied onto an aluminum current collector base material having a thickness of 15 μm by extrusion type die coating and dried, and the active material was bound to the current collector by a binder to form a porous material. A positive electrode active material layer made of a film was formed, and then, after consolidation using a roll press (calender), the electrode portion was cut into a size of 3.2 cm × 5.2 cm to obtain a positive electrode 5. The thickness of the formed positive electrode active material layer is 51 μm.

[Manufacture of Negative Electrode] Graphite (average particle size 1
5 μm) 90 parts, polyvinylidene fluoride 10 parts and N-
100 parts of methyl-2-pyrrolidone was kneaded with a kneader for 2 hours to obtain a negative electrode coating material 3.

Next, the negative electrode coating material 1 was applied onto a copper current collector base material having a thickness of 10 μm by extrusion type die coating and dried, and a porous film in which an active material was bound on the current collector by a binder. Was formed into a negative electrode active material layer, which was then compacted using a roll press (calender), and the electrode portion was cut into 3.3 cm × 5.25 cm to obtain a negative electrode 5. The thickness of the formed negative electrode active material layer is 60.2 μ.
m.

[Production of Electrolyte Paint] 1M LiPF
Mixed solution of ethylene carbonate and propylene carbonate containing ₆ (volume ratio; ethylene carbonate:
Propylene carbonate = 1: 1) 921 parts, phenyl ether 20 parts, tetraethylene glycol diacrylate 47 parts, polyethylene oxide triacrylate 2
3 parts, 10 parts of dimethyl sulfone, 5 parts of a surfactant, 2 parts of a polymerization initiator and 9 parts of an additive (succinic anhydride) were mixed and stirred to prepare an electrolyte paint 3.

[Battery Preparation and Overcharge Test] The positive electrode 5 and the negative electrode 5 were coated with the electrolyte paint 3, and a polyethylene porous film (thickness: 9 μm) soaked in the electrolyte paint 3 was sandwiched between them for lamination. The electrolyte was non-fluidized by heating at 90 ° C. for 10 minutes to prepare a flat unit battery element having a positive electrode, a negative electrode, and a non-fluidizable electrolyte as shown in FIG.

Then, in the same manner as in Example 3, 22 unit battery elements were laminated, the terminal portions of the obtained unit battery elements were put together, and the lead for taking out the current was connected to this. Then, a polypropylene layer (thickness 40 μm) inside the aluminum layer (thickness 40 μm) and a polyamide layer (thickness 25 μm) on the outside, a laminate film having a thickness of about 110 μm, a long side of 6.1 cm, and a short piece of 4 cm is formed by facing. After being housed in the material, vacuum sealing was performed to obtain a flat lithium secondary battery H as shown in FIGS. The battery capacity C of the flat battery H thus created is 767 mAh, the battery surface area S is 54.8 cm ² , the joint piece area ratio is 20%, the battery thickness is 3.66 mm, and the surface area capacity ratio S is
/ C was 0.072.

An overcharge test was conducted on this flat plate battery H.

In the overcharge test, the upper limit voltage is set to 10V,
The battery was charged from the discharged state at a constant current equivalent to 1.8 C (1296 mA) for 120 minutes. As a result, no smoking or ignition of the battery was observed in the overcharged state, and it was confirmed that this flat plate battery H is a highly safe battery capable of withstanding overcharge equivalent to 1.8C.

[0195]

As described in detail above, according to the present invention, a lithium secondary battery using a high-capacity lithium nickel composite oxide as a positive electrode active material, which is highly safe against overcharge, is used. Batteries are provided. The lithium secondary battery of the present invention imparts an essential safety function to the lithium secondary battery by controlling the area value per capacity of the lithium secondary battery, and other overcharging measures should be taken. And a highly safe lithium secondary battery can be realized. Further, by using it together with other measures against overcharge, it is possible to provide a safer lithium secondary battery.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a battery according to an embodiment.

FIG. 2 is a cross-sectional view of a main part of the battery according to the embodiment.

FIG. 3 is a schematic perspective view of a battery element.

FIG. 4 is a perspective view of the battery according to the embodiment (before fixing the joining piece portion).

FIG. 5 is a perspective view of the battery according to the embodiment (after fixing the joining piece portion).

FIG. 6 is a perspective view of a battery according to another embodiment in the process of being manufactured.

FIG. 7 is a perspective view of the battery according to still another embodiment in the process of being manufactured.

FIG. 8 is a perspective view of the battery according to another embodiment during manufacturing.

9 is a plan view of the battery of FIG. 8 during manufacture.

FIG. 10 is a perspective view of a battery according to another embodiment.

FIG. 11 is a schematic perspective view of a unit battery element.

FIG. 12 is a schematic cross-sectional view of a positive electrode or a negative electrode.

FIG. 13 is a schematic cross-sectional view of a battery element.

14A to 14C are vertical cross-sectional views showing an example of a composite material that constitutes an exterior material.

[Explanation of symbols]

1 Battery element 2,3,6,7,8,9 Exterior material 4a, 4b tabs 21 lead 22 Positive electrode current collector 23 Positive electrode active material 24 Spacer (electrolyte layer) 25 Negative electrode active material 26 Negative electrode current collector 31 Positive electrode 31a Positive electrode active material 32 negative electrode 32b Negative electrode active material 33 Non-fluidic electrolyte layer 35a Positive electrode current collector 35b Negative electrode current collector 40 gas barrier layer 41,42 Synthetic resin layer 43 Adhesive layer

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01M 4/58 H01M 4/58 F term (reference) 5H011 AA13 BB03 CC10 DD06 DD13 KK00 KK01 5H029 AJ12 AK03 AK05 AK15 AK16 AK18 AL01 AL02 AL06 AL07 AL12 AM03 AM04 AM05 AM07 AM16 BJ04 BJ12 BJ27 CJ08 DJ02 DJ16 HJ02 HJ04 HJ07 HJ19 5H050 AA03 AA15 BA16 BA17 CA02 CA08 CA11 CA19 CA20 CA26 CA29 CB01 HA07 HA04 HA07 GA07 HA04 GA02 HA04 GA02

Claims (10)

[Claims] 1. A lithium secondary battery in which a lithium secondary battery element using a lithium nickel composite oxide containing lithium and nickel as a positive electrode active material is housed in a case. Surface area is 0.1-1
A lithium secondary battery having a surface area capacity ratio S / C of 0 to 5 m ² and a ratio of the battery surface area S (cm ² ) to the battery capacity C (mAh) of 0.05 to 5. 2. The lithium secondary battery according to claim 1, wherein the battery surface area S is 1 to ²⁰⁰ cm ² . 3. The lithium secondary battery according to claim 1, wherein the battery capacity C is 1 to 2000 mAh. 4. The lithium secondary battery according to claim 1, wherein the case is made of a laminate film provided with a gas barrier layer and a resin layer. 5. The method according to claim 1, wherein the thickness is 4 mm or less.
The lithium secondary battery according to any one of 1. 6. The lithium secondary battery according to claim 1, wherein the lithium secondary battery element has an electrolytic solution containing propylene carbonate. 7. The lithium secondary battery according to claim 1, wherein the lithium secondary battery element has a non-fluidic electrolyte. 8. The lithium secondary battery according to claim 1, wherein the lithium secondary battery element contains a compound represented by the following general formula (1). A1-X-A2 (1) (X is an element of Group 6 of the periodic table, A1 and A2 represent an aromatic group, and A1 and A2 may be the same or different. , May be bonded to each other to form a ring.) 9. The lithium secondary battery according to claim 8, wherein X is oxygen. 10. The lithium secondary battery according to claim 8, wherein A1 and A2 are each independently one of a phenyl group, a naphthyl group, and an anthryl group.