JP2000277151A - How to use lithium secondary battery - Google Patents

Abstract

(57) [Problem] To provide a method of using a lithium secondary battery which is not only excellent in battery performance at a high temperature but also has high safety due to suppression of electric heat generation. SOLUTION: The composition formula LiNi _1-x M _x O ₂ (M: T
It is composed of one or a combination of two or more elements selected from i, Mn, Co, Al, Mg, and Ga. 0 ≦ x <1)
In the lithium secondary battery using the positive electrode active material represented by the following formula, charge and discharge were repeatedly used in a region of 30% or more and 100% or less of the charge capacity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium secondary battery, and more particularly to a method of using a lithium secondary battery using a lithium nickel composite oxide having a layered rock salt type crystal structure as a positive electrode active material. .

[0002]

2. Description of the Related Art A lithium secondary battery of this type has a high voltage and a high voltage.
High energy density can be obtained and it can be made smaller and lighter, so it has already been put into practical use in the field of information and communication equipment such as personal computers and mobile phones. It is also used in electric vehicles and hybrid electric vehicles due to resource and environmental issues. Practical use has also been advanced considerably for power supplies.

Under such circumstances, lithium cobalt oxide (LiCoO ₂ ) has been generally used as a positive electrode active material of a commercially available lithium secondary battery. As an alternative material, a lithium-manganese composite oxide (LiMn ₂ O ₄ ) -based material having a spinel-type crystal structure is also employed. This Li
Up to now, the Mn ₂ O ₄ -based material has been evaluated not only for the problem of resources and cost, but also for maintaining a discharge voltage of about 4 V which is comparable to that of the LiCoO ₂ material.

[0004] On the other hand, although the LiMn ₂ O ₄ -based material has an almost sufficient initial discharge capacity, there is a problem that the discharge capacity is greatly reduced due to repetition of charge / discharge, and the charge / discharge cycle characteristics are inferior. This is because the crystal lattice expands and contracts due to the intercalation (insertion) and deintercalation (desorption) behavior of lithium ions in the crystal structure due to repeated charge and discharge, and lattice destruction occurs due to a change in crystal volume. It is believed that there is.

In order to suppress the decrease in discharge capacity due to the repetition of charge and discharge and to improve the charge and discharge cycle characteristics, for example, Mn of LiMn ₂ O ₄ cathode active material is used.
Introducing lithium into the site (Y. Gao and JKDah
n, J. Electrochem. Soc., 143, 100 (1996)), or by introducing a divalent or higher valent metal into the Li site (see JP-A-6-215772).
Substituting elements are introduced into each of the Li site and the Mn site of the iMn ₂ O ₄ cathode active material (JP-A-10-19953).
No. 2) has already been proposed.

Further, a lithium nickel composite oxide (LiNiO ₂₎ having a layered rock salt type crystal structure similar to LiCoO _2
2 ) Promising materials are also considered promising and have not yet been used commercially, but for example, US Pat. No. 4,302,518;
Alternatively, a part of Ni of LiNiO ₂ may be replaced with another element (for example,
Co., for example, as a material substituted with
No. 8, JP-A-63-299056 and the like disclose such technical contents.

On the other hand, as a method of using these lithium secondary batteries, the basic usage has been to use up a wide range of charge / discharge capacity from full charge to full discharge. It has been questioned whether it can be used. Patents relating to the use of lithium secondary batteries include, for example, Japanese Patent Application Laid-Open No. 9-163618, which discloses that a constant voltage charge is performed in a low current region when full charge is desired, and a current value ( It has been proposed to prevent the battery from deteriorating by changing the charging condition such that the power value is reduced and constant voltage charging is not performed.

[0008]

However, the above-mentioned LiMn ₂ O ₄ -based cathode active material also has poor cycle life characteristics and storage characteristics, and particularly has poor life and storage characteristics in a high-temperature use environment. . Therefore, this LiM
The n ₂ O ₄ -based positive electrode active material is used for applications having a relatively low use environment temperature (approximately 40 ° C. or less) such as a mobile phone, but has a temperature of 60 ° C. or more, such as a battery for an electric vehicle. However, there remains a problem that it is not suitable for use in which the temperature rises to.

On the other hand, the LiNiO ₂ -based positive electrode active material had a defect that cycle life characteristics were poor in the past, but the cycle characteristics were improved and the high temperature (60 ° C.) characteristics were satisfied by examining substitutes and the like. It is said that it has reached a level where it can be done.

In view of such circumstances, the present inventors have conducted various studies. As a result, the use of a LiNiO ₂ -based positive electrode active material has excellent cycle characteristics and storage characteristics even in a use environment at a high temperature. In addition, by controlling the use conditions of the battery, it is possible to prevent the battery temperature from being increased due to energized heat generation, thereby preventing the battery from being deteriorated. For example, in an electric vehicle battery pack or the like, the battery temperature is controlled. (E.g., air cooling, water cooling, etc.) are required, but the idea was that if the rise in battery temperature could be solved technically, the load could be reduced.

The problem to be solved by the present invention is that L
By using an iNiO ₂ -based active material (including a substitute), a large-sized battery that is inexpensive and has excellent cycle life is provided.
Further, a method of using the battery to suppress heat generation of the battery due to energization is proposed. As a result, the load on the temperature control (for example, air cooling, water cooling) of the large battery pack, which is conventionally required, is reduced, and the life of the battery is prolonged by avoiding the battery from being heated to a high temperature. The goal is to ensure safety.

[0012]

Using Means for Solving the Problems The lithium secondary battery according to the present invention in order to solve this problem, the composition formula _{LiNi 1-x M x O 2} (M: Ti, Mn, Co, A
It is composed of one or a combination of two or more elements selected from 1, Mg, and Ga. In a lithium secondary battery using a positive electrode active material represented by 0 ≦ x <1), a charge capacity of 30
It is intended to be used in the region of not less than 100% and not more than 100%.

In this case, the positive electrode active material of the lithium secondary battery
Composition formula LiNi_1-xM_xO₂(M is Ti, M
one selected from n, Co, Al, Mg, Ga or
It consists of a combination of two or more elements. 0 ≦ x <1)
Lithium Nickel Composite Oxide with Layered Rock Salt Type Crystal Structure
LiMn with spinel crystal structure₂O
₄The problem of deterioration in high-temperature use environment, which is the disadvantage of
You.

At this time, charge and discharge are repeatedly used in a region of 30% or more of the charge capacity, whereby heat generation due to energization during use of the battery is suppressed, and an over-output state due to rapid progress of the battery reaction is prevented. Be avoided. In addition, the risk of the battery being ruptured or ignited due to the temperature rise can be avoided.

In this case, a lithium metal, a lithium alloy, a lithium compound, a carbon material, or the like, which can occlude and release lithium ions, can be used as the negative electrode active material. And, as a carbon material that can be used as the negative electrode active material, natural graphite, artificial graphite, coke, carbon black, vapor grown carbon, carbon fiber, a material obtained by carbonizing an organic polymer compound, or a heat treatment thereof, Examples thereof include mixed materials.

The separator provided between the positive electrode and the negative electrode has a function of separating the positive electrode and the negative electrode, holding a non-aqueous electrolyte, and passing lithium ions. For this separator, a porous film such as polyethylene or polypropylene, a nonwoven fabric or a woven fabric can be used.

Further, the non-aqueous electrolytic solution is stable with respect to the positive electrode active material and the negative electrode active material, and performs movement for lithium ions to undergo an electrochemical reaction with the positive electrode active material and the negative electrode active material. Any non-aqueous substance obtained can be used. Usually, a lithium salt as an electrolyte is used by dissolving it in an organic solvent. Salts which can be used for the electrolyte, _{specifically,} LiPF _6, LiAsF _6, LiSb
F ₆ , LiBF ₄ , LiClO ₄ , LiI, LiBr,
LiCl, LiAlCl, LiHF ₂ , LiSCN, L
ISO ₃ CF _2, and the like. Of these,
LiPF ₆ , LiBF ₄ and LiClO ₄ are preferred.

The solvent for dissolving the electrolyte can be arbitrarily selected, but an organic solvent having a relatively high dielectric constant is preferably used. For example, cyclic carbonates such as ethylene carbonate and propylene carbonate, acyclic carbonates such as dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate, glymes such as tetrahydrofuran and 2-methyltetrahydrofuran, γ
One or more solvents such as lactones such as -butyl lactone, sulfur compounds such as sulfolane, and nitriles such as acetonitrile. Among these, ethylene carbonate, cyclic carbonates such as propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, one or two or more kinds of mixed solvents selected from non-cyclic carbonates such as diethyl carbonate are preferable. Used.

The non-aqueous electrolyte is impregnated with a polymer such as polyethylene oxide, polypropylene oxide, a cross-linked isocyanate of polyethylene oxide, phenylene oxide, or a phenylene sulfide-based polymer as a solid electrolyte instead of the non-aqueous electrolyte. Organic solid electrolyte, Li ₃ N, LiBCl ₄ , Li ₄ SiO
₄ , an inorganic solid electrolyte of lithium glass such as Li ₃ BO ₃ can also be used.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a schematic configuration of a cylindrical lithium secondary battery. The lithium secondary battery 10 has an electrode power generator 14 formed by spirally winding a positive electrode sheet and a negative electrode sheet through a separator in a battery can 12, and a non-aqueous battery in the battery can 12. The organic electrolyte 15 is filled. Then, the positive electrode current collecting lead 16 pulled out from the positive electrode sheet is connected to the cap attached to the battery can 12, and the negative electrode current collecting lead 18 pulled out from the negative electrode sheet is connected to the battery can 12. It has become. An insulator (insulating plate 20) is mounted on the inner bottom surface of the battery can 12. The lithium secondary battery shown in FIG. 1 is shown as an experimental device, and is provided with a thermocouple 22 for detecting the heat generation temperature of the electrode generator 14 when the battery is repeatedly charged and discharged. I have.

Next, a method of manufacturing this battery will be described.
You. First, the positive electrode active material has a composition formula of LiNi_0.8C
o_0.15Al_0.05O ₂The layered salt type nick represented by
A lithium chelate-based composite oxide was used. And the positive electrode
This LiNi_0.8Co_0.15Al
_0.05O₂Dry positive electrode active material powder and carbon-based conductive material
Mix with a mixer and add 12% polyvinylidene fluoride
(PVDF) / n-methyl-2-pyrrolidone solution
Further, an n-methyl-2-pyrrolidone solution is further added to increase the viscosity.
It was kneaded while adjusting. Apply the paste thus obtained.
Apply on both sides of 20μm thick aluminum foil by machine tool
And dried to remove n-methyl-2-pyrrolidone solvent.
I left. Then, the obtained positive electrode sheet is placed on a roller press machine.
Pressed by The coating part of the positive electrode sheet is 243 on one side.
cm²Area. The positive electrode composition is LiNi
_0.8Co_0.15Al_0.05O ₂: Conductive auxiliary material: PV
DF binder = 85: 5: 5 weight ratio.

Next, artificial graphite powder was used as the negative electrode active material, and this artificial graphite powder was added to 12% PVDF / n-methyl-
A 2-pyrrolidone solution was added, and further kneaded while adjusting the viscosity by adding an n-methyl-2-pyrrolidone solution. The paste thus obtained was applied on both sides of a copper foil having a thickness of 10 μm using a coating machine and dried to remove the n-methyl-2-pyrrolidone solvent. Then, the obtained negative electrode sheet was pressed by a roller press. The coated part of the negative electrode sheet had an area of 280 cm ^{2 on} one side. The composition of the negative electrode was artificial graphite: PVDF binder = 95: 5 by weight.

Both the positive electrode sheet and the negative electrode sheet have an uncoated portion other than the above-mentioned coated portion, and a current collecting lead is welded to the uncoated portion, and the positive electrode sheet and the negative electrode sheet have a thickness of 25 μm. To form a spirally wound electrode. The size of the wound electrode is about 13 mmφ × 58 mm. This one
It was inserted into a battery can of 8 mmφ × 65 mm, and a non-aqueous electrolyte was injected. The electrolytic solution contains 1 mol of lithium hexafluorophosphate (L) in a solution in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 1: 1.
iPF ₆₎ was prepared by dissolving the. In addition, a thermocouple was fixed substantially at the center in the height direction of the winding core portion of the winding electrode. FIG. 1 shows this state, and this battery was further placed in a separable flask filled with dry argon gas to obtain an evaluation battery.

On the other hand, as a comparative battery, a battery using LiMn _1.9 Ni _0.1 O ₄ as a positive electrode active material was also manufactured. For this comparative battery, the positive electrode composition was LiMn.
_1.9 Ni _0.1 O ₄ : conductive additive: PVDF binder =
Except that the weight ratio was 90: 7: 9, all the battery configurations such as the negative electrode and the electrolyte were manufactured under the same conditions.

Next, an evaluation method will be described. Evaluation temperature is 20
° C. In the following, the current values are all based on the area of the positive electrode (486
It is expressed in current density per cm ² ). First, a current value of 1 mA
/ Cm ² , and the upper limit voltage was 4.1 V, and the battery was charged by a constant current and constant voltage method. The total charging time was 4 hours. This state is defined as a SOC (state of charge) of 100%. Thereafter, a pause was performed for 10 minutes, and then the current value was increased to 2
The discharge was performed by a constant current method with mA / cm ² and a lower limit voltage of 3.0 V. This state is called SOC (state of cha
rge) 0%. FIG. 2 shows the voltage change between the positive electrode and the negative electrode during this discharge and the temperature rise of the electrode generator.

Further, with the current value being set to 0.5 mA / cm ² , and discharging to 3.0 V by the constant current method, 1
After a pause, the battery was charged by a constant current method at a current value of ² mA / cm ² and an upper limit voltage of 4.1 V.
FIG. 3 shows a change in voltage between the positive electrode and the negative electrode and the temperature rise of the electrode power generator during this charging.

The charge and charge of the comparative batteries were the same under the same conditions except that the upper limit voltage was set to 4.2 V.
Discharge was performed, and a change in voltage between terminals and a temperature rise value were measured.
The results are shown in FIGS. 2 and 3. In addition, in the case of the comparative battery, in the constant current type charging with the current value of ² mA / cm ² and the upper limit voltage of 4.2 V, the SOC cannot be charged up to the SOC of 100%.
It could only be charged up to OC 66%.

In FIG. 2, the abscissa represents the charging capacity SOC (%).
The vertical axis indicates the voltage between the positive and negative terminals (V) and the electrode power generation.
The temperature rise value ΔT (° C.) of the body is taken. And this
As shown in FIG. 2, when the battery is discharged, the evaluation temperature 2
0 ° C, current density 2mA / cm ²(Total current 972 mA)
In the energized state, the voltage between the positive and negative terminals
Battery (Positive electrode active material: LiNi_0.8Co_0.15Al
_0.05O₂) And a comparative battery (cathode active material: LiMn)
_1.9Ni_0.1O₄), And there is almost no difference
Although it is a discharge curve, when comparing the temperature rise value of the battery
In this case, the comparative battery is better than the present invention in the region of SOC 60% or less.
Temperature rise is large, especially SOC 40% or less
In the lower region, the difference in the temperature rise is remarkable.

At the time of charging shown in FIG. 3, the evaluation temperature was 20 ° C., the current density was ² mA / cm ² (total current 972 mA).
When the battery temperature rise values are compared in the energized state of
Although the battery of the present invention tends to have a slightly higher temperature rise value than the comparative battery, it can be seen that the battery of the present invention keeps almost parallel lines.

The following Table 1 shows the temperature rise values at the time of charging and discharging shown in FIGS. 2 and 3 for each of the 20% SOC regions.

[0031]

[Table 1]

FIGS. 4 and 5 show Table 1 in a graph. FIG. 4 shows a battery of the present invention (cathode active material: LiN
i _0.8 Co _0.15 Al _0.05 O ₂ ). FIG. 5 shows a comparative battery (positive electrode active material: LiMn _1.9 Ni).
_0.1 O ₄ ). As can be seen from the comparison between FIG. 4 and FIG. 5, in the comparative battery, the average temperature rise during charging and during discharging is substantially constant over the entire SOC range (FIG. 5). In the battery of the present invention of Example, the temperature rise was large both during charging and during discharging, particularly in the region where the SOC was 30% or less. This is LiN
This is a feature of a battery using an iO ₂ -based positive electrode active material. Therefore, in a lithium secondary battery using a LiNiO ₂ -based positive electrode active material, a large temperature rise of the battery can be suppressed unless charge / discharge is performed in this SOC 30% or less region.

Next, another evaluation method will be described. First, using the above-described battery of the present invention, the evaluation temperature was set to 60 ° C.,
With a current density of 6 mA / cm ² , continuous charge / discharge of a constant capacity corresponding to 20% of SOC was performed in each SOC region. The charge and discharge cycles were not performed at all and the charge and discharge cycles were not performed at all, and the temperature rise of the battery was examined. FIG. 6 shows the result.

When continuous charge / discharge was performed in the SOC range of 0 to 20%, the temperature was significantly increased. Also, the SOC regions 20 to 4
The temperature rise at 0% is also large. However, SOC area 40%
In the case of the continuous charge and discharge described above, it is understood that the temperature rise can be suppressed to some extent.

From this fact, if a battery using a LiNiO ₂ -based positive electrode active material is made not to use an SOC region of about 30% or less, the temperature control (cooling) of a battery pack for an electric vehicle or the like can be reduced. It can be seen that the burden is reduced. In addition, since the temperature does not greatly increase, the life of the battery is prolonged, and since there is no sharp rise in temperature, the risk of runaway or rupture of the battery is reduced, and safety can be ensured.

Although the embodiments have been described above, when the use area of the battery is limited as in the present invention, the energy density of the battery decreases. In this case, there is a drawback that the use time of one charge is reduced in the use of a mobile phone or a notebook personal computer, and the running distance is shortened in the case of an electric vehicle using only a battery as an output source. But,
In the case of a hybrid electric vehicle that uses both a battery and an internal combustion engine, the battery does not fully charge and discharge,
It is used only in a limited area. In addition, charging and discharging are frequently performed at short time intervals. Therefore, the method of using the range of use for suppressing heat generation proposed in the present invention is particularly effective for batteries for hybrid electric vehicles,
This is effective in reducing the temperature control load, extending the life of the battery, and ensuring high safety.

The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, in the above embodiment, the composition formula LiNi _0.8 Co _0.15 Al _0.05 O is used as the positive electrode active material.
₂ was used, but of course is not limited to this, and LiNiO ₂ or Ni was partially replaced with other elements Ti, M
It is apparent from the gist of the present invention that the present invention is also applied to a composition substituted with n, Co, Al, Mg, and Ga.

Further, in the above embodiment, an example of a cylindrical lithium secondary battery has been described, but other box type, button type,
It can be applied to various forms such as a paper type and a card type.

[0039]

According to the method of using the lithium ion secondary battery according to the present invention, the use of the LiNiO ₂ -based positive electrode active material not only improves the battery performance, particularly the battery performance at high temperature, but also improves the battery performance. By controlling the battery so that it is not used in an area of 30% or less of the charging capacity where the heat generated by the current flow is large, the heat generated by the current flow of the battery can be reduced. Therefore, the battery reaction does not suddenly proceed due to the rise in the battery temperature, resulting in an over-output state, and the danger of causing a runaway of the battery reaction, rupture of the battery, ignition or the like is also avoided.

For this purpose, for example, control of the battery temperature (air cooling,
The load of water cooling is reduced, and the battery is not heated to a high temperature, so that the battery life is prolonged and high safety can be ensured.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a lithium secondary battery as one embodiment to which the present invention is applied.

FIG. 2 is a graph showing a usage area of a charge capacity (SOC) during discharge and a positive electrode in a charge / discharge test of the lithium secondary battery shown in FIG.
FIG. 5 is a diagram showing a relationship between a voltage between negative electrodes and a battery temperature rise value (evaluation temperature: 20 ° C.).

FIG. 3 is a diagram showing a relationship at the time of charging.

FIG. 4 shows a battery of the present invention (cathode active material: LiNi _0.8 Co)
_0.15 Al _0.05 O ₂ )
It is the figure which showed the temperature rise value in C area | region in the graph.

FIG. 5 shows a comparative example battery (cathode active material: LiMn _1.9 Ni)
Is a diagram showing a temperature rise value in each SOC range when charging and discharging a _{0.1 O 4)} in the graph.

6 is a diagram showing a relationship between a use area of a charge capacity (SOC) and a temperature rise value under a continuous charge and discharge condition at an evaluation temperature of 60 ° C. in a charge and discharge test of the lithium secondary battery shown in FIG. 1. is there.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Lithium secondary battery 12 Battery can 14 Electrode generator 15 Electrolyte 16 Positive current collecting lead 18 Negative current collecting lead 20 Insulator 22 Thermocouple

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takuaki Okuda 41-Cho, Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Laboratory Co., Ltd. (72) Inventor Takahiko Homma Nagakute-cho, Aichi-gun, Aichi Prefecture No. 41, Toyota-Chuo Yokomichi, Toyota Chuo Research Institute Co., Ltd. (72) Inventor Tatsuo Noritake 41, Nagakute-cho Yokomichi, Aichi-gun, Aichi-gun, Aichi Prefecture Toyota Chuo Research Institute, Inc. (72) Inventor Yuji Takeuchi 41 Toyota Chuo R & D Co., Ltd., Toyota Chuo R & D Co., Ltd. (72) Inventor Hideyuki Nakano 41 Toyota Chuo R & D Co., Ltd. 72) Inventor Takeshi Sasaki 41, 41, Chuchu-ji, Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Laboratory Co., Ltd. (72) Inventor Kazuhiko 41, Ochi-cho, Yoji, Nagakute-cho, Aichi-gun, Aichi Prefecture F-term in Toyota Central R & D Laboratories Co., Ltd. (Reference) HJ19

Claims (1)

[Claims] 1. A composition formula of LiNi _1-x M _x O ₂ (M: T
It is composed of one or a combination of two or more elements selected from i, Mn, Co, Al, Mg, and Ga. 0 ≦ x <1)
A method for using a lithium secondary battery using a positive electrode active material represented by the following formula, wherein the lithium secondary battery is used in a range of 30% to 100% of a charging capacity.