JP2001052704A - Lithium secondary battery - Google Patents

Abstract

[PROBLEMS] A lithium secondary battery is required to have a high output, a high voltage, and a high capacity, and a battery capable of charging and discharging in a high voltage region and a material capable of withstanding the demand have been desired. . A positive electrode active material having a mixed phase structure composed of two or more phases is used as a positive electrode active material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium secondary battery and a positive electrode active material used for the lithium secondary battery.

[0002]

2. Description of the Related Art In recent years, lithium secondary batteries are one of the essential components that are indispensable as power sources for personal computers and mobile phones, or as power sources for electric vehicles and power storage.
Has become one.

A portable computer (including a pen computer) and a personal digital assistant (Personal Digita)
l Assistant or Personal Intelligent Communic
A demand for mobile communication (mobile computing) such as an ator or a hand-held communicator includes miniaturization and weight reduction. However, it is difficult to make the system compact and lightweight because of the high power consumed by the backlight and drawing control of the liquid crystal display panel, and the fact that the capacity of the secondary battery is still insufficient at present. It is in. In particular, personal computers tend to be multifunctional with DVDs and the like, and power consumption tends to increase. Therefore, there is an urgent need to increase the power capacity, particularly the constant power discharge capacity when the voltage of the cell is 3.3 V or more.

[0004] Further, with the increase of global environmental problems, electric vehicles that do not emit exhaust gas and noise have attracted attention.
In recent years, parallel hybrid electric vehicles employing a system in which regenerative energy at the time of braking is stored in a battery for effective use, or a system for increasing efficiency by using electric energy stored in the battery at the time of starting, have become popular. However, the current battery has a low power capacity, so it is necessary to increase the number of batteries to gain voltage.
There are problems such as a reduced space inside the vehicle.

[0005] Among secondary batteries, lithium secondary batteries using a non-aqueous electrolyte are particularly attracting attention because of their high voltage, light weight, and high energy density. Particularly, Li _x Co disclosed in JP-A-55-136131 is disclosed.
Since a secondary battery positive electrode such as O ₂ has an electromotive force of 4 V or more when Li metal is used as the negative electrode, a high energy density can be expected. In order to improve the cycle characteristics, a chemical formula Li _x MO ₂ (M is Co, Ni, Fe, Mn)
Represents one or more elements selected from)
Lithium-containing composite oxide represented by the formula (JP-A-2-306022)
No.), chemical formula Li _x Co _{1- y My} O ₂ (M is W, Mn, T
at least one selected from a, Ti, and Nb;
0.85 ≦ x ≦ 1.3,0.05 ≦ y ≦ 0.35) lithium-containing composite oxide represented by (Japanese Patent Laid-Open No. 3-201368), or the formula _{Li x M y Ge z O p} (M is One or more transition metal elements selected from Co, Ni, Mn, 0.9 ≦ x ≦ 1.
3,0.8 ≦ y ≦ 2.0,0.01 ≦ z ≦ 0.2,2.0 ≦
Composite oxide represented by p ≦ 4.5 (JP-A-7-29603)
Or Li _x M _1-y A _y O ₂ (M is a transition metal, A is a metal having a smaller ionic radius than transition metal M, and the cation of which is coordinated to 6; x ≦ 1 0.0, 0.1 ≦
a composite oxide represented by the formula: y ≦ 0.4 (JP-A-5-283075)
No.), capacity, as to improve the cycle characteristics, Li _a
Ni _b M _1c M _2d O ₂ (M1 is Co, M2 is Si, P, G
1 selected from the group of a, Ge, Sb, Tl, Pb, Bi
Complex oxides having a layered structure represented by
_{(JP-A-8-78005), Li a Ni b M} 1c M 2d O 2 (M1 is Mn, Ti, Cr, Fe, V, Cu, M2 is Al, I
a composite oxide having a layered structure represented by at least one element selected from the group consisting of n and Sn) (JP-A-8-78007);
_{i a Ni b M 1c M 2d} O 2 (M1 is Ti, V, Cr, Cu, M2 is B, Si, P, Ga, Ge, Sb, Tl,
A composite oxide having a layered structure represented by at least one element selected from the group consisting of Pb and Bi) (JP-A-8-78008);
_{Li a M b Ni c Co d} O e (M is Al, Mn, Sn, I
at least one metal selected from n, Fe, V, Cu, Mg, Ti, Zn, and Mo; 0 <a <1.3, 0.02 ≦
b ≦ 0.5, 0.02 ≦ d / c + d ≦ 0.9, 1.8 <e <
2.2, b + c + d = 1) (JP-A-5-242891) and the like.

[0006]

A secondary battery is required to have a higher power capacity than ever before.
LixCoO ₂ disclosed in the above-mentioned publication has reached its limit. In particular, for the positive electrode, a material having a higher electromotive force than Li _x CoO ₂ is required. The end-of-charge voltage of Li _x CoO ₂ cells is conventionally 4.2V. Under these charging conditions, the charging amount is about 60% of the theoretical capacity of Li _x CoO ₂ . Therefore, the cell end-of-charge voltage is set to 4.2V.
If the charge capacity is larger than that, it is possible to increase the power capacity, but as the charge amount increases, the crystal structure of Li _x CoO ₂ collapses and the life is shortened. As described above, in order to respond to the demand for higher power capacity, a battery capable of charging and discharging in a voltage region higher than the conventional one, that is, a voltage region exceeding 4.4 V with a single cell, and a stable material having a crystal structure that can withstand it. is necessary. When charging and discharging are performed in such a high voltage region, in addition to the collapse of the crystal structure of the positive electrode active material described above, the presence of the active site of the positive electrode active material causes the electrolyte to oxidize and decompose to form a film on the electrode surface. However, the internal resistance may be increased to extend the life. Chemical formula Li _x MO ₂ (M is Co, N
The lithium-containing composite oxide (which represents one or more elements selected from i, Fe, and Mn) (JP-A-2-306022) has a conventional operating voltage, that is, a single cell. In the voltage range of 4.2 V or less, the effect of improving the cycle life is seen. However, when a single cell is charged and discharged in a voltage region exceeding 4.4 V, the crystal structure of the positive electrode active material is destroyed, the electrolyte is decomposed to form a film on the positive electrode surface, and the internal resistance increases. In addition, troubles such as a decrease in electricity efficiency occur, and the battery life is short. Formula Li _x Co _1-y M
_y O ₂ (M is at least one selected from W, Mn, Ta, Ti and Nb, 0.85 ≦ x ≦ 1.3, 0.05 ≦ y
Lithium-containing composite oxide represented by ≦ 0.35) (JP-A-3-201368), _{or, Li x M 1-y A} y O 2 (M is a transition metal, A is smaller than the transition metal M A metal having an ionic radius and whose cation is coordinated to six, x ≦ 1.
A composite oxide represented by the following formula: 0.1, y ≦ 0.4
5-283075 _{Patent), Li a Ni b M 1c} M 2d O 2 (M1 is Co,
M2 is Si, P, Ga, Ge, Sb, Tl, Pb, Bi
Complex oxide having a layered structure represented by at least one element selected from the group consisting of ( _a ) and Li _a Ni _b
M _1c M _2d O ₂ (M1 is Mn, Ti, Cr, Fe, V, C
u, M2 composite oxide having Al, In, a layered structure represented by Sn 1 or more elements selected from the group consisting of) _{(JP-A-8-78007), Li a Ni b M} 1c M 2d O 2 ( M1 is T
i, V, Cr, Cu, M2 is B, Si, P, G
1 selected from the group of a, Ge, Sb, Tl, Pb, Bi
Complex oxide having a layered structure represented by the species of element) _{(JP-A-8-78008), Li a M b Ni} c Co d O e (M is Al, M
n, Sn, In, Fe, V, Cu, Mg, Ti, Zn,
At least one metal selected from Mo, 0 <a <1.
3,0.02 ≦ b ≦ 0.5,0.02 ≦ d / c + d ≦ 0.
The same applies to the composite oxide (JP-A-5-242891) represented by 9, 1.8 <e <2.2, b + c + d = 1). On the other hand, the chemical formula _{Li x M y Ge z O p} (M is Co, Ni,
One or more transition metal elements selected from Mn, 0.9 ≦ x
≤ 1.3, 0.8 ≤ y ≤ 2.0, 0.01 ≤ z ≤ 0.2, 2.0
.Ltoreq.p.ltoreq.4.5 (JP-A-7-29603)
), The cycle characteristics when charging and discharging are performed under the condition that the upper limit voltage is 4.5 V are improved, and the capacity retention after 50 cycles is improved to 70 to 75%. However, an actual battery needs a capacity retention ratio of 80% or more even after 500 cycles, and is still insufficient in terms of cycle life. As described above, a positive electrode active material having a stable crystal structure in a voltage region higher than that of the related art and a battery capable of reversible charge / discharge even at a high voltage have not been found.

An object of the present invention is to provide a positive electrode active material and a lithium secondary battery that can withstand a high voltage.

[0008]

Means for Solving the Problems The positive electrode active material of the present invention comprises:
It is mainly characterized in that it has a hexagonal and / or monoclinic crystal structure, and the crystal structure is a multiphase structure composed of two or more phases having different lattice constants. In addition, a secondary battery using the positive electrode active material is characterized.
Further, the positive electrode active material of the present invention is characterized in that it is mainly a layered and / or zigzag layered crystal structure, and the crystal structure is a mixed phase structure composed of two or more phases having different lattice constants. .

The positive electrode active material of the present invention is significantly different from a single-phase material. Further, the positive electrode active material of the present invention is not simply a powder mixture of two or more different materials which are made into a single phase with hexagonal and / or monoclinic crystals. The effect of the present invention cannot be obtained only by mixing two or more kinds of different particles. The positive electrode material of the present invention has a structure in which two or more phases having the same crystal form but different lattice constants are in contact with each other with a grain boundary interposed therebetween. Therefore, in the cathode material of the present invention,
Lithium ions can be inserted into a specific phase with a certain regularity.

The cathode active material of the present invention comprises Li and M (where M
Is at least one selected from Ni, Mn, Co, Fe, and Al) and Ge and / or Ti as essential elements, and has a hexagonal and / or monoclinic, or a laminar and / or zigzag layered crystal structure And the crystal structure is a multiphase structure composed of two or more phases having different lattice constants.

In particular, the positive electrode active material of the present invention comprises Li and Co
And / or Ni and Ge and / or Ti as essential elements,
And a hexagonal and / or monoclinic or a layered and / or zigzag layered crystal structure, and the crystal structure is a multiphase structure composed of two or more phases having different lattice constants. . In addition, a secondary battery using the positive electrode active material is characterized.

The combination of essential elements is Li-Co-Ge Li-Ni-Ge Li-Co-Ni-Ge Li-Co-Ti Li-Ni-Ti Li-Co-Ni-Ti Li-Co-Ge-Ti Li —Ni—Ge—Ti Li—Co—Ni—Ge—Ti, and particularly desirable is Li—Co—Ni—Ge Li—Co—Ni—Ge—Ti.

The cathode material of the present invention is obtained in a specific material synthesis process. That is, in order to obtain such a composite, it is necessary to select a specific firing temperature, firing atmosphere, firing time, and starting materials. The most preferable firing temperature is 850 ° C.
1050 ° C. The most desirable firing atmosphere is an oxygen atmosphere, and the most desirable firing time is 20 hours to 6 hours.
0 hours. Furthermore, the most desirable starting material is LiOH · H ₂ O for the Li raw material, and Ni (N
O ₃₎ is ₂ · 6H ₂ O, the Ge raw material are GeO _2,
The Ti raw material is TiO ₂ .

Further, the positive electrode active material of the present invention has a general formula L
i _{w Av} Q _x Co _y O ₂ (where A is Ge, Y, Si, Zr, T
i is at least one member selected from i, and Q is Ni,
At least one selected from Mn, Fe, and Al, and w, v, x, and y are each 0 ≦ w ≦ 1.2, 0.02.
≦ v ≦ 0.125, 0.01 ≦ x ≦ 0.175, 0.01 ≦
(x / y ≦ 0.25). In addition, a secondary battery using the positive electrode active material is characterized.

The value of w representing the amount of Li fluctuates due to charging and discharging. That is, de-intercalation of Li ions occurs by charging, and the value of w decreases, and L decreases by discharging.
Intercalation of i-ions occurs and the value of w increases. If the amount of Li is more than 1.2, the amount of by-products such as lithium carbonate, lithium oxide, and lithium hydroxide generated in the firing process becomes too large, and these substances are used in the production of the electrode. Reacts with the agent, making it difficult to produce an electrode. In order to manufacture an electrode successfully, the smaller the amount of by-products, the better, and the value of w is 1.2 or less.

Ge, Y, Si, Z represented as A
It is desirable to replace Co with at least one or more selected from r and Ti. The value of v representing the amount of A does not fluctuate due to charging and discharging, but is in the range of 0.02 ≦ v ≦ 0.125. When the value of v is less than 0.02, the effect of A is not sufficiently exerted, the average voltage is significantly reduced, and the cyclability in charging at a high voltage is not preferable. v
Is greater than 0.125, the amount of by-products is large,
In particular, since A which cannot be reacted completely remains as an oxide, the capacity is undesirably reduced. Further, at least one selected from Ni, Mn, Fe, and Al shown as Q
It is desirable to replace Co with more than one species. The value of x representing the Q amount is in the range of 0.01 ≦ x ≦ 0.175. When the value of x is less than 0.01, the cyclability in charging at a high voltage is poor, and the capacity is undesirably reduced. Also, x
Is greater than 0.175, the amount of by-products is large,
In particular, Q that cannot be completely reacted remains as an oxide, which is not preferable because the capacity is reduced. Further, x / y which is a ratio between the value of x representing the Q amount and the value of y representing the Co amount
Is in the range of 0.01 ≦ x / y ≦ 0.25. If the value of x / y is less than 0.01, the cyclability in charging at a high voltage is poor, which is not preferable. Also, the value of x / y is 0.2
If it exceeds 5, the amount of by-products is large, and particularly, Q, which cannot be reacted completely, remains as an oxide.

The positive electrode active material of the present invention has a general formula Li _w Ge _{a
Ti b Ni x Co y O 2} (w, a, b, x, y are each 0
≦ w ≦ 1.2, 0.02 ≦ a ≦ 0.125, 0.01 ≦ b ≦
0.10,0.02 ≦ x ≦ 0.175,0.021 ≦ x / y ≦
(In the range of 0.25). In addition, a lithium secondary battery using the positive electrode active material is characterized.

The value of w representing the amount of Li fluctuates due to charging and discharging. That is, de-intercalation of Li ions occurs by charging, and the value of w decreases, and L decreases by discharging.
Intercalation of i-ions occurs and the value of w increases. If the amount of Li is more than 1.2, the amount of by-products such as lithium carbonate, lithium oxide, and lithium hydroxide generated in the firing process becomes too large, and these substances are used in the production of the electrode. Reacts with the agent, making it difficult to produce an electrode. In order to manufacture an electrode successfully, the smaller the amount of by-products, the better, and the value of w is 1.2 or less. The value of a representing the Ge amount does not fluctuate due to charging and discharging, but is in the range of 0.02 ≦ a ≦ 0.125. a
Is less than 0.02, the effect of Ge is not sufficiently exerted, the average voltage is significantly reduced, and the cyclability in charging at a high voltage is not preferable. Also, a
Is greater than 0.125, the amount of by-products is large,
In particular, Ge that cannot be completely reacted remains as an oxide, which is not preferable because the capacity is reduced. The value of b representing the Ti amount does not fluctuate due to charging and discharging, but 0.01 ≦≦
b ≦ 0.10. When the value of b is less than 0.01, the effect of Ti is not sufficiently exhibited, and the average voltage is remarkably lowered, and the cycleability in charging at a high voltage is not preferable. On the other hand, when the value of b exceeds 0.10, the amount of by-products is large, and particularly, Ti which cannot be completely reacted remains as an oxide, which is not preferable because the capacity is reduced. The value of x representing the amount of Ni is 0.02 ≦ x ≦
The range is 0.175. When the value of x is less than 0.02, a decrease in the average voltage is extremely undesirable. Also, Ni
Is not sufficiently exhibited, and the cyclability in charging at a high voltage is poor, which is not preferable. If the value of x exceeds 0.175, the amount of by-products is large, and particularly, Ni which cannot be completely reacted remains as an oxide, which is not preferable because the capacity is reduced. Further, the value of x representing the amount of Ni and C
x / y, which is a ratio to the value of y representing the amount of o, is 0.021 ≦
x / y ≦ 0.25. When the value of x / y is less than 0.021, the cyclability in charging at a high voltage is poor,
The amount of by-products is large, and particularly, Ge which cannot be completely reacted remains as an oxide, which is not preferable because the capacity is reduced.

On the other hand, when the value of x / y exceeds 0.25, the average voltage is remarkably lowered, the safety in overcharging is poor, the amount of by-products is large, and especially Ge that cannot be completely reacted is oxidized. Since it is left as an object, the capacity is undesirably reduced.

[0020] The positive electrode active material of the present invention is characterized in that it has a spinel crystal structure and a multiphase structure in which the crystal structure is composed of two or more phases having different lattice constants. In addition, a secondary battery using the positive electrode active material is characterized.

The cathode active material of the present invention comprises Li and M (where M
Is at least one selected from the group consisting of Ni, Mn, Co, Cr, Fe, and Al) and Ge and / or Ti as essential elements, and has two or more phases having a spinel crystal structure and different lattice constants. Characterized in that it is a multiphase structure composed of In addition, a secondary battery using the positive electrode active material is characterized.

Further, the positive electrode active material of the present invention may contain LiAO ₂ and / or Li ₂ AO ₃ and / or AO ₂ as by-products (where A is at least one selected from Ge and Ti).
Or more).

Although a large amount of the above-mentioned oxide causes a decrease in capacity, a small amount of the oxide leads to an improvement in cycle characteristics. Since this is a very small amount, it may not be confirmed by powder X-ray diffraction. In this case, it can be confirmed by a transmission electron microscope.

Furthermore, in the battery using the positive electrode active material of the present invention, the cell end-of-charge voltage and / or the voltage for constant voltage charging is higher than 4.4 V, and the cell end-of-discharge voltage is 3.4 V.
It is characterized by being larger than 2V. Further, the method is an operation method of the secondary battery described above.

The use of the reversibly chargeable / dischargeable battery of the present invention is not particularly limited. For example, notebook personal computers, pen input personal computers, pocket personal computers, notebook word processors, pocket word processors, electronic book players, mobile phones, cordless phones Phone handset, pager, handy terminal, portable copy, electronic organizer, calculator, LCD TV, electric shaver, power tool, electronic translator, car phone, transceiver, voice input device, memory card, backup power supply, tape recorder, radio, Power supply for equipment such as headphone stereo, portable printer, handy cleaner, portable CD, video movie, navigation system, refrigerator, air conditioner, television, stereo, water heater, oven microwave oven, dishwasher, washing machine, dryer, game Equipment, lighting equipment, toys It can be used load conditioners, medical equipment, automobiles, electric automobiles, golf carts, electric cart, as a power source, such as a power storage system. It can be used not only for civilian purposes but also for military use and space.

In a conventional secondary battery, when charged at a voltage higher than 4.4 V, the crystal structure of the positive electrode collapses, causing a reduction in capacity, and it has been difficult to use the secondary battery as a secondary battery.

This problem can be solved by using the positive electrode material of the present invention. That is, even if the battery is charged at a voltage higher than 4.4 V, the crystal structure of the positive electrode does not collapse, and there is almost no decrease in capacity, and the battery can be used as a secondary battery.

Since the conventional positive electrode material has a low average voltage, when the charge / discharge cycle test is repeated under the condition that the cell end-of-charge voltage is higher than 4.4 V, the positive electrode has a large capacity Li which is almost close to the theoretical capacity. Put ions in and out. This is the same as performing a cycle test on a conventional battery under overcharge conditions. Under such severe conditions, when a conventional cathode material is used, the crystal structure cannot be maintained, and disadvantages such as a short cycle life have occurred. On the other hand, such a disadvantage can be solved by using the positive electrode material of the present invention.

Since the positive electrode active material of the present invention controls the amount of released Li ions to an optimum value, the crystal structure does not collapse even when charged under the condition that the cell end-of-charge voltage is higher than 4.4V. Absent. In addition, a high average voltage not achieved by conventional materials is realized.

The operation of the present invention will be specifically described. The positive electrode active material of the present invention is Ge, Ti, Zr, Y, Si, such as Co or N.
It is obtained by substituting i, Mn, Fe, and Al.

Ge, Ti, Zr, Y and Si are apparently
It seems that Co, Ni, Mn, Fe, and Al sites are substituted, but actually, fine LiMO ₂ (M = G
e, Ti, Zr, Y, Si). Furthermore, LiM _x Q _1-x O ₂ (M = Ge, Ti, Zr, Y, S
It is possible to form a plurality of phases having different solid solution amounts x of M in the composition of (i, Q = Co, Ni, Mn, Fe, Al).

FIG. 1 shows a crystal model of the present invention. As shown in FIG. 2, the crystal model of the conventional complex oxide represented by the general formula LiQO ₂ is, for example, an M-octahedron in which the apexes of the octahedron are replaced by oxygen ions, the center is replaced by Q ions 2 and Q ion sites
The octahedron has a structure in which octahedrons are regularly arranged at a fixed lattice size. Lithium ions 3 enter between the connected octahedral layers to form an interlayer compound. The lithium ions 3 that have entered between the layers are desorbed by charging, inserted again between the layers by discharging, and the cycle is repeated. In the prior art, even if M ions are substituted for Q ions, the crystal layer spacing is constant and a single phase is formed.
As shown in FIG. 1, the crystal model of the present invention
The octahedron that replaced the ions is greatly distorted,
The octahedron around its surrounding Q ions is similarly distorted. A crystal lattice significantly distorted by the presence of M ions,
Since the lattice constant is different from that of a crystal lattice not containing M ions, the material is a material in which two or more phases are mixed.

FIG. 3 is a schematic diagram showing the charging reaction of the cathode active material of the present invention, ie, the Li elimination reaction. In the positive electrode active material of the present invention, a crystal lattice significantly distorted due to the presence of M ions,
Two or more types of crystal lattices containing no ions exist in a patch shape. Therefore, different energy levels are generated in Li desorption in each lattice.
When the charging reaction proceeds, the unit cell 5 in which Li still remains is 5
And the unit cells 6 from which Li has been eliminated are arranged in a patch shape due to the presence of the two or more lattices. On the other hand, in the conventional positive electrode material, even if M ions are present, they are formed into a single phase.
The unit cell 5 in which Li still remains and the unit cell 6 in which Li has been eliminated are uniformly present.

When a material in which two or more phases are mixed is charged and discharged, Li in the LiQO ₂ crystal and LiMO ₂
Li in the _second crystal _{or,, LiM x Q 1-x} O 2 (0 <
Since the energy level of Li in the crystal of x <1) is different in the desorption of Li, the desorption becomes uneven. This non-uniformity becomes a resistance when Li enters and exits, and raises the potential. This is the reason why the average voltage rises. The same applies to the case where the crystal form has a spinel structure. Since the conventional material has a single phase, such non-uniformity does not occur, and an increase in potential cannot be obtained. In addition, in the heterogeneous desorption, the unit cells 5 in which Li still remains are densely present, so that the strength of the bonds supporting the layers is increased, the crystal structure is not collapsed, and even if the battery is charged to a high potential, the cycle is increased. Long service life.

LiQO ₂ , LiMO ₂ , LiM _x Q _1-x O
_As a method for confirming the generation of ₂ (0 <x <1), there are an X-ray diffraction method and an electron diffraction method using a transmission electron microscope. In the prior art, as shown in FIG. 5, only a single crystal-shaped diffraction image 7 is observed, which is a so-called single-phase structure. On the other hand, in the positive electrode active material of the present invention, a lattice is formed as shown in FIG. Diffraction images 8 having different constants are obtained in an overlapping manner. Further, in the positive electrode active material of the present invention, since there are a plurality of crystals having different lattice constants, Li ₂ MO ₃ besides LiMO ₂ is also present at the crystal and crystal grain boundaries.
Also, there are diffraction images 9 of MO ₂ . This provides a pinning effect, which can suppress the collapse of the crystal structure even when charged to a high potential, and is one of the factors that extend the cycle life.

In order to obtain the mixed phase structure of the present invention in which a plurality of phases are mixed, it is desirable to use particularly Ge and Ti among Ge, Ti, Zr, Y and Si. More desirably, the general formula Li _w Ge _a Ti _b Ni _x Co _y O ₂ (w,
a, b, x, y are respectively 0 ≦ w ≦ 1.2, 0.02 ≦ a
≤0.125, 0.01≤b≤0.10, 0.02≤x≤
0.175 ≦ 0.021 ≦ x / y ≦ 0.25). Thereby, the mixed phase structure of the present invention can be obtained relatively easily.

[0037]

(Example 1) As a raw material of a cathode material of the present invention, LiOH.H ₂ O and Co ₃ O ₄ are mixed at a molar ratio of 3: 1, and GeO ₂ is mixed with Co at a ratio of 10: 1. Add the amount to be replaced by atomic%, and use a ball mill for 15 hours at room temperature.
Mixed. This was kept at 150 ° C. for 1 hour in an oxygen atmosphere, further kept at 470 ° C. for 5 hours, and then kept at 630 ° C. for 20 hours.
h and finally calcined at 850 ° C. for 20 h. Although the composition of the obtained positive electrode active material was LiCo _0.9 Ge _0.1 O ₂ , diffraction patterns of two kinds of hexagonal crystals having different lattice constants were confirmed by X-ray diffraction. In addition, Li ₂ GeO ₃ was confirmed as a by-product. Then, polyvinylidene fluoride is weighed in a weight ratio of 88: 7: 5 using graphite as a binder and a kneader for 30 minutes, and then applied to both sides of a 10 μm thick aluminum foil. did. However, it was confirmed that the value of w representing the amount of Li changed by charging and discharging, and the range was from 0 to 1.2. If the value exceeds 1.2, the slurry changes into a gel at the stage when the binder is added,
It was difficult to apply in the form of aluminum foil. When the value of w was 1.05 or less, no gel was formed even when the humidity at the time of application was 70% or more.

A mixture prepared by preparing 93% by weight of artificial graphite as a negative electrode material and 7% by weight of polyvinylidene fluoride as a binder was applied to both surfaces of a 10 μm thick copper foil. The positive and negative electrodes were roll-formed by a press, and the terminals were spot-welded and then vacuum-dried at 150 ° C. for 5 hours. FIG. 7 shows an example of the battery structure according to the present invention. The positive electrode 11 and the negative electrode 12 were laminated via a microporous polypropylene separator 10, wound in a spiral shape, and inserted into a battery can 13 made of SUS. The negative electrode terminal 14 was welded to the battery can 13 and the positive electrode terminal 15 was welded to the battery inner lid 16. As a non-aqueous solvent for the electrolyte, ethylene carbonate and ethyl methyl carbonate are mixed,
1 mol of LiPF ₆ was dissolved and injected into the battery can 13. The battery cover 16 is attached to the battery can 13 to have a diameter of 18 mm.
A cylindrical battery having a height of 65 mm was produced.

The battery was charged at a constant current of 4.2 V to 4.8 V at 1 CmA, and then charged at a constant voltage at the above voltage for 3 hours.
A constant current discharge was performed at A to 3.2 V, and the cycle life and volume energy density were evaluated. FIG. 8A shows the volume energy density and the cycle life of Example 1. Each of them has a long cycle life, and particularly has a large volume energy density and a long cycle life in a charging voltage range of 4.4V to 4.8V.

Comparative Example 1 Lithium was used as a raw material for a positive electrode material.
₂ CO ₃ and Co ₃ O ₄ are mixed at a molar ratio of 3: 2, and GeO ₂
Was added in an amount to replace 10 at% with respect to Co, and mixed at room temperature for 15 h using a ball mill. This was calcined at 850 ° C. for 5 hours in an air atmosphere. The composition of the obtained positive electrode active material was LiCo _0.9 Ge _0.1 O ₂ , and a single-phase hexagonal crystal was confirmed by X-ray diffraction. A charge / discharge test was performed in the same manner as in Example 1. FIG. 9A shows the volume energy density and the cycle life. The cycle life is short in the region where the discharge end voltage is higher than 4.4V.

(Example 2) As the raw material of the cathode material of the present invention, LiOH.H ₂ O and Co ₃ O ₄ are mixed at a molar ratio of 3: 1 to replace TiO ₂ by 10 atomic% with respect to Co. Then, the mixture was added at room temperature for 15 hours using a ball mill. This was kept in an oxygen atmosphere at 150 ° C. for 1 hour, further kept at 470 ° C. for 5 hours, kept at 610 ° C. for 20 hours, and finally kept at 950 ° C. for 20 hours and fired. Although the composition of the obtained positive electrode active material was LiCo _0.9 Ti _0.1 O ₂ , diffraction images of hexagonal and monoclinic having different lattice constants were confirmed by X-ray diffraction. In addition, LiTiO ₂ was confirmed as a by-product. A charge / discharge test was performed in the same manner as in Example 1. FIG. 8B shows the volume energy density and the cycle life. Each of them has a long cycle life, and particularly has a large volume energy density and a long cycle life in a charging voltage range of 4.4V to 4.8V.

Comparative Example 2 As a raw material of a positive electrode material, Li was used.
₂ CO ₃ and Co ₃ O ₄ were mixed at a molar ratio of 3: 2, and T
iO ₂ was added in an amount to substitute 10 atomic% with respect to Co, and mixed at room temperature for 15 h using a ball mill. This was calcined at 850 ° C. for 5 hours in an air atmosphere. The composition of the obtained positive electrode active material was LiCo _0.9 Ti _0.1 O ₂ , and a single-phase hexagonal crystal was confirmed by X-ray diffraction. Example 1
A charge / discharge test was performed in the same manner as described above. FIG. 9B shows the volume energy density and the cycle life. Discharge end voltage is 4.
The cycle life is short in the region larger than 4V.

[0043] (Example 3) positive electrode material of the present invention as a raw _{material, LiOH · H 2 O, Co} 3 O 4, Ni (NO 3) 2 · 6H 2
Positive electrode materials of various compositions were synthesized in the same manner as in Example 1 using O, GeO ₂ , and TiO ₂ . The composition of the obtained positive electrode active material is _{Li 1.01 Ge a Ti b Ni c} Co d O 2. A cylindrical battery was produced in the same manner as in Example 1, and the battery was 1 cm
After charging at 4.5 A with a constant current, charging at a constant voltage with the above voltage for 3 hours, and discharging at a constant current of 1 CmA up to 3.2 V, the cycle life, volume energy density, and firing rate during overcharge were measured. Evaluated in the laboratory. FIG. 10 shows Li _1.01
The relationship between Ge substitution amount x, volume energy density, and cycle life in Ge _x Ti _0.01 Ni _0.15 Co _0.84-x O ₂ is shown.

In the range of 0.02 ≦ x ≦ 0.125, the volume energy density is high and the cycle life is long. FIG. 11 shows the relationship between the Ti substitution amount x, the volume energy density, and the firing rate during overcharging in Li _1.01 Ge _0.11 T _x Ni _0.15 Co _0.74-x O ₂ . In the range of 0.01 ≦ x ≦ 0.10, the volume energy density is high, and the firing rate during overcharge is low. FIG. 12 shows Li _1.01 Ge _0.11 Ti _0.01 Ni _x Co
The relationship between the Ni substitution amount x in _0.88-x O ₂ , the volume energy density, and the cycle life is shown. 0.02 ≦ x ≦ 0.1
In the range of 75, the volume energy density is high and the cycle life is long. FIG. 13 shows Li _1.01 Ge _0.11 Ti _0.01 Ni _x C
The relationship between the Ni / Co substitution ratio x / y in o _y O ₂ , the volume energy density, and the cycle life is shown. 0.02
In the range of 1 ≦ x / y ≦ 0.25, the volume energy density is high and the cycle life is long.

(Embodiment 4)

[0046]

A positive electrode active material having the composition shown in Table 1 was synthesized and used in the same manner as in Example 1. The obtained positive electrode active material is
X-ray diffraction or transmission electron microscopy confirmed multiple diffraction images of hexagonal, monoclinic, layered, zigzag layered, and spinel structures with different lattice constants. The average discharge voltage, volume energy density, and cycle life were evaluated in the same manner as in Example 1. Furthermore, a nail penetration test and an overcharge test were also performed among the safety tests. Table 1 shows the results. In each case, the average discharge voltage is high, the cycle life is long, and the safety is high.

Comparative Example 3 A positive electrode active material having the composition shown in Table 1 was synthesized and used in the same manner as in Comparative Example 1. The obtained positive electrode active material was confirmed by X-ray diffraction or transmission electron microscopy to have a single-phased hexagonal system, a monoclinic system, or a layer, or a zigzag layer, or a spinel structure. . The average discharge voltage, volume energy density, and cycle life were evaluated in the same manner as in Example 1. Table 1 shows the results of the nail penetration test and the overcharge test among the safety tests. In each case, the average discharge voltage was lower than that of Example 4, and the cycle life was shorter.

[0049]

As described above, according to the present invention, it is possible to obtain a positive electrode material having a high power capacity, a secondary battery, and a method of operating the same.

[Brief description of the drawings]

FIG. 1 is an example of a crystal model according to the present invention.

FIG. 2 is an example of a crystal model according to the related art.

FIG. 3 is an example of a schematic view of a charging reaction of a positive electrode active material according to the present invention.

FIG. 4 is an example of a schematic view of a charging reaction of a positive electrode active material according to a conventional technique.

FIG. 5 is an example of an X-ray diffraction image of a positive electrode active material according to the related art.

FIG. 6 is an example of an X-ray diffraction image of the positive electrode active material according to the present invention.

FIG. 7 shows an example of a battery structure according to the present invention.

FIG. 8 shows the volume energy density and cycle life of Examples 1 and 2.

FIG. 9 shows volume energy densities and cycle life of Comparative Examples 1 and 2.

FIG. 10: Li _1.01 Ge _x Ti _0.01 Ni _{0.15 of} Example 3
Relationship between Ge substitution amount x in Co _0.84-x O ₂ , volume energy density, and cycle life.

FIG. 11: Li _1.01 Ge _0.11 Ti _x Ni _{0.15 of} Example 3
The relationship between the Ti substitution amount x in Co _0.74-x O ₂ , the volume energy density, and the firing rate during overcharging.

FIG. 12: Li _1.01 Ge _0.11 Ti _0.01 Ni _{x of} Example 3
The relationship between the Ni substitution amount x in Co _0.88-x O ₂ , the volume energy density, and the cycle life.

FIG. 13: Li _1.01 Ge _0.11 Ti _0.01 Ni _{x of} Example 3
Relationship between Ni / Co substitution amount ratio x / y in Co _y O ₂ , volume energy density, and cycle life.

[Explanation of symbols]

1 ... oxygen ion, 2 ... Q ion, 3 ... lithium ion,
4 ... M ion, 5 ... Unit cell with lithium remaining, 6 ...
Unit cell from which lithium has been desorbed, 7: X-ray diffraction image of the positive electrode active material according to the prior art, 8: X-ray diffraction image of the positive electrode active material according to the present invention having a different lattice constant, 9: Li ₂ MO ₃ or MO ₂ X
X-ray diffraction image, 10 ... separator, 11 ... positive electrode, 12 ... negative electrode, 13 ... battery can, 14 ... negative electrode terminal, 15 ... positive electrode terminal,
16 Battery cover.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Ren Muranaka 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture F-term in Hitachi Research Laboratory, Hitachi, Ltd. F-term (reference) 5H003 AA02 AA04 BB05 BC05 BC06 BD00 5H014 AA01 CC01 CC07 EE10 HH00 5H029 AJ03 AJ05 AK03 AL06 AM03 AM04 AM05 AM07 BJ02 BJ14 DJ12 DJ16 DJ17 HJ02 HJ13 HJ18

Claims (11)

[Claims] 1. A rechargeable lithium secondary battery comprising a negative electrode, a positive electrode and a non-aqueous electrolyte containing a lithium salt and capable of being charged and discharged a plurality of times reversibly, mainly comprising a hexagonal crystal and / or a single cell as an active material of the positive electrode. A lithium secondary battery having a crystal structure of an oblique crystal and a multi-phase structure in which the crystal structure is composed of two or more phases having different lattice constants. 2. A rechargeable lithium secondary battery having a negative electrode, a positive electrode, and a non-aqueous electrolyte containing a lithium salt, which can be charged and discharged a plurality of times reversibly, mainly as a layered material and / or a zigzag layered material as an active material of the positive electrode. A lithium secondary battery having a crystal structure, wherein the crystal structure is a mixed phase structure composed of two or more phases having different lattice constants. 3. An active material for the positive electrode comprising Li and M (where M
2. The lithium secondary battery according to claim 1, wherein Ge is at least one selected from Ni, Mn, Co, Fe, and Al) and Ge and / or Ti are essential elements. 4. The method according to claim 1, wherein Li and Co and / or
2. The lithium secondary battery according to claim 1, wherein Ni, Ge and / or Ti are essential elements. 5. The method according to claim 1, wherein the positive electrode active material has a general formula Li _w A _v Q _x.
Co _y O ₂ (where A is at least one selected from Ge, Y, Si, Zr and Ti, and Q is Ni, Mn, F
e, at least one selected from Al, w,
v, x, and y are respectively 0 ≦ w ≦ 1.2, 0.02 ≦ v ≦
0.125, 0.01 ≦ x ≦ 0.175, 0.01 ≦ x / y
2. The lithium secondary battery according to claim 1, further comprising a composite oxide represented by the following formula: (≦ 0.25). 6. A rechargeable lithium secondary battery having a negative electrode, a positive electrode, and a non-aqueous electrolyte containing a lithium salt and capable of being charged and discharged a plurality of times reversibly, wherein the positive electrode active material is represented by a general formula Li _w Ge _{a
Ti b Ni x Co y O 2} (w, a, b, x, y are each 0 ≦
w ≦ 1.2, 0.02 ≦ a ≦ 0.125, 0.01 ≦ b ≦
0.10, 0.02 ≦ x ≦ 0.175, 0.021 ≦ x / y
≦ 0.25), comprising a complex oxide represented by the following formula: 7. A rechargeable lithium secondary battery having a negative electrode, a positive electrode, and a non-aqueous electrolyte containing a lithium salt, which can be charged and discharged a plurality of times reversibly, mainly has a spinel crystal structure as an active material of the positive electrode, and A lithium secondary battery, wherein the crystal structure is a mixed phase structure composed of two or more phases having different lattice constants. 8. An active material for the positive electrode comprising Li and M (where M
8. The lithium secondary battery according to claim 7, wherein Ge is at least one selected from the group consisting of Ni, Mn, Co, Cr, Fe, and Al) and Ge and / or Ti. 9. The positive electrode active material according to any one of claims 3 to 6 and 8, wherein LiAO ₂ and / or
Or Li ₂ AO ₃ and / or AO ₂ (where A is Ge, T
(i) at least one oxide selected from i). 10. The battery according to claim 1, wherein the cell has a charging end voltage and / or a constant voltage charging voltage higher than 4.4 V, and the cell has a discharging end voltage higher than 3.2 V. 10. The lithium secondary battery according to any one of items 1 to 9. 11. A notebook personal computer, a pen input personal computer, a pocket personal computer, a notebook word processor, a pocket word processor, an electronic book player, a mobile phone, a cordless phone handset, a pager, a handy terminal, a mobile copy, an electronic notebook, a calculator, a liquid crystal television, Electric shavers, power tools,
Electronic translator, car phone, transceiver, voice input device, memory card, backup power supply, tape recorder, radio, headphone stereo, portable printer, handy cleaner, portable CD, video movie, navigation system, refrigerator, air conditioner, television, stereo, Claims for use in water heaters, microwave ovens, dishwashers, washing machines, dryers, game equipment, lighting equipment, toys, road conditioners, medical equipment, automobiles, electric vehicles, golf carts, electric carts, and power storage systems. 11. The lithium secondary battery according to any one of 1 to 10.