JP2000231937A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a cost, enhance cycle characteristics and secure safety when overcharging as well as to stabilize a positive electrode active material itself, by using a positive electrode active material of a lithium nickel composite oxide having a rock-salt structure with orderly arranged layers obtained by substituting a part of a Ni site by other elements for the positive electrode and a negative electrode active material of a mixture of graphite and coke for the negative electrode. SOLUTION: The composition of a composite oxide for a positive electrode active material is shown by the formula LiNixM1yM2zO2z. (In the formula, Mi: At least one kind Selected from Co, Mn, M2: one or more kinds selected from Al, B, Fe, Cr, Mg; x+y+z=1, 0.5<x<0.95, 0.01<y<0.4, 0.001<z<0.2. A part of inexpensive Ni contained in the positive electrode active material is substituted by two or more elements to improve cycle characteristics. A negative electrode active material of a mixture of highly crystalline graphite and inexpensive coke increases a battery capacity, and suppresses a crystal from being collapsed by restricting a movement of a Li ion between both electrodes during normal charge and discharge. In addition, deposition of a dendrite on the negative electrode at the time of excessive charging is prevented by irreversible large capacity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery utilizing the occlusion and release of lithium ions, and more particularly to a non-aqueous electrolyte secondary battery which is inexpensive and has good cycle characteristics.

[0002]

2. Description of the Related Art With the miniaturization of personal computers, video cameras, mobile phones, and the like, in the fields of information-related equipment and communication equipment, lithium secondary batteries are used as power sources for these equipments because of their high energy density. Has been put to practical use and has spread widely. On the other hand, in the field of automobiles, the development of electric vehicles is urgent due to environmental problems and resource problems, and lithium secondary batteries are being studied as power sources for electric vehicles. With lithium secondary batteries,
Most commonly used are rocking chair type secondary batteries, which use lithium composite oxide for the positive electrode and carbon material for the negative electrode, and repeat the insertion and extraction of lithium ions to and from both electrodes as they are charged and discharged. Have been.

As a lithium composite oxide serving as a positive electrode active material of a lithium ion secondary battery, a layered rock salt structure LiCoO ₂ , a layered rock salt structure LiNiO ₂ , and a spinel structure LiMn ₂ O ₄ can be obtained as a material capable of obtaining an operating voltage of 4 V class. well known. Among these, LiCo is currently used for reasons such as easy synthesis and the highest operating voltage.
Secondary batteries using O ₂ as a positive electrode active material dominate.

[0004] However, cobalt, which is an element constituting LiCoO ₂ , is an extremely expensive element with a small amount of resources, and is a major factor that increases the cost of lithium ion secondary batteries. Therefore, for example, when a lithium ion secondary battery is used as a power source for an electric vehicle, a large capacity is required.
It is considered that practical use of a lithium ion secondary battery using O ₂ as a positive electrode active material is extremely difficult.

A promising alternative to this LiCoO ₂ is a layered rock salt structure LiNiO ₂ . Since nickel, which is cheaper than cobalt, is used as a constituent element, the cost is excellent, and the theoretical discharge capacity is LiCoO ₂
Although it is not much different from the above, it is expected that a battery with a large capacity can be constructed from the advantage that the effective capacity (capacity that can be actually taken out when the battery is constructed) is excellent.

However, since LiNiO ₂ absorbs and releases a lot of lithium during charging and discharging due to its large effective capacity, there is a disadvantage that the crystal structure is easily collapsed by repeating large expansion and contraction of LiNiO ₂ itself. . Therefore, when a battery is configured, there is a problem of so-called cycle deterioration in which the discharge capacity of the battery is reduced by repeated charging and discharging. In particular, in the case of an application such as a power source for an electric vehicle that may be left outdoors, the secondary battery also has a small cycle deterioration at a high temperature because the deterioration proceeds further at a high temperature at which the battery reaction is activated. It is one of the important characteristics required for

Conventionally, as means for solving the problem of cycle deterioration caused by a positive electrode using LiNiO ₂ as an active material,
Those in which a P or B-based compound is coated on the surface of LiNiO ₂ or added into the positive electrode (JP-A-7-142055 or the like);
One in which a part of Ni site is replaced with B (Japanese Patent Laid-Open No. 8-45)
509), and those in which part of the Li site is replaced with an alkaline earth metal (Japanese Patent Application Laid-Open No. 9-274917). However, even with these means, it has been difficult to obtain a secondary battery having practically satisfactory cycle characteristics.

Also, LiNiO ₂ has a large effective capacity and can easily extract lithium because a secondary battery using LiNiO ₂ as a positive electrode active material is overcharged with a large amount of lithium ions. It leads to being released toward. When a large amount of lithium ions are released, lithium ions that cannot be completely absorbed in the negative electrode active material precipitate on the negative electrode surface in the form of metallic lithium and grow as dendrites. This precipitation of dendrites may break through the separator between the positive and negative electrodes, causing an internal short circuit in the battery, and eventually leading to ignition and rupture of the battery. That is, in the case of a secondary battery using LiNiO ₂ as the positive electrode active material, it is necessary to sufficiently consider safety due to overcharging.

[0009]

As described above, in a secondary battery using LiNiO ₂ as a positive electrode active material, the main cause of cycle deterioration is the crystal structure accompanying the occlusion / release of lithium ions into / from LiNiO ₂ . It is thought to be in collapse. The present inventors have conducted intensive studies and found that by selecting an appropriate carbon material as an active material of a negative electrode to be opposed, the amount of lithium ions absorbed and released by LiNiO ₂ during charge and discharge can be regulated. I got Also, regarding the precipitation of dendrite on the negative electrode surface during overcharge,
It has been found that the problem can be solved by selecting an appropriate material for the carbon material serving as the negative electrode active material.

The present invention is based on the above findings,
Stabilization of the positive electrode active material itself by using a layered rock-salt structure lithium nickel composite oxide in which part of the Ni site is replaced with another element as the positive electrode active material, and in addition, use of an appropriate carbon material for the negative electrode active material Is inexpensive and
An object of the present invention is to provide a non-aqueous electrolyte secondary battery having excellent cycle characteristics and capable of ensuring safety during overcharge.

[0011]

The non-aqueous electrolyte secondary battery of the present invention has a composition formula of LiNi _x M1 _y M2 _z O ₂ (M1 is Co, M
at least one selected from n; M2 is Al, B, F
at least one selected from e, Cr, and Mg; x + y +
z = 1; 0.5 <x <0.95; 0.01 <y <0.
4; a positive electrode using a lithium nickel composite oxide having an ordered layered rock salt structure represented by 0.001 <z <0.2) as a positive electrode active material, and a mixture of graphite and coke as a negative electrode active material. And a negative electrode.

The positive electrode active material of the non-aqueous electrolyte secondary battery of the present invention is based on a layered rock salt structure LiNiO ₂ , which is less expensive than the layered rock salt structure LiCoO ₂ , in order to stabilize the crystal structure of the LiNiO ₂ . The Ni site is partially substituted with atoms of two or more kinds of predetermined elements. Therefore, this lithium-nickel composite oxide can constitute a secondary battery which is inexpensive and has good cycle characteristics.

[0013] A mixture of graphite and coke is used as the negative electrode active material of the nonaqueous electrolyte secondary battery of the present invention. Graphite has high crystallinity and has a clear stage in which lithium ions are occluded, so that lithium ions can be smoothly inserted and extracted, and the reversible charge / discharge capacity is large. On the other hand, coke is extremely cheap among carbon materials,
In addition, it is a substance with low degree of graphitization and low crystallinity.
The capacity that can be released is small. The negative electrode active material in which the two different carbon materials are mixed keeps the battery capacity large and effectively restricts the transfer of lithium ions between the positive and negative electrodes in the normal charge / discharge range, thereby storing and storing a large amount of lithium. It is possible to suppress the collapse of the crystal structure of the lithium nickel composite oxide as the positive electrode active material due to the release, and to configure a secondary battery having good cycle characteristics. In addition, due to the size of the irreversible capacity of coke, even if the secondary battery is once overcharged, the negative electrode active material can prevent dendrite from depositing on the surface of the negative electrode. Thus, a battery having excellent performance can be formed.

The non-aqueous electrolyte secondary battery of the present invention is constructed by combining the above-mentioned positive electrode active material and negative electrode active material.
A secondary battery that is inexpensive and has good cycle characteristics, particularly also has excellent cycle characteristics in a high-temperature environment where the internal resistance of the secondary battery is reduced, and has excellent safety during overcharge.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail in the order of the structure and manufacture of a positive electrode active material, a negative electrode active material, and a non-aqueous electrolyte secondary battery. <Positive Electrode Active Material> As described above, the nonaqueous electrolyte secondary battery of the present invention uses the composition formula LiNi _x M1 _y M2 _z O ₂
(M1 is at least one selected from Co and Mn; M2 is at least one selected from Al, B, Fe, Cr and Mg)
Species; x + y + z = 1; 0.5 <x <0.95; 0.01
<Y <0.4; 0.001 <z <0.2) A lithium nickel composite oxide having an ordered layered rock salt structure represented by: This LiNi _x M1 _y M2 _z O ₂ is composed of M having different roles.
1, a part of the Ni site is substituted by two or more elements of M2. The substitution ratio, that is, the value of x in the composition formula, is set to 0.5 <x <0.95. x ≦ 0.
In the case of 5, not only a layer having a layered rock salt structure but also a second phase such as a spinel structure is formed.
In the case of 0.95, the replacement effect is too small, so that a battery having good desired cycle characteristics cannot be formed.
It is more preferable to set the range of 0.7 <x <0.9.

The element M1 selected from Co and Mn mainly plays a role of stabilizing the crystal structure of the lithium nickel composite oxide. By stabilizing the crystal structure at M1, the cycle characteristics of the non-aqueous electrolyte secondary battery are kept good, and deterioration of the battery capacity due to charge / discharge at high temperature and storage at high temperature is particularly suppressed. In order to sufficiently exert the effect of improving the cycle characteristics, the substitution ratio of M1, that is, the value of y in the composition formula, is set to 0.01 <y <0.4. y
When ≦ 0.01, the crystal structure of the formed secondary battery is not sufficiently stabilized, so that the cycle characteristics are not good.
If ≧ 0.4, the crystallinity of the lithium-nickel composite oxide is undesirably reduced. It is more preferable that 0.05 <y <0.3. Further, Co has a capacity reduction due to element substitution, and Li (Co, Ni) O
₂ is an all-solid solution type and has the advantage of minimizing the decrease in crystallinity. Therefore, considering this, it is desirable to use Co for M1.

The element M2 selected from Al, B, Fe, Cr and Mg mainly serves to suppress the decomposition reaction of the active material due to the release of oxygen and to improve the thermal stability. Due to this role, the substitution ratio of M2, that is, the value of z in the composition formula, is set to 0.001 <z <0.2. z ≦
In the case of 0.001, a sufficient effect on safety cannot be obtained, and in the case of z ≧ 0.2, the capacity of the positive electrode decreases, which is not preferable. In addition, 0.004 <z <
More preferably, it is 0.1. Furthermore, Al has the advantage of minimizing the capacity loss while improving the thermal stability.
It is desirable to use

The layered rock salt structure lithium nickel composite oxide represented by the composition formula LiNi _x M1 _y M2 _z O ₂ is, for example, L
iOH.H ₂ O, Ni (OH) ₂ , Co ₃ O ₄ , Al (O
H) A predetermined amount of each of ₃ was mixed and 850 ° C in an oxygen stream.
It can be synthesized by firing at a temperature of about 20 hours for about 20 hours. <Negative electrode active material> In the nonaqueous electrolyte secondary battery of the present invention, a mixture of graphite and coke is used as the negative electrode active material.

The graphite constituting the mixture has advantages such as a high true density, a large volume specific capacity, a good flatness at a low charge / discharge potential, and a high energy density of a nonaqueous electrolyte secondary battery. To contribute. In this secondary battery, this graphite is used as a base carbon material to secure a discharge capacity. As the graphite, various materials such as natural graphite, for example, artificial graphite obtained by heat-treating coke at 2800 ° C. or more can be used. Among these,
Graphitized mesophase microspheres (MCM) obtained by graphitizing mesophase microspheres having optical anisotropy obtained in the process of heating pitches at about 400 ° C. at a temperature of 2000 ° C. or more.
It is desirable to use B). In MCMB, since the crystallites are oriented in a lamellar shape in spherical particles and the crystallite end faces are exposed on the particle surface, the absorption and release of lithium ions are performed more smoothly, and the charging and discharging of a large current is performed. This is because it becomes a suitable material.

Coke to be mixed with graphite can be obtained, for example, by subjecting a tar pitch raw material obtained from coal or petroleum to a heat treatment at a relatively low temperature of about 1500 ° C. It is one type of carbon material having low degree of graphitization and low crystallinity. Coke has an advantage of being extremely inexpensive among carbon materials used as a negative electrode active material of a nonaqueous electrolyte secondary battery. In addition, graphite stores lithium in the stage between the carbon nets, whereas coke does not have a definite stage. Therefore, it is considered that there are many sites where lithium is stored compared to graphite. Therefore, coke can constitute a negative electrode having a larger theoretical capacity than graphitic carbon. However, when an actual secondary battery is constructed, the reversibility of the lithium insertion / removal reaction is low (the charge / discharge efficiency is low), so the effective discharge capacity of the battery is smaller than that of a battery using graphite as the negative electrode active material. Becomes In other words, coke is a carbon material that has a potential (irreversible) lithium storage capacity, despite the fact that only a smaller amount of lithium ions can be stored and released reversibly than graphite in the normal range of charging and discharging of batteries. It is. By utilizing this characteristic of coke, the movement of lithium ions between the positive and negative electrodes in the normal charge and discharge range is restricted, the collapse of the crystal structure of the lithium nickel composite oxide, which is the positive electrode active material, is suppressed, and the cycle characteristics are improved. It ensures safety even if the secondary battery is overcharged.

From the above, it is desirable that the mixing ratio of coke in the mixture be 10 wt% or more and 90 wt% or less. If the mixing ratio of coke is too large, the battery capacity during normal charging and discharging of the secondary battery will be small. Conversely, if the mixing ratio of coke is too small, the cycle characteristics will deteriorate. In addition, when coke is used alone as the negative electrode active material, the battery voltage of the configured secondary battery becomes considerably low. Even in consideration of this point, it can be said that it is desirable to use a mixture of graphite and coke for the negative electrode active material.

<Structure and Production of Non-Aqueous Electrolyte Secondary Battery> The non-aqueous electrolyte secondary battery of the present invention comprises a mixture of the above-mentioned lithium nickel composite oxide as a positive electrode active material, graphite and coke. And a negative electrode having a negative electrode active material as a main component, and a positive electrode and a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, a non-aqueous electrolyte, and the like may be assembled in a battery case. it can.

The positive electrode was prepared by mixing a powder of the above-mentioned lithium nickel composite oxide, which is a positive electrode active material, with a conductive material and a binder, and adding an appropriate solvent to form a paste-like positive electrode mixture. And the like, can be applied to the surface of a current collector made of metal foil and dried, and if necessary, compressed to increase the electrode density. The conductive material is for ensuring the electrical conductivity of the positive electrode, and may be a mixture of one or more of carbon material powders such as carbon black, acetylene black, and graphite. The binding agent plays a role of binding the active material particles and the conductive material particles, and may be a fluororesin such as polytetrafluoroethylene, polyvinylidene fluoride, or fluororubber, or a thermoplastic resin such as polypropylene or polyethylene. . An organic solvent such as N-methyl-2-pyrrolidone can be used as a solvent in which the active material, the conductive material, and the binder are dispersed.

The negative electrode is prepared by mixing a powder of a mixture of graphite and coke as the negative electrode active material with a binder and adding water as a solvent to form a paste into a paste. It can be formed by coating and drying on the surface of the current collector and, if necessary, compressing it to increase the electrode density. Like the positive electrode, the binder may be a fluororesin such as polyvinylidene fluoride, and the active material may be an organic solvent such as N-methyl-2-pyrrolidone as a solvent for dispersing the binder. Can be.

A secondary battery is constructed with a positive electrode and a negative electrode facing each other. However, in order to prevent dendrite deposition on the negative electrode surface, the battery is designed with a larger capacity of the negative electrode than the positive electrode. It is desirable to do. When considering the theoretical capacity of the positive and negative electrodes (capacity including irreversible capacity) as a reference, the capacity ratio per area (positive and negative electrode area capacity ratio)
Is preferably in the range of 1.1 to 2.5. It is desirable to determine the active material density of the positive electrode and the negative electrode and the coating thickness of the mixture layer of the positive electrode and the negative electrode so as to be within this preferable range.

The separator sandwiched between the positive electrode and the negative electrode configured as described above separates the positive electrode and the negative electrode and holds the electrolyte, and a thin microporous film such as polyethylene or polypropylene can be used. . The non-aqueous electrolyte is obtained by dissolving a lithium salt as an electrolyte in an organic solvent. The lithium salt is dissociated by dissolving in an organic solvent and forms lithium ions in the electrolyte. LiBF ₄ , Li
PF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiAsF ₆ ,
LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) _{2 and the} like. Each of these lithium salts may be used alone, or two or more of these lithium salts may be used in combination.

An aprotic organic solvent is used as the organic solvent for dissolving the lithium salt. For example, a solvent mixture of one or more of cyclic carbonate, chain carbonate, cyclic ester, cyclic ether or chain ether can be used. Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate.Examples of the chain carbonate include dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.Examples of the cyclic ester include gamma butyl lactone and gamma. Examples of barrel lactone include cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, and examples of chain ether include dimethoxyethane and ethylene glycol dimethyl ether. Any one of these can be used alone, or two or more can be used as a mixture.

It is preferable that the lithium salt and the organic solvent serving as the electrolyte are mixed in a sufficiently dehydrated state in order to prevent generation of free acid such as HF. Further, the electrolyte concentration in the electrolyte is preferably at least 0.1 M or more in order to reduce the internal resistance. In a normal non-aqueous electrolyte secondary battery, the concentration is 0.2 to 1.5 M. Is more preferred.

The non-aqueous electrolyte secondary battery having the above-mentioned components as constituent elements can be of various shapes such as a cylindrical type and a laminated type. In any case, a separator is sandwiched between the positive electrode and the negative electrode, and the positive electrode and the negative electrode are alternately laminated or wound into a roll to form an electrode body. The negative electrode current collector is connected to the positive electrode terminal and the negative electrode terminal that communicate with the outside using a current collecting lead, etc., and the electrode body is impregnated with a non-aqueous electrolyte solution, and sealed in a battery case to form a secondary battery. Is completed.

[0030]

EXAMPLE Based on the above embodiment, a positive electrode using a lithium nickel composite oxide in which a Ni site was substituted with a predetermined element as a positive electrode active material, and a negative electrode using a mixture of graphite and coke as a negative electrode active material were used. The provided 18650 type cylindrical secondary battery was manufactured as an example. Furthermore, for comparison with this secondary battery, a secondary battery using graphite alone as the negative electrode active material, a secondary battery using coke alone as the negative electrode active material, and a lithium-nickel composite oxide without replacing Ni sites A secondary battery using the product as a positive electrode active material was produced as a comparative example. Then, charge and discharge cycle tests were performed on the secondary batteries of the example and the comparative example, and the cycle characteristics of both the secondary batteries were evaluated. Hereinafter, these will be described.

<Non-Aqueous Electrolyte Secondary Battery of Example> In this secondary battery, a layered rock salt structure LiNi _0.895 Co _0.1 Al _0.005
O ₂ was used as the positive electrode active material. LiNi _0.895 Co _0.1 Al
_0.005 O ₂ is based on LiOH ·
Baking at a temperature of 800 ° C. a mixture of H ₂ O, Ni (OH) ₂ , Co ₃ O ₄ , and Al (OH) ₃ in a molar ratio of 102: 89.5: 10: 5, respectively. Was used. The mixture used as the negative electrode active material is a graphitized mesophase microsphere (MCM) as graphite.
B) and coke obtained by baking the tar at 1000 ° C. were mixed.

The positive electrode of this secondary battery was prepared as follows. First, 100 parts by weight of the above LiNi _0.895 Co _0.1 A
l _0.005 O ₂ powder, 7 parts by weight of acetylene black (manufactured by Denka) as a conductive material and 10 parts by weight of polyvinylidene fluoride (PVDF) as a conductive material were mixed, and an appropriate amount of N-methyl-2- Pyrrolidone (NMP) was added to obtain a paste-like positive electrode mixture. Next, this positive electrode mixture was applied to both surfaces of a positive electrode current collector and an aluminum foil, dried, and compression-molded by a roll press to obtain a sheet-shaped positive electrode.

The negative electrode was manufactured as follows. First, the MCMB and the coke in a weight ratio of 3: 7, 5: 5,
Three kinds of mixed powders mixed at 7: 3 were prepared. To 100 parts by weight of each mixed powder, 10 parts by weight of PVDF was mixed as a binder, and an appropriate amount of NMP was added.
A kind of paste-like negative electrode mixture was obtained. Next, similarly to the positive electrode, each negative electrode mixture was applied to both surfaces of a copper foil serving as a negative electrode current collector, dried, and compression-molded by a roll press to obtain three types of sheet-shaped negative electrodes.

The above positive electrode and each negative electrode were each
Wound through a polypropylene separator of μm,
A roll-shaped electrode body was formed. This electrode body is 1865
The battery was inserted into a 0-type battery can, a non-aqueous electrolyte was injected to impregnate the electrode body, and then the battery can was sealed to complete the assembly of the secondary battery. As the non-aqueous electrolyte, a solution obtained by dissolving LiPF ₆ at a concentration of 1 M in a mixed solvent obtained by mixing ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1 was used.

A non-aqueous electrolyte secondary battery using a mixed powder obtained by mixing MCMB and coke in a ratio of 3: 7 as a negative electrode active material was used as the secondary battery in Example 1, and a mixed powder mixed in a ratio of 5: 5 was used. The secondary battery according to Example 2 was used as the secondary battery, and the secondary battery according to Example 3 using the mixed powder mixed at 7: 3. <Non-aqueous electrolyte secondary battery of Comparative Example 1> Instead of the mixed powder of MCMB and coke, the above-mentioned MCM was used as a negative electrode active material.
A non-aqueous electrolyte secondary battery using B alone was produced and used as a secondary battery of Comparative Example 1. Except for the negative electrode active material, the structure and manufacturing method of the secondary battery were the same as those in the example.

<Non-aqueous electrolyte secondary battery of Comparative Example 2> MCM
A non-aqueous electrolyte secondary battery using the above coke alone as a negative electrode active material instead of the mixed powder of B and coke was produced, and the secondary battery of Comparative Example 2 was obtained. Except for the negative electrode active material, the structure and manufacturing method of the secondary battery were the same as those in the example.

<Non-aqueous electrolyte secondary battery of Comparative Example 2>
Instead of iNi _0.895 Co _0.1 Al _0.005 O ₂ , a secondary battery using LiNiO ₂ having a layered rock salt structure in which the Ni site was not replaced with another element as a positive electrode active material was produced, and the secondary battery of Comparative Example 3 was produced. And Except for the positive electrode active material, the structure and manufacturing method of the secondary battery were the same as those of the secondary battery of Example 1 using a mixed powder of MCMB and coke mixed at 3: 7 as the negative electrode active material.

<Evaluation of Cycle Characteristics> Each of the secondary batteries of the examples and the comparative examples was subjected to a charge / discharge cycle test to evaluate the cycle characteristics. The charge / discharge cycle test was performed at a high temperature of 60 ° C., which is generally assumed to be the upper limit of the operating temperature of the battery. The conditions of the charge / discharge cycle test are as follows: a current density of 2.0 mA / cm ^{2 at which} a relatively large current is charged and discharged;
, And then discharging to 3.0 V at the same current density of 2.0 mA / cm ² was defined as one cycle, and this was performed for 300 cycles or more.

The initial discharge capacity per unit weight of the positive electrode active material (discharge capacity at the first cycle) of each secondary battery obtained as a result of the test, and the capacity retention rate at the tenth cycle (discharge capacity in the cycle / initial discharge capacity) × 100 (%)) and the capacity retention rate at the 300th cycle are shown in Table 1 below.
FIG. 1 shows the discharge capacities per unit weight of the positive electrode active material in each cycle of the secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2, and the secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2. 2 shows the capacity retention ratio in each cycle.

[0040]

[Table 1]

Comparing the secondary batteries of Example 1 and Comparative Example 3 in Table 1 above, the effect of replacing the Ni site of the lithium manganese composite oxide having a layered rock salt structure used as a positive electrode active material with a predetermined element is clear. Becomes The secondary battery of Comparative Example 3 using LiNiO ₂ in which the Ni site was not substituted showed a high value in the initial discharge capacity, but had a low capacity maintenance rate at the 10th cycle of 50% in terms of the capacity maintenance rate, and further increased the cycle. In the 300th cycle where is repeated, the value is as extremely low as only 10%. On the other hand, LiNi in which Ni site is replaced with a predetermined element is used.
Secondary battery of Example 1 using _0.895 Co _0.1 Al _{0. 005} O ₂ is 97% at 10 cycle, 85 in the 300th cycle
%, Which is far superior in cycle characteristics.

Further, from Table 1, FIG. 1 and FIG. 2, the effect of mixing coke with the negative electrode active material becomes clear.
The secondary battery of Comparative Example 1 in which coke was not mixed was 2
Although the discharge capacity increases at the cycle, the discharge capacity rapidly decreases thereafter, and the cycle deterioration considerably progresses. On the other hand, the secondary batteries of Examples 1 to 3 in which coke was mixed and Comparative Example 2 using coke alone had 85% or more even when cycles of 300 cycles or more were repeated. And a secondary battery having good cycle characteristics. However, the secondary battery of Comparative Example 2 using only coke as the negative electrode active material has a small initial discharge capacity and is not a practical battery. From the results of these data, the mixing ratio of coke in the mixture serving as the negative electrode active material was 10 w
It can be inferred that it is desirable that the content be at least t% and at most 90 wt%.

From the above evaluation results of the cycle characteristics of each secondary battery, it was found that a positive electrode using an ordered layered rock-salt structure lithium nickel composite oxide in which a part of Ni site was replaced with a predetermined element as a positive electrode active material, The non-aqueous electrolyte secondary battery of the present invention comprising a negative electrode using a mixture of graphite and coke as a negative electrode active material is a secondary battery having excellent cycle characteristics, especially in high temperature environments. Can be confirmed.

[0044]

As described above, the nonaqueous electrolyte secondary battery of the present invention comprises a positive electrode using an ordered layered rock-salt structure lithium nickel composite oxide in which a part of Ni site is replaced with a predetermined element as a positive electrode active material, and a graphite. And a negative electrode using a mixture of coke as a negative electrode active material. With such a configuration, the nonaqueous electrolyte secondary battery of the present invention is a secondary battery that is inexpensive, has excellent cycle characteristics, and can ensure safety during overcharge.

[Brief description of the drawings]

FIG. 1 shows the relationship between the number of cycles in a charge / discharge cycle test and the discharge capacity per positive electrode active material of each secondary battery in which the mixing ratio of graphite and coke in the negative electrode active material was changed.

FIG. 2 shows the relationship between the number of cycles in a charge / discharge cycle test and the capacity retention of each secondary battery in which the mixing ratio of graphite and coke in the negative electrode active material was changed.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takahiko Homma 41 Toyota Chuo Research Institute, Inc. 41, Yokomichi, Toyota Central Research Laboratory Co., Ltd. 41 Toyota Chuo R & D Co., Ltd., No. 41, Chuchu-Yokomichi, Nagakute-cho, Aichi-gun, Japan ) Inventor, Takeshi Sasaki 41-cho, Yojimichi, Nagakute-cho, Aichi-gun, Aichi, Japan 1 Toyota Central Research Laboratory Co., Ltd. 41F, Toyoda Central R & D Co., Ltd. F-term (reference) 5H003 AA04 AA08 AA10 BA03 BB01 BB05 BC06 BD00 BD04 5H014 AA02 EE08 EE10 HH00 HH01 5H029 AJ05 AJ12 AL06 AL06 AM03 AM04 AM05 AM07 DJ17 HJ01 HJ02

Claims (3)

[Claims] A composition formula LiNi _x M1 _y M2 _z O ₂ (M1 is C
at least one selected from o and Mn; M2 is Al;
At least one selected from B, Fe, Cr, and Mg; x
+ Y + z = 1; 0.5 <x <0.95; 0.01 <y <
0.4; 0.001 <z <0.2) A positive electrode using a lithium nickel composite oxide having an ordered layered rock-salt structure represented by the following formula as a positive electrode active material, and a mixture of graphite and coke as a negative electrode active material. A non-aqueous electrolyte secondary battery comprising the negative electrode used. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein a mixing ratio of the coke in the mixture is 10 wt% or more and 90 wt% or less. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein M1 in the composition formula of the lithium nickel composite oxide is Co, and M2 is Al. .