JP2000200624A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a nonaqueous electrolyte secondary battery at low cost and secure superiority in cycle characteristics and safety against overcharging by providing a positive electrode using lithium-nickel complex oxide of regular laminar rock salt structure for a positive electrode active material and a negative electrode using graphitization retarding carbon for a negative electrode active material. SOLUTION: Graphitization retarded carbon is used for a negative electrode active material. Among the graphitization retarded carbons, phenol resin burned substance, furfuryl alcohol resin burned substance, polyacrylonitrile carbon fiber, pseudo-isotropic carbon are given. The graphitization retarded carbon is formed by burning, for example, organic compound. Among starting materials, conjugation type resin such as furfuryl alcohol resin, furfuranol resin, and furan resin and organic polymer compound such as cellulose and its derivative are given. Lithium-nickel complex oxide of regular laminar rock salt structure is used for a positive electrode active material and the stoichiometry of this substance is expressed by LiNiO2.

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 so as to obtain 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 raises the cost of lithium ion secondary batteries. When used as a power source for electric vehicles, a large capacity is required, so a large amount of positive electrode active material must be used, and expensive LiCo
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, when used as a power source for an electric vehicle that may be left outdoors, the secondary battery also has low cycle deterioration at high temperatures, since the deterioration proceeds further at high temperatures where the battery reaction is activated. It is one of the important characteristics required.

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, since they are coated or replaced with other elements, there is a problem that the other elements may cause a reduction in battery capacity and a deterioration in rate characteristics, and even if these means are practically satisfactory. It has been difficult to obtain a secondary battery having some 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 . In collapse. As a result of intensive studies, the present inventor has found that by selecting an appropriate carbon material as an active material of a negative electrode to be opposed, LiNi
It has been found that the amount of lithium ions inserted into and released from O ₂ can be regulated. In addition, it has been found that the precipitation of dendrite on the surface of the negative electrode during overcharge can be solved by selecting an appropriate carbon material as the negative electrode active material.

The present invention is based on the above findings,
By using a layered rock-salt structure lithium nickel composite oxide as the positive electrode active material and using an appropriate carbon material for the negative electrode active material, it is inexpensive, has excellent cycle characteristics, and can ensure safety during overcharge. An object of the present invention is to provide an electrolyte secondary battery.

[0011]

The non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode using a lithium nickel composite oxide having a regularly arranged layered rock salt structure as a positive electrode active material, and a non-graphitizable carbon used as a negative electrode active material. A negative electrode used for the substance.
The non-graphitizable carbon used as the negative electrode active material of the nonaqueous electrolyte secondary battery is a so-called hard carbon, and is a carbonaceous material having an amorphous structure represented by glassy carbon. . This non-graphitizable carbon is generally a material obtained by carbonizing a thermosetting resin, and means a material that has a low degree of graphitization and does not develop a graphitized structure even when the heat treatment temperature is increased. I do.

[0012] The graphite material occludes lithium at the stage between the carbon nets, whereas the non-graphitizable carbon does not have a definite stage, so that lithium is occluded compared to the graphite material. It is thought that there are many sites.
Therefore, non-graphitizable carbon 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 storage / release reaction is low (the charge / discharge efficiency is low), so the effective discharge capacity of the battery is lower than that of the battery using graphite carbon as the negative electrode active material. It will be small. In other words, non-graphitizable carbon is a potential (irreversible) lithium, despite the fact that only a smaller amount of lithium ions can be reversibly absorbed and released than graphitic carbon in the normal range of charging and discharging of batteries. It is a carbon material with storage capacity.

The nonaqueous electrolyte secondary battery of the present invention utilizes the above characteristics of non-graphitizable carbon when used as a negative electrode active material. In other words, in a non-aqueous electrolyte using non-graphitizable carbon as the negative electrode active material, during charge and discharge in the normal use range, lithium ions are transferred to the lithium nickel composite oxide, which becomes the positive electrode active material on the negative electrode active material side. It regulates the amount of occlusion and release, and acts to suppress the collapse of the crystal structure associated with large expansion and contraction of the lithium nickel composite oxide. Once overcharged, its large irreversible lithium storage capacity allows it to absorb a large amount of lithium ions released from the positive electrode active material, preventing the deposition of metallic lithium dendrite on the negative electrode surface. Acts to be.

The non-aqueous electrolyte secondary battery of the present invention comprises a negative electrode active material.
Due to the above-mentioned effect of non-graphitizable carbon,
Effective use of layered rock-salt lithium nickel composite oxide
Can be used as positive electrode active material, repeated charging and discharging
Discharge capacity is less degraded by electricity and overcharge
It becomes a secondary battery with excellent safety. In addition, the non-aqueous
In lyolysis secondary batteries, ordered positively active layered rock salt
The basic composition is Li
NiO_TwoA part of the Ni site for the one represented by
By substituting the element, the composition formula LiNi_xM1 _yM2
_zO_Two(M1 is at least one selected from Co and Mn;
M2 is at least one selected from Al, B, Fe, Cr, and Mg.
X + y + z = 1; 0.5 <x <0.95;
0.01 <y <0.4; 0.001 <z <0.2)
What is done can also be used. Thus, Ni
By replacing part of the site with another element, the lithium nickel
Stabilization of the crystal structure of the composite oxide
It is possible to further improve the cycle characteristics of secondary batteries.
You.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS <Negative electrode active material> In the non-aqueous electric liquid secondary battery of the present invention, non-graphitizable carbon is used as the negative electrode active material. The non-graphitizable carbon that can be used includes a phenol resin fired body, a furfuryl alcohol resin fired body,
Examples thereof include polyacrylonitrile-based carbon fiber and pseudo-isotropic carbon.

The non-graphitizable carbon can be produced, for example, by firing an organic compound. Starting materials include furfuryl alcohol resin, furfuranol resin, furan resin, phenolic resin, acrylic resin, vinyl halide resin, polyimide resin, polyamideimide resin, polyamide resin, conjugated resin such as polyacetylene, cellulose and its derivatives, etc. And the like. These starting materials are, for example, carbonized in a stream of an inert gas such as nitrogen at 300 to 700 ° C., and thereafter 900 to 15 at a rate of 1 to 100 ° C./min.
By raising the temperature to 00 ° C. and maintaining the temperature at the ultimate temperature for 0 to 30 hours, non-graphitizable carbon can be obtained.

The non-aqueous graphitizable carbon used in the non-aqueous electrolyte secondary battery of the present invention has a (002) plane spacing of at least 0.34 nm and a (002) plane obtained by X-ray diffraction. It is desirable that the C-axis crystallite thickness is 10.0 nm or more.
The reason for this is that if the interplanar spacing is less than 0.34 nm, a carbon hexagonal structure develops into a graphitized structure, and if the crystallite thickness is less than 10.0 nm, the true density becomes less than half that of graphite and the volume becomes less. This is because the capacity per unit decreases.

As an example of non-graphitizable carbon, a non-graphitizable carbon used in later examples, Carb manufactured by Osaka Gas Co., Ltd.
FIG. 1 shows a diffraction chart based on the on-S X-ray diffraction method. This Carbon-S is non-graphitizable carbon obtained by pulverizing isotropic pitches and carbonizing at 900 ° C. FIG. 1 also shows, for comparison, a diffraction chart of MCMB25-28 manufactured by Osaka Gas, which is a kind of graphitic carbon and is a graphitized mesophase sphere used in a comparative example described later.

As can be seen from the comparison, the non-graphitizable carbon does not have a sharp peak unlike the graphitic carbon, so that it can be confirmed that the carbon is almost amorphous. In addition, by analyzing from the peak position of the (002) plane in the chart, the present non-graphitizable carbon is (00)
2) It can be confirmed that the spacing between the surfaces is 0.38 nm.

<Positive Electrode Active Material> In the nonaqueous electrolyte secondary battery of the present invention, a lithium nickel composite oxide having an ordered layered rock salt structure is used as the positive electrode active material. The stoichiometric composition of the lithium-nickel composite oxide having this ordered layered rock salt structure is represented by LiNiO ₂ . As described above, LiNiO ₂ having a layered rock salt structure is inexpensive and has an amount of lithium that can be released, compared to the layered rock salt structure LiCoO ₂ that is currently mainstream in current nonaqueous electrolyte secondary batteries. More is an advantage.

In the non-aqueous electrolyte secondary battery of the present invention,
LiNiO having the above stoichiometric composition _TwoOr stoichiometry
Use of lithium nickel composite oxide with composition close to
it can. In addition, this lithium nickel composite oxide crystal structure
Non-aqueous electrolysis with stable structure and less cycle deterioration
To obtain a liquid, replace part of the Ni site with another element
The composition formula LiNi_xM1_yM2_zO_Two(M1 is Co, Mn
M2 is Al, B, Fe,
At least one selected from Cr and Mg; x + y + z =
1; 0.5 <x <0.95; 0.01 <y <0.4;
0.001 <z <0.2)
Is desirable. Among them, M1 is Co,
A composition formula LiNi wherein M2 is Al_xCo_yAl_zO_TwoIn table
Used lithium nickel composite oxide with layered rock salt structure
Is more desirable. Co, which is a substitution element, is smaller than Ni.
All have the property of being hardly oxidized, and this Co is partially
By forming a solid solution, it remains in the structure even when fully charged.
LiCoO_TwoTo stabilize the layered structure.
Yes, stabilization of crystal structure of lithium nickel composite oxide
High effect. Al is excessively charged, such as when overcharged.
Even if the positive electrode active material is oxidized, oxygen
It plays a role of suppressing, and has a high effect of improving safety.

The layered rock salt-structured lithium composite oxide is prepared, for example, by mixing a mixture of Li ₂ O ₃ and NiO in oxygen at 650-700.
By baking at ℃, it is possible to synthesize a material having a stoichiometric composition. In addition, the composition formula LiNi _x Co _y Al _z
When synthesizing a compound represented by O ₂ , for example, Li
OH, Ni (OH) ₂ , Co ₂ O ₃ and Al ₂ O ₃
A mixture of i: Ni: Co: Al = 1: x: y: z can be synthesized by firing at 800 ° C. for 8 hours in an oxygen atmosphere.

The lithium nickel composite oxide is represented by X
Of diffraction peak by (003) plane in X-ray diffraction method
I₍₀₀₃₎Of diffraction peak due to (104) plane and I₍₁₀₄₎
Is less than 1.4 <I₍₀₀₃₎/ I₍₁₀₄₎<2.0
It is desirable to use I ₍₀₀₃₎/ I₍₁₀₄₎= 2
Is in a state where Li and Ni are completely ordered,
I₍₀₀₃₎/ I₍₁₀₄₎Is closer to 1, Li and Ni and
Are randomly mixed. I₍₀₀₃₎/ I₍₁₀₄₎
> 1.4, it is judged that the order is over 80%.
This is because it can be cut off and has excellent performance as an active material.

As an example of a lithium nickel composite oxide which can be used as a positive electrode active material, a lithium nickel composite oxide manufactured by Fuji Chemical Co., Ltd. and represented by a composition formula of LiNi _0.85 Co _0.1 Al _0.05 O ₂ used in the following examples. FIG. 2 shows a diffraction chart based on the X-ray diffraction method. By comparing the peak intensities of the (003) plane and the (104) plane in the diffraction chart, the lithium nickel composite oxide has a value of I ₍₀₀₃₎ / I ₍₁₀₄₎ of 1.93. It can be confirmed that the material belongs to a suitable range.

<Structure and Production of Nonaqueous Electrolyte Secondary Battery> The nonaqueous electrolyte secondary battery of the present invention comprises a positive electrode using the above-mentioned lithium nickel composite oxide as an active material, and a negative electrode comprising the above non-graphitizable carbon. A negative electrode as an active material is used as a main component, and the positive electrode and the negative electrode, a separator sandwiched between the positive electrode and the negative electrode, a non-aqueous electrolyte, and the like can be assembled in a battery case.

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 binder with the powder of the non-graphitizable carbon, which is a negative electrode active material, and adding water as a solvent to form a paste. It can be formed by coating and drying on the surface of the electric body and, if necessary, compressing to increase the electrode density. Like the positive electrode, the binder includes
A fluorine-containing resin such as polyvinylidene fluoride can be used, and N.sub.2 is used as a solvent for dispersing the active material and the binder.
Organic solvents such as -methyl-2-pyrrolidone can be used.

A secondary battery is constructed with the positive electrode and the negative electrode facing each other. However, in order to prevent dendrite deposition on the negative electrode surface, it is necessary to design the battery with a larger negative electrode capacity than the positive electrode. Is desirable. The counter electrode of the positive electrode and the negative electrode is L
When considering the capacity that can be taken out as i, the capacity ratio per area (positive / negative electrode area capacity ratio) is 1.1 to 2.0.
The following range is preferable. To be in this preferred range,
It is desirable to determine the active material density of the positive and negative electrodes and the coating thickness of the mixture layer of the positive and negative electrodes.

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 is present in the electrolyte as lithium ions. 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 acids 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 above-described non-aqueous electrolyte secondary battery is a non-aqueous electrolyte secondary battery. The shape of the non-aqueous electrolyte secondary battery may be various types 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.

[0033]

EXAMPLE Based on the above embodiment, a 18650 type cylindrical secondary battery provided with a positive electrode using a lithium nickel composite oxide as a positive electrode active material and a negative electrode using a non-graphitizable carbon as a negative electrode active material, It was produced as an example. Further, for comparison with this secondary battery, a secondary battery using graphite carbon as the negative electrode active material as a negative 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>
The pond uses LiNi as the positive electrode active material._0.85Co_0.1Al_0.05O
_Two(Manufactured by Fuji Chemical Co., Ltd.).
Battery using carbon (Carbon-S: Osaka Gas)
It is. The positive electrode of this secondary battery was produced as follows. Ma
85 parts by weight of the above LiNi _0.85Co_0.1Al_0.05O_Two
Acetylene black (HS-100:
Powder was mixed with 5 parts by weight of
12% polyvinylidene fluoride (PVDF) / N-methyl
Ru-2-pyrrolidone (NMP) solution, PVDF solid content
Is 5 parts by weight, and an appropriate amount of NMP is further added.
The viscosity was adjusted by adding the mixture to obtain a paste-like positive electrode mixture. Next
Then, this positive electrode mixture was formed into a 20 μm thick positive electrode current collector.
Apply to both sides of aluminum foil, dry and apply to positive electrode mixture layer
Active material density at 2.3g / cm^ThreeUntil compression
It was shaped into a sheet-shaped positive electrode.

The negative electrode was manufactured as follows. First, 9
5 parts by weight of the above non-graphitizable carbon, like the positive electrode,
12% PVDF / NMP solution, PVDF solid content
5 parts by weight, and add an appropriate amount of NMP.
To adjust the viscosity to obtain a paste-like negative electrode mixture. Next
Next, this negative electrode mixture was formed into a 10 μm thick negative electrode current collector.
Apply to both sides of the copper foil, dry it, and use the active material in the negative electrode mixture layer.
1.2g / cm ^ThreeCompression molding until
The negative electrode was in the form of a sheet. The positive and negative electrode mixture layers are
Based on the positive and negative electrode active material capacity obtained in advance
And a thickness such that the above-described positive / negative electrode area capacity ratio becomes 1.5.
Formed.

The positive electrode and the negative electrode were wound through a 22 μm-thick polypropylene separator to form a roll-shaped electrode body. This electrode body was inserted into a 18650 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.

<Non-Aqueous Electrolyte Secondary Battery of Comparative Example> In this secondary battery, LiNi was used as the positive electrode active material in the same manner as in the example.
_A secondary battery using _0.85 Co _0.1 Al _0.05 O ₂ (manufactured by Fuji Chemical Co., Ltd.) and a graphitized mesophase sphere (MCMB25-28: manufactured by Osaka Gas Co., Ltd.) was used as the negative electrode active material, unlike the case of the embodiment. is there.

The positive electrode of this secondary battery was produced in the same manner as in the example. The negative electrode was prepared by mixing 95 parts by weight of the MCMB with a 12% PVDF / NMP solution serving as a binder so that the PVDF solid content was 5 parts by weight, in the same manner as in Example. Then, it was applied to the surface of a copper foil current collector, and compression molded until the active material density became 1.2 g / cm ³ . The positive / negative electrode area capacity ratio was set to 1.5 as in the case of the example. The assembling of the battery with the positive electrode and the negative electrode was completed in the same process as in the example. In addition,
Other components except the negative electrode such as the separator, the non-aqueous electrolyte, and the battery can were the same as those in the examples.

<Evaluation of Cycle Characteristics> The secondary batteries of Examples and Comparative Examples were subjected to a charge / discharge cycle test to evaluate the cycle characteristics. The tests on the secondary batteries of the examples were performed as follows. First, before the test, as conditioning, 0.25 mA in a thermostat at 20 ° C.
/ Cm ^{2 at} a current density of 4.1 V, and after a 10-minute pause, discharging was performed at a current density of 0.25 mA / cm ² to 2.5 V. Next, the battery was stored in a constant temperature bath at 20 ° C. for 3 days in a discharged state, and then subjected to a charge / discharge cycle test.
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 for the charge / discharge cycle test were as follows: a current density of 1.0 mA / cm ² and 4.1.
Discharge to 2.5 V at a current density of 1.0 mA / cm ² after charging for 10 minutes and resting for 10 minutes.
This was performed up to 500 cycles.

The same charge / discharge cycle test was performed on the secondary battery of the comparative example. However, because the oxidation-reduction potential is about 0.5 V higher than the non-graphitizable carbon of the example,
The discharge end voltage in the conditioning and charge / discharge cycle test was 3.0 V, and charge / discharge was performed between 4.1 V and 3.0 V. In each of the secondary batteries of the example and the comparative example, a test was performed on two batteries and evaluated.

FIG. 3 shows the change in the discharge capacity per unit weight of the positive electrode active material of the secondary batteries of the examples and the comparative examples with respect to the results of the charge and discharge cycle test. FIG. 4 shows the change in the capacity retention ratio when 100% is set. Furthermore, the initial discharge capacity of each of the secondary batteries of Example and Comparative Example was 1
Table 1 below shows the average capacity deterioration rate per cycle from 1 to 100 cycles and the average capacity deterioration rate per cycle from 101 to 500 cycles in the case of 00%.
Shown in

[0042]

[Table 1] As shown in FIG. 3, the secondary battery of the comparative example has an initial discharge capacity of about 150 mAh / g, whereas the secondary battery of the example has an initial discharge capacity of about 120 mAh / g, which is small. This is due to the fact that the non-graphitizable carbon as the active material has a large ability to irreversibly occlude lithium (has a large irreversible capacity). However, the reverse was observed after about the 350th cycle, and it was found that the secondary battery of the example using the non-graphitizable carbon as the negative electrode active material had a larger discharge capacity.

Focusing on the change in the capacity retention ratio shown in FIG. 4, the secondary battery of the comparative example shows an increase in capacity up to about 10 cycles, and thereafter degrades while drawing an upwardly convex curve. You can check the situation. On the other hand, in the secondary battery of the example, although the capacity deterioration is slightly large at the beginning of the cycle, it can be confirmed that the capacity deterioration is almost constant at a very small rate. If this is clarified by the average capacity deterioration rate shown in Table 4, in the secondary battery of the comparative example, 10
The deterioration rate up to 0 cycles is as small as 0.06%, and the subsequent cycle shows a large value of 0.13%. On the other hand, in the secondary battery of the embodiment, the deterioration rate up to 100 cycles is 0%. It can be seen that the value is relatively large at 0.1% and is extremely small at 0.02% in the subsequent cycles.

Summarizing the above results, the nonaqueous electrolyte secondary battery using the lithium nickel composite oxide as the positive electrode active material is more difficult to graphitize than the secondary battery using graphite carbon as the negative electrode active material. Secondary batteries using carbonizable carbon have better cycle characteristics when viewed over a long period of time,
It can be said that this is a more practical secondary battery. In addition, the charge / discharge cycle test was conducted at 60
Since it is performed at a temperature of ° C., it can be said that a secondary battery using non-graphitizable carbon as the negative electrode active material is a secondary battery having excellent high-temperature cycle characteristics.

[0045]

According to the present invention, a non-aqueous electrolyte secondary battery is used for a positive electrode using a lithium nickel composite oxide having an ordered layered rock salt structure as a positive electrode active material and a non-graphitizable carbon as a negative electrode active material. And the negative electrode. With such a configuration, the nonaqueous electrolyte secondary battery of the present invention is a secondary battery that is less expensive than a conventional secondary battery using a lithium cobalt composite oxide as a positive electrode active material, and In addition, a secondary battery having good cycle characteristics, especially cycle characteristics at high temperatures, and excellent safety during overcharge can be obtained.

[Brief description of the drawings]

FIG. 1 shows a diffraction chart of non-graphitizable carbon and graphitic carbon by an X-ray diffraction method.

FIG. 2 shows a diffraction chart of an ordered layered rock salt structure lithium nickel composite oxide by an X-ray diffraction method.

FIG. 3 shows a change in discharge capacity per unit weight of a positive electrode active material of the secondary batteries of Examples and Comparative Examples.

FIG. 4 shows changes in the capacity retention ratio of the secondary batteries of the example and the comparative example.

Continued on the front page (72) Inventor Takahiko Homma 41, Chuchu-ji, Yoji, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Institute, Inc. (72) Inventor Tatsuo Noriku, Tatsuo Noriku, Nagatsu-cho, Aichi-gun, Aichi, 41 No. 1 in Toyota Central Research Institute, Inc. (72) Inventor Takuaki Okuda 41, Oku-cho, Yoji, Nagakute-cho, Aichi-gun, Aichi Prefecture No. 1 in Toyota Central Research Institute, Inc. (72) Inventor Yuji Takeuchi Aichi, Aichi (71) Inventor Tetsuro Kobayashi Tetsuro Kobayashi, 41-Cho, Yokomichi, Nagakute-cho, Gunaga-cho, Gunichi Person Takeshi Sasaki 41-Chome, Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Institute Co., Ltd. (72) Inventor Kazuhiko Mukai 41-Cho, Yakumichi, Nagakute-cho, Aichi-gun, Aichi Prefecture 1 Toyota-Chuo Corporation F-term in the laboratory (reference) 5H003 AA04 AA10 BB01 BB05 BC06 BD00 BD03 5H014 AA02 EE08 EE10 HH00 HH01 5H029 AJ05 AJ12 AK03 AL06 AM01 AM02 AM03 AM04 AM05 AM07 BJ02 BJ14 DJ17 HJ02 HJ04 HJ13

Claims (5)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode using a lithium nickel composite oxide having an ordered layered rock salt structure as a positive electrode active material and a negative electrode using non-graphitizable carbon as a negative electrode active material. . 2. The non-graphitizable carbon has a (002) plane spacing of at least 0.34 nm and a (002) C-axis crystallite thickness of at least 10.0 nm obtained by X-ray diffraction. The non-aqueous electrolyte secondary battery according to claim 1, wherein 3. The lithium-nickel composite oxide comprises a set
Formula LiNi_xM1_yM2 _zO_Two(M1 is selected from Co and Mn
M2 is Al, B, Fe, Cr, M
g + x + y + z = 1;
5 <x <0.95; 0.01 <y <0.4; 0.001
<Z <0.2) according to claim 1 or claim 2.
A non-aqueous electrolyte secondary battery according to any of the above. 4. The composition according to claim 1, wherein said M1 is Co,
The non-aqueous electrolyte secondary battery according to claim 3, wherein M2 is Al. 5. The lithium-nickel composite oxide comprises X
Of diffraction peak of (003) plane in X-ray diffraction method
The ratio of the diffraction peak intensity I ₍₁₀₄₎ of the ₍₀₀₃₎ plane to the (104) plane is 1.4 <I ₍₀₀₃₎ / I ₍₁₀₄₎ <2.0. A non-aqueous electrolyte secondary battery according to any of the above items.