JP2938430B1 - Lithium secondary battery - Google Patents

Abstract

An object of the present invention is to provide a lithium secondary battery having excellent charge / discharge cycle life characteristics. SOLUTION: A positive electrode 4 and a negative electrode 6 are provided.
And at least one electrode of the negative electrode 6 is A (C
OOLi) _n (where A is an organic substance containing H or containing C and H, and n represents 1 ≦ n).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery having an improved positive electrode or negative electrode.

[0002]

2. Description of the Related Art In recent years, as electronic devices such as mobile phones and VTRs have been reduced in size and demand has increased, there has been a demand for higher capacity secondary batteries which are power sources for these electronic devices. In addition, air pollution due to exhaust gas from automobiles has become a social problem, and there is a demand for a lightweight and high-performance secondary battery as a power supply for electric vehicles.

As such a secondary battery, a non-aqueous electrolyte secondary battery having a negative electrode containing a substance capable of occluding and releasing lithium has been developed and is becoming popular as a power source for portable electronic devices. In this nonaqueous electrolyte secondary battery, a carbon material is used for the negative electrode, and propylene carbonate (P
C), ethylene carbonate (EC), methyl ethyl carbonate (MEC), dimethyl carbonate (DM
C), diethyl carbonate (DEC), 1,2-dimethoxyethane (DME), γ-butyrolactone (γ-B
L), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF) or other non-aqueous solvent.
iClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ ,
The positive electrode is made of a material in which a lithium salt (electrolyte) such as LiCF ₃ SO ₃ or LiAlCl ₄ is dissolved. As the positive electrode, a positive electrode containing LiCoO ₂ as an active material utilizing intercalation of a layered compound is used.

[0004] More recently, the LiCoO ₂ has a
, Which is expensive and has resource constraints, so LiNi _1-x Co _x O ₂ , LiNi _{1-x in which} LiNiO ₂ or Ni is partially substituted with Co or Mn as an alternative material
Metal oxides such as Mn _x O ₂ have been proposed and actively researched.

[0005] Such a secondary battery is characterized by having a high electromotive force of about 4 V, and its excellent performance has attracted attention. However, on the other hand, there was a problem that the charge / discharge cycle life, which is considered to be caused by oxidation / reduction decomposition of the electrolytic solution, was reduced.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object thereof is to provide a lithium secondary battery having excellent charge-discharge cycle life characteristics.

[0007]

SUMMARY OF THE INVENTION A lithium secondary battery according to the present invention comprises a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material.
A lithium secondary battery comprising a negative electrode and a non-aqueous electrolyte.
In addition, at least one of the positive electrode and the negative electrode contains a lithium salt of an unsaturated carboxylic acid .

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a lithium secondary battery (for example, a cylindrical lithium secondary battery) according to the present invention will be described with reference to FIG. For example, a cylindrical container 1 with a bottom made of stainless steel has an insulator 2 disposed at the bottom. Electrode group 3
Are stored in the container 1. The electrode group 3 includes:
It has a structure in which a belt-like material in which a positive electrode 4, a separator 5 and a negative electrode 6 are laminated in this order is spirally wound.

A non-aqueous electrolyte is contained in the container 1. A PTC element 7 having an opening in the center,
A safety valve 8 disposed on the TC element 7 and a hat-shaped positive terminal 9 disposed on the safety valve 8 are caulked and fixed to an upper opening of the container 1 via an insulating gasket 10. The positive electrode terminal 9 has a vent hole (not shown). One end of the positive electrode lead 11 is connected to the positive electrode 4, and the other end is connected to the PTC element 7. The negative electrode 6 is connected to the container 1 as a negative terminal via a negative lead (not shown).

Next, the positive electrode 4, the separator 5, the negative electrode 6, and the non-aqueous electrolyte will be described in detail. 1) Positive electrode 4 This positive electrode 4 is represented by a positive electrode active material and A (COOLi) _n (where A is an organic substance containing H or containing C and H, and n represents 1 ≦ n). And a compound containing a compound having a composition of the formula:

As the positive electrode active material, a general formula Li _x M
O ₂ (where M is one or more transition elements, x is x ≦ 1.1
Is shown)). Specifically, Li _x CoO ₂ , Li _x NiO ₂ ,
Li _x Mn ₂ O ₄ , Li _x Ni _1-y Co _y O ₂ (where 0 <y <
_{1), Li x Ni 1-} y Mn y O 2 ( where, 0 <y <1), L
_{i x Ni 1-y Fe y} O 2 ( where, 0 <y <1), Li x Ni
_{1-yz Co y Mn z O} 2 ( where, 0 <z + y <1 ) can be exemplified.

Examples of the compound having a composition represented by A (COOLi) _n include lithium formate, lithium acetate, lithium propionate, lithium butyrate, lithium valerate, lithium valerate, and lithium caproate, which are lithium salts of aliphatic carboxylic acids. , Lithium caprylate, lithium succinate, lithium glutarate, lithium adipate, lithium malonate, lithium propenoate (acrylate), lithium methacrylate, lithium maleate, lithium maleate, lithium fumarate, which is a lithium salt of unsaturated carboxylic acid Lithium salts of aromatic carboxylic acids lithium phthalate, lithium benzoate, lithium benzenetetracarboxylate, lithium naphthalenetetracarboxylate, lithium ethylenediaminetetraacetate (EDTA) lithium salts of polyaminocarboxylic acid, ethylene Diamine triacetic acid (HEDTA)
And the like. Above all, lithium salts of unsaturated carboxylic acids such as lithium acrylate, lithium methacrylate, lithium maleate, lithium fumarate and the like are preferable because they have a large effect of improving cycle life characteristics. Examples of the lithium salt of an aliphatic dicarboxylic acid, which is an example of the aliphatic carboxylic acid, include LiOOC (CH ₂ ) _m C
OOLi (where m indicates m ≧ 1) is preferably used. If any one of the positive electrode and the negative electrode contains lithium oxalate having m of 0, high-temperature performance such as cycle life in a high-temperature environment tends to decrease. Lithium oxalate tends to undergo a decarboxylation reaction when heated. For this reason,
A lithium secondary battery in which lithium oxalate is added to one of the positive electrode and the negative electrode has problems such as a decrease in high-temperature storage characteristics and a high-temperature cycle life. In order to more effectively suppress the decarboxylation reaction, m is 2
It is preferable that it is above. Generally, the above A (C
In the case where n ≧ 2 in OOLi) _n , A preferably contains two or more C (carbon).

The content of the compound having the composition represented by A (COOLi) _n in the mixture is 0.001% by weight (1%).
0 ppm) to 1.5% by weight. This is due to the following reasons. When the content is 0.
If the content is less than 001% by weight, it may be difficult to sufficiently exert the effect of improving the cycle life. on the other hand,
If the content exceeds 1.5% by weight, the packing density of the active material is reduced, so that the capacity characteristics of the battery may be reduced, or the high-current discharge performance may be reduced. A more preferable range of the content is 0.01% by weight (100 ppm) to 1.
0% by weight.

As the current collector, for example, a thickness of 10 to 4
Examples thereof include an aluminum foil of 0 μm, a stainless steel foil, and a titanium foil. The positive electrode 4 may be, for example, (1) a pellet formed by molding the positive electrode active material together with a compound having a composition represented by A (COOLi) _n , a conductive agent and a binder into the current collector. Affixing or (2) kneading the positive electrode active material together with a compound having a composition represented by A (COOLi) _n , a conductive agent and a binder,
The sheet-like sheet is attached to the current collector, or (3) the positive electrode active material, the A (COOLi) _n
A paste obtained by dispersing a compound having a composition represented by, a conductive agent and a binder in an appropriate solvent is applied to a current collector,
It is produced by drying to make a thin plate.

Examples of the conductive agent include acetylene black, graphite, carbon black and the like. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), a copolymer of vinylidene fluoride-6-propylene fluoride, and polyvinylidene fluoride-tetrafluoroethylene-6-propylene fluoride. An original copolymer and various fluorine rubbers can be used.

As an organic solvent for dispersing the binder, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF) and the like are used. The compounding amount of the positive electrode active material is the same as the positive electrode active material and the A (COOL).
i) 80 to 98% by weight based on 100 parts by weight of the compound having the composition represented by _n and the binder (or 100 parts by weight of the conductive agent when including the conductive agent). It is preferable to be within the range.

The compounding amount of the binder is 100 parts by weight in total of the cathode active material, the compound having the composition represented by A (COOLi) _n and the binder (when the conductive agent is contained, 2% by weight based on 100 parts by weight of conductive agent)
It is preferable to set it in the range of 20 to 20% by weight.

The amount of the conductive agent is 0 to 100 parts by weight of the total of the positive electrode active material, the compound having the composition represented by A (COOLi) _n , the binder and the conductive agent.
It is preferable that the content be in the range of 18% by weight to 18% by weight.

The amount of the organic solvent for dispersing the binder may be appropriately determined depending on the viscosity of the paste. It is preferable that at least a part of the surface of the positive electrode 4, particularly at least a part of the surface of the positive electrode active material, is coated with a compound having a composition represented by A (COOLi) _n . Such a positive electrode 4 allows an alkaline component such as lithium carbonate to remain on the surface of the positive electrode active material by synthesizing a positive electrode active material such as a lithium composite metal oxide by increasing the amount of the lithium compound added. And by treating it with a carboxylic acid or carboxylic acid esters. The treatment method using a carboxylic acid or a carboxylic acid ester is not particularly limited, and for example, a method of adding a carboxylic acid or a carboxylic acid ester in a paste preparation step and stirring and mixing the mixture can be employed.

However, when carboxylic acid is added to the paste, if the acidity of the carboxylic acid is too high, the cathode active material may be deteriorated. Therefore, the carboxylic acid preferably has a pKa value (in an aqueous solution), which is a negative logarithm of the acidity Ka, of 1.5 or more.

Examples of the carboxylic acid include aliphatic carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, succinic acid, glutaric acid, adipic acid and unsaturated carboxylic acid. Acrylic acid,
Examples thereof include methacrylic acid, maleic acid, fumaric acid, and aromatic carboxylic acids such as phthalic acid and benzoic acid.
In particular, unsaturated carboxylic acids having a double bond in the molecule (for example, acrylic acid, maleic acid, methacrylic acid, fumaric acid, etc.) are preferable because they have a large effect of improving cycle life characteristics. The carboxylic acid may be any of these acid anhydrides.

Examples of the carboxylic esters include ethyl acetate, methyl butanoate, methyl acrylate, methyl methacrylate and the like. In addition, in the lithium secondary battery according to the present invention, when a compound containing a compound represented by A (COOLi) _n is used as the negative electrode, it is allowed to use a compound without the compound as the positive electrode.

2) Separator 5 The separator 5 may be, for example, a synthetic resin nonwoven fabric,
A polyethylene porous film, a polypropylene porous film, or the like can be used.

3) Negative Electrode 6 The negative electrode 6 comprises a negative electrode active material and A (COOLi) _n (where A is H or an organic substance containing C and H, and n represents 1 ≦ n) And a compound containing a compound having a composition represented by the formula:

Examples of the negative electrode active material include carbonaceous materials that occlude and release lithium ions, chalcogen compounds that occlude and release lithium ions, and light metals that occlude and release lithium ions. Above all, a negative electrode containing a carbonaceous substance or a chalcogen compound that occludes and releases lithium ions is preferable because battery characteristics such as cycle life of the secondary battery are improved.

Examples of the carbonaceous material that occludes and releases lithium ions include coke, carbon fiber, pyrolysis gas phase carbonaceous material, graphite, fired resin, fired mesophase pitch-based carbon fiber, and fired mesophase spherical carbon. be able to. Above all, mesophase pitch-based carbon fiber or mesophase spherical carbon which is graphitized at 2500 ° C. or higher is preferable because the electrode capacity is increased.

The chalcogen compounds that occlude and release lithium ions include titanium disulfide (TiS ₂ ), molybdenum disulfide (MoS ₂ ), and niobium selenide (NbS).
e ₂ ). When such a chalcogen compound is used for the negative electrode, the capacity of the negative electrode increases although the voltage of the secondary battery drops, and the capacity of the secondary battery is improved. Further, since the negative electrode has a high diffusion rate of lithium ions, the rapid charge / discharge performance of the secondary battery is improved.

Examples of the light metal include aluminum, aluminum alloy, magnesium alloy, lithium metal, lithium alloy and the like. A (COOL)
i) _Examples of the compound having the composition represented by _n include the same compounds as those described for the positive electrode.

The content of the compound having the composition represented by A (COOLi) _n in the mixture is 0.001% by weight (1
0 ppm) to 1.5% by weight. This is due to the following reasons. When the content is 0.
If the content is less than 001% by weight, it may be difficult to sufficiently exert the effect of improving the cycle life. on the other hand,
If the content exceeds 1.5% by weight, the packing density of the active material is reduced, so that the capacity characteristics of the battery may be reduced and the high-current discharge performance may be reduced. A more preferable range of the content is 0.01% by weight (100 ppm) to
1.0% by weight.

As the current collector, for example, a copper foil, a nickel foil or the like can be used, but a copper foil is most preferable in consideration of electrochemical stability and flexibility at the time of winding. At this time, the thickness of the foil is 8 μm or more and 40 μm or more.
It is preferably not more than μm.

It is preferable that at least a part of the surface of the negative electrode is coated with a compound having a composition represented by A (COOLi) _n . The negative electrode (for example, a negative electrode using a carbonaceous material as a negative electrode active material) is specifically manufactured by the method described in the following (1) to (3).

(1) The carbonaceous material and the A (COOL)
i) The negative electrode is produced by attaching a pellet formed by molding a compound having a composition represented by _n together with a binder to the current collector.

(2) The carbonaceous material and the A (COOL)
i) kneading a compound having a composition represented by _n together with a binder,
The negative electrode is manufactured by sticking the sheet into the current collector.

(3) The carbonaceous material, A (COOL)
i) A paste obtained by dispersing a compound having a composition represented by _n and a binder in an appropriate solvent is applied to a current collector, and dried to form a thin plate, thereby producing the negative electrode.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), and styrene-butadiene rubber (SBR). it can. The mixing ratio of the negative electrode material and the binder is preferably in the range of 80 to 98% by weight of the negative electrode material and 2 to 20% by weight of the binder. In particular, the carbon material was applied in an amount of 50 per one surface in a state where the negative electrode 6 was produced.
It is preferable to set it in the range of 500 g / m ² .

In the lithium secondary battery according to the present invention, when a positive electrode containing a compound having a composition represented by A (COOLi) _n is used, a negative electrode to which no such compound is added is used. Allow.

4) Non-aqueous electrolyte The non-aqueous electrolyte has a composition in which an electrolyte is dissolved in a non-aqueous solvent. Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), for example, dimethyl carbonate (DM)
C), linear carbonates such as methyl ethyl carbonate (MEC) and diethyl carbonate (DEC);
Chain ethers such as 2-dimethoxyethane (DME) and diethoxyethane (DEE), tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2-Me
Cyclic ethers such as THF) and crown ethers;
At least one selected from fatty acid esters such as butyrolactone (γ-BL), nitrogen compounds such as acetonitrile (AN), and sulfur compounds such as sulfolane (SL) and dimethylsulfoxide (DMSO) can be used.

Among them, those composed of at least one selected from EC, PC and γ-BL, EC, PC and γ-B
At least one selected from L and DMC, MEC, DE
It is desirable to use a mixed solvent comprising at least one selected from C, DME, DEE, THF, 2-MeTHF, and AN. Further, when using a negative electrode containing a carbonaceous material that occludes and releases lithium ions, from the viewpoint of improving the cycle life of a secondary battery including the negative electrode, EC, PC and γ-BL, EC and PC And MEC, E
C and PC and DEC, EC and PC and DEE, EC and AN,
EC and MEC, PC and DMC, PC and DEC, or E
It is desirable to use a mixed solvent consisting of C and DEC.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ) and lithium hexafluorophosphate (Li
PF ₆ ), lithium borofluoride (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), lithium trifluoromethasulfonate (LiCF ₃ SO ₃ ), lithium aluminum tetrachloride (LiAlCl ₄ ), lithium bistrifluoromethylsulfonylimide [LiN (CF ₃ SO
₂ ) ₂ ] and the like. Among them, LiPF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂
The use of is preferred because conductivity and safety are improved.

The amount of the electrolyte dissolved in the non-aqueous solvent is preferably in the range of 0.5 mol / L to 2.0 mol / L. In FIG. 1, the non-aqueous electrolyte is used as the non-aqueous electrolyte. However, the lithium secondary battery according to the present invention can use a solid or gel non-aqueous electrolyte.

As the solid or gelled non-aqueous electrolyte, for example, a polymer solid electrolyte or an inorganic solid electrolyte can be used. As the polymer solid electrolyte,
Polyacrylonitrile (PAN), polyvinylidene fluoride (PVdF), polyethylene oxide (PEO),
For polymer materials such as polypropylene oxide (PPO), LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , Li
A solid electrolyte to which a lithium salt such as N (CF ₃ SO ₂ ) ₂ is added, the polymer material, the lithium salt and a non-aqueous solvent (eg, ethylene carbonate (EC), propylene carbonate (PC), trifluoropropylene carbonate ( TFPC), diethyl carbonate (DE
C), methyl ethyl carbonate (MEC), acetonitrile (AN), etc.).

Examples of the inorganic solid electrolyte include lithium sulfide glass and lithium oxide glass. In particular, Li ₃ P having high ion conductivity
O ₄ -Li ₂ S-SiS ₂ glasses are preferred.

As described in detail above, in the lithium secondary battery according to the present invention, at least one of the positive electrode and the negative electrode has A (COOLi) _n (where A is H or an organic substance containing H and C). And n represents 1 ≦ n). According to such a secondary battery, charge / discharge cycle life characteristics can be improved. The reason for this is not clear, but it is presumed that the decomposition of the non-aqueous electrolyte on the electrode surface was suppressed, possibly due to the formation of a stable film on the electrode surface by the compound having the composition represented by A (COOLi) _n. Is done. One possible reason for the stability of the compound is that the carboxylic acid is relatively stable even in a strong oxidizing atmosphere such as the positive electrode side because the carboxylic acid is a final oxide obtained by oxidizing an alcohol or an aldehyde. In addition, when the compound having the composition represented by A (COOLi) _n is added to the positive electrode, the cycle life of the secondary battery can be further improved as compared with the case where the compound is added to the negative electrode. .

At least a part of the surface of at least one of the positive electrode and the negative electrode has the A (COOL)
i) By being coated with the compound having the composition represented by _n , the secondary battery can further improve the charge / discharge cycle life.

Further, as the active material of the positive electrode, Li _x MO
₂ (where M represents one or more transition elements, x represents x ≦ 1.1), whereby a positive electrode containing the lithium composite metal oxide as a positive electrode active material Since the cycle life can be improved while taking advantage of the high voltage that is a feature of the above, a lithium secondary battery having a high voltage and a long life can be realized.

The positive electrode contains 0.001% by weight (10 ppm) of a compound having a composition represented by A (COOLi) _n.
By having a structure in which the mixture containing about 1.5% by weight is supported on the current collector, the cycle life can be improved without lowering the packing density of the positive electrode active material and increasing the internal pressure. Become.

[0047]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. Example 1 <Preparation of Positive Electrode> A nickel hydroxide powder [Ni _0.8 Co _0.2 (OH) ₂ ] in which a part of Ni was substituted by Co and lithium hydroxide monohydrate (LiOH · H ₂ O) were used as Li: (Ni +
Co) = 1.05: 1, and heat-treated at 700 ° C. for 5 hours in an air stream to obtain a LiNi _0.8 Co _0.2 O ₂ powder having an average particle size of 10 μm. From the X-ray diffraction pattern, it was confirmed that the obtained powder had a LiNiO ₂ structure.

Subsequently, the LiNi _0.8 Co _0.2 O ₂
90 parts by weight of powder, 5 parts by weight of acetylene black and 1 part by weight of lithium caproate are mixed, and the resulting mixture is added to an N-methyl-2-pyrrolidone solution in which 4 parts by weight of polyvinylidene fluoride as a binder is dissolved. A paste was prepared by mixing and dispersing.

The obtained paste was applied to both sides of an aluminum foil having a thickness of 20 μm as a current collector so that the amount of active material applied per side was 230 g / m ² , dried, and rolled by a roll press. Then, a positive electrode having a lithium caproate content of 1.0% by weight in the mixture was prepared.

<Preparation of Negative Electrode> After carbonizing mesophase pitch carbon fiber from mesophase pitch as a raw material at 1000 ° C. in an argon atmosphere, the average fiber length was 30 μm.
After appropriately pulverizing so that 90 volume% is present at an average fiber diameter of 11 μm and a particle size of 1 to 80 μm, and particles having a particle size of 0.5 μm or less (5% or less) are reduced to 3000 ° C. in an argon atmosphere. To produce a carbonaceous material.

Subsequently, a mixture of 5 parts by weight of graphite and 5 parts by weight of polyvinylidene fluoride with respect to 100 parts by weight of the carbonaceous material was dispersed in N-methylpyrrolidone to form a paste. Quantity 1
A compound having a composition represented by A (COOLi) _n is applied to both surfaces of a copper foil (thickness: 12 μm), which is a current collector substrate, at a concentration of 20 g / m ^2, and dried and then roll-pressed. An additive-free negative electrode was produced.

The positive electrode, the separator made of a porous film made of polyethylene, and the negative electrode were laminated in this order, and then spirally wound to form an electrode group.
As a non-aqueous electrolyte, lithium hexafluorophosphate (LiPF) was mixed in a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (mixing volume ratio 1: 2).
₆ ) is dissolved in 1M, and the electrode group and the non-aqueous electrolyte are respectively accommodated in a stainless steel bottomed cylindrical container, and a cylindrical lithium ion secondary battery (18650 size) having a designed rated capacity of 1900 mAh is used. ) Assembled.

Example 2 A positive electrode having a lithium maleate content of 1.0% by weight in the mixture was prepared in the same manner as in Example 1 except that lithium maleate was used instead of lithium caproate. . A cylindrical lithium ion secondary battery was assembled from the positive electrode in the same manner as in Example 1.

Example 3 Nickel hydroxide powder in which a part of Ni was replaced with Co [Ni
_0.8 Co _0.2 (OH) ₂ ] and lithium hydroxide monohydrate (LiOH · H ₂ O), Li: (Ni + Co) = 1.
It is blended to have a ratio of 14: 1, and in an air stream, 700
Heat treatment at a temperature of 5 ° C. for 5 hours.
An iNi _0.8 Co _0.2 O ₂ powder was obtained. The resulting powder is
It was confirmed from the X-ray diffraction diagram that the structure had a LiNiO ₂ structure.

Subsequently, the LiNi _0.8 Co _0.2 O ₂
90 parts by weight of the powder (positive electrode active material) and 5 parts by weight of acetylene black are mixed, and this mixture is mixed with N-methyl-2-amine in which 4 parts by weight of polyvinylidene fluoride as a binder is dissolved.
The resulting mixture was mixed and dispersed in a pyrrolidone solution to prepare a dispersion. Further, an excessive amount of methyl methacrylate was added to this dispersion, and the mixture was sufficiently stirred and mixed to perform a surface treatment of the positive electrode active material.

The paste thus obtained was applied to both sides of an aluminum foil having a thickness of 20 μm as a current collector so that the active material applied amount per one side was 230 g / m ^2, and dried. Rolling was performed by a roll press to produce a positive electrode in which the content of lithium methacrylate in the mixture was 1% by weight.

In order to examine the distribution state of lithium methacrylate in the positive electrode, the carbonyl group of the carboxylic acid was electronically stained with osmium tetroxide, and the element mapping of osmium (Os) was performed with an X-ray microanalyzer (EPMA). As a result, it was found that a large amount of lithium methacrylate was present on the surface of the positive electrode, and in particular, was present so as to cover a part of the surface of the positive electrode active material.

From this positive electrode, a cylindrical lithium ion secondary battery was assembled in the same manner as in Example 1. Example 4 LiNi _0.8 Co _0.2 O similar to that described in Example 3
₂ 90 parts by weight of powder (positive electrode active material) and 5 parts by weight of acetylene black are mixed, and this mixture is mixed with N-methyl-2 in which 4 parts by weight of polyvinylidene fluoride as a binder is dissolved.
-It was mixed and dispersed in a pyrrolidone solution to prepare a dispersion.
Further, 1 part by weight of maleic anhydride was added to this dispersion, and the mixture was sufficiently stirred and mixed to perform a surface treatment of the positive electrode active material to prepare a paste.

The obtained paste was applied to both sides of an aluminum foil having a thickness of 20 μm as a current collector so that the amount of active material applied per side was 230 g / m ² , dried, and rolled by a roll press. Then, a positive electrode having a lithium maleate content of 1.0% by weight in the mixture was prepared.

In order to examine the distribution state of lithium maleate in the positive electrode, the carbonyl group of the carboxylic acid was electronically stained with osmium tetroxide as in Example 3, and then osmium was analyzed with an X-ray microanalyzer (EPMA). (O
Element mapping of s) was performed. As a result, similarly to the case of lithium methacrylate, it was confirmed that lithium maleate was present in a large amount on the surface of the positive electrode and was present so as to cover a part of the surface of the positive electrode active material.

From this positive electrode, a cylindrical lithium ion secondary battery was assembled in the same manner as in Example 1. Example 5 A positive electrode in which the content of lithium maleate in the mixture was 0.001% by weight (10 ppm) in the same manner as in Example 4 except that the addition amount of maleic anhydride was 0.001 part by weight. Was prepared. A cylindrical lithium ion secondary battery was assembled from this positive electrode in the same manner as in Example 1.

Example 6 A positive electrode having a lithium maleate content of 0.01% by weight in the mixture in the same manner as in Example 4 except that the addition amount of maleic anhydride was changed to 0.01 part by weight. Was prepared.
A cylindrical lithium ion secondary battery was assembled from this positive electrode in the same manner as in Example 1.

Example 7 A positive electrode in which the content of lithium maleate in the mixture was 0.1% by weight in the same manner as in Example 4 except that the addition amount of maleic anhydride was 0.1 part by weight. Was prepared. A cylindrical lithium ion secondary battery was assembled from this positive electrode in the same manner as in Example 1.

Example 8 A positive electrode having a lithium maleate content of 1.5% by weight in the mixture in the same manner as in Example 4 except that the addition amount of maleic anhydride was 1.5 parts by weight. Was prepared. A cylindrical lithium ion secondary battery was assembled from this positive electrode in the same manner as in Example 1.

Example 9 A positive electrode having a lithium maleate content of 2.0% by weight in the mixture in the same manner as in Example 4 except that the addition amount of maleic anhydride was 2.0 parts by weight. Was prepared. A cylindrical lithium ion secondary battery was assembled from this positive electrode in the same manner as in Example 1.

Example 10 <Production of positive electrode> LiNi similar to that described in Example 1 was used.
100 parts by weight of _0.8 Co _0.2 O ₂ powder and 5 parts by weight of acetylene black are mixed, and this mixture is mixed with an N-methyl-2-pyrrolidone solution in which 4.4 parts by weight of polyvinylidene fluoride as a binder is dissolved. Dispersed to prepare a paste.

The obtained paste was applied to both sides of an aluminum foil having a thickness of 20 μm as a current collector so that the amount of active material applied per side was 230 g / m ² , dried, and rolled by a roll press. Then, a positive electrode to which no compound having a composition represented by A (COOLi) _n was added was prepared.

<Preparation of Negative Electrode> A mixture comprising 90 parts by weight of a carbonaceous substance, 4.5 parts by weight of graphite and 1 part by weight of lithium caproate as described in Example 1 was mixed with polyvinylidene fluoride as a binder. 4.5 parts by weight of N-methyl-2-pyrrolidone solution was mixed and dispersed to prepare a paste.

The obtained paste is applied on both sides of a copper foil (thickness: 12 μm) as a current collector substrate so that the active material application amount per one side is 120 g / m ² , dried, and rolled by a roll press. Then, a negative electrode in which the content of lithium caproate in the mixture was 1.0% by weight was produced.

From the obtained positive electrode and negative electrode, a cylindrical lithium ion secondary battery was assembled in the same manner as in Example 1. Example 11 A negative electrode having a lithium caproate content of 0.001% by weight (10 ppm) in the mixture in the same manner as in Example 10 except that the addition amount of lithium caproate was changed to 0.001 part by weight. Produced.

An electrode group was prepared by spirally winding this negative electrode and the same positive electrode as described in Example 10 with a separator similar to that described in Example 1 interposed therebetween. A cylindrical lithium ion secondary battery (18650 size) having a designed rated capacity of 1900 mAh was accommodated by storing the electrode group and the same nonaqueous electrolyte solution as described in Example 1 in a stainless steel bottomed cylindrical container. Assembled.

Example 12 A negative electrode containing 0.01% by weight of lithium caproate in the mixture was prepared in the same manner as in Example 10 except that the addition amount of lithium caproate was changed to 0.01 part by weight. Produced.

An electrode group was produced by spirally winding this negative electrode and the same positive electrode as described in Example 10 with a separator similar to that described in Example 1 interposed therebetween. A cylindrical lithium ion secondary battery (18650 size) having a designed rated capacity of 1900 mAh was accommodated by storing the electrode group and the same nonaqueous electrolyte solution as described in Example 1 in a stainless steel bottomed cylindrical container. Assembled.

Example 13 A negative electrode containing 0.1% by weight of lithium caproate in the mixture was prepared in the same manner as in Example 10 except that the addition amount of lithium caproate was 0.1 part by weight. Produced.

An electrode group was prepared by spirally winding this negative electrode and the same positive electrode as described in Example 10 with a separator similar to that described in Example 1 interposed therebetween. A cylindrical lithium ion secondary battery (18650 size) having a designed rated capacity of 1900 mAh was accommodated by storing the electrode group and the same nonaqueous electrolyte solution as described in Example 1 in a stainless steel bottomed cylindrical container. Assembled.

Example 14 A negative electrode containing 1.5% by weight of lithium caproate in the mixture was prepared in the same manner as in Example 10 except that the amount of lithium caproate added was 1.5 parts by weight. Produced.

An electrode group was produced by spirally winding this negative electrode and the same positive electrode as described in Example 10 with a separator similar to that described in Example 1 interposed therebetween. A cylindrical lithium ion secondary battery (18650 size) having a designed rated capacity of 1900 mAh was accommodated by storing the electrode group and the same nonaqueous electrolyte solution as described in Example 1 in a stainless steel bottomed cylindrical container. Assembled.

Example 15 A negative electrode containing 2.0% by weight of lithium caproate in the mixture was prepared in the same manner as in Example 10 except that the addition amount of lithium caproate was changed to 2.0 parts by weight. Produced.

An electrode group was produced by spirally winding this negative electrode and the same positive electrode as described in Example 10 with a separator similar to that described in Example 1 interposed therebetween. A cylindrical lithium ion secondary battery (18650 size) having a designed rated capacity of 1900 mAh was accommodated by storing the electrode group and the same nonaqueous electrolyte solution as described in Example 1 in a stainless steel bottomed cylindrical container. Assembled.

Example 16 A negative electrode in which the content of lithium maleate in the mixture was 1.0% by weight was produced in the same manner as in Example 10 except that lithium maleate was used instead of lithium caproate. .

An electrode group was produced by spirally winding the negative electrode and the positive electrode similar to that described in Example 10 with a separator similar to that described in Example 1 interposed therebetween. A cylindrical lithium ion secondary battery (18650 size) having a designed rated capacity of 1900 mAh was accommodated by storing the electrode group and the same nonaqueous electrolyte solution as described in Example 1 in a stainless steel bottomed cylindrical container. Assembled.

Example 17 A positive electrode similar to that described in Example 4 and a negative electrode similar to that described in Example 10 were spirally interposed therebetween with a separator similar to that described in Example 1 interposed therebetween. The electrode group was produced by winding. The electrode group and the same non-aqueous electrolyte as described in Example 1 were respectively housed in a stainless steel bottomed cylindrical container, and the design rated capacity was 1900 m.
An Ah cylindrical lithium ion secondary battery (18650 size) was assembled.

Comparative Example 1 An anode similar to that described in Example 1 and without a lithium salt of a carboxylic acid and a cathode similar to that described in Example 10 and without a lithium salt of a carboxylic acid were used. An electrode group was produced by spirally winding the same separator as described in 1. The electrode group and the same nonaqueous electrolyte solution as described in Example 1 were respectively housed in a stainless steel bottomed cylindrical container, and a cylindrical lithium ion secondary battery (1900 mAh in design rated capacity) (18)
650 size).

Comparative Example 2 A positive electrode having a lithium oxalate content of 1.0% by weight in the mixture was prepared in the same manner as in Example 1 except that lithium oxalate was added instead of lithium caproate. .

A cylindrical lithium ion secondary battery was assembled from the obtained positive electrode in the same manner as in Example 1. For the obtained secondary batteries of Examples 1 to 17 and Comparative Examples 1 and 2, a battery capacity test and a cycle life test were performed. Charging is 20
After charging to 900 V at a charging current of 900 mA to 4.2 V, the voltage was maintained at a constant voltage of 4.2 V, and the operation was performed for a total of 8 hours. The discharge was performed at a constant current of 900 mA, and the discharge end voltage was 2.7.
V. The rest time after charging and discharging was 30 minutes, respectively. Such charge / discharge was repeated, and the discharge capacity was measured for each cycle. The number of cycles at which the discharge capacity reached 80% of the capacity of the first cycle was defined as the battery life, and is shown in Table 1 below.

The high-temperature storage characteristics of the secondary batteries of Examples 1 to 17 and Comparative Examples 1 and 2 were measured. The high-temperature storage test was performed by the following method. First, the above-described charge / discharge was performed for 10 cycles, and after completion of the charge in the eleventh cycle, the charge / discharge was interrupted, and each battery was left in a thermostat controlled at 60 ° C. for 10 days. Afterwards, the temperature is increased again
C., and discharged under the same conditions to measure the battery capacity.
The ratio of the discharge capacity before and after storage, that is, (discharge capacity at the eleventh cycle) / (discharge capacity at the tenth cycle) is defined as the capacity retention ratio, and the results are shown in Table 1 below.

[0087]

[Table 1]

As is clear from Table 1, the secondary batteries of Examples 1 to 17 in which at least one of the positive electrode and the negative electrode contains a compound having a composition represented by A (COOLi) _n , It can be seen that, compared to the secondary battery of Comparative Example 1 including the positive electrode and the negative electrode, the cycle life was as long as 500 cycles or more, and the capacity retention under a high temperature environment was high. This is because the decomposition of the non-aqueous electrolyte on the electrode surface is suppressed because the compound having the composition represented by A (COOLi) _n forms a stable film on the electrode surface. Guessed. Particularly, the content of the compound in the mixture is 0.01% by weight (100 ppm).
Example 4 with a positive electrode in the range of ~ 1.0 wt%
It can be seen that the cycle life of the secondary batteries of Examples 6 and 7 is longer than those of Examples 5, 8 and 9 in which the content is out of the above range.

On the other hand, the secondary battery of Comparative Example 2 provided with the positive electrode containing lithium oxalate was found to have a remarkably low capacity retention of 20% in a high-temperature environment. In the above-described embodiment, an example in which the present invention is applied to a cylindrical lithium ion secondary battery has been described. However, a structure in which a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte are accommodated in a bottomed rectangular cylindrical container is described. The same can be applied to a prismatic lithium ion secondary battery.

[0090]

As described in detail above, according to the present invention, a lithium secondary battery having excellent charge-discharge cycle life characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing a lithium secondary battery (for example, a cylindrical lithium secondary battery) according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... container, 3 ... electrode group, 4 ... positive electrode, 5 ... separator, 6 ... negative electrode, 8 ... insulating sealing plate.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takahisa Osaki 72 Horikawa-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Pref. (56) References JP-A-9-180758 (JP, A) JP-A-8-64245 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 4/62 H01M 4/02 H01M 10/40

Claims (3)

(57) [Claims] A positive electrode containing a positive electrode active material and a negative electrode active material are provided.
Lithium secondary battery comprising a negative electrode containing
In at least one of the positive electrode and the negative electrode,
A lithium secondary battery comprising a lithium salt of an unsaturated carboxylic acid . Wherein said positive electrode active material, Li _x MO ₂ (where,
M is one or more transition elements and at least nickel
Are those containing, x is a lithium secondary battery according to claim 1, wherein the lithium composite metal oxide composition represented by showing the x ≦ 1.1). 3. The lithium salt of an unsaturated carboxylic acid,
Lithium propenoate (acrylic acid), Lithium methacrylate
, Lithium maleate and lithium fumarate
Claims 1 to 2 lithium secondary battery according to any one of to, characterized in that the barrel.