JPH11250910A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a service capacity and a cycle life by containing boron and oxygen at a specific ratio in a carbonaceous material contained in a nega tive electrode and storing/releasing lithium ions, and processing it with an alka line solution containing an alkali metal. SOLUTION: Boron of 0.1-5 wt.% is contained in a carbonaceous material such as a graphite structure preferably in a solid solution state, the deposition of lithium on the carbonaceous material is suppressed at the time of a rapid charge, graphite crystallinity is improved, and a service capacity is increased. Oxygen of 0.05-1 wt.% is contained, bonding with carbon is preferable, and the charge/discharge efficiency is increased by the improvement of the lithium ion storage/release potential of a negative electrode and the function of a protective film against a nonaqueous electrolyte. It is attained by the heat treatment of a graphitized carbon material and a boron oxide or a boron compound in the prescribed atmosphere. An alkaline solution treatment is preferably applied at 60 deg.C, alkali metal ions are stably fixed on the surface of the carbonaceous material, and a reversible storage/release site of lithium ions is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery having an improved negative electrode containing a carbonaceous material.

[0002]

2. Description of the Related Art In recent years, non-aqueous electrolyte batteries using lithium as a negative electrode active material have attracted attention as high energy density batteries, and manganese dioxide (MnO ₂ ) has been used as a positive electrode active material.
Fluorocarbon [(CF ₂ ) _n ], thionyl chloride (SOCl
Primary batteries using ₂ ) and the like are already widely used as power supplies for calculators, watches, and as backup batteries for memories.

Further, in recent years, with the reduction in size and weight of various electronic devices such as VTRs and communication devices, the demand for secondary batteries having a high energy density as a power source for these devices has increased, and lithium secondary batteries using lithium as a negative electrode active material have been required. Battery research is being actively conducted.

A lithium secondary battery uses lithium as a negative electrode and propylene carbonate (PC), 1,2-dimethoxyethane (DME), γ-butyrolactone (γ-
BL), a non-aqueous electrolyte in which a lithium salt such as LiClO ₄ , LiBF ₄ , or LiAsF ₆ is dissolved in a non-aqueous solvent such as tetrahydrofuran (THF) or a lithium ion conductive solid electrolyte. TiS ₂ ,
The use of compounds that undergo a topochemical reaction with lithium, such as MoS ₂ , V ₂ O ₅ , V ₆ O ₁₃ , and MnO ₂ , has been studied.

[0005] However, the above-mentioned lithium secondary battery has not yet been put to practical use. The main reason for this is that the charge / discharge efficiency is low and the number of times that charge / discharge can be performed (cycle life) is short. It is considered that this is largely due to the deterioration of lithium due to the reaction between the lithium of the negative electrode and the non-aqueous electrolyte. That is, lithium dissolved in the non-aqueous electrolyte as lithium ions at the time of discharge reacts with the solvent at the time of deposition at the time of charging, and its surface is partially inactivated. Therefore, when charge and discharge are repeated, lithium precipitates in a dendritic (dendritic) or small spherical shape, and further, phenomena such as detachment of lithium from the current collector occur.

[0006] Therefore, by using a carbonaceous material that absorbs and releases lithium, for example, coke, a resin fired body, carbon fiber, and pyrolysis gas phase carbon, as the negative electrode incorporated in the lithium secondary battery, lithium and lithium can be removed. It has been proposed to improve the reaction with a non-aqueous electrolyte and the deterioration of the negative electrode characteristics due to the precipitation of dendrites.

[0007] The negative electrode containing the carbonaceous material has a structure (graphite structure) in which hexagonal mesh layers mainly composed of carbon atoms are stacked in the carbonaceous material, and lithium ions are present in a portion between the layers. It is considered that charging and discharging are performed by going in and out. For this reason, it is necessary to use a carbonaceous material having a somewhat developed graphite structure for the negative electrode of the lithium secondary battery. However, when a carbonaceous material obtained by pulverizing a graphitized giant crystal is used as a negative electrode in a non-aqueous electrolyte, the non-aqueous electrolyte is decomposed, and as a result, the capacity and charge / discharge efficiency of the battery are reduced. In addition, there is a problem that the cycle life is shortened because the capacity decrease increases as the charge / discharge cycle progresses.

Further, when a secondary battery provided with a negative electrode containing a carbonaceous material is subjected to rapid charging or charging in a low-temperature environment of 0 ° C. or less, the charging potential of the negative electrode becomes 0 V or less. Metallic lithium is precipitated. As a result, the secondary battery has a problem that the discharge capacity under such severe conditions is low because the amount of insertion and extraction of lithium ions is reduced.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a lithium secondary battery having a high capacity and an improved initial charge / discharge efficiency by improving a negative electrode containing a carbonaceous material, and having improved discharge capacity and cycle life. It is intended to provide.

[0010]

The lithium secondary battery according to the present invention is treated with an alkaline solution containing alkali metal ions, and contains 0.1 to 5% by weight of boron and 0.05 to 1% by weight. % Of oxygen, and a negative electrode containing a carbonaceous material that occludes and releases lithium ions.

[0011]

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 in detail 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. The electrode group 3 is housed in the container 1. The electrode group 3 has a structure in which a band formed by laminating a positive electrode 4, a separator 5 and a negative electrode 6 in this order is spirally wound.

The container 1 contains an electrolytic solution. The insulating paper 7 having a central portion opened is placed above the electrode group 3 in the container 1. The insulating sealing plate 8
The sealing plate 8 is disposed at the upper opening of the container 1 and caulked in the vicinity of the upper opening inward.
Is fixed to the container 1 in a liquid-tight manner. The positive terminal 9 is
The insulating sealing plate 8 is fitted at the center. Positive lead
One end of the cathode 10 is connected to the positive electrode 4, and the other end is connected to the positive electrode terminal 9.
Connected to each other. 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 electrolytic solution will be described in detail. 1) Positive Electrode 4 The positive electrode 4 is produced by suspending a conductive agent and a binder in a suitable solvent in a positive electrode active material, applying the suspension to a current collector, and drying to form a thin plate.

As the positive electrode active material, various oxides,
For example, manganese dioxide, lithium manganese composite oxide,
Examples include lithium-containing nickel oxide, lithium-containing cobalt compound, lithium-containing nickel-cobalt oxide, lithium-containing iron oxide, lithium-containing vanadium oxide, and chalcogen compounds such as titanium disulfide and molybdenum disulfide. Among them, lithium-containing cobalt oxide (for example, LiCoO ₂ ), lithium-containing nickel oxide (for example, LiNiO ₂ ), lithium-manganese composite oxide (for example, LiMn ₂ O ₄ , LiMnO ₂ )
_{Use of 2} ) is preferable because a high voltage can be obtained.

Examples of the conductive agent include acetylene black, carbon black, graphite and the like. Examples of the binder include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVd).
F), ethylene-propylene-diene copolymer (EPD)
M), styrene-butadiene rubber (SBR) and the like can be used.

The mixing ratio of the positive electrode active material, the conductive agent and the binder is 80 to 95% by weight of the positive electrode active material, 3 to 2% of the conductive agent.
It is preferable that the content be in the range of 0% by weight and 2 to 7% by weight of the binder.

As the current collector, for example, an aluminum foil, a stainless steel foil, a nickel foil or the like can be used. 2) Separator 5 As the separator 5, 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 is treated with an alkaline solution containing alkali metal ions, and contains 0.1 to 5% by weight of boron (B) and 0.05 to 1% by weight of oxygen ( O)
Mainly carbonaceous materials that occlude and release lithium ions.

The boron may be present in the carbonaceous material in an atomic state or in a compound form.
The boron is preferably dissolved in the carbonaceous material. However, when the content of the boron compound in the carbonaceous material increases, the performance of the lithium secondary battery may be deteriorated.

By setting the boron content in the carbonaceous material within the above range, the lithium ion occlusion / release potential of the negative electrode can be increased, so that it can be charged at the time of rapid charging or in a low-temperature (0 ° C. or lower) environment. It is possible to suppress the deposition of metallic lithium on the carbonaceous material when discharging. Further, since the graphite crystallinity can be improved, the lithium ion occlusion / release speed of the negative electrode can be improved, and the discharge capacity can be improved. When the content is less than 0.1% by weight, it becomes difficult to sufficiently increase the occlusion / release potential, and further, the graphite crystallinity cannot be improved. On the other hand, when the content exceeds 5% by weight, B ₄ C is generated in the carbonaceous material, and since this compound does not occlude or release lithium ions, the capacity of the negative electrode decreases. In the carbonaceous material, the content of the boron compound tends to increase as the boron content increases. A more preferred boron content is in the range of 0.5% to 3% by weight.

The oxygen may be present in the carbonaceous material in an atomic state or in the form of a compound. The oxygen is preferably bonded to carbon in the carbonaceous material. However, when the oxide content of the carbonaceous material increases, the performance of the lithium secondary battery may be deteriorated.

By setting the oxygen content of the carbonaceous material within the above range, the lithium ion occlusion / release potential of the negative electrode, particularly the occlusion / release potential at the time of initial charge / discharge, can be improved. Can be increased, and the discharge capacity can be improved. In the carbonaceous material,
It is presumed that the oxygen atom combines with the carbon atom and exists mainly on the surface of the hexagonal mesh layer. As a result, since the oxygen atoms function as a protective film for the non-aqueous electrolyte of the carbonaceous material, the reductive decomposition reaction of the non-aqueous electrolyte during the initial charge and discharge is suppressed and the initial charge and discharge efficiency is improved. it is conceivable that. If the content is less than 0.05% by weight,
It becomes difficult to sufficiently increase the emission potential. On the other hand, when the content exceeds 1% by weight, a reductive decomposition reaction of the nonaqueous electrolyte may occur due to oxygen atoms. A more preferred oxygen content is in the range of 0.1% to 0.8% by weight.

The carbonaceous material preferably has a (002) plane spacing (d ₀₀₂ ) of the graphite structure of 0.344 nm or less. A lithium secondary battery including such a negative electrode containing a carbonaceous material can dramatically improve discharge capacity and cycle life. The carbonaceous material has a (002) plane spacing (d ₀₀₂ ) of 0.344 n like an amorphous structure.
It is allowed to include a region exceeding m. The surface distance d
₀₀₂ can be determined from the position of the peak in the diffraction pattern obtained by powder X-ray diffraction. As the calculation method, the half-width half-point method specified in the Gakushin method is used. The half-width half-point method is described in “Tanso (carbon)”, 1963, p.
In the literature.

The carbonaceous material has a peak intensity ratio (P ₁₀₁ / P) between a diffraction peak P ₁₀₁ on the ( ₁₀₁ ) plane and a diffraction peak P ₁₀₀ on the (100) plane by powder X-ray diffraction of a graphite structure.
₁₀₀ ) is preferably 2 or more. A lithium secondary battery including such a negative electrode containing a carbonaceous material can improve discharge capacity. The peak intensity ratio (P ₁₀₁ /
P ₁₀₀ ) is obtained by measuring the diffraction peak P ₁₀₁ on the ( ₁₀₁ ) plane and the diffraction peak P ₁₀₀ on the (100) plane by powder X-ray diffraction, and determining the height ratio of these peaks. In the powder X-ray diffraction measurement, CuKα is used as an X-ray source, and high-purity silicon is used as a standard substance.

The carbonaceous material is obtained by treating a graphite material containing 0.1 to 5% by weight of boron and 0.05 to 1% by weight of oxygen with an alkaline solution containing alkali metal ions.

The graphite material may be, for example, the following (1)
It can be manufactured by the method described in (3). (1) A graphitized carbon-based material and a boron oxide are mixed and heat-treated in an inert atmosphere at 1500 to 3000 ° C., so that 0.1 to 5% by weight of boron and 0.1 to 5% by weight.
A graphite material containing 0.5 to 1% by weight of oxygen is produced. In the graphite obtained by such a method, it is presumed that the boron forms a solid solution in the graphite and the oxygen is bonded to carbon in the graphite. The graphite material is allowed to contain an unreacted material such as boron oxide.

In the above method (1), if a non-graphitized carbon-based material is used, the oxygen atoms in the boron oxide are released as carbon dioxide (CO ₂ ) during the heat treatment. It becomes difficult to introduce oxygen atoms into the material. Examples of the graphitized carbon-based material include artificial graphite, natural graphite, graphitized coke, graphitized mesophase pitch, graphitized pitch,
Graphitized mesophase pitch-based carbon fibers or graphitized mesophase spheres can be mentioned.

Examples of the boron oxide include diboron trioxide (B ₂ O ₃ ) and boric acid (H ₃ BO ₃ ). The boron oxide is preferably mixed at a ratio of 1 to 25% by weight based on the carbon-based material. When the amount of boron oxide is out of this range,
The boron content in the graphite substance may deviate from 0.1 to 5% by weight. A more preferred amount is 1 to 10% by weight,
More preferably, it is 1 to 5% by weight.

As the inert gas atmosphere, for example,
An argon gas atmosphere can be used. The temperature of the heat treatment is defined in the above range for the following reason. When the heat treatment temperature is lower than 1500 ° C., it becomes difficult to form a solid solution of carbon atoms and boron atoms, and therefore, the boron compound content of the graphite may increase. On the other hand, it is technically difficult to make the heat treatment temperature higher than 3000 ° C. A more preferable range of the heat treatment temperature is 1500 to 2800 ° C.

(2) A carbon-based material and a boron compound are mixed, heat-treated in an inert atmosphere at 1500 to 3000 ° C., and then heat-treated in an oxidizing atmosphere at 400 to 800 ° C. 0.1 to 5% by weight of boron and 0.0
A graphite material containing 5 to 1% by weight of oxygen is produced.
In the graphite obtained by such a method, it is presumed that the boron forms a solid solution in the graphite and the oxygen is bonded to carbon in the graphite. Note that the graphite material is allowed to contain unreacted substances such as boron compounds and boron oxides.

Examples of the carbon-based material include artificial graphite, natural graphite, coke, mesophase pitch, pitch, mesophase pitch-based carbon fiber, and mesophase small spheres. This carbon-based material may be subjected to a graphitization treatment. Further, the carbon-based material can be made infusible as necessary.

Examples of the boron compound include boron carbide (B ₄ C), boric acid (H ₃ BO ₃ ), diboron trioxide (B ₂ O ₃ ) and the like. The boron compound is preferably mixed at a ratio of 1 to 25% by weight based on the carbon-based material. If the compounding amount of the boron compound is out of this range, the boron content in the graphite may deviate from 0.1 to 5% by weight. A more preferred amount is 1 to 10% by weight, and still more preferably 1 to 5% by weight.
It is.

As the inert gas atmosphere, for example,
An argon gas atmosphere can be used. The reason for setting the temperature of the heat treatment in the inert gas atmosphere to the above range is as follows. The heat treatment temperature is 1
If the temperature is lower than 500 ° C., it becomes difficult to form a solid solution of carbon atoms and boron atoms, and therefore, the content of the boron compound in the graphite may increase. On the other hand, it is technically difficult to make the heat treatment temperature higher than 3000 ° C. A more preferred range of the heat treatment temperature is 150
0 to 2800 ° C.

The oxidizing atmosphere can be formed by air or oxygen gas. The reason why the heat treatment temperature in the oxidizing atmosphere is specified in the above range is as follows. If the heat treatment temperature is lower than 400 ° C., it may be difficult to introduce oxygen atoms into the carbon-based material. On the other hand, if the heat treatment temperature exceeds 800 ° C., the surface of the graphite material becomes rough, and it may be difficult to improve the capacity and the capacity retention of the lithium secondary battery. A more preferred range of the heat treatment temperature is 65
0-700 ° C.

The oxygen content of the carbonaceous material can be controlled by adjusting the oxygen gas concentration in the oxidizing atmosphere, the heat treatment temperature and the heat treatment time in the oxidizing atmosphere.

(3) By subjecting the carbon-based material and the boron compound to a heat treatment under the same conditions as in the above (2), 0.1
A graphite containing 1 to 5% by weight of boron is prepared.
By subjecting the obtained graphite substance to oxidation treatment with sulfuric acid, nitric acid, a hydrogen peroxide solution or the like, the graphite substance is treated with 0.0
The desired graphite material is obtained by containing 5 to 1% by weight of oxygen.

Next, the alkali treatment will be described. Examples of the alkali metal ion include a lithium ion, a sodium ion, and a potassium ion. Particularly, lithium ion is preferable.

As the alkaline solution containing the alkali metal ion, a lithium hydroxide solution can be used. The concentration of the lithium hydroxide is 1 to 10 M (mol
/ L).

By treating with the alkaline solution containing the alkali metal ion, it is possible to stably fix the alkali metal ion on the surface of the graphite material, and to form a site capable of reversibly storing and releasing lithium ions. it can. Preferably, the alkaline solution is heated. The treatment of the graphite material with the heated alkaline solution is advantageous not only in terms of improving the production efficiency of the carbonaceous material, but also in terms of fixing alkali metal ions and forming occlusion / release sites. . In particular, the temperature of the solution is desirably 60 ° C. or higher from the viewpoint of improving the production efficiency of the carbonaceous material and the amount of lithium ion occlusion / release. A more preferred range of the solution temperature is 8
0 ° C. or higher.

The carbonaceous material can be present in the negative electrode in the form of fibers, particles, or a mixture of fibers and particles. Fibrous carbonaceous material (hereinafter referred to as carbon fiber)
It is desirable that the granular carbonaceous material (hereinafter, referred to as carbon particles) has the characteristics described in the following (1) and (2).

(1) Carbon Fiber The carbon fiber may or may not be pulverized. The average length of the carbon fiber is 10 to 1
It is preferable that the thickness be in the range of 00 μm. The average diameter of the carbon fibers is preferably in the range of 1 to 20 μm.

The carbon fiber has an average length of 10 to 100.
When the diameter is in the range of μm and the average diameter is in the range of 1 to 20 μm, the aspect ratio is preferably in the range of 2 to 10. Here, the aspect ratio is calculated from the ratio of the average length to the average diameter.

In the carbon fiber, it is preferable that the orientation of graphite crystallites in a cross section belongs to a radial type or isotropic. The radial orientation includes an orientation belonging to a lamellar type and an orientation belonging to a Brooks-Taylor type. In addition, the radial orientation may be entirely or partially folded.

It is desirable that the carbon fibers that have been subjected to the pulverization treatment have an average particle size of 1 to 100 μm, more preferably 2 to 40 μm. (2) Carbon particles The shape of the carbon particles is preferably spherical or substantially spherical.

The average particle size of the carbon particles is 1 to 100 μm.
m, more preferably in the range of 2 to 40 μm. The ratio of the minor axis to the major axis of the carbon particles is 1 /
It is desirable to make it 10 or more. More preferably, 1 /
It is desirable to make the shape close to a true sphere as two or more.

The carbon particles preferably have a graphite crystallite orientation in a cross section belonging to a radial type or isotropic. The radial orientation includes an orientation belonging to a lamella type and an orientation belonging to a Brooks-Taylor type. In addition, the radial orientation may be entirely or partially folded.

The negative electrode 6 is prepared, for example, by kneading the carbonaceous material and the binder in the presence of a solvent, applying the resulting suspension to a current collector, drying the resultant, and then once applying a desired pressure. It can be produced by pressing or multi-stage pressing 2 to 5 times.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR),
Carboxymethyl cellulose (CMC) or the like can be used.

The mixing ratio of the carbonaceous material and the binder is as follows:
It is preferable that the carbon material is in the range of 90 to 98% by weight and the binder is in the range of 2 to 10% by weight. In particular, it is preferable that the carbonaceous material be in the range of 5 to ²⁰ mg / cm ^{2 when} the negative electrode 6 is manufactured.

As the current collector, for example, a copper foil, a stainless steel foil, a nickel foil or the like can be used. 4) Electrolyte The non-aqueous electrolyte is prepared by dissolving an electrolyte in a non-aqueous solvent.

As the non-aqueous solvent, a known non-aqueous solvent can be used as a solvent for a lithium secondary battery, and is not particularly limited. Ethylene carbonate (EC) has a melting point lower than that of the ethylene carbonate and a donor. It is preferable to use a non-aqueous solvent mainly composed of a mixed solvent with one or more non-aqueous solvents having a number of 18 or less (hereinafter, referred to as a second solvent).

As the second kind of solvent, for example, chain carbon is preferable, and among them, dimethyl carbonate (DM
C), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), ethyl propionate, methyl propionate, or propylene carbonate (P
C), γ-butyrolactone (γ-BL), acetonitrile (AN), ethyl acetate (EA), toluene, xylene or methyl acetate (MA). These second solvents can be used alone or in the form of a mixture of two or more. In particular, the second type solvent more preferably has a donor number of 16.5 or less.

The viscosity of the second solvent is 2 at 25 ° C.
It is preferably 8 mp or less. The blending amount of the ethylene carbonate in the mixed solvent is 10 to 10 by volume.
Preferably it is 80%. A more preferable blending amount of the ethylene carbonate is 20 to 75% by volume ratio.

The more preferable composition of the mixed solvent is EC
And MEC, EC and PC and MEC, EC and MEC and DE
C, EC, MEC, DMC, EC, MEC, PC, DE
In the mixed solvent of C, the volume ratio of MEC is preferably 30 to 80%. A more preferred volume ratio of MEC is:
It is in the range of 40-70%.

Examples of the electrolyte contained in the non-aqueous electrolyte include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), and lithium arsenide hexafluoride (LiBF ₄ ). LiAsF
₆ ), lithium trifluorometasulfonate (LiCF
₃ SO ₃ ) and lithium bis (trifluoromethylsulfonylimide) [LiN (CF ₃ SO ₂ ) ₂ ]. Among them, LiPF ₆ , LiB
Preferably, F ₄ is used.

The amount of the electrolyte dissolved in the non-aqueous solvent is desirably 0.5 to 2.0 mol / 1. The lithium secondary battery according to the present invention described above is treated with an alkaline solution containing an alkali metal ion.
The negative electrode includes a carbonaceous material containing 1 to 5% by weight of boron and 0.05 to 1% by weight of oxygen. Such a negative electrode can increase the amount of insertion and extraction of lithium ions. Further, the negative electrode can suppress the reductive decomposition of the non-aqueous electrolyte on the surface of the carbonaceous material, and can improve the initial charge / discharge efficiency. Therefore, the secondary battery can significantly improve the discharge capacity and the charge / discharge cycle life.

[0057]

An embodiment of the present invention will be described below in detail with reference to FIG. Example 1 <Preparation of Positive Electrode> First, lithium cobalt oxide (LiC
oO ₂ ) 91% by weight of powder were mixed with 3.5% by weight of acetylene black, 3.5% by weight of graphite and 2% by weight of ethylene propylene diene monomer powder and mixed together, and applied to an aluminum foil (30 μm) current collector After pressing, a positive electrode was produced by pressing. <Preparation of Negative Electrode> Boron oxide (B ₂ O ₃ ) powder was added to artificial graphite powder having a spherical shape with an average particle diameter of 15 μm in an amount of 10% by weight based on the artificial graphite powder. , A spherical graphite material powder was produced. The obtained graphite powder had a boron content of 3% by weight and an oxygen content of 0.1%.
It was 5% by weight. P ₁₀₁ / P ₁₀₀ by powder X-ray diffraction
Was 3. In addition, by powder X-ray diffraction (00
2) The plane distance d ₀₀₂ between the planes was 0.3354 nm. The average particle size was 15 μm. Cross-section of the powder by SEM
Observation with a (scanning electron microscope) revealed that the graphite crystallites had no orientation and were isotropic.

The graphite powder was heated to 80 ° C.
The graphite material was subjected to chemical treatment and heat treatment by immersing in a mol / L lithium hydroxide aqueous solution and stirred for 10 hours, washed with water, and then vacuum dried at 200 ° C. to produce a carbonaceous material powder.

Next, 96.7% by weight of the carbonaceous material powder
Was mixed with 2.2% by weight of styrene-butadiene rubber and 1.1% by weight of carboxymethylcellulose, applied to a copper foil as a current collector, dried, and pressed to produce a negative electrode.

The positive electrode, the separator made of a polyethylene porous film and the negative electrode were laminated in this order, and then spirally wound to form an electrode group.
Further, 1.0 mol / 1 of lithium hexafluorophosphate (LiPF ₆ ) was dissolved in a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (mixing volume ratio: 50:50) to prepare a non-aqueous electrolyte. Was prepared.

The above-mentioned electrode group and the above-mentioned electrolytic solution were housed in a stainless steel bottomed cylindrical container, respectively, to assemble the above-mentioned cylindrical lithium secondary battery having the structure shown in FIG. Example 2 A cylindrical lithium secondary battery having the same configuration as that of Example 1 except that the carbonaceous material described below was used for the negative electrode was assembled.

The mesophase pitch-based carbon fiber powder was heat-treated at 3000 ° C. in an argon gas atmosphere. Boron oxide (B ₂ O ₃ ) powder was added to this powder in an amount of 20% by weight based on the powder, and the powder was heat-treated at 2000 ° C. in an argon gas stream. This was further heat-treated at 700 ° C. for 1 hour in the air to produce a fibrous graphite powder. The obtained graphite powder had a boron content of 4% by weight and an oxygen content of 0.3% by weight. P ₁₀₁ / P by powder X-ray diffraction
The ratio of ₁₀₀ was 2.1. Further, the plane distance d ₀₀₂ of the (002) plane determined by powder X-ray diffraction was 0.3360 nm. The average particle size was 20 μm. Observation of the cross section of the powder with a scanning electron microscope (SEM) revealed that the orientation of graphite crystallites was radial.

The graphite material powder is immersed in a 3 mol / L aqueous solution of lithium hydroxide heated to 100 ° C., and stirred for 10 hours to perform chemical treatment and heat treatment on the graphite material. Drying was performed to produce a carbonaceous material powder.

Example 3 A cylindrical lithium secondary battery having the same structure as in Example 1 except that a carbonaceous material described below was used for the negative electrode was assembled.

The mesophase pitch-based carbon fiber powder was heat-treated at 900 ° C. in an argon gas atmosphere. Boron carbide (B ₄ C) powder was added to this powder in an amount of 5% by weight with respect to the powder, and heat-treated at 3000 ° C. in an argon gas stream. Then, a heat treatment was performed at 700 ° C. for 10 hours in air to produce a fibrous graphite powder. The obtained graphite powder had a boron content of 2% by weight and an oxygen content of 0.1%.
It was 1% by weight. P ₁₀₁ / P ₁₀₀ by powder X-ray diffraction
Was 2.2. The plane distance d ₀₀₂ of the (002) plane determined by powder X-ray diffraction was 0.3358 nm. The average particle size was 20 μm. Observation of the cross section of the powder with a scanning electron microscope (SEM) revealed that the orientation of graphite crystallites was radial.

The graphite material powder is immersed in a 3 mol / L aqueous solution of lithium hydroxide heated to 100 ° C. and stirred for 3 hours to perform a chemical treatment and a heat treatment on the graphite material, and then vacuum heated at 250 ° C. for 5 hours. Was given. afterwards,
After washing with water and vacuum drying at 200 ° C., a carbonaceous material powder was produced.

Example 4 A cylindrical lithium secondary battery having the same structure as in Example 1 except that the carbonaceous material described below was used for the negative electrode was assembled.

Boron oxide (B ₂ O ₃ ) powder was added to the powder of the mesophase small spheres extracted from the pitch at 15% by weight based on the powder, pressed under pressure, and heat-treated at 2800 ° C. in an argon gas stream. And then pulverized. This was further saturated with ammonium persulfate to 1 m
The resultant was immersed in an aqueous ol / L sulfuric acid solution, stirred for 100 hours, sufficiently washed with water, and dried to produce a granular graphite powder. The obtained graphite powder had a boron content of 2.5% by weight and an oxygen content of 0.8% by weight. The ratio of P ₁₀₁ / P ₁₀₀ by powder X-ray diffraction is 2.5
Met. Further, the plane distance d ₀₀₂ of the (002) plane determined by powder X-ray diffraction was 0.3370 nm. Average particle size is 6
μm. Observation of the cross section of the powder with a scanning electron microscope (SEM) revealed that the crystallites were not oriented and were isotropic.

The graphite material powder is immersed in a 3 mol / L aqueous solution of lithium hydroxide heated to 100 ° C., and stirred for 3 hours to perform chemical treatment and heat treatment on the graphite material, and then to vacuum heating at 250 ° C. for 5 hours. Was given. afterwards,
After washing with water and vacuum drying at 200 ° C., a carbonaceous material powder was produced.

Example 5 A cylindrical lithium secondary battery having the same structure as in Example 1 except that the carbonaceous material described below was used for the negative electrode was assembled.

[0071] mesophase was extracted from the pitch globules of powder boric acid (H ₃ B0 ₃₎ 5 powder to the powder
% By weight, press-pressed, heat-treated at 3000 ° C. in an argon gas stream, and then pulverized. This was further subjected to a heat treatment at 700 ° C. for 1 hour under air to produce a granular graphite powder. The obtained graphite powder had a boron content of 1% by weight,
The oxygen content was 0.5% by weight. The ratio of P ₁₀₁ / P ₁₀₀ by powder X-ray diffraction was 2.1. The distance d ₀₀₂ of the (002) plane determined by powder X-ray diffraction was 0.3.
It was 360 nm. The average particle size was 10 μm. Observation of the cross section of the powder with a scanning electron microscope (SEM) revealed that the crystallites were not oriented and were isotropic.

The graphite material powder is immersed in a 3 mol / L aqueous solution of lithium hydroxide heated to 100 ° C., and stirred for 10 hours to perform chemical treatment and heat treatment on the graphite material. Drying was performed to produce a carbonaceous material powder.

Example 6 A cylindrical lithium secondary battery having the same structure as in Example 1 except that the carbonaceous material described below was used for the negative electrode was assembled.

A spherical artificial graphite powder containing no boron and having an oxygen content of 0.1% by weight was prepared. Powder X
The ratio of P ₁₀₁ / P ₁₀₀ by line diffraction was 3. The plane distance d ₀₀₂ of the (002) plane determined by powder X-ray diffraction was 0.3354 nm. The average particle size was 20 μm. Observation of the cross section of the powder with a scanning electron microscope (SEM) revealed that the crystallites were not oriented and were isotropic.

By subjecting this artificial graphite powder to the same alkali treatment as in Example 1, a carbonaceous material powder was produced. Example 7 A cylindrical lithium secondary battery having the same configuration as in Example 1 except that the carbonaceous material described below was used for the negative electrode was assembled.

The fibrous carbonaceous material powder was prepared by subjecting the mesophase pitch-based carbon fiber powder to heat treatment at 3000 ° C. in an argon gas atmosphere. Therefore, no alkali treatment was performed. The obtained carbonaceous material powder did not contain any boron and oxygen. The ratio of P ₁₀₁ / P ₁₀₀ by powder X-ray diffraction was 1.8. Further, the plane distance d of the (002) plane by powder X-ray diffraction
₀₀₂ was 0.3370 nm. Average particle size is 20 μm
Met. Observation of the cross section of the powder with a scanning electron microscope (SEM) revealed that the orientation of graphite crystallites was radial.

Example 8 A cylindrical lithium secondary battery having the same structure as in Example 1 except that the carbonaceous material described below was used for the negative electrode was assembled.

The mesophase pitch-based carbon fiber powder was heat-treated at 3000 ° C. in an argon gas atmosphere. Boron oxide (B ₂ O ₃ ) powder was added to this powder in an amount of 20% by weight based on the powder, and the powder was heat-treated at 2000 ° C. in an argon gas stream. This was further heat-treated at 700 ° C. for 1 hour in air to produce a fibrous carbonaceous material powder. Therefore, no alkali treatment was performed. The obtained carbonaceous material powder has a boron content of 4% by weight and an oxygen content of 0.3% by weight.
Met. The ratio of P ₁₀₁ / P ₁₀₀ by powder X-ray diffraction is
2.1. Further, (002) by powder X-ray diffraction
The interplanar spacing d ₀₀₂ was 0.3354 nm. The average particle size was 20 μm. Observation of the cross section of the powder with a scanning electron microscope (SEM) revealed that the orientation of graphite crystallites was radial.

The obtained secondary batteries of Examples 1 to 8 were rapidly charged to 4.2 V at a charging current of 1.5 A for 2 hours.
A rapid charge / discharge cycle test of discharging at 1.5 A to 2.7 V was performed in an environment of 20 ° C. Regarding this cycle test, the discharge capacity at the first cycle and the capacity retention rate at 300 cycles (relative to the discharge capacity at the first cycle)
Was measured, and the results are shown in Table 1 below.

[0080]

[Table 1]

As is apparent from Table 1, the treatment was performed with an alkaline solution containing an alkali metal ion, and the content of boron was 0.1 to 5% by weight and the content of oxygen was 0.05 to 5%.
It can be seen that the secondary batteries of Examples 1 to 5 provided with the negative electrode containing 1% by weight of the carbonaceous material can improve the initial capacity and the capacity retention when the battery is rapidly charged at 20 ° C. (normal temperature).

On the other hand, the secondary battery of Example 6 provided with the negative electrode containing the carbonaceous material not containing boron, which has been subjected to the above-described alkali treatment, and the secondary battery containing boron and oxygen, The secondary battery of Example 8 provided with the negative electrode containing the carbonaceous material that had not been subjected to the alkali treatment had an initial capacity and a capacity retention rate when rapidly charged at 20 ° C. of Examples 1 to 5.
It turns out that it is low compared with. Further, the secondary battery of Example 7 including a negative electrode containing a carbonaceous material that did not contain boron and oxygen and was not subjected to an alkali treatment had an initial capacity of Examples 1 to 5.
It turns out that it is low compared with 5.

Also, in the low-temperature cycle evaluation at 0 ° C., it was found that the secondary batteries of Examples 1 to 5 had higher capacities and a higher capacity retention ratio than Examples 6 to 8. Example 9 A cylindrical lithium secondary battery having the same configuration as that of Example 1 except that the carbonaceous material described below was used for the negative electrode was assembled.

Boron oxide (B ₂ O ₃ ) powder was added to the powder of the mesophase small spheres extracted from the pitch at 10% by weight based on the powder, press-pressed, and heat-treated at 2100 ° C. in an argon gas stream. And then pulverized to produce a granular graphite powder. The obtained graphite powder had a boron content of 2% by weight and an oxygen content of 0.1% by weight. The ratio of P ₁₀₁ / P ₁₀₀ by powder X-ray diffraction was 0.5. The distance d ₀₀₂ of the (002) plane determined by powder X-ray diffraction was 0.34.
It was 50 nm. The average particle size was 10 μm. Observation of the cross section of the powder with a scanning electron microscope (SEM) revealed that the crystallites were not oriented and were isotropic.

The graphite material powder is immersed in a 3 mol / L aqueous solution of lithium hydroxide heated to 100 ° C. and stirred for 3 hours to perform a chemical treatment and a heat treatment on the graphite material, and then vacuum heated at 250 ° C. for 5 hours. Was given. afterwards,
After washing with water and vacuum drying at 200 ° C., a carbonaceous material powder was produced.

When the initial capacity and the capacity retention of the obtained secondary battery of Example 9 were measured in the same manner as described above, the initial capacity was 1350 mAh and the capacity retention was 70%.
%Met.

In the above embodiment, an example in which the present invention is applied to a cylindrical lithium secondary battery is described. However, the present invention can be similarly applied to a prismatic lithium secondary battery. Further, the electrode group housed in the battery container is not limited to the spiral shape, but may be a form in which a plurality of positive electrodes, separators, and negative electrodes are stacked in this order.

[0088]

As described in detail above, according to the present invention,
It is possible to provide a lithium secondary battery capable of maintaining a high discharge capacity and a long life even when rapid charging and discharging are performed.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing an example of a lithium secondary battery according to the present invention.

[Explanation of symbols]

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

Claims (3)

[Claims] 1. A treatment with an alkaline solution containing an alkali metal ion, containing 0.1 to 5% by weight of boron and 0.05 to 1% by weight of oxygen, and storing and releasing lithium ions. A lithium secondary battery comprising a negative electrode containing a carbonaceous material. 2. The lithium secondary battery according to claim 1, wherein the temperature of the alkaline solution is 60 ° C. or higher. 3. The carbonaceous material has a graphite structure (002).
2. The lithium secondary battery according to claim 1, wherein the plane spacing (d ₀₀₂ ) is 0.344 nm or less.