JP2001229916A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which is superior in input/output characteristics at a low temperature and battery performance stability. SOLUTION: The nonaqueous electrolyte secondary battery uses a negative electrode, having a lithium insertion coefficient K with 0.70<=K and a nonaqueous electrolyte, as an electrolyte.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high capacity non-aqueous electrolyte secondary battery, and more particularly to an improvement in cycle life, particularly at low temperatures, by regulating the lithium insertion rate of a negative electrode. It is.

[0002]

2. Description of the Related Art In recent years, along with the development of electronic portable devices, there has been a remarkable progress in the development of batteries as driving sources thereof. Among them, lithium ion secondary batteries have attracted particular attention because of their high energy density. At present, generally known lithium ion secondary batteries use a material capable of reversibly inserting and extracting lithium, such as a carbon material, an amorphous alloy, or an amorphous metal oxide, as a negative electrode active material, and a positive electrode active material. Using a lithium composite oxide containing a transition metal such as cobalt, nickel, and manganese, a mechanism is provided for charging and discharging by moving lithium ions between the two electrodes. Since the active material used for both electrodes has a high energy density, the size and weight of the battery can be reduced. For this reason, lithium ion secondary batteries are increasingly used in portable devices such as camera-integrated VTRs and mobile phones, for which reduction in size and weight is desired.

[0003] More recently, attempts have been made to use lithium ion secondary batteries not only in portable equipment but also in medium-sized and large-sized power supplies. Medium- and large-sized power supplies are used as power supplies for driving motors of electric vehicles and bicycles with electric motors, load levelers that are energy storage devices for home use, backup power supplies for offices that handle a large amount of communication equipment and OA equipment, etc. It has a wide range of applications, including large-volume laboratories and power storage devices attached to private power generators at factories.

Most commercially available lithium ion secondary batteries use graphite for the negative electrode and lithium cobalt oxide for the positive electrode. This battery system is to exhibit a well-balanced battery performance. However, the demands on the performance of lithium-ion secondary batteries are increasing year by year, and users are demanding strict specifications regarding the stability of battery performance during charge / discharge cycles, especially when used at low temperatures. I have.

[0005]

However, it has been pointed out that the batteries reported so far have insufficient battery performance stability under the following conditions. That is, there is a problem that the battery capacity is reduced in charging / discharging at a low temperature assuming use in a cold region. This is because lithium moves from the positive electrode to the negative electrode during charging, and the lithium absorbed in the negative electrode cannot be sufficiently intercalated into the negative electrode because of the low temperature.
It is interpreted that the dendrite is deposited on the negative electrode, but a method for solving this problem has been strongly desired.

[0006]

Means for Solving the Problems The present inventors have made intensive studies to solve the above problems. As a result, they have found that a battery system using a negative electrode that stipulates the lithium insertion rate of the negative electrode and satisfies the performance has excellent battery performance stability when used at a low temperature. In particular, in many cases, graphite having a high crystal structure is used for the negative electrode from the viewpoint of improving the battery capacity.However, the inventor coated the graphite surface with non-graphitic carbon having a high lithium insertion rate, or combined graphite having different particle sizes. The present inventors have found that the lithium insertion speed of the negative electrode can be improved by preparing an electrode, and have reached the present invention.

That is, the present invention provides the following secondary battery. (1) A non-aqueous electrolyte secondary battery, wherein the lithium insertion coefficient K of the negative electrode is 0.70 ≦ K. (2) The active material of the negative electrode in (1) is (00)
2) d002 indicating the average distance between planes is 0.3350 nm
As described above, the range of less than 0.3380 nm
A nonaqueous electrolyte secondary battery comprising a carbon material having an axial size Lc of 10 nm or more, an average particle size of 10 to 30 μm, and a specific surface area of 5 m ² / g or less. (3) The active material of the negative electrode in (1) is (00)
2) d002 indicating the average distance between planes is 0.3350 nm
As described above, the range of less than 0.3380 nm
The material having an average particle size of 10 to 30 μm and a specific surface area of 5 m ² / g or less obtained by coating the surface of a carbon material having an axial size Lc of 10 nm or more with non-graphitic carbon. Characteristic non-aqueous electrolyte secondary battery. (4) In the mixture obtained by mixing the carbon material having an average particle size of 2 to 8 μm with the active material of the negative electrode in the above (1), the carbon material having an average particle size of 2 to 8 μm is mixed with the carbon material of 5 to 4
A non-aqueous electrolyte secondary battery using a carbon mixture for a negative electrode, which is contained in a range of 0 wt%.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the rate of insertion of lithium into a negative electrode active material is important, and the lithium insertion coefficient K
Must be 0.70 ≦ K. Here, the lithium insertion coefficient K is a parameter for characterizing the negative electrode obtained as follows. A negative electrode active material is applied on a current collector using a suitable binder and molded, and a three-electrode electrochemical cell is used in which a counter electrode and a reference electrode are lithium.
The negative electrode and the counter electrode are opposed to each other via a separator for preventing short circuit, and are overlapped while applying a pressure of 0.05 to 5.00 MPa. As an electrolytic solution, ethylene carbonate and methyl ethyl carbonate are mixed at a volume ratio of 1: 2, and lithium phosphorus hexafluoride is dissolved in the mixture at a concentration of 1 mol / liter. This electrolytic solution was injected into the cell, charged at a current rate of 0.5 C at 25 ° C. until the negative electrode potential became 10 mV, and after reaching 10 mV,
Constant-current constant-voltage charging is performed in which charging is continued for another 10 hours while maintaining this potential. Here, 1.0 C refers to a current value at which a charged amount of electricity in a fully charged state can be discharged in one hour.
As shown in FIG. 1, when the charging curve is plotted with the charged cumulative electric quantity on the horizontal axis and the current value on the vertical axis, the cumulative electric quantity X when the potential reaches 10 millivolts, and charging is started. When the integrated amount of electricity from when the current value reaches 1/50 of the initial current value is Y, the lithium insertion coefficient K is K
= X / Y. This value reflects the resistance when lithium intercalates into the negative electrode during charging. As this value increases, lithium is more smoothly intercalated into the negative electrode under the conditions. Lithium insertion coefficient is 0.
A negative electrode material satisfying 70 ≦ K exhibits good charge / discharge characteristics without depositing lithium as a dendride on the negative electrode. This tendency appears more remarkably in charging and discharging at low temperatures. The lithium insertion coefficient K is more preferably 0.80 or more, and particularly preferably 0.85 or more.

The negative electrode of the present invention is preferably a carbon material.
No. Here, the carbon material is a material containing carbon as its main component.
Refers to graphite and graphite materials, coke, carbon fiber,
Bon Black, Acetylene Black, Mesomicroca
Bon beads, pitch coke, mesophase carb
Firing of carbon, whisker, hard carbon and resin
The body is raised. In particular, the average spacing of the (002) plane
D002 shown is from 0.3350 nm or more to 0.3380
less than nm, indicating the size of the crystallite in the c-axis direction.
Lc is 10 nm or more, and the average particle size is 10 to 30 μm.
m, specific surface area is 5m ^Two/ G or less.
The size of d002 is 0.3380 nm or more, or Lc
Is less than 10 nm, the crystal structure is undeveloped,
The charge / discharge amount is not large enough. Average particle size is 10μm or less
Carbon materials have lower charging / discharging efficiency and lower battery capacity
You. If the average particle size is 30 μm or more, lithium in the carbon particles
Diffusion becomes slow, and it is difficult to maintain 0.7 ≦ K.
Become. The specific surface area is 5m^Two/ G is overcharged
The reaction between the negative electrode and the electrolyte during the reaction occurs rapidly,
The characteristics deteriorate.

In the present invention, d002 and Lc were calculated by measuring a mixture of each carbon material and silicon powder at a weight ratio of 1: 1 using an X-ray diffractometer. d0
The value of 02 is the diffraction angle of the (002) plane of the carbon material: 2θ
Is corrected by the diffraction angle of the (111) plane of silicon, and B
ragg was obtained from equation (1). 2d sin θ = λ (1) On the other hand, the value of Lc was obtained from Scherrer's formula (2) using the diffraction angle of the (002) plane: 2θ and the half width of the diffraction peak: β. Lc = Kλ / βcosθ (2) The BET specific surface area was measured using SA3100 manufactured by Coulter Corporation. Particle size measurement is SYMPATE
Dry flow dispersion unit RODOS and laser diffraction type particle size distribution measuring optical system HEROS-BASI manufactured by Company C
The average particle diameter was measured using S / KA (0.5 to 175 μm range), and the value of the 50% cumulative diameter value D (50%) was used. However, this does not apply to the analyzer that performs these measurements.

[0011] The above-mentioned carbon material having a high crystalline structure is coated with non-graphitic carbon having a high lithium insertion rate, or a carbon material having a different particle size is combined to form an electrode to further improve the lithium insertion rate of the negative electrode. can do. When coating a carbon material with non-graphitic carbon, the precursors of non-graphitic carbon include heavy oils such as coal tar pitch, petroleum oil and coal oil, naphthalene, anthracene, phenanthrene, pyrene, chrysene, and perylene. Tars, vinyl chloride, vinylidene chloride, polyacrylonitrile, phenolic resins, aromatic polyamides, furfuryl alcohol resins, imide resins, and other resins obtained by heating and pressurizing the condensed polycyclic aromatic resin. After that, it can be obtained by performing firing. The coating of the carbon material with these precursors comprises the steps of mixing the precursor and the carbon material, washing with a solvent, and firing. For mixing, a general mixer such as a ribbon mixer, a screw mixer, and a paddle mixer can be used. As the solvent used for washing, solvents such as acetone, quinoline, toluene, benzene, petroleum and coal-based light oils and medium oils can be used. The firing temperature after coating is preferably from 700 ° C to 2000 ° C, more preferably from 900 ° C to 1500 ° C. At temperatures lower than 700 ° C., carbonization of the coated organic material is not sufficient, and the charge / discharge efficiency of the obtained coated carbon material is low. At 1500 ° C. or higher, the coated precursor is separated from the base carbon. And the charging / discharging efficiency is reduced. The firing can be performed in an atmosphere of nitrogen, argon, helium, hydrogen, or the like, or in a vacuum. When the heat treatment is performed in a vacuum, the obtained carbonization yield is reduced, but the charge and discharge efficiency tends to be improved, which is particularly effective.
The fired particles are pulverized, crushed, and classified to obtain particles having a target diameter.

In order to improve the lithium insertion speed by combining carbon materials having different particle diameters, the average particle diameter is 2 to 8 μm.
It is effective to mix a carbon material having an average particle diameter of 2 to 8 μm in a range of 5 to 40 wt%. If the content is 5 wt% or less, the effect of improving the lithium insertion rate is small, and if the content is 40 wt% or more, the specific surface area of the negative electrode active material becomes too large, and the performance such as overcharge resistance deteriorates, so that a battery with a good performance balance cannot be obtained. Mixing range is 10-30
wt% is particularly desirable. The mixing can be performed by dry mixing before adding to an aqueous or solvent or organic solvent as a dispersion, or wet mixing after adding each particle to the dispersion.

As the current collector of the negative electrode, a metal foil or net having a thickness of about 8 to 100 μm, such as Cu, Ni, and stainless steel, is used. Teflon as a binder,
Polyethylene, nitrile rubber, polybutadiene, butyl rubber, styrene / butadiene rubber, styrene butadiene latex, polysulfide rubber, nitrocellulose, cyanoethylcellulose, various compositions of latex and acrylonitrile, polyvinyl fluoride, fluorinated rubber, chloroprene, polyvinylidene fluoride, hexa A copolymer of one or more of fluoropropylene, tetrafluoroethylene, trifluoromonochloroethylene, and maleic anhydride with vinylidene fluoride is used.
Particularly preferred binders include copolymers of one or more of styrene / butadiene rubber, styrene butadiene latex, and maleic anhydride with vinylidene fluoride. The active material bulk density of the negative electrode is 1.0 g
/ Cm ³ or more and less than 1.6 g / cm ³ . 1.0
If it is less than g / cm ³ , the amount of the active material put in the battery becomes small, and the battery capacity becomes small. In addition, 1.6 g / cm
^{If it is} larger than ^3, it becomes difficult to make the lithium insertion coefficient K 0.7 or more. More preferably 1.1 g / cm ³ or more, in the range of less than 1.55 g / cm ^3. The coating amount of the negative electrode is preferably 150 g / m ² or less, more preferably 13 g / m ² or less.
0 g / m ² . If the coating amount of the negative electrode is larger than 150 g / m ² , the overvoltage increases, and the performance such as low temperature cyclability deteriorates.

Next, the positive electrode of the battery of the present invention will be described. As the positive electrode material of the battery of the present invention, a material having a high electron conductivity is preferable so that lithium ions can be reversibly released and occluded and electron transport can be easily performed. As this material, for example, TiS ₂ , TiS ₃ , MoS ₂ , MoS ₃ , F
eS, FeS ₂ , TaS ₂ , CuS, Cu ₂ S, CuCo
Metal sulfides such as _{S 4, V 2 O 5,} V 6 O 13, MoO 3, M
_{nO 2, CuO, Cu 5 V} 2 O 1 2, Cr 2 O 3, metal oxides such as TiO _2, NbSe _3, metal selenides such as _{VSe 2, LiVO 2, LiCrO 2} , LiFeO 2, L
iNiO ₂ , LiCoO ₂ , LiMnO ₂ , LiMn ₂ O
₄ , LiCo _x Sn _y O ₂ , LiCoNiO ₂ , LiCo _x F
An alkali metal-containing composite oxide such as e _y O ₂ can be used. Usually, it is preferable to use a material having a large capacity, such as a lithium cobalt composite oxide, a lithium nickel composite oxide, and a lithium manganese composite oxide. As a processing method using these materials as electrodes, the same method as in the case of the negative electrode can be used.

As the current collector of the positive electrode, Al, Cu, Ni,
A metal foil or mesh such as stainless steel having a thickness of about 8 to 100 μm is used, but it is particularly preferable to use a metal foil or mesh made of Al. Next, the lithium ion moving medium will be described. Examples of the ion transfer medium include a solution of an aprotic organic solvent in which a lithium salt is uniformly dissolved, a solid or viscous body in which a lithium salt is uniformly dispersed in a polymer matrix, and a solvent of the aprotic organic solvent. And a polymer matrix mixture. Specific examples of the lithium salt used for these include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiC
10 ₄ , LiSbF ₆ , LiI, LiBr, LiCl, L
iAlCl ₄ , LiHF ₂ , LiSCN, CF ₃ SO ₃ L
i, C ₄ F ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, (CF
₃ SO ₂ ) ₃ CLi, (C ₄ F ₉ SO ₂ ) ₂ NLi, or a mixture thereof. Further, as the aprotic organic solvent used for the moving medium, propylene carbonate,
Organic carbonates such as ethylene carbonate, diethyl carbonate, methyl ethyl carbonate and dimethyl carbonate, gamma butyrolactone, propiolactone, ethyl acetate, butyl acetate, propyl acetate, aliphatic organic esters such as ethyl propionate and butyl propionate, grime, diglyme, Triglyme, tetrahydrofuran, dioxane, diethyl ether, organic ethers such as silicon oil, pyridine, organic amines such as triethylamine, acetonitrile, organic nitriles such as propionitrile or a mixture of at least a part thereof, and other Aprotic organic solvents, for example, aromatic hydrocarbons such as benzene, toluene, xylene and decalin, and aliphatic hydrocarbons such as hexane, pentane and decane Phenol, catechol, alkyl esters such as bisphenol, aromatic ester or chloroform, carbon tetrachloride, dichloromethane, fluorocarbons, it is also possible to use mixtures of halogenated hydrocarbons, such as trichlorethylene. It is not preferable to use a protic organic solvent as the ion transfer medium because protons of the organic solvent are reduced on the electrode surface, thereby generating hydrogen gas and lowering the charge / discharge efficiency. Next, as the polymer matrix, for example, polyethylene oxide, polypropylene oxide, polytetramethylene oxide, polyvinyl alcohol, aliphatic polyethers such as polyvinyl butyral, polyethylene sulfide, aliphatic polythioethers such as polypropylene sulfide, polyethylene succinate, Aliphatic polyesters such as polybutylene adipate and polycaprolactone, polyethyleneimine,
Polyimide and its precursors, polyacrylonitrile,
For example, polyvinylidene fluoride can be used.

Further, a separator for preventing short circuit between the positive electrode and the negative electrode can be provided in a part of the moving medium. Examples of the separator include a porous sheet and a nonwoven fabric of a material such as polyethylene, polypropylene, and cellulose. Further, in the present invention, the battery form of the secondary battery is not particularly limited, cylindrical, square, thin square, card type,
The present invention can be applied to any form such as a coin type and a sheet type. The battery of the present invention has a higher lithium insertion speed and a stable charge / discharge cycle life at a low temperature as compared with a battery using a conventional negative electrode material, and is extremely industrially useful.
Hereinafter, the present invention will be described in more detail with reference to Examples.
The scope of the present invention is not limited to this.

[0017]

EXAMPLE 1 Natural graphite: BF-15SP as negative electrode material
(Manufactured by Chuetsu Graphite Industry Co., Ltd.) containing carboxymethyl cellulose and styrene / butadiene latex in a weight ratio of 1
00 parts, 1 part, and 2 parts were mixed and dissolved in water to form a slurry. This was applied to a copper foil having a thickness of 12 μm to a uniform thickness, followed by drying and roll pressing. The coating amount of the obtained negative electrode was 98 g / m ² , and the bulk density of the active material was 1.32 g / cm ³ . The lithium insertion coefficient of the negative electrode was measured using the method described above.
72. D002 of BF-15SP is 0.335
4 nm, Lc is 64 nm, and specific surface area is 4.87 m ² /
g, average particle size was 16.4 μm.

Next, after mixing lithium hydroxide and cobalt hydroxide as positive electrode materials, the mixture was heated at 800 ° C. for 8 hours in the atmosphere to synthesize LiCoO ₂ . This LiCoO ₂ 1
With respect to 00 parts by weight, the average particle size is 3.3 μm as a conductive material.
Was mixed with 2.5 parts by weight of non-graphitic carbon powder having an average particle size of 0.04 μm to obtain a compound. Polyvinylidene fluoride 3 for compound
This compound was dispersed in an N-methylpyrrolidone solution containing parts by weight, and the resulting dispersion was applied on a 20 μm-thick aluminum foil so as to have a uniform thickness, followed by drying and low pressing. The coating amount of the obtained positive electrode was 268
g / m ³ and the bulk density of the active material was 2.95 g / cm ³ .

Subsequently, the positive electrode and the negative electrode prepared as described above were cut to a width of about 55 mm and a length of about 80 cm, and the resultant was cut into a roll having a diameter of about 17 mm through a 25 μm-thick polyethylene microporous membrane separator. Rolled up. The wound coil is placed in an iron can having a diameter of about 18 mm and a length of 65 mm, and about 6 g of an electrolytic solution having a volume ratio of ethylene carbonate and methyl ethyl carbonate in which 1 mol / l of LiPF ₆ is dissolved is further added. Then, the battery was sealed. The battery is placed in a constant temperature bath at a constant temperature of 20 ° C., and after a constant current of 0.3 C at the first cycle, a constant potential of 4.2 V (potential between positive and negative electrodes)
After charging for 8 hours, the battery was discharged to a potential of 3.0 V at a constant current of 0.3 C to evaluate the charge / discharge characteristics. 1 of this battery
OC corresponds to 1450 mA.

After the first charge / discharge, a cycle of charging at 0.5 C and 4.2 V for 3 hours in a constant temperature bath at a constant temperature of 0 ° C. for 3 hours and then discharging at 0.5 C to 3.0 V. 50
Repeated times. At this time, the 50-cycle discharge amount maintenance ratio represented by the following equation was 89%. 50-cycle discharge amount maintenance ratio (%) = [(50th cycle discharge amount) / (2nd cycle discharge amount)] × 100 Under this condition, the battery was disassembled in a charged state and observed on the negative electrode. No lithium was observed. After the first charge / discharge, 1.0 C in a constant temperature bath at 20 ° C .;
After charging for 3 hours with constant current and constant voltage at 2V, 1.0C
The cycle of discharging to 3.0 V was repeated 100 times. At this time, the 100-cycle discharge amount maintenance ratio represented by the following equation was 91%. 100 cycle discharge amount maintenance rate (%) = [(100th cycle discharge amount) / (2nd cycle discharge amount)] × 100

[0021]

Example 2 As a negative electrode material, KS44 (manufactured by Lonza) and pitch in a coal system (softening point: 80 ° C.) were stirred and mixed at a weight ratio of 1: 3 at 300 ° C. for 1 hour in a vacuum. The mixture was filtered and washed with quinoline at 100 ° C. for 1 hour, and then dried. Then, at 1100 ° C. in a firing furnace in an Ar atmosphere,
Firing was performed for 2 hours to obtain a carbon material coated with an organic fired body.
100 parts, 1 part, and 2 parts by weight of carboxymethyl cellulose and styrene / butadiene latex were added to this carbon material.
Parts and mixed in water to form a slurry. This was applied to a copper foil having a thickness of 12 μm to a uniform thickness, followed by drying and roll pressing. The coating amount of the obtained negative electrode was 95 g / m ² , and the bulk density of the active material was 1.41 g / m ^2.
cm ³ . The lithium insertion coefficient K of this negative electrode was 0.85 as measured by the method described above.
Further, d002 of KS44 was 0.3350 nm, Lc was 87 nm, the specific surface area of the carbon material after coating with the organic fired body was 2.27 m ² / g, and the average particle size was 18.3 μm.
A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except for the negative electrode. The 50-cycle discharge amount maintenance ratio at 0 ° C. was 96%. Under this condition, the battery was disassembled in a charged state, and the deposited lithium was observed. As a result, no deposited lithium was observed. The 100-cycle discharge amount maintenance ratio at 20 ° C. was 90%.

[0022]

Example 3 As a negative electrode material, BF-15SP (manufactured by Chuetsu Graphite Industry Co., Ltd.) was mixed with SFG6 (manufactured by Lonza) at a weight ratio of 4: 1. The average particle size of SFG6 was 3.4 μm. Mixing was performed by dry mixing with a Turbula mixer. Carboxymethyl cellulose and styrene / butadiene latex were added to these mixtures in a weight ratio of 1: 1.
00 parts, 1 part, and 2 parts were mixed and dissolved in water to form a slurry. This was applied to a copper foil having a thickness of 12 μm to a uniform thickness, followed by drying and roll pressing. The coating amount of the obtained negative electrode was 102 g / m ² , and the bulk density of the active material was 1.38 g / cm ³ . The lithium insertion coefficient K of this negative electrode was 0.80 as measured using the method described above. The average particle size of SFG6 is 3.2.
It was 4 μm. A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except for the negative electrode. The 50-cycle discharge amount maintenance ratio at 0 ° C. was 94%. Under this condition, the battery was disassembled in a charged state, and the deposited lithium was observed. As a result, no deposited lithium was observed. The 100-cycle discharge amount maintenance ratio at 20 ° C. was 93%.

[0023]

Comparative Example 1 KS44 (manufactured by Lonza) as a negative electrode material
Carboxymethyl cellulose, styrene / butadiene
Mix 100 parts by weight of Tex, 1 part and 2 parts by weight
And dissolved in water to form a slurry. This has a thickness of 12μ
After coating to a uniform thickness on copper foil of
Performed The coating amount of the obtained negative electrode was 93 g / m. ^Two
And the bulk density of the active material is 1.41 g / cm.^ThreeSo
Was. The lithium insertion coefficient K of the negative electrode is calculated by the method described above.
It was 0.68 when it measured using it. Actual except for the negative electrode
A lithium ion secondary battery was fabricated and evaluated in the same manner as in Example 1.
Was done. The 50-cycle discharge capacity maintenance rate at 0 ° C. is 7
2%. Under this condition, disassemble the battery while charging
Observation on the negative electrode revealed that the deposited lithium with a gray tint was
Was observed. 100 cycle discharge at 20 ° C
The retention was 84%.

[0024]

Comparative Example 2 The negative electrode material used in Example 2 was used. 100 parts by weight of carboxymethyl cellulose and styrene / butadiene latex, 1 part by weight,
Two parts were mixed and dissolved in water to form a slurry.
After coating this to a uniform thickness on a copper foil with a thickness of 12 μm,
Drying and roll pressing were performed. The coating amount of the obtained negative electrode was 97 g / m ² , and the bulk density of the active material was 1.62 g.
/ Cm ³ . The lithium insertion coefficient K of this negative electrode was 0.65 as measured by the method described above. A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except for the negative electrode. The 50-cycle discharge amount maintenance ratio at 0 ° C. was 66%. Under this condition, the battery was disassembled in a charged state and observed on the negative electrode, whereupon depositing lithium having a gray tint was observed. 10 ° C at 20 ° C
The zero cycle discharge maintenance rate was 86%.

[0025]

Comparative Example 3 The negative electrode material used in Example 3 was used. 100 parts by weight of carboxymethyl cellulose and styrene / butadiene latex, 1 part by weight,
Two parts were mixed and dissolved in water to form a slurry.
After coating this to a uniform thickness on a copper foil with a thickness of 12 μm,
Drying and roll pressing were performed. The coating amount of the obtained negative electrode was 93 g / m ³ , and the bulk density of the active material was 1.64 g.
/ Cm ³ . The lithium insertion coefficient K of this negative electrode was 0.62 as measured by the method described above. A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except for the negative electrode. The battery was disassembled in a charged state under the condition that the 50-cycle discharge capacity maintenance ratio at 0 ° C. was 58%, and a grayish electrodeposited lithium was observed. 100 ° C at 20 ° C
The cycle discharge maintenance rate was 88%.

Table 1 shows the lithium insertion coefficient, 5 at 0 ° C.
The 0 cycle discharge amount maintenance ratio and the 100 cycle discharge amount maintenance ratio at 20 ° C. are shown.

[0027]

[Table 1]

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a lithium insertion coefficient.

According to the present invention, a non-aqueous electrolyte secondary battery having excellent cycle stability at low temperatures can be realized by using a negative electrode having a lithium insertion coefficient K of 0.70 ≦ K.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Koji Kiyoyoshi 1-3-1 Yoko, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture F-term within Asahi Kasei Kogyo Co., Ltd. 5H029 AJ05 AK02 AK03 AK05 AL07 AM02 AM03 AM04 AM05 AM07 HJ00 HJ01 HJ04 HJ05 HJ07 HJ13 5H050 AA07 CA02 CA07 CA08 CA09 CA11 CB08 HA00 HA01 HA05 HA07 HA13

Claims (4)

[Claims] 1. The lithium insertion coefficient K of a negative electrode is 0.70 ≦
K is a non-aqueous electrolyte secondary battery. 2. The negative active material according to claim 1, wherein d002, which indicates the average spacing between (002) planes, is 0.335.
It is in the range of 0 nm or more and less than 0.3380 nm, Lc indicating the size of the crystallite in the c-axis direction is 10 nm or more, the average particle size is 10 to 30 μm, and the specific surface area is 5 m ² / g.
A non-aqueous electrolyte secondary battery comprising the following carbon materials. 3. The method according to claim 1, wherein the active material of the negative electrode has an average spacing d002 of the (002) plane, and d002 is 0.335.
The average particle size obtained by coating the surface of a carbon material having a range of 0 nm or more and less than 0.3380 nm and having a crystallite size in the c-axis direction of Lc of 10 nm or more with non-graphitic carbon is 10 to 10 nm. A non-aqueous electrolyte secondary battery comprising a material having a thickness of 30 μm and a specific surface area of 5 m ² / g or less. 4. A mixture of the negative electrode active material according to claim 1 and a carbon material having an average particle size of 2 to 8 μm, wherein the carbon material having an average particle size of 2 to 8 μm is 5 to 40 wt%. A non-aqueous electrolyte secondary battery using a carbon mixture for a negative electrode, characterized in that the carbon mixture is contained in the range described above.