JPH10223229A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery to prevent degradation of the performance of the battery characteristics by the reaction of the filler with the electrolyte in the excessively charged condition by using the carbon material, in which the surface of the base carbon is covered with a layer consisting of the amorphous carbon as the filler contained in the positive electrode material. SOLUTION: Electric conductivity is improved by mixing 0.1-10wt.% carbon material such as hard carbon of about 0.01-10μm in grain size as the filler in the positive electrode material. The carbon material is covered by a layer, in which the surface of the base carbon consists of amorphous carbon to the thickness of 10-1000Å. The amorphous carbon layer can be formed through the CVD treatment, in which the base carbon is brought into contact with the vapor of the organic compound such as methane at a high temperature of 500-2000 deg.C, or formed by covering the base carbon with the organic matter such as petroleum pitch, and then baking it around 500-2000 deg.C. The surface of the carbon material is covered with the chemically unactive carbon base surface, and does not react chemically with the electrolyte, and is not subjected to the ingress of the cathodic ion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to an improvement in a filler contained in a positive electrode material.

[0002]

2. Description of the Related Art In recent years, secondary batteries using an organic electrolyte, particularly secondary batteries using lithium, have been receiving attention because of their high energy density. Since the size and weight of the device can be reduced, lithium ion secondary batteries have recently been widely used for portable devices such as a camera-integrated VTR and a mobile phone. However, since lithium is used as the material, which is a chemically active substance, safety issues at the time of using the battery have been pointed out from various aspects since its development. For this reason, today's lithium-ion secondary batteries are safe in terms of the type and shape of the active material, the structure of the electrodes and battery can, etc., so that the battery does not burst or ignite due to overcharge, overdischarge, internal short circuit, etc. Various innovations have been made to improve the performance.

[0003] Currently, commercially available lithium ion secondary batteries are charged by using a lithium composite oxide such as lithium cobalt oxide as a positive electrode material and carbon as a negative electrode material, and moving lithium ions between the two electrodes. It has a mechanism for discharging. At this time, since the lithium composite oxide of the positive electrode has insufficient conductivity, a filler mainly composed of a carbon material is mixed in the positive electrode to improve the conductivity.
As a result, sufficient conductivity can be exhibited, and a lithium ion secondary battery with less deterioration of battery characteristics even when used for a long time can be provided.

[0004]

However, as a result of the study by the present inventors, it has been found that the positive electrode mixed with the filler has a safety problem in the following points. That is, during charging of the lithium ion secondary battery, in an overcharged state in which the battery is charged beyond the capacity of the negative electrode, the filler in the positive electrode reacts with the electrolytic solution to be denatured, and the impedance of the entire positive electrode increases. As a result, the entire positive electrode generates heat, which causes decomposition of the electrolytic solution and generation of gas, resulting in deterioration of battery characteristics and deformation of the battery can. Although the reason for this is not clear, in the overcharged positive electrode, the high potential causes anions in the electrolyte to enter the filler,
This is presumed to cause structural destruction and change in battery characteristics. There have been reports on methods for preventing overcharge of lithium ion secondary batteries (for example, JP-A-5-35034 and JP-A-6-338347). There were no reports of prevention laws.

[0005] Lithium-ion secondary batteries currently on the market take measures such as protection circuits and safety valves to prevent overcharge. However, in order to further improve the safety and reliability of lithium-ion secondary batteries. It can be said that the above problems are problems to be solved. The present invention provides a non-aqueous electrolyte secondary battery in which a positive electrode contains, as a filler, a carbon material capable of stably existing even in an overcharged state.

[0006]

The present inventors have conducted intensive studies to solve the above-mentioned problems. As a result, if the filler contained in the positive electrode material is a carbon material having the following characteristics, overcharging is performed. The present inventors have found that they can stably exist in the electrolyte even in the state, and do not lower the battery performance, and have completed the present invention.

That is, the present invention relates to a non-aqueous electrolyte secondary battery characterized in that a positive electrode contains a carbon material whose surface is covered with a layer made of amorphous carbon. The layer made of amorphous carbon coated on the surface of carbon
A layer formed of the amorphous carbon coated on the surface of the base carbon, which is formed by the treatment, is obtained by baking after coating the base carbon with an organic substance.

A first feature of the present invention is that in the nonaqueous electrolyte secondary battery, the positive electrode contains, as a filler, a carbon material in which the surface of the base carbon is covered with a layer made of amorphous carbon. Here, the amorphous carbon coated on the base carbon surface is
It refers to carbon having low material permeability as compared with base carbon. The characteristics of the amorphous carbon are clarified by observing the orientation of the carbon network (002) plane on the carbon material surface with a transmission electron microscope. That is, the amorphous carbon in the present invention has a feature that the orientation of the carbon network plane (002) plane is oriented parallel to the surface of the base carbon.
This can be more clearly characterized by image analysis of a section photograph near the surface of the carbon material by a transmission electron microscope. Specifically, in the section photograph near the surface of the carbon material, the vicinity of the surface of the carbon material mainly composed of the coated amorphous carbon is selected as a square having a side of 200 °, and the (002) plane of the carbon network plane in that region is selected. Import the image into the image analysis device. At this time, the power spectrum (angle VS intensity) can be obtained by obtaining the intensity distribution of the spatial frequency in the angular direction. In the present invention, this spectrum shows a peak at an angle parallel to the base carbon surface, and the peak height at this time is 1
Assuming that the half-value width of / 2 is α, the degree of orientation represented by the following formula has a characteristic of exhibiting a value of 70% or more.

The degree of orientation (%) = (180−α) × 100/180 The fact that the vicinity of the surface of the carbon material in the present invention is:
This indicates that the substrate is covered with amorphous carbon oriented parallel to the base carbon surface. On the other hand, the orientation of the carbon network plane of the base carbon is often different from the orientation of the amorphous carbon, and the boundary between the base carbon and the amorphous carbon to be coated can be confirmed by the difference in the orientation state. . In the present invention, it is recommended that this boundary exists in a region of 10 to 1000 °, preferably 50 to 500 ° in the depth direction from the carbon material surface (including the coated amorphous carbon). The carbon material having the degree of orientation represented by the above formula of less than 70%, or the boundary between the base carbon and the amorphous carbon is 1
In a positive electrode using a carbon material having a temperature of less than 0 ° as a filler, an increase in impedance in an overcharged state is recognized, and the effect of the present invention cannot be sufficiently exhibited. Also, the boundary between the base carbon and the amorphous carbon is 10
The positive electrode using a carbon material having a temperature of not less than 00 ° as a filler does not exhibit an increase in impedance, but the surface conductivity is reduced, the function as a filler is reduced, and the weight is increased more than necessary, which is not preferable. .

The carbon material having such characteristics is hardly subjected to electrochemical modification even when it comes into contact with an electrolytic solution because the surface of the particle is covered with a chemically inert carbon base. Since the structure in the vicinity of the surface is dense, even if it is exposed to a high potential, no anions enter therein. For this reason, the positive electrode using the carbon material as a filler according to the present invention does not generate heat or increase in impedance even in an overcharged state, and as a result, provides a lithium ion secondary battery with less deterioration in battery characteristics even when used for a long time. It is possible to do.

A carbon material having the above characteristics can exhibit excellent performance as a filler for a positive electrode of a lithium ion secondary battery. However, in order to obtain the carbon material specified in the present invention, the particle surface must be modified to a specific structure, and it is not easy to stably produce it at an industrial level. The present inventors have conducted intensive studies on this point, and as a result, have found that the following method can efficiently and stably produce a carbon material having the characteristics defined in the present invention. That is, another feature of the present invention is that
It is to use a CVD process when coating the surface of the base carbon with a layer made of amorphous carbon.

[0012] The CVD treatment in the present invention refers to a method in which an organic compound vapor is introduced into base carbon under a high temperature condition for a certain period of time. According to this method, the gaseous organic compound diffuses uniformly on the surface of the carbon substrate and causes a carbonization reaction while adhering to the surface of the carbon substrate. An amorphous carbon layer to be filled can be formed with a uniform thickness. The organic compound used here is preferably one which easily forms amorphous carbon and has a relatively low boiling point, and is preferably methane, ethane, propane, butane, ethylene, propylene, butene, benzene, toluene, ethylbenzene, cyclohexane, or cyclohexane. Hydrocarbons such as pentane or derivatives thereof, and halogenated hydrocarbons such as dichloromethane, dichloroethane, trichloromethane, and trichloroethane are recommended. Further, the treatment temperature is set to a temperature range that promotes vaporization of the introduced organic compound and its carbonization reaction.
0-2000 ° C, preferably 800-1200 ° C, is suitable. At a treatment temperature of 500 ° C. or less, the carbonization reaction on the substrate carbon surface hardly proceeds, and at a temperature of 2000 ° C. or more, the organic compound vapor carbonizes before reaching the substrate carbon surface. It becomes difficult to form a prescribed amorphous carbon layer. About the method of introducing organic compound vapor into the base carbon, after heating and vaporizing the organic compound,
A simple method is to send nitrogen or an inert gas as a carrier into a container containing base carbon. The thickness of the amorphous carbon coated on the surface of the base carbon can be adjusted by adjusting the time of the CVD treatment.

Further, the present inventors have found another effective method for coating the surface of the base carbon with a layer made of amorphous carbon. This method is characterized in that the surface of the base carbon is coated with a layer made of amorphous carbon by baking after coating the base carbon with an organic substance. In this method, a highly viscous liquid or solid organic compound is dissolved in an appropriate solvent to form a solution, and the solution is impregnated with carbon as a base material, and then the excess liquid is removed and the solvent is evaporated. It is fired later, and exhibits the same effect as the CVD process. At this time, hydrocarbon compounds such as petroleum pitch, tar, mesocarbon microbeads, naphthalene, phenanthrene, pyrene, triphenylene, chrysene, coronene, pentacene and derivatives thereof, and furfuryl alcohol are used as highly viscous liquid or solid organic compounds. Resins, acrylonitrile resins, styrene resins, vinyl chloride resins, polymers such as phenol resins, and oligomers thereof, and the like, and solvents such as acetone, benzene, and quinoline, which have a relatively low boiling point and a high solubility, are suitable. The firing temperature is the same as in the CVD process.
500 to 2000 as the temperature range for promoting the carbonization reaction
° C, preferably 800-1200 ° C. 50
At a treatment temperature of 0 ° C. or lower, the carbonization reaction on the surface of the base carbon hardly proceeds, and at a temperature of 2000 ° C. or higher, the decomposition of the organic compound is promoted simultaneously with the carbonization reaction. It becomes difficult to form a carbon layer.

Next, the material of the base carbon material in the present invention will be described. In the present invention, the material of the carbon material serving as the base material is preferably a material having sufficient conductivity per se and improving the conductivity of the positive electrode when used as a filler,
Materials that can be expected to sufficiently improve conductivity include hard carbon, natural graphite, artificial graphite, carbon black, acetylene black, pitch coke, mesophase carbon, and the like.

The average particle size of the carbon material in the present invention is preferably in the range of 0.01 to 10 μm, more preferably 0.01 to 1 μm. Obtaining submicron particles is impractical in terms of grinding technology,
When particles having a size of 10 μm or more are used, the contact between the particles is not sufficient and the resistance of the electrode increases, which is not preferable. Further, in the present invention, the proportion of the carbon material contained in the positive electrode as a filler does not provide sufficient conductivity if too small,
If it is too large, the capacity of the positive electrode is reduced.
6.0% by weight is suitable.

Next, the positive electrode material 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
Metal oxides such as nO ₂ , CuO, Cu ₅ V ₂ O ₁₂ , Cr ₂ O ₃ and TiO ₂ , metal selenides such as NbSe ₃ and VSe ₂ , LiVO ₂ , LiCrO ₂ , LiFeO ₂ and LiN
iO ₂ , LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , L
iCo _x Sn _y O ₂ , LiCoNiO ₂ , LiCo _x Fe _y O
An alkali metal-containing composite oxide such as 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.

The method of mixing these materials with the carbon material obtained by the present invention as a filler and then processing the mixture into a positive electrode includes, for example, polytetrafluoroethylene,
After mixing a fluorine-based binder and a positive electrode active material mainly containing a polymer such as polyvinylidene fluoride and polyhexafluoropropylene or a copolymer thereof,
A method of applying the mixture on a current collector such as a copper foil, an aluminum foil, and a nickel foil may be used.

Next, the negative electrode material of the battery of the present invention will be described. As the negative electrode material, like the positive electrode material, a material having high electron conductivity is preferable so that lithium ions can be reversibly released and inserted and electron transport can be easily performed. Examples of this material include hard carbon, natural graphite, artificial graphite, carbon materials such as carbon black, acetylene black, pitch coke, and mesophase carbon, tin oxide, germanium oxide, lead oxide, silicon oxide, antimony oxide, and bismuth oxide. Oxide materials,
Metal materials such as aluminum, tin, germanium, antimony, aluminum tin alloy, aluminum manganese alloy, and aluminum magnesium alloy are exemplified. In addition, as for the method of processing such a negative electrode material into a negative electrode, as in the case of the positive electrode, for example, a fluorinated binder such as styrene butadiene latex, polyvinylidene fluoride, or polytetrafluoroethylene is mixed with the negative electrode material, and then copper foil, aluminum foil, or the like. And the like.

Next, the lithium ion moving medium will be described. As the ion transfer medium, for example, 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, or a mixture thereof with an aprotic organic solvent And the like. Specific examples of the lithium salt used for these include LiPF ₆ , LiBF ₄ , and LiAsF.
₆ , LiClO ₄ , LiSbF ₆ , LiI, LiBr, L
iCl, LiAlCl ₄ , LiHF ₂ , LiSCN, CF
₃ SO ₃ Li, C ₄ F ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NL
i, (CF ₃ SO ₂ ) ₃ CLi, (C ₄ F ₉ SO ₂ ) ₂ NLi
and so on. Further, as the aprotic organic solvent used for the transfer medium, propylene carbonate, ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, organic carbonates such as dimethyl carbonate, butyrolactone, propiolactone, ethyl acetate,
Aliphatic organic esters such as butyl acetate, propyl acetate, ethyl propionate, and butyl propionate, organic ethers such as glyme, diglyme, triglyme, tetrahydrofuran, dioxane, diethyl ether, and silicone oil; organic amines such as pyridine and triethylamine; acetonitrile; It contains at least a part or a mixture of organic nitriles such as pionitrile and other aprotic organic solvents, for example, aromatic hydrocarbons such as benzene, toluene, xylene and decalin, hexane, pentane and decane. Such as aliphatic hydrocarbons, alkyl esters such as phenol, catechol and bisphenol, aromatic esters and halogenated hydrocarbons such as chloroform, carbon tetrachloride, dichloromethane, freon and trichlene It is also possible to mix used.
Using a protic organic solvent for the ion transfer medium
Since the protons of the organic solvent are reduced on the electrode surface, hydrogen gas is generated and the charge / discharge efficiency is reduced, which is not preferable.

Next, examples of the polymer matrix include aliphatic polyethers such as polyethylene oxide, polypropylene oxide, polytetramethylene oxide, polyvinyl alcohol and polyvinyl butyral;
Polyethylene sulfide, aliphatic polythioethers such as polypropylene sulfide, polyethylene succinate, polybutylene adipate, aliphatic polyesters such as polycaprolactone, polyethylene imine, polyimide and its precursors, polyacrylonitrile, polyvinylidene fluoride and the like 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.

When a battery can is manufactured using the above-described negative electrode and positive electrode, as shown in FIG. 1, the foil of the negative electrode and the positive electrode is wound in a state where the foil faces each other with a separator interposed therebetween, and is filled in a metal can. Further, a battery can is obtained by a method of injecting an electrolytic solution.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail by way of examples.

[0023]

Example 1 100 g of hard carbon was charged into a rotary kiln type firing furnace as base carbon, and
While rotating at a constant speed while maintaining the temperature at 0 ° C., toluene vapor was supplied into the furnace using nitrogen as a carrier gas. After reacting for 1 hour, the supply of toluene was stopped, the furnace was cooled, and the hard carbon powder subjected to the CVD treatment was taken out and used as a carbon material for the positive electrode filler. The obtained carbon material was subjected to a high-resolution transmission electron microscope JEM-400 manufactured by JEOL Ltd.
Observation was performed at 0FX, and a section photograph (magnification: 2,000,000 times) of a (002) plane of carbon was taken with a transmission electron microscope. This photograph is shown in FIG. This photograph was subjected to image analysis processing using an image analysis system IP-1000 manufactured by Asahi Kasei Corporation. The vicinity of the surface of the carbon material is selected as a square having a side of 200 °, and the image of the (002) plane of the carbon network in that region is taken into an image analyzer, and the peak half width of the power spectrum is obtained from the angular intensity distribution of the spatial frequency. Thus, the degree of orientation was calculated. FIG. 3 shows an example of the power spectrum.

The thus obtained hard carbon powder was used as a positive electrode filler to prepare a positive electrode according to the following procedure.
A paste obtained by kneading and dispersing 10 g of the obtained hard carbon powder, 143 g of LiCoO ₂ powder, and 10 g of polytetrafluoroethylene powder (average particle size: 1 μm) together with 200 g of toluene was applied on an aluminum foil to prepare a positive electrode coating film.

Next, a negative electrode was manufactured in the following procedure. A paste prepared by kneading and dispersing 6 g of styrene-butadiene latex in 280 g of graphite powder in 200 g of water was applied to a copper foil to obtain a negative electrode coating film.
Next, using the negative electrode and positive electrode coating films, a battery can shown in FIG. 1 was produced as follows. A separator (5 in FIG. 1) made of a polyethylene microporous film is interposed between the positive electrode (1 in FIG. 1) and the negative electrode (2 in FIG. 1), and is laminated many times. By turning, a spiral electrode body was produced. Further, the spiral electrode body was housed in a SUS battery container (6 in FIG. 1). The negative electrode lead terminal (4 in FIG. 1) was connected to the inner bottom of the battery container by spot welding, and the positive electrode lead terminal (3 in FIG. 1) was similarly connected to the battery sealing plate (7 in FIG. 1). .

Next, 1 mol of LiPF ₆ was used as an electrolyte in a mixed solvent in which ethyl methyl carbonate and ethylene carbonate were mixed at a volume ratio of 1: 1 in the battery can.
/ L of the electrolyte solution prepared by dissolving to give
The battery container and the battery sealing plate were fitted and sealed via a polypropylene packing (8 in FIG. 1) to produce a cylindrical nonaqueous electrolyte battery having an outer diameter of 20 mm and a length of 50 mm. To evaluate the overcharge characteristics of this battery,
The battery was charged at a charging end voltage of 5.0 V and a current of 1 mA for 48 hours. After the charging was completed, the battery was stored at 85 ° C. for 48 hours, and the change in impedance was measured at a measurement frequency of 1 kHz. The results are shown in Table 1.

[0027]

Example 2 The same treatment as in Example 1 was carried out except that graphite powder was used as the base carbon to obtain a CVD-treated graphite powder. Using this as a positive electrode filler, a battery was assembled, and the same evaluation as in Example 1 was performed. The results are shown in Table 1.

[0028]

Example 3 The same treatment as in Example 1 was carried out except that carbon black powder was used as the base carbon to obtain a carbon black powder subjected to CVD treatment. Using this as a positive electrode filler, a battery was assembled, and the same evaluation as in Example 1 was performed. The results are shown in Table 1.

[0029]

Examples 4 and 5 A graphite powder was obtained in the same manner as in Example 2 except that the time of the CVD treatment was changed to 30 minutes and 120 minutes. Assembling the battery using this as the positive electrode filler,
The same evaluation as in Example 1 was performed. The results are shown in Table 1.

[0030]

[Embodiments 6 and 7] The processing temperature of the CVD process is 800 ° C.,
A graphite powder was obtained by performing the same process as in Example 2 except that the temperature was changed to 200 ° C. Using this as a positive electrode filler, a battery was assembled, and the same evaluation as in Example 1 was performed. The results are shown in Table 1.

[0031]

Example 8 The same treatment as in Example 2 was carried out except that benzene was supplied instead of toluene, to obtain a graphite powder subjected to CVD treatment. Using this as a positive electrode filler, a battery was assembled, and the same evaluation as in Example 1 was performed. The results are shown in Table 1.

[0032]

Embodiments 9 to 11 LiClO ₄ ,
A battery was assembled and evaluated in the same manner as in Example 2 except that LiBF ₄ and LiAsF ₆ were used. The results are shown in Table 1.

[0033]

Example 12 Graphite powder 10 as base carbon
0 g of acetone solution of petroleum pitch (weight concentration 20%)
After immersion in the furnace, the excess adhering liquid was removed, and the mixture was charged into a rotary kiln-type firing furnace. The furnace was rotated at a constant speed for 60 minutes at room temperature using nitrogen as a purge gas.
The inside of the furnace was heated to 1000 ° C. and fired while rotating at a constant speed. After reacting for 180 minutes, the furnace was cooled and the treated graphite powder was taken out. Using this as a carbon material for a positive electrode filler, a battery was assembled and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0034]

Comparative Example 1 A positive electrode was prepared without mixing a filler into the positive electrode, and a battery was assembled and evaluated in the same manner as in Example 1 except for the above. The results are shown in Table 1 together with the results of the examples.

[0035]

Comparative Example 2 A battery was assembled and evaluated in the same manner as in Example 1 except that the filler mixed with the positive electrode was hard carbon not subjected to the treatment according to the present invention. The results are shown in Table 1 together with the results of the examples.

[0036]

Comparative Example 3 A battery was assembled and evaluated in the same manner as in Example 1 except that the filler mixed with the positive electrode was graphite not subjected to the treatment according to the present invention. The results are shown in Table 1 together with the results of the examples.

[0037]

Comparative Example 4 Example 1 except that the filler to be mixed with the positive electrode was carbon black not subjected to the treatment according to the present invention.
A battery was assembled and evaluated in the same manner as described above. The results are shown in Table 1 together with the results of the examples.

[0038]

Comparative Example 5 A battery was assembled and evaluated in the same manner as in Example 9 except that the filler mixed with the positive electrode was graphite not subjected to the treatment according to the present invention. The results are shown in Table 1 together with the results of the examples.

[0039]

Comparative Example 6 A battery was assembled and evaluated in the same manner as in Example 10 except that the filler mixed with the positive electrode was graphite not subjected to the treatment according to the present invention. The results are shown in Table 1 together with the results of the examples.

[0040]

Comparative Example 7 A battery was assembled and evaluated in the same manner as in Example 11 except that the filler mixed with the positive electrode was graphite not subjected to the treatment according to the present invention. The results are shown in Table 1 together with the results of the examples.

[0041]

[Table 1]

From the results shown in the examples, those using the positive electrode containing the carbon material having the characteristics defined in the present invention as a filler were different from those of the comparative example even in the overcharged state.
It can be seen that the rise in impedance is small and the deterioration in battery characteristics is small.

[0043]

As is apparent from the above description, the use of the positive electrode containing the carbon material defined in the present invention as a filler makes it possible to minimize the deterioration of battery characteristics even in an overcharged state and to improve the safety. , A non-aqueous electrolyte secondary battery having a high value can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a battery structure.

FIG. 2 is a transmission electron micrograph of the vicinity of the surface of the carbon material obtained in Example 1 of the present invention.

FIG. 3 is an example of a power spectrum obtained by performing image analysis on a transmission electron micrograph near the surface of the carbon material obtained in Example 1 of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Strip positive electrode 2 Strip negative electrode 3 Positive electrode lead terminal 4 Negative lead terminal 5 Separator 6 Battery container 7 Battery sealing plate 8 Packing 9 Insulating plate

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[Procedure amendment]

[Submission date] February 13, 1997

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Figure 2

[Correction method] Change

[Correction contents]

FIG. 2

Claims (3)

[Claims] 1. A non-aqueous electrolyte secondary battery characterized in that a positive electrode contains a carbon material whose surface is coated with a layer made of amorphous carbon. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the layer made of amorphous carbon coated on the surface of the base carbon is formed by a CVD process. 3. The non-aqueous solution according to claim 1, wherein the layer made of amorphous carbon coated on the surface of the base carbon is obtained by coating the base carbon with an organic substance and then firing. Electrolyte secondary battery.