JPH1040914A - Manufacture of nonaqueous secondary battery and negative pole active substance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a conductor from being decomposed due to a negative pole active substance and improve battery capacity, cycle characteristic, and voltage flatness by constituting which a specific negative pole and respective specific positive pole and conductor. SOLUTION: A battery is constituted with a negative pole, a positive pole, and a nonaqeous ion conductor. The negative pole is subjected to oxidizing process at temperatures of 200-700 degrees C in air for example, and made to have a negative pole active substance of graphite grains, as amorphous carbon is made to adhere to its surface by vapor-phase heat decomposition of propane for example. The positive pole has an active substance of a chalcogen compound (such as LiCoO2 ) containing Li. The nonaqueous ion conductor is for example a conductor comprising propylene carbonate and ethylene carbonate by a volume ratio of 9:1-1:9. That is, since graphite particles are oxidation-treated, amorphous carbon adheres securely to the graphite particles and the conductor is prevented from decomposing due to separation of a amorphous carbon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous secondary battery and a method for producing a negative electrode active material. More specifically, the present invention relates to a nonaqueous secondary battery using graphite particles capable of inserting and removing lithium for a negative electrode, and a method for producing a negative electrode active material.

[0002]

2. Description of the Related Art Secondary batteries using alkali metals such as lithium have attracted attention as electronic devices and the like have become lighter, thinner and shorter, and have reduced power consumption. When metal lithium is used alone for the negative electrode, repetition of charge / discharge (precipitation-dissolution of metal lithium) generates dendrites (dendritic crystals) on the metal surface, which grows and penetrates through the separator to form a positive electrode. And cause a short circuit inside the battery. It has been found that when a lithium alloy is used for the negative electrode of the secondary battery instead of metallic lithium, the generation of dendrites is suppressed as compared with the case of a single battery, and the characteristics of the charge / discharge cycle are improved.
However, the use of the alloy does not completely suppress the generation of dendrites, and the possibility of short-circuiting inside the battery remains to some extent. In addition, the use of an alloyed negative electrode increases the weight, which may impair the light weight characteristic of a lithium secondary battery.

[0003] In recent years, instead of using metallic lithium or its alloys for the negative electrode, matrix materials such as carbon materials and conductive polymers utilizing the occlusion-release process of lithium ions have been developed. As a result, the generation of dendrite, which occurs when metal lithium or its alloy is used, does not occur in principle, and the problem of a short circuit inside the battery has been drastically reduced. In particular, it is known that the carbon material has a lithium absorption-release potential closer to the lithium extraction-dissolution potential than other materials. Above all, a graphite material is a carbon material having a high capacity per unit weight and unit volume, since lithium can theoretically be taken into the crystal lattice at a ratio of one lithium atom to six carbon atoms. Further, the potential for lithium insertion and desorption is flat, chemically stable, and greatly contributes to the cycle stability of the battery.

[0004] For example, in J. Electrochm. Soc., Vol. 13
7, 2009 (1990), JP-A-4-115457, JP-A-4-115458, JP-A-4-237971.
Using graphite-based carbon material as a negative electrode active material disclosed in JP-A-4-368778, JP-A-4-368778,
Japanese Patent Application Laid-Open No. 28996/1993, Japanese Unexamined Patent Application Publication No. 5-114421 and the like use a surface-treated graphite-based carbon material for a negative electrode active material.

[0005] As described above, the graphite-based carbon material has a discharge capacity close to the theoretical capacity in an organic electrolyte mainly composed of ethylene carbonate (EC). In addition, since the charge and discharge potential is slightly higher than the potential of lithium dissolution and deposition and is very flat, when a battery is manufactured using a graphite-based carbon material as the negative electrode active material, a high capacity and A secondary battery having high flatness of battery voltage can be realized.

[0006]

Although the graphite-based carbon material can achieve a high capacity as described above, it still has the problem of causing decomposition of the electrolyte (non-aqueous ionic conductor) due to its high crystallinity. Have been. For example, propylene carbonate (PC), which is a solvent for an organic electrolyte, has a wide potential window, a low freezing point (-170 ° C.), or a high chemical stability, and is therefore used as a solvent for an electrolyte for a lithium battery. Widely used. However, when a graphite-based carbon material is used as the negative electrode active material, the decomposition reaction of PC occurs remarkably,
The fact that a negative electrode made of a graphite-based carbon material cannot be charged / discharged because only 0% of PC is present in the electrolytic solution has been reported by J.-J. Elect
rochm. Soc., Vol. 142, 1746 (1995).

It is widely known that a graphite-based carbon material can be used as a negative electrode for a lithium secondary battery only when an electrolytic solution of a mixed solvent system of EC and a low-viscosity solvent is used. However, the electrolyte mainly composed of EC has low ionic conductivity at a low temperature, and when a secondary battery using this electrolyte and a graphite-based carbon material as a negative electrode is manufactured, the temperature characteristics or current characteristics of the battery are reduced by the electrolyte. It is very difficult to improve by selection because there are few choices of solvents that can be used for the secondary battery.

To solve such a problem, Japanese Patent Laid-Open Publication No.
As disclosed in Japanese Patent No. 68778 or Japanese Patent Application Laid-Open No. 5-110666, it has been proposed to use a carbon material in which the surface of graphite particles is coated with low crystalline carbon as a negative electrode active material for a secondary battery. These are effective means for suppressing decomposition of the electrolytic solution, increasing discharge capacity, and improving cycle characteristics.
However, when a secondary battery is manufactured using an electrolyte mainly composed of PC, kneading at the time of pulverization or electrode manufacturing in order to uniform the particle diameter in the manufacturing process of the negative electrode active material,
Low-crystalline carbon coated on the graphite particle surface is reduced by coating on the current collector plate, etc., and the electrode is destroyed by gas generation due to decomposition of the electrolytic solution, resulting in a problem of reduced battery capacity and deterioration of cycle characteristics. Has arisen.

Further, as a production method expected to reduce costs, there is a method of mixing and firing graphite and a carbon precursor such as pitch as disclosed in JP-A-6-84516. In the case of this production method, graphite particles coated with low crystalline carbon adhere to each other to take a liquid phase process,
There is a problem that the active surface of the graphite reappears due to pulverization or the like in the negative electrode manufacturing process, and PC is decomposed.

[0010] When the surface of the graphite particles is coated with low-crystalline carbon as described above, the problem that the graphite particles have a low adhesive strength to the low-crystalline carbon and are quickly separated, causing the decomposition of the electrolytic solution is apparent. became. Therefore, this method also causes a problem that the characteristics of the battery are deteriorated and the yield is reduced in the manufacture of the battery.

[0011]

Means for Solving the Problems In order to solve the above problems, the inventors of the present invention have conducted intensive studies and as a result, oxidized the graphite particles before attaching the amorphous carbon to the surface of the graphite particles. By doing so, it was found that amorphous carbon can be more firmly attached, and the present invention has been achieved. Furthermore, it has been found that by oxidizing graphite particles, amorphous carbon can be deposited quickly when amorphous carbon is adhered to the surface of graphite particles by a vapor phase pyrolysis deposition method.

Thus, according to the present invention, there is provided a negative electrode using black supply particles having amorphous carbon adhered to the surface as a negative electrode active material, a positive electrode using lithium-containing chalcogenide as a positive electrode active material, a nonaqueous ion A non-aqueous secondary battery comprising a conductor, wherein the negative electrode active material is formed by oxidizing graphite particles and then attaching amorphous carbon to the surface of the graphite particles. .

Further, according to the present invention, the graphite particles are oxidized by heat treatment in air, in an oxidizing gas atmosphere, in an oxidizing solution, or mixed with an alkali, and then the amorphous carbon is converted into graphite particles. A negative electrode active material is formed by attaching the negative electrode active material to a surface of the negative electrode active material.

[0014]

DETAILED DESCRIPTION OF THE INVENTION The graphite particles used in the present invention are:
Those capable of inserting and removing lithium are preferred. Examples of the graphite particles include natural graphite, artificial graphite, and expanded graphite. Furthermore, the average interplanar spacing (d ₀₀₂ ) of the (002) plane of the graphite particles before the oxidation treatment by the X-ray wide angle diffraction method is 0.335 to 0.340 nm, and the crystallite thickness (Lc) in the (002) plane direction is Graphite particles having a crystallite thickness (La) of 10 nm or more and (110) plane direction of 10 nm or more and / or
Or peak intensity ratio of L360cm ^-1 for 1580 cm ^-1 by argon laser Raman of the graphite particles before the oxidation treatment is 0.4 or less, the graphite particles wherein the intensity ratio after the amorphous carbon deposition is 0.4 or more Is preferred.

Here, d ₀₀₂ of the graphite particles before the oxidation treatment is larger than 0.340 nm, Lc and La are smaller than 10 nm, and 1580 c by argon laser Raman.
When the peak intensity ratio of 1360 cm ^{-1 to} m ^-1 is more than 0.4, the crystallinity is lowered and a high capacity as a negative electrode active material cannot be achieved, which is not preferable. BET specific surface area of graphite particles before oxidation treatment is 5 to 150 m
² / g and an average particle size of 0.7 to 80 μm are preferred. When the specific surface area of the graphite particles is smaller than 5 m ² / g, the contact area with the non-aqueous ionic conductor is reduced and the current characteristics of the electrode are reduced. When the specific surface area is larger than 150 m ² / g, the contact with the non-aqueous ionic conductor is reduced. It is not preferable because the area becomes too large and self-discharge increases. Further, when the average particle size of the graphite particles is smaller than 0.7 μm, there is a high possibility that the graphite particles will pass through the pores of the battery separator and cause an internal short circuit. This is not preferred because the handleability of the product becomes poor.

Next, in the present invention, the graphite particles are oxidized before the amorphous carbon is attached to the surface of the graphite particles.
Oxidation of graphite particles generates oxygen-containing functional groups on the surface, and amorphous carbon is chemically bonded through the functional groups, so graphite particles and amorphous carbon adhere more firmly. It is thought to be. In addition, it is considered that the surface of the particles is physically roughened by oxidizing the graphite particles, so that the bonding strength of the amorphous carbon adhered to the surface is improved.

The oxidation treatment may be performed in air or oxygen,
A method of oxidizing graphite particles in an atmosphere of oxidizing gas such as carbon dioxide and water vapor, inorganic acids such as nitric acid, sulfuric acid, hydrochloric acid and hydrofluoric acid, organic acids such as formic acid, acetic acid, propionic acid and phenol, and potassium permanganate solution A method of oxidizing graphite particles in an oxidizing agent solution such as aqueous hydrogen peroxide, or an oxidation method of heat-treating by mixing with an alkali solution or an alkali molten salt such as potassium hydroxide, sodium hydroxide or lithium hydroxide. However, the present invention is not limited to this.

Of these, in the case of air oxidation, the oxidation temperature is preferably from 200 to 700 ° C. If the oxidation temperature is lower than 200 ° C., the oxidation time becomes longer and the production cost becomes higher,
On the other hand, if the temperature exceeds 700 ° C., graphite burns, which is not preferable.

When performing nitric acid oxidation, the nitric acid oxidation temperature is preferably from 20 ° C. to 130 ° C. or lower. If the temperature is lower than 20 ° C., the graphite particles are not oxidized, which is not preferable. 13
If the temperature is higher than 0 ° C., it exceeds the boiling point of nitric acid, so that safety is undesirably lowered. The nitric acid concentration is preferably from 5% by weight to 99% by weight. If the concentration is lower than 5% by weight, the oxidation time is long, and the production cost is undesirably high. Fuming nitric acid is 99% by weight, and nitric acid having a higher concentration is not preferable because it is difficult to obtain. The oxidation time is preferably, but not limited to, 20 hours or less.

When the oxidation is carried out using an alkali, a solid alkali and graphite powder are mixed and heat-treated, or
It is preferable to disperse the graphite powder in an alkali solution, dry the graphite powder, and then heat-treat the graphite powder, but the invention is not limited thereto.
The heat treatment temperature is preferably near the melting point of the alkali,
700 ° C. is preferred. If the temperature is lower than 300 ° C., the alkali does not melt, which is not preferable. If the temperature is higher than 700 ° C., the heat treatment chamber is significantly corroded, which is not preferable.

Next, by attaching amorphous carbon to the surface of the oxidized graphite particles, a negative electrode active material is obtained. As a method for attaching amorphous carbon to the surface of oxidized graphite particles, a method for attaching amorphous carbon by vapor phase pyrolysis deposition of hydrocarbons, or a method for depositing a carbon precursor in a liquid phase And a method of baking after mixing with graphite particles is preferred, but not limited thereto. The thickness of the attached amorphous carbon is preferably 0.001 to 1 μm. 0.00
If the thickness is less than 1 μm, the portion of the graphite particles that decomposes the electrolyte is not deactivated, which is not preferable. On the other hand, when the thickness is more than 1 μm, the ratio of graphite particles serving as nuclei decreases, and the capacity as a negative electrode decreases, which is not preferable. Incidentally, the amorphous carbon in the present invention is defined as one that satisfies that hexagonal mesh planes of crystallites are irregularly stacked as compared with graphite particles and that the average interplanar spacing by powder X-ray diffraction is larger than that of graphite particles. Say.

The negative electrode is formed by mixing the above-described negative electrode active material having amorphous carbon adhered to the surface of the graphite particles with a binder. As the binder, a fluorine-based polymer such as polyvinylidene fluoride and polytetrafluoroethylene, a polyolefin-based polymer such as polyethylene and polypropylene, and synthetic rubbers can be used, but are not limited thereto.

Mixing ratio (weight ratio) of carbon material and binder
Is preferably from 99: 1 to 70:30. When the weight ratio of the binder is more than 70:30, the internal resistance or polarization of the electrode becomes large, and the discharge capacity becomes low, so that a practical lithium secondary battery cannot be produced, which is not preferable. On the other hand, if the weight ratio of the binder is less than 99: 1, the binding capacity of the negative electrode active material itself or the negative electrode active material and the current collector becomes insufficient, and the negative electrode active material falls off or the mechanical strength decreases, resulting in a decrease in the battery strength. Is not preferable because it makes the production difficult. In the preparation of the negative electrode, in order to improve the binding property and remove the solvent of the binder, heat treatment in a vacuum, an inert gas, or air at a temperature above the boiling point of the solvent and around the melting point of the binder. Is preferably performed.

The non-aqueous ion conductor used in the present invention may be, for example, an organic electrolyte, a polymer solid electrolyte, an inorganic solid electrolyte, a molten salt, or the like. Among them, an organic electrolyte can be suitably used.

Here, the solvent of the non-aqueous ionic conductor is a solvent obtained by combining at least a mixed solvent of PC: EC = 9: 1 to 1: 9 (volume ratio) and optionally combining another solvent. Is preferred. More preferably, PC: EC = 9:
It is a solvent obtained by combining a mixed solvent of 1 to 5: 5 (volume ratio) and optionally another solvent. Here, the other solvent is preferably a low-viscosity solvent, and the mixing ratio of the mixed solvent and the low-viscosity solvent is not limited. If PC: EC is greater than 9: 1, the solvent is preferentially decomposed and cannot be used for an actual secondary battery, which is not preferable. PC: EC =
If the PC is less than 1: 9, the non-aqueous ionic conductor characteristics at -40 ° C or lower deteriorate, and the secondary battery does not operate at low humidity, which is not preferable.

Other solvents contained in the non-aqueous ion conductor include cyclic carbonates such as butylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and dipropyl carbonate, γ-butyrolactone, lactones such as γ-valerolactone, furans such as tetrahydrofuran and 2-methyltetrahydrofuran, diethyl ether, 1,2-dimethoxyethane, ethers such as 1,2-diethoxyethane, ethoxymethoxyethane and dioxane, and dimethyl sulfoxide , Sulfolane, methylsulfolane, acetonitrile, methyl formate, methyl acetate and the like.

The electrolyte salt of the non-aqueous ion conductor includes lithium perchlorate, lithium borofluoride, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium halide, lithium chloride and aluminate chloride. And lithium salts such as lithium. These can be used alone or in combination of two or more.

The non-aqueous ion conductor is prepared by dissolving an electrolyte salt in the above-mentioned solvent. The solvent and the electrolyte salt used when preparing the non-aqueous ion conductor are not limited to those described above. The positive electrode of the non-aqueous secondary battery of the present invention comprises a positive electrode active material, a conductive material, a binder, and in some cases, a solid electrolyte.

As the positive electrode active material, it is preferable to use a chalcogenide containing lithium. For example, Li
_x M _1-y N _y O ₂ (where M is any of Fe, Co, Ni, N is a transition metal, preferably a Group 4B or 5B metal, x is 0 ≦ x ≦ 1, y represents 0 ≦ y ≦ 1)
The chalcogenide represented by can be used. Specifically, LiCoO ₂ , LiNiO ₂ , LiFeO ₂ ,
LiMnO _{2 and the} like. Further, for example, LiMn
Chalcogenides represented by _2-x N _y O ₄ (where N is a transition metal, preferably a Group 4B or 5B metal, and z represents 0 ≦ z ≦ 2) can also be used. Specifically, LiM
n ₂ O _{4 and the} like.

As the conductive material, carbons such as carbon black (acetylene black, thermal black, channel black, etc.), graphite powder, metal powder and the like can be used, but are not limited thereto. As the binder, a fluorine-based polymer such as polytetrafluoroethylene or polyvinylidene fluoride, a polyolefin-based polymer such as polyethylene or polypropylene, or a synthetic rubber can be used, but is not limited thereto.

The mixing ratio of the conductive material and the binder can be 5 to 50 parts by weight of the conductive material and 1 to 30 parts by weight of the binder with respect to 100 parts by weight of the positive electrode active material. If the amount of the conductive material is less than 5 parts by weight or the amount of the binder is more than 30 parts by weight, the internal resistance or polarization of the electrode becomes large, and the discharge capacity of the electrode becomes low, so that a practical lithium secondary battery cannot be manufactured. Not preferred. If the amount of the conductive material is more than 50 parts by weight, the amount of active material contained in the electrode is relatively reduced, so that the discharge capacity as a positive electrode is reduced. If the amount of the binder is less than 1 part by weight, the binding ability of the active material is lost, and it is difficult to manufacture a battery because the active material falls off and the mechanical strength is reduced. 3 binders
If the amount is more than 0 parts by weight, as in the case of the conductive material, the amount of the active material contained in the electrode is reduced, and the internal resistance or polarization of the electrode is increased, so that the discharge capacity is lowered, which is not practical.

In the preparation of the positive electrode, it is preferable to perform a heat treatment at a temperature around the melting point of each binder and at least the boiling point of the solvent in order to improve the binding property. Further, a separator is used to hold the non-aqueous ion conductor. Examples of the separator include non-woven fabrics or woven fabrics such as synthetic resin fibers, glass fibers, and natural fibers having electrical insulation properties, and lost molded articles such as alumina. Among them, non-woven fabrics such as synthetic resins such as polyethylene and polypropylene are preferable in terms of quality stability and the like. Some of these synthetic resin non-woven fabrics have a function that when the battery abnormally generates heat, the separator is melted by heat and a function of shutting off the gap between the positive electrode and the negative electrode is added. From the viewpoint of battery safety, these are preferably used. Can be used. The thickness of the separator is not particularly limited, but may have a thickness capable of holding a required amount of the nonaqueous ion conductor and preventing a short circuit between the positive electrode and the negative electrode, and is usually about 0.01 to 1 mm. And it is preferably about 0.02 to 0.05 mm.

By adopting the structure of the present invention, it is possible to use graphite particles having excellent flatness in potential as a negative electrode active material and to combine them with a non-aqueous ionic conductor mainly composed of propylene carbonate and having excellent low-temperature characteristics. . Therefore, a non-aqueous secondary battery having high flatness of the discharge voltage of the battery and excellent low-temperature characteristics can be manufactured. In addition, the excellent characteristics of the graphite particles to which amorphous carbon is attached are not impaired even after the process of pulverization or kneading in battery production by the configuration of the present invention, and the cost in material production can be reduced. Becomes

[0034]

The present invention will be described below in detail with reference to examples. In addition, the average plane spacing (d ₀₀₂ ) by the X-ray wide-angle diffraction method
Alternatively, a method for measuring the crystallite size (Lc, La) is as follows:
A known method, for example, “Charcoal material experiment technique 1, p.
63, edited by Japan Society for Carbon Materials (Science and Technology Co., Ltd.). The shape factor K for obtaining Lc and La was 0.9. The specific surface area of the particles was BE.
The particle size was measured by T method, and the particle size was determined by using a laser diffraction type particle size distribution analyzer, and the peak in the particle size distribution was defined as the average particle size. Example 1 Artificial graphite (flaky, particle size 9 μm, d ₀₀₂ 0.337 nm, LC 100 nm, La 100 n) was used as graphite particles.
m, and a specific surface area of 14 m ² / g), a carbon material having amorphous carbon attached to the surface of graphite particles was prepared by the following method.

5 g of the graphite powder was placed on a sample dish in a box furnace and oxidized in air at 600 ° C. for 5 hours. as a result,
The amount of graphite powder was 4.9 g. Next, 1 g of the oxidized graphite powder was placed on the sample stage 6 of the electric furnace shown in FIG. 1, and argon gas and propane gas were supplied into the quartz tube 5 through the carrier gas supply line 1 and the raw material gas supply line 2, respectively. By operating the needle valves 3 and 4, the raw material gas concentration was set to 5% by volume. Gas flow rate in chamber is 12c
m / min. Thereafter, the graphite powder is heated to 800 ° C. on the sample table 6 by the heating furnace 7, and the propane gas supplied from the gas inlet 8 is thermally decomposed to deposit amorphous carbon on the surface of the graphite particles, thereby forming a negative electrode active material. Material was obtained. The deposition time was 3 hours, and the weight increase rate at this time was 11%.
In FIG. 1, reference numeral 9 denotes a gas exhaust port.

The negative electrode active material prepared by the above method is dispersed in a solution in which polyvinylidene fluoride as a binder is dissolved in a solvent N-methyl-2-pyrrolidone in a mortar, and the paste of the negative electrode active material is kneaded. Was prepared. This paste was applied to both surfaces of a copper foil current collector, temporarily dried at 60 ° C. in air, and then dried under reduced pressure at 240 ° C. to produce a negative electrode sheet electrode. Further, what was vacuum-dried at 200 ° C. for removing water was used as a negative electrode. This negative electrode has an apparent surface area of 8 cm ² and an electrode thickness of 150 μm (of which the current collector thickness is 50 μm).

The current was collected from the copper current collector with a lead wire to obtain a negative electrode for negative electrode single electrode evaluation. The evaluation was performed using a three-electrode cell in a glove box under an argon atmosphere, and lithium as a counter electrode and a reference electrode. Non-aqueous ionic conductor is P
C, EC and diethyl carbonate (DEC) are mixed with 1 m of lithium perchlorate as an electrolyte salt in three kinds of mixed solvents.
One dissolved to a concentration of o1 / 1 was used.
At this time, the volume ratio between the mixture of PC and EC and DEC was set to 1: 1 and the electrode was evaluated using the solvent composition shown in Table 1. The charge / discharge test was performed on 1 g of the negative electrode active material.
The battery was charged to 0 V (relative to Li / Li ⁺ ) at a current density of 30 mA per unit, and subsequently discharged to 2.5 V at the same current density. The results are shown in Table 1 and FIG.

Comparative Example 1 A negative electrode active material obtained by depositing amorphous carbon on the surface of graphite particles under the same conditions as in Example 1 without oxidizing the graphite particles (artificial graphite) used in Example 1 as the negative electrode active material was used. The negative electrode was evaluated in the same manner as in Example 1. In this case, the weight increase after carbon deposition was 9%. The result is shown in FIG.

As shown in FIG. 2, a graphite material obtained by attaching amorphous carbon to the surface of oxidized graphite particles is used as a negative electrode active material, and a mixed solvent containing at least PC and EC in a non-aqueous ionic conductor. By using, a high charge / discharge capacity and a high initial charge / discharge efficiency were obtained. This is considered to be because the adhesion strength between the graphite particles and the amorphous carbon was improved. In particular, it can be seen that these effects are remarkable when EC is 0.5 or less in volume ratio. Further, when amorphous carbon was adhered under the same conditions based on the results of Example 1 and Comparative Example 1,
It can be seen that the oxidation treatment results in a larger deposition amount and higher carbon deposition efficiency.

Example 2 Natural graphite (made in Madagascar; scaly, particle size: 12 μm, d ₀₀₂ : 0.336 nm, Lc: 17 nm, La: 27 nm, specific surface area: 8 m ² / g) was used as graphite material as a raw material. A negative electrode was prepared and evaluated in the same manner as in Example 1 except that the oxidation temperature was 700 ° C. and the oxidation treatment time was 2.5 hours. In this case, the weight increase ratio after the deposition of the amorphous carbon was 70%. The non-aqueous ionic conductors used here were PC, EC and dimethyl carbonate (D
A mixed solvent of MC) having a volume ratio of 2: 1: 2, in which lithium hexafluorophosphate as an electrolyte salt was dissolved to a concentration of 1 mol / 1, was used. Table 1 shows the results.

Comparative Example 2 A negative electrode active material obtained by depositing amorphous carbon on the surface of graphite particles under the same conditions as in Example 1 without oxidizing the natural graphite (produced in Madagascar) used in Example 2 as the negative electrode active material. Use
A negative electrode evaluation was performed in the same manner as in Example 2. In this case, the weight increase ratio after the deposition of the amorphous carbon was 11%. Table 1 shows the results.

Example 3 Artificial graphite (flaky, particle size 0.7) was added to graphite particles as a raw material.
μm, d ₀₀₂ is 0.338 nm, Lc is 14 nm, La
A negative electrode was prepared and evaluated in the same manner as in Example 1 except that the oxidation temperature was 200 ° C. and the oxidation treatment time was 5 hours, using 25 nm and a specific surface area of 150 m ² / g). In this case, the weight increase ratio after the deposition of the amorphous carbon was 38%. The non-aqueous ionic conductor used here is P
As a mixed solvent of C, EC and ethyl methyl carbonate (EMC), a solution obtained by dissolving lithium borofluoride as an electrolyte salt to a concentration of 1 mo1 / 1 at a product ratio of 2: 1: 5 was used. Table 1 shows the results.

COMPARATIVE EXAMPLE 3 The negative electrode active material obtained by depositing amorphous carbon on the surface of graphite particles under the same conditions as in Example 1 without oxidizing the artificial graphite used in Example 3 was used as the negative electrode active material. As in the case of No. 3, the negative electrode was evaluated. In this case, the weight increase ratio after the deposition of the amorphous carbon was 29%. Table 1 shows the results.

As shown in Table 1, the decomposition of the non-aqueous ionic conductor is suppressed, and even if natural graphite having high crystallinity is oxidized at 700 ° C., amorphous carbon can be more firmly attached to the particle surface. Possible, and artificial graphite having a large specific surface area has a large contact area with air.
It can be seen that the amorphous carbon can be more firmly attached to the surface of the graphite particles even by the oxidation treatment in the above.

Example 4 An artificial graphite was used as a raw material for graphite particles, oxidized under the same conditions as in Example 1, mixed with coal tar pitch, and the resultant was heated at 300 ° C. for 2 hours in a nitrogen atmosphere. Then, it was baked at 1000 ° C. for 3 hours in a nitrogen atmosphere. The sample was taken out of the electric furnace, pulverized in a mortar, the particle size was adjusted by a sieve, and the powder was used to produce a negative electrode in the same manner as in Example 1. As the non-aqueous ionic conductor at this time, one obtained by dissolving lithium perchlorate in a mixed solvent of PC, EC and DEC at a volume ratio of 1: 1: 2 so as to have a concentration of 1 mo1 / 1 was used. Table 1 shows the results.

COMPARATIVE EXAMPLE 4 The artificial graphite used in Example 4 was not oxidized as the negative electrode active material, but a negative electrode active material having amorphous carbon adhered to the surface of graphite particles under the same conditions as in Example 4 was used. A negative electrode evaluation was performed in the same manner as in Example 4. Table 1 shows the results.

[0047]

[Table 1]

As shown in Table 1, even when amorphous carbon is adhered to the surface of graphite particles in the liquid phase, decomposition of the amorphous ion conductor is suppressed, and graphite is oxidized to form non-graphite particles. It can be seen that the bonding strength with the crystalline carbon is improved.

Example A Using the artificial graphite used in Example 1 for graphite particles, a carbon material having amorphous carbon adhered to the surface of the graphite particles was prepared by the following method.

5 g of the above graphite powder was added to 200 ml of 70% nitric acid.
The mixture was refluxed at 110 ° C. for 10 hours, washed with water and dried to obtain oxidized graphite powder. There was no change in weight after the treatment. Next, using an electric furnace shown in FIG. 1, nitrogen gas was used as a carrier gas and ethane gas was used as a source gas. Source gas concentration is 3
%. The reaction temperature was 830 ° C., and the deposition time was 2.5
Time.

The method of manufacturing the electrode and the method of evaluating the negative electrode were performed in the same manner as in Example 2. The results are shown in Table 1 below. Comparative Example A The graphite powder used in Example 1 was not oxidized as the negative electrode active material, and the negative electrode active material in which amorphous carbon was adhered to the surface of graphite particles under the same conditions as in Example A was used. Similarly, the negative electrode was evaluated. The results are shown in Table 1 above.

Example B A negative electrode evaluation was carried out in the same manner as in Example A, except that a negative electrode active material having amorphous carbon adhered to the surface of graphite particles under the same conditions as in Example A was used except that the nitric acid concentration was 5%. Was done. The results are shown in Table 1 above.

Example C An oxidized graphite powder was obtained in the same manner as in Example A, except that fuming nitric acid (99% by weight nitric acid) was used as the method for oxidizing the graphite particles, and the reaction temperature was 20 ° C. . The method of adhering the surface amorphous carbon to the graphite powder and the method of evaluating the negative electrode single electrode were performed in the same manner as in Example A. The results are shown in the above table.

Example D Using the artificial graphite used in Example 1 for graphite particles, a carbon material having amorphous carbon adhered to the surface of the graphite particles was prepared by the following method.

5 g of the above graphite was placed in a solution of 120% of 98% sulfuric acid and 2.5 g of sodium nitrate, potassium permanganate was added at 20 ° C. or less, then kept at 35 ° C. for 30 minutes, 230 ml of water was added, and the mixture was heated to 98 ° C. Then, excess potassium permanganate was decomposed with hydrogen peroxide, and then sufficiently washed with water to obtain graphite oxide powder.

The method of adhering the surface amorphous carbon to the graphite powder and the method of evaluating the negative electrode single electrode were performed in the same manner as in Example A. The results are shown in Table 1 above.

Example A, Example B, Example C, Example D
From the results of Comparative Example A, it was found that by oxidizing the surface of the graphite particles with a mixed acid of nitric acid or inorganic acid and potassium permanganate, the initial efficiency was improved in an electrolyte system containing a large amount of PC. It can be seen that the adhesion strength with the crystalline carbon is improved.

Example E The graphite particles used in Example 1 were oxidized by the following method.

First, 2 g of graphite powder and 5 g of lithium hydroxide monohydrate were mixed in a mortar and heat-treated at 700 ° C. for 2 hours in the air. Thereafter, it was sufficiently washed with water and dried to obtain a graphite oxide powder.

The method for adhering the surface amorphous carbon to the graphite powder and the method for evaluating the negative electrode single electrode were performed in the same manner as in Example A. The results are shown in Table 1 above.

Example F The graphite particles used in Example 1 were oxidized by the following method.

First, 60 g of graphite powder was dispersed in 200 ml of a 1.5 N aqueous sodium hydroxide solution,
Stirred for hours. After that, it is dried and placed in nitrogen at 300 ° C, 5
The mixture was heat-treated for an hour, washed sufficiently with water, and dried to obtain graphite oxide powder.

The method for adhering the surface amorphous carbon to the graphite powder and the method for evaluating the negative electrode single electrode were performed in the same manner as in Example A. The results are shown in Table 1 above.

From the results of Example E and Example F, it was found that the graphite particles were heat-treated with an alkali and oxidized to improve the initial efficiency in an electrolyte system containing a large amount of PC. It can be seen that the adhesion strength with the amorphous carbon is improved.

Example 5 Preparation of Negative Electrode Using a negative electrode active material prepared by the same method as in Example 1 and having amorphous carbon adhered to the surface, a nonionic dispersant was added, and polytetrafluoroethylene (dried Thereafter, the weight ratio of the negative electrode active material to polytetrafluoroethylene was 91:
9), and the resulting mixture was made into a paste in a mortar, and the paste was applied to the holes of a nickel three-dimensional porous current collector. This was preliminarily dried at 60 ° C., heat-treated at 240 ° C., pressed, and then vacuum-dried at 200 ° C. to remove moisture, and used as a negative electrode. This negative electrode has a diameter of 1
The tablet had a size of 4.5 mm and an electrode thickness of 0.4 lmm.

Preparation of Positive Electrode Lithium carbonate and cobalt carbonate, and antimony trioxide were mixed in a ratio of lithium atom to cobalt atom and antimony atom of 1:
Each was weighed to 9.95: 0.05, mixed in a mortar, baked in air at 900 ° C. for 20 hours, and then ground in a mortar to obtain a powder of a positive electrode active material. The active material had a composition of _{Li 0.98 Co 0. 95 Sb 0.05} O 2. The thus obtained positive electrode active material is mixed with acetylene black, a nonionic dispersant is added, and polytetrafluoroethylene (after drying, the weight ratio of the positive electrode active material to acetylene black and polytetrafluoroethylene is , 100: 10: 5), and the mixture was made into a paste by applying a dispersion liquid onto a titanium mesh current collector. This is preliminarily dried at 60 ° C., 24
After heat treatment at 0 ° C, press, and then 20 to remove moisture
What was dried under reduced pressure at 0 ° C. was used as a negative electrode. This positive electrode was a tablet having a diameter of 15 mm and an electrode thickness of 0.9 mm.

Assembling of Battery As shown in FIG. 3, the positive electrode current collector 14 was previously attached to the inner bottom surface by welding, and the positive electrode 13 was crimped to the positive electrode battery can 17 on which the sealing packing 15 was placed. Next, a polypropylene nonwoven fabric separator 12 is placed on this,
A non-aqueous ion conductor in which an electrolyte salt LiPF ₆ was dissolved to a concentration of 1 mol / 1 in a mixed solvent having a volume ratio of C, EC and DEC of 1: 1: 2 was impregnated. On the other hand, the negative battery cover 1
The negative electrode current collector 10 was welded to the inner surface of No. 6, and the negative electrode 11 was pressed on the negative electrode current collector. Next, the negative electrode 11 was overlaid on the separator 12, and the positive electrode battery can 17 and the negative electrode battery lid 16 were caulked with the sealing gasket 15 interposed therebetween, thereby producing a coin-type battery.

Evaluation of Battery The produced coin-type battery was charged at a charge / discharge current of 1 mA and reached a charging upper limit voltage of 4.2 V, and then was charged at a constant voltage of 4.2 V. The charging time was set at 12:00. 1. The lower limit voltage of discharge
A charge / discharge test was performed at 5 V. The temperature dependence of the capacity of the obtained battery was measured, and the results are shown in Table 2.

Example G Except that the carbon material of Example A was used as the negative electrode active material,
A negative electrode was produced by the method described in Example 5. The size and thickness of the produced negative electrode were the same as those described in Example 5. The method for producing the positive electrode and the method for assembling the battery were also produced by the method described in Example 5.

This battery was evaluated by the method described in Example 5. Table 2 shows the results.

Example H Except that the carbon material of Example E was used for the negative electrode active material,
A negative electrode was produced by the method described in Example 5. The size and thickness of the produced negative electrode were the same as those described in Example 5. The method for producing the positive electrode and the method for assembling the battery were also produced by the method described in Example 5.

This battery was evaluated by the method described in Example 5. The results are shown in Table 2 above.

Comparative Example 5 A negative electrode was produced in the same manner as in Example 5 except that the carbon material of Comparative Example 1 was used as the negative electrode active material. The size and thickness of the produced negative electrode were the same as those described in Example 5. The method of manufacturing the positive electrode and the method of assembling the battery are also described in Example 5.
Was prepared by the method described in (1).

This battery was evaluated by the method described in Example 5. Table 2 shows the results.

[0075]

[Table 2]

As shown in Table 2, by oxidizing the graphite particles, the adhesion strength between the amorphous carbon on the surface and the graphite particles is improved, and the secondary battery has excellent cycle characteristics and excellent characteristics even at low temperatures. It can be seen that can be prepared.

[0077]

As described above, the non-aqueous secondary battery of the present invention comprises a negative electrode using graphite particles having amorphous carbonic acid adhered on the surface as a negative electrode active material, and a positive electrode using lithium-containing chalcogenide as a positive electrode active material. And a non-aqueous ion conductor, wherein the negative electrode active material is formed by oxidizing graphite particles and then attaching amorphous carbon to the surface of the graphite particles.

Therefore, by oxidizing the graphite particles before attaching the amorphous carbon, the adhesion strength between the amorphous carbon and the graphite particles can be improved. The deposition time of the crystalline carbon can be shortened, and the manufacturing cost can be reduced. In addition, a non-aqueous ionic conductor mainly composed of propylene carbonate having excellent low-temperature characteristics and a graphite-based carbon material having excellent electric potential flatness and excellent low-temperature characteristics can be combined, and high capacity and high voltage flatness can be obtained. A secondary battery having excellent cycle characteristics and excellent low-temperature characteristics can be manufactured.

[Brief description of the drawings]

FIG. 1 is a view showing an apparatus for producing amorphous carbon according to the present invention.

FIG. 2 is a diagram showing a discharge capacity and an initial charge / discharge efficiency of Example 1 and Comparative Example 1 in the present invention.

FIG. 3 is a sectional view of a coin-type battery according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Carrier gas supply line 2 Source gas supply line 3 Needle valve 4 Needle valve 5 Quartz tube 6 Sample stand 7 Heating furnace 8 Gas inlet 9 Gas exhaust port 10 Negative current collector 11 Negative electrode 12 Separator 13 Positive electrode 14 Positive electrode collector 15 Sealed packing 16 Negative battery lid 17 Positive battery can

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takehito Mitate 22-22, Nagaikecho, Abeno-ku, Osaka, Osaka Inside Sharp Corporation (72) Inventor Kazuaki Minato 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp Corporation

Claims (18)

[Claims] 1. A negative electrode comprising graphite particles having amorphous carbon adhered to the surface thereof as a negative electrode active material, a positive electrode comprising a lithium-containing chalcogenide as a positive electrode active material, and a non-aqueous ion conductor, A non-aqueous secondary battery, wherein the negative electrode active material is formed by oxidizing graphite particles and then attaching an amorphous element to the surface of the graphite particles. 2. The method according to claim 1, wherein the graphite particles are obtained by X-ray wide-angle diffraction.
02) The average plane spacing (d ₀₀₂ ) of the planes is 0.335 to 0.3
40 nm, crystallite thickness (Lc) in the (002) plane direction is 1
The non-aqueous secondary battery according to claim 1, wherein the crystallite thickness (La) in the (110) plane direction is 0 nm or more and 10 nm or more. 3. The graphite particles having a BE of 5 to 150 m ² / g.
The non-aqueous secondary battery according to claim 1, which has a specific surface area according to a T method and an average particle size of 0.7 to 80 μm. 4. The non-aqueous secondary battery according to claim 1, wherein the non-aqueous ion conductor comprises a mixed solvent containing at least propylene carbonate and ethylene carbonate. 5. The volume ratio of propylene carbonate to ethylene carbonate is from 9: 1 to 1: 9.
The non-aqueous secondary battery according to 1. 6. The volume ratio of propylene carbonate to ethylene carbonate is from 9: 1 to 5: 5.
The non-aqueous secondary battery according to 1. 7. The non-aqueous secondary battery according to claim 1, wherein the chalcogenide is a metal oxide containing lithium. 8. The method according to claim 1, wherein the metal oxide containing lithium is Li
_X M _1-y N _y O ₂ (where M is any of Fe, Co, and Ni, N is a transition metal, x represents 0 ≦ x ≦ 1, and y represents 0 ≦ y ≦ 1) or _{LiMn 2-z N z 0 4} ( here, N is a transition metal, z is 0 ≦ z ≦ 2 are expressed) non-aqueous secondary battery according to an a lecture Motomeko 7. 9. The method according to claim 8, wherein the metal oxide containing lithium is Li
The non-aqueous secondary battery according to claim 8, which is CoO ₂ , LiNiO ₂ , LiFeO ₂ , LiMnO ₂ or LiMn ₂ O ₄ . 10. After oxidizing graphite particles in air,
A method for producing a negative electrode active material, wherein amorphous carbon is attached to the surface of graphite particles to form a negative electrode active material. 11. The oxidation treatment in air is performed at 200 to 70.
The method for producing a negative electrode active material according to claim 10, which is performed at 0 ° C. 12. The amorphous carbon is attached to the surface of graphite particles by gas phase pyrolysis of hydrocarbons.
Or the method for producing a negative electrode active material according to item 11. 13. The method according to claim 1, wherein the oxidation treatment is performed with nitric acid.
9. The non-aqueous secondary battery according to any one of 9. 14. The non-aqueous secondary battery according to claim 13, wherein the nitric acid oxidation is performed at a temperature of 20 to 130 ° C. and a nitric acid concentration of 5 to 99% by weight. 15. The non-aqueous secondary battery according to claim 1, wherein the oxidation treatment is a heat treatment with an alkali. 16. The temperature of the heat treatment with an alkali is 300.
The non-aqueous secondary battery according to claim 15, which is at -700C. 17. A method for producing a negative electrode active material, comprising oxidizing graphite particles with nitric acid, and then attaching amorphous carbon to the surface of the graphite particles to form a negative electrode active material. 18. After the graphite particles are heat-treated with an alkali,
A method for producing a negative electrode active material, wherein amorphous carbon is attached to the surface of graphite particles to form a negative electrode active material.