JP2005135755A - Method of manufacturing carbon material for negative electrode of nonaqueous secondary battery and nonaqueous secondary battery using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a carbon material for a negative electrode of a nonaqueous secondary battery enhancing cycle characteristics, quick discharge characteristics, namely, load characteristics by lowering impedance of an SEI surface film, and to provide the nonaqueous secondary battery using the same. <P>SOLUTION: The carbon material for the negative electrode of the nonaqueous secondary battery is manufactured by treating at least one carbon raw material selected from natural graphite, artificial graphite, mesophase carbon microbeads, mesophase pitch base graphite fibers, vapor phase growth carbon fibers, and graphite whiskers with microwave induced plasma 15 produced by exciting gas containing carbon dioxide. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a carbon material for a negative electrode of a non-aqueous secondary battery and a non-aqueous secondary battery using the same, and in particular, a carbon material for a negative electrode of a non-aqueous secondary battery excellent in cycle characteristics and rapid discharge characteristics. The present invention relates to a manufacturing method and a non-aqueous secondary battery using the same.

  With the rapid spread of portable electronic devices, the required specifications for the batteries used for them are becoming stricter year by year, and in particular, small and thin, high capacity, excellent cycle characteristics, and stable performance are required. Yes. In the field of secondary batteries, lithium non-aqueous secondary batteries, which have a higher energy density than other batteries, are attracting attention, and the proportion of these lithium non-aqueous secondary batteries shows a significant increase in the secondary battery market. .

  This lithium non-aqueous secondary battery is composed of a negative electrode in which a negative electrode active material mixture is applied in a film form on both sides of a negative electrode core (current collector) made of an elongated sheet-like copper foil, and an elongated sheet-like aluminum foil A separator made of a microporous polypropylene film or the like is disposed between both sides of a positive electrode core body made of, for example, a positive electrode active material mixture coated in a film, and the negative electrode and the positive electrode are insulated from each other by the separator In the case of a prismatic battery, the wound electrode body is further crushed to form a flat shape, and the negative electrode lead and the positive electrode lead are connected to the predetermined portions of the negative electrode and the positive electrode, respectively. And having a configuration housed in an exterior of a predetermined shape.

Among these lithium non-aqueous secondary batteries, particularly as a 4V class non-aqueous secondary battery having a high energy density, the positive electrode active material is made of a lithium composite oxide such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiFeO _2, etc. Therefore, many non-aqueous secondary batteries in which the negative electrode active material is made of a carbonaceous material have been developed. The non-aqueous solvent used in such a non-aqueous secondary battery needs to have a high dielectric constant in order to ionize the electrolyte, and has a high ionic conductivity in a wide temperature range. Organic solvents such as carbonates such as propylene carbonate and ethylene carbonate, lactones such as γ-butyrolactone, ethers, ketones, and esters are also used.

  The carbonaceous material as the negative electrode active material, in particular, the negative electrode active material made of graphite material has a discharge potential comparable to that of lithium metal or lithium alloy, but the dendrite does not grow, so safety is ensured. In addition, it has excellent properties such as high initial efficiency, good potential flatness, and high density.

  However, when a carbonaceous material such as graphite or amorphous carbon is used as the negative electrode active material, the organic solvent is reduced and decomposed on the surface of the electrode during the charge and discharge process, and negative electrode impedance is reduced due to generation of gas, deposition of side reaction products, etc. There has been a problem in that it causes an increase in charge / discharge efficiency and deterioration in cycle characteristics.

  Therefore, conventionally, in order to suppress the reductive decomposition of the organic solvent, various compounds are added to the non-aqueous electrolyte so that the negative electrode active material does not directly react with the organic solvent. A technique for controlling a negative electrode surface coating (SEI: Solid Electrolyte Interface. Hereinafter referred to as “SEI surface coating”) is important. For example, in Patent Documents 1 and 2 below, as a non-aqueous electrolyte solution for a non-aqueous secondary battery, at least one selected from vinylene carbonate and derivatives thereof in the non-aqueous electrolyte solution (Patent Document 1) or vinyl ethylene carbonate A compound (Patent Document 2) is added, and by these additives, an SEI surface film is formed on the negative electrode active material layer before insertion of lithium into the negative electrode by the first charge, and the solvent molecules around the lithium ions are A device that functions as a barrier to prevent insertion is disclosed.

  However, non-aqueous secondary batteries are used as driving power sources for recent portable personal computers, portable information terminals (PDAs), cellular phones, digital cameras, CD players, and for high load applications such as electric vehicles. Since use as a drive power supply has been studied, not only cycle characteristics but also characteristics when discharging at a high current density in a short time, that is, improvement of load characteristics have been required. However, the SEI surface coating obtained by adding an additive as disclosed in Patent Documents 1 and 2 below to the non-aqueous electrolyte still has only a high resistance with low lithium ion conductivity. In other words, the negative electrode impedance is remarkably increased, and the load characteristic is particularly deteriorated.

On the other hand, many attempts have been made to improve various characteristics of non-aqueous secondary batteries by changing the physical characteristics of the graphite material as the negative electrode active material. For example, in Patent Document 3 below, the capacity of graphite is increased, and then the efficiency is increased without contact with air, so that the discharge capacity is the theoretical capacity (lithium ions are regularly packed between the graphite layers). When the lithium / graphite intercalation compound LiC ₆ is stored, the negative electrode active material for a lithium non-aqueous secondary battery having a value exceeding 372 Ah / kg) on a carbon basis and the non-aqueous system using the negative electrode active material An invention of a secondary battery is disclosed.

  The increase in the capacity of graphite in the present invention is oxidation treatment, crushing treatment, etc. In the case of oxidation treatment, heating is performed at 250 to 650 ° C., preferably about 300 ° C. for 30 minutes to 1 hour in an atmosphere of oxygen, ozone and NOx. Is done by doing. Since this oxidation treatment usually produces an oxygen-containing functional group, it is removed by heating at about 800 to 1200 ° C. for about 3 to 6 hours in an inert gas atmosphere. After being immersed in a liquid heavy hydrocarbon such as the above, a high-capacity processed product is obtained by a method of carbonizing the heavy hydrocarbon adhered or laminated on the high-capacity processed product or a chemical vapor deposition method (hereinafter referred to as “CVD method”). A method of depositing a carbonaceous film on the surface is employed.

  In the invention disclosed in the following Patent Document 3, by combining the above-described high capacity processing and high efficiency processing, the discharge capacity is higher than the theoretical capacity, the irreversible capacity is small, and the initial efficiency is 90%. % Of graphite can be obtained, but such a method requires the removal of the oxygen-containing functional groups generated during the high-efficiency treatment and the step of forming a new carbon film. Not only was the manufacturing method very complex and very expensive, but no consideration was given to the load characteristics.

  Further, in Patent Document 4 below, when a carbon material subjected to a thermal plasma treatment at 3000 ° C. or higher in a reducing atmosphere or a reactive atmosphere is used as a negative electrode material of a lithium secondary battery, carbon having a small potential change. Although it has been disclosed that the material exhibits the larger discharge capacity while maintaining the characteristics of the material and has better resistance to overdischarge, no consideration is given to the cycle characteristics and the load characteristics.

Furthermore, in Patent Document 5 below, in order to improve not only the cycle characteristics of a lithium secondary battery but also the load characteristics, 10 ² to 10 ⁶の (10 to 10 ⁵ nm) of a graphite material used as a negative electrode active material. In addition to limiting the pore volume of pores having a size in the range of 0.4 to 2.0 cc / g per mass of graphite particles, a plurality of flat particles as the graphite particles, so that the orientation planes are non-parallel Although it is disclosed that aggregated or bonded graphite particles should be used, a specific charge / discharge characteristic is disclosed in which charge / discharge is performed at a very low current density of 0.5 mA / cm ^2. No charge / discharge characteristics at high current density beyond that are disclosed.

JP 08-045545 A (claims, paragraphs [0009] to [0012], [0023] to [0036]) JP 2001-006729 A (claims, paragraphs [0006] to [0014]) JP 2001-273894 A JP-A-10-092432 (Claims, paragraphs [0012], [0016] to [0018], [0026]) Japanese Patent Laid-Open No. 10-236809

  As a result of various studies on the formation process of the SEI surface coating formed by the carbonaceous material used as the negative electrode active material of the non-aqueous secondary battery, the present inventors have found that this SEI surface coating is the surface of the carbonaceous material. It was found that the presence of various functional groups and moisture present in the battery hindered the formation of a good quality film and affected the battery characteristics.

Therefore, the present inventors have conventionally confirmed the presence of lithium carbonate in the SEI surface film, and therefore modified the surface of the carbonaceous material to change the functional group present on the surface of the carbonaceous material to CO. As a result of repeating various experiments based on the prediction that a high-quality SEI surface coating should be formed if the water can be removed and unified to those derived from No. _2, the surface modification of such carbonaceous materials Has found that it can be achieved by treating a carbonaceous material with microwave plasma excited with a gas containing CO ₂ , and has completed the present invention.

  Accordingly, an object of the present invention is to provide a method for producing a carbon material for a negative electrode, which can reduce the impedance of the SEI surface coating and obtain a non-aqueous secondary battery excellent in cycle characteristics, rapid discharge characteristics, that is, load characteristics, and the same. An object is to provide a non-aqueous secondary battery.

  The above object of the present invention can be solved by the following configuration. That is, the invention of the method for producing a carbon material for a negative electrode of a non-aqueous secondary battery according to claim 1 of the present application is characterized in that a carbonaceous material is treated with microwave plasma excited with a gas containing carbon dioxide.

According to the method for producing a carbon material for a negative electrode of a nonaqueous secondary battery according to claim 1 of the present application, moisture attached to the surface of the carbonaceous material is removed by a relatively low temperature microwave plasma treatment. At the same time, a functional group derived from CO ₂ is introduced, and at the same time, adsorption of carbon dioxide occurs. On the other hand, in the invention described in Patent Document 3, various functional groups present on the surface of the carbonaceous material are “removed by heating at about 800 to 1200 ° C. for about 3 to 6 hours in an inert gas atmosphere”. In addition, in the invention described in Patent Document 4, “nitrogen, argon, hydrogen, oxygen + argon, etc.” is used as a plasma gas to be introduced in the thermal plasma treatment at 3000 ° C. or higher for the carbonaceous material. (See paragraph [0026]) is used to change the surface state and advance graphitization (see paragraph [0017]). Therefore, a method for producing a carbon material for a negative electrode of a nonaqueous secondary battery according to claim 1 of the present application and a method for producing a carbon material for a negative electrode of a nonaqueous secondary battery disclosed in Patent Documents 3 and 4 above Is clearly different.

  The invention according to claim 2 of the present application is the method for producing a carbon material for a negative electrode of a non-aqueous secondary battery according to claim 1, wherein the carbonaceous material is a graphite-based carbonaceous material. And

  The invention according to claim 3 of the present application is the method for producing a carbon material for a negative electrode of a non-aqueous secondary battery according to claim 2, wherein the graphite-based carbonaceous material is natural graphite, artificial graphite, or mesophase carbon. It is at least one selected from microbeads (MCMB), mesophase pitch-based graphite fibers, vapor-grown carbon fibers, and graphite whiskers.

  Further, the invention of the non-aqueous secondary battery according to claim 4 of the present application includes: a positive electrode having a positive electrode material that reversibly occludes / releases lithium; and a negative electrode having a carbonaceous material that reversibly occludes / releases lithium. A non-aqueous secondary battery comprising a non-aqueous electrolyte is characterized in that the carbonaceous material treated with microwave plasma excited with a gas containing carbon dioxide is used.

  Nonaqueous solvents (organic solvents) constituting the nonaqueous electrolyte include carbonates, lactones, ethers, esters, aromatic hydrocarbons, etc. Among these, carbonates, lactones, ethers, Ketones and esters are preferred, and carbonates are more preferably used.

  Specific examples of carbonates include propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, γ-dimethoxyethane, tetrahydrofuran, anisole, 1,4-dioxane, diethyl carbonate, and the like. Propylene carbonate and ethylene carbonate are preferably used from the viewpoint of increasing charge / discharge efficiency. Two or more of these solvents can be mixed and used.

The electrolyte constituting the non-aqueous electrolyte is lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), trifluoro Examples thereof include lithium salts such as lithium methyl sulfonate (LiCF ₃ SO ₃ ) and lithium bistrifluoromethylsulfonylimide [LiN (CF ₃ SO ₂ ) ₂ ]. Of these, LiPF ₆ and LiBF ₄ are preferably used, and the amount dissolved in the non-aqueous solvent is preferably 0.5 to 2.0 mol / l.

The positive electrode active material, a lithium transition metal composite oxide, i.e. _{LiCoO 2, LiNiO 2, LiNiCo 1} -y O 2 (y = 0.01~0.99), Li 0.5 MnO 2, LiMnO 2, LiCo x Mn _y Ni _z O ₂ (x + y + z = 1), LiMn ₂ O ₄ , and those obtained by substituting part of Co, Ni, and Mn of these oxides with other elements or adding other elements These are used alone or in combination.

  The invention according to claim 5 of the present application is characterized in that, in the nonaqueous secondary battery according to claim 4, the electrolyte is gelled.

  Examples of the polymer that holds the electrolytic solution in the gel electrolyte include polymers such as an alkylene oxide polymer and a fluorine polymer such as a polyvinylidene fluoride-hexafluoropropylene copolymer. A method for forming a gel electrolyte using such a polymer material can be obtained by immersing the electrolytic solution in a polymer such as an isocyanate cross-linked product of polyethylene oxide, polypropylene oxide, or polyalkylene oxide.

  In addition, a method of subjecting an electrolytic solution containing a polymerizable gelling agent to a polymerization treatment such as ultraviolet curing or thermosetting, or a method of cooling a solution obtained by dissolving a polymer that forms a gel electrolyte at room temperature at a high temperature. Are also preferably used. When using a polymerizable gelling agent-containing electrolyte, examples of the polymerizable gelling agent include those having an unsaturated double bond such as acryloyl group, methacryloyl group, vinyl group, allyl group, epoxy, oxetane, Examples thereof include those having a cationically polymerizable cyclic ether group such as formal.

  Specifically, acrylic acid, methyl acrylate, ethyl acrylate, ethoxyethyl acrylate, methoxyethyl acrylate, ethoxyethoxyethyl acrylate, polyethylene glycol monoacrylate, ethoxyethyl methacrylate, ethoxyethyl methacrylate, polyethylene glycol monomethacrylate, N, N- Diethylaminoethyl acrylate, glycidyl acrylate, allyl acrylate, acrylonitrile, diethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, polypropylene glycol diacrylate, polypropylene glycol dimethacrylate, polyalkylene glycol dimethacrylate Monomers having unsaturated double bonds, such as methyl methacrylate, trimethylolpropane alkoxylate triacrylate, pentaerythritol alkoxylate triacrylate, pentaerythritol alkoxylate tetraacrylate, methyl methacrylate and (3-ethyl-3-oxetanyl) methyl acrylate Examples thereof include a copolymer (a molecular weight of 400,000) and a cyclic ether group-containing compound such as tetraethylene glycol bisoxetane.

  A monomer having an unsaturated bond can be polymerized by heat, ultraviolet light, electron beam, or the like, but a polymerization initiator may be added to the electrolytic solution in order to effectively advance the reaction. Examples of the polymerization initiator include organic compounds such as benzoyl peroxide, t-butyl peroxycumene, lauroyl peroxide, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, and t-hexyl peroxyisopropyl monocarbonate. Peroxides can be used.

Polymerization of the cyclic ether group-containing compound is initiated by heat or charge / discharge due to Li ⁺ or a small amount of H ⁺ in the electrolyte.

  On the other hand, a method of cooling a polymer that forms a gel electrolyte at room temperature at a high temperature is dissolved in an electrolyte solution. As such a polymer, a gel is formed with respect to the electrolyte solution and is stable as a battery material. Anything may be used. For example, polymers having a ring such as polyvinyl pyridine and poly-N-vinyl pyrrolidone; acrylic derivative polymers such as methyl polyacrylate and polyethyl acrylate; fluorine-based resins such as polyvinyl fluoride and polyvinylidene fluoride; polyacrylonitrile CN group-containing polymers such as polyvinylidene cyanide; polyvinyl alcohol polymers such as polyvinyl acetate and polyvinyl alcohol; halogen-containing polymers such as polyvinyl chloride and polyvinylidene chloride. Moreover, it can be used even if it is a mixture with said polymer | macromolecule, a modified body, a derivative | guide_body, a random copolymer, a graft copolymer, a block copolymer etc. The weight average molecular weight of these polymers is usually in the range of 10,000 to 5,000,000. When the molecular weight is low, it is difficult to form a gel. If the molecular weight is high, the viscosity becomes too high and handling becomes difficult.

  The invention according to claim 6 of the present application is the nonaqueous secondary battery according to claim 5, wherein the content of the electrolyte in the gelled nonaqueous electrolyte is gelled. It is 50 mass% or more and 99.5 mass% or less with respect to the total amount of aqueous electrolyte solution.

  If the content of the electrolytic solution in the gelled non-aqueous electrolytic solution is too small, less than 50% by mass, the ionic conductivity decreases and the high load discharge capacity decreases. More preferably, it is 75 mass% or more with respect to the total amount of the gel electrolyte. Furthermore, when the content of the electrolytic solution exceeds 99.5% by mass, the mechanical strength of the gelled non-aqueous electrolytic solution cannot be obtained.

According to the above configuration of the present invention, when the carbonaceous raw material is treated with microwave plasma in which a gas containing carbon dioxide is excited, moisture attached to the carbon surface is removed and at the same time, a functional group derived from CO _2. At the same time, carbon dioxide is adsorbed, and as a result, a good-quality SEI film is formed on the negative electrode surface during the initial charge and discharge of the battery, and the load characteristics and cycle characteristics are improved. To do.

  When the electrolyte is gelled, the negative electrode interface resistance increases because the polymer component adheres to the surface of the negative electrode active material, so the characteristics are significantly reduced compared to non-aqueous secondary batteries using liquid electrolytes. Therefore, the effect of using a material treated with microwave plasma excited with a gas containing carbon dioxide as a carbonaceous material as in the present invention is remarkable.

  BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the best mode for carrying out the present invention will be described in detail using examples and comparative examples. However, the following examples are intended to limit the present invention to those shown in these examples. It is not disclosed. The following examples and comparative examples were all performed in a dry room.

<Plasma treatment of carbonaceous raw material>
FIG. 1 shows a schematic view of a plasma processing apparatus 10 used in the present invention. The plasma processing apparatus 10 includes a microwave generation unit 11, a waveguide 12, a quartz plasma reaction chamber 13, and a powder recovery chamber 14 for recovering a plasma-treated carbonaceous material. ing. A microwave having a frequency of 2.45 GHz generated in the microwave generator 11 is applied to the plasma reaction chamber 13 through the waveguide 12, and the microwave plasma 15 is applied to the central portion of the plasma reaction chamber 13. It is supposed to occur. In the plasma reaction chamber 13, a supply port 16 of carbonaceous raw material powder conveyed by a carrier gas is provided in the upper center, and the plasma reaction chamber 13 has a uniform plasma around the supply port 16 of the carbonaceous raw material powder. A plasma generation gas inlet 17 for introducing the generated gas is provided, and a powder recovery chamber 14 is provided at the lower part of the plasma reaction chamber 13.

First, evacuation is performed to 1 × 10 ⁻⁷ Torr in order to remove the influence of oxygen and moisture. Then, a mixed gas of argon (Ar) gas and CO ₂ gas is introduced into the plasma reaction chamber 13 through the plasma generation gas introduction port 17, and a microwave with a frequency of 2.45 GHz is applied from the side to microwave plasma. 15 is generated. The plasma generation conditions at this time were pressure: 5 Torr and input power: 2.5 kW. The carbonaceous raw material powder was supplied into the plasma reaction chamber 13 using Ar as a carrier gas. The supply rate of the carbonaceous raw material powder was 10 g / min.

<Preparation of negative electrode plate>
Next, a specific method for manufacturing a non-aqueous secondary battery common to the examples and comparative examples will be described. The negative electrode plate is prepared by mixing a negative electrode active material made of graphite powder, a binder (for example, 10% by mass) made of polyvinylidene fluoride (PVdF) and the like and an organic solvent made of N-methylpyrrolidone. A slurry or paste is used. These slurries or pastes are uniformly applied over the entire surface of the negative electrode core (for example, a steel foil having a thickness of 10 μm) by using a die coater, a doctor blade or the like in the case of slurry, or by a roller coating method in the case of paste. The negative electrode plate which apply | coated and applied the active material layer is formed. Thereafter, the negative electrode plate coated with the active material layer is passed through a drier to remove the organic solvent that was necessary when the slurry or paste was prepared, and then dried. After drying, this dried negative electrode plate is rolled by a roll press to produce a negative electrode plate having a thickness of 120 μm.

<Preparation of positive electrode plate>
A positive electrode active material made of lithium cobaltate (LiCoO ₂ ) is made of graphite (for example, 5% by mass), a binder made of polyvinylidene fluoride (PVdF) (for example, 5% by mass), or the like, and an organic material made of N-methylpyrrolidone. What was melt | dissolved in the solvent etc. is mixed and it is set as an active material slurry or an active material paste. These active material slurries or active material pastes, in the case of slurry using a die coater, a doctor blade, etc., in the case of paste, a positive electrode core (for example, an aluminum foil or aluminum mesh having a thickness of 20 μm) by a roller coating method or the like The positive electrode plate which apply | coated uniformly on both surfaces and apply | coated the active material layer is formed. Then, the positive electrode plate coated with the active material layer is passed through a dryer to remove and dry the organic solvent necessary for slurry or paste preparation. After drying, the positive electrode plate is rolled with a roll press. Thus, a positive electrode plate having a thickness of 125 μm is produced.

<Preparation of electrolyte>
A non-aqueous electrolyte is prepared by dissolving 1.0M-LiPF ₆ in a solvent mixed at a volume ratio of ethylene carbonate (EC) / propylene carbonate (PC) / diethyl carbonate (DEC) = 10/10/80. Produced. This is mixed with ethylene glycol diacrylate so that ethylene glycol diacrylate: non-aqueous electrolyte = 10: 90 (mass ratio) to prepare a pregel.
<Production of electrode body>
The positive electrode plate and the negative electrode plate produced as described above are sandwiched with a microporous membrane (for example, a polyethylene separator having a thickness of 20 μm) made of a polyolefin-based resin that has low reactivity with an organic solvent and is inexpensive, and Then, the center lines in the width direction of each electrode plate are made to coincide with each other. Then, it winds with a winder and tapes the outermost periphery, and it is set as the spiral electrode body of an Example and a comparative example. Next, the electrode bodies produced as described above are inserted into the exterior bodies made of aluminum laminate, and the positive electrode current collecting tab and the negative electrode current collection tab extending from the electrode bodies are welded together with the exterior body.

<Production of battery>
Next, after the required amount of the pregel was injected from the opening of the outer package, the opening was sealed and polymerized by heating at 70 ° C. for 3 hours. Lithium ion having a design capacity of 700 mAh for all of the examples and comparative examples A non-aqueous secondary battery was produced.

  The carbonaceous material used in the examples was obtained by performing the above-described microwave plasma treatment on commercially available graphite powder, and as a comparative example, the examples of the examples except that the microwave plasma treatment was not performed. The same commercially available graphite powder as the carbonaceous material was used.

<Charging / discharging conditions>
Each of the non-aqueous secondary batteries of Examples and Comparative Examples produced as described above was subjected to various charge / discharge tests under the following charge / discharge conditions. The ambient temperature during the charge / discharge test is 25 ° C.

<Measurement of load characteristics>
First, each battery is charged with a constant current of 1 It (1 C) = 700 mA, and after the battery voltage reaches 4.2 V, the current value becomes 35 mA (1 It / 20) with a constant voltage of 4.2 V. Until charged. Then, after resting for 10 minutes, discharging is performed at a constant current of 1 It until the battery voltage reaches 2.75V. A discharge time of 10 minutes was inserted after the discharge, the charging conditions were the same as those described above, the discharge capacity was determined with the discharge current set to 0.2 It = 140 mA, and the discharge capacity at that time was set to the 0.2 It discharge capacity. Separately, the discharge capacity was obtained by setting the discharge current to 3 It = 2100 mA, and the discharge capacity at that time was taken as the 3 It discharge capacity. And the load characteristic was calculated | required with the following formulas. The results are shown in Table 1.
Load characteristics (%) = (3 It discharge capacity / 0.2 It discharge capacity) × 100

<Measurement of cycle characteristics>
The cycle characteristics were measured by charging at a constant current of 1 It = 700 mA until the battery voltage reached 4.2 V, and after the battery voltage reached 4.2 V, the current value was 35 mA (1 It at a constant voltage of 4.2 V. / 20) until charged. Then, after resting for 10 minutes, discharging is performed at a constant current of 1 It until the battery voltage reaches 2.75V. After the discharge, a 10-minute pause is inserted, and the charge / discharge including this pause is defined as one cycle, and the test is continued up to 500 cycles. The discharge capacity at the first cycle and the discharge capacity at the 500th cycle were obtained, and the cycle characteristics were measured by the following formula. The results are summarized in Table 1.
Cycle characteristics (%) = (discharge capacity at 500th cycle / discharge capacity at the first cycle) × 100

  From the results of Table 1, the non-aqueous secondary battery of the example using the negative electrode containing the carbonaceous material treated by the microwave plasma excited with the gas containing carbon dioxide is a carbonaceous material not subjected to such plasma treatment. It was confirmed that both the load characteristics and the cycle characteristics were significantly superior as compared with the non-aqueous secondary battery of the comparative example.

  Further, in the above examples, only an example using a gel-like non-aqueous electrolyte solution was shown, but the effect of the present invention is a phenomenon caused by SEI at the interface of the negative electrode, so it does not change depending on the property of the electrolyte solution. It will be apparent to those skilled in the art that the same effect can be obtained even when the non-aqueous electrolyte is liquid.

It is the schematic of the plasma processing apparatus used by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Plasma processing apparatus 11 Microwave generation part 12 Waveguide 13 Plasma reaction chamber 14 Powder recovery chamber 15 Microwave plasma 16 Supply port 17 of carbonaceous raw material powder 17 Plasma generation gas introduction port

Claims (6)

  A method for producing a carbon material for a negative electrode of a non-aqueous secondary battery, wherein a carbonaceous raw material is treated with microwave plasma excited with a gas containing carbon dioxide.   The said carbonaceous raw material is a graphite-type carbonaceous raw material, The manufacturing method of the carbon material for negative electrodes of the non-aqueous secondary battery of Claim 1 characterized by the above-mentioned.   3. The graphite-based carbonaceous raw material is at least one selected from natural graphite, artificial graphite, mesophase carbon microbeads, mesophase pitch-based graphite fibers, vapor-grown carbon fibers, and graphite whiskers. The manufacturing method of the negative electrode-like carbon material of the non-aqueous secondary battery as described in 2.   In the non-aqueous secondary battery comprising a positive electrode having a positive electrode material that reversibly occludes / releases lithium, a negative electrode having a carbonaceous material that reversibly occludes / releases lithium, and a non-aqueous electrolyte, the carbon A non-aqueous secondary battery using a material treated with microwave plasma excited with a gas containing carbon dioxide as a material.   The non-aqueous secondary battery according to claim 4, wherein the non-aqueous electrolyte is gelled. The content of the electrolyte solution in the gelled non-aqueous electrolyte solution is 50% by mass or more and 99.5% by mass or less based on the total amount of the gelled non-aqueous electrolyte solution. Item 6. The nonaqueous secondary battery according to Item 5.

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