JP4792618B2 - Carbonaceous particles for negative electrode of lithium secondary battery, manufacturing method thereof, negative electrode of lithium secondary battery and lithium secondary battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a carbonaceous particle for a lithium secondary battery negative electrode, a method for producing the same, a negative electrode for a lithium secondary battery and a lithium secondary battery using the same.
[0002]
[Prior art]
In recent years, there has been a growing demand for secondary batteries that are small, lightweight, and have a high energy density for portable devices, electric vehicles, and power storage. In response to such a demand, non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, are attracting attention as batteries having high voltage and high energy density.
[0003]
As a negative electrode material for a lithium ion secondary battery, metallic lithium, low graphitized carbon particles, highly graphitized carbon particles, and the like are used. Metallic lithium can achieve a high charge / discharge capacity, but due to its high reactivity, it reacts with the solvent in the electrolyte solution as the charge / discharge cycle progresses, resulting in a decrease in capacity. In addition, dendritic metallic lithium is easily generated and has a problem that it easily causes a short circuit through a separator provided between the positive and negative electrodes. Low graphitized carbonaceous materials are characterized by low reactivity with electrolytes and difficulty in forming dendritic metallic lithium, but charge / discharge capacity per volume due to generally low charge / discharge capacity and low true density. The capacity is low. On the other hand, highly graphitized carbon particles have a high charge / discharge capacity compared to low graphitized carbon particles, and are less reactive with the electrolyte than metallic lithium, making it difficult to form dendritic metallic lithium. In recent years, it has been actively studied as a negative electrode material because of its high discharge voltage and flatness.
[0004]
However, highly graphitized carbon particles have a problem that their discharge capacity is limited (372 mAh / g) by an intercalation compound (LiC ₆ ) formed with lithium. Development of highly graphitized carbon materials having capacities exceeding the theoretical capacity has been studied in various departments, but no one having both workability and cycle characteristics has been found yet.
[0005]
As other negative electrode materials, silicon-containing carbonaceous particles obtained by firing a mixture of an organic silicon polymer compound such as polycarbosilane or polydisilazane, or an organic silicon compound such as silicon alkoxide and a carbon precursor such as a phenol resin are used. , It is reported to show a high discharge capacity of 500 Ah / kg or more. However, the former has a large irreversible capacity, and the silicon-containing organic polymer compound as a precursor is an extremely expensive material, which causes a problem such as an increase in the cost of the negative electrode material. There are problems such as poor characteristics.
[0006]
[Problems to be solved by the invention]
The present invention relates to a silicon-containing carbonaceous particle that can be expected to have a high discharge capacity, and is a silicon-containing carbonaceous particle produced by firing a mixture of an organic silicon compound and a carbon precursor capable of reducing costs, and is irreversible. An object of the present invention is to provide a material having a small capacity and improved charge / discharge efficiency and cycle characteristics.
[0007]
[Means for Solving the Problems]
The present invention provides the following carbonaceous particles for a negative electrode of a lithium secondary battery, a production method thereof, a negative electrode for a lithium secondary battery and a lithium secondary battery using the same.
(1) A carbonaceous particle for a lithium secondary battery negative electrode comprising a silicon-containing carbonaceous particle and a carbonaceous layer substantially covering no silicon covering the silicon-containing carbonaceous particle.
(2) The silicon content of the silicon-containing carbonaceous particles is 15 to 45% by weight, and the amount of the carbonaceous layer in the carbonaceous particles for a lithium secondary battery negative electrode is 10 to 50% by weight. Carbonaceous particles for negative electrodes of lithium secondary batteries.
(3) A mixture of a carbon precursor and a silicon precursor is fired and pulverized to produce silicon-containing carbonaceous particles, and then the surface of the silicon-containing carbonaceous particles is coated with the carbon precursor, and then the carbon precursor is coated The method for producing carbonaceous particles for a lithium secondary battery negative electrode according to (1), wherein carbonization is performed by firing to form a carbonaceous layer.
(4) A negative electrode for a lithium secondary battery comprising the carbonaceous particles for a lithium secondary battery negative electrode according to (1) and an organic polymer binder.
(5) The negative electrode for a lithium secondary battery according to (4), comprising 0.1 to 30 parts by weight of an organic polymer binder with respect to 100 parts by weight of carbonaceous particles for a lithium secondary battery negative electrode.
(6) The negative electrode for a lithium secondary battery according to (4), which is a molded product of a mixture comprising carbonaceous particles for a lithium secondary battery negative electrode and an organic polymer binder.
(7) The negative electrode for a lithium secondary battery according to (4), comprising a current collector and a mixture comprising a carbonaceous particle for a lithium secondary battery negative electrode covering the current collector and an organic polymer binder.
(8) A lithium secondary battery, wherein the negative electrode for a lithium secondary battery and the positive electrode according to (4) are arranged to face each other with an electrolytic solution containing a lithium salt.
(9) The lithium secondary battery according to (8), wherein the negative electrode for a lithium secondary battery and the positive electrode are arranged to face each other with a separator holding an electrolytic solution.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
[0009]
The carbonaceous particles for a negative electrode of a rechargeable lithium battery of the present invention (hereinafter referred to as carbonaceous particles) are silicon-containing carbonaceous particles and carbonaceous materials substantially free of silicon covering the silicon-containing carbonaceous particles. It is characterized by comprising a layer (hereinafter sometimes referred to as a carbonaceous layer). When the silicon-containing carbonaceous particles are not covered with silicon-free carbon, the irreversible capacity at the first charge / discharge increases, and significant cycle deterioration occurs. The carbonaceous particles of the present invention may be a single silicon-containing carbonaceous particle coated with a carbonaceous layer, or a plurality of silicon-containing carbonaceous particles each coated with a carbonaceous layer. It may be one in which the children gather to form one particle. Moreover, the carbonaceous layer substantially free of silicon means a carbonaceous layer formed without using a silicon-containing compound as a raw material when forming the carbonaceous layer, and silicon as a foreign material, for example, a raw material Silicon or the like that is included in the trace amount as an impurity may be contained therein.
[0010]
The silicon content in the silicon-containing carbonaceous particles is not particularly limited in the present invention, but is preferably 15 to 45% by weight and more preferably 25 to 40% by weight in that a high discharge capacity can be obtained. When the silicon content is low, there is a tendency that a sufficient discharge capacity cannot be obtained, and when the silicon content is too high, the discharge capacity tends to decrease. This silicon content can be determined, for example, by fluorescent X-ray analysis.
[0011]
The silicon-containing carbonaceous particles coated with the substantially silicon-free carbonaceous layer are obtained by, for example, firing and pulverizing a mixture of a carbon precursor and a silicon precursor by the method of the present invention. The particles can be prepared, and then the surface of the silicon-containing carbonaceous particles can be coated with a carbon precursor, and then the carbon precursor is carbonized by firing to form a carbonaceous layer.
[0012]
That is, first, a carbon precursor and a silicon precursor are mixed and fired to obtain silicon-containing carbon, which is pulverized to produce silicon-containing carbonaceous particles. Next, the obtained silicon-containing carbonaceous particles and a carbon precursor are mixed, fired, and crushed as necessary to obtain a desired particle size.
[0013]
As the silicon precursor used in the present invention, for example, silicon alkoxide and / or a partially condensed polymer thereof can be used. As the silicon alkoxide, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, trimethoxymethylsilane, triethoxymethylsilane, or the like can be used. Partially condensed polymers are generally prepared by partial hydrolysis and polycondensation of the above silicon alkoxide in the presence of an acid catalyst. For example, partial condensed polymers of tetramethoxysilane and tetraethoxysilane are easily available. Can be used.
[0014]
Examples of the carbon precursor used in the present invention include petroleum-based, coal-based and synthetic pitches, tars, phenol resins, furan resins, polyacrylonitrile, poly (α-halogenated acrylonitrile) acrylic resins, polyamideimide resins, polyamide resins. Polyimide resin or the like can be used.
[0015]
The method for producing the mixture of the silicon precursor and the carbon precursor is not particularly limited, but in order to obtain a negative electrode material having excellent characteristics, it is important to uniformly mix the two. For this reason, you may use the suitable solvent which melt | dissolves both. Examples of the solvent that can be used include ketones such as ethylene glycol, tetrahydrofuran, and acetone, alcohols such as methanol and ethanol, dimethylformamide, dimethylacetamide, and the like. Moreover, not only physically mixing both, but a chemical reaction may be caused between them. When silicon alkoxide and / or a partially condensed polymer thereof is used as the silicon precursor, an acid catalyst such as p-toluenesulfonic acid is further added to and mixed with the silicon precursor and the carbon precursor, and then heated. The silicon precursor may be polymerized to cure the mixture. The heating temperature is usually preferably from room temperature to 170 ° C, more preferably from 50 to 150 ° C.
[0016]
The obtained mixture of silicon precursor and carbon precursor is fired to obtain silicon-containing carbon. Prior to firing, the mixture may be crushed. Firing is preferably performed in a low oxygen-containing atmosphere in which carbon and silicon are not substantially oxidized, and an inert atmosphere such as nitrogen, argon, helium, or a reduced pressure atmosphere can be used. The firing temperature is preferably 500 ° C to 1400 ° C, and more preferably 900 ° C to 1380 ° C. When the firing temperature is too low, it is not preferable because the obtained silicon-containing carbonaceous particles tend to be difficult to grind. On the other hand, if it is too high, the reaction between the silicon precursor decomposition product and the carbon precursor decomposition product occurs remarkably, and the diffraction lines of silicon carbide are recognized in the wide-angle X-ray diffraction diagram. When used, the charge / discharge capacity tends to decrease significantly. The firing time is preferably 0.1 to 10 hours, and more preferably 0.5 to 2 hours.
[0017]
Moreover, when using a thermosetting resin as a carbon precursor, before baking at 500 to 1400 degreeC, the mixture of a silicon precursor and a carbon precursor is 100 to 200 degreeC, More preferably, 120 to It is preferable to heat at 180 ° C. for 0.1 to 10 hours, more preferably 0.5 to 2 hours. This heating accelerates the curing of the carbon precursor and improves the carbonization yield during firing.
[0018]
After firing, the obtained carbon containing silicon is pulverized and further classified as necessary. A known mechanical grinding device can be used for this grinding. The average particle diameter of the produced silicon-containing carbonaceous particles is preferably in the range of 1 to 30 μm, and more preferably in the range of 2 to 20 μm. When the average particle diameter exceeds 30 μm, the finally obtained carbonaceous particles for negative electrode are coarse, and unevenness is likely to occur on the electrode surface. On the other hand, if the average particle diameter is less than 1 μm, the carbonaceous particles for the negative electrode finally obtained are also fine, and the workability at the time of electrode preparation may be deteriorated.
[0019]
Next, the silicon-containing carbonaceous particles and the carbon precursor are mixed, and the surface of the silicon-containing carbonaceous particles is coated with the carbon precursor. Carbon precursors include petroleum-based, coal-based and synthetic pitches, tars, phenolic resins, furan resins, polyacrylonitrile, poly (α-halogenated acrylonitrile) and other acrylic resins, polyamideimide resins, polyamide resins, polyimide resins, etc. Can be used. In mixing, a solvent that dissolves these carbon precursors may be used. Examples of the solvent include ketones such as tetrahydrofuran and acetone, various alcohols such as methanol and ethanol, amides such as dimethylformamide and dimethylacetamide, and hydrocarbons such as toluene, xylene, and benzene. When a solvent is used for mixing, the solvent is removed by heating the mixture at a temperature of 50 to 150 ° C., preferably under reduced pressure, before firing. If the mixture is agglomerated and partially or wholly agglomerated, the mixture is crushed as necessary.
[0020]
The obtained silicon-containing carbonaceous particles coated with the carbon precursor are fired to carbonize the carbon precursor to obtain silicon-containing carbonaceous particles coated with the carbonaceous layer. The amount of the covering carbon constituting the carbonaceous layer is preferably 10 to 50% by weight, more preferably 15 to 30% by weight, based on the total amount of the carbonaceous particles for the negative electrode. If it is less than 10% by weight, the cycle characteristics and the charge / discharge efficiency may be insufficiently improved. On the other hand, if it exceeds 50% by weight, the discharge capacity tends to decrease. The atmosphere during firing is preferably an atmosphere containing low oxygen so that carbon is not substantially oxidized, and an inert atmosphere such as nitrogen, argon or helium, or a reduced pressure atmosphere can be used. The firing temperature is preferably 900 to 1400 ° C, more preferably 1100 to 1380 ° C. Below 900 ° C., the irreversible capacity due to the coated carbon tends to increase. On the other hand, when the temperature exceeds 1400 ° C., a significant reaction between silicon and carbon occurs in the silicon-containing carbonaceous particles, and the charge / discharge capacity tends to decrease.
[0021]
If the carbonaceous particles for negative electrode obtained by firing are partially or wholly agglomerated, they are crushed as necessary. The average particle diameter of the carbonaceous particles for negative electrode of the present invention is preferably in the range of 10 to 50 μm, and more preferably in the range of 15 to 40 μm. When the average particle diameter exceeds 50 μm, irregularities are likely to occur on the electrode surface. On the other hand, if the average particle size is less than 10 μm, the workability at the time of electrode preparation may deteriorate, which is not preferable.
[0022]
The carbonaceous particles for negative electrode of the present invention can be made into an electrode molded body for a lithium secondary battery, for example, as follows.
[0023]
The carbonaceous particles for negative electrode of the present invention are mixed with an organic polymer binder and then formed into the shape of an electrode. Organic polymer binders include dendritic polymers such as polyethylene, polypropylene, polyethylene terephthalate, aromatic polyamide, aromatic polyimide, cellulose, polyvinylidene fluoride, polytetrafluoroethylene, and copolymerized fluoropolymers including tetrafluoroethylene. Molecular materials: Rubber-like polymer materials such as styrene / butadiene rubber, isoprene rubber, butadiene rubber, ethylene / propylene rubber, soft dendritic polymer materials such as ethylene / vinyl acetate copolymer, propylene / α-olefin copolymer Ion-conductive polymer materials such as organic polymer materials such as polyethylene oxide, polypropylene oxide, polyepichlorohydrin, polyphazene, polyvinylidene fluoride, and polyacrylonitrile can be used. In addition, it is also possible to use a material in which ion conductivity is improved by combining a lithium salt or an alkali metal salt mainly composed of lithium with these ion conductive polymer materials.
[0024]
In addition to these organic polymer binders, carboxymethyl cellulose, polysodium acrylate, other acrylic polymers, and the like may be added as viscosity modifiers. The mixing ratio of these organic polymer binder and the carbonaceous particles for negative electrode of the present invention is such that the binder is usually 0.1 to 30 parts by weight with respect to 100 parts by weight of the carbonaceous particles for negative electrode. Preferably it is 0.5-20 weight part, More preferably, it is 1-15 weight part.
[0025]
The carbonaceous particles for negative electrode of the present invention can be mixed with the organic polymer binder described above and directly formed into the shape of an electrode by a method such as roll molding or compression molding to produce a negative electrode. Further, the mixture of the carbonaceous particles for negative electrode of the present invention and the organic polymer binder described above is dispersed in a solvent to form a slurry, which is applied to a metal current collector and dried, and then the carbonaceous material for negative electrode. The current collector or the like may be covered with a layer made of a mixture of particles and an organic polymer binder. There is no restriction | limiting in particular as a solvent, For example, N-methyl- 2-pyrrolidone, a dimethylformamide, isopropanol, water etc. are used. The amount is not particularly limited as long as it can be adjusted to a desired viscosity. Usually, the solid content is used in an amount of 30 to 50% by weight.
[0026]
As the current collector, rolled copper foil, electrolytic copper foil, punched copper foil, nickel foil, nickel copper foil, titanium foil, stainless steel foil, mesh of these metals, and the like are used. The shape of the negative electrode can be arbitrarily set such as a sheet shape or a pellet shape.
[0027]
A battery is assembled using the negative electrode thus obtained, but prior to this or when assembling, lithium metal as an active material may be supported on the negative electrode. Thereby, the irreversible capacity | capacitance at the time of first charge can be reduced significantly. This supporting method includes a chemical method, a physical method, and an electrochemical method. For example, a method in which a negative electrode is immersed in a lithium ion-containing electrolytic solution and electroimpregnation is performed using metallic lithium as a counter electrode. And a method of electrically contacting metal lithium and the negative electrode.
[0028]
The lithium secondary battery of the present invention can be obtained by disposing the negative electrode and the positive electrode manufactured as described above so as to face each other with an electrolytic solution containing a lithium salt. In the lithium secondary battery of the present invention, in addition to the positive electrode, the negative electrode, and the electrolytic solution, a separator having a function of preventing contact between both electrodes and holding the electrolytic solution and allowing lithium ions to pass through, and an electrode material are held. It is preferable to use in combination with the above current collector having a function of collecting current.
[0029]
Although it does not specifically limit as a positive electrode material, For example, vanadium oxide, vanadium sulfide, molybdenum oxide, molybdenum sulfide, manganese oxide, manganese sulfide, chromium oxide, chromium sulfide, titanium oxide, titanium sulfide These metal oxides, metal chalcogen compounds such as composite sulfides, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ , LiMnO ₃ ), lithium nickel A composite oxide such as a cobalt oxide {Li _x Ni _y Co _(1-y) O ₂ } or a composite oxide obtained by adding other metal elements (Al, Fe, Mn, Mg, Co, etc.) to these is used. be able to. Moreover, electroconductive polymers, such as polyaniline and polypyrrole, can also be used. Among these, when using a material that does not contain lithium, a predetermined amount of lithium can be occluded in advance in the negative electrode, or a predetermined amount of lithium can be pressure-bonded.
[0030]
For the positive electrode, for example, the positive electrode material is mixed with a conductive agent and a binder that are blended as necessary, and then directly molded into the shape of the electrode by a method such as roll molding or compression molding to produce a positive electrode. be able to. As the conductive agent, for example, graphite powder or the like can be used. As the binder, for example, the organic polymer binder described above for the negative electrode can be used. Also, a mixture of the positive electrode material and a conductive agent and a binder used as necessary is dispersed in a solvent to form a slurry, which is applied to a metal positive electrode current collector, etc., dried and formed into a positive electrode. May be. As the solvent, for example, N-methyl-2-pyrrolidone or the like is used. The shape of the positive electrode can be arbitrarily set such as a sheet shape or a pellet shape.
[0031]
As the electrolytic solution, a solution obtained by dissolving a lithium salt serving as an electrolyte in a non-aqueous solvent is usually used. As the electrolyte, lithium metal salts such as LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSO ₃ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , tetraalkylammonium salts, and the like can be used. The concentration of the lithium salt is preferably 0.2 to 2 mol / l, more preferably 0.3 to 1.9 mol / l. Non-aqueous solvents include propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, cyclic esters such as γ-butyrolactone, chain esters such as diethyl carbonate, ketones such as methyl ethyl ketone, 1,2-dimethoxyethane, dioxolane. , Tetrahydrofuran, 1,2-dimethyltetrahydrofuran, and ethers such as crown ether can be used. In addition, a solid electrolyte obtained by mixing the above salts with polyethylene oxide, polyphosphazene, polyaziridine, polyacrylonitrile, polyethylene sulfide or the like, derivatives, mixtures or composites thereof can also be used. In this case, the solid electrolyte can also serve as a separator, and the separator becomes unnecessary.
[0032]
As a separator for separating the negative electrode and the positive electrode and holding the electrolytic solution, a microporous film such as polyethylene, polypropylene, polypropylene / polypropylene composite system, polypropylene / fluororesin composite system, nonwoven fabric, woven fabric, or the like can be used. . The thickness of the separator is preferably about 20 to 200 μm.
[0033]
The lithium secondary battery of the present invention can have various shapes such as a cylindrical shape, a box shape, a coin shape, a button shape, a paper shape, and a card shape.
[0034]
FIG. 1 shows a partial cross-sectional front view of a cylindrical lithium secondary battery which is an embodiment of the lithium secondary battery of the present invention. This lithium secondary battery can be manufactured as follows, for example. A current collector made of a metal foil is covered with a positive electrode material (including additives such as a conductive agent and a binder as necessary) except for both ends to produce a positive electrode 1, and one end of the current collector The positive electrode tab 4 is pressure-bonded to the exposed portion by ultrasonic bonding. A current collector made of a metal foil is coated with a mixture of the carbonaceous particles for a negative electrode of the present invention and an organic polymer binder except for both ends to produce a negative electrode 2, and an exposed portion at one end of the current collector The negative electrode tab 5 is pressure-bonded by ultrasonic bonding. The positive electrode 1, the microporous membrane separator 3, the negative electrode 2, and the separator 3 are stacked in this order, and are wound to form an electrode group. This is inserted into a battery can, the negative electrode tab 5 is welded to the bottom of the can, a throttle part for crimping the positive electrode lid 6 is provided, and the gasket 8 is attached. Then, after pouring electrolyte solution into the battery can 7, the positive electrode tab 4 is welded to the positive electrode lid 6. The positive electrode lid 6 is caulked to obtain a lithium secondary battery.
[0035]
【Example】
EXAMPLES Hereinafter, examples of the present invention and comparative examples thereof will be shown to specifically explain the effects, but the present invention is not limited to the following examples.
[0036]
Example 1
100 parts by weight of furan resin (manufactured by Hitachi Chemical Co., Ltd., HQRVF 303), 100 parts by weight of polymethoxysilane (manufactured by Tama Chemical Industries, M-silicate 51, partial condensation polymer of tetramethoxysilane), p-toluenesulfonic acid / ethylene 1 part by weight of a glycol solution (50% by weight) was mixed at room temperature for 1 hour. Next, the temperature was raised to 120 ° C. at 10 ° C./h, and the mixture was cured by heating at 120 ° C. for 1 hour. The obtained cured product was pulverized with a cutter mill, heated to 160 ° C. at 20 ° C./h in nitrogen, held for 10 hours, then heated to 900 ° C. at 20 ° C./h and held for 1 hour to contain silicon. Carbonaceous particles were used. The obtained silicon-containing carbonaceous particles were pulverized with a cutter mill to an average particle size of 15 μm. The silicon content measured by X-ray fluorescence analysis was 25%.
[0037]
100 parts by weight of the above silicon-containing carbonaceous particles are dispersed and mixed in tetrahydrofuran (200 parts by weight) in which 40 parts by weight of coal tar pitch is dissolved, and then the tetrahydrofuran is removed using a rotary evaporator, followed by vacuum drying at 100 ° C. for 3 hours. Thus, silicon-containing carbonaceous particles coated with coal tar pitch were obtained. This was crushed by a cutter mill, heated to 1300 ° C. at 20 ° C./h in nitrogen, and held for 1 hour to carbonize the coal tar pitch. The obtained silicon-containing carbonaceous particles coated with carbon were pulverized with a cutter mill to an average particle size of 22 μm. The amount of coated carbon determined from the weight reduction rate was 20% by weight.
[0038]
10% by weight of polyvinylidene fluoride (N-methyl-2-pyrrolidone solution, manufactured by Kureha Chemical Co., Ltd., trade name: # 1120) was added to the carbon-containing silicon-containing particles coated with the obtained carbon. It knead | mixed and it was set as the slurry. This slurry was applied to an electrolytic copper foil with a thickness of 100 μm to a diameter of 9 mm and a thickness of 200 μm, and vacuum dried at 110 ° C. for 2 hours and then at 150 ° C. for 8 hours to prepare a sample electrode.
[0039]
The prepared sample electrode was used for constant current charge / discharge by the three-terminal method, and evaluated as a negative electrode for a lithium secondary battery. FIG. 2 is a schematic diagram of a lithium secondary battery used in the experiment. An ethylene carbonate / diethyl carbonate mixed solution (volume ratio 1/2) in which 1M LiPF ₆ is dissolved as an electrolytic solution 10 is placed in a glass cell 9, and a sample electrode 11, a separator 12 and a counter electrode 13 are stacked and arranged. The electrode 14 was suspended from the top. For the counter electrode 13 and the reference electrode 14, metallic lithium (thickness: 0.5 mm, φ20 mm) was used, and for the separator 12, a polyethylene microporous film (thickness: 200 μm) was used. Charge / discharge was performed up to 40 cycles at a charge / discharge current of 0.2 mA and 0 to 1.5V. The initial charge capacity and discharge capacity were 790 Ah / kg and 490 Ah / kg, respectively. FIG. 3 shows the cycle change of the discharge capacity.
[0040]
Comparative Example 1
Using silicon-containing carbonaceous particles produced in the same manner as in Example 1, electrodes were produced in the same manner as in Example 1, and charge / discharge characteristics were measured. The initial charge capacity and discharge capacity were 910 Ah / kg and 256 Ah / kg, respectively. FIG. 3 shows the cycle change of the discharge capacity.
[0041]
【The invention's effect】
Compared with the case where it is not coated with carbon, the silicon-containing carbonaceous particles coated with carbon of the present invention have improved charge / discharge efficiency and cycle characteristics, and a large discharge capacity. By using the carbonaceous particles for negative electrode of the present invention, a lithium secondary battery having a high discharge capacity and good cycle characteristics can be produced.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional front view showing one embodiment of a lithium secondary battery of the present invention.
FIG. 2 is a schematic view of a lithium secondary battery used in the experiment.
FIG. 3 is a graph showing the cycle change of the discharge capacity of an electrode produced using the carbonaceous particles of Examples and Comparative Examples.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Positive electrode tab 5 Negative electrode tab 6 Positive electrode lid 7 Battery can 8 Gasket 9 Glass cell 10 Electrolytic solution 11 Sample electrode 12 Separator 13 Counter electrode 14 Reference electrode

Claims (8)

A carbon precursor for a lithium secondary battery negative electrode comprising a silicon-containing carbonaceous particle and a substantially silicon-free carbonaceous layer covering the silicon-containing carbonaceous particle, the carbon precursor A silicon-containing carbonaceous particle is produced by firing and pulverizing a mixture of silicon and a silicon precursor, and then coating the surface of the silicon-containing carbonaceous particle with a carbon precursor, and then carbonizing the carbon precursor by firing to obtain carbon. A method for producing carbonaceous particles for a negative electrode of a lithium secondary battery, comprising forming a porous layer. 2. The lithium secondary according to claim 1, wherein the silicon content of the silicon-containing carbonaceous particles is 15 to 45% by weight, and the amount of the carbonaceous layer in the carbonaceous particles for a lithium secondary battery negative electrode is 10 to 50% by weight. A method for producing carbonaceous particles for battery negative electrodes. The negative electrode for lithium secondary batteries containing the carbonaceous particle for lithium secondary battery negative electrodes obtained by the method of Claim 1, and an organic polymer binder. The negative electrode for a lithium secondary battery according to claim 3, comprising 0.1 to 30 parts by weight of an organic polymer binder with respect to 100 parts by weight of carbonaceous particles for a lithium secondary battery negative electrode. The negative electrode for a lithium secondary battery according to claim 3 , wherein the negative electrode is a mixture of carbonaceous particles for a lithium secondary battery negative electrode and an organic polymer binder. 4. The negative electrode for a lithium secondary battery according to claim 3, comprising a current collector, and a mixture comprising a carbonaceous particle for a lithium secondary battery negative electrode and an organic polymer binder covering the current collector. The lithium secondary battery according to claim 3 , wherein the negative electrode for a lithium secondary battery and the positive electrode are disposed to face each other with an electrolyte containing a lithium salt. The lithium secondary battery according to claim 7 , wherein the negative electrode for the lithium secondary battery and the positive electrode are arranged to face each other with a separator holding an electrolytic solution.

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