JP2015022964A - Negative electrode material for lithium ion secondary battery, method for producing the same, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a negative electrode material with which deterioration of durability of a lithium ion secondary battery is minimized; a method for producing the negative electrode material; and a lithium ion secondary battery.SOLUTION: A negative electrode material of the present invention is a negative electrode material including a core part and a shell part, and has a ratio between the mass of carbon and the mass of oxygen of 0.33 or less. A production method of the present invention includes a step of mixing a silicon-based compound with a solution of an organic compound and firing the silicon-based compound and the solution in an inert atmosphere in a state where both are in contact with each other. In a lithium ion secondary battery of the present invention, the negative electrode material or a negative electrode material produced by the production method is used.

Description

  The present invention relates to a negative electrode material for a lithium ion secondary battery, a manufacturing method thereof, and a lithium ion secondary battery.

  A lithium ion secondary battery using carbon (graphite) as a negative electrode active material has been put into practical use. In general, a negative electrode of a lithium ion secondary battery is prepared by kneading a negative electrode active material, a conductive auxiliary agent such as carbon black, and a resin binder to prepare a slurry, which is applied on a current collector such as a copper foil. -It is formed by drying.

  On the other hand, aiming at higher capacity of the battery, a lithium ion secondary battery using a metal or alloy having a large theoretical capacity as a negative electrode active material, in particular, silicon or silicon oxide or silicon alloy (hereinafter referred to as silicon compound). (Negative anode) is being developed.

  Among these silicon-based compounds, silicon oxide, which is known as a long-life negative electrode active material, has a problem of low electronic conductivity as compared with conventional carbon (graphite). In order to solve this problem of electronic conductivity, a technique for coating the surface with carbon excellent in electronic conductivity is known. The coating of carbon on the surface of this silicon compound is described in Patent Document 1, for example.

JP 2012-84521 A

  Patent Document 1 describes a method in which a silicon oxide is heated in a hydrocarbon gas atmosphere, and the hydrocarbon gas is thermally decomposed to coat the surface of the silicon oxide with carbon.

  However, the method of thermally decomposing this hydrocarbon gas to form a carbon coating has a problem in that silicon oxide is reduced to produce silicon (metal silicon). Metallic silicon has a problem of promoting the decomposition of the electrolytic solution in the lithium ion secondary battery. That is, the conventional lithium ion secondary battery using a negative electrode active material made of a silicon compound has a problem that the decomposition of the electrolytic solution progresses, thereby reducing the durability of the secondary battery.

  The present invention has been made in view of the above situation, and when used for a negative electrode of a lithium ion secondary battery, a negative electrode material for a lithium ion secondary battery in which a decrease in durability of the lithium ion secondary battery is suppressed, It is an object to provide a manufacturing method thereof and a lithium ion secondary battery.

  In order to solve the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by suppressing the reduction of the silicon oxide when the surface of the silicon oxide is coated with carbon.

  The negative electrode material for a lithium ion secondary battery of the present invention is SiLy, SiMxLy, or SiMx (M; As, Ba, C, Ca, Ce, Co, Cr, Cu, Er, Fe, Gd, Hf, Lu, Mg, Mn. , Mo, Nb, Nd, Ni, P, Pd, Pr, Pt, Pu, Re, Rh, Ru, Sc, Sm, Sr, Ta, Te, Th, Ti, Tm, U, V, W, Y, Yb , Zr, at least one selected from L; N, O, at least one selected from the group consisting of silicon compounds represented by 0 ≦ x ≦ 1, 0 ≦ y ≦ 2), and carbon covering the core A negative electrode material for a lithium ion secondary battery, wherein the ratio of the mass of carbon to the mass of oxygen is 0.33 or less.

  The negative electrode material for a lithium ion secondary battery of the present invention is a negative electrode material provided with a core portion made of a silicon-based compound and a shell portion made of carbon. The negative electrode material of the present invention is in a state where generation of silicon formed by reducing the silicon compound on the surface of the core portion is suppressed. That is, when the negative electrode material of the present invention is used in a lithium ion secondary battery, a decrease in durability due to the presence of silicon on the surface of the core portion is suppressed.

  The method for producing a negative electrode material for a lithium ion secondary battery of the present invention includes SiLy, SiMxLy, or SiMx (M; As, Ba, C, Ca, Ce, Co, Cr, Cu, Er, Fe, Gd, Hf, Lu, Mg, Mn, Mo, Nb, Nd, Ni, P, Pd, Pr, Pt, Pu, Re, Rh, Ru, Sc, Sm, Sr, Ta, Te, Th, Ti, Tm, U, V, W, A step of synthesizing a silicon compound represented by at least one selected from Y, Yb, Zr, L; at least one selected from N, O, 0 ≦ x ≦ 1, 0 ≦ y ≦ 2, and a silicon compound And a step of baking in an inert atmosphere in a state where the organic compound solution is in contact with the silicon-based compound.

  The method for producing a negative electrode material for a lithium ion secondary battery according to the present invention includes a core portion made of a silicon compound and carbon by firing in an inert atmosphere while the organic compound solution is in contact with the silicon compound. A negative electrode material provided with a shell portion. According to the manufacturing method of the present invention, when the shell portion made of carbon is formed, reduction of the silicon-based compound (particularly, silicon oxide) in the core portion is suppressed. That is, according to the manufacturing method of the present invention, it is possible to manufacture a negative electrode material in which generation of silicon formed by reducing a silicon compound on the surface of the core portion is suppressed. That is, when the negative electrode material manufactured by the manufacturing method of the present invention is used for a lithium ion secondary battery, deterioration of the battery characteristics due to the presence of silicon on the surface of the core portion can be suppressed.

  Furthermore, the lithium ion secondary battery of this invention is the negative electrode material for lithium ion secondary batteries of any one of Claims 1-3, The manufacturing method of any one of Claims 4-7. It has at least one of the manufactured negative electrode material for lithium ion secondary batteries in a negative electrode, It is characterized by the above-mentioned.

  The lithium ion secondary battery of the present invention uses a negative electrode material that exhibits the above effects. That is, in the lithium ion secondary battery of the present invention, a decrease in battery durability due to the presence of silicon on the surface of the core part is suppressed.

It is sectional drawing which showed the structure of the coin-type battery of the Example.

[Anode material for lithium ion secondary batteries]
The negative electrode material for a lithium ion secondary battery of the present invention is SiLy, SiMxLy, or SiMx (M; As, Ba, C, Ca, Ce, Co, Cr, Cu, Er, Fe, Gd, Hf, Lu, Mg, Mn. , Mo, Nb, Nd, Ni, P, Pd, Pr, Pt, Pu, Re, Rh, Ru, Sc, Sm, Sr, Ta, Te, Th, Ti, Tm, U, V, W, Y, Yb , Zr, at least one selected from L; N, O, at least one selected from the group consisting of silicon compounds represented by 0 ≦ x ≦ 1, 0 ≦ y ≦ 2), and carbon covering the core A negative electrode material for a lithium ion secondary battery. That is, the negative electrode material of the present invention is a negative electrode material in which a core portion made of a silicon-based compound exhibits a high capacity and a shell portion made of carbon has improved electronic conductivity.

  In the negative electrode material of the present invention, the ratio of the mass of carbon to the mass of oxygen (hereinafter referred to as C / O ratio) is 0.33 or less. When the C / O ratio of the negative electrode material is 0.33 or less, the reduced silicon is not included in the core portion (the amount included is reduced).

  The C / O ratio is a value that decreases as the amount of oxygen contained in the negative electrode material increases. When the silicon-based compound has reduced silicon, the amount of oxygen contained in the silicon-based compound decreases, and as a result, the C / O ratio increases. That is, when the C / O ratio of the negative electrode material is 0.33 or less, the amount (ratio) in which reduced silicon is contained in the core portion is reduced. As a result, when the negative electrode material is used for a lithium ion secondary battery, decomposition of the electrolyte is suppressed, so that the durability is prevented from being lowered and high durability can be exhibited. When the C / O ratio increases beyond 0.33, the amount (ratio) of the reduced silicon contained in the core portion increases, and the electrolyte solution is used when the negative electrode material is used in a lithium ion secondary battery. As a result, the durability is degraded. A preferable C / O ratio is 0.33 or less, and a more preferable C / O ratio is 0.19 or less.

  The negative electrode material of the present invention preferably has an oxygen content (hereinafter referred to as oxygen content) of 34.0% or less when the total mass is 100%. When the oxygen content ratio of the negative electrode material is 34.0% or less, the negative electrode material can exhibit a high capacity, and the battery capacity of the lithium ion secondary battery using the negative electrode material is increased.

Oxygen in the negative electrode material is included in a silicon compound represented by SiOy (0 ≦ y ≦ 2) of the silicon compound. And as oxygen increases, the proportion of SiO ₂ in SiOy increases. SiO ₂ has a low battery capacity and electronic conductivity as a negative electrode material. That is, when the proportion of SiO ₂ increases, battery characteristics such as battery capacity decrease. Thus, when the oxygen content ratio of the negative electrode material is 34.0% or less, the negative electrode material can exhibit a high capacity, and the battery capacity of the lithium ion secondary battery using the negative electrode material is increased.

  In addition, when the oxygen content ratio of the negative electrode material exceeds 34.0%, the battery capacity and battery characteristics are likely to deteriorate when used in a lithium ion secondary battery. A preferable oxygen content is 34.0% or less, and a more preferable content is 29.0% or less.

The mass ratio of the shell portion to the BET specific surface area (hereinafter referred to as C / BET) is preferably 0.60 [(mass%) / (m ² / g)] or more. When C / BET is 0.60 [(mass%) / (m ² / g)] or more, the shell portion can exhibit sufficient electronic conductivity.

C / BET corresponds to the formation state of the shell portion. This value increases as the proportion of the shell portion increases. In other words, this value decreases when a sufficient shell portion is not formed. And if this C / BET becomes small, it will be in the state where a shell part cannot fully cover a core part. That is, it is also in a state where the effect of forming the shell portion cannot be exhibited. Thus, C / BET is 0.60 [(mass%) / (m ² / g)] or more, so that the effect of the structure including the core portion and the shell portion of the negative electrode material of the present invention can be obtained. Can demonstrate.

A preferable C / BET is 0.60 [(mass%) / (m ² / g)] or more, and a more preferable content ratio is 1.16 [(mass%) / (m ² / g)] or more.
The negative electrode material of the present invention can be configured in the same manner as the conventional negative electrode material provided with the core part and the shell part, except for the above.

  In the negative electrode material of the present invention, the silicon-based compound forming the core portion can be configured in the same manner as the silicon-based compound used in the conventional negative electrode material, except for the configuration described above.

That is, the silicon compound is SiLy, SiMxLy, or SiMx (M; As, Ba, C, Ca, Ce, Co, Cr, Cu, Er, Fe, Gd, Hf, Lu, Mg, Mn, Mo, Nb, Nd. , Ni, P, Pd, Pr, Pt, Pu, Re, Rh, Ru, Sc, Sm, Sr, Ta, Te, Th, Ti, Tm, U, V, W, Y, Yb, Zr One compound, L; at least one compound selected from N and O, 0 ≦ x ≦ 1, 0 ≦ y ≦ 2) may be used. For example, metal silicon (Si), silicon oxide (SiOy) , Preferably an alloy of silicon and another metal element (SiMx; SiNiTi) or the like.
Similarly, the carbon forming the shell part is preferably carbon having a graphite structure.

[Method for producing negative electrode material for lithium ion secondary battery]
The method for producing a negative electrode material for a lithium ion secondary battery of the present invention includes SiLy, SiMxLy, or SiMx (M; As, Ba, C, Ca, Ce, Co, Cr, Cu, Er, Fe, Gd, Hf, Lu, Mg, Mn, Mo, Nb, Nd, Ni, P, Pd, Pr, Pt, Pu, Re, Rh, Ru, Sc, Sm, Sr, Ta, Te, Th, Ti, Tm, U, V, W, A step of synthesizing a silicon compound represented by at least one selected from Y, Yb, Zr, L; at least one selected from N, O, 0 ≦ x ≦ 1, 0 ≦ x ≦ 2, and a silicon compound And a step of baking in an inert atmosphere with the organic compound solution in contact with the silicon-based compound.
The production method of the present invention can produce the above-described negative electrode material for a lithium ion secondary battery of the present invention.

  In the production method of the present invention, a silicon compound is first synthesized. The silicon compound synthesized in this step forms the core part when the negative electrode material is formed. That is, in this step, a silicon compound that forms the core portion of the negative electrode material is synthesized.

  In the production method of the present invention, a silicon compound is mixed with a solution of an organic compound. The organic compound in the organic compound solution forms a shell part when the negative electrode material is formed in the subsequent process.

  By mixing the silicon compound with the organic compound solution, the entire surface of the silicon compound comes into contact with the organic compound solution, and when the shell portion is formed in the subsequent process, the entire core portion becomes the shell portion. It will be covered with.

  The production method of the present invention is fired in an inert atmosphere in a state where the organic compound solution is in contact with the silicon compound. By baking in an inert atmosphere, the organic compound contained in the organic compound solution in contact with the silicon compound forms a shell portion. In this step, since the firing is performed in a state where the organic compound solution is in contact with the silicon compound, the organic compound in the organic compound solution is converted to carbon (graphite) at the position (on the surface) in contact with the silicon compound, A shell portion is formed.

  In the production method of the present invention, the reduction of the silicon-based compound is suppressed (no longer generated) when the shell portion is formed. In other words, in the manufacturing method of the present invention, when the shell portion made of carbon is formed, the reduction of the silicon compound (particularly, silicon oxide) in the core portion is suppressed, and the silicon compound is reduced on the surface of the core portion. Thus, it is possible to manufacture a negative electrode material in which generation of silicon is suppressed. As a result, when the negative electrode material produced by the production method of the present invention is used in a lithium ion secondary battery, the battery characteristics (particularly durability) are reduced due to the presence of silicon on the surface of the core part. Is suppressed.

  In the production method of the present invention, the negative electrode material is produced by liquid phase synthesis in which it is synthesized from a liquid phase state. By producing the negative electrode material by liquid phase synthesis, the produced negative electrode material is one in which the reduction of the silicon compound is suppressed.

  In the production method of the present invention, the organic compound solution with which the silicon-based compound is mixed is not particularly limited as long as it is a solution containing an organic compound that can form a shell portion in a subsequent step. That is, the organic compound solution may be a solution in which an organic compound is dispersed or dissolved, a solution made of a liquid organic compound, or a mixed solution thereof. Examples of the solution in which the organic compound is dispersed or dissolved include a dispersion solution of an organic compound and a solution of an organic acid. Examples of the solution made of a liquid organic compound include a chain hydrocarbon, an aromatic hydrocarbon, and the like. And liquid hydrocarbons.

  The organic compound is not limited as long as the organic compound can form a shell portion in a subsequent process, that is, can function as a carbon source. Examples of such an organic compound include sugar compounds such as CMC, organic acids, aromatic hydrocarbons, and the like.

  The organic compound solution is preferably an organic acid solution. Since the organic compound is an organic acid solution, a shell portion made of carbon can be formed on the surface of the silicon compound by subsequent firing.

In the organic acid solution, the organic acid (organic compound) and the solvent are not limited. Examples of the organic acid used in the present invention include citric acid, sulfonic acid, ascorbic acid, formic acid, oxalic acid, and acetic acid.
As the solvent, either water (aqueous solvent) or an organic solvent may be used, but it is preferable to use water as the solvent because it is easy to handle and disappears by firing.

  The organic acid solution is preferably an aqueous solution having a pH of 2 to 4. When the pH of the organic acid solution is in the range of 2 to 4, a shell portion made of carbon can be formed on the surface of the silicon compound by subsequent firing. When the pH is less than 2, the pH becomes too low and the silicon compound is dissolved in the acid (acidic organic acid solution). On the other hand, if the pH exceeds 4 and the pH is too high, a shell portion made of carbon cannot be formed on the surface of the silicon compound.

  The firing conditions when firing in an inert atmosphere in a state where the organic compound solution is in contact with the silicon compound are not limited as long as the firing conditions can form a shell portion made of carbon. That is, the firing here indicates a heat treatment for forming a shell portion made of carbon.

  Firing is preferably performed at a temperature of 550 to 750 ° C. By firing at this temperature, the organic compound (for example, organic acid) that has come into contact with the silicon-based compound is carbonized (graphitized) at that position, and a shell portion made of carbon is formed.

  The state in which the organic compound solution is in contact with the silicon compound indicates, for example, a state in which the organic compound solution is in contact with the silicon compound and is wet. That is, the firing may be performed in a state where the silicon compound is immersed in an organic compound solution, or may be performed in a state where the silicon compound is taken out from the organic compound solution.

  In the manufacturing method of the present invention, the steps (configurations) other than the above can be the same as those in the conventional manufacturing method. For example, the negative electrode material to be produced can be crushed and classified to control the particle size to a desired particle size, and can be a step such as washing or drying.

[Lithium ion secondary battery]
The lithium ion secondary battery of this invention is manufactured with the negative electrode material for lithium ion secondary batteries of any one of Claims 1-3, and the manufacturing method of any one of Claims 4-7. At least one of the negative electrode materials for a lithium ion secondary battery is provided in the negative electrode.

  The lithium ion secondary battery of the present invention can be the same as the conventional lithium ion secondary battery except that the above material is used as the negative electrode material (negative electrode active material). That is, the lithium ion secondary battery has a positive electrode, a negative electrode, an electrolyte, and other necessary members.

  The positive electrode is prepared by suspending and mixing a positive electrode mixture composed of a positive electrode active material, a conductive agent and a binder in an appropriate solvent, applying a slurry on one or both sides of the current collector, and drying. Produced.

As the positive electrode active material, various oxides, sulfides, lithium-containing oxides, conductive polymers, and the like can be used. For example, MnO ₂ , TiS ₂ , TiS ₃ , MoS ₃ , FeS ₂ , LiFePO ₄ , Li _1-z MnO ₂ , Li _1-z Mn ₂ O ₄ , Li _1-z CoO ₂ , Li _1-z NiO ₂ , Examples include LiV ₂ O ₃ , V ₂ O ₅ , polyaniline, polyparaphenylene, polyphenylene sulfide, polyphenylene oxide, polythiophene, polypyrrole, and derivatives and stable radical compounds thereof. In addition, z in these positive electrode active materials shows the number of 0-1. A material obtained by adding or substituting a transition metal such as Li, Mg, Al, or Co, Ti, Nb, or Cr may be used. Moreover, not only these lithium-metal composite oxides are used alone, but also a plurality of them can be mixed and used. Among these, the lithium-metal composite oxide is preferably at least one of a lithium manganese-containing composite oxide having a layered structure or a spinel structure, a lithium nickel-containing composite oxide, and a lithium cobalt-containing composite oxide.
Examples of the binder include, but are not limited to, PVDF, EPDM, SBR, NBR, fluororubber, and the like.

  Examples of the conductive material for the positive electrode include graphite fine particles, acetylene black, ketjen black, carbon black such as carbon nanofiber, and amorphous carbon fine particles such as needle coke, but are not limited thereto.

  As the solvent in which the positive electrode active material is dispersed, an organic solvent that dissolves the binder is usually used. Examples thereof include, but are not limited to, NMP, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran. In some cases, the active material is slurried with PTFE or the like by adding a dispersant, a thickener or the like to water.

Further, as the current collector of the positive electrode, for example, a material obtained by processing a metal such as aluminum or stainless steel, for example, a foil processed into a plate shape, a net, a punched metal, a foam metal, or the like can be used.
The negative electrode can have the same configuration as a conventionally known negative electrode except that the negative electrode material is used as a negative electrode active material.

  The negative electrode is prepared by suspending and mixing a negative electrode mixture composed of a negative electrode active material, a conductive agent and a binder in an appropriate solvent, applying a slurry on one or both sides of the current collector, and drying. Produced.

  Further, the negative electrode active material may include not only the negative electrode material described above but also a conventionally known negative electrode active material for a non-aqueous electrolyte battery. That is, the negative electrode can further include a negative electrode material containing at least one element of Sn, Si, Sb, Ge, and C.

  Among these negative electrode materials, C is preferably a carbon material capable of occluding and desorbing electrolyte ions of the nonaqueous electrolyte battery (for example, having Li storage capability), and more preferably amorphous coated natural graphite. preferable.

  Of these negative electrode materials, Sn, Sb, and Ge are alloy materials having a large volume change. These negative electrode materials may form an alloy with another metal such as Ti—Si, Ag—Sn, Sn—Sb, Ag—Ge, Cu—Sn, and Ni—Sn.

  As the conductive agent, a carbon material, metal powder, conductive polymer, or the like can be used. From the viewpoint of conductivity and stability, it is preferable to use a carbon material such as acetylene black, ketjen black, or carbon black.

As the binder, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluororesin copolymer (tetrafluoroethylene / hexafluoropropylene copolymer) SBR, acrylic rubber, fluororubber, Examples thereof include polyvinyl alcohol (PVA), styrene / maleic acid resin, polyacrylate, carboxymethyl cellulose (CMC) and the like.
Examples of the solvent include organic solvents such as N-methyl-2-pyrrolidone (NMP) or water.

The weight blending ratio of the negative electrode active material, the conductive agent and the binder, which are the negative electrode materials of the present invention, varies depending on the characteristics of the negative electrode to be produced and cannot be determined unconditionally, but the negative electrode material (negative electrode active material) 60 to 98 wt. %, A conductive agent of 0 to 20 wt%, and a binder of 2 to 10 wt% are preferable.
As the current collector, a conventionally known current collector can be used, and a foil, mesh, or the like made of copper, stainless steel, titanium, or nickel can be used.

The type of the electrolyte is not particularly limited, but an inorganic salt selected from LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ , derivatives of these inorganic salts, LiSO ₃ CF ₃ , LiC (SO ₃ CF ₃ ) ₃ and LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), and organic salts thereof It is desirable that it is at least one of the derivatives. These electrolytes can further improve the battery performance, and can maintain the battery performance higher even in a temperature range other than room temperature. The concentration of the electrolyte is not particularly limited, and it is preferable to appropriately select the electrolyte and the organic solvent in consideration of the use.

  The organic solvent that dissolves the electrolyte is not particularly limited as long as it is an organic solvent that is usually used in an electrolyte solution of a lithium secondary battery. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, Lactones and oxolane compounds can be used. In particular, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, vinylene carbonate and the like, and mixed solvents thereof are suitable. Among these organic solvents mentioned in the examples, in particular, by using one or more non-aqueous solvents selected from the group consisting of carbonates and ethers, the solubility, dielectric constant and viscosity of the electrolyte are excellent, and the battery It is preferable because the charge / discharge efficiency is high.

  The positive electrode and the negative electrode are arranged via a separator. The separator plays a role of electrically insulating the positive electrode and the negative electrode and holding the electrolytic solution. For example, a porous synthetic resin film, particularly a polyolefin polymer (polyethylene, polypropylene) porous film may be used. The separator is preferably larger than the positive electrode and the negative electrode in order to ensure insulation between the positive electrode and the negative electrode.

  The lithium ion secondary battery of the present invention comprises other elements as necessary in addition to the above elements. The lithium ion secondary battery of the present invention is not particularly limited in its shape, and can be used as batteries having various shapes such as a coin shape, a cylindrical shape, and a square shape.

Hereinafter, the present invention will be specifically described with reference to examples.
As an example for specifically explaining the present invention, a negative electrode material (negative electrode active material) for a lithium ion secondary battery and a lithium ion secondary battery were produced.
[Manufacture of negative electrode materials]

Example 1
First, a silicon-based compound (Si, SiO, SiNiTi) was obtained.
A commercially available product (manufactured by Wako Pure Chemical Industries, Ltd., trade name: silicon, powder 198-05455) was used for SiO of the silicon compound used for Samples 1-9, 22-25, 28-30.
A commercially available product (manufactured by Wako Pure Chemical Industries, Ltd., trade name: silicon monoxide, 99.9% 198-05612) was used as Si of the silicon compound used for Samples 10-15, 26, and 31.
Silicon (SiNiTi), which is a silicon compound used for Samples 16 to 21, 27, and 32, includes Si (commercially available product) and Ni (commercially available product, manufactured by Wako Pure Chemical Industries, Ltd., trade name; nickel powder 145-00982) and Ti ( A commercial product, manufactured by Wako Pure Chemical Industries, Ltd., trade name: titanium powder 200-05202) was used by mixing for 3 hours at room temperature by the mechanical alloying method.

  Next, the organic acid shown as the carbon source in Table 1 was mixed with ion-exchanged water and stirred for 10 minutes to prepare a 30 mass% organic acid aqueous solution. Here, 30 mass% indicates the ratio of the mass of the organic acid when the total mass of the organic acid and ion-exchanged water is 100 mass%.

The pH of this aqueous organic acid solution was measured and shown in Table 1. As shown in Table 1, the pH was in the range of 2 to 4 in any sample.
The prepared organic acid aqueous solution (2 g) was transferred to an alumina crucible, and 3 g of the above silicon compound was added. Then, it stirred for 1 minute and mixed thoroughly.

The crucible after stirring and mixing was placed in a heating furnace, and the temperature was raised to 650 ° C. at a rate of temperature increase of 5 ° C./min in an N ₂ gas atmosphere. After the temperature rise, the mixture was held at 650 ° C. for 3 hours and fired (heat treatment).
After cooling to room temperature after firing, the product was taken out from the furnace and stirred for 5 minutes in a mortar.

  Thus, the negative electrode materials (negative electrode material powders) of Samples 1 to 21 were manufactured. In the manufactured negative electrode material, Samples 1 to 9 have a structure in which a shell portion made of carbon is formed on a core portion made of SiOy (0 <y <2). Samples 10 to 15 have a structure in which a shell portion made of carbon is formed in a core portion made of Si. Samples 16 to 21 have a structure in which a shell portion made of carbon is formed in a core portion made of SiNiTi.

(Example 2)
Negative electrode materials (negative electrode material powders) of Samples 22 to 27 were produced in the same manner as in Example 1 except that the organic compounds shown in Table 2 were used instead of the organic acids.

  In the manufactured negative electrode material, Samples 22 to 25 have a structure in which a shell portion made of carbon is formed on a core portion made of SiOy (0 <y <2). The sample 26 has a structure in which a shell portion made of carbon is formed in a core portion made of Si. The sample 27 has a structure in which a shell portion made of carbon is formed in a core portion made of SiNiTi.

(Comparative example)
A silicon compound was obtained in the same manner as in the above example.

Next, the silicon-based compound was heated to 600 ° C. at a temperature increase rate of 100 K / min or more in an atmosphere containing 10% by volume or more of butadiene gas (remainder; inert gas). After the temperature rise, it was fired (heat treatment) by holding at 600 ° C. for 3 hours.
Thus, the negative electrode material (negative electrode material powder) of Samples 28 to 32 was manufactured. The organic compounds of Samples 28 to 32 are shown in Table 3.

  In the manufactured negative electrode material, samples 28 to 30 have a structure in which a shell portion made of carbon is formed on a core portion made of SiOy (0 <y <2). The sample 31 has a structure in which a shell portion made of carbon is formed in a core portion made of Si. The sample 32 has a structure in which a shell portion made of carbon is formed in a core portion made of SiNiTi.

  (Evaluation of negative electrode material)

  C / O ratio of the negative electrode materials of Samples 1 to 21, Samples 22 to 27, and Samples 28 to 32, oxygen content ratio (shown as O content ratio in the table), mass ratio value of shell part to BET specific surface area ( (Shown as C / BET in the table) was measured, and the measurement results are shown in Tables 1-3.

  The C / O ratio and the oxygen content ratio were obtained by XPS analysis of the surface of the negative electrode material of each sample. The BET specific surface area was measured using a pore distribution measuring apparatus (manufactured by Yuasa Ionics), and the value of the ratio of the shell part to the specific surface area was calculated from the mass ratio of the shell part determined by XPS analysis.

As shown in Tables 1-2, the negative electrode materials of Samples 1-21, 22-27 have a C / O ratio of 0.33 or less and a C / BET of 0.60 [(mass%) / (m ² / G)]. And as shown in Table 1, the negative electrode materials of Samples 1 to 21 had an oxygen content of 34.0% or less, which was a lower value than the negative electrode materials of Samples 22 to 27.

  On the other hand, as shown in Table 3, the negative electrode material of sample 28 has an excessively large C / O ratio and excessive C / BET compared to the negative electrode materials of samples 1 to 21 and samples 22 to 27. It was getting smaller. Similarly, the negative electrode materials of Samples 29 to 32 have an excessively large C / O ratio as compared with the negative electrode materials of Samples 1 to 21 and Samples 22 to 27.

  According to Tables 1 to 3, the negative electrode materials of Samples 29 to 32 in which a shell portion was formed by thermal decomposition of butadiene gas (gas phase synthesis) had an excessively large C / O ratio of 0.35 or more. On the other hand, the negative electrode materials of Samples 1 to 21 and Samples 22 to 27 using liquid phase synthesis have a C / O ratio of 0.33 or less, and the reduction of the silicon compound is suppressed. That is, in the manufacture of the negative electrode material, it was confirmed that the reduction of the silicon compound in the core portion can be suppressed by baking the silicon compound together with the organic compound solution.

[Manufacture of lithium ion secondary batteries]
Using the negative electrode material powder of each sample, a coin-type lithium ion secondary battery 10 whose structure is shown in FIG. 1 was produced.

Negative electrode material mixture of 50.0 parts by mass of negative electrode material powder, 40.0 parts by mass of acetylene black (conductive material), 5.0 parts by mass of CMC (binder), and 5.0 parts by mass of SBR (binder) of each sample Was prepared. This negative electrode mixture is dispersed in NMP and made into a slurry using a cell master and a homogenizer. This slurry is applied onto the negative electrode current collector 1a made of electrolytic copper foil having a thickness of 18 μm, and then dried and press-molded. Thus, a negative electrode plate was obtained. On the negative electrode plate, the negative electrode mixture 1b is applied and press-molded so that the obtained mixture becomes 2.66 mg / cm ² and 1.5 g / cm ³ .

  Next, this negative electrode plate was extracted with a circular punch having a diameter of 14 mm and vacuum-dried at 120 ° C. for 6 hours to obtain a negative electrode. Thereby, the negative electrode 1 was manufactured.

Using the manufactured negative electrode 1, positive electrode 2 (counter electrode), and electrolyte solution 3, a coin-type lithium ion secondary battery 10 (CR2025 type) was produced in a dry box.
In the positive electrode 2, a positive electrode active material 2 b made of metallic lithium is integrally formed on the surface of the positive electrode current collector 2 a.

The electrolytic solution was prepared by dissolving LiPF ₆ in a mixed solvent of 30% by volume of ethylene carbonate (EC), 30% by volume of dimethyl carbonate (DMC) and 30% by volume of ethyl methyl carbonate (EMC) to 1 mol / liter. Have been prepared. Moreover, the electrolyte solution is added so that vinylene carbonate (VC) may be 1 mass% as an additive.

  A coin-type lithium ion secondary battery 10 includes a stainless steel case (a positive electrode case 4 and a negative electrode case 5) together with an electrolytic solution 3 in which a separator 7 (polyethylene porous film) is sandwiched between positive and negative electrodes. And a coin-type lithium ion secondary battery. The positive electrode case 4 and the negative electrode case 5 serve as a positive electrode terminal and a negative electrode terminal. A gasket 6 made of polypropylene is interposed between the positive electrode case 4 and the negative electrode case 5, thereby ensuring sealing and insulating properties between the positive electrode case 4 and the negative electrode case 5.

(Evaluation of lithium ion secondary battery)
As the evaluation of the lithium ion secondary battery of each sample, the initial discharge capacity, the initial charge / discharge efficiency, and the capacity maintenance rate after the cycle test were determined. Each measurement result was shown according to each of Tables 1-3.

(Initial discharge capacity measurement method)
The initial discharge capacity of the lithium ion secondary battery of each sample was performed under the following conditions.

First, constant current charging at a charging current 0.10mA / cm ² to 0.01 V, was constant current discharge to 1.5V at a discharge current 0.10mA / cm ^2. The discharge capacity at this time was defined as the initial discharge capacity.

(Initial charge / discharge efficiency measurement method)
From the obtained initial charge capacity and initial discharge capacity, the initial charge / discharge efficiency (%) was determined by the following formula.
Initial charge / discharge efficiency (%) = [(initial discharge capacity) / (initial charge capacity)] × 100

(Cycle characteristic test method)
After initial charge and discharge, a constant current charging at a charging current 0.10mA / cm ² to 0.01 V, was repeated 90 times at 60 ° C. The cycle of constant current discharge at a discharge current of 0.10mA / cm ² to 1.5V It was. The obtained discharge capacity retention rates are shown in Tables 1 and 2 together. And the discharge capacity maintenance rate (%) was calculated | required by the following formula from the discharge capacity of 90th cycle, and initial stage discharge capacity. In addition, the measurement of charging / discharging and discharge capacity was performed in 25 degreeC atmosphere.
Discharge capacity retention rate (%) = [(discharge capacity at 90th cycle) / (initial discharge capacity)] × 100

  As shown in Tables 1 to 3, the lithium ion secondary batteries of samples 1 to 21 and samples 22 to 27 corresponding to the examples of the present invention are the lithium ion secondary batteries of samples 28 to 32 corresponding to the comparative examples. On the other hand, the capacity retention rate after the cycle test (durability of the secondary battery) and the initial discharge capacity (capacity of the secondary battery itself) were excellent. That is, the Example of this invention is a secondary battery excellent not only in durability but in battery capacity.

  Specifically, the lithium ion secondary batteries of Samples 28 to 32, in which the shell portion is formed by vapor decomposition of butadiene gas (gas phase synthesis), the capacity is maintained when compared with each sample in which the core portion of the negative electrode material is the same material. It can be seen that the rate has dropped by nearly 10%.

  That is, by producing the shell portion of the negative electrode material by gas phase synthesis, the C / O ratio of the negative electrode material increases beyond 0.36, and as a result, the capacity of the lithium ion secondary batteries of Samples 28 to 32 is maintained. It can be seen that the rate (durability of the secondary battery) is reduced.

In addition, the lithium ion secondary batteries of samples 28 to 32 in which the shell portion was vapor-phase synthesized had a lower initial discharge capacity than the lithium ion secondary batteries of samples 1 to 21, 22 to 27 in which the liquid phases were synthesized. You can see that
In other words, the initial discharge capacity (battery capacity) of a lithium ion secondary battery using the negative electrode material can be increased by manufacturing the shell portion of the negative electrode material by liquid phase synthesis compared to the case of vapor phase synthesis. it can. In other words, the embodiment of the present invention (the negative electrode material) increases the battery performance including not only the capacity retention rate (durability) but also the initial capacity and the initial charge / discharge efficiency as compared with the comparative example (the negative electrode material). be able to.

  In addition, the lithium ion secondary batteries of Samples 1 to 21 using an organic acid as the carbon source of the shell portion have an initial discharge capacity of 200 (as compared with the corresponding lithium ion secondary batteries of Samples 22 to 27). (mAh / g) or more (2 or more depending on the material of the core portion), the initial charge / discharge efficiency is about 5%, and the capacity retention rate is nearly 5%, which is improved.

  That is, by using an organic acid as the carbon source of the shell portion, the O content of the negative electrode material can be reduced to 34% or less, and not only the capacity maintenance rate (durability) but also the initial capacity and initial charge / discharge efficiency It can be seen that the battery performance can be further enhanced.

1: Negative electrode 1a: Negative electrode current collector 1b: Negative electrode active material 2: Positive electrode 2a: Positive electrode current collector 2b: Positive electrode active material 3: Electrolytic solution 4: Positive electrode case 5: Negative electrode case 6: Gasket 7: Separator 10: Coin type battery

Claims (8)

SiLy or SiMxLy or SiMx (M; As, Ba, C, Ca, Ce, Co, Cr, Cu, Er, Fe, Gd, Hf, Lu, Mg, Mn, Mo, Nb, Nd, Ni, P, Pd, At least one selected from Pr, Pt, Pu, Re, Rh, Ru, Sc, Sm, Sr, Ta, Te, Th, Ti, Tm, U, V, W, Y, Yb, Zr, L; N, O A core portion made of a silicon compound represented by at least one selected from 0 ≦ x ≦ 1 and 0 ≦ y ≦ 2), and a shell portion made of carbon covering the core portion. A negative electrode material for a secondary battery,
A negative electrode material for a lithium ion secondary battery, wherein the ratio of the mass of carbon to the mass of oxygen is 0.33 or less.   The negative electrode material for a lithium ion secondary battery according to claim 1, wherein the content ratio of oxygen is 34.0% or less when the total mass is 100%. ^3. The lithium ion secondary battery according to claim 1, wherein a mass ratio of the shell portion to a BET specific surface area is 0.60 [(mass%) / (m ² / g)] or more. Negative electrode material. SiLy or SiMxLy or SiMx (M; As, Ba, C, Ca, Ce, Co, Cr, Cu, Er, Fe, Gd, Hf, Lu, Mg, Mn, Mo, Nb, Nd, Ni, P, Pd, At least one selected from Pr, Pt, Pu, Re, Rh, Ru, Sc, Sm, Sr, Ta, Te, Th, Ti, Tm, U, V, W, Y, Yb, Zr, L; N, O A step of synthesizing a silicon compound represented by at least one selected from 0 ≦ x ≦ 1, 0 ≦ y ≦ 2);
Mixing the silicon-based compound with a solution of an organic compound;
Firing in an inert atmosphere with the organic compound solution in contact with the silicon compound;
The manufacturing method of the negative electrode material for lithium ion secondary batteries characterized by having.   The said negative electrode material is a manufacturing method of the negative electrode material for lithium ion secondary batteries of Claim 4 manufactured by the liquid phase synthesis | combination synthesize | combined from a liquid phase state.   The said organic compound solution is an organic acid solution, The manufacturing method of the negative electrode material for lithium ion secondary batteries of any one of Claims 4-5.   The said baking is a manufacturing method of the negative electrode material for lithium ion secondary batteries of any one of Claims 4-6 performed at the temperature of 550-750 degreeC.   The negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 3, and the negative electrode material for a lithium ion secondary battery produced by the production method according to any one of claims 4 to 7. A lithium ion secondary battery having at least one of the above as a negative electrode.

Images