JP6589513B2 - Method for producing silicon material - Google Patents

Description

  The present invention relates to a method for producing a silicon material.

  Silicon materials are known to be used as components of semiconductors, solar cells, secondary batteries, etc. Therefore, research on silicon materials has been actively conducted.

For example, in Patent Document 1, a layered silicon compound mainly composed of polysilane obtained by reacting CaSi ₂ and an acid in an aqueous solution to remove Ca is synthesized, and the layered silicon compound is heated at 300 ° C. or higher to generate hydrogen. And a lithium ion secondary battery including the silicon material as an active material is described.

Furthermore, the inventors synthesized a layered silicon compound mainly composed of polysilane from which Ca is removed by reacting CaSi ₂ with an acid in an aqueous solution in Patent Document 2, and the layered silicon compound is heated to 300 ° C. A silicon material from which hydrogen has been released by heating as described above was manufactured, and a carbon-silicon composite in which the silicon material was coated with carbon was manufactured, and a lithium ion battery comprising the composite as an active material. The next battery is reported.

International Publication No. 2014/080608 Japanese Patent Application No. 2014-037833

  As described above, various silicon materials have been intensively studied. The industry demands the provision of new silicon materials and new methods for manufacturing silicon materials.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a new method for manufacturing a silicon material.

The present inventor recalled that CaSi is used as a raw material in place of CaSi ₂ in the silicon material manufacturing methods described in Patent Document 1 and Patent Document 2. However, when the above production method was attempted using CaSi as a raw material, a silicon compound corresponding to the intermediate could not be isolated, and a desired silicon material could not be obtained. The reason is considered that the intermediate is unstable.

The present inventor separately found a method for producing a silicon material including a step of heating at a temperature equal to or higher than the carbonization temperature of the halogen-containing polymer in the presence of CaSi ₂ and the halogen-containing polymer. In the production method, it is not necessary to isolate the intermediate.

From these findings, the present inventor, instead of CaSi ₂ as a raw material, in a silicon material manufacturing method including a step of heating at a temperature equal to or higher than the carbonization temperature of the halogen-containing polymer in the presence of CaSi ₂ and the halogen-containing polymer. Recalling the use of CaSi, the present invention has been completed.

  That is, the method for producing a silicon material according to the present invention includes a step of heating at a temperature equal to or higher than a carbonization temperature of the halogen-containing polymer in the presence of CaSi and the halogen-containing polymer.

  The silicon material manufacturing method of the present invention can provide a new silicon material manufacturing method.

2 is an SEM image of the silicon material of Example 1. 2 is a SEM image of a cross section of the silicon material of Example 1. FIG. 2 is an X-ray diffraction chart of the silicon material of Example 1. FIG. 2 is a charge / discharge curve of lithium ion secondary batteries of Example 1 and Comparative Example 1. FIG.

  The best mode for carrying out the present invention will be described below. Unless otherwise specified, the numerical range “x to y” described in this specification includes the lower limit x and the upper limit y. The numerical range can be configured by arbitrarily combining these upper limit value and lower limit value and the numerical values listed in the examples. Furthermore, numerical values arbitrarily selected from the numerical value range can be used as upper and lower numerical values.

  Method for Producing Silicon Material of the Present Invention (hereinafter, simply referred to as “Production Method of the Present Invention”. The silicon material produced by the production method of the present invention may also be referred to as “silicon material of the present invention”. Of the silicon materials of the present invention, those coated with carbon may be referred to as “the carbon-coated silicon material of the present invention.” “The silicon material of the present invention” includes “the carbon-coated silicon material of the present invention.” Includes a step of heating at a temperature equal to or higher than the carbonization temperature of the halogen-containing polymer in the presence of CaSi and the halogen-containing polymer.

  The reaction mechanism of the production method of the present invention when polyvinyl chloride is employed as the halogen-containing polymer will be described below.

First, polyvinyl chloride is decomposed by heating to release hydrogen chloride.
_{- (CH 2 CHCl) n- →} nHCl + - (CH = CH) n-

Next, it is presumed that CaSi acts with the released hydrogen chloride to become an active intermediate represented by the composition formula SiH ₂ .
CaSi + 2HCl → SiH ₂ + CaCl ₂

Since it is under heating conditions, it is presumed that hydrogen of the active intermediate represented by the composition formula SiH ₂ is released and silicon is obtained.
SiH ₂ → Si + H ₂ ↑

Further, (CH═CH) n, which is a decomposition product of polyvinyl chloride, is carbonized under heating conditions equal to or higher than its carbonization temperature. At that time, since silicon and (CH = CH) n carbide coexist, a carbon-coated silicon material in which carbon is integrated on the silicon surface can be obtained.
Si + (CH = CH) n → carbon-coated silicon material + nH ₂ ↑

  Hereinafter, the production method of the present invention will be described in detail.

CaSi generally has a structure with a CrB type crystal (TlI type crystal) and a space group Cmcm (Atta Crystallogr., 1967, vol. 22, pages 919 to 922). The CaSi ₂ used in the conventional manufacturing method generally has a layered crystal structure in which a Ca atom layer is inserted between (111) faces of diamond-type Si and the Ca layer and the Si layer are laminated. . Therefore, the crystal structures of CaSi and CaSi ₂ are different.

  CaSi may be synthesized by a known production method or commercially available. As a method for producing CaSi, for example, Ca may be added to a molten Si.

  The CaSi used in the production method of the present invention is preferably pulverized in advance. A preferable average particle diameter of CaSi can be exemplified by a range of 0.1 to 50 μm, more preferably within a range of 0.3 to 20 μm, further preferably within a range of 0.5 to 10 μm, particularly preferably 1 to 5 μm. The range can be illustrated. In addition, the average particle diameter in this specification means D50 when measured with a general laser diffraction type particle size distribution measuring apparatus.

The halogen-containing polymer may be any polymer that contains halogen in its chemical structure. The reason is as follows. Under the heating conditions of the production method of the present invention, hydrohalic acid and / or halogen molecules are released from the halogen-containing polymer. Then, the negatively charged halogen constituting the hydrohalic acid or the halogen molecule reacts with Ca of CaSi. That is, in the case of a halogen-containing polymer, it becomes a source of minus-charged halogen, and a desired reaction proceeds. When CaSi reacts with hydrohalic acid, an active intermediate represented by the composition formula SiH ₂ and calcium halide are produced. When CaSi reacts with a halogen molecule, the composition formula SiX ₂ (X is It is considered that an active intermediate represented by (halogen element) and calcium halide are formed.

As a halogen-containing polymer, what has a monomer unit of General formula (1) can be mentioned.
General formula (1)

  Hydrocarbons include saturated hydrocarbons and unsaturated hydrocarbons. Saturated hydrocarbons include chain saturated hydrocarbons and cyclic saturated hydrocarbons. The unsaturated hydrocarbon includes a chain unsaturated hydrocarbon and a cyclic unsaturated hydrocarbon.

Among the chemical structures of R ^1, the chemical structure that is the main chain of the monomer unit (chemical structure including carbon involved in the polymerization reaction) is a chain saturated hydrocarbon, a cyclic saturated hydrocarbon, a chain unsaturated hydrocarbon, a cyclic Any of unsaturated hydrocarbons may be used. Specific examples of the chemical structure serving as the main chain of the monomer unit include CH, CH ₂ —CH, CH═CH, a cyclohexane ring, and a benzene ring.

Among the chemical structures of R ^1, the chemical structure bonded to the main chain of the monomer unit (hereinafter sometimes referred to as a side chain) is hydrogen, chain saturated hydrocarbon, cyclic saturated hydrocarbon, chain unsaturated hydrocarbon. Any of cyclic unsaturated hydrocarbons may be used. Moreover, hydrogen of each hydrocarbon may be substituted with another element or another hydrocarbon.

X is any of fluorine, chlorine, bromine and iodine. When n is 2 or more, each X may be the same type or other types. X may be directly bonded to the carbon that is the main chain of the monomer unit, or may be bonded to the carbon of the side chain. The upper limit of n is determined by the chemical structure of R ¹ .

  The halogen-containing polymer may be composed of only a single type of monomer unit of general formula (1), or may be composed of a plurality of types of monomer units of general formula (1). May be. Moreover, the halogen-containing polymer may be composed of a monomer unit of the general formula (1) and a monomer unit having another chemical structure.

  Here, if a halogen-containing polymer having a high halogen mass% is employed, it is considered that the desired reaction proceeds more efficiently. Therefore, the halogen-containing polymer is composed only of the monomer unit of the general formula (1). preferable.

  The molecular weight of the halogen-containing polymer is preferably in the range of 1,000 to 1,000,000, more preferably in the range of 1,000 to 500,000, and still more preferably in the range of 3,000 to 100,000. The degree of polymerization of the halogen-containing polymer is preferably within the range of 50,000 to 100,000, more preferably within the range of 10 to 50,000, and even more preferably within the range of 100 to 10,000.

A suitable thing is shown by the following general formula (2) among the monomer units of General formula (1).
General formula (2)

  The description about the hydrocarbon and the halogen is as described above. Preferred hydrocarbons in the general formula (2) include alkyl groups having 1 to 6 carbon atoms, vinyl groups, and phenyl groups.

As described above, since it is considered that the halogen-containing polymer has a high halogen mass%, it is preferable that R ² , R ³ and R ⁴ of the monomer unit of the general formula (2) are independently hydrogen or halogen.

  Particularly suitable halogen-containing polymers include polyvinylidene fluoride, polyvinyl fluoride, polyvinylidene chloride, and polyvinyl chloride.

  The amount of CaSi and halogen-containing polymer used is preferably an amount of halogen-containing polymer in which the molar ratio of halogen is 2 or more with respect to Ca of CaSi to be used.

  CaSi and the halogen-containing polymer may be in contact with each other or in a non-contact state. In order to bring CaSi and the halogen-containing polymer into contact with each other, CaSi and the halogen-containing polymer may be mixed.

  The heating temperature of the production method of the present invention is a temperature equal to or higher than the carbonization temperature of the halogen-containing polymer. Here, in general, the organic compound is carbonized from around 400 ° C. And the higher the heating temperature, the higher the conductivity of the carbide. Therefore, the heating temperature of the production method of the present invention is preferably within the range of 400 to 1500 ° C, more preferably within the range of 500 to 1300 ° C, and even more preferably within the range of 600 to 1200 ° C. Depending on the heating temperature, the ratio of amorphous silicon and silicon crystallites contained in the silicon material of the present invention and the size of the silicon crystallites can also be adjusted.

  The size of the silicon crystallite is preferably in the range of 0.5 nm to 300 nm, more preferably in the range of 1 nm to 100 nm, still more preferably in the range of 1 nm to 70 nm, and particularly preferably in the range of 1 nm to 30 nm. The size of the silicon crystallite is measured by the X-ray diffraction measurement (XRD measurement) on the silicon material of the present invention, and the Scherrer's half width of the diffraction peak on the Si (111) plane of the obtained XRD chart is used. Calculated from the formula.

The generation of the silicon crystallites in the production process of the present invention, rather than the conventional manufacturing method the raw material is CaSi _2, is considered to be achieved at low temperature. Further, when the heating temperature is the same, it is considered that the production method of the present invention produces a larger amount of silicon crystallites than the conventional production method in which the raw material is CaSi ₂ . These reasons are as follows.

In the conventional manufacturing method, CaSi ₂ is first treated with an acid to become Si ₆ H ₆ having a Si layer. Here, when the Si ₆ H ₆ is heated to release hydrogen and change to silicon, a silicon crystal is formed. It is considered necessary to supply the rearrangement energy to the crystal.

On the other hand, in the production method of the present invention, the active intermediate obtained by treating CaSi with an acid does not have the Si layer that Si ₆ H ₆ has, and is unstable. Then, when the active intermediate is heated and hydrogen is released to change to silicon, silicon crystal is generated, so that the Si bond cleavage energy in the Si layer, which was required in the conventional manufacturing method, is unnecessary. It is. Further, although rearrangement energy of Si atoms to the silicon crystal is necessary, the energy can be supplemented by a stabilization energy when the unstable active intermediate is changed to a stable silicon material or silicon crystal. The presence of an unstable active intermediate is presumed to be a driving force for generating silicon crystals in the production method of the present invention.

  By the production method of the present invention, the silicon material of the present invention having voids dispersed therein can be obtained. This void can be confirmed by observation with a scanning electron microscope or the like. Considering the use of the silicon material of the present invention as an active material for a lithium ion secondary battery, the void is considered to play a role of relaxing expansion and contraction of the active material during charge / discharge. Is considered to be a lithium ion transfer path when the electrolyte is filled with the electrolyte.

  Further, in the production method of the present invention, the heating conditions include two or more stages including a step of heating at a temperature higher than the decomposition temperature of the halogen-containing polymer and a step of heating at a temperature higher than the carbonization temperature of the polymer after decomposition. It is good also as multistage heating conditions. Here, the decomposition temperature of the halogen-containing polymer is a temperature at which hydrohalic acid or halogen molecules are released from the halogen-containing polymer. It is good also as a multistage heating condition by changing a temperature increase rate.

  Furthermore, in the production method of the present invention, the heating conditions are a step of heating at a temperature equal to or higher than the melting point of the halogen-containing polymer or the glass transition point, a step of heating at a temperature equal to or higher than the decomposition temperature of the halogen-containing polymer, and It is good also as multistage heating conditions of 3 steps or more including the process heated at the temperature more than the carbonization temperature of a polymer.

  Taking polyvinyl chloride as an example, the melting point of polyvinyl chloride is approximately in the range of 85 to 210 ° C., and the decomposition temperature of polyvinyl chloride, that is, the hydrogen chloride generation temperature is approximately in the range of 210 to 300 ° C. . Then, in the production method of the present invention, when polyvinyl chloride is employed as the halogen-containing polymer, the first heating step for heating the heating conditions at around 200 ° C., the second heating step for heating at around 300 ° C., and around 900 ° C. It is good also as a three-step heating condition used as the 3rd heating process heated by. By passing through the first heating step, it is estimated that CaSi can be more uniformly dispersed in the polyvinyl chloride matrix. Next, it is presumed that the conversion ratio of CaSi to an active intermediate and Si is increased because the suitable dispersion state of CaSi can efficiently react with HCl through the second heating step. Finally, through the third heating step, the final conversion rate from CaSi to Si is improved, the amount of silicon crystals in the silicon material is increased, and more uniform with respect to the silicon material. It is presumed that a carbon-coated silicon material with a carbon coating is obtained.

  The production method of the present invention is preferably carried out in an inert gas atmosphere such as argon, helium, or nitrogen gas.

  Examples of the manufacturing apparatus specifically used in the manufacturing method of the present invention include heating furnaces such as a high-frequency induction heating furnace, an electric furnace, an arc furnace, and a gas furnace. The heating furnace may be partitioned into a plurality of rooms. CaSi and halogen-containing polymer may be arranged directly in the heating furnace, or CaSi and / or halogen-containing polymer arranged in the same or another container may be arranged in the heating furnace together with the container.

  Containers are made of high melting point metals such as molybdenum, tungsten, tantalum or niobium, or alumina, zirconia, silicon nitride, aluminum nitride, silicon carbide, cordierite, mullite, steatite, calcia, magnesia, sialon, quartz Ceramics such as Vycor or sapphire glass are preferable.

  The container may be hermetically sealed, may be provided with a vent, and may be provided with a valve that opens and closes according to the internal pressure. A crucible with a lid or the like may be used as the container.

  As described above, the CaSi and the halogen-containing polymer may be in contact with each other or in a non-contact state. Here, in order to bring CaSi and the halogen-containing polymer into contact with each other, a mixture in which CaSi and the halogen-containing polymer are mixed may be provided to a manufacturing apparatus, and CaSi and halogen-containing polymer may be provided in a heating furnace having a mixing function. A polymer may be provided. In order to make CaSi and the halogen-containing polymer in a non-contact state, they may simply be placed apart from each other in the heating furnace. Specifically, using a compartment or a room in the heating furnace, Both may be brought into a non-contact state.

  By bringing CaSi and the halogen-containing polymer in a non-contact state, advantageous effects such as improvement in the ease of reaction control, suppression of local heat generation, and particle size distribution control of the carbon-coated silicon material of the present invention are exhibited.

  The silicon material of the present invention may be pulverized and classified into particles having a certain particle size distribution. As a preferable particle size distribution of the silicon material of the present invention when measured with a general laser diffraction particle size distribution measuring apparatus, it can be exemplified that the average particle diameter (D50) is in the range of 1 to 30 μm, and more preferable. Can exemplify that the average particle diameter (D50) is in the range of 1 to 10 μm.

The silicon material of the present invention may contain impurities derived from raw materials such as Ca and halogen, and inevitable impurities. Examples of the abundance (% by mass) of such impurities include the following ranges.
Ca: 0 to 5% by mass, 0 to 3% by mass, 0 to 2% by mass, 0.1 to 3% by mass, 0.5 to 2% by mass
Halogen: 0 to 10% by mass, 0.001 to 6% by mass

The silicon material of the present invention is preferably subjected to a cleaning step of cleaning with a solvent having a relative dielectric constant of 5 or more. The cleaning step is a step of removing unnecessary components adhering to the silicon material of the present invention by cleaning with a solvent having a relative dielectric constant of 5 or more (hereinafter sometimes referred to as “cleaning solvent”). This step is mainly intended to remove salts that can be dissolved in a washing solvent such as calcium halide. For example, when polyvinyl chloride is used as the halogen-containing polymer, it is presumed that CaCl ₂ remains in the silicon material of the present invention. Therefore, by washing the silicon material of the present invention with a washing solvent, unnecessary components including CaCl ₂ can be dissolved and removed in the washing solvent. The cleaning step may be a method of immersing the silicon material of the present invention in a cleaning solvent, or a method of exposing the silicon material of the present invention to a cleaning solvent.

  As the washing solvent, a solvent having a higher relative dielectric constant is preferable from the viewpoint of ease of dissolution of the salt, and a solvent having a relative dielectric constant of 10 or more or 15 or more can be presented as a more preferable one. The range of the relative dielectric constant of the cleaning solvent is preferably within the range of 5 to 90, more preferably within the range of 10 to 90, and even more preferably within the range of 15 to 90. In addition, as the cleaning solvent, a single solvent may be used, or a mixed solvent of a plurality of solvents may be used.

  Specific examples of the washing solvent include water, methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, sec-butanol, tert-butanol, ethylene glycol, glycerin, and N-methyl-2-pyrrolidone. , N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, acetonitrile, ethylene carbonate, propylene carbonate, benzyl alcohol, phenol, pyridine, tetrahydrofuran, acetone, ethyl acetate, and dichloromethane. Of these specific solvent chemical structures, a part or all of hydrogen substituted with fluorine may be employed as the cleaning solvent. The water as the washing solvent is preferably distilled water, reverse osmosis membrane permeated water, or deionized water.

  For reference, the relative dielectric constants of various solvents are shown in Table 1.

  As the washing solvent, water, methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, sec-butanol, tert-butanol, and acetone are particularly preferable.

  When a mixed solvent of a plurality of solvents is used as the washing solvent, the other solvent is preferably 1 to 100 parts by volume, more preferably 2 to 50 parts by volume, further preferably 5 to 30 parts by volume with respect to 100 parts by volume of water. It is advisable to employ a mixed solvent mixed at a ratio of parts. By using a mixed solvent as the cleaning solvent, the dispersibility and affinity of the silicon material of the present invention for the cleaning solvent may be improved, and as a result, unnecessary components are preferably eluted in the cleaning solvent.

  After the washing step, it is preferable to remove the washing solvent from the silicon material of the present invention by filtration and drying.

  The washing process may be repeated multiple times. In that case, the washing solvent may be changed. For example, water with an extremely high relative dielectric constant is selected as the cleaning solvent in the first cleaning process, and water is efficiently removed by using ethanol or acetone with low boiling point that is compatible with water as the next cleaning solvent. In addition, the cleaning solvent can be easily prevented from remaining.

  The drying step after the washing step is preferably performed in a reduced pressure environment, and more preferably at a temperature equal to or higher than the boiling point of the washing solvent. As temperature, 80 to 110 degreeC is preferable.

  As described above, the silicon material of the present invention is manufactured through the manufacturing method of the present invention. Here, the silicon material of the present invention which has undergone only the step of heating at a temperature equal to or higher than the carbonization temperature of the halogen-containing polymer in the presence of CaSi and the halogen-containing polymer is coated with carbon. In the production method of the present invention, the carbon-coated silicon material can be produced in a single-stage production process.

  Moreover, you may perform the additional carbon coating process which coat | covers with carbon further with respect to the carbon covering silicon material obtained with the manufacturing method of this invention. Moreover, you may perform the carbon removal process which removes at least one part carbon of a carbon covering silicon material before an additional carbon coating process.

  As the additional carbon coating step, a conventional known technique may be applied. For example, what is necessary is just to apply what is called thermal CVD method which contacts and heats material by organic substance gas in non-oxidizing atmosphere, and carbonizes organic substance gas.

  As the organic gas, a gas obtained by vaporizing an organic material, a gas obtained by sublimating an organic material, or an organic vapor can be used. In addition, organic substances that generate organic gases include those that can be thermally decomposed and carbonized by heating in a non-oxidizing atmosphere. For example, saturated fats such as methane, ethane, propane, butane, isobutane, pentane, and hexane. Hydrocarbons, unsaturated aliphatic hydrocarbons such as ethylene, propylene, acetylene, alcohols such as methanol, ethanol, propanol, butanol, benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, benzoic acid , One or a mixture selected from aromatic hydrocarbons such as salicylic acid, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, phenanthrene, esters such as ethyl acetate, butyl acetate, amyl acetate, and fatty acids Thing, and the like. The organic substance is preferably a saturated aliphatic hydrocarbon such as propane.

  The treatment temperature in the additional carbon coating step varies depending on the type of organic matter, but is preferably set to a temperature higher by 50 ° C. or more than the temperature at which the organic gas is thermally decomposed. However, when the temperature is too high or the organic gas concentration is too high, so-called soot is generated, so it is preferable to select a condition that does not generate soot. The thickness of the carbon layer to be formed can be controlled by the amount of organic matter and the processing time.

  The additional carbon coating step is preferably performed with the material in a fluid state. By doing in this way, the whole surface of material can be made to contact organic substance gas, and a uniform carbon layer can be formed. There are various methods such as using a fluidized bed to bring the material into a fluid state, but it is preferable to contact the material with an organic gas while stirring the material. For example, if a rotary furnace having a baffle plate is used, the material staying on the baffle plate is stirred by dropping from a predetermined height along with the rotation of the rotary furnace, and in this case, the carbon layer comes into contact with the organic gas. Thus, a uniform carbon layer can be formed throughout.

  The carbon-coated silicon material of the present invention obtained by performing the additional carbon coating step is in a state where carbon coating is performed by two kinds of methods. Such a carbon-coated silicon material of the present invention is in a state in which a coating state that has been insufficient with one carbon coating method is complemented with another carbon coating method. Therefore, it is considered that the secondary battery including the carbon-coated silicon material of the present invention as a negative electrode active material has favorable battery characteristics.

  In the carbon removal step, the carbon-coated silicon material may be heated in the presence of oxygen to remove carbon as carbon dioxide or carbon monoxide. In the carbon removal step, a part or all of the carbon of the carbon-coated silicon material can be removed. As heating temperature, 350-650 degreeC can be illustrated.

  In the carbon removal step, it can be expected that impurities contained in the carbon-coated silicon material are also removed at the same time. Therefore, it is inferred that the silicon material of the present invention that has undergone the carbon removal step is a suitable material, and further, the carbon-coated silicon material of the present invention that is manufactured by being subjected to an additional carbon coating step is also a suitable material. Is done.

  The carbon-coated silicon material of the present invention contains carbon and silicon as essential components. When the carbon-coated silicon material of the present invention is 100, carbon is preferably contained within a range of 1 to 30% by mass, more preferably within a range of 3 to 20% by mass, and 5 to 15%. More preferably, it is contained within the range of mass%. When the carbon-coated silicon material of the present invention is defined as 100, silicon is preferably contained within a range of 50 to 99% by mass, more preferably within a range of 60 to 97% by mass, and 65 to 95%. More preferably, it is contained within the range of mass%.

  The silicon material of the present invention can be used as a negative electrode active material for a secondary battery such as a lithium ion secondary battery. Hereinafter, the secondary battery of the present invention will be described by taking a lithium ion secondary battery as an example. The lithium ion secondary battery of the present invention comprises the silicon material of the present invention as a negative electrode active material. Specifically, the lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode including the silicon material of the present invention as a negative electrode active material, an electrolytic solution, and a separator.

  The positive electrode has a current collector and a positive electrode active material layer bound to the surface of the current collector.

  The current collector refers to a chemically inert electronic conductor that keeps a current flowing through an electrode during discharge or charging of a lithium ion secondary battery. As the current collector, at least one selected from silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, and stainless steel Metal materials can be exemplified. The current collector may be covered with a known protective layer. What collected the surface of the electrical power collector by the well-known method may be used as an electrical power collector.

  The current collector can take the form of a foil, a sheet, a film, a linear shape, a rod shape, a mesh, or the like. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector. When the current collector is in the form of foil, sheet or film, the thickness is preferably in the range of 1 μm to 100 μm.

  The positive electrode active material layer includes a positive electrode active material and, if necessary, a conductive additive and / or a binder.

As the positive electrode active material, the layered compound Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, Cu, At least one element selected from Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La, 1.7 ≦ f ≦ 3 ), Li ₂ MnO ₃ . Further, as a positive electrode active material, a solid solution composed of a spinel such as LiMn ₂ O ₄ and a mixture of a spinel and a layered compound, LiMPO ₄ , LiMVO ₄ or Li ₂ MSiO ₄ (wherein M is Co, Ni, Mn, And a polyanionic compound represented by (selected from at least one of Fe). Furthermore, as the positive electrode active material, tavorite compound (the M a transition metal) LiMPO ₄ F, such as LiFePO ₄ F represented by, Limbo ₃ such LiFeBO ₃ (M is a transition metal) include borate-based compound represented by be able to. Any metal oxide used as the positive electrode active material may have the above-described composition formula as a basic composition, and those obtained by substituting the metal elements contained in the basic composition with other metal elements can also be used as the positive electrode active material. . Further, as the positive electrode active material, a positive electrode active material that does not contain lithium ions contributing to charge / discharge, for example, sulfur alone (S), a compound in which sulfur and carbon are combined, a metal sulfide such as TiS ₂ , V ₂ O, etc. ₅ , oxides such as MnO ₂ , polyaniline and anthraquinone, compounds containing these aromatics in the chemical structure, conjugated materials such as conjugated diacetic acid organic materials, and other known materials can also be used. Further, a compound having a stable radical such as nitroxide, nitronyl nitroxide, galvinoxyl, phenoxyl, etc. may be adopted as the positive electrode active material. When using a positive electrode active material that does not contain lithium, it is necessary to add ions to the positive electrode and / or the negative electrode in advance by a known method. Here, in order to add the ion, a metal or a compound containing the ion may be used.

  The conductive assistant is added to increase the conductivity of the electrode. Therefore, the conductive auxiliary agent may be added arbitrarily when the electrode conductivity is insufficient, and may not be added when the electrode conductivity is sufficiently excellent. The conductive auxiliary agent may be any chemically inert electronic high conductor such as carbon black, graphite, vapor grown carbon fiber (VGCF), and various metal particles. Illustrated. Examples of carbon black include acetylene black, ketjen black (registered trademark), furnace black, and channel black. These conductive assistants can be added to the active material layer alone or in combination of two or more.

  The blending ratio of the conductive additive in the active material layer is preferably a mass ratio of active material: conductive additive = 1: 0.005 to 1: 0.5, and 1: 0.01 to 1: 0. .2 is more preferable, and 1: 0.03 to 1: 0.1 is even more preferable. This is because if the amount of the conductive auxiliary is too small, an efficient conductive path cannot be formed, and if the amount of the conductive auxiliary is too large, the moldability of the active material layer is deteriorated and the energy density of the electrode is lowered.

  The binder plays a role of securing an active material or a conductive auxiliary agent to the surface of the current collector and maintaining a conductive network in the electrode. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins, poly ( Examples thereof include acrylic resins such as (meth) acrylic acid, styrene-butadiene rubber (SBR), and carboxymethyl cellulose. These binders may be used singly or in plural.

  The blending ratio of the binder in the active material layer is preferably a mass ratio of active material: binder = 1: 0.001 to 1: 0.3, and 1: 0.005 to 1: 0. .2 is more preferable, and 1: 0.01 to 1: 0.15 is still more preferable. This is because when the amount of the binder is too small, the moldability of the electrode is lowered, and when the amount of the binder is too large, the energy density of the electrode is lowered.

  The negative electrode has a current collector and a negative electrode active material layer bound to the surface of the current collector. What is necessary is just to employ | adopt suitably what was demonstrated with the positive electrode about a collector. The negative electrode active material layer includes a negative electrode active material and, if necessary, a conductive additive and / or a binder.

  The negative electrode active material only needs to contain the silicon material of the present invention, and only the silicon material of the present invention may be employed, or the silicon material of the present invention and a known negative electrode active material may be used in combination. .

  About the conductive support agent and binder used for a negative electrode, what was demonstrated in the positive electrode should just be employ | adopted suitably suitably with the same mixture ratio.

  In order to form an active material layer on the surface of the current collector, a current collecting method such as a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method can be used. An active material may be applied to the surface of the body. Specifically, an active material, a solvent, and, if necessary, a binder and / or a conductive aid are mixed to prepare a slurry. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. The slurry is applied to the surface of the current collector and then dried. In order to increase the electrode density, the dried product may be compressed.

  The electrolytic solution includes a nonaqueous solvent and an electrolyte dissolved in the nonaqueous solvent.

  As the non-aqueous solvent, cyclic esters, chain esters, ethers and the like can be used. Examples of the cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, fluorinated ethylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, ethyl methyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. Examples of ethers include tetrahydrofuran, 2-methyltetrahydrofuran / BR> A1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane. As the non-aqueous solvent, a compound in which part or all of hydrogen in the chemical structure of the specific solvent is substituted with fluorine may be employed.

Examples of the electrolyte include lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂ ) ₂ .

As an electrolytic solution, 0.5 mol / L to 1.7 mol of a lithium salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO _{3 in} a nonaqueous solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, and diethyl carbonate. A solution dissolved at a concentration of about / L can be exemplified.

  The separator separates the positive electrode and the negative electrode and allows lithium ions to pass while preventing a short circuit due to contact between the two electrodes. As separators, natural resins such as polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polymer), polyester, polyacrylonitrile and other polysaccharides, cellulose, amylose and other polysaccharides, fibroin, keratin, lignin and suberin Examples thereof include porous bodies, nonwoven fabrics, and woven fabrics using one or more electrically insulating materials such as polymers and ceramics. The separator may have a multilayer structure.

  Next, the manufacturing method of a lithium ion secondary battery is demonstrated.

  A separator is sandwiched between the positive electrode and the negative electrode as necessary to form an electrode body. The electrode body may be either a stacked type in which the positive electrode, the separator and the negative electrode are stacked, or a wound type in which the positive electrode, the separator and the negative electrode are sandwiched. After connecting the current collector of the positive electrode and the current collector of the negative electrode to the positive electrode terminal and the negative electrode terminal that communicate with the outside using a lead for current collection, etc., an electrolyte is added to the electrode body and a lithium ion secondary Use batteries. Moreover, the lithium ion secondary battery of this invention should just be charged / discharged in the voltage range suitable for the kind of active material contained in an electrode.

  The shape of the lithium ion secondary battery of the present invention is not particularly limited, and various shapes such as a cylindrical shape, a square shape, a coin shape, and a laminate shape can be adopted.

  The lithium ion secondary battery of the present invention may be mounted on a vehicle. The vehicle may be a vehicle that uses electric energy from a lithium ion secondary battery for all or a part of its power source, and may be, for example, an electric vehicle or a hybrid vehicle. When a lithium ion secondary battery is mounted on a vehicle, a plurality of lithium ion secondary batteries may be connected in series to form an assembled battery. Examples of devices equipped with lithium ion secondary batteries include various home appliances driven by batteries such as personal computers and portable communication devices, office devices, and industrial devices in addition to vehicles. Furthermore, the lithium ion secondary battery of the present invention includes wind power generation, solar power generation, hydroelectric power generation and other power system power storage devices and power smoothing devices, power supplies for ships and / or auxiliary power supply sources, aircraft, Power supply for spacecraft and / or auxiliary equipment, auxiliary power supply for vehicles that do not use electricity as a power source, power supply for mobile home robots, power supply for system backup, power supply for uninterruptible power supply, You may use for the electrical storage apparatus which stores temporarily the electric power required for charge in the charging station for electric vehicles.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. In addition, this invention is not limited by these Examples.

Example 1
The silicon material and lithium ion secondary battery of Example 1 were manufactured as follows.

2 g of CaSi and 4 g of polyvinyl chloride (degree of polymerization 1100) were mixed to obtain a mixture. In the mixture, the molar ratio of Ca to Cl was 1: 2.2. Under an argon atmosphere, the mixture was placed in an alumina crucible, capped, and placed in an electric furnace. The inside of the electric furnace was heated by the following program, and the mixture was used as a fired body.
From room temperature to 250 ° C, 5 ° C / min. The temperature is increased from 250 ° C. to 350 ° C. at 100 ° C./60 min. The temperature was increased from 350 ° C to 900 ° C at a rate of 5 ° C / min. When the temperature reaches 900 ° C, the heating ends.

  The obtained fired body was washed with water, then washed with acetone, and then dried under reduced pressure to obtain the silicon material of Example 1 coated with carbon in black.

  45 parts by mass of the silicon material of Example 1 as a negative electrode active material, 40 parts by mass of natural graphite as a negative electrode active material, 5 parts by mass of acetylene black as a conductive auxiliary agent, 10 parts by mass of polyamideimide as a binder, and N-methyl-2- 2 as a solvent Pyrrolidone was mixed to prepare a slurry. The slurry was applied to the surface of an electrolytic copper foil having a thickness of about 20 μm as a current collector using a doctor blade and dried to form a negative electrode active material layer on the copper foil. Thereafter, the current collector and the negative electrode active material layer were firmly and closely joined by a roll press. This was vacuum dried at 200 ° C. for 2 hours to form a negative electrode having a negative electrode active material layer thickness of 20 μm.

  A lithium ion secondary battery (half cell) was produced using the negative electrode produced by the above procedure as an evaluation electrode. The counter electrode was a metal lithium foil (thickness 500 μm).

The counter electrode was cut to φ15 mm and the evaluation electrode was cut to φ11 mm, and a separator (Hoechst Celanese glass filter and Celgard “Celgard 2400”) was interposed between the two electrodes to form an electrode body. This electrode body was accommodated in a battery case (CR2032-type coin battery member, manufactured by Hosen Co., Ltd.). Into the battery case, a non-aqueous electrolyte solution in which LiPF ₆ was dissolved at a concentration of 1M was injected into a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a ratio of 1: 1 (volume ratio), and the battery case was sealed. 1 lithium ion secondary battery was obtained.

(Comparative Example 1)
Except for using CaSi ₂ as a raw material and mixing 1 g of CaSi ₂ and 1.3 g of polyvinyl chloride (degree of polymerization 1100) to obtain a mixture, the silicon material of Comparative Example 1 and A lithium ion secondary battery was manufactured. In the above mixture, the molar ratio of Ca to Cl was 1: 2.

(Evaluation example 1)
The silicon material of Example 1 and its cross section were observed with a scanning electron microscope (SEM). The obtained SEM images are shown in FIGS. 1 and 2, it can be seen that the silicon material of Example 1 is a particle coated with carbon. FIG. 2 shows that many voids are dispersed inside the silicon material.

(Evaluation example 2)
The silicon material of Example 1 was subjected to X-ray diffraction measurement with a powder X-ray diffractometer. FIG. 3 shows an X-ray diffraction chart of the silicon material of Example 1.

  From the X-ray diffraction chart of FIG. 3, a peak indicating silicon crystallites was confirmed. When the size of the silicon crystallite was calculated from the Scherrer equation, it was about 60 nm.

(Evaluation example 3)
The lithium ion secondary battery of Example 1 and the lithium ion secondary battery of Comparative Example 1 were discharged at a temperature of 25 ° C. and a current of 0.2 mA until the voltage with respect to the counter electrode of the evaluation electrode became 0.01 V, and then the temperature of 25 Charging was performed until the voltage with respect to the counter electrode of the evaluation electrode reached 1 V at 0 ° C. and a current of 0.2 mA. The charge / discharge curve at this time is shown in FIG.

  From FIG. 4, it can be seen that the charging curve of the lithium ion secondary battery of Example 1 has a wider flat portion with a small potential change existing at 0.4 V to 0.5 V. The flat portion is considered to appear when the silicon crystal contributes to charging. Therefore, it can be said that the silicon material of Example 1 has more silicon crystal than the silicon material of Comparative Example 1. In view of the same heating conditions in the silicon material manufacturing method of Example 1 and the silicon material manufacturing method of Comparative Example 1, the silicon material manufacturing method of Example 1 using CaSi as a raw material is more preferable. It can be said that silicon crystals can be easily manufactured.

Claims (9)

The manufacturing method of the negative electrode active material containing the silicon material characterized by including the process heated at the temperature more than the carbonization temperature of the said halogen-containing polymer in coexistence of CaSi and a halogen-containing polymer. 2. The silicon material according to claim 1, wherein the heating is multistage heating including a step of heating at a temperature equal to or higher than a decomposition temperature of the halogen-containing polymer and a step of heating at a temperature equal to or higher than a carbonization temperature of the polymer after decomposition. The manufacturing method of the negative electrode active material containing this . The manufacturing method of the negative electrode active material containing the silicon material of Claim 1 or 2 in which the said halogen-containing polymer has a monomer unit of the following general formula (1).
General formula (1)
The manufacturing method of the negative electrode active material containing the silicon material in any one of Claims 1-3 in which the said halogen-containing polymer has a monomer unit of following General formula (2).
General formula (2)
The said silicon material is a carbon covering silicon material, The manufacturing method of the negative electrode active material containing the silicon material in any one of Claims 1-4. The manufacturing method of a secondary battery including the process of manufacturing a negative electrode using the negative electrode active material containing the silicon material manufactured with the manufacturing method in any one of Claims 1-5. Silicone material containing silicon crystallites having a size of 0.5 to 300 nm (however, it has a structure in which a plurality of plate-like silicon bodies are laminated in the thickness direction). Negative electrode active material containing silicon material) . The negative electrode active material containing the silicon material according to claim 7, wherein the silicon material is coated with carbon. Secondary battery having a negative electrode active material containing silicon material according to any of claims 7-8.