JP2017095326A - M-CONTAINING SILICON MATERIAL, WHERE M IS AT LEAST ONE ELEMENT SELECTED FROM Sn, Pb, Sb, Bi, In, Zn OR Au, AND MANUFACTURING METHOD THEREFOR - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel silicon material which functions as an anode active material.SOLUTION: There is provided an M-containing silicon material containing an M element, where M is at least one element selected from Sn, Pb, Sb, Bi, In, Zn or Au, having a crystal structure. There is provided a manufacturing method including a process for cooling a molten metal containing Ca, M and Si to obtain an M-containing calcium silicate, a process for reacting the M-containing calcium silicate with acid to obtain M-containing polysilane and a process of heating the M-containing polysilane at 300°C or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an M-containing silicon material (M is at least one element selected from Sn, Pb, Sb, Bi, In, Zn, or Au) and a manufacturing method thereof.

  Silicon materials are known to be used as components of semiconductors, solar cells, secondary batteries and the like, and in recent years, research on silicon materials has been actively conducted.

For example, Non-Patent Document 1 describes that layered polysilane is synthesized by reacting CaSi ₂ with an acid.

Patent Document 1 describes that CaSi ₂ is reacted with an acid to synthesize layered polysilane, and that a lithium ion secondary battery including the layered polysilane as an active material exhibits a suitable capacity. ing.

  Patent Document 2 describes an alloy made of silicon, aluminum, iron, and titanium, and describes a lithium ion secondary battery using the alloy as a negative electrode active material.

In Patent Document 3, a layered polysilane was synthesized by reacting CaSi ₂ with an acid, and the layered polysilane was heated at 300 ° C. or higher to produce a silicon material from which hydrogen was released, and the silicon material was activated. It is described that the lithium ion secondary battery provided as a substance exhibits a suitable capacity maintenance rate.

  Moreover, the present inventors have reported in Patent Document 4 that an alloy made of silicon, calcium and copper was manufactured, and a silicon material was manufactured using the alloy as a raw material.

JP 2011-090806 A Special table 2009-517850 International Publication No. 2014/080608 Japanese Patent Application No. 2014-110821

PHYSICAL REVIEW B, Volume48, 1993, p.8172-p.8189

  As described above, research on silicon materials has been conducted eagerly, and provision of new silicon materials is eagerly desired in the technical fields such as semiconductors, solar cells, and secondary batteries.

  This invention is made | formed in view of this situation, and it aims at providing a new silicon material and its manufacturing method.

The present inventor has intensively studied through trial and error in order to provide a new silicon material. And when the molten metal manufactured by heating Ca, Si and Sn is cooled, not the three-component alloy obtained in Patent Document 4, but a material in which Sn alone is dispersed in a CaSi ₂ matrix is obtained. I discovered that. Then, polysilane is synthesized from the CaSi ₂ matrix, and further, a silicon material from which hydrogen is released from the polysilane is synthesized, and the silicon material is tested. The silicon material functions suitably as a negative electrode active material. The inventor has found out and completed the present invention.

  That is, the M-containing silicon material of the present invention is characterized by containing M alone having a crystal structure (M is at least one element selected from Sn, Pb, Sb, Bi, In, Zn, or Au).

The method for producing the M-containing silicon material of the present invention includes:
A step of cooling the molten metal containing Ca, M (M is at least one element selected from Sn, Pb, Sb, Bi, In, Zn or Au) and Si to obtain M-containing calcium silicide,
Reacting the M-containing calcium silicide with an acid to obtain an M-containing polysilane;
Heating the M-containing polysilane at 300 ° C. or higher;
It is characterized by including.

  The M-containing silicon material of the present invention can be a suitable silicon material.

2 is an X-ray diffraction profile of an M-containing silicon material of Example 1. FIG. 2 is a scanning electron microscope image of a cross section of the M-containing calcium silicide particles of Example 1. FIG. 2 is a scanning electron microscope image of a cross section of particles of the M-containing silicon material of Example 1. FIG. It is a graph of the relationship between the cycle number in Evaluation Example 3 and a capacity maintenance rate.

  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.

  The M-containing silicon material of the present invention is characterized by containing M alone having a crystal structure (M is at least one element selected from Sn, Pb, Sb, Bi, In, Zn, or Au).

The method for producing the M-containing silicon material of the present invention includes:
A step of cooling the molten metal containing Ca, M (M is at least one element selected from Sn, Pb, Sb, Bi, In, Zn or Au) and Si to obtain M-containing calcium silicide,
Reacting the M-containing calcium silicide with an acid to obtain an M-containing polysilane;
Heating the M-containing polysilane at 300 ° C. or higher;
It is characterized by including.

  Hereinafter, the present invention will be described along with a method for producing an M-containing silicon material.

First, a step of cooling the molten metal containing Ca, M (M is at least one element selected from Sn, Pb, Sb, Bi, In, Zn, or Au) and obtaining M-containing calcium silicide (hereinafter referred to as the first) (Sometimes referred to as a process). As Ca, M, and Si used in the first step, elemental elements or alloys of these elements are preferable. CaSi ₂ may be used as a raw material.

  M is a metal that does not form a compound with Si. In other words, when comparing the thermodynamic stability between Si and M alone and a compound of MSi, M is a more stable metal. Sn, Pb, Sb, Bi, In, Zn, and Au are all metals that satisfy this condition. Furthermore, Sn, Pb, Sb, Bi, In, Zn, and Au are all reported to function as a negative electrode active material for a battery, and the M-containing silicon material of the present invention is used as a negative electrode active material for a battery. Is advantageous in some cases.

Each of Ca, M and Si may be melted separately and mixed to form a molten metal, or the two may be mixed and melted, and the remaining one may be mixed to form a molten metal. Three members may be mixed and melted. The melting point of Ca is 842 ° C., the melting point of Si is 1410 ° C., the melting point of M is Sn 232 ° C., Pb is 327 ° C., Sb is 631 ° C., Bi is 272 ° C., In is 157 ° C., Zn is 420 ° C. Au is 1064 ° C. And since Ca is a light metal which has a boiling point of 1484 ° C. and easily scatters, it is preferable to use molten metal at a temperature lower than the boiling point of Ca in order to suppress a decrease in Ca. Further, since the melting point of CaSi ₂ is 1020 ° C., after melting CaSi ₂ , M may be mixed to form a molten metal. In a molten metal, what is necessary is just to determine the compounding quantity of Ca, M, and Si along the composition of desired M containing calcium silicide. In the case where Ca or a metal having a low boiling point is used, it is preferable that the amount is increased more than the composition of the desired M-containing calcium silicide considering that it can be reduced in the first step. In particular, since Zn has a boiling point of 907 ° C., when using Zn, it is preferable to use a pressure type device capable of suppressing the vaporization of Zn or a device capable of changing the air density.

  As the heating device in the first step, for example, a high frequency induction heating device, an electric furnace, or a gas furnace can be used. The molten metal process may be performed under pressure or reduced pressure, or in an inert gas atmosphere such as argon.

When M is Sn, Pb, Sb, Bi, In, or Zn, when the molten metal is cooled, first, layered crystals of CaSi ₂ are formed, and then M alone precipitates as crystals in the CaSi ₂ matrix. Thus, it is estimated that M-containing calcium silicide is produced. When M is Au, when the molten metal is cooled, first, Au alone is precipitated in a dispersed state in CaSi ₂ in a solution state, and then CaSi ₂ becomes a crystal and M-containing calcium silicide is produced. Presumed. It is preferable that the M simple substance is uniformly dispersed in the CaSi ₂ matrix.

When the M-containing calcium silicide is expressed by a composition formula, CaM _e Si _f (0 <e <1.2, 1.2 ≦ f ≦ 3) is obtained. Note that inevitable impurities and the like are not considered in the above composition formula. In an ideal composition formula of calcium silicide, f = 2 is satisfied. However, since Si alone or CaSi may be present in the M-containing calcium silicide, the above composition formula is obtained.

If the value of e is too large, the state where M is present in the CaSi ₂ matrix may not be maintained.

If the value of f is too small, the state in which M is present in the CaSi ₂ matrix may not be maintained. Moreover, the amount of Ca becomes relatively high, and Ca ₁₄ Si _{19 that} is not layered in the M-containing calcium silicide exists, which may adversely affect the performance of the M-containing silicon material of the present invention. If the value of f is too large, the amount of Si alone becomes too large, which may adversely affect the performance of the M-containing silicon material of the present invention.

  Preferred e and f ranges are 0.1 ≦ e ≦ 1, 0.3 ≦ e ≦ 0.9, 0.5 ≦ e ≦ 0.8, 1.7 ≦ f ≦ 2.7, 1.8 ≦. For example, f ≦ 2.5 and 1.9 ≦ f ≦ 2.3.

  The obtained M-containing calcium silicide may be pulverized or further classified.

Next, a process of obtaining M-containing polysilane by reacting the M-containing calcium silicide with an acid (hereinafter sometimes referred to as a second process) will be described. In the second step, Si forms Si—H bonds while Ca is substituted with acid H in the layered CaSi ₂ constituting the M-containing calcium silicide. The M-containing polysilane has a layer shape because the basic skeleton of the Si layer of CaSi ₂ of the raw material M-containing calcium silicide is maintained.

  Acids include hydrofluoric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, nitric acid, phosphoric acid, formic acid, acetic acid, methanesulfonic acid, tetrafluoroboric acid, hexafluorophosphoric acid, hexafluoro Examples include arsenic acid, fluoroantimonic acid, hexafluorosilicic acid, hexafluorogermanic acid, hexafluorotin (IV) acid, trifluoroacetic acid, hexafluorotitanic acid, hexafluorozirconic acid, trifluoromethanesulfonic acid, and fluorosulfonic acid The These acids may be used alone or in combination.

  As the acid, it may be preferable to employ an acid capable of generating a fluorine anion. By adopting the acid, Si—O bonds that can occur in the M-containing polysilane and bonds between Si and anions of other acids (for example, Si—Cl bond in the case of hydrochloric acid) can be reduced. In addition, when a Si-O bond and a Si-Cl bond exist in M containing polysilane, a Si-O bond and a Si-Cl bond may exist in M containing silicon material even if it passes through the following process. In a lithium ion secondary battery employing an M-containing silicon material having a Si—O bond or a Si—Cl bond as a negative electrode active material, if the Si—O bond or the Si—Cl bond inhibits the migration of lithium ions to some extent. Presumed.

In the second step, the acid is preferably used in excess of Ca contained in the M-containing calcium silicide in a molar ratio. The second step may be performed without a solvent, but it is preferable to employ water as a solvent from the viewpoint of separation of the target product and removal of by-products such as CaCl ₂ . That is, the acid is preferably used as an aqueous solution. In addition, depending on the type of M, M may react with an acid to form M ions, which may be eluted into an acid aqueous solution. In order to suppress the elution of M, the acid aqueous solution preferably has a low concentration.

  The reaction conditions in the second step are preferably reduced pressure conditions such as vacuum or an inert gas atmosphere, and are preferably temperature conditions of room temperature or lower such as an ice bath. What is necessary is just to set the reaction time of a 2nd process suitably.

The chemical reaction of the second step when hydrochloric acid is used as the acid is shown as an ideal reaction formula as follows.
3CaSi ₂ + 6HCl → Si ₆ H ₆ + 3CaCl ₂
In the above reaction formula, Si ₆ H ₆ corresponds to an ideal polysilane.

In the second step, it is preferably carried out in the presence of water, and because Si ₆ H ₆ is capable of reacting with water, will usually be obtained with compounds polysilane is Si ₆ H ₆ hardly, Si ₆ Obtained as a compound represented by H _s (OH) _t X _u (X is an element or group derived from an anion of acid, s + t + u = 6, 0 <s <6, 0 <t <6, 0 <u <6) . Here, inevitable impurities such as Ca that can remain in the polysilane are not considered.

Therefore, when the M-containing polysilane is represented by a composition formula, M _e Si _f H _a (OH) _b X _c (X is an element or group derived from an anion of an acid, 0 <e <1.2, 1.2 ≦ f ≦ 3, 0 <a <f, 0 <b <f, 0 <c <f, a + b + c ≦ f).

For ease of understanding, indicating composition formula of only M and Si in M-containing _polysilane, and _{M e Si f (0 <e} <1.2,1.2 ≦ f ≦ 3). Preferred ranges of e and f are 0.1 ≦ e ≦ 1, 0.3 ≦ e ≦ 0.9, 0.5 ≦ e ≦ 0.8, 1.7 ≦ f ≦ 2.7, 1.8 ≦ For example, f ≦ 2.5 and 1.9 ≦ f ≦ 2.3.

  In the acid treatment in the second step, although M may be slightly eluted, the crystalline state of M is maintained even in the M-containing polysilane. It is preferable that M alone is uniformly dispersed in the polysilane matrix.

  Next, a step of heating the M-containing polysilane at 300 ° C. or higher (hereinafter sometimes referred to as a third step) will be described. In the third step, the M-containing polysilane is heated at 300 ° C. or higher to release hydrogen, water, and the like, thereby obtaining an M-containing silicon material. In the M-containing silicon material, M exists in a crystalline state. In the M-containing silicon material, it is preferable that M is uniformly dispersed in the silicon matrix.

The chemical reaction in the third step is represented by an ideal reaction formula as follows.
Si ₆ H ₆ → 6Si + 3H ₂ ↑

However, M-containing polysilane actually used in the third step _{M e Si f H a (OH} ) b X c (X is an anion derived from an element or group of acid, 0 <e <1.2,1.2 ≦ f ≦ 3, 0 <a <f, 0 <b <f, 0 <c <f, a + b + c ≦ f), and also contains inevitable impurities, so that the actually obtained M-containing silicon material _{is, M e Si f H p O} q X r (X is an anion derived from an element or group of acid, 0 <e <1.2,1.2 ≦ f ≦ 3,0 ≦ p <a, 0 ≦ q ≦ b, 0.ltoreq.r.ltoreq.c, p + q + r.ltoreq.f, where a, b and c are defined by the composition formula of the M-containing polysilane), and further contain inevitable impurities.

  In the composition formula of the M-containing silicon material, p is preferably in the range of 0 ≦ p <0.5, more preferably in the range of 0 ≦ p <0.3, and in the range of 0 ≦ p <0.1. More preferably, p = 0 is most preferable. In the composition formula of the M-containing silicon material, q is preferably in the range of 0 ≦ q <0.7, more preferably in the range of 0 ≦ q <0.5, and in the range of 0 ≦ q <0.3. More preferably, the range of 0 ≦ q ≦ 0.2 is particularly preferable. In the composition formula of the M-containing silicon material, r is preferably in the range of 0 ≦ r <0.7, more preferably in the range of 0 ≦ r <0.5, and in the range of 0 ≦ r <0.3. More preferably, the range of 0 ≦ r ≦ 0.2 is particularly preferable.

For ease of understanding, indicating composition formula of only M and Si in M-containing silicon _material, the _{M e Si f (0 <e} <1.2,1.2 ≦ f ≦ 3). Preferred ranges of e and f are 0.1 ≦ e ≦ 1, 0.3 ≦ e ≦ 0.9, 0.5 ≦ e ≦ 0.8, 1.7 ≦ f ≦ 2.7, 1.8 ≦ For example, f ≦ 2.5 and 1.9 ≦ f ≦ 2.3.

  The third step is preferably performed in a non-oxidizing atmosphere having a lower oxygen content than in normal air. Examples of the non-oxidizing atmosphere include a reduced pressure atmosphere including a vacuum and an inert gas atmosphere. The heating temperature is preferably in the range of 350 ° C to 950 ° C, more preferably in the range of 400 ° C to 800 ° C. If the heating temperature is too low, hydrogen may not be released sufficiently, and if the heating temperature is too high, energy is wasted.

  In addition, depending on the type of M, there are those having a low boiling point. Therefore, in order to prevent a decrease in M, the heating temperature in the third step is preferably performed at a temperature lower than the boiling point of M.

  What is necessary is just to set a heating time suitably according to heating temperature. It is preferable to determine the heating time while measuring the amount of hydrogen or the like that escapes from the reaction system. By appropriately selecting the heating temperature and the heating time, the ratio of amorphous silicon and silicon crystallites contained in the produced M-containing silicon material and the size of the silicon crystallites can also be adjusted. By appropriately selecting the heating temperature and the heating time, the shape of the nano-level layer containing amorphous silicon and silicon crystallites contained in the produced M-containing silicon material can be prepared.

The size of the silicon crystallite is preferably nano-sized. Specifically, the silicon crystallite size 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 50 nm, and particularly in the range of 1 nm to 10 nm. preferable. The silicon crystallite size is calculated from Scherrer's equation using X-ray diffraction measurement (XRD measurement) on the silicon material and using the half width of the diffraction peak of the Si (111) plane of the obtained XRD chart.

By the third step, an M-containing silicon material having a structure in which a plurality of plate-like silicon bodies are laminated in the thickness direction can be obtained.

Considering the use of M-containing silicon material as the active material of the secondary battery, the plate-like silicon body has a thickness of 10 nm to 10 nm for efficient insertion and desorption reaction of charge carriers such as lithium ions. The thing within the range of 100 nm is preferable, and the thing within the range of 20 nm-50 nm is more preferable. The length of the plate-like silicon body in the major axis direction is preferably in the range of 0.1 μm to 50 μm. The plate-like silicon body preferably has a (length in the major axis direction) / (thickness) range of 2 to 1000.

  The obtained M-containing silicon material may be pulverized or further classified. As a preferable particle size distribution of the particles of the M-containing silicon material when measured with a general laser diffraction type particle size distribution measuring device, it can be exemplified that the average particle diameter (D50) is in the range of 1 to 40 μm. Preferably, it can be exemplified that the average particle diameter (D50) is in the range of 1 to 30 μm.

  The M-containing silicon material of the present invention can be used as a negative electrode active material for power storage devices such as secondary batteries such as lithium ion secondary batteries, electric double layer capacitors, and lithium ion capacitors. Further, the M-containing silicon material of the present invention can also be used as a material such as a CMOS, a semiconductor memory and a solar cell, or a photocatalytic material.

  Since the M-containing silicon material of the present invention contains a simple substance of metal M, when the M-containing silicon material of the present invention is used as a negative electrode active material of a power storage device, the presence of the M of the present invention is due to the presence of the simple substance of metal M. It can be expected that the conductivity of the silicon material will increase. Furthermore, since the simple substance of the metal M has a lithium ion diffusion coefficient larger than that of silicon, it is presumed that rapid charging / discharging is possible in the power storage device including the M-containing silicon material of the present invention.

  Hereinafter, as a typical example of the power storage device, a lithium ion secondary battery of the present invention including an M-containing silicon material as a negative electrode active material will be described. The lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode including an M-containing silicon material 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, etc. 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 a positive electrode active material, a positive electrode active material that does not contain lithium ions that contribute to charge / discharge, for example, sulfur alone, a compound in which sulfur and carbon are combined, a metal sulfide such as TiS ₂ , V ₂ O ₅ , MnO ₂ and other oxides, polyaniline and anthraquinone, compounds containing these aromatics in the chemical structure, conjugated materials such as conjugated diacetate-based organic substances, 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, acetylene black, ketjen black (registered trademark), vapor grown carbon fiber (Vapor Grown Carbon). Fiber: VGCF) and various metal particles are exemplified. 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 include acrylic resins such as (meth) acrylic acid, styrene-butadiene rubber (SBR), carboxymethylcellulose, alginate such as sodium alginate, ammonium alginate, water-soluble cellulose ester crosslinked product, starch-acrylic acid graft polymer. it can. 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.

  As the negative electrode active material, an M-containing silicon material may be used, and only the M-containing silicon material may be employed, or an M-containing silicon material and a known negative electrode active material may be used in combination. A material in which an M-containing silicon material is coated with carbon may be used as the negative electrode active material.

  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 cyclic esters include ethylene carbonate, propylene carbonate, butylene 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, 1,4-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 M-containing calcium silicide, the M-containing polysilane, the M-containing silicon material, and the lithium ion secondary battery of Example 1 were manufactured as follows.

First Step: Weigh 4.59 g (0.1145 mol) of massive Ca, 5.82 g (0.0490 mol) of powdered Sn, and 4.59 g (0.1634 mol) of powdered Si, In a carbon crucible, the crucible was heated at about 1000 ° C. in an argon gas atmosphere by a high frequency induction heating device to obtain a molten metal containing Ca, Sn, and Si. The molten metal was poured into a predetermined mold and cooled to obtain Sn-containing calcium silicide containing Sn in the calcium silicide matrix. The obtained Sn-containing calcium silicide was pulverized in a mortar and passed through a sieve having an opening of 53 μm. The Sn-containing calcium silicide that passed through a sieve having a mesh size of 53 μm was used as the M-containing calcium silicide of Example 1.

Second Step 5 g of the M-containing calcium silicide of Example 1 was added to 100 mL of 2.5 mass% HCl aqueous solution in an ice bath under an argon gas atmosphere, and stirred for 1.5 hours. The reaction solution was filtered, the residue was washed with distilled water and acetone, and further dried under reduced pressure at room temperature for 12 hours or more to obtain 3 g of Sn-containing polysilane. This was designated M-containing polysilane of Example 1.

Third Step The M-containing polysilane of Example 1 was heated at 900 ° C. for 1 hour in an argon gas atmosphere to obtain a Sn-containing silicon material. The Sn-containing silicon material was pulverized in a mortar and passed through a sieve having an opening of 20 μm. The Sn-containing silicon material that passed through a sieve having an opening of 20 μm was used as the M-containing silicon material of Example 1.

-Lithium ion secondary battery manufacturing process Using the M containing silicon material of Example 1, the lithium ion secondary battery of Example 1 was manufactured as follows.

  45 parts by mass of the M-containing silicon material of Example 1 as the negative electrode active material, 40 parts by mass of graphite as the negative electrode active material, 10 parts by mass of polyamideimide as the binder, 5 parts by mass of acetylene black as the conductive auxiliary agent, and An appropriate amount of N-methyl-2-pyrrolidone was mixed to form a slurry.

  An electrolytic copper foil having a thickness of 20 μm was prepared as a current collector. The slurry was applied to the surface of the copper foil using a doctor blade so as to form a film. The copper foil coated with the slurry was dried at 80 ° C. for 20 minutes to remove N-methyl-2-pyrrolidone by volatilization. As a result, a copper foil having a negative electrode active material layer formed on the surface was obtained. The copper foil was compressed with a roll press so that the negative electrode active material layer had a thickness of 20 μm to obtain a bonded product. This joined product was dried by heating under reduced pressure at 200 ° C. for 2 hours to obtain a negative electrode.

The negative electrode was cut into a diameter of 11 mm and used as an evaluation electrode. A metal lithium foil was cut to a diameter of 13 mm to make a counter electrode. As a separator, a glass filter (Hoechst Celanese) and celgard 2400 (Polypore Corporation), which is a single-layer polypropylene, were prepared. It was also prepared an electrolyte solution obtained by dissolving LiPF ₆ at 1 mol / L in a solvent obtained by mixing 50 parts by volume of ethylene carbonate and diethyl carbonate 50 parts by volume. Two kinds of separators were sandwiched between the counter electrode and the evaluation electrode in the order of the counter electrode, the glass filter, celgard 2400, and the evaluation electrode, thereby forming an electrode body. This electrode body was accommodated in a coin-type battery case CR2032 (Hosen Co., Ltd.), and an electrolyte was further injected to obtain a coin-type battery. This was designated as the lithium ion secondary battery of Example 1.

(Comparative Example 1)
The lithium ion secondary battery of Comparative Example 1 was manufactured in the same manner as in Example 1 except that CaSi ₂ was used in place of the M-containing calcium silicide of Example 1 in the second process without performing the first process. did.

(Evaluation example 1)
The X-ray diffraction of the M-containing calcium silicide, M-containing polysilane and M-containing silicon material of Example 1 was measured with a powder X-ray diffractometer. From any X-ray diffraction profile, a peak of Sn crystal was observed. FIG. 1 shows an X-ray diffraction profile of the M-containing silicon material of Example 1. In FIG. 1, the peak marked with ● is the peak of Sn crystal. From the X-ray diffraction profile of FIG. 1, a broad peak showing nano-sized silicon crystallites was confirmed at around 28 degrees along with the Sn crystal peak. In addition, from the X-ray diffraction profile of the M-containing calcium silicide of Example 1, a peak indicating the CaSi ₂ crystal was confirmed together with the peak of the Sn crystal.

(Evaluation example 2)
The cross sections of the particles of M-containing calcium silicide and M-containing silicon material of Example 1 were observed with a scanning electron microscope (SEM), and further elemental analysis was performed with energy dispersive X-ray analysis (EDX). FIG. 2 shows an SEM image of the M-containing calcium silicide of Example 1, and FIG. 3 shows an SEM image of the M-containing silicon material of Example 1. From the result of EDX, it was confirmed in the SEM image of FIG. 2 that Ca and Si were present throughout and that the light color was Sn. Similarly, from the results of EDX, it was confirmed that Si was present throughout the SEM image of FIG. 3 and that Sn was present dispersed in the form of dots throughout.

(Evaluation example 3)
For each of the three lithium ion secondary batteries of Example 1 and Comparative Example 1, discharge was performed at 0.2 mA until the voltage of the evaluation electrode with respect to the counter electrode reached 0.01 V, and until the voltage of the evaluation electrode with respect to the counter electrode reached 1 V 50 charge / discharge cycles for charging at 0.5 mA were performed. (Capacity of each cycle / initial charge capacity) × 100 was calculated as a capacity maintenance rate (%). The results are shown in FIG.

  In Evaluation Example 3, occlusion of Li in the evaluation electrode is called discharge, and discharging Li from the evaluation electrode is called charging.

  FIG. 4 shows that the capacity retention rate of the lithium ion secondary battery of Example 1 is significantly superior to the capacity retention rate of the lithium ion secondary battery of Comparative Example 1. The main reason for this result was that M of the M-containing silicon material used in the lithium ion secondary battery of Example 1 improved the conductivity of the active material and improved the diffusion rate of lithium ions. Therefore, it is considered that the lithium ion desorption / insertion in the negative electrode active material proceeded efficiently. It was confirmed that the M-containing silicon material of the present invention is a suitable silicon material.

Claims (10)

A step of cooling the molten metal containing Ca, M (M is at least one element selected from Sn, Pb, Sb, Bi, In, Zn or Au) and Si to obtain M-containing calcium silicide,
Reacting the M-containing calcium silicide with an acid to obtain an M-containing polysilane;
Heating the M-containing polysilane at 300 ° C. or higher;
A method for producing an M-containing silicon material, comprising:   The method for producing an M-containing silicon material according to claim 1, wherein M contained in the M-containing calcium silicide, the M-containing polysilane, and / or the M-containing silicon material has a crystal structure of M alone.   An M-containing calcium silicide containing M alone having a crystal structure (M is at least one element selected from Sn, Pb, Sb, Bi, In, Zn, or Au).   The M-containing calcium silicide according to claim 3, wherein M is contained in the calcium silicide matrix.   An M-containing polysilane containing M alone having a crystal structure (M is at least one element selected from Sn, Pb, Sb, Bi, In, Zn, or Au).   6. The M-containing polysilane according to claim 5, wherein M is contained in the polysilane matrix.   An M-containing silicon material containing M alone (M is at least one element selected from Sn, Pb, Sb, Bi, In, Zn, or Au) having a crystal structure.   The M-containing silicon material according to claim 7, wherein M is contained in a silicon matrix.   The M-containing silicon material according to claim 7 or 8, wherein the M-containing silicon material is a particle having a structure in which a plurality of plate-like silicon bodies are laminated in a thickness direction.   A power storage device comprising the M-containing silicon material according to claim 7.