JP5737447B2 - Copper-containing layered polysilane, negative electrode active material, and power storage device - Google Patents

Description

  The present invention relates to a layered polysilane for a negative electrode active material used in a power storage device such as a lithium ion secondary battery, and a power storage device such as a secondary battery, an electric double layer capacitor, and a lithium ion capacitor using the negative electrode active material. It is.

  A lithium ion secondary battery is a secondary battery having a high charge / discharge capacity and capable of high output. Currently, it is mainly used as a power source for portable electronic devices, and further expected as a power source for electric vehicles that are expected to be widely used in the future. Lithium ion secondary batteries have active materials capable of inserting and extracting lithium (Li) in the positive electrode and the negative electrode, respectively. And it operates by moving lithium ions in the electrolyte provided between the two electrodes.

  In lithium ion secondary batteries, lithium-containing metal composite oxides such as lithium cobalt composite oxide are mainly used as the active material for the positive electrode, and carbon materials having a multilayer structure are mainly used as the active material for the negative electrode. Yes. The performance of the lithium ion secondary battery depends on the materials of the positive electrode, the negative electrode, and the electrolyte constituting the secondary battery. In particular, research and development of active material that forms an active material is being actively conducted. For example, silicon or silicon oxide having a higher capacity than carbon has been studied as a negative electrode active material.

  By using silicon as the negative electrode active material, a battery having a higher capacity than that using a carbon material can be obtained. However, silicon has a large volume change due to insertion and extraction of Li during charge and discharge. Therefore, there is a problem that silicon is pulverized and falls off or peels from the current collector, and the charge / discharge cycle life of the battery is short. Therefore, by using silicon oxide as the negative electrode active material, volume change associated with insertion and extraction of Li during charge and discharge can be suppressed more than silicon.

For example, the use of silicon oxide (SiO _x : x is about 0.5 ≦ x ≦ 1.5) as a negative electrode active material has been studied. It is known that SiO _x decomposes into Si and SiO ₂ when heat-treated. This is called disproportionation reaction, and it is separated into two phases of Si phase and SiO ₂ phase by solid internal reaction. The Si phase obtained by separation is very fine. Further, the SiO ₂ phase covering the Si phase has a function of suppressing the decomposition of the electrolytic solution. Therefore, the secondary battery using the negative electrode active material composed of SiO _x decomposed into Si and SiO ₂ has excellent cycle characteristics.

As the silicon particles constituting the Si phase of SiO _x are finer, the secondary battery using the silicon particles as the negative electrode active material has improved cycle characteristics. Therefore, Japanese Patent No. 3806333 (Patent Document 1) describes a method of heating and sublimating metallic silicon and SiO ₂ to form silicon oxide gas and cooling it to produce SiO _x . According to this method, the particle size of the silicon particles constituting the Si phase can be set to a nanosize of 1-5 nm.

JP 2009-102219 (Patent Document 2) discloses that a silicon raw material is decomposed to an elemental state in a high-temperature plasma, and rapidly cooled to a liquid nitrogen temperature to obtain silicon nanoparticles. A manufacturing method for fixing in a SiO ₂ —TiO ₂ matrix by a sol-gel method or the like is described.

  However, in the manufacturing method described in Patent Document 1, the matrix is limited to a sublimable material. Further, in the manufacturing method described in Patent Document 2, high energy is required for plasma discharge. Furthermore, the silicon composites obtained by these production methods have a disadvantage that the dispersibility of Si-phase silicon particles is low and they are likely to aggregate. When Si particles are aggregated to increase the particle size, a secondary battery using the same as a negative electrode active material has a low initial capacity and cycle characteristics.

By the way, in recent years, nanosilicon materials that are expected to be used in various fields such as semiconductors, electrical / electronics, and the like have been developed. For example, Physical Review B (1993), vol 48, 8172-8189 (Non-Patent Document 1) describes a method of synthesizing layered polysilane by reacting hydrogen chloride (HCl) with calcium disilicide (CaSi ₂ ). In addition, it is described that the layered polysilane thus obtained can be used for a light emitting device or the like.

  JP 2011-090806 A (Patent Document 3) describes a lithium ion secondary battery using layered polysilane as a negative electrode active material.

Japanese Patent No. 3806333 JP 2009-102219 A JP 2011-090806 JP

Physical Review B (1993), vol48,8172-8189

  However, the negative electrode active material composed of layered polysilane described in Patent Document 3 has low electron conductivity and insufficient rate characteristics, and initial efficiency is also insufficient. The present invention has been made in view of such circumstances, and a power storage device including a copper-containing layered polysilane used as a negative electrode active material with improved electron conductivity and a negative electrode using the copper-containing layered polysilane as a negative electrode active material. Providing a device is a problem to be solved.

The feature of the copper-containing layered polysilane of the present invention that solves the above problems is for a negative electrode active material of a secondary battery, and has a structure in which a plurality of six-membered rings composed of silicon atoms are linked to each other as a basic skeleton ( The layered polysilane represented by (SiH) _n , and copper which is present between the layers of the layered polysilane and contained in an amount of 0.01 to 50% by mass.

The feature of the copper-containing layered polysilane of the second invention is for a negative electrode active material of a secondary battery, and has a structure in which a plurality of six-membered rings composed of silicon atoms are connected to each other as a basic skeleton (SiH) _n The layered polysilane represented by the formula (1) and copper contained in the pores of the layered polysilane and contained in an amount of 0.01 to 50% by mass.

A feature of the copper-containing layered polysilane of the third invention is for a negative electrode active material of a secondary battery, and has a structure in which a plurality of six-membered rings composed of silicon atoms are connected to each other and has a composition formula (SiH) _n as a basic skeleton. It is to consist of the layered polysilane shown by (5) and copper which is grown on the layered polysilane and contained in an amount of 0.01 to 50% by mass.

  In addition, the negative electrode active material of the present invention is characterized by comprising copper-containing nanosilicon obtained by heat-treating the copper-containing layered polysilane according to the present invention.

  And the characteristic of the electrical storage apparatus of this invention exists in having a negative electrode containing the negative electrode active material of this invention.

  According to the negative electrode active material of the present invention, the electronic conductivity is improved by including copper. Therefore, the power storage device using the negative electrode active material for the negative electrode has improved rate characteristics.

4 shows an SEM image of nanosilicon according to Example 3. FIG. 3 shows an X-ray diffraction spectrum of nanosilicon according to Example 3. FIG. 2 shows charge / discharge curves of lithium ion secondary batteries according to Example 1, Reference Example and Comparative Example 1. FIG. The charge curve of the lithium ion secondary battery which concerns on Example 1, 2 is shown. The charging / discharging curve of the lithium ion secondary battery which concerns on Example 1, 2 is shown. The charging / discharging curve of the lithium ion secondary battery which concerns on Example 1, 3 is shown.

The copper-containing layered polysilane constituting the negative electrode active material according to the present invention has a structure in which a plurality of six-membered rings composed of silicon atoms are connected, and has a layered polysilane represented by the composition formula (SiH) _n as a basic skeleton. This structure is the same as the layered polysilane produced by the production method described in Non-Patent Document 1, except that it contains copper.

  Copper is contained in the copper-containing layered polysilane in the range of 0.01 to 50% by mass. If the copper content is less than 0.01% by mass, the electron conductivity is slightly improved and is not practical. On the other hand, if the copper content exceeds 50% by mass, the amount of the layered polysilane is relatively reduced, and the charge / discharge capacity is extremely reduced.

  In order to include copper in the layered polysilane, there is a method in which a compound containing copper is mixed when the layered polysilane is produced by the method described in Non-Patent Document 1. According to this method, it is considered that the bonding force between the layered polysilane and copper is improved, and the charge / discharge capacity is improved when the power storage device is used as compared with the case where the copper powder is simply mixed.

  In the copper-containing layered polysilane of the present invention, it is considered that copper particles enter between the layers of the layered polysilane to cover the layered polysilane. Therefore, the oxidation of the layered polysilane is prevented and the irreversible capacity is reduced. Further, expansion / contraction during charging / discharging is suppressed, and cycle characteristics are improved. Furthermore, copper fills the pores and layers of the layered polysilane, thereby reducing the specific surface area and preventing the loss of irreversible capacity due to the generation of SEI.

To produce the copper-containing layered polysilane of the present invention, for example, calcium disilicide (CaSi ₂ ), an acid that extracts calcium (Ca) from calcium disilicide (CaSi ₂ ), and a compound containing copper. React. Here, as an acid for extracting calcium (Ca) from calcium disilicide (CaSi ₂ ), hydrogen chloride (HCl), a mixture of hydrogen fluoride (HF) and hydrogen chloride (HCl) can be used.

The compound containing copper may be metallic copper, but is preferably a compound that dissolves in an aqueous solution of acid that extracts calcium (Ca) from calcium disilicide (CaSi ₂ ). By doing in this way, copper grows on layered polysilane at the time of reaction, and it is thought that copper and layered polysilane become surface contact and bond strength increases.

By the way, the layered polysilane produced by using hydrogen chloride (HCl) described in Non-Patent Document 1 has a large specific surface area and contains a large amount of SiO ₂ component, so that it is used as a negative electrode active material for secondary batteries. There was a defect that was not suitable. For example, in the negative electrode of a lithium ion secondary battery, if the specific surface area is large, the decomposition of the electrolytic solution is promoted, so that the irreversible capacity consumed by the negative electrode increases, and it is difficult to increase the capacity. In addition, if Si, there is no problem, but it is known that when the SiO ₂ component is contained in the negative electrode active material, the initial characteristics are deteriorated.

As a result of intensive research, it became clear that the specific surface area and oxygen content of the resulting layered polysilane change depending on the production conditions of the layered polysilane, and the specific surface area and oxygen content of the nanosilicon obtained by heat-treating it also change. It was. In Non-Patent Document 1 and Patent Document 3, hydrogen chloride (HCl) and calcium disilicide (CaSi ₂ ) are reacted to obtain layered polysilane. Calcium disilicide (CaSi ₂ ) forms a layered crystal in which a Ca atomic layer is inserted between the (111) faces of diamond-type Si, and the layered polysilane is formed by extracting calcium (Ca) by reaction with acid. Is obtained.

  However, it is clear that the use of a mixture of hydrogen fluoride (HF) and hydrogen chloride (HCl) as the acid for extracting Ca increases the specific surface area of the resulting layered polysilane and nanosilicon material, but reduces the amount of oxygen. became. Hereinafter, a method using hydrogen chloride (HCl) is referred to as a first production method, and a method using a mixture of hydrogen fluoride (HF) and hydrogen chloride (HCl) is referred to as a second production method.

<First manufacturing method>
In the first production method, hydrogen chloride (HCl), calcium disilicide (CaSi ₂ ), and a copper compound are reacted. Calcium disilicide (CaSi ₂ ) forms a layered crystal in which a Ca atomic layer is inserted between the (111) faces of diamond-type Si, and the layered polysilane is formed by extracting calcium (Ca) by reaction with acid. Is obtained.

  During the reaction, copper grows on the layered polysilane, and the copper and the layered polysilane are brought into surface contact to increase the bond strength of copper.

<Second production method>
In the second production method, a mixture of hydrogen fluoride (HF) and hydrogen chloride (HCl), calcium disilicide (CaSi ₂ ), and a copper compound are reacted. Calcium disilicide (CaSi ₂ ) forms a layered crystal in which a Ca atomic layer is inserted between the (111) faces of diamond-type Si, and the layered polysilane is formed by extracting calcium (Ca) by reaction with acid. Is obtained.

  In this production method, a mixture of hydrogen fluoride (HF) and hydrogen chloride (HCl) is used as the acid. By using hydrogen fluoride (HF), SiO generated during synthesis or purification is etched, thereby reducing the amount of oxygen. Even when only hydrogen fluoride (HF) is used, a layered polysilane can be obtained, but it is not preferable because it has high activity and is oxidized by a small amount of air, and conversely increases the amount of oxygen. When only hydrogen chloride (HCl) is used, it is the same as in the first production method, and only layered polysilane having a large amount of oxygen can be obtained.

The composition ratio of hydrogen fluoride (HF) and hydrogen chloride (HCl) is preferably in the range of HF / HCl = 1/10000 to 1/1 in molar ratio. If the amount of hydrogen fluoride (HF) exceeds this ratio, impurities such as CaF ₂ and CaSiO are generated, and it is difficult to separate this impurity from the layered polysilane, which is not preferable. If the amount of hydrogen fluoride (HF) is less than this ratio, the effect of etching with HF may be weakened.

As for the compounding ratio of the mixture of hydrogen fluoride (HF) and hydrogen chloride (HCl) and calcium disilicide (CaSi ₂ ), it is desirable to make the acid excessive from the equivalent. In the actual reaction, hydrogen fluoride (HF) and Si react as a side reaction to produce SiF ₄ , and CaF ₂ is hardly produced. The reaction atmosphere is preferably carried out in a vacuum or an inert gas atmosphere. In a nitrogen gas atmosphere, silicon nitride (SiN) may be generated, which is not preferable. It has also been clarified that according to the production method of the present invention, the reaction time is shorter than that in the first production method. If the reaction time is too long, Si and HF further react to produce SiF ₄ , and therefore a reaction time of about 0.25 to 24 hours is sufficient. The reaction easily occurs even at room temperature.

CaCl _{2 and the} like are generated by the reaction, but can be easily removed by washing with water, and purification of the layered polysilane containing copper is easy.

<Negative electrode active material of the present invention>
This negative electrode active material is made of copper-containing nanosilicon obtained by heat-treating the copper-containing layered polysilane of the present invention. Heat treatment is preferably performed at a temperature exceeding 300 ° C. in a non-oxidizing atmosphere excluding nitrogen gas.

  Examples of the non-oxidizing atmosphere include an inert gas atmosphere and a vacuum atmosphere. In a nitrogen gas atmosphere, silicon nitride may be generated, which is not preferable. The heat treatment temperature is preferably in the range of 300 ° C to 800 ° C, particularly preferably in the range of 400 ° C to 600 ° C.

The specific surface area of the layered polysilane produced by the first production method is relatively small as about 20 m ² / g, but the specific surface area of the layered polysilane produced by the second production method is as large as about 122.3 m ² / g. .

The specific surface area of nanosilicon obtained by heat-treating the layered polysilane produced by the first production method is as small as about 7 m ² / g, and by heat-treating the layered polysilane produced by the second production method The specific surface area of the obtained nanosilicon is 55 m ² / g or less, which is smaller than that of the layered polysilane.

  The oxygen content of the layered polysilane produced by the first production method is relatively high at about 40% by mass, but the oxygen content of the layered polysilane produced by the second production method is very small at 30% by mass or less. The oxygen amount is a numerical value measured by energy dispersive X-ray spectroscopy (EDX).

  The amount of oxygen in nanosilicon obtained by heat-treating the layered polysilane produced by the first production method is relatively large at about 39% by mass, but the layered polysilane produced by the second production method is heat-treated. The amount of oxygen in the nanosilicon obtained in this way is as small as 20% by mass or less.

  The particle diameter of the nanosilicon material thus obtained is preferably from 0.5 nm to 30 nm, particularly preferably from 1 nm to 10 nm, when used as an electrode active material for a power storage device.

<Negative electrode of power storage device>
In order to produce, for example, a negative electrode of a non-aqueous secondary battery using the copper-containing layered polysilane or copper-containing nanosilicon of the present invention as a negative electrode active material, a negative electrode active material powder, a conductive aid such as carbon powder, and a binder Apply a suitable amount of an organic solvent and mix to make a slurry. It can be produced by drying or curing.

  The binder is required to bind the active material or the like in as small an amount as possible, but the addition amount is preferably 0.5 wt% to 50 wt% of the total of the active material, the conductive auxiliary agent, and the binder. When the binder is less than 0.5 wt%, the moldability of the electrode is lowered, and when it exceeds 50 wt%, the energy density of the electrode is lowered.

  The binder includes Polyvinylidene Fluoride (PVdF), Polytetrafluoroethylene (PTFE), Styrene-Butadiene Rubber (SBR), Polyimide (PI), Polyamideimide (PAI), Carboxymethylcellulose (CMC), Polychlorinated Examples include vinyl (PVC), methacrylic resin (PMA), polyacrylonitrile (PAN), modified polyphenylene oxide (PPO), polyethylene oxide (PEO), polyethylene (PE), polypropylene (PP), polyacrylic acid (PAA), etc. The Among these, when polyvinylidene fluoride (PVdF) is used, initial efficiency is improved and cycle characteristics are also improved.

  A current collector is a chemically inert electronic high conductor that keeps current flowing through an electrode during discharging or charging. The current collector can adopt a shape such as a foil or a plate, but is not particularly limited as long as it has a shape according to the purpose. As the current collector, for example, a copper foil or an aluminum foil can be suitably used.

As the negative electrode active material, known materials such as graphite, hard carbon, silicon, carbon fiber, tin (Sn), and silicon oxide may be mixed with the above-described copper-containing layered polysilane or copper-containing nanosilicon. Among these, a silicon oxide represented by SiO _x (0.3 ≦ x ≦ 1.6) is particularly preferable. Each particle of the silicon oxide powder is composed of SiO _x decomposed into fine Si and SiO ₂ covering Si by a disproportionation reaction. When x is less than the lower limit value, the Si ratio increases, so that the volume change during charge / discharge becomes too large and the cycle characteristics deteriorate. When x exceeds the upper limit value, the Si ratio decreases and the energy density decreases. A range of 0.5 ≦ x ≦ 1.5 is preferable, and a range of 0.7 ≦ x ≦ 1.2 is more desirable.

In general, when oxygen is turned off, it is said that almost all SiO disproportionates and separates into two phases at 800 ° C. or higher. Specifically, the raw material silicon oxide powder containing amorphous SiO powder is subjected to heat treatment at 800 to 1200 ° C. for 1 to 5 hours in an inert atmosphere such as in a vacuum or an inert gas. A silicon oxide powder containing two phases of an amorphous SiO ₂ phase and a crystalline Si phase is obtained.

As silicon oxides, with respect to SiO _x may be used as complexed with from 1 to 50% by weight of carbon material. By combining carbon materials, cycle characteristics are improved. If the composite amount of the carbon material is less than 1% by mass, the effect of improving the conductivity cannot be obtained, and if it exceeds 50% by mass, the proportion of SiO _x is relatively decreased and the negative electrode capacity is decreased. The composite amount of the carbon material is preferably in the range of 5 to 30% by mass, more preferably in the range of 5 to 20% by mass with respect to SiO _x . A CVD method or the like can be used to combine a carbon material with SiO _x .

  The silicon oxide powder desirably has an average particle size in the range of 1 μm to 10 μm. When the average particle size is larger than 10 μm, the charge / discharge characteristics of the power storage device are deteriorated, and when the average particle size is smaller than 1 μm, the particles are aggregated into coarse particles.

  The conductive assistant is added to increase the conductivity of the electrode. Carbon black, graphite, acetylene black (AB), ketjen black (KB), vapor grown carbon fiber (VGCF), etc., which are carbonaceous fine particles, are used alone or in combination of two or more as conductive aids. Can be added. The amount of the conductive aid used is not particularly limited, but can be, for example, about 20 to 100 parts by mass with respect to 100 parts by mass of the active material. If the amount of the conductive auxiliary is less than 20 parts by mass, an efficient conductive path cannot be formed, and if it exceeds 100 parts by mass, the moldability of the electrode deteriorates and the energy density decreases. Note that when the silicon oxide combined with the carbon material is used as the active material, the amount of the conductive auxiliary agent added can be reduced or eliminated.

  There is no restriction | limiting in particular in an organic solvent, The mixture of a some solvent may be sufficient. N-methyl-2-pyrrolidone and N-methyl-2-pyrrolidone and ester solvents (ethyl acetate, n-butyl acetate, butyl cellosolve acetate, butyl carbitol acetate, etc.) or glyme solvents (diglyme, triglyme, tetraglyme, etc.) The mixed solvent is particularly preferred.

  When the power storage device of the present invention is a lithium ion secondary battery, the negative electrode can be pre-doped with lithium. In order to dope lithium into the negative electrode, for example, an electrode formation method in which a half battery is assembled using metallic lithium as the counter electrode and electrochemically doped with lithium can be used. The amount of lithium doped is not particularly limited.

  When the power storage device of the present invention is a lithium ion secondary battery, known positive electrodes, electrolytic solutions, and separators that are not particularly limited can be used. The positive electrode may be anything that can be used in a non-aqueous secondary battery. The positive electrode has a current collector and a positive electrode active material layer bound on the current collector. The positive electrode active material layer includes a positive electrode active material and a binder, and may further include a conductive additive. The positive electrode active material, the conductive additive, and the binder are not particularly limited as long as they can be used in the nonaqueous secondary battery.

Examples of the positive electrode active material include lithium metal, LiCoO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , Li ₂ MnO ₃ , and sulfur. The current collector is not particularly limited as long as it is generally used for the positive electrode of a lithium ion secondary battery, such as aluminum, nickel, and stainless steel. As the conductive auxiliary agent, the same ones as described in the above negative electrode can be used.

The electrolytic solution is obtained by dissolving a lithium metal salt as an electrolyte in an organic solvent. The electrolytic solution is not particularly limited. As the organic solvent, an aprotic organic solvent such as propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) or the like should be used. Can do. As the electrolyte to be dissolved, a lithium metal salt soluble in an organic solvent such as LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiI, LiClO ₄ , LiCF ₃ SO ₃ can be used.

For example, lithium metal salts such as LiClO ₄ , LiPF ₆ , LiBF ₄ , and LiCF ₃ SO ₃ in organic solvents such as ethylene carbonate, dimethyl carbonate, propylene carbonate, and dimethyl carbonate at a concentration of about 0.5 mol / L to 1.7 mol / L. A dissolved solution can be used.

  A separator will not be specifically limited if it can be used for a non-aqueous secondary battery. The separator separates the positive electrode and the negative electrode and holds the electrolytic solution, and a thin microporous film such as polyethylene or polypropylene can be used.

  When the power storage device of the present invention is a non-aqueous secondary battery, the shape thereof is not particularly limited, and various shapes such as a cylindrical shape, a stacked shape, and a coin shape can be adopted. Regardless of the shape, a separator is sandwiched between the positive electrode and the negative electrode to form an electrode body, and the space between the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal is used for current collection. After connecting using a lead or the like, the electrode body is sealed in a battery case together with an electrolytic solution to form a battery.

  Hereinafter, embodiments of the present invention will be specifically described with reference to Examples and Comparative Examples.

20 ml of a 36 wt% HCl aqueous solution was brought to 0 ° C. in an ice bath, and 2 g of calcium disilicide (CaSi ₂ ) and 1 g of copper acetate were added thereto and stirred in an argon gas stream. After confirming the completion of foaming, the temperature was raised to room temperature, and the mixture was further stirred at room temperature for 2 hours. Then, 20 ml of distilled water was added, and the mixture was further stirred for 10 minutes. At this time, yellow powder floated.

  The obtained mixed solution was filtered, and the residue was washed with 10 ml of distilled water, then washed with 10 ml of ethanol, and dried under vacuum to obtain 2 g of copper-containing layered polysilane.

  A slurry was prepared by mixing 45 parts by mass of the obtained copper-containing layered polysilane powder, 40 parts by mass of natural graphite powder, 5 parts by mass of acetylene black, and 33 parts by mass of the binder solution. As the binder solution, a solution in which 30% by mass of polyvinylidene fluoride (PVdF) is dissolved in N-methyl-2-pyrrolidone (NMP) is used. This slurry was applied to the surface of an electrolytic copper foil (current collector) having a thickness of about 20 μm using a doctor blade 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 120 ° C. for 56 hours to form a negative electrode having a negative electrode active material layer thickness of 16 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 φ14 mm and the evaluation electrode was cut to φ11 mm, and a separator (Hoechst Celanese glass filter and Celgard “Celgard2400”) was interposed between them to form an electrode body battery. This electrode body battery was accommodated in a battery case (CR2032 type coin battery member, manufactured by Hosen Co., Ltd.). In the battery case, a nonaqueous 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). A secondary battery was obtained.

  Using the copper-containing layered polysilane synthesized in Example 1, a negative electrode was formed in the same manner as in Example 1. A lithium ion secondary battery was obtained in the same manner as in Example 1 except that this negative electrode was used and that polyamide imide (PAI) was used in place of polyvinylidene fluoride (PVdF) as a binder.

1 g of the copper-containing layered polysilane synthesized in Example 1 was weighed and subjected to a heat treatment that was held at 500 ° C. for 1 hour in an argon gas containing O ₂ of 1% by volume or less to obtain a copper-containing nanosilicon powder. An SEM image of this copper-containing nanosilicon powder is shown in FIG. 1, and an XRD diffraction chart is shown in FIG. In FIG. 2, a Cu peak is observed, and it can be seen that Cu is contained in the copper-containing nanosilicon.

  A negative electrode was formed in the same manner as in Example 1 except that this copper-containing nanosilicon powder was used in place of the copper-containing layered polysilane, and a lithium ion secondary battery was obtained in the same manner as in Example 1.

[Reference example]
A layered polysilane powder was obtained in the same manner as in Example 1 except that copper acetate was not added. The layered polysilane powder was mixed with copper powder at 30% by mass and mixed well with stirring. A negative electrode was formed in the same manner as in Example 1 except that this mixed powder was used, and a lithium ion secondary battery was obtained in the same manner as in Example 1.

[Comparative Example 1]
A layered polysilane powder was obtained in the same manner as in Example 1 except that copper acetate was not added. A negative electrode was formed in the same manner as in Example 1 except that this layered polysilane powder was used, and a lithium ion secondary battery was obtained in the same manner as in Example 1.

<Battery characteristics test>
FIG. 3 shows initial charge / discharge characteristics of the lithium ion secondary batteries of Example 1, Reference Example and Comparative Example 1 when charged at 1V. The horizontal axis shows the ratio when each discharge capacity is 100.

  From the comparison between the reference example and the comparative example 1, it can be seen that the charging capacity is increased by adding the copper powder. As shown in Example 1, it can be seen that the inclusion of copper during the synthesis of the layered polysilane significantly increases the charge capacity compared to the case where copper powder is added after the synthesis.

  FIG. 4 shows the initial charging characteristics when the lithium ion secondary batteries of Examples 1 and 2 were charged at 1V. The horizontal axis shows the ratio when each charge capacity is 100. Fig. 5 shows the initial charge / discharge characteristics when charged at 1V. The horizontal axis shows the ratio when each discharge capacity is 100.

  4 and 5 show that it is preferable to use polyvinylidene fluoride (PVdF) rather than polyamideimide (PAI) as the binder of the negative electrode active material layer.

  The initial charge / discharge characteristics of the lithium ion secondary batteries of Examples 1 and 3 when charged at 1 V are shown in FIG. The horizontal axis shows the ratio when each discharge capacity is 100.

  FIG. 6 shows that it is preferable to use copper-containing nanosilicon as the negative electrode active material rather than copper-containing layered polysilane.

  The power storage device of the present invention can be used for secondary batteries, electric double layer capacitors, lithium ion capacitors, and the like. It is also useful as a non-aqueous secondary battery for motor drive of electric vehicles and hybrid vehicles, personal computers, portable communication devices, home appliances, office equipment, industrial equipment, etc. It can be suitably used for driving a motor of an electric vehicle or a hybrid vehicle.

Claims (6)

A layered polysilane represented by a composition formula (SiH) _n as a basic skeleton having a structure in which a plurality of six-membered rings composed of silicon atoms are connected, and a layered polysilane between layers of the layered polysilane. A copper-containing layered polysilane , characterized by comprising copper present in an amount of 0.01 to 50% by mass with respect to the copper-containing layered polysilane. Layered polysilane represented by a composition formula (SiH) _n as a basic skeleton having a structure in which a plurality of six-membered rings composed of silicon atoms are connected, and a pore of the layered polysilane, for a negative electrode active material of a secondary battery A copper-containing layered polysilane comprising copper contained in an amount of 0.01 to 50% by mass relative to the copper-containing layered polysilane. A layered polysilane represented by the composition formula (SiH) _n as a basic skeleton and grown on the layered polysilane, for a negative electrode active material of a secondary battery, having a structure in which a plurality of six-membered rings composed of silicon atoms are connected. The copper-containing layered polysilane is characterized by comprising 0.01 to 50% by mass of copper with respect to the copper-containing layered polysilane.   4. A negative electrode active material comprising a copper-containing nanosilicon obtained by heat-treating the copper-containing layered polysilane according to any one of claims 1 to 3.   5. A power storage device comprising a negative electrode including the negative electrode active material according to claim 1.   6. The power storage device according to claim 5, wherein the negative electrode includes a current collector and a negative electrode active material layer formed on the current collector, and the negative electrode active material layer includes polyvinylidene fluoride (PVdF) as a binder.