JP2011187434A - Negative electrode active material for electricity storage device, and method for producing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode material for an electricity storage device excellent in initial charge and discharge efficiency and cycle characteristics. <P>SOLUTION: In the negative electrode material for an electricity storage device containing at least SnO in the composition thereof, assuming a binding energy value of electrons in an Sn3d<SB>5/2</SB>orbit of an Sn atom in the negative electrode material for electricity storage device as Pl and the binding energy value of electrons in the Sn3d<SB>5/2</SB>orbit of metal Sn as Pm, (Pl-Pm) is 0.01-3.5 eV. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a negative electrode active material used for power storage devices such as non-aqueous secondary batteries represented by lithium ion secondary batteries used in portable electronic devices and electric vehicles, and a method for producing the same.

  In recent years, with the spread of portable personal computers and mobile phones, there is an increasing demand for higher capacity and smaller size of power storage devices such as lithium ion secondary batteries. If the capacity of the electricity storage device is increased, it will be easy to reduce the size of the battery material. Therefore, there is an urgent need to develop an electrode material for the electricity storage device with a higher capacity.

For example, high-potential type LiCoO ₂ , LiCo _1-x Ni _x O ₂ , LiNiO ₂ , LiMn ₂ O _{4 and the} like are widely used as positive electrode materials for lithium ion secondary batteries. On the other hand, a carbonaceous material is generally used as the negative electrode material. These materials function as electrode active materials that reversibly occlude and release lithium ions by charging and discharging, and constitute so-called rocking chair type secondary batteries that are electrochemically connected by a non-aqueous electrolyte or a solid electrolyte. .

  Carbonaceous materials used as active materials (negative electrode active materials) that can occlude or release lithium ions in the negative electrode include graphitic carbon materials, pitch coke, fibrous carbon, and high-capacity soft carbon that is fired at low temperatures. There is. However, since the carbon material has a relatively small lithium insertion capacity, there is a problem that the battery capacity is low. Specifically, even if a stoichiometric amount of lithium insertion capacity can be realized, the battery capacity of the carbon material is limited to about 372 mAh / g.

  Therefore, a negative electrode active material containing SnO has been proposed as a negative electrode active material capable of inserting and extracting lithium ions and having a high capacity density exceeding that of a carbon-based material (see, for example, Patent Document 1). . However, the negative electrode active material proposed in Patent Document 1 cannot relieve the volume change due to the insertion and extraction reactions of Li ions during charge and discharge, and the structure deterioration of the negative electrode active material is significantly cracked when repeatedly charged and discharged. Is likely to occur. As cracks progress, in some cases, cavities are formed in the negative electrode active material and may be pulverized. When a crack occurs in the negative electrode active material, the electron conduction path is interrupted, so that a reduction in discharge capacity (charge / discharge cycle characteristics) after repeated charge / discharge has been a problem.

  In order to solve the above problem, a negative electrode active material composed of an oxide mainly composed of tin oxide and a method for producing the negative electrode active material by a melting method have been proposed (for example, see Patent Document 2). . Furthermore, a manufacturing method by a sol-gel method has been proposed as a method for manufacturing a negative electrode active material made of an oxide containing tin oxide and silicon and having a large specific surface area (see, for example, Patent Document 3). However, the negative electrode active material manufactured by these manufacturing methods has a low ratio of the discharge capacity to the initial charge capacity (initial charge / discharge efficiency), and a decrease in the discharge capacity (cycle characteristics) after repeated charge / discharge is a problem. It was.

  In addition, by using an amorphous oxide mainly composed of tin oxide, a negative electrode active material for a non-aqueous secondary battery that can relieve the volume change associated with insertion and extraction of lithium ions and has an excellent charge / discharge cycle has been proposed. (For example, see Patent Documents 4 and 5). However, these negative electrode active materials contain a considerable amount of oxides other than tin oxide, which are not related to occlusion and release of lithium ions, so as to be amorphous oxides. For this reason, there is a problem that the tin oxide content per unit mass of the negative electrode active material is small and it is difficult to further increase the capacity.

Japanese Patent No. 2887632 Japanese Patent No. 3498380 Japanese Patent No. 3890671 Japanese Patent No. 3605866 Japanese Patent No. 3605875

  A first problem of the present invention is to provide a negative electrode active material for an electricity storage device that can be further increased in capacity as compared with a conventional negative electrode active material and is excellent in charge / discharge cycle characteristics and safety. .

  A second problem of the present invention is to provide a negative electrode active material for an electricity storage device that is excellent in initial charge / discharge efficiency and cycle characteristics.

  A third problem of the present invention is to provide a negative electrode active material for an electricity storage device that is excellent in cycle characteristics as compared with a conventional negative electrode active material.

  As a result of various studies, the present inventors have found that the first problem can be solved by using a negative electrode active material for an electricity storage device containing a high proportion of tin oxide in the composition, and proposed as the present invention. To do. In this specification, the “electric storage device” includes a non-aqueous secondary battery, in particular, a lithium-ion non-aqueous secondary battery used in portable electronic devices such as notebook computers and mobile phones, electric vehicles, and the like. Hybrid capacitors such as ion capacitors are included.

That is, the present invention is the mole% of oxides terms containing the composition of the _{SnO 70~95%, P 2 O 5} 5~30% (SnO 70 mol%, P ₂ O ₅ 30 mole% is not included) The present invention relates to a negative electrode active material for an electricity storage device.

Since the negative electrode active material for an electricity storage device of the present invention contains SnO at a high ratio of 70 to 95% (not including 70 mol%), the content of tin oxide per unit mass of the negative electrode active material is large, and the further high Capacitance can be achieved. Incidentally, SnO ingredient content in the present invention, the tin oxide component other than SnO (SnO _2, etc.) also refers to that summed in terms of SnO.

  In the present invention, the negative electrode active material is preferably substantially amorphous.

  With the above structure, a volume change accompanying insertion and extraction of lithium ions can be reduced, and a negative electrode active material for an electricity storage device having an excellent charge / discharge cycle can be obtained. Note that “substantially amorphous” means that the degree of crystallinity is substantially 0%, which is a 2θ value obtained by powder X-ray diffraction measurement using CuKα rays and is 10 to 60. A diffraction line profile having a broad diffraction line at 10 to 40 ° in a diffraction line profile of 0 ° and no diffraction peak being confirmed.

  The present invention also relates to a method for producing the above negative electrode active material for an electricity storage device, wherein the raw material powder is melted and vitrified in a reducing atmosphere or an inert atmosphere.

  According to this method, it is possible to obtain a negative electrode active material that can be a secondary battery having excellent initial charge / discharge efficiency (ratio of discharge capacity to initial charge capacity). The reason for this can be explained as follows.

  For example, as an example of a non-aqueous secondary battery, it is known that a lithium ion secondary battery undergoes the following reaction at the negative electrode during charging and discharging.

Sn ^{x +} + xe ⁻ → Sn (1)
Sn + yLi ⁺ + ye ⁻ ← → Li _y Sn (2)

First, during the first charge, a reaction in which Sn ^{x +} ions accept electrons and produce metal Sn occurs irreversibly (formula (1)). Subsequently, the produced metal Sn combines with Li ions that have moved from the positive electrode through the electrolytic solution and electrons supplied from the circuit, and a reaction occurs to form a Sn—Li alloy. This reaction occurs as a reversible reaction that proceeds rightward during charging and proceeds leftward during discharging (formula (2)).

Here, focusing on the reaction of the formula (1) that occurs during the first charge, the smaller the energy required for the reaction, the smaller the initial charge capacity, and as a result, the first charge / discharge efficiency is excellent. Here, the smaller the valence of Sn ^{x +} ions (reduced state), the fewer electrons required for the reduction, which is advantageous for improving the initial charge / discharge efficiency of the secondary battery. Therefore, by melting the raw material powder in a reducing atmosphere or an inert atmosphere and vitrifying it, Sn ^{x +} ions can be reduced effectively and the valence can be reduced, and a secondary battery with excellent initial charge efficiency can be obtained. Can be obtained.

  The raw material powder used in the above production method is preferably a composite oxide containing phosphorus and tin.

  By using a composite oxide containing phosphorus and tin as the starting raw material powder, a negative electrode active material excellent in homogeneity can be easily obtained. And the non-aqueous secondary battery with stable discharge capacity is obtained by using the negative electrode material containing the said negative electrode active material as a negative electrode.

In addition, as a result of various studies, the present inventors have used negative electrode active materials containing at least SnO and P ₂ O _5, which are used in power storage devices such as non-aqueous secondary batteries, and used CuKα rays. In the diffraction line profile obtained by powder X-ray diffraction (powder XRD) measurement, by controlling the halo pattern (amorphous halo) due to a broad amorphous component detected at 2θ value of 10 to 45 °, the first The present inventors have found that the second problem can be solved and propose the present invention.

That is, the present invention is a negative electrode active material for an electricity storage device containing at least SnO and P ₂ O _5, and has a 2θ value of 10 to 45 ° in a diffraction line profile obtained by powder X-ray diffraction measurement using CuKα rays. When the curve fitting is performed with two components of a peak component P1 having an amorphous halo and a 2θ value fixed at 22.5 ° in the range and a peak component P2 higher than 22.5 °, P2 The peak apex position is 25.0 to 29.0 ° as a 2θ value.

The present inventors pay attention to the valence of Sn ^{x +} (0 <x ≦ 4) ions in the negative electrode active material for power storage devices and the inclusion state of Sn ^{x +} ions in the phosphate network, and control them for the first time. It has been found that an electricity storage device having excellent discharge efficiency and cycle characteristics can be obtained. Specifically, in the diffraction line profile obtained by the powder X-ray diffraction measurement, the peak component P1 in which the 2θ value is fixed at 22.5 ° for an amorphous halo having a 2θ value of 10 to 45 ° is the phosphate network. It was found that the peak component P2 higher than 22.5 ° can be attributed to a component derived from tin, and the peak apex of P2 obtained by curve fitting an amorphous halo with these two components. It was found that by limiting the position to 25.0 to 29.0 ° with a 2θ value, an electricity storage device having excellent initial charge / discharge efficiency and cycle characteristics can be obtained. The detailed mechanism will be described below.

  For example, as an example of a non-aqueous secondary battery, it is known that a lithium ion secondary battery undergoes the following reaction at the negative electrode during charging and discharging.

Sn ^{x +} + xe ⁻ → Sn (1)
Sn + yLi ⁺ + ye ⁻ ← → Li _y Sn (2)

First, during the first charge, a reaction in which Sn ^{x +} ions accept electrons and produce metal Sn occurs irreversibly (formula (1)). Subsequently, the produced metal Sn combines with Li ions that have moved from the positive electrode through the electrolytic solution and electrons supplied from the circuit, and a reaction occurs to form a Sn—Li alloy. This reaction occurs as a reversible reaction that proceeds rightward during charging and proceeds leftward during discharging (formula (2)).

Here, focusing on the reaction of the formula (1) that occurs during the first charge, the smaller the energy required for the reaction, the smaller the initial charge capacity, and as a result, the first charge / discharge efficiency is excellent. Therefore, the smaller the valence of Sn ^{x +} ions, the fewer the electrons required for reduction, which is advantageous for improving the initial charge / discharge efficiency of the secondary battery.

In the powder X-ray diffraction measurement using CuKα ray, the main peak of the crystalline diffraction line of SnO ₂ (Cassiterite, tetragonal system, space group P4 / nmm) whose Sn atom has a valence of 4 is 26.6 °. (Miller index (hkl) = (110)). On the other hand, the main peak of the crystalline diffraction line of SnO (Romarchite, tetragonal system, space group P42 / mnm) in which the valence of Sn atom is 2 is 29.9 ° (Miller index (hkl) = (101)) Detected. For this reason, the main peak is detected on the high angle side as the Sn atom is lowered in valence.

Since the Sn ^{x +} ion in the negative electrode active material of the present invention is not a crystalline substance (ordered structure) such as SnO or SnO ₂ but an amorphous oxide (disordered structure), the valence x is Sn ^{x +} ion. It exists in a continuously changing state. For this reason, the diffraction line profile obtained by the powder X-ray diffraction measurement becomes a broad scattering band, and the 2θ value at the peak apex of the peak component P2 detected at a higher angle than 22.5 ° is the average of the Sn ^{x +} ions. Reflects the valence. Therefore, by restricting the position of the peak apex of P2 within the above range, it is possible to obtain a secondary battery with excellent initial charge / discharge efficiency.

By the way, when Li _y Sn alloy formation occurs from Sn ^{x +} ions during the initial charge, the negative electrode active material occludes y lithium ions released from the positive electrode material and causes volume expansion. This volume change can be estimated from the viewpoint of crystal structure. For example, since the SnO crystal is a tetragonal system having a crystal unit lattice length of 3.802 Å x 3.802 Å x 4.836 Å, the crystal unit volume is 69.9 Å ³ . Since there are two Sn atoms in this crystal unit cell, the occupied volume per Sn atom is 34.95 ³ . On the other hand, Li _2.6 Sn, Li _3.5 Sn, Li _4.4 Sn, and the like are known as Li _y Sn alloys formed during charging. For example, considering the case where an alloy of Li _4.4 Sn is formed during charging, the length of the unit cell of Li _4.4 Sn (cubic system, space group F23) is 19.78Å × 19.78Å × 19.78Å. The lattice unit volume is 7739 ³ . Since there are 80 Sn atoms in this unit cell, the occupied volume per Sn atom is 96.7 ³ . For this reason, when SnO crystal is used for the negative electrode material, the occupied volume of Sn atoms expands 2.77 times (96.7Å ³ /34.95 ³ ) at the first charge.

Next, at the time of discharge, the reaction formula (2) proceeds leftward, and _y ions of Li ions and electrons are released from the Li _y Sn alloy to form metal Sn, so that the negative electrode active material shrinks in volume. The shrinkage rate in this case is obtained from the crystallographic viewpoint as described above. The length of the unit cell of metal Sn is a tetragonal system of 5.831 Å x 5.831 Å x 3.182 、, and the unit cell volume is 108.2 Å ³ . Since Sn atoms are present four in this lattice, the volume occupied per Sn1 atoms becomes 27.05Å ^3. Therefore, when the Li _y Sn alloy is Li _4.4 Sn, when the discharge reaction in the negative electrode active material proceeds and metal Sn is generated, the occupied volume of Sn atoms is 0.28 times (27.5２ ³ / Shrink to 96.7 cm ³ ).

Further, during the second and subsequent charging, the reaction formula (2) proceeds in the right direction, and the metal Sn occludes y Li ions and electrons, respectively, and an Li _y Sn alloy is formed. Volume expansion. At this time, when Li _4.4 Sn is formed from the metal Sn, the occupied volume of Sn atoms expands to 3.52 times (96.7Å ³ /27.5Å ³ ).

  As described above, since the negative electrode active material containing SnO is remarkably accompanied by a volume change during charge and discharge, the negative electrode active material is easily cracked when repeatedly charged and discharged. As cracks progress, in some cases, cavities are formed in the negative electrode active material and may be pulverized. When a crack occurs in the negative electrode active material, the electron conduction network is divided, so that the charge / discharge capacity is likely to be reduced, which causes a reduction in cycle characteristics.

In the present invention, Sn ^{x +} ions in the negative electrode active material exist in a state where they are included in the phosphate network, so that the volume change of Sn atoms accompanying charge / discharge can be mitigated by the phosphate network. Here, since the valence of the Sn ^{x +} ion is affected by the coordination due to the lone electron pair of the oxygen atom of the phosphate network, the 2θ value at the peak apex of the peak component P2 is only the average valence of the Sn ^{x +} ion. It is also considered that the inclusion state of the phosphate network to Sn ^{x +} ions is also reflected. The negative electrode active material of the present invention controls the inclusion state of the phosphate network to Sn ^{x +} ions by regulating the position of the peak apex of P2 within the above range, and effectively changes the volume of Sn atoms accompanying charging and discharging. Can be relaxed. As a result, it is possible to obtain a secondary battery having excellent cycle characteristics when repeatedly charged and discharged.

Further, the present invention is a negative electrode active material for an electricity storage device containing at least SnO and P ₂ O _5, and has a 2θ value of 10 to 45 ° in a diffraction line profile obtained by powder X-ray diffraction measurement using CuKα rays. When the curve fitting is performed with two components of a peak component P1 having an amorphous halo and a 2θ value fixed at 22.5 ° in the range and a peak component P2 higher than 22.5 °, P1 The peak area A1 and the peak area A2 of P2 satisfy the relationship of A1 / A2 = 0.01-8.

As described above, the peak component P1 can be attributed to a component of the phosphate network, and the peak component P2 can be attributed to a component derived from tin. Therefore, by limiting the peak area ratio A1 / A2 for these peak components to the above range, the inclusion state of the phosphate network to Sn ^{x +} ions can be controlled, and the volume change of Sn atoms accompanying charge / discharge Can be effectively mitigated. As a result, it is possible to obtain a power storage device such as a secondary battery having excellent cycle characteristics when repeatedly charged and discharged.

The negative electrode active material of the present invention preferably contains a composition of mol% and SnO 45 to 95% and P ₂ O _{5 5 to} 55%.

  Moreover, it is preferable that the negative electrode active material of this invention is substantially amorphous.

  With this configuration, a negative electrode active material that can relieve volume changes associated with insertion and extraction of lithium ions, and an electric storage device such as a secondary battery that has excellent charge / discharge cycle characteristics can be obtained. “Substantially amorphous” means that no crystalline diffraction line is detected in powder X-ray diffraction measurement using CuKα rays, and the crystallinity is substantially 0%, specifically Indicates that the crystallinity is 0.1% or less.

  Further, the present invention is a method for producing the above negative electrode active material for an electricity storage device, wherein the raw material powder is melted and vitrified in a reducing atmosphere or an inert atmosphere.

  According to this method, since the valence of Sn ions in the negative electrode material can be reduced, an electricity storage device having excellent initial charge / discharge efficiency can be obtained for the reasons already described.

  The raw material powder used in the above production method is preferably a composite oxide containing phosphorus and tin.

  By using a composite oxide containing phosphorus and tin as the starting raw material powder, a negative electrode active material excellent in homogeneity can be easily obtained. Furthermore, by using a negative electrode material containing the negative electrode active material as a negative electrode, an electricity storage device having a stable discharge capacity can be obtained.

  In addition, as a result of various studies, the present inventors have found that when a negative electrode active material used for an electricity storage device such as a non-aqueous secondary battery is subjected to powder X-ray diffraction measurement using CuKα rays, It has been found that a negative electrode active material having a diffraction line profile can solve the third problem, and is proposed as the present invention.

  That is, the present invention is a negative electrode active material used for an electricity storage device composed of at least a negative electrode and a positive electrode, and has a 2θ value of 30 to 30 of a diffraction line profile obtained by powder X-ray diffraction measurement using CuKα rays when charging is completed. The half-value width of the diffraction line peak detected in the range of 50 ° and / or the range of 2θ value of 10 to 30 ° is 0.5 ° or more.

In the present invention, “when charging is completed” means that the negative electrode material containing the negative electrode active material for an electricity storage device of the present invention is used for the negative electrode, metallic lithium for the positive electrode, 1M LiPF ₆ solution / EC: DEC = 1 for the electrolyte. 1 (EC = ethylene carbonate, DEC = diethyl carbonate) In a test battery using a constant current of 0.2 mA, the battery is charged to 0V.

  Further, the present invention is a negative electrode active material used for an electricity storage device composed of at least a negative electrode and a positive electrode, and has a 2θ value of 15 to 15 of a diffraction line profile obtained by powder X-ray diffraction measurement using CuKα rays at the completion of discharge. The half width of the diffraction line peak detected in the range of 40 ° is 0.1 ° or more.

In the present invention, “when the discharge is completed” means that the negative electrode material containing the negative electrode active material for an electricity storage device of the present invention is used for the negative electrode, metal lithium for the positive electrode, 1M LiPF ₆ solution / EC: DEC = 1 for the electrolyte. 1 indicates a state where the battery is discharged to 1 V at a constant current of 0.2 mA in the test battery using 1.

  For example, as an example of a non-aqueous secondary battery, it is known that a lithium ion secondary battery undergoes the following reaction at a negative electrode containing Sn during charging and discharging.

Sn + yLi ⁺ + ye ⁻ ← → Li _y Sn (1)

First, at the time of charging, metal Sn combines with Li ions that have moved from the positive electrode through the electrolyte and electrons supplied from the circuit to form a reaction that forms a Sn—Li alloy (Li _y Sn) (formula (1)). ).

When Li _y Sn alloy formation from Sn metal occurs during charging, the negative electrode active material occludes y Li ions released from the positive electrode and causes volume expansion. This volume change can be estimated from the viewpoint of crystal structure.

For example, the length of the unit lattice of the metal Sn is tetragonal in 5.831Å × 5.831Å × 3.182Å, unit cell volume becomes 108.2Å ^3. Since Sn atoms are present four in this lattice, the volume occupied per Sn1 atoms becomes 27.05Å ^3. On the other hand, Li _2.6 Sn, Li _3.5 Sn, Li _4.4 Sn, and the like are known as Li _y Sn alloys formed during charging. For example, considering the case where an alloy of Li _4.4 Sn is formed during charging, the length of the unit cell of Li _4.4 Sn (cubic, space group F23) is 19.78） × 19.78Å × 19.78Å. Therefore, the lattice unit volume is 7739 ³ . Since there are 80 Sn atoms in this unit cell, the occupied volume per Sn atom is 96.7 ³ . For this reason, the occupied volume of Sn atoms expands 3.52 times (96.7Å ³ /27.05Å ³ ) during charging.

Next, at the time of discharge, the reaction formula (1) proceeds leftward, and _y ions of Li ions and electrons are released from the Li _y Sn alloy to form metal Sn, so that the negative electrode active material shrinks in volume. In this case, the occupied volume of Sn atoms contracts by 0.28 times (27.5Å ³ /96.7Å ³ ).

  Thus, since the negative electrode active material containing metal Sn is accompanied by a significant volume change during charge and discharge, as described above, the negative electrode active material is likely to crack when repeatedly charged and discharged, resulting in cycle characteristics. Causes a drop.

  By the way, as for the negative electrode active material for non-aqueous secondary batteries, Sn-Li alloy fine particles are formed when charging is completed, and Li ions are released when discharging is completed to form metal Sn fine particles. Therefore, the present inventors have a structure in which Sn-Li alloy fine particles and Sn fine particles, which are Li ion storage / release sites, are nano-sized (approximately 0.1 to 100 nm) and uniformly dispersed in the negative electrode active material. It has been found that a secondary battery having excellent cycle characteristics can be obtained because the volume change of the active material associated with the charge / discharge reaction can be reduced. Accordingly, paying attention to the diffraction line profile obtained by powder X-ray diffraction measurement using CuKα rays, if the negative electrode active material has a specific diffraction line profile, the crystallite size of the Sn—Li alloy fine particles and Sn fine particles Is nano-sized, and it has been clarified that these fine particles are uniformly present in a matrix such as a network-forming oxide.

Specifically, it is detected in the range of 2θ value of 30 to 50 ° or the range of 2θ value of 10 to 30 ° of the diffraction line profile obtained by powder X-ray diffraction measurement using CuKα ray in the negative electrode active material when charging is completed. If the diffraction line peak can be attributed to the metal crystal phase of Li _y Sn (y = 0.3 to 4.4) and the half width of the diffraction line peak is 0.5 ° or more, the crystallite of the metal crystal The size is nano-sized. Further, in the negative electrode active material at the completion of discharge, the diffraction line peak detected in the range of 2θ value of 15 to 40 ° of the diffraction line profile obtained by powder X-ray diffraction measurement using CuKα ray is the metal crystal phase of the metal Sn. It was found that if the half width of the diffraction line peak is 0.1 ° or more, the crystallite size of the metal crystal is a nano-sized fine particle. And by restricting each half-value width to the above range, it is possible to absorb and relax the volume change of Sn atoms associated with charge / discharge, and as a result, a secondary battery excellent in cycle characteristics when repeatedly charged / discharged. Can be obtained.

When the discharge is completed, the negative electrode active material for an electricity storage device of the present invention is expressed in mol% in terms of oxide, and SnO 10-70%, Li ₂ O 20-70%, P ₂ O ₅ 2-40% It is preferable to contain.

In the present specification, the content of SnO refers to those Sn components other than SnO (SnO _2, metal Sn, etc.) were also combined in terms of SnO.

  Further, as a result of various studies, the present inventors have determined that the second problem is that in the negative electrode active material for an electricity storage device containing tin oxide, the binding energy of electrons of Sn atoms in the negative electrode material is controlled. It is found that the problem can be solved and is proposed as the present invention.

That is, the present invention is a negative electrode active material for an electricity storage device containing at least SnO as a composition, wherein the binding energy value of electrons in the Sn3d _5/2 orbit of Sn atoms in the negative electrode material for the electricity storage device is Pl, and metal Sn (Pl-Pm) is 0.01 to 3.5 eV, where Pm is the electron binding energy value in the Sn3d _5/2 orbital.

  For example, as an example of a non-aqueous secondary battery that is an electricity storage device, it is known that a lithium ion secondary battery undergoes the following reaction at the negative electrode during charge and discharge.

Sn ^{x +} + xe ⁻ → Sn (1)
Sn + yLi ⁺ + ye ⁻ ← → Li _y Sn (2)

First, during the first charge, a reaction in which Sn ^{x +} ions accept electrons and produce metal Sn occurs irreversibly (formula (1)). Subsequently, the produced metal Sn combines with Li ions that have moved from the positive electrode through the electrolytic solution and electrons supplied from the circuit, and a reaction occurs to form a Sn—Li alloy. This reaction occurs as a reversible reaction that proceeds rightward during charging and proceeds leftward during discharging (formula (2)).

Here, focusing on the reaction of the formula (1) that occurs during the first charge, the smaller the energy required for the reaction, the smaller the initial charge capacity, and as a result, the first charge / discharge efficiency is excellent. Therefore, the smaller the valence of Sn ^{x +} ions, the fewer the electrons required for reduction, which is advantageous for improving the initial charge / discharge efficiency of the secondary battery.

The present inventors have introduced the electron binding energy value Pl in the Sn3d _5/2 orbit of the Sn atom as an index indicating the valence state of the Sn ^{x +} ion in the negative electrode. Then, by regulating the difference (Pl−Pm) between the bond energy value Pl and the electron bond energy value Pm in the Sn3d _5/2 orbit of the metal Sn to 3.5 eV or less, it is possible to store electricity with excellent initial charge / discharge efficiency. I found that the device was obtained.

  On the other hand, if (Pl-Pm) is too small, the negative electrode active material has a structure close to metal Sn, and the volume of the negative electrode active material changes significantly due to insertion and extraction of lithium ions. The capacity tends to decrease greatly. Therefore, by restricting (Pl-Pm) to 0.01 eV or more, it is possible to relieve the volume change due to insertion and extraction of lithium ions when repeatedly charged and discharged, and to obtain an electricity storage device having excellent cycle characteristics. I found it.

In the present invention, the binding energy value of electrons in the Sn3d _5/2 orbit of the Sn atom is the binding energy value of the point where the maximum detected intensity is obtained in the X-ray electron spectroscopy spectrum of the Sn3d _5/2 orbit using MgKα ray. Say.

  The negative electrode active material for an electricity storage device of the present invention is preferably substantially amorphous.

  With the above-described configuration, a negative electrode active material that can alleviate a volume change associated with insertion and extraction of lithium ions can be obtained, and an electric storage device having excellent charge / discharge cycle characteristics can be obtained. In the present invention, “substantially amorphous” means that the crystallinity is substantially 0%. Specifically, in powder X-ray diffraction measurement using CuKα rays. Means that no crystalline diffraction line is detected.

  The negative electrode active material for an electricity storage device of the present invention is preferably in a powder form.

  If the negative electrode active material for an electricity storage device is in powder form, the specific surface area can be increased to increase the capacity.

  The negative electrode active material for an electricity storage device of the present invention preferably has an average particle size of 0.1 to 10 μm and a maximum particle size of 75 μm or less.

  The present invention is also a method for producing the negative electrode active material for an electricity storage device, wherein the raw material powder is melted and vitrified in a reducing atmosphere or an inert atmosphere.

  According to this method, since the valence of Sn ions in the negative electrode active material can be reduced, an electricity storage device having excellent initial charge / discharge efficiency can be obtained for the reasons already described.

  The raw material powder used in the production method of the present invention preferably contains metal powder or carbon powder.

  According to this method, the Sn component in the negative electrode active material can be reduced, and the valence of Sn ions can be reduced. Therefore, an electrical storage device having excellent initial charge / discharge efficiency can be obtained for the reasons already described.

  The raw material powder used in the production method of the present invention is preferably a composite oxide containing phosphorus and tin.

  By using a composite oxide containing phosphorus and tin as the starting raw material powder, a negative electrode material having excellent homogeneity can be easily obtained. By using the negative electrode material containing the negative electrode active material as a negative electrode, an electricity storage device having a stable discharge capacity can be obtained.

It is a figure which shows the powder X-ray-diffraction line profile of the negative electrode material of Example 4 of Table 2. It is the figure which showed the base line at the time of subtracting a background by linear fitting with respect to the powder X-ray-diffraction line profile of the negative electrode material of Example 4 of Table 2. FIG. It is the figure which carried out curve fitting of the diffraction line profile which subtracted the background about the negative electrode material of Example 4 of Table 2 by peak component P1 and P2. It is the figure which showed the profile obtained by subtracting a background from the diffraction-line profile at the time of charging to 0V about the negative electrode active material of Example 2 of Table 5. FIG. It is the figure which showed the profile obtained by subtracting a background from the diffraction line profile at the time of discharging to 1V about the negative electrode active material of Example 2 of Table 5. FIG. It is a figure which shows the XPS spectrum of 3d5 _{/ 2} orbit of Sn atom of the negative electrode material of Example 5 of Table 7, and the 3D5 _{/ 2} orbital of metal Sn.

The negative electrode active material for an electricity storage device according to the first embodiment of the present invention is expressed in mol%, and includes SnO 70 to 95%, P ₂ O ₅ 5 to 30% (SnO 70% and P ₂ O ₅ 30%). Not included). The reason for limiting the composition in this way will be described below. In the following description, “%” means “mol%” unless otherwise specified.

  SnO is an active material component that serves as a site for occluding and releasing lithium ions in the negative electrode active material. The SnO content is preferably 70 to 95% (70% not included), 70.1 to 87%, 70.5 to 82%, and particularly 71 to 77%. When the SnO content is 70% or less, the discharge capacity per unit mass of the negative electrode active material becomes small. Moreover, the charging / discharging efficiency at the time of first charge / discharge becomes small. When the content of SnO is more than 95%, the amorphous component in the negative electrode active material is reduced, and the volume change due to insertion and extraction of lithium ions during charging and discharging cannot be sufficiently relaxed, and charging and discharging are repeated. There is a risk of rapid capacity loss.

P ₂ O ₅ is a matrix component that includes SnO, which is a site for the insertion and release of lithium ions, and the effect of relaxing the volume change associated with the storage and release of lithium ions by SnO to improve the charge / discharge cycle characteristics. There is. Furthermore, P ₂ O ₅ is a network-forming oxide and functions as a solid electrolyte to which lithium ions can move. The content of P ₂ O ₅ is preferably 5 to 30% (not including 30%), 5 to 29.2%, and particularly preferably 8 to 29.5%. When the content of P ₂ O ₅ is less than 5%, the volume change associated with insertion and extraction of lithium ions during charge and discharge cannot be relaxed, and structural deterioration is likely to occur. Therefore, the cycle performance is very poor and there is a risk of causing a rapid capacity drop. When the content of P ₂ O ₅ is 30% or more, the discharge capacity per unit mass of the negative electrode active material tends to decrease. In addition, the water resistance is likely to deteriorate, and when exposed to high temperature and high humidity for a long time, undesired foreign crystals (for example, SnHPO ₄ etc.) are formed, and moisture is easily impregnated or adsorbed in the negative electrode active material. As a result, water is decomposed inside the non-aqueous secondary battery, and it is inferior in safety because it causes explosion due to release of oxygen and heat generation due to reaction between lithium and water.

The total amount of SnO and P ₂ O ₅ is preferably 80% or more, 85% or more, particularly 87% or more. If the total amount of SnO and P ₂ O ₅ is less than 80%, it becomes difficult to achieve both cycle characteristics and high capacity.

The molar ratio of SnO to P ₂ O ₅ (SnO / P ₂ O ₅ ) is preferably 2.3 to 19, 2.3 to 18, and particularly preferably 2.4 to 17. When SnO / P ₂ O ₅ is smaller than 2.3, the Sn atom in SnO tends to be affected by the coordination of P ₂ O ₅ , and the valence of Sn atom tends to increase, resulting in the initial charge efficiency. Tends to decrease. If SnO / P ₂ O ₅ is greater than 19, the reduction in discharge capacity during repeated charge / discharge tends to increase. This is because the P ₂ O ₅ coordinated to SnO in the negative electrode active material is reduced and the P ₂ O ₅ component cannot contain SnO, and as a result, the volume change of SnO associated with insertion and extraction of lithium ions is mitigated. This is considered to be because it becomes impossible to cause structural deterioration.

Further, various components can be added in addition to the above components within the range not impairing the effects of the present invention. Examples of such components include CuO, ZnO, B ₂ O ₃ , MgO, CaO, Al ₂ O ₃ , SiO ₂ , R ₂ O (R represents Li, Na, K, or Cs). The total content of the above components is preferably 0 to 20%, 0 to 15%, particularly preferably 0.1 to 13%.

  The negative electrode active material for an electricity storage device according to the first embodiment preferably has a crystallinity of 95% or less, 80% or less, 70% or less, 50% or less, particularly 30% or less, most preferably substantially It is preferably amorphous (the crystallinity is substantially 0%). In a negative electrode active material containing SnO in a high proportion, the smaller the crystallinity (the larger the proportion of the amorphous phase), the more the volume change during repeated charging / discharging can be reduced, which is advantageous from the viewpoint of suppressing the reduction in discharge capacity. is there.

  The degree of crystallinity of the negative electrode active material is a 2θ value obtained by powder X-ray diffraction measurement using CuKα rays, and in a diffraction line profile of 10 to 60 °, the crystal diffraction line and the amorphous halo are separated into peaks. Desired. Specifically, the integrated intensities obtained by peak-separating a broad diffraction line (amorphous halo) at 10 to 40 ° from the total scattering curve obtained by subtracting the background from the diffraction line profile are Ia, 10 When the sum of integrated intensities obtained by peak-separating each crystalline diffraction line detected at 60 ° is Ic, the degree of crystallinity Xc is obtained from the following equation.

    Xc = [Ic / (Ic + Ia)] × 100

  The negative electrode active material according to the first embodiment may contain a phase composed of a complex oxide of metal and oxide, or an alloy phase of metal and metal.

  In addition, after charging / discharging electrical storage devices, such as a non-aqueous secondary battery using the negative electrode material containing the negative electrode active material which concerns on 1st Embodiment, the said negative electrode material is lithium oxide, a Sn-Li alloy, or a metal. May contain tin.

  The negative electrode active material according to the first embodiment is manufactured, for example, by heating and melting raw material powder to vitrify it. Here, it is preferable to melt the raw material powder in a reducing atmosphere or an inert atmosphere.

  An oxide containing Sn is likely to change the oxidation state of Sn atoms depending on the melting condition, and the bond energy of electrons is likely to change. By performing melting in a reducing atmosphere or an inert atmosphere, the change in the oxidation state of Sn atoms can be suppressed as described above, and a secondary battery excellent in initial charge / discharge efficiency can be obtained.

In order to melt in a reducing atmosphere, it is preferable to supply a reducing gas into the melting tank. As the reducing gas, it is preferable to use a mixed gas of N ₂ 90 to 99.5% and H ₂ 0.5 to 10%, particularly N ₂ 92 to 99% and H ₂ 1 to 8% in volume%. .

  When melting in an inert atmosphere, it is preferable to supply an inert gas into the melting tank. As the inert gas, it is preferable to use any of nitrogen, argon, and helium.

In the method for producing a negative electrode active material according to the first embodiment, it is preferable to use a composite oxide containing phosphorus and tin as a starting material powder. By using a composite oxide containing phosphorus and tin for the starting raw material powder, a negative electrode active material with few devitrified foreign substances and excellent uniformity is easily obtained. By using the negative electrode material containing the negative electrode active material as a negative electrode, a nonaqueous secondary battery with a stable discharge capacity can be obtained. Examples of the composite oxide containing phosphorus and tin include stannous pyrophosphate (Sn ₂ P ₂ O ₇ ).

The negative electrode active material for an electricity storage device according to the second embodiment of the present invention contains at least SnO and P ₂ O ₅ and has a 2θ value of 10 in a diffraction line profile obtained by powder X-ray diffraction measurement using CuKα rays. When curve fitting is performed with two components of a peak component P1 having an amorphous halo at ˜45 ° and a 2θ value fixed at 22.5 ° in the range, and a peak component P2 at a higher angle side than 22.5 ° In addition, the peak apex position of P2 is 25.0 to 29.0 ° in terms of 2θ.

When the position of the peak component P2 is 2θ smaller than 25.0 °, the Sn ion in the negative electrode active material is strongly influenced by the coordination due to the lone pair of oxygen atoms present in the phosphate network. Will do. As a result, the initial charge / discharge efficiency is significantly reduced because the electrons required to reduce Sn atoms in the negative electrode active material to metal Sn and the lithium ions required for charge compensation are excessively required during the initial charge. . On the other hand, when the peak position of the peak component P2 is larger than 29.0 °, it means that the tin oxide in the negative electrode active material is not sufficiently included in the phosphate network and mainly exists in the SnO molecular group. For this reason, when charging / discharging repeatedly, a volume change occurs locally in the negative electrode active material, and the skeleton of the phosphate network is destroyed to cause a structure. As a result, there is a tendency that the discharge capacity decreases when charging and discharging are repeated. The preferable range of the peak position of the peak component P2 is 25.1 to 28.8 °, 25.3 to 28.5 °, 25.5 to 28.3 °, and further 25.7 to 28.0 °. The peak position of the peak component P2 can be regulated within the above range by appropriately adjusting the ratio of SnO and P ₂ O _{5 in} the negative electrode active material and the melting atmosphere.

In another embodiment, the negative electrode active material for an electricity storage device according to the second embodiment of the present invention contains at least SnO and P ₂ O ₅ and is obtained by powder X-ray diffraction measurement using CuKα rays. In the line profile, the 2θ value has an amorphous halo at 10 to 45 °, and the peak component P1 in which the 2θ value is fixed at 22.5 ° in the range and the peak component P2 on the higher angle side than 22.5 ° When curve fitting is performed with two components, the peak area A1 of P1 and the peak area A2 of P2 satisfy the relationship of A1 / A2 = 0.01-8.

  When the peak area ratio A1 / A2 is smaller than 0.01, chain-like phosphoric acid is present only in the negative electrode active material, and the chain is cleaved and is present in an isolated phosphoric acid state. Is not well covered by the phosphate network. For this reason, the phosphoric acid skeleton is likely to be destroyed due to the volume change of the negative electrode active material due to repeated charge and discharge, which may cause structural destruction. As a result, there is a tendency that the discharge capacity decreases when charging and discharging are repeated. On the other hand, when the peak area ratio A1 / A2 is larger than 8, Sn ions in the negative electrode active material exist in a state in which they are strongly influenced by coordination by the lone electron pairs of oxygen atoms in the phosphate network. For this reason, the electrons required to reduce Sn atoms in the negative electrode active material to metal Sn at the time of the first charge, and further lithium ions required for charge compensation are required, and the initial charge / discharge efficiency is significantly reduced. The preferable ranges of the peak area ratio A1 / A2 are 0.02 to 7.5, 0.1 to 6.5, 0.2 to 5.5, and further 0.3 to 4.5.

The peak area ratio A1 / A2 can be regulated within the above range by appropriately adjusting the ratio of SnO to P ₂ O _{5 in} the negative electrode active material and the melting atmosphere.

As described above, the negative electrode active material for an electricity storage device according to the second embodiment contains SnO and P ₂ O ₅ at least as a composition.

SnO is an active material component that becomes a site for inserting and extracting lithium ions in the negative electrode material. The content of SnO is preferably 45 to 95%, 50 to 90%, particularly 55 to 85% in terms of mol%. When the content of SnO is less than 45%, the capacity per unit mass of the negative electrode active material becomes small. If the content of SnO is more than 95%, the amorphous component in the negative electrode active material decreases, so that the volume change associated with insertion and extraction of lithium ions during charge and discharge cannot be mitigated, and rapid discharge capacity is reduced. There is a risk of lowering. Incidentally, SnO ingredient content in the present invention, the tin oxide component other than SnO (SnO _2, etc.) also refers to that summed in terms of SnO.

P ₂ O ₅ is a network-forming oxide, covers the lithium ion storage and release sites of SnO, and functions as a solid electrolyte to which lithium ions can move. Content of P ₂ O _5, in mole percent, from 5 to 55%, 10-50%, particularly preferably 15% to 45%. If the content of P ₂ O ₅ is less than 5%, the volume change of SnO associated with insertion and extraction of lithium ions during charge / discharge cannot be alleviated, resulting in structural deterioration. Easy to grow. When the content of P ₂ O ₅ is more than 55%, it is easy to form a stable crystal (for example, SnP ₂ O ₇ ) together with Sn atoms, and Sn atoms due to lone pair of electrons in the chain P ₂ O ₅ The effect of the coordination bond of is more intense. As a result, since the peak position of the peak component P2 shifts to the low angle side, the initial charge / discharge efficiency tends to decrease.

The molar ratio of SnO to P ₂ O ₅ (SnO / P ₂ O ₅ ) is preferably 0.8 to 19, 1 to 18, and particularly preferably 1.2 to 17. When SnO / P ₂ O ₅ is smaller than 0.8, Sn atoms in SnO are easily affected by the coordination of P ₂ O ₅ , and the peak position of peak component P2 is shifted to the lower angle side, so that the first charge / discharge is performed. Efficiency tends to decrease. On the other hand, if SnO / P ₂ O ₅ is greater than 19, the discharge capacity tends to decrease when charging and discharging are repeated. This is because P ₂ O ₅ coordinated to SnO in the negative electrode active material decreases and P ₂ O ₅ cannot sufficiently contain SnO. As a result, the volume change of SnO due to insertion and extraction of lithium ions This is thought to be due to the fact that the structure cannot be relaxed and structural deterioration occurs.

In addition to the above components, various components can be further added to the negative electrode active material according to the second embodiment. For example, CuO, ZnO, B ₂ O ₃ , MgO, CaO, Al ₂ O ₃ , SiO ₂ , R ₂ O (R represents Li, Na, K or Cs) in a total amount of 0 to 20%, 0 to It can contain 10%, especially 0-7%. If it exceeds 20%, vitrification tends to occur, but the phosphate network tends to be cut. As a result, the discharge capacity tends to decrease when the battery is repeatedly charged and discharged. Moreover, since A1 decreases and the peak area ratio A1 / A2 decreases, the cycle characteristics deteriorate.

  The negative electrode active material according to the second embodiment is made of, for example, amorphous and / or crystalline material containing a plurality of oxide components as a composition. The negative electrode active material preferably has a crystallinity of 95% or less, 80% or less, 70% or less, 50% or less, particularly 30%, and most preferably substantially amorphous. In a negative electrode active material containing SnO in a high proportion, the smaller the degree of crystallinity (the larger the proportion of the amorphous phase), the more the volume change during repeated charge / discharge can be reduced, which is advantageous from the viewpoint of suppressing the reduction in discharge capacity. .

  The degree of crystallinity of the negative electrode active material is determined by separating the peak into a crystalline diffraction line and an amorphous halo in a diffraction line profile of 10 to 60 ° with 2θ values obtained by powder X-ray diffraction measurement using CuKα rays. Desired. Specifically, the integrated intensity obtained by peak-separating a broad diffraction line (amorphous halo) at 10 to 45 ° from the total scattering curve obtained by subtracting the background from the diffraction line profile is Ia, 10 When the total integrated intensity obtained by peak separation of each crystalline diffraction line detected at ˜60 ° is Ic, the crystallinity Xc can be obtained from the following equation.

    Xc = [Ic / (Ic + Ia)] × 100 (%)

  The negative electrode active material according to the second embodiment may contain a phase composed of a complex oxide of a metal and an oxide or an alloy phase of a metal and a metal.

  In addition, after charging / discharging electrical storage devices, such as a non-aqueous secondary battery using the negative electrode material containing the negative electrode active material which concerns on 2nd Embodiment, the said negative electrode material is a lithium oxide, Sn-Li alloy, or a metal. May contain tin.

  The negative electrode active material according to the second embodiment is produced, for example, by heating and melting raw material powder to vitrify it. Here, it is preferable to melt the raw material powder in a reducing atmosphere or an inert atmosphere.

An oxide containing Sn is likely to change the oxidation state of Sn atoms depending on the melting conditions, and when melted in the atmosphere, undesired SnO ₂ crystals are formed on the surface of the melt or in the melt, resulting in the initial charge / discharge efficiency. Lowers the cycle characteristics and deteriorates the cycle characteristics. However, an increase in the valence of Sn ions in the negative electrode active material can be suppressed by melting in a reducing atmosphere or an inert atmosphere. As a result, it is possible to suppress the formation of undesired crystals such as SnO ₂ and SnP ₂ O ₇ and to obtain a power storage device such as a secondary battery excellent in initial charge / discharge efficiency and cycle characteristics.

In order to melt in a reducing atmosphere, it is preferable to supply a reducing gas into the melting tank. The reducing gas, by _{volume%, N 2 90~99.5%, H} 2 0.5~10%, in particular N ₂ 92~99%, H ₂ is be used from 1 to 8% of the mixed gas preferable.

  When melting in an inert atmosphere, it is preferable to supply an inert gas into the melting tank. As the inert gas, it is preferable to use any of nitrogen, argon, and helium.

  The reducing gas or the inert gas may be supplied to the upper atmosphere of the molten glass in the melting tank, may be supplied directly from the bubbling nozzle into the molten glass, or both methods may be performed simultaneously.

The melting temperature is preferably 500 ° C to 1300 ° C. When the melting temperature is higher than 1300 ° C., the phosphoric acid network in the negative electrode active material is easily cut. In addition, isolated phosphoric acid and tin oxide form crystals, or SnO components not included in the phosphoric acid network tend to decompose into metallic Sn and SnO ₂ crystals, leading to a decrease in initial charge / discharge efficiency and cycle characteristics. is there. On the other hand, when the melting temperature is lower than 500 ° C., it is difficult to obtain a homogeneous amorphous material.

In the above production method, it is preferable to use a composite oxide containing phosphorus and tin as the starting material powder. By using a composite oxide containing phosphorus and tin for the starting raw material powder, a negative electrode active material with few devitrified foreign substances and excellent uniformity is easily obtained. By using the negative electrode material containing the negative electrode active material as a negative electrode, an electricity storage device having a stable discharge capacity can be obtained. Examples of the composite oxide containing phosphorus and tin include stannous pyrophosphate (Sn ₂ P ₂ O ₇ ).

The negative electrode active material for an electricity storage device according to the third embodiment of the present invention has a 2θ value in the range of 30 to 50 ° of the diffraction line profile obtained by powder X-ray diffraction measurement using CuKα rays at the completion of charging, and / or Alternatively, the half width of the diffraction line peak detected in the range of 2θ value of 10 to 30 ° is 0.5 ° or more, 0.6 ° or more, 0.7 ° or more, 0.8 ° or more, 0.9 It is preferably at least 1 °, particularly at least 1 °. When the half width of the diffraction line peak is smaller than 0.5 °, the crystallite size of the Li _y Sn alloy crystal in the negative electrode active material is large, indicating that submicron (approximately 100 nm or more) particles are formed. ing. For this reason, when Li ions are released due to a discharge reaction, a large volume shrinkage occurs locally in the negative electrode active material, and the negative electrode active material itself is easily cracked. Micronization and peeling from the electrode occur, and as a result, the cycle characteristics tend to deteriorate. The upper limit of the half width of the diffraction line peak is not particularly limited, but in reality, it is 15 ° or less, 14 ° or less, 13.5 ° or less, 13 ° or less, 12.5 ° or less, particularly 12 ° or less. Preferably there is. When the half width of the diffraction line peak is larger than 15 °, it means that the amount of Li _y Sn alloy crystal formed in the negative electrode active material is small, and as a result, the capacity tends to be small.

  In addition, the negative electrode active material according to the third embodiment has a diffraction line detected in the range of 2θ value of 15 to 40 ° of the diffraction line profile obtained by powder X-ray diffraction measurement using CuKα ray at the completion of discharge. The half width of the peak is 0.1 ° or more, preferably 0.12 ° or more, 0.15 ° or more, 0.2 ° or more, 0.3 ° or more, and particularly preferably 0.5 ° or more. When the half width of the diffraction line peak is larger than 0.1 °, it indicates that the crystallite size of the metal Sn crystal in the negative electrode active material is a particle of submicron. For this reason, when Li ions are occluded by a charging reaction, a large volume expansion occurs locally, and the active material itself is easily cracked, pulverized, and peeled off from the electrode. There is a tendency to decrease. The upper limit of the half-value width of the diffraction line peak is not particularly limited, but in reality, it is preferably 15 ° or less, 14 ° or less, 13 ° or less, 12.5 ° or less, 12 ° or less, particularly 11 ° or less. . When the half width of the diffraction line peak is greater than 15 °, it indicates that the amount of metal Sn formed in the negative electrode active material is small, and as a result, the capacity tends to be small.

When the discharge is completed, the negative electrode active material for an electricity storage device according to the third embodiment is represented by mol% in terms of oxide, and the composition is SnO 10 to 70% Li ₂ O 20 to 70% P ₂ O ₅ 2 to 40 % Is preferably contained. The reason why the content of each component is defined in this way will be described below.

  SnO is an active material component that serves as a site for occluding and releasing Li ions in the negative electrode active material. The SnO content is preferably 10 to 70%, 12 to 68%, 14 to 66%, particularly preferably 16 to 64%. When the content of SnO is less than 10%, the capacity per unit mass of the negative electrode active material becomes small. When the content of SnO is more than 70%, the amorphous component in the negative electrode active material is reduced, so that the volume change associated with insertion and extraction of Li ions during charge / discharge cannot be reduced, and the discharge capacity rapidly increases. May decrease.

Li ₂ O has a role of improving Li ion conductivity of the negative electrode active material. The content of Li ₂ O is preferably 20 to 70%, 22 to 68%, 24% to 66%, particularly preferably 25% to 65%. If the content of Li ₂ O is less than 20%, the Li ion conductivity may decrease and the discharge capacity may decrease. When the content of Li ₂ O is more than 70%, the size of the Sn—Li alloy or Sn metal particles increases, and the cycle characteristics may be deteriorated.

P ₂ O ₅ is a network-forming oxide, covers the sites of insertion and release of Li ions of the SnO component, and functions as a solid electrolyte to which Li ions can move. The content of P ₂ O ₅ is preferably 2 to 40%, 3 to 38%, 4 to 36%, particularly preferably 5 to 35%. If the content of P ₂ O ₅ is less than 2%, the volume change of the SnO component accompanying the absorption and release of Li ions during charge / discharge cannot be alleviated, resulting in structural deterioration. Therefore, the discharge capacity decreases during repeated charge / discharge. It becomes easy. When the content of P ₂ O ₅ is more than 40%, the discharge capacity per unit mass of the negative electrode active material tends to decrease. In addition, the water resistance is likely to deteriorate, and when exposed to high temperature and high humidity for a long time, undesired foreign crystals (for example, SnHPO ₄ etc.) are formed, and moisture is easily impregnated or adsorbed in the negative electrode active material. As a result, water is decomposed inside the electricity storage device, and it is inferior in safety because it causes explosion due to release of oxygen and heat generation due to reaction between lithium and water.

The negative electrode active material for an electricity storage device according to the third embodiment is made of a material containing at least SnO and P ₂ O ₅ as a composition before the first charge (when the battery is incorporated). The content of these components, for example, SnO 45 to 95%, is adjusted in a range of P ₂ O ₅ 5~55%.

  SnO is an active material component that serves as a site for occluding and releasing Li ions in the negative electrode active material. The content of SnO is preferably 45 to 95%, 50 to 90%, particularly 55 to 85% in terms of mol%. When the content of SnO is less than 45%, the capacity per unit mass of the negative electrode active material becomes small. If the content of SnO is more than 95%, the amorphous component in the negative electrode active material decreases, so that the volume change associated with insertion and extraction of Li ions during charge and discharge cannot be mitigated, and rapid discharge capacity is reduced. There is a risk of lowering.

P ₂ O ₅ is a network-forming oxide, covers the storage and release sites of SnO Li ions, and functions as a solid electrolyte to which Li ions can move. Content of P ₂ O _5, in mole percent, from 5 to 55%, 10-50%, particularly preferably 15% to 45%. If the content of P ₂ O ₅ is less than 5%, the change in volume of SnO associated with insertion and extraction of Li ions during charge / discharge cannot be alleviated, resulting in structural deterioration, resulting in a decrease in discharge capacity during repeated charge / discharge. Easy to grow. When the content of P ₂ O ₅ is more than 55%, it is easy to form a stable crystal (for example, SnP ₂ O ₇ ) together with Sn atoms, and Sn atoms due to lone pair of electrons in the chain P ₂ O ₅ The effect of the coordination bond of is more intense. As a result, the initial charge / discharge efficiency tends to decrease.

The molar ratio of SnO to P ₂ O ₅ (SnO / P ₂ O ₅ ) in the negative electrode active material is preferably 0.8 to 19, 1 to 18, particularly 1.2 to 17. When SnO / P ₂ O ₅ is smaller than 0.8, Sn atoms in SnO are easily affected by the coordination of P ₂ O ₅ , and the initial charge / discharge efficiency tends to be reduced. On the other hand, if SnO / P ₂ O ₅ is greater than 19, the discharge capacity tends to decrease when charging and discharging are repeated. This is because P ₂ O ₅ coordinated with SnO in the negative electrode active material is reduced and P ₂ O ₅ cannot sufficiently contain SnO. As a result, the volume change of SnO due to insertion and extraction of Li ions is caused. This is thought to be due to the fact that the structure cannot be relaxed and structural deterioration occurs.

Moreover, in addition to the said component, a various component can be further added to the negative electrode active material (at the time of incorporating in an electrical storage device) which concerns on 3rd Embodiment. For example, CuO, ZnO, B ₂ O ₃ , MgO, CaO, Al ₂ O ₃ , SiO ₂ , R ₂ O (R represents Li, Na, K or Cs) in a total amount of 0 to 20%, 0 to It is preferable to contain 10%, especially 0 to 7%. If it exceeds 20%, vitrification tends to occur, but the phosphate network tends to be cut. As a result, the cycle characteristics deteriorate.

  The negative electrode active material for an electricity storage device according to the third embodiment is manufactured, for example, by heating and melting raw material powder at 500 to 1300 ° C. to vitrify it. Here, it is preferable to melt the raw material powder in a reducing atmosphere or an inert atmosphere.

An oxide containing Sn is likely to change the oxidation state of Sn atoms depending on the melting conditions, and when melted in the atmosphere, undesired SnO ₂ crystals are formed on the surface of the melt or in the melt, resulting in the initial charge / discharge efficiency. Lowers the cycle characteristics and deteriorates the cycle characteristics. However, an increase in the valence of Sn ions in the negative electrode active material can be suppressed by melting in a reducing atmosphere or an inert atmosphere. As a result, it is possible to suppress the formation of unwanted crystals such as SnO ₂ and SnP ₂ O ₇ and to obtain a secondary battery excellent in initial charge / discharge efficiency and cycle characteristics.

In the above production method, it is preferable to use a composite oxide containing phosphorus and tin as the starting material powder. By using a composite oxide containing phosphorus and tin as the starting raw material powder, it is easy to obtain a negative electrode active material with few devitrified foreign substances and excellent uniformity. By using the negative electrode material containing the negative electrode active material for the electrode, an electricity storage device having a stable discharge capacity can be obtained. Examples of the composite oxide containing phosphorus and tin include stannous pyrophosphate (Sn ₂ P ₂ O ₇ ).

  In addition, the negative electrode of electrical storage devices, such as a nonaqueous secondary battery, is formed using the negative electrode material containing the negative electrode active material of embodiment described above. Specifically, the negative electrode material is obtained by adding a binder such as a thermosetting resin or a conductive auxiliary agent such as acetylene black, ketjen black, highly conductive carbon black, or graphite to the negative electrode active material. .

The fourth negative active material for a power storage device according to an embodiment of the present invention, the electron binding energy value Pl in Sn3d _5/2 orbit of Sn atom of the negative electrode active material in, in Sn3d _5/2 orbital of the metal Sn The difference (Pl−Pm) in the electron binding energy value Pm is 0.01 to 3.5 eV. When (Pl-Pm) is smaller than 0.01 eV, it means that Sn atoms hardly form bonds with other atoms and exist in a structure close to metal Sn. When the Sn atom is close to the metal Sn in the negative electrode active material, the Sn component tends to exist in the negative electrode active material as an aggregate. In such a state, when charging and discharging are repeated, insertion and extraction of lithium ions occur locally, so that a significant volume change cannot be mitigated and the structure is easily destroyed. As a result, there is a tendency that the discharge capacity is greatly reduced when repeatedly used. On the other hand, if (Pl-Pm) exceeds 3.5 eV, the electrons required to reduce Sn atoms in the negative electrode material to metal Sn at the time of the first charge, and more lithium ions as charge compensation are required. Therefore, the initial charge / discharge efficiency is significantly reduced. A preferable range of the bond energy difference (Pl-Pm) is 0.05 to 3.4 eV, 0.1 to 3.35 eV, and further 0.12 to 3.3 eV.

  The negative electrode active material for an electricity storage device according to the fourth embodiment contains at least SnO as a composition. SnO is an active material component that serves as a site for occluding and releasing lithium ions in the negative electrode active material. The content of SnO is preferably 45 to 95%, 50 to 90%, particularly 55 to 85% in terms of mol%. When the content of SnO is less than 45%, the capacity per unit mass of the negative electrode active material becomes small. If the content of SnO is more than 95%, the amorphous component in the negative electrode active material decreases, so that the volume change associated with insertion and extraction of lithium ions during charge and discharge cannot be mitigated, and rapid discharge capacity is reduced. There is a risk of lowering.

Examples of the component constituting the negative electrode active material include P ₂ O _{5 in} addition to SnO. P ₂ O ₅ is a network-forming oxide, covers the lithium ion storage and release sites of SnO, and functions as a solid electrolyte to which lithium ions can move. Content of P ₂ O _5, in mole percent, from 5 to 55%, 10-50%, particularly preferably 15% to 45%. If the content of P ₂ O ₅ is less than 5%, the volume change of SnO associated with insertion and extraction of lithium ions during charge / discharge cannot be alleviated, resulting in structural deterioration. Easy to grow. When the content of P ₂ O ₅ is more than 55%, it is easy to form a stable crystal (for example, SnP ₂ O ₇ ) with Sn atoms, and the 3d _5/2 electron binding of Sn atoms becomes stronger, The value of the binding energy Pl increases. As a result, the binding energy difference (Pl−Pm) increases, and the initial charge efficiency tends to decrease.

The molar ratio of SnO to P ₂ O ₅ (SnO / P ₂ O ₅ ) is preferably 0.8 to 19, 1 to 18, and particularly preferably 1.2 to 17. If SnO / P ₂ O ₅ is smaller than 0.8, the Sn atom in SnO is easily affected by the coordination of P ₂ O ₅ , and the bond between the inner electron of the 3d _5/2 orbit of the Sn atom and the nucleus Since the energy becomes stronger, the value of the binding energy Pl increases. As a result, the binding energy difference (Pl−Pm) increases, and the initial charge efficiency tends to decrease. On the other hand, if SnO / P ₂ O ₅ is greater than 19, the reduction in discharge capacity during repeated charge / discharge tends to increase. This is because the amount of P ₂ O ₅ coordinated with SnO in the negative electrode active material is reduced and P ₂ O ₅ cannot contain SnO. As a result, the volume change of SnO due to insertion and extraction of lithium ions can be mitigated. This is thought to be due to the loss of structure and structural degradation.

In addition to the above components, various components can be added. For example, CuO, ZnO, B ₂ O ₃ , MgO, CaO, Al ₂ O ₃ , SiO ₂ , R ₂ O (R represents Li, Na, K, or Cs) can be contained. These components have a role of improving cycle characteristics.

  The negative electrode active material for an electricity storage device according to the fourth embodiment is made of an amorphous material and / or a crystalline material containing, for example, a plurality of oxide components as a composition. This negative electrode active material preferably has a crystallinity of 95% or less, 80% or less, 70% or less, 50% or less, particularly 30%, most preferably substantially amorphous. In a negative electrode active material containing SnO in a high proportion, the smaller the degree of crystallinity (the larger the proportion of the amorphous phase), the more the volume change during repeated charge / discharge can be reduced, which is advantageous from the viewpoint of suppressing the reduction in discharge capacity. .

  The degree of crystallinity of the negative electrode active material is a 2θ value obtained by powder X-ray diffraction measurement using CuKα rays, and in a diffraction line profile of 10 to 60 °, the crystal diffraction line and the amorphous halo are separated into peaks. Desired. Specifically, the integrated intensities obtained by peak-separating a broad diffraction line (amorphous halo) at 10 to 40 ° from the total scattering curve obtained by subtracting the background from the diffraction line profile are Ia, 10 When the sum of integrated intensities obtained by peak-separating each crystalline diffraction line detected at 60 ° is Ic, the degree of crystallinity Xc is obtained from the following equation.

    Xc = [Ic / (Ic + Ia)] × 100

  The negative electrode active material according to the fourth embodiment may contain a phase composed of a composite oxide of metal and oxide or an alloy phase of metal and metal.

  In addition, after charging / discharging the electrical storage device using the negative electrode active material which concerns on 4th Embodiment, the said negative electrode active material may contain a lithium oxide, Sn-Li alloy, or metallic tin.

  Examples of the form of the negative electrode active material according to the fourth embodiment include a powder form and a bulk form, and are not particularly limited. However, if the form is a powder form, the specific surface area can be increased to increase the capacity. Therefore, it is advantageous.

  As the particle size of the powder, the average particle size is 0.1 to 10 μm and the maximum particle size is 75 μm or less, the average particle size is 0.3 to 9 μm and the maximum particle size is 65 μm or less, the average particle size is 0.5 to 8 μm, and the maximum particle size is 55 μm. In particular, the average particle diameter is preferably 1 to 5 μm and the maximum particle diameter is 45 μm or less. When the average particle size of the powder is larger than 10 μm or the maximum particle size is larger than 75 μm, the negative electrode material is easily peeled off from the current collector due to volume change associated with insertion and extraction of Li ions during charging and discharging. As a result, when charge / discharge is repeated, the capacity tends to be significantly reduced. On the other hand, if the average particle diameter of the powder is smaller than 0.1 μm, the powder is in a poorly dispersed state when formed into a paste, and it tends to be difficult to produce a uniform electrode.

  In addition, the average particle diameter and the maximum particle diameter are values measured by a laser diffraction particle size distribution measuring apparatus, which indicate D50 (50% volume cumulative diameter) and D100 (100% volume cumulative diameter) as median diameters of primary particles, respectively. Say.

The specific surface area of the powder by the BET method is preferably 0.1 to ²⁰ m ² / g, 0.15 to 15 m ² / g, particularly preferably 0.2 to 10 m ² / g. When the specific surface area of the powder is smaller than 0.1 m ² / g, the insertion and extraction of Li ions cannot be performed quickly, and the charge / discharge time tends to be long. On the other hand, if the specific surface area of the powder is larger than 20 m ² / g, the powder tends to be charged with static electricity, and when it is made into a paste, it tends to be inferior in the dispersed state of the powder, making it difficult to produce a homogeneous electrode.

Furthermore, the tap density of the powder is preferably 0.5 to 2.5 g / cm ³ , particularly preferably 1.0 to 2.0 g / cm ³ . If the tap density of the powder is less than 0.5 g / cm ³ , the amount of the negative electrode active material per electrode unit volume is small, so that the electrode density is inferior and it is difficult to achieve high capacity. On the other hand, if the tap density of the powder is larger than 2.5 g / cm ³ , the filling state of the negative electrode active material is too high, and the electrolytic solution is difficult to permeate, so that a sufficient capacity may not be obtained.

  The tap density here is a value measured under the conditions of a tapping stroke of 18 mm, a tapping frequency of 180 times, and a tapping speed of 1 time / 1 second.

  In order to obtain a powder of a predetermined size, a general pulverizer or classifier is used. For example, a mortar, a ball mill, a vibrating ball mill, a satellite ball mill, a planetary ball mill, a jet mill, a sieve, a centrifugal separator, an air classification, or the like is used.

  The negative electrode active material for an electricity storage device according to the fourth embodiment is produced, for example, by heating and melting raw material powder to vitrify it. Here, it is preferable to melt the raw material powder in a reducing atmosphere or an inert atmosphere.

  An oxide containing Sn is likely to change the oxidation state of Sn atoms depending on the melting condition, and the bond energy of electrons is likely to change. For example, by performing melting in a reducing atmosphere or an inert atmosphere, the valence of Sn ions in the negative electrode material can be reduced. As a result, as described above, (Pl-Pm) can be reduced, and an electricity storage device having excellent initial charge / discharge efficiency can be obtained.

In order to melt in a reducing atmosphere, it is preferable to supply a reducing gas into the melting tank. The reducing gas, by _{volume%, N 2 90~99.5%, H} 2 0.5~10%, in particular N ₂ 92~99%, H ₂ is be used from 1 to 8% of the mixed gas preferable.

  When melting in an inert atmosphere, it is preferable to supply an inert gas into the melting tank. As the inert gas, it is preferable to use any of nitrogen, argon, and helium. The reducing gas or the inert gas may be supplied to the upper atmosphere of the molten glass in the melting tank, may be supplied directly from the bubbling nozzle into the molten glass, or both methods may be performed simultaneously.

  In the method for producing a negative electrode active material for an electricity storage device according to the fourth embodiment, the raw material powder preferably contains a metal powder or a carbon powder. Thereby, Sn atom in a negative electrode active material can be shifted to a reduction state, and Pl can be reduced. As a result, the value of (Pl-Pm) in the negative electrode active material becomes small, and the initial charge efficiency of the electricity storage device can be improved.

  As the metal powder, any one of Sn, Al, Si, and Ti is preferably used. Among these, Sn and Al powders are preferably used.

  The content of the metal powder is preferably 0 to 20%, particularly preferably 0.1 to 10% in terms of mol%. When the content of the metal powder is more than 20%, an excess metal lump may be deposited from the negative electrode material, or SnO in the negative electrode active material may be reduced and deposited as metallic Sn particles.

  The content of the carbon powder is preferably 0 to 20% by mass, particularly 0.05 to 10% by mass in the raw material powder.

In the above production method, it is preferable to use a composite oxide containing phosphorus and tin as the starting material powder. By using a composite oxide containing phosphorus and tin as the starting raw material powder, it is easy to obtain a negative electrode active material with few devitrified foreign substances and excellent uniformity. By using the negative electrode active material as an electrode, an electricity storage device having a stable discharge capacity can be obtained. Examples of the composite oxide containing phosphorus and tin include stannous pyrophosphate (Sn ₂ P ₂ O ₇ ).

  In addition, the negative electrode of electrical storage devices, such as a non-aqueous secondary battery, is formed using the negative electrode material containing the negative electrode active material demonstrated above. Specifically, the negative electrode material is obtained by adding a binder such as a thermosetting resin or a conductive auxiliary agent such as acetylene black, ketjen black, highly conductive carbon black, or graphite to the negative electrode active material. .

  Moreover, the negative electrode active material and the negative electrode material of the present invention are not limited to lithium ion secondary batteries, but other nonaqueous secondary batteries, and further, positive electrode materials and lithium ion secondary batteries for nonaqueous electric double layer capacitors It can also be applied to a hybrid capacitor combined with a negative electrode material.

  A lithium ion capacitor, which is a hybrid capacitor, is a type of asymmetric capacitor that has different charge / discharge principles for a positive electrode and a negative electrode. The lithium ion capacitor has a structure in which a negative electrode for a lithium ion secondary battery and a positive electrode for an electric double layer capacitor are combined. Here, the positive electrode forms an electric double layer on the surface and is charged / discharged by utilizing a physical action (electrostatic action), whereas the negative electrode has a lithium ion chemistry similar to the lithium ion secondary battery described above. Charge and discharge by reaction (occlusion and release).

  A positive electrode material made of a carbonaceous powder having a high specific surface area such as activated carbon, polyacene, or mesophase carbon is used for the positive electrode of the lithium ion capacitor. On the other hand, as the negative electrode, the negative electrode material of the present invention in which lithium ions and electrons are occluded can be used.

  The means for occluding lithium ions and electrons in the negative electrode active material of the present invention is not particularly limited. For example, a metal lithium electrode as a supply source of lithium ions and electrons may be disposed in a capacitor cell, and may be brought into contact with the negative electrode containing the negative electrode active material of the present invention directly or through a conductor, or in another cell. The negative electrode active material may be preliminarily occluded with lithium ions and electrons and then incorporated into the capacitor cell.

  Hereinafter, although the negative electrode active material for electrical storage devices which concerns on 1st Embodiment is demonstrated in detail using an Example, this invention is not limited to these Examples.

(1) Production of negative electrode active material for non-aqueous secondary battery Table 1 shows Examples 1 to 6 and Comparative Examples 1 to 3. Each negative electrode active material was produced as follows.

In order to obtain the composition shown in Table 1, stannous pyrophosphate (Sn ₂ P ₂ O ₇ ) is used as the main raw material, and the raw material powder is made of various oxides, phosphate raw materials, carbonate raw materials, metals, carbon raw materials, etc. Prepared. The raw material powder was put into an alumina crucible and melted at 950 ° C. for 40 minutes in a nitrogen atmosphere using an electric furnace to be vitrified.

  Next, the molten glass was poured out between a pair of rotating rollers and molded into a film having a thickness of 0.1 to 2 mm while rapidly cooling to obtain a glass sample. The glass sample was pulverized with an alumina separator and then passed through a sieve having an opening of 20 μm to obtain a glass powder having a mean particle size of 5 μm (a negative electrode active material for a non-aqueous secondary battery).

The structure was identified by powder X-ray diffraction measurement for each sample. The negative electrode active materials of Examples 1 to 6 except Example 5 were amorphous, and no crystals were detected. In Example 5, fine crystal precipitation of SnO ₂ was confirmed in the amorphous material, and the crystallinity Xc was 4%. Since the negative electrode active material of Comparative Example 1 had deliquescence immediately after production, the precipitated crystals were not measurable. The negative electrode active materials of Comparative Examples 2 and 3 had a structure in which an amorphous part and a crystalline part were mixed.

(2) Production of Negative Electrode For the glass powders (negative electrode active materials) of Examples and Comparative Examples, polyimide resin as a binder, ketjen black as a conductive material, glass powder: binder: conductive material = 85: 10: 5 (Mass ratio) was weighed and these were dispersed in N-methylpyrrolidone (NMP), and then sufficiently stirred with a rotation / revolution mixer to obtain a slurry-like negative electrode material. Next, using a doctor blade with a gap of 150 μm, the obtained slurry was coated on a copper foil having a thickness of 20 μm as a negative electrode current collector, dried at 70 ° C. with a dryer, and then between a pair of rotating rollers. An electrode sheet was obtained by pressing through a sheet. The electrode sheet was punched to a diameter of 11 mm with an electrode punching machine and imidized while reducing pressure at 200 ° C. for 10 hours to obtain a circular working electrode.

(3) Preparation of test battery The above working electrode was placed on the lower lid of the coin cell with the copper foil surface facing downward, and dried on the polypropylene for 8 hours at 60 ° C. under reduced pressure for 16 hours. A separator comprising Cellguard # 2400 manufactured by Needs Co., Ltd. and metallic lithium as a counter electrode were laminated to prepare a test battery. As the electrolytic solution, 1M LiPF ₆ solution / EC (ethylene carbonate): DEC (diethyl carbonate) = 1: 1 was used. The test battery was assembled in an environment with a dew point temperature of −60 ° C. or lower.

(4) Charging / discharging test Charging (occlusion of lithium ions into the negative electrode active material) was performed by CC (constant current) charging from 2 V to 0 V at 0.2 mA. Next, discharge (release of lithium ions from the negative electrode active material) was discharged from 0 V to 2 V at a constant current of 0.2 mA. This charge / discharge cycle was repeated.

  Table 1 shows the results of the initial charge / discharge characteristics when the charge / discharge test was performed for each sample and the cycle characteristics when the charge / discharge was repeated.

  The initial discharge capacity of the batteries using the negative electrode active materials of Examples 1 to 6 was 680 mAh / g or more, and the discharge capacity at the 50th cycle was good at 382 mAh / g or more. On the other hand, the negative electrode active material of Comparative Example 1 had deliquescence immediately after production and could not be used as a non-aqueous secondary battery electrode. The battery using the negative electrode active material of Comparative Example 2 had a low initial discharge capacity of 392 mAh / g. In addition, the battery using the negative electrode active material of Comparative Example 3 had an initial discharge capacity of 901 mAh / g, but the discharge capacity at the 50th cycle was significantly reduced to 52 mAh / g.

  Hereinafter, although the negative electrode active material for electrical storage devices which concerns on 2nd Embodiment is demonstrated in detail using an Example, this invention is not limited to these Examples.

(1) Production of negative electrode material for non-aqueous secondary battery Tables 2 and 3 show Examples 1 to 6 and Comparative Examples 1 and 2. Each negative electrode active material was produced as follows.

A composite oxide of tin and phosphorus (stannous pyrophosphate: Sn ₂ P ₂ O ₇ ) is used as the main raw material so that the compositions shown in Tables 2 and 3 are used, and the raw material powder includes various oxides and carbonate raw materials. Was prepared. The raw material powder was put into a quartz crucible and melted at 950 ° C. for 40 minutes in a nitrogen atmosphere using an electric furnace to be vitrified.

Next, the molten glass was poured out between a pair of rotating rollers and molded while being rapidly cooled to obtain a film-like glass having a thickness of 0.1 to 2 mm. This film-like glass was put into a ball mill using zirconia balls having a diameter of 2 to 3 cm, pulverized at 100 rpm for 3 hours, then passed through a resin sieve having an opening of 120 μm, and a glass coarse particle having an average particle diameter D _{50 of 8} to 15 μm. A powder was obtained. Next, this glass coarse powder was put into a ball mill using zirconia balls having a diameter of 5 mm, ethanol was added and pulverized at 40 rpm for 5 hours, and then dried at 200 ° C. for 4 hours to obtain a glass powder having an average particle diameter of 2 to 5 μm ( Negative electrode active material for non-aqueous secondary battery) was obtained.

  The crystal structure was identified by performing powder X-ray diffraction measurement for each sample. The negative electrode active materials of Examples 1 to 4 and 6 were amorphous, and no crystals were detected. Example 5 was almost amorphous, but some crystals were detected.

(2) Measurement of powder X-ray diffraction (powder XRD) Diffraction line profile by measuring each sample under the following conditions using RINT2000 made by RIGAKU as a powder X-ray diffraction measurement device and using Cu-Kα ray as an X-ray source. Was obtained (see FIG. 1).

Tube voltage / tube current: 40 kV / 40 mA
Divergence / scattering slit: 1 °
Receiving slit: 0.15mm
Sampling width: 0.01 °
Measurement range: 10-60 °
Measurement speed: 0.1 ° / sec
Integration count: 5 times

(3) Analysis and data analysis Materials Data Inc. as analysis / quantification software. JADE Ver. Using 6.0, the data analysis of the diffraction line profile was performed by the following procedure.

  (a) First, in the diffraction line profile in the range of 10 to 60 °, amorphous halos other than the crystalline diffraction lines were smoothed. Specifically, after smoothing with 99 data points using a parabolic filter based on the Savitzky-Golay filter method, a range where 2θ is 10 to 45 ° was trimmed. The diffraction line profile was fitted linearly (see FIG. 2) so that the intensity of the diffraction line profile did not become negative within this range, and the background was subtracted.

  (b) In the diffraction line profile obtained by subtracting the background, the peak component P1 in which the 2θ value of the peak apex is fixed at 22.5 ° and the peak apex is not fixed on the higher angle side than 22.5 ° Peak component P2 was created (here, peak component P1 is derived from the phosphoric acid component in the negative electrode material. Peak component P2 is derived from the tin component in the negative electrode material, and the 2θ value at the apex reflects the oxidation state of tin) is doing). When a crystalline diffraction line is observed in a diffraction line profile with 2θ of 10 to 45 °, a peak component of the crystalline diffraction line in which the peak apex and the asymmetry parameter are not fixed is added.

  (c) For the peak components P1 and P2, curve fitting was performed by the pseudo-Voight function. Here, the asymmetry parameters of the peak components P1 and P2 were fixed to -0.75 and -0.55, respectively, so that the peak components P1 and P2 can be uniquely determined by curve fitting.

  (d) The fitting residual of the curve obtained by curve fitting with the diffraction line profile is 22% or less, and the half width (FWHM) of the peak of each peak component P1 and P2 is in the range of 2-20. The refinement was repeated repeatedly (see FIG. 3).

  (e) The 2θ value at the peak apex of the obtained peak component P2 and the peak areas A1 and A2 of the peak components P1 and P2 were determined, respectively.

(4) Production of Negative Electrode For the glass powder (negative electrode active material) obtained above, polyimide resin as a binder and ketjen black as a conductive substance, glass powder: binder: conductive substance = 85: 10: 5 ( (Weight ratio) and weighed it in N-methylpyrrolidone (NMP), and then sufficiently stirred with a rotation / revolution mixer to obtain a slurry-like negative electrode material. Next, using a doctor blade with a gap of 150 μm, the obtained slurry was coated on a 20 μm thick copper foil as a negative electrode current collector, dried at 70 ° C. using a dryer, and then between a pair of rotating rollers. An electrode sheet was obtained by pressing through a sheet. This electrode sheet was punched to a diameter of 11 mm with an electrode punching machine and dried under reduced pressure at 200 ° C. for 10 hours to imidize the polyimide resin to obtain a circular working electrode.

(5) Production of test battery The working electrode was placed on the lower lid of the coin cell so that the copper foil surface was facing downward, and then dried on a polypropylene porous membrane having a diameter of 16 mm (Hoechst) at 60 ° C. for 8 hours under reduced pressure. A test battery was produced by laminating a separator made of Celanese Cellguard # 2400) and metallic lithium as a counter electrode. As the electrolytic solution, 1M LiPF ₆ solution / EC: DEC = 1: 1 (EC = ethylene carbonate, DEC = diethyl carbonate) was used. The test battery was assembled in an environment with a dew point temperature of −60 ° C. or lower.

(6) Charging / discharging test Charging (occlusion of lithium ions into the negative electrode material) performed CC (constant current) charging from 2 V to 0 V at 0.2 mA. Next, discharge (release of lithium ions from the negative electrode material) was discharged from 0 V to 2 V at a constant current of 0.2 mA. This charge / discharge cycle was repeated.

Tables 2 and 3 show the results of the initial charge / discharge characteristics when the charge / discharge test was performed and the cycle characteristics when the battery was repeatedly charged / discharged, with respect to the batteries using the negative electrode active materials of Examples and Comparative Examples.

  The initial discharge capacity of the batteries using the negative electrode active materials of Examples 1 to 6 was 670 mAh / g or more, and the discharge capacity at the 50th cycle was favorable to 411 mAh / g or more. On the other hand, the battery using the negative electrode active material of Comparative Example 1 had a low initial discharge capacity of 392 mAh / g. In addition, the battery using the negative electrode active material of Comparative Example 2 had an initial discharge capacity of 901 mAh / g, but the discharge capacity at the 50th cycle was significantly reduced to 52 mAh / g.

  Hereinafter, although the negative electrode active material for electrical storage devices which concerns on 3rd Embodiment is demonstrated in detail using an Example, this invention is not limited to these Examples.

(1) Production of negative electrode active material for non-aqueous secondary battery A composite oxide of tin and phosphorus (stannous pyrophosphate: Sn ₂ P ₂ O ₇ ) was used as the main raw material so as to have the composition shown in Table 4. Raw material powders were prepared from various oxides and carbonate raw materials. The raw material powder was put into a quartz crucible and melted at 950 ° C. for 40 minutes in a nitrogen atmosphere using an electric furnace to be vitrified.

Next, the molten glass was poured out between a pair of rotating rollers and molded while being rapidly cooled to obtain a film-like glass having a thickness of 0.1 to 2 mm. The film-like glass was put into a ball mill using zirconia balls of Fai2～3cm, was ground for 3 hours at 100 rpm, passed through a resin sieve having a mesh size of 120 [mu] m, an average particle diameter D ₅₀ of the glass crude 8~15μm A powder was obtained. Next, this glass coarse powder was put into a ball mill using zirconia balls having a diameter of 5 mm, ethanol was added and pulverized at 40 rpm for 5 hours, and then dried at 200 ° C. for 4 hours to obtain a glass powder having an average particle diameter of 2 to 5 μm ( Negative electrode active material for non-aqueous secondary battery) was obtained. In Comparative Examples 2 and 3, the pure material sample was used as it was as the negative electrode active material.

(2) Powder X-ray diffraction (powder XRD) measurement The crystal structure was identified by performing the powder X-ray diffraction measurement for each sample. A diffraction line profile was obtained by measuring each sample under the following conditions using RINT2000 manufactured by RIGAKU as a powder X-ray diffraction measurement apparatus and using Cu-Kα ray as an X-ray source.

Tube voltage / tube current: 40 kV / 40 mA
Divergence / scattering slit: 1 °
Receiving slit: 0.15mm
Sampling width: 0.01 °
Measurement range: 10-60 °
Measurement speed: 0.1 ° / sec
Integration count: 5 times

Table 4 shows the precipitated crystal phase and crystallinity of the negative electrode active material. The negative electrode active materials of Examples 1 to 4 and 6 were amorphous, and no crystals were detected. Example 5 was almost amorphous, but some crystals were detected. In the negative electrode active material of Comparative Example 1, the SnO raw material was oxidized, and SnO ₂ crystals and SnO crystals were detected. In Comparative Example 2, SnO crystals were detected, and in Comparative Example 3, metal Sn crystals were detected at a rate of 100%.

(3) Production of Negative Electrode For the glass powder (negative electrode active material) obtained above, polyimide resin as binder and ketjen black as conductive substance, glass powder: binder: conductive substance = 85: 10: 5 ( (Weight ratio) and weighed it in N-methylpyrrolidone (NMP), and then sufficiently stirred with a rotation / revolution mixer to obtain a slurry-like negative electrode material. Next, using a doctor blade with a gap of 150 μm, the obtained negative electrode material was coated on a 20 μm thick copper foil as a negative electrode current collector, dried at 70 ° C. using a dryer, and then a pair of rotating rollers An electrode sheet was obtained by pressing in between. This electrode sheet was punched to a diameter of 11 mm with an electrode punching machine and dried under reduced pressure at 200 ° C. for 10 hours to imidize the polyimide resin to obtain a circular working electrode (negative electrode).

(4) Production of test battery The above working electrode was placed on the lower lid of the coin cell so that the copper foil surface was facing downward, and then dried on a polypropylene porous membrane having a diameter of 16 mm (Hoechst) dried at 60 ° C. for 8 hours under reduced pressure. A test battery was produced by laminating a separator made of Celanese Cellguard # 2400) and metallic lithium as a counter electrode. As the electrolytic solution, 1M LiPF ₆ solution / EC: DEC = 1: 1 (EC = ethylene carbonate, DEC = diethyl carbonate) was used. The test battery was assembled in an environment with a dew point temperature of −60 ° C. or lower.

(5) Evaluation test of charge / discharge characteristics Table 4 shows the results when the coin cells were charged / discharged. As an evaluation condition, the charge (Occlusion of Li ions in the negative electrode active material) was CC (constant current) charge up to 0 V at 0.2 mA. Next, discharge (release of Li ions from the negative electrode active material) was discharged to 1 V at a constant current of 0.2 mA. This charge / discharge was repeated to evaluate the cycle characteristics of the negative electrode.

(6) XRD measurement of the negative electrode active material at the time of completion of charging / discharging The negative electrode is taken out from the coin cell when charging is completed to 0V and the coin cell when discharging is completed to 1V, and the negative electrode is immersed in dimethyl carbonate (DMC). And washed. Thereafter, the negative electrode was dried under reduced pressure at room temperature overnight. A M06XCE manufactured by Bruker AXS was used as an X-ray diffraction measurement device, and a diffraction line profile of the negative electrode active material in the negative electrode was obtained by measurement under the following conditions using Cu-Kα rays as the X-ray source.

Tube voltage / tube current: 40 kV / 100 mA
Divergence / scattering slit: 1 °
Receiving slit: 0.15mm
Sampling width: 0.02 °
Measurement range: 5-70 °

(7) Analysis and data analysis Materials Data Inc. as analysis / quantification software. JADE Ver. Data analysis of the diffraction line profile was performed using 6.0. First, the diffraction line profile of the negative electrode active material was obtained by subtracting the background diffraction line profile from the diffraction line profile in the range of 5 to 70 ° (FIGS. 4 and 5). In this diffraction line profile, the peak apex and half width (FWHM) of each diffraction line peak were determined.

Table 5 shows the results of peak apexes and half-value widths obtained from the diffraction line profile of the negative electrode active material after completion of charge and discharge of Comparative Example in Table 5. Further, the composition of the negative electrode active material after completion of the discharge is shown in mol%. Here, the Sn component shows a value converted as SnO.

  The discharge capacity at the 50th cycle of the batteries using the negative electrode active materials of Examples 1 to 6 was as good as 406 mAh / g or more. On the other hand, in the batteries using the negative electrode active materials of Comparative Examples 1 to 3, the initial discharge capacity significantly decreased to 50 mAh / g or less at the 50th cycle.

  Hereinafter, although the negative electrode active material for electrical storage devices which concerns on 4th Embodiment is demonstrated in detail using an Example, this invention is not limited to these Examples.

(1) Preparation of negative electrode active material for non-aqueous secondary battery Tables 7 and 8 show Examples 1 to 14 and Comparative Examples 1 and 2. Each negative electrode active material was produced as follows.

  A composite oxide of tin and phosphorus (stannous pyrophosphate: Sn2P2O7) is used as the main raw material so that the compositions shown in Tables 7 and 8 are used, and raw material powders with various oxides, carbonate raw materials, metals, carbon raw materials, etc. Was prepared. The raw material powder was put into an alumina crucible and melted at 950 ° C. for 40 minutes in a nitrogen atmosphere using an electric furnace to be vitrified.

  Next, the molten glass was poured out between a pair of rotating rollers, and molded while rapidly cooling with a rotating roller to obtain a film-like glass having a thickness of 0.1 to 2 mm. For Examples 1 to 14 and Comparative Example 1, the film-like glass was pulverized with an alumina separator and then passed through a sieve having a mesh size of 20 μm to obtain a glass powder having a mean particle size of 5 μm (a negative electrode for non-aqueous secondary batteries). Material). For Example 15, the glass film was subjected to alcohol wet pulverization using a bead mill. In Example 16, alcoholic wet pulverization was performed on the film-like glass using a ball mill. In Example 17, the film-like glass was dry-ground using a ball mill and passed through a sieve having an opening of 75 μm. In Comparative Example 2, metal Sn powder (manufactured by Kanto Chemical Co., Inc.) was used as it was as a negative electrode active material for a non-aqueous secondary battery.

  The structure was identified by powder X-ray diffraction measurement for each sample. The negative electrode active materials of Examples 3 to 7, 9 to 13, and 15 to 17 were amorphous, and no crystals were detected. Examples 1, 2, 8, and 14 were almost amorphous, but some crystals were detected.

(2) Preparation of X-ray electron spectroscopic spectrum measurement sample The glass formed into a film shape in (1) was cut into 1 cm square, then subjected to surface polishing and washed with acetone. As a measurement sample for obtaining Sn3d _5/2 binding energy Pm of metal Sn, metal tin (granularity, purity 99.9%) manufactured by Kanto Chemical Co., Ltd. is pressed into a metal plate, and then surface polished. What was washed with acetone was used.

  Subsequently, gold was adhered to a part of the sample surface as an internal standard substance of an X-ray electron spectroscopy spectrum. Specifically, the sample surface was partially masked, and a sample for evaluation was prepared by depositing gold with a film thickness of 30 nm in vacuum using an ion sputtering apparatus (Quick Auto Coater JFC-1500, manufactured by JEOL). It was.

  After the powder sample was dispersed and cured in a silicon resin, gold was vapor-deposited on the surface in the same manner as the film-like sample to prepare an evaluation sample.

(3) X-ray Electron Spectroscopy (XPS) Measurement In the present invention, Perkin Elmer Phi MODEL 5400 ESCA was used as the X-ray electron spectroscopic spectrum measurement apparatus, and Mg—Kα ray (1253.6 eV) was used as the X-ray source. The sample for evaluation was fixed to a sample holder with a conductive carbon tape, then introduced into the XPS apparatus, and allowed to stand for 1 hour under reduced pressure in a preliminary chamber in the apparatus. Subsequently, the sample for evaluation was loaded into a measurement chamber of ultra-vacuum (10-8 Pa level). The measurement position was adjusted so that information of gold deposited on the sample surface and the measurement sample could be obtained simultaneously. Note that if the height of the sample for evaluation (Z-axis direction) differs between samples, the focal position of the X-rays on the surface of the sample shifts and affects the detection intensity of photoelectrons, so the samples for evaluation are aligned at the same height. It was.

  Furthermore, the sample surface was cleaned by etching with Ar ions.

<Etching conditions>
Ion current: 3 μA
Raster range: 50% x 50% (50mm x 50mm)
Acceleration voltage: 3 kV
Emission current in ion gun: 25 mA
Etching time: 2 minutes <Measurement conditions>
In the spectral region of each element,
Repeat count: 3
Number of cycles: 5
X-ray output: 15kV 400W
Pass energy: 44.75 eV
Measurement step: 0.1 eV
Each step time: 50ms
Analysis area: 0.6 mmφ
Detection angle: 45 °

(4) Analysis and data analysis As analysis / quantification software, PHI MultiPak Ver. Data analysis of the XPS spectrum was performed using 6.0. First, the Au 4f _7/2 orbit of gold deposited as an internal standard substance was subjected to charge correction to a value of 83.8 eV. Next, the binding energy values Pl and Pm at 3d _5/2 of the Sn atoms of the negative electrode active material and the metal Sn were obtained, respectively. Tables 1 and 2 show Pl and Pm and binding energy difference (Pl-Pm) of each sample.

FIG. 6 shows the XPS spectrum of the Sn atom 3d _5/2 orbital and the metal Sn 3d _5/2 orbital XPS spectrum of the negative electrode active material of Example 5. The binding energy values at the points where the maximum detected intensity was obtained in the XPS spectrum are shown in the figure as Pl and Pm, respectively.

(5) Measurement of powder properties The average particle diameter D50 and the maximum particle diameter D100 were measured using a laser diffraction particle size distribution analyzer SALD-2000J manufactured by Shimadzu Corporation.

  The tap density was measured under the above-described conditions using a powder tester PT-S manufactured by Hosokawa Micron Corporation.

  The BET specific surface area was measured by using FlowSorbII2200 manufactured by Micromeritex.

(6) Production of Negative Electrode For the glass powder (negative electrode active material) obtained above, polyvinylidene fluoride (PVDF) as a binder, ketjen black as a conductive substance, glass powder: binder: conductive substance = 85: After weighing to a ratio of 10: 5 (weight ratio) and dispersing in N-methylpyrrolidone (NMP), the mixture was sufficiently stirred with a rotation / revolution mixer to obtain a slurry-like negative electrode material. Next, using a doctor blade with a gap of 150 μm, the obtained slurry was coated on a 20 μm thick copper foil as a negative electrode current collector, dried with a dryer at 70 ° C., and then passed between a pair of rotating rollers. To obtain an electrode sheet. This electrode sheet was punched to a diameter of 11 mm with an electrode punching machine and dried under reduced pressure at 120 ° C. for 3 hours to obtain a circular working electrode.

(7) Production of test battery The above working electrode was placed on the lower lid of the coin cell with the copper foil surface facing down, and dried on it at 60 ° C. for 8 hours under reduced pressure for 16 hours in diameter. A separator comprising Cellguard # 2400 manufactured by Needs Co., Ltd. and metallic lithium as a counter electrode were laminated to prepare a test battery. As the electrolytic solution, 1M LiPF ₆ solution / EC (ethylene carbonate): DEC (diethyl carbonate) = 1: 1 was used. The test battery was assembled in an environment with a dew point temperature of −60 ° C. or lower.

(8) Charging / discharging test Charging (occlusion of lithium ions into the negative electrode material) performed CC (constant current) charging from 2 V to 0 V at 0.2 mA. Next, discharge (release of lithium ions from the negative electrode active material) was discharged from 0 V to 2 V at a constant current of 0.2 mA. This charge / discharge cycle was repeated.

  Tables 7 to 9 show the results of the initial charge / discharge characteristics when the charge / discharge test was performed and the cycle characteristics when the battery was repeatedly charged / discharged, with respect to the batteries using the negative electrode active materials of Examples and Comparative Examples.

  The binding energy difference (Pl-Pm) by XPS in Examples 1 to 14 was in the range of 1.6 to 3.2 eV, and the initial charge / discharge efficiency was excellent at 52% or more. On the other hand, in Comparative Example 1, since the bond energy difference (Pl-Pm) by XPS was as large as 3.6 eV, the initial charge / discharge efficiency was as low as 47%. In Examples 1 to 14, the discharge capacity was 253 mAh / g or more even after repeated charging and discharging for 20 cycles. On the other hand, in Comparative Example 2, since the binding energy difference (Pl-Pm) by XPS is as small as 0 eV, the initial charge / discharge efficiency was 60%, but the discharge capacity after repeated charge / discharge for 20 cycles was 15 mAh / g. It was low.

  The binding energy difference (Pl-Pm) by XPS of Examples 15 to 17 is 2.4 eV, the initial charge / discharge efficiency is 54% or more, and the discharge capacity after 20 cycles of repeated charge / discharge is 407 mAh / g or more. It was excellent. In particular, since Example 16 had a predetermined powder property and a homogeneous electrode could be produced, the initial charge / discharge efficiency and cycle characteristics were excellent.

  The negative electrode active material for an electricity storage device of the present invention is suitable for a portable electronic device such as a notebook computer or a mobile phone, a lithium ion non-aqueous secondary battery used for an electric vehicle, and a hybrid capacitor such as a lithium ion capacitor. is there.

Claims (24)

An electricity storage device characterized by containing a composition of SnO 70 to 95% and P ₂ O ₅ 5 to 30% (not including SnO 70% and P ₂ O ₅ 30%) in terms of mol% in terms of oxide Negative electrode active material.   The negative electrode active material for an electricity storage device according to claim 1, wherein the negative electrode active material is substantially amorphous.   The negative electrode material for electrical storage devices containing the negative electrode active material for electrical storage devices of Claim 1 or 2.   A method for producing a negative electrode active material for an electricity storage device according to claim 1 or 2, wherein the raw material powder is melted and vitrified in a reducing atmosphere or an inert atmosphere. .   The method for producing a negative electrode active material for an electricity storage device according to claim 4, wherein the raw material powder is a complex oxide containing phosphorus and tin. A negative electrode active material for an electricity storage device containing at least SnO and P ₂ O ₅ , wherein an amorphous halo is formed at 10 to 45 ° in terms of 2θ in a diffraction line profile obtained by powder X-ray diffraction measurement using CuKα rays. And when the curve fitting is performed with two components of the peak component P1 in which the 2θ value is fixed at 22.5 ° and the peak component P2 on the higher angle side than 22.5 °, the position of the peak apex of P2 is A negative electrode active material for an electricity storage device, wherein the 2θ value is 25.0 to 29.0 °. A negative electrode active material for an electricity storage device containing at least SnO and P ₂ O ₅ , wherein an amorphous halo is formed at 10 to 45 ° in terms of 2θ in a diffraction line profile obtained by powder X-ray diffraction measurement using CuKα rays. When the curve fitting is performed with two components of the peak component P1 having a 2θ value fixed at 22.5 ° and the peak component P2 on the higher angle side than 22.5 ° in the range, the peak areas A1 and P2 of P1 The negative electrode active material for an electricity storage device is characterized in that the peak area A2 satisfies the relationship of A1 / A2 = 0.01-8. 8. The negative electrode active material for an electricity storage device according to claim 6, wherein the negative electrode active material contains a composition of SnO 45 to 95% and P ₂ O _{5 5 to} 55% in mol%.   The negative electrode active material for an electricity storage device according to claim 6, wherein the negative electrode active material is substantially amorphous.   The negative electrode material for electrical storage devices containing the negative electrode active material for electrical storage devices in any one of Claims 6-9.   A method for producing the negative electrode active material for an electricity storage device according to any one of claims 6 to 9, wherein the raw material powder is melted and vitrified in a reducing atmosphere or an inert atmosphere. A method for producing a negative electrode active material.   The method for producing a negative electrode active material for an electricity storage device according to claim 11, wherein the raw material powder is a composite oxide containing phosphorus and tin.   A negative electrode active material used in an electricity storage device having at least a negative electrode and a positive electrode, and at the time of completion of charging, a 2θ value in a range of 30 to 50 ° of a diffraction line profile obtained by powder X-ray diffraction measurement using CuKα rays and / or Alternatively, a negative electrode active material for an electricity storage device, wherein a half width of a diffraction line peak detected in a range of 2θ value of 10 to 30 ° is 0.5 ° or more.   A negative electrode active material used for an electricity storage device composed of at least a negative electrode and a positive electrode, and detected at the time of completion of discharge within a 2θ value of 15 to 40 ° of a diffraction line profile obtained by powder X-ray diffraction measurement using CuKα rays A negative electrode active material for an electricity storage device, wherein the half width of the diffraction line peak is 0.1 ° or more. During discharge completion, as represented by mol% based on oxides terms, SnO 10 to 70% as a composition, Li ₂ O 20 to 70%, or claim 13, characterized in that it contains P ₂ O ₅ 2 to 40% 14. The negative electrode active material for an electricity storage device according to 14.   The negative electrode material for electrical storage devices containing the negative electrode active material for electrical storage devices in any one of Claims 13-15. A negative electrode active material for an electricity storage device containing at least SnO as a composition, wherein the binding energy value of electrons in the Sn3d _5/2 orbit of Sn atoms in the negative electrode active material for the electricity storage device is Pl, and Sn3d _{5/2 of} metal Sn A negative electrode active material for an electricity storage device, wherein (Pl-Pm) is 0.01 to 3.5 eV, where Pm is an electron binding energy value in orbit.   The negative electrode active material for an electricity storage device according to claim 17, wherein the negative electrode active material is substantially amorphous.   The negative electrode active material for an electricity storage device according to claim 17 or 18, wherein the negative electrode active material is in a powder form.   20. The negative electrode active material for an electricity storage device according to claim 19, wherein the average particle size is 0.1 to 10 [mu] m and the maximum particle size is 75 [mu] m or less.   The negative electrode material for electrical storage devices containing the negative electrode active material for electrical storage devices in any one of Claims 17-20.   A method for producing a negative electrode active material for an electricity storage device according to any one of claims 17 to 20, wherein the raw material powder is melted and vitrified in a reducing atmosphere or an inert atmosphere. A method for producing a negative electrode active material.   The method for producing a negative electrode active material for an electricity storage device according to claim 22, wherein the raw material powder contains a metal powder or a carbon powder.   The method for producing a negative electrode active material for an electricity storage device according to claim 22 or 23, wherein the raw material powder is a composite oxide containing phosphorus and tin.

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