Negative electrode active material, negative electrode active material precursor and method for producing the same, and secondary battery including such negative electrode active material

Abstract

To provide: a negative electrode active material excellent in initial coulomb efficiency and capacity retention rate; a negative electrode active material precursor and a method for producing the same; and a secondary battery including such a negative electrode active material.SOLUTION: A negative electrode active material contains a silicon-based matrix, silicon particles and a metal silicate. The silicon particles are dispersed in a silicon-based matrix phase. A chemical shift value belonging to Si and a chemical shift value belonging to SiO4 in a solid NMR spectrum are detected as a peak A around -80 ppm and a peak B around -110 ppm, respectively, a ratio R of the peak A to the peak B being in the range of 1.0 to 10.0.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a negative electrode active material, a negative electrode active material precursor and a method for producing the same, and a secondary battery having such a negative electrode active material. More specifically, the present invention relates to a negative electrode active material that can be suitably used as a negative electrode active material for secondary batteries, a negative electrode active material precursor and a method for producing the same, and a secondary battery including such a negative electrode active material in its negative electrode. [Background technology]

[0002] In recent years, the demand for small, high-capacity secondary batteries has increased with the advancement of performance and miniaturization in various portable electronic and communication devices. In particular, various lithium-ion batteries, which are non-aqueous electrolyte secondary batteries that use lithium intercalation compounds as the negative electrode active material, which can absorb and release lithium ions between the layers of crystal planes during charging and discharging, have been rapidly deployed in hybrid vehicles, electric vehicles, home storage batteries, and other applications, and their range of use is expanding. Therefore, there is a demand for lithium-ion batteries with higher capacity and improved battery characteristics such as cycle characteristics and discharge rate characteristics. Conventional lithium-ion batteries primarily use graphite as the anode material, but the low theoretical capacity density of graphite (372 mAh / g) limits the development of lithium-ion batteries with higher energy densities. To compensate for the low theoretical capacity density of graphite, anode materials using elements capable of absorbing and releasing lithium ions, such as silicon and tin, or alloys and oxides with other elements, are being investigated. Silicon, in particular, has a theoretical capacity (4200 mAh / g) more than 10 times that of graphite, so silicon and silicon-containing anode active materials are attracting attention as next-generation anode materials capable of achieving higher capacities.

[0003] However, silicon oxide (SiO2) is generally present on the surface of silicon, and this silicon oxide forms lithium silicate (lithium silicate salt) with lithium ions supplied from the positive electrode during the initial charge, stabilizing and making the reaction irreversible. This reduces the amount of lithium ions released to the positive electrode, and the initial charge-discharge efficiency is likely to decrease. In other words, silicon and silicon-containing negative electrode active materials have a low initial efficiency (hereinafter referred to as "initial coulombic efficiency"), i.e., a large irreversible capacity during the initial absorption and desorption of lithium ions, making it difficult to utilize the capacity of the positive electrode. Many attempts have been made to improve the initial coulombic efficiency of such silicon-containing negative electrode active materials. For example, Patent Document 1 discloses a negative electrode active material for non-aqueous electrolyte secondary batteries, which is represented by a specific composition formula containing an alkaline earth metal, silicon, oxygen, carbon, and hydrogen, and which contains a silicate composed of a silicon-based inorganic compound and an alkaline earth metal. It is said that when used as a negative electrode material for non-aqueous electrolyte secondary batteries, the irreversible capacity can be reduced. Patent Document 2 discloses a negative electrode active material containing silicon compound particles that contain Li2SiO3 produced by reacting a charge-transfer complex of Li and a polycyclic aromatic with a silicon oxide, at least a portion of the surface of which is coated with a carbon layer, and the negative electrode active material particles contain a substance having a carboxylic acid structure in the surface layer. Patent Document 3 discloses a negative electrode active material for a non-aqueous electrolyte secondary battery, which contains silicon oxycarbide represented by a specific composition formula and an alkali metal salt produced by reacting Li with a charge-transfer complex of a polycyclic aromatic compound. Patent Document 4 discloses a negative electrode active material that contains a silicon oxide composite containing MgSiO3 as magnesium silicate produced by a reaction between silicon, silicon oxide, and elemental inorganic Mg, and that has a ratio of specific diffraction peaks in a specific range in X-ray diffraction analysis. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-125826 [Patent Document 2] Patent Publication No. 2021-048049 [Patent Document 3] Japanese Patent Application Publication No. 2017-195083 [Patent Document 4] Special Publication No. 2021-506059 Summary of the Invention [Problem to be solved by the invention]

[0005] The negative electrode active material for non-aqueous electrolyte secondary batteries disclosed in Patent Document 1 is produced by doping silicon oxycarbide (a composite oxide composed of silicon, oxygen, and carbon) produced by sintering methylsiloxanes at high temperatures with an inorganic alkaline earth metal compound or a lower fatty acid salt soluble only in highly polar organic solvents, with the silicate being intended to be dispersed throughout the composite oxide. In this case, due to the low solubility of the alkaline earth metal source, some unreacted alkaline earth metal source tends to remain within the silicon oxycarbide. Therefore, the reaction between lithium and silicon oxide (SiO2) during the first charge is insufficient, resulting in limited improvement in the initial coulombic efficiency. Furthermore, silicon-hydrogen bonds remain in such negative electrode active materials, and there is still room for improvement in suppressing the generation of irreversible capacity due to the presence of these bonds. The negative electrode active material disclosed in Patent Document 2 is produced by generating silicon oxide gas, mixing it with metal particles, and solidifying it on an adsorption plate. The resulting silicon monoxide particles as the negative electrode active material are then immersed in a solution of a lithium and polycyclic aromatic charge-transfer complex dissolved in an ether-based solvent to dope them with lithium by a redox process, and silicate is formed dispersed throughout the silicon monoxide particles. Meanwhile, the negative electrode active material disclosed in Patent Document 3 is produced by reacting silicon oxycarbide as the negative electrode active material with a one-electron reducing agent, such as lithium naphthalenide, composed of an alkali metal and a polycyclic aromatic compound to dope the silicon monoxide particles with an alkali metal such as lithium. The lithium and polycyclic aromatic charge-transfer complexes used in Patent Documents 2 and 3 are flammable in the presence of humidity, unstable, and difficult to handle, resulting in significant labor and constraints in the production of the negative electrode active material, making them unsuitable for industrial application. The negative electrode active material disclosed in Patent Document 4 is produced using a specific manufacturing method based on a gas-phase reaction, and is therefore essentially limited to a negative electrode active material containing silicon monoxide, and the alkali metal doping source is also limited to inorganic substances. Therefore, it cannot be applied to the production of negative electrode materials using organic precursors, and its range of application is also limited. Therefore, there remains a need for the development of a simpler, more versatile alkali metal source doping method that can be applied to a wide range of negative electrode active material precursors, as well as for improving the initial coulombic efficiency by reducing the irreversible capacity of silicon-containing negative electrode active materials.

[0006] The present inventors have investigated ways to improve the initial coulombic efficiency of silicon-containing negative electrode active materials by suppressing the formation of lithium silicate during the initial charge / discharge cycle. As a result, they have found that a negative electrode active material containing a specific metal silicate and having a specific relationship between the peak ratios attributable to Si and SiO4 in its solid-state NMR spectrum is effective in improving the initial coulombic efficiency and capacity retention, leading to the completion of the present invention. An object of the present invention is to provide a negative electrode active material that is excellent in initial coulombic efficiency and capacity retention rate, and a secondary battery that includes such a negative electrode active material. Another object of the present invention is to provide a negative electrode active material precursor useful for producing such a negative electrode active material, and a method for producing the same. [Means for solving the problem]

[0007] The present invention has the following aspects. [1] A silicon-based matrix, silicon particles, and a metal silicate, the silicon particles are dispersed in a silicon-based matrix phase, A negative electrode active material in which a chemical shift value attributable to Si is detected as peak A at around −80 ppm and a chemical shift value attributable to SiO4 is detected as peak B at around −110 ppm in a solid-state NMR spectrum, and the ratio R of peak A to peak B is in the range of 1.0 to 10.0. [2] The negative electrode active material according to [1], wherein the metal silicate is a silicate of at least one metal selected from Li, Na, K, Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca. [3] The negative electrode active material according to [1] or [2], wherein the atomic ratio of metal atoms in the metal silicate to silicon atoms in the silicon particles is in the range of 0.00001 to 0.2. [4] The negative electrode active material according to any one of [1] to [3], wherein the silicon particles have an average particle size of 150 nm or less and a crystallite size of 35 nm or less, as determined from the half-width of the peak at 2θ=28.4° in an X-ray crystal structure diffraction spectrum. [5] The negative electrode active material according to any one of [1] to [4], wherein at least one of the lattice structure attributed to the metal silicate and the lattice structure attributed to silicon nitride is present in the vicinity of the surface of the silicon particles. [6] The negative electrode active material according to any one of [1] to [5], wherein the content of the silicon particles is in the range of 10 to 70 mass % based on the total amount of the negative electrode active material. [7] The negative electrode active material according to any one of [1] to [6], wherein the silicon-based matrix contains at least a compound represented by SiOxCyNz (wherein x, y, and z are positive numbers satisfying 1≦x≦2, 1≦y≦20, and 0≦z≦0.5, respectively). [8] The average particle size is 1 μm or more and 15 μm or less, and the specific surface area is 1 m 2 / g or more 30m 2 / g or less of the negative electrode active material [1] to [7].

[0008] [9] A precursor of a negative electrode active material, comprising a metal complex containing a metal cation whose counter ion is an organic anion, silicon particles, and an organosilicon polymer material.

[10] The negative electrode active material precursor according to [9], wherein the metal cation is a cation of at least one metal selected from Li, Na, K, Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca.

[11] The negative electrode active material precursor according to [9] or

[10] , wherein the metal cation is at least one metal cation selected from Mg and Mn.

[12] The negative electrode active material precursor according to any one of [9] to

[11] , wherein the organic anion contains a carboxylate anion having a hydrocarbon group having 2 to 20 carbon atoms.

[13] The negative electrode active material precursor according to any one of [9] to

[12] , wherein the silicon particles have an average particle size of 150 nm or less.

[14] The negative electrode active material precursor according to any one of [9] to

[13] , wherein the organosilicon polymer material has a polymer structure containing silicon, carbon, and oxygen elements.

[15] The negative electrode active material precursor according to any one of [9] to

[14] , wherein the organosilicon polymer material has a polymer structure consisting of a mixture of a polysiloxane compound and a carbon source resin, or a composite of a polysiloxane compound and a carbon source resin.

[0009]

[16] A method for producing a negative electrode active material precursor, comprising the following steps a1 and b1: Step a1: A step of adding an organic solvent, a dispersant, and a metal complex containing a metal cation and whose counter ion is an organic anion to silicon particles, followed by stirring or pulverizing the mixture to obtain a slurry 1. Step b1: A step of mixing an organosilicon polymer material with the slurry 1 obtained in step a1, followed by removing the solvent and drying to obtain a negative electrode active material precursor.

[17] A method for producing a negative electrode active material precursor, comprising the following steps a2 and b2: Step a2: A step of adding an organic solvent and a dispersant to silicon particles and stirring or pulverizing the mixture to obtain a slurry 2 Step b2: A step of mixing an organosilicon polymer material, the slurry 2 obtained in step a2, and a metal complex containing a metal cation and whose counter ion is an organic anion, followed by removing the solvent and drying to obtain a negative electrode active material precursor.

[18] The method for producing a negative electrode active material precursor according to

[16] or

[17] , wherein the metal cation is a cation of at least one metal selected from Li, Na, K, Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca.

[19] The method for producing a negative electrode active material precursor according to any one of

[16] to

[18] , wherein the metal cation is at least one metal cation selected from Mg and Mn.

[20] The method for producing a negative electrode active material precursor according to any one of

[16] to

[19] , wherein the organic anion contains a carboxylate anion having a hydrocarbon group having 2 to 20 carbon atoms.

[21] The method for producing a negative electrode active material precursor according to any one of

[16] to

[20] , wherein the silicon particles have an average particle size of 150 nm or less.

[22] The method for producing a negative electrode active material precursor according to any one of

[16] to

[21] , wherein the organosilicon polymer material has a polymer structure containing silicon, carbon, and oxygen elements.

[23] The method for producing a negative electrode active material precursor according to any one of

[16] to

[22] , wherein the organosilicon polymer material has a polymer structure consisting of a mixture of a polysiloxane compound and a carbon source resin, or a composite of a polysiloxane compound and a carbon source resin.

[24] The method for producing a negative electrode active material precursor according to any one of

[16] to

[23] , wherein the metal complex is used as a solution of the metal complex containing a solvent.

[25] A method for producing a negative electrode active material precursor according to

[24] , comprising mixing an oxide or hydroxide of at least one metal selected from Li, Na, K, Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca with a carboxylic acid having a hydrocarbon group having 2 to 20 carbon atoms in an amount of 100 to 500 times by mole relative to the oxide or hydroxide of the metal, heating the resulting mixture, and removing the resulting water while allowing the mixture to react. The method also includes adding a solvent to the resulting mixture, and using the metal complex solution.

[26] A method for producing a negative electrode active material precursor according to

[24] , comprising: mixing at least one metal hydroxide selected from Li, Na, K, Rb, and Cs with a carboxylic acid having a hydrocarbon group having 2 to 20 carbon atoms in an amount of 100 to 500 times by molar ratio relative to the metal hydroxide, and water in an amount of 300 times by mass or less relative to the metal hydroxide; heating the mixture; then adding an inorganic salt of at least one metal selected from Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca and heating the mixture to carry out a metal exchange reaction; separating the aqueous phase; and then dehydrating the resulting mixture; adding a solvent to the resulting mixture to prepare the metal complex solution.

[27] A method for producing a negative electrode active material, comprising the step of firing the negative electrode active material precursor according to any one of [9] to

[15] in an inert gas atmosphere.

[28] A secondary battery having a negative electrode active material according to any one of [1] to [8]. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a negative electrode active material that is excellent in initial coulombic efficiency and capacity retention rate, and a secondary battery that includes such a negative electrode active material and has excellent battery properties such as charge-discharge characteristics. Furthermore, the present invention can provide a negative electrode active material precursor useful for producing such a negative electrode active material, and a method for producing the same. [Brief explanation of the drawings]

[0011] [Figure 1] 1(a) shows the results of HR-TEM observation of the surface of a silicon particle in the negative electrode active material (1-2), and FIG. 1(b) shows the results of calculation of the lattice spacing by fast discrete Fourier transform (FFT). DETAILED DESCRIPTION OF THE INVENTION

[0012] <Negative electrode active material> The negative electrode active material of the present invention (hereinafter also referred to as "the present negative electrode active material") contains a silicon-based matrix, silicon particles, and a metal silicate, the silicon particles being dispersed in the silicon-based matrix phase, and in a solid-state NMR spectrum, a chemical shift value attributable to Si is detected as Peak A at around -80 ppm, and a chemical shift value attributable to SiO4 is detected as Peak B at around -110 ppm, and the ratio R of Peak A to Peak B is in the range of 1.0 to 10.0.

[0013] The silicon particles contained in this negative electrode active material are composed of zero-valent silicon. The average particle size of the silicon particles is preferably 150 nm or less, more preferably 120 nm or less, and even more preferably 100 nm or less. The average particle size of the silicon particles is preferably 1 nm or more, more preferably 20 nm or more, and even more preferably 30 nm or more. When the average particle size of the silicon particles is within the above range, it is easy to improve the charge / discharge performance of a secondary battery containing this negative electrode active material, and it is easy to maintain a high capacity retention rate over a long period of time. Here, the average particle size of silicon particles is the particle size (D50) at which the cumulative volume distribution curve reaches 50% of the total when measured by dynamic light scattering using a laser diffraction particle size analyzer or the like, starting from the small diameter side.

[0014] Silicon particles exceeding 300 nm tend to form large agglomerates, which can easily cause pulverization during charging and discharging in secondary batteries containing this negative electrode active material, resulting in a decrease in capacity retention. Silicon particles less than 10 nm tend to aggregate, reducing their dispersibility in the negative electrode active material. Furthermore, their surface activation energy increases, which can lead to increased by-products on the silicon particle surface during high-temperature firing of the negative electrode active material, leading to a decrease in charge-discharge performance. Therefore, it is preferable that the content of silicon particles exceeding 300 nm and silicon particles less than 10 nm in this negative electrode active material be as small as possible.

[0015] The silicon particles may be granular, needle-like, or flake-like in shape. From the viewpoint of the charge-discharge performance of the present negative electrode active material, the length in the major axis direction is preferably 30 to 150 nm, the thickness is preferably 15 to 70 nm, and the ratio of the thickness to the length, that is, the aspect ratio, is preferably 0.5 or less. Although the average particle size of silicon particles can be measured by dynamic light scattering, silicon particles with the above aspect ratios can be identified more easily and precisely using a transmission electron microscope (TEM) or a field emission scanning electron microscope (FE-SEM). In the case of this anode active material, the sample to be measured can be cut with a focused ion beam (FIB) and the cross section can be observed with an FE-SEM, or the sample can be sliced ​​and the state of the silicon particles can be identified by TEM observation. The aspect ratio of silicon particles is a calculation result based on 50 particles that are the main part of silicon particles within the field of view of the TEM image.

[0016] The silicon particles contained in the present negative electrode active material preferably have an average particle size of 150 nm or less and a crystallite size of 35 nm or less, as determined from the half-width of the peak at 2θ=28.4° in the X-ray crystal structure diffraction spectrum. A crystallite size of 35 nm or less is preferable from the viewpoint of initial coulombic efficiency and capacity retention. The crystallite size is more preferably 25 nm or less, and even more preferably in the range of 3 to 22 nm.

[0017] The silicon particle content in this negative electrode active material is preferably in the range of 10 to 70 mass% of the total negative electrode active material. Since the maximum value when assuming body-centered cubic close-packing is 68 mass%, taking into consideration that the silicon particle surfaces are completely surrounded by the silicon-based matrix phase, a range of 40 to 65 mass% is more preferable. When the silicon particle content is in this range, the silicon particle surfaces are completely covered by the silicon-based matrix phase, protecting them from the intrusion of the electrolyte, so the negative electrode active material is likely to have excellent initial coulombic efficiency and capacity retention. Furthermore, secondary batteries containing this negative electrode active material are likely to have excellent battery properties such as charge / discharge characteristics.

[0018] In this negative electrode active material, silicon particles are dispersed as primary particles in a silicon-based matrix phase. The silicon-based matrix phase is preferably composed of a compound containing silicon, oxygen, and carbon. The silicon-based compound preferably has a structure containing free carbon and a three-dimensional network structure of the silicon-oxygen-carbon skeleton of SiOC (silicon oxycarbide). Here, free carbon refers to carbon that is not contained in the silicon-oxygen-carbon three-dimensional skeleton of SiOC, and includes carbon present in the carbon phase, carbon bonded to carbon in the carbon phase, and carbon bonded to the silicon-oxygen-carbon skeleton and the carbon phase.

[0019] The silicon-based matrix phase is composed of compounds containing silicon, oxygen, and carbon. When the silicon-based matrix phase has a three-dimensional network structure of the silicon-oxygen-carbon skeleton of SiOC and a structure containing free carbon, the silicon-oxygen-carbon skeleton in the silicon-based matrix phase has high chemical stability. The composite structure with the free carbon reduces the electron transition resistance and facilitates lithium ion diffusion. The silicon particles are tightly enclosed within the composite structure of the silicon-oxygen-carbon skeleton and the free carbon, preventing direct contact between the silicon particles and the electrolyte. As a result, when this anode active material is used in a negative electrode, the silicon particles in the anode play a key role in achieving charge / discharge performance. Chemical reactions between the silicon particle surface and the electrolyte during charge / discharge are avoided, minimizing performance degradation of the silicon particles themselves. Furthermore, when the compound constituting the silicon-based matrix phase has a three-dimensional network structure of the silicon-oxygen-carbon skeleton of SiOC and a structure containing free carbon, the approach of lithium ions causes a change in the electron distribution within the silicon-oxygen-carbon skeleton, resulting in the formation of electrostatic and coordinate bonds between the silicon-oxygen-carbon skeleton and the lithium ions. These electrostatic and coordinate bonds allow lithium ions to be stored within the silicon-oxygen-carbon skeleton. Meanwhile, the relatively low coordinate bond energy facilitates lithium ion desorption reactions. In other words, the silicon-oxygen-carbon skeleton is thought to be capable of reversibly intercalating and deintercalating lithium ions during charging and discharging.

[0020] When the compound that constitutes the silicon-based matrix phase contains silicon, oxygen, and carbon, the silicon-based matrix phase preferably contains a compound represented by the following formula (1). SiOxCy (1) In formula (1), x represents the molar ratio of oxygen to silicon (ratio of the number of atoms), and y represents the molar ratio of carbon to silicon (ratio of the number of atoms). When this negative electrode active material is used in a secondary battery, from the viewpoint of achieving an advantageous balance between charge / discharge performance and capacity retention rate, 1≦x<2 is preferable, 1≦x≦1.9 is more preferable, and 1≦x≦1.8 is even more preferable. When the present negative electrode active material is used in a secondary battery, 1≦y≦20 is preferable, and 1.2≦y≦15 is more preferable, from the viewpoint of the balance between charge / discharge performance and initial coulombic efficiency.

[0021] The compound constituting the silicon-based matrix phase may contain nitrogen in addition to silicon, oxygen, and carbon. Here, nitrogen can be introduced into the silicon-based matrix phase due to nitrogen derived from the polysiloxane compound, phenolic resin, dispersant, other nitrogen compounds, etc. contained as components of the negative electrode active material precursor in the method for producing the present negative electrode active material described below, which have nitrogen-containing atomic groups as functional groups in their molecules, or due to nitrogen gas used in the firing step. When the silicon-based matrix phase contains nitrogen, the charge / discharge performance and capacity retention rate of the present negative electrode active material tend to be more excellent.

[0022] When the compound constituting the silicon-based matrix phase contains silicon, oxygen, carbon, and nitrogen, the silicon-based matrix phase preferably contains a compound represented by the following formula (2). SiOxCyNz (2) In formula (2), x and y have the same meanings as described above, and z represents the molar ratio (atomic ratio) of nitrogen to silicon. When the silicon-based matrix phase contains the compound represented by the formula (2), from the viewpoints of charge-discharge performance and capacity retention rate when the present negative electrode active material is used in a secondary battery, 1≦x≦2, 1≦y≦20, 0<z≦0.5 are preferable, and 1≦x≦1.9, 1.2≦y≦15, 0<z≦0.4 are more preferable. Here, x, y, and z are all positive numbers. x, y, and z can be obtained by measuring the mass content of each element and then converting it to a molar ratio (atomic ratio). At this time, the contents of oxygen and carbon can be quantified by using an inorganic element analyzer, and the content of silicon can be quantified by using an inductively coupled plasma optical emission spectrometer (ICP-OES).

[0023] In addition, although it is preferable to measure x, y, and z by the above method, it may also be obtained by performing local analysis of the present negative electrode active material, acquiring a large number of measurement points of the content ratio data obtained thereby, and extrapolating the content ratio of the entire present negative electrode active material. Examples of local analysis include energy dispersive X-ray spectroscopy (SEM-EDX) and electron probe microanalyzer (EPMA).

[0024] The metal silicate contained in the present negative electrode active material is preferably a silicate of at least one metal selected from Li, Na, K, Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca. Furthermore, in the present negative electrode active material, the atomic ratio of metal atoms in the metal silicate to silicon atoms in the silicon particles is preferably in the range of 0.00001 to 0.2. The preferred range of this atomic ratio may vary depending on the type of metal atom. For example, when the metal atom is Mg, the atomic ratio is more preferably in the range of 0.01 to 0.1, and when the metal atom is Mn, the atomic ratio is more preferably in the range of 0.00005 to 0.0005. In this specification, the "atomic ratio of metal atoms in the metal silicate to silicon atoms in the silicon particles" refers to the atomic ratio (molar ratio) of metal atoms in the metal silicate to silicon atoms in the silicon particles. The atomic ratio of "metal atoms in the metal silicate to silicon atoms in the silicon particles" may also be referred to as the atomic ratio (molar ratio).

[0025] In the present negative electrode active material, at least one of a lattice structure attributed to a metal silicate and a lattice structure attributed to silicon nitride is preferably present near the surface of the silicon particles. At least one of the lattice structures belonging to metal silicates or silicon nitride may be chemically or physically directly bonded or adsorbed to the surface of the silicon particles, and may be present near the surface of the silicon particles. Note that the near-surface of the silicon particles means, for example, within 10 nm, preferably within 5 nm from the surface.

[0026] In particular, it is preferred that at least one of the lattice structure attributed to metal silicate or the lattice structure attributed to silicon nitride is present near the surface of silicon particles, and it is more preferred that both the lattice structure attributed to metal silicate and the lattice structure attributed to silicon nitride are present.When both of the lattice structures are present, the lattice structure attributed to silicon nitride is first present near the surface of the silicon particles so as to cover at least a part of the silicon particle surface, preferably in a shell-like covering manner, and the lattice structure attributed to metal silicate may further be present so as to cover at least a part of the outer surface of the lattice structure attributed to silicon nitride, preferably in a shell-like covering manner. Here, the lattice structure attributable to the metal silicate is preferably a lattice structure attributable to a crystalline body of the metal silicate, and the lattice structure attributable to silicon nitride is preferably a lattice structure attributable to a crystalline body of silicon nitride.

[0027] The presence of a lattice structure attributed to metal silicate near the surface of silicon particles can be confirmed by slicing the negative electrode active material using a focused ion beam (FIB) and observing the sliced ​​material with a high-resolution transmission electron microscope (hereinafter also referred to as "HR-TEM"). In addition, using STEM-EDS (Scanning Transmission Electron Microscope Energy-Dispersive-Spectroscopy), the concentrations of metal elements, Si elements, and O elements present near the surface of silicon particles can be detected in a mapping image, and the concentration of metal silicates can be determined by combining the metal elements, Si elements, and O elements.

[0028] When at least one of the lattice structures belonging to metal silicates and silicon nitride covers at least a portion of the surface of the silicon particles, the coverage is preferably 1 to 100%, more preferably 10% or more. The thickness of the covering crystalline film is preferably 0.2 to 10 nm, more preferably 1 to 8 nm. The coverage and the thickness of the crystalline film can be measured by the above-mentioned HR-TEM, and the coverage can be calculated from the ratio of the amount of silicon particles to the amount of metal silicate.

[0029] It is believed that a silicon oxide film is always present on the surface of silicon particles due to natural oxidation when the silicon particles are not doped with an alkali metal source. Such silicon oxide has Lewis acidity, and it is believed that during the first charge, lithium silicate is produced by a neutralization reaction between the silicon oxide film on the silicon particle surface and lithium ions. The present anode active material is preferably obtained by calcining the present anode active material precursor described below, which is prepared during production via a process of uniformly dissolving a metal complex having a specific metal cation. During calcination, the silicon oxide film on the silicon particle surface is converted to metal silicate by reaction with the specific metal cation before the first charge operation. This conversion prevents lithium ions from being stabilized as the lithium silicate in the anode active material during the first charge operation, preventing them from returning to the positive electrode during discharge and resulting in a decrease in capacity. Therefore, if at least one of the lattice structures belonging to metal silicates or the lattice structure belonging to silicon nitride is present near the surface of the silicon particles before the initial charging operation, it is believed that the production of lithium silicate can be effectively suppressed during the initial charging operation, thereby improving the initial coulombic efficiency and capacity retention rate of the present negative electrode active material. From the viewpoint of suppressing the generation of lithium silicate during the initial charging operation, it is more preferable that the lattice structure attributable to metal silicate is converted to the surface silicon oxide film originally contained in the present negative electrode active material by 50 mass% or more before the initial charging operation (i.e., upon completion of firing) and is present in the vicinity of the silicon particle surface.

[0030] Here, the nitrogen in the lattice structure attributed to silicon nitride is thought to be introduced in the same manner as in the case where the compound constituting the silicon-based matrix phase contains silicon, oxygen, carbon, and nitrogen. That is, in the method for producing the present negative electrode active material described below, nitrogen is thought to be introduced due to the polysiloxane compound, phenolic resin, dispersant, other nitrogen compounds, etc. contained as components of the negative electrode active material precursor having nitrogen-containing atomic groups as functional groups in their molecules, and due to the nitrogen gas used in the baking process. The lattice structure attributed to silicon nitride can suppress contact between the silicon particle surface and oxidizing substances such as oxygen gas, thereby suppressing the growth and increase of silicon oxide films. Therefore, it is thought that the generation of lithium silicate during the initial charging operation of a secondary battery containing this negative electrode active material can be reduced, and the initial coulombic efficiency and capacity retention rate can be improved.

[0031] In this negative electrode active material, the chemical shift value attributable to Si is detected as Peak A near -80 ppm in the solid-state NMR spectrum, and the chemical shift value attributable to SiO4 is detected as Peak B near -110 ppm, with the ratio R of Peak A to Peak B being in the range of 1.0 to 10.0. Specifically, the integral of the peak at -80 ppm attributable to Si is determined as the value of Peak A, which is the integral of the Si peak having its top at -80 ppm in the range of -50 to -90 ppm. Meanwhile, the integral of the peak at -110 ppm attributable to SiO4 is determined as the integral of the SiO4 peak having its top at -110 ppm in the range of -90 to -150 ppm. The ratio R is then calculated. The ratio R is more preferably in the range of 3.0 to 10.0. When the ratio R is within the above range, the negative electrode active material exhibits excellent initial coulombic efficiency and capacity retention. Furthermore, a secondary battery containing this negative electrode active material has excellent battery characteristics such as charge and discharge characteristics. In this negative electrode active material, the silicon particles are not aggregated but are all dispersed as primary particles in the silicon-based matrix phase. In other words, there are no aggregated secondary silicon particles, and the primary silicon particles are monodispersed. The present negative electrode active material exhibiting such properties can be preferably obtained from a negative electrode active material precursor described later, and in particular, can be suitably obtained from a negative electrode active material precursor produced by adding, as a raw material, a metal complex solution prepared by a specific manufacturing method.

[0032] The average particle size of the present negative electrode active material is preferably 1 μm or more and 15 μm or less, more preferably 2 μm or more and 8 μm or less. The average particle size is the D50 value as described above, and the measurement method is also the same as described above. When the average particle size is within the above range, when a secondary battery is formed using the present negative electrode active material, it is easy to suppress the generation of solid-phase interface electrolyte decomposition products during charge and discharge, and it is easy to prevent a decrease in the reversible charge and discharge capacity per unit volume. In addition, it is easy to suppress peeling of the electrode film from the current collector during electrode film production. The specific surface area of ​​this negative electrode active material is 1m 2 / g or more 30m 2 / g or less, and 2 / g or more 15m 2 / g or less is more preferable. When the specific surface area is within this range, the amount of solvent absorbed during electrode preparation can be kept appropriate, and the amount of binder used to maintain binding properties can also be kept appropriate. The specific surface area of ​​the present negative electrode active material can be measured, for example, by the BET method using a specific surface area measurement device and nitrogen gas adsorption measurement. The negative electrode active material has an average particle size of 1 μm or more and 15 μm or less, and a specific surface area of ​​1 m 2 / g or more 30m 2 The negative electrode active material preferably has an average particle size of 2 μm or more and 8 μm or less, and a specific surface area of ​​2 m 2 / g or more 15m 2 It is more preferable that the molecular weight is not more than 1 / g.

[0033] The negative electrode active material may contain other necessary third components in addition to those mentioned above. The surface of the negative electrode active material may be coated with a coating material, preferably a material that is expected to have electron conductivity, lithium ion conductivity, and the effect of inhibiting decomposition of the electrolyte. When the surface of the present negative electrode active material is coated with a coating material, the average thickness of the coating layer is preferably 10 nm to 300 nm, more preferably 20 nm to 200 nm. When the present negative electrode active material has a coating layer with this average thickness, silicon particles that happen to be exposed on the cross section, i.e., the surface, of the present negative electrode active material can be protected during pulverization after firing, which tends to further improve the chemical stability and thermal stability of the present negative electrode active material and suppress deterioration in the charge / discharge performance of the resulting secondary battery. When the surface of the present negative electrode active material is coated with a coating material, the content of the coating material is preferably 1 to 30 mass %, more preferably 3 to 25 mass %, based on the total amount of the components of the present negative electrode active material and the coating material, from the viewpoint of improving the chemical stability and thermal stability of the present negative electrode active material. Examples of coating materials include electron-conductive materials such as carbon, titanium, and nickel. Among these, carbon is preferred, and low-crystalline carbon is more preferred, from the viewpoint of improving the chemical stability and thermal stability of the present negative electrode active material. When the coating material is low-crystalline carbon, the average thickness of the coating layer is preferably 10 nm or more and 300 nm or less. The content of low-crystalline carbon is preferably 1 to 30 mass% based on the total amount of the constituent components of the present negative electrode active material and the low-crystalline carbon as the coating material.

[0034] <Negative electrode active material precursor> The present invention also provides a negative electrode active material precursor (hereinafter also referred to as "the present precursor") that contains a metal complex (hereinafter also referred to as "metal complex") that contains a metal cation whose counter ion is an organic anion, silicon particles, and an organosilicon-based polymer material. The present negative electrode active material is preferably obtained from the present precursor by the process described below.

[0035] The metal cation in the metal complex contained in the precursor is preferably a cation of at least one metal selected from Li, Na, K, Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca. In the metal complex, the valence of the metal cation can be any of the valences that each of the above-mentioned metals can have. The valence of the metal cation in the metal complex contained in the precursor is usually preferably monovalent, divalent, or trivalent, from the viewpoint that the present negative electrode active material obtained from the precursor is likely to have excellent initial coulombic efficiency and capacity retention. However, for example, Mn, Bi, and Zr also have a valence of 4 to 6, and the metal cation may have such a valence. In particular, it is more preferable that the metal cation in the metal complex contained in the precursor is at least one metal cation selected from Mg and Mn, from the viewpoints of reactivity with the native oxide film on the surface of silicon particles, stability of the resulting Mg silicate, and production efficiency of silicon nitride produced by a catalytic reaction with Mn, within the firing temperature range when the precursor is fired to obtain the present negative electrode active material.

[0036] In the metal complex, the counter ion of the metal cation is an organic anion. Examples of the organic anion include an alkoxy anion, an aryloxy anion, a carboxylate anion, a phosphate anion having an organic group, a phosphite anion having an organic group, and a sulfonate anion having an organic group. Among these, a carboxylate anion is preferred, and a carboxylate anion having a hydrocarbon group having 2 to 20 carbon atoms is more preferred from the viewpoint of facilitating coordination and adsorption of the metal complex to the silicon particle surface in the process for producing the precursor described below. Examples of hydrocarbon groups having 2 to 20 carbon atoms include linear or branched alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, undecyl, and dodecyl; cycloalkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, methylcyclohexyl, and cyclooctyl; aryl groups such as phenyl, methylphenyl, ethylphenyl, and naphthyl; and aralkyl groups such as benzyl. Among these, n-pentyl, isopentyl, 2-ethylhexyl, and decyl are preferred. These groups may be in the form of a structural isomer mixture. The carboxylate anion having a hydrocarbon group having 2 to 20 carbon atoms may be a monocarboxylate anion or a polycarboxylate anion, but is preferably a monocarboxylate anion from the viewpoint of facilitating coordination and adsorption of a metal complex onto the surface of silicon particles in the process for producing the precursor described below. The precursor may contain one type of metal complex or a mixture of two or more types of metal complexes.

[0037] The silicon particles contained in this precursor are composed of zero-valent silicon. The average particle size of the silicon particles is preferably 150 nm or less, more preferably 120 nm or less, and even more preferably 100 nm or less. The average particle size of the silicon particles is preferably 1 nm or more, more preferably 20 nm or more, and even more preferably 30 nm or more. The average particle size of the silicon particles is D50, as described above for the average particle size of the silicon particles contained in this negative electrode active material. The details of the shape, length in the major axis direction, thickness, and aspect ratio of the silicon particles contained in the present precursor are the same as those described above for the silicon particles contained in the present negative electrode active material. The silicon particles contained in this precursor preferably have an average particle size of 150 nm or less and a crystallite size of 35 nm or less, as determined from the half-width of the peak at 2θ=28.4° in the X-ray crystal structure diffraction spectrum. A crystallite size of 35 nm or less is preferable from the viewpoint of initial coulombic efficiency and capacity retention. The crystallite size is more preferably 25 nm or less, and even more preferably in the range of 3 to 22 nm.

[0038] The organosilicon polymer material contained in the present precursor preferably has a polymer structure containing silicon, carbon, and oxygen elements. Among these, it is more preferable that the organosilicon polymer material has a polymer structure consisting of a mixture of a polysiloxane compound and a carbon source resin, or a composite of a polysiloxane compound and a carbon source resin.

[0039] The polysiloxane compound constituting the organosilicon polymer material is preferably a resin containing at least one of a polycarbosilane structure, a polysilazane structure, a polysilane structure, and a polysiloxane structure, but may be a resin containing only these structures, or a composite resin having at least one of these structures as a segment and chemically bonded to other polymer segments. Examples of the composite form include graft copolymerization, block copolymerization, random copolymerization, alternating copolymerization, etc. Examples of composite resins include composite resins having a graft structure in which a polysiloxane segment is chemically bonded to the side chain of a polymer segment, and composite resins having a block structure in which a polysiloxane segment is chemically bonded to the end of a polymer segment. The polysiloxane segment preferably has at least one structural unit represented by the following general formula (S-1) or (S-2): It is particularly preferred that the polysiloxane compound has a carboxy group, an epoxy group, an amino group, or a polyether group on a side chain or terminal of the siloxane bond (Si-O-Si) main skeleton.

[0040] [ka]

[0041] [ka]

[0042] (In the formula, R 1 represents an alkyl group, an aryl group, an epoxy group, or a carboxy group. 2 and R 3 each independently represents an alkyl group, a cycloalkyl group, an aryl group, an aralkyl group, an epoxy group, or a carboxy group. R 1 , R 2 and R 3Examples of the alkyl group represented by each of the formulas include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 1,2-dimethylpropyl group, a 1-ethylpropyl group, a hexyl group, an isohexyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 1,1-dimethylbutyl group, a 1,2-dimethylbutyl group, a 2,2-dimethylbutyl group, a 1-ethylbutyl group, a 1,1,2-trimethylpropyl group, a 1,2,2-trimethylpropyl group, a 1-ethyl-2-methylpropyl group, and a 1-ethyl-1-methylpropyl group. R 1 , R 2 and R 3 Examples of the aryl group represented by each of the above include a phenyl group, a naphthyl group, a 2-methylphenyl group, a 3-methylphenyl group, a 4-methylphenyl group, a 4-vinylphenyl group, and a 3-isopropylphenyl group. R 2 and R 3 Examples of the cycloalkyl group represented by each of the above include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. R 2 and R 3 Examples of the aralkyl group represented by each of the above include a benzyl group, a diphenylmethyl group, and a naphthylmethyl group.

[0043] Examples of polymer segments other than polysiloxane segments contained in the polysiloxane compound include vinyl polymer segments such as acrylic polymers, fluoroolefin polymers, vinyl ester polymers, aromatic vinyl polymers, and polyolefin polymers; polyurethane polymer segments, polyester polymer segments, and polyether polymer segments. Of these, vinyl polymer segments are preferred.

[0044] The polysiloxane compound may be a composite resin in which polysiloxane segments and polymer segments are bonded in a structure represented by the following structural formula (S-3), or may have a three-dimensional network polysiloxane structure.

[0045] [ka]

[0046] (In the formula, the carbon atom is a carbon atom that constitutes a polymer segment, and the two silicon atoms are silicon atoms that constitute a polysiloxane segment.) The polysiloxane segment of the polysiloxane compound may have a functional group capable of reacting by heating, such as a polymerizable double bond, in the polysiloxane segment. In this case, by subjecting the polysiloxane compound to a heat treatment before baking, the crosslinking reaction can proceed and the compound can be solidified, making it easy to perform the baking treatment. Examples of such polymerizable double bonds include vinyl groups and (meth)acryloyl groups. Preferably, two or more polymerizable double bonds are present in the polysiloxane segment, more preferably 3 to 200, and even more preferably 3 to 50. When a composite resin having two or more polymerizable double bonds is used as the polysiloxane compound, the crosslinking reaction can be easily promoted.

[0047] The polysiloxane segment may have at least one of a silanol group or a hydrolyzable silyl group. Examples of the hydrolyzable group in the hydrolyzable silyl group include a halogen atom, an alkoxy group, a substituted alkoxy group, an acyloxy group, a phenoxy group, a mercapto group, an amino group, an amide group, an aminooxy group, an iminoxy group, and an alkenyloxy group. Hydrolysis of these groups converts the hydrolyzable silyl group into a silanol group. In parallel with the crosslinking reaction due to the heat treatment, a hydrolysis condensation reaction occurs between the hydroxyl groups in the silanol groups and the hydrolyzable groups in the hydrolyzable silyl groups, thereby obtaining a solid polysiloxane compound. In this specification, a silanol group refers to a silicon-containing group having a hydroxyl group directly bonded to a silicon atom. Also, in this specification, a hydrolyzable silyl group refers to a silicon-containing group having a hydrolyzable group directly bonded to a silicon atom, and specific examples include groups represented by the following general formula (S-4):

[0048] [ka]

[0049] (In the formula, R 4 represents a monovalent organic group, and R 5 represents a halogen atom, an alkoxy group, an acyloxy group, an allyloxy group, a mercapto group, an amino group, an amido group, an aminooxy group, an iminoxy group, or an alkenyloxy group; and b is an integer of 0 to 2.

[0050] R 4 The monovalent organic group represented by may be an alkyl group, an aryl group, an aralkyl group, etc. Specific examples of the alkyl group, the aryl group, and the aralkyl group are those represented by R 2 and R 3 are the same as the alkyl group, aryl group or aralkyl group represented by each of the above. R 5 Examples of the halogen atom represented by include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. R 5 Examples of the alkoxy group represented by include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, a sec-butoxy group, and a tert-butoxy group. R 5 Examples of the acyloxy group represented by include a formyloxy group, an acetoxy group, a propanoyloxy group, a butanoyloxy group, a pivaloyloxy group, a pentanoyloxy group, a phenylacetoxy group, an acetoacetoxy group, a benzoyloxy group, and a naphthoyloxy group. R 5 Examples of the aryloxy group represented by include a phenyloxy group and a naphthyloxy group. R 5 Examples of the alkenyloxy group represented by include a vinyloxy group, an allyloxy group, a 1-propenyloxy group, an isopropenyloxy group, a 2-butenyloxy group, a 3-butenyloxy group, a 2-pentenyloxy group, a 3-methyl-3-butenyloxy group, and a 2-hexenyloxy group.

[0051] The polymer segment may contain various functional groups as needed, as long as the effects of the present invention are not impaired. Examples of such functional groups include a carboxyl group, a protected carboxyl group, a carboxylic anhydride group, a tertiary amino group, a hydroxyl group, a protected hydroxyl group, a cyclocarbonate group, an epoxy group, a carbonyl group, a primary amide group, a secondary amide group, a carbamate group, and a functional group represented by the following structural formula (S-5). The polymer segment may also contain a polymerizable double bond such as a vinyl group or a (meth)acryloyl group.

[0052] [ka]

[0053] The polysiloxane compound can be produced, for example, by the following methods (1) to (3). (1) A method in which a polymer segment containing at least one of a silanol group and a hydrolyzable silyl group is prepared in advance as a raw material for the polymer segment, and this polymer segment is mixed with a silane compound having at least one of a silanol group and a hydrolyzable silyl group and a polymerizable double bond, followed by a hydrolysis and condensation reaction. (2) A method in which a polymer segment containing at least one of a silanol group and a hydrolyzable silyl group is prepared in advance as a raw material for the polymer segment. A polysiloxane is also prepared in advance by subjecting a silane compound having both a silanol group and a hydrolyzable silyl group and a polymerizable double bond to a hydrolysis-condensation reaction. The polymer segment and the polysiloxane are then mixed together to carry out the hydrolysis-condensation reaction. (3) A method in which a polymer segment, a silane compound having at least one of a silanol group or a hydrolyzable silyl group and a polymerizable double bond, and a polysiloxane are mixed together, and a hydrolysis condensation reaction is carried out. Alternatively, commercially available polysiloxane compounds may be used, such as the "Ceranate (registered trademark)" series (organic-inorganic hybrid coating resins; manufactured by DIC Corporation) and the "Compoceran (registered trademark) SQ" series (silsesquioxane organic-inorganic hybrid materials; manufactured by Arakawa Chemical Industries, Ltd.).

[0054] The carbon source resin constituting the organosilicon polymer material is preferably a synthetic resin or natural chemical raw material, which has good miscibility with polysiloxane compounds and is easily carbonized by high-temperature baking in an inert gas atmosphere. Examples of synthetic resins include thermoplastic resins such as polyvinyl alcohol and polyacrylic acid, and thermosetting resins such as phenol resin and furan resin. Examples of natural chemical raw materials include heavy oils, particularly tar pitches such as coal tar, light tar oil, medium tar oil, heavy tar oil, naphthalene oil, anthracene oil, coal tar pitch, pitch oil, mesophase pitch, oxygen-crosslinked petroleum pitch, and heavy oil. Among these, from the viewpoints of price, availability, and impurity exclusion, the carbon source resin is preferably a synthetic resin containing an aromatic hydrocarbon moiety, and is preferably a phenolic resin, an epoxy resin, or a thermosetting resin, and more preferably a resol-type phenolic resin. As the phenolic resin, commercially available products can be used, for example, the "Sumilite Resin (registered trademark)" series (resol type phenolic resin, manufactured by Sumitomo Bakelite Co., Ltd.).

[0055] The polysiloxane compound and the carbon source resin may be used as a mixture, or may be used as a composite of the polysiloxane compound and the carbon source resin. The composite of the polysiloxane compound and the carbon source resin is a composite in which the polysiloxane compound and the carbon source resin are bonded to each other via a covalent bond, and can be produced, for example, by using a silane compound having an epoxy group and a hydrolyzable silyl group (hereinafter also referred to as an "epoxysilane compound") or a silane compound having an isocyanate group and a hydrolyzable silyl group (hereinafter also referred to as an "isocyanatesilane compound") as part of the raw materials of the polysiloxane compound, and polycondensing a silane compound containing the epoxysilane compound or the isocyanatesilane compound in the presence of a carbon source resin having a substituent (such as a hydroxyl group, an amino group, a carboxyl group, or a thiol group) that can react with the epoxy group or the isocyanate group. Furthermore, a composite in which a polysiloxane compound and a carbon source resin are bonded to each other can also be produced by a method of polymerizing a monomer having a substituent reactive with an epoxy group or an isocyanate group, which can form a carbon source resin, in the presence of a polysiloxane compound having a polymer segment containing an epoxy group or an isocyanate group and at least one type of hydrolyzable silyl group, preferably a structural unit derived from an epoxysilane compound or an isocyanatesilane compound; or a method of polycondensing a silane compound containing an epoxysilane compound or an isocyanatesilane compound and a monomer having a substituent reactive with an epoxy group or an isocyanate group, which can form a carbon source resin, all at once. The covalent bond in the composite of the polysiloxane compound and the carbon source resin is not limited to the bond derived from the epoxy group or isocyanate group described above, but may be, for example, an ester bond, an ether bond, or the like.

[0056] The content of the metal complex in the precursor is preferably 0.1 to 30 mass %, more preferably 1 to 15 mass %, when the metal species constituting the metal complex is an alkaline earth metal or alkali metal such as Mg, while it is preferably 0.0001 to 0.1 mass % when the metal species constituting the metal complex is a transition metal such as Mn. The content of silicon particles in the precursor is preferably in the range of 10 to 30 mass %, more preferably in the range of 15 to 25 mass %. The content of the organosilicon polymeric material in this precursor is preferably in the range of 30 to 90% by mass, more preferably 35 to 60% by mass. When the organosilicon polymeric material has a polymer structure consisting of a mixture of a polysiloxane compound and a carbon source resin, or a composite of a polysiloxane compound and a carbon source resin, the content of the polysiloxane compound relative to the total amount of the organosilicon polymeric material is preferably in the range of 1 to 50% by mass, and the content of the carbon source resin is preferably in the range of 50 to 99% by mass.

[0057] <Method of manufacturing a negative electrode active material precursor> The precursor can be produced, for example, by the following method. [I] A production method including the following steps a1 and b1 (hereinafter referred to as "Production Method I") Step a1: A step of adding an organic solvent, a dispersant, and a metal complex containing a metal cation and whose counter ion is an organic anion to silicon particles, followed by stirring or pulverizing the mixture to obtain a slurry 1. Step b1: A step of mixing an organosilicon polymer material with the slurry 1 obtained in step a1, followed by desolvation and drying to obtain the precursor. [II] A production method comprising the following steps a2 and b2 (hereinafter referred to as "Production Method II"). Step a2: A step of adding an organic solvent and a dispersant to silicon particles and stirring or pulverizing the mixture to obtain a slurry 2 Step b2: A step of mixing an organosilicon polymer material, the slurry 2 obtained in step a2, and a metal complex containing a metal cation whose counter ion is an organic anion, followed by desolvation and drying to obtain the precursor.

[0058] The silicon particles used in step a1 of Production Method I and step a2 of Production Method II are composed of zero-valent silicon, and the details of their average particle size, shape, length in the major axis direction, thickness, and aspect ratio are the same as those described above for the silicon particles contained in the present negative electrode active material and the present precursor. The silicon particles preferably have an average particle size of 150 nm or less and a crystallite size of 35 nm or less, determined from the half-width of the peak at 2θ=28.4° in the X-ray crystal structure diffraction spectrum. A crystallite size of 35 nm or less is preferable from the viewpoints of initial coulombic efficiency and capacity retention. The crystallite size is more preferably 25 nm or less, and even more preferably in the range of 3 to 22 nm.

[0059] The silicon particles used in the above steps a1 and a2 can be obtained, for example, by pulverizing silicon chunks into particles and then adjusting the average particle size to fall within the above-mentioned range by classification or the like. Pulverization can be carried out using a pulverizer such as a ball mill, bead mill, or jet mill. In the case of a bead mill, silicon particles having an average particle size within the above-mentioned range can be easily obtained by controlling conditions such as bead particle size, compounding ratio, rotation speed, and pulverization time. Alternatively, silicon particles may be obtained as a slurry solution in an organic solvent by wet-pulverizing a silicon lump using a wet-pulverizing device such as a roller mill, a high-speed rotary pulverizer, a container-driven mill, or a bead mill in the presence of an organic solvent described below, and adjusting the average particle size to fall within the above-mentioned range. In such wet pulverization, a dispersant, which will be described later, may be present to promote dispersion of the silicon particles obtained by pulverization. In the above step a1, silicon particles that have been previously pulverized may be used, or a slurry solution obtained by the above-mentioned wet pulverization may be used. When a slurry solution obtained by the above-mentioned wet pulverization is used, the organic solvent constituting the slurry solution and the dispersant that is optionally added may be the same as or different from the organic solvent and dispersant used in obtaining the slurry 1. The concentration of silicon particles in the slurry 1 is not particularly limited, but is preferably in the range of 5 to 40 mass % relative to the total amount of the slurry 1, and more preferably in the range of 10 to 30 mass %. On the other hand, step a2 can be said to be synonymous with performing the above-mentioned wet pulverization in the presence of a dispersant to obtain silicon particles as a slurry solution in an organic solvent (slurry 2). The concentration of silicon particles in slurry 2 is not particularly limited, but is preferably in the range of 5 to 40 mass % relative to the total amount of slurry 2, and more preferably in the range of 10 to 30 mass %.

[0060] The organic solvent used in step a1 of Production Method I and step a2 of Production Method II is preferably a solvent that is non-reactive with silicon particles, and examples thereof include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, and cyclohexanone; alcohols such as ethanol, methanol, n-propanol, isopropanol, benzyl alcohol, and diacetone alcohol; aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as hexane, cyclohexane, octane, and nonane; ethers such as tetrahydrofuran, diethyl ether, and glyme; and esters such as ethyl acetate and butyl acetate. Of these, acetone, methyl ethyl ketone, and toluene are preferred from the standpoints of cost, solvent removal ability, and solubility of the aforementioned organosilicon polymer material.

[0061] The dispersant used in step a1 of Production Method I and step a2 of Production Method II can be either an aqueous dispersant or a non-aqueous dispersant, but non-aqueous dispersants are preferred from the viewpoint of suppressing the progression of oxidation on the silicon particle surface. Examples of non-aqueous dispersants include polymeric non-aqueous dispersants such as polyethers, polyalkylene polyamines, and polycarboxylic acid partial alkyl esters; low molecular weight non-aqueous dispersants such as polyhydric alcohol esters and alkyl polyamines; and polyphosphates.

[0062] The organosilicon polymer material used in step b1 of Production Method I and step b2 of Production Method II preferably has a polymer structure containing silicon, carbon, and oxygen elements, and more preferably has a polymer structure consisting of a mixture of a polysiloxane compound and a carbon source resin, or a composite of a polysiloxane compound and a carbon source resin. Here, the details of the polymer structure containing silicon, carbon, and oxygen elements, the polysiloxane compound, the carbon source resin, the mixture of the polysiloxane compound and the carbon source resin, and the composite of the polysiloxane compound and the carbon source resin in the organosilicon-based polymer material are the same as those of the organosilicon-based polymer material contained in the present precursor, as described above.

[0063] The metal complex used in step a1 of Production Method I and step a2 of Production Method II is a complex containing a metal cation whose counter ion is an organic anion. The metal cation in such a metal complex is preferably a cation of at least one metal selected from Li, Na, K, Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca. In the metal complex, the valence of the metal cation can be any of the valences that each of the above-mentioned metals can have. The valence of the metal cation in the metal complex contained in the precursor is usually preferably monovalent, divalent, or trivalent, from the viewpoint that the present negative electrode active material obtained from the precursor is likely to have excellent initial coulombic efficiency and capacity retention. However, for example, Mn, Bi, and Zr also have a valence of 4 to 6, and the metal cation may have such a valence. In particular, it is more preferable that the metal cation in the metal complex is at least one metal cation selected from Mg and Mn, from the viewpoints of reactivity with the native oxide film on the surface of silicon particles, stability of the resulting Mg silicate, and production efficiency of silicon nitride produced by a catalytic reaction with Mn, within the firing temperature range when the present negative electrode active material is obtained by firing the present precursor. The details of the organic anion in the metal complex are the same as those described above for the metal complex contained in the precursor, and it is more preferable that the anion contains a carboxylic acid anion having a hydrocarbon group having 2 to 20 carbon atoms, from the viewpoint of facilitating coordination and adsorption of the metal complex to the silicon particle surface.

[0064] In step a1 of Production Method I and step b2 of Production Method II, the amount of metal complex added is preferably in the range of 0.00001 to 0.2, as the ratio (molar ratio) of the number of atoms (molar number) of metal anions contained in the metal complex to the number of atoms (molar number) of Si contained in the silicon particles. In producing the precursor, it is particularly preferred to use the metal complex as a metal complex solution containing a solvent (hereinafter also simply referred to as "metal complex solution") in step a1 of production method I and step b2 of production method II.

[0065] Such a metal complex solution can be preferably prepared by the following method [i] or [ii]. [i] A metal complex solution is prepared by mixing an oxide or hydroxide of at least one metal selected from Li, Na, K, Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca with a carboxylic acid having a hydrocarbon group having 2 to 20 carbon atoms in an amount of 100 to 500 times by mole relative to the oxide or hydroxide of the metal, heating the resulting mixture, and removing the water produced by the reaction. To the resulting mixture, a solvent is added, thereby preparing a metal complex solution.

[0066] In the method [i] above, examples of carboxylic acids having a hydrocarbon group having 2 to 20 carbon atoms include saturated or unsaturated monocarboxylic acids such as acetic acid, propionic acid, butyric acid, pentanoic acid (valeric acid), hexanoic acid (caproic acid), heptanoic acid (enanthic acid), octanoic acid (caprylic acid), 2-ethylhexanoic acid, nonanoic acid (pelargonic acid), decanoic acid (capric acid), dodecanoic acid (lauric acid), tetradecanoic acid (myristic acid), hexadecanoic acid (palmitic acid), and octadecanoic acid (stearic acid); and saturated or unsaturated dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, and maleic acid. Among these, saturated monocarboxylic acids are preferred from the viewpoints of ease of metal complex formation, stability of the formed metal complex, and charge / discharge characteristics of the present negative electrode active material obtained from the present precursor. The amount of such carboxylic acid used is in the range of 100 to 500 times by mole, preferably 150 to 400 times by mole, relative to the metal oxide or hydroxide. Using such a carboxylic acid in this range facilitates the formation of a metal complex by reaction with the metal oxide or hydroxide. Furthermore, excess carboxylic acid remains relative to the formed metal complex, acting as a solvent for the metal complex, making the mixture easier to handle in a solution state. Furthermore, this is thought to contribute to the stabilization of the metal complex in the state of the mixture and in a metal complex solution prepared by adding a solvent to the mixture. The preferred amount of excess carboxylic acid relative to the metal complex in the metal complex solution is 10 to 200% by mass, more preferably 20 to 100% by mass.

[0067] In the method [i] above, from the viewpoint of efficiently proceeding the reaction between the solid metal oxide or hydroxide and the carboxylic acid, which has a melting point of 20°C under atmospheric pressure and is normally a liquid, it is preferable that the solid metal oxide or hydroxide has a large surface area. In other words, it is preferable that the primary particle size of the metal oxide or hydroxide is 10 nm to 500 μm. The primary particles may be in the form of aggregated secondary particles, in which case it is preferable that the secondary particle size is 1 mm or less. In the above method [i], a solvent capable of forming an azeotropic distillation with water may be present when the metal oxide or hydroxide and the carboxylic acid are mixed and heated to react while removing the generated water. Examples of such a solvent capable of forming an azeotropic distillation with water include cyclohexane, benzene, ethanol, propanol, toluene, and xylene. Among these, a solvent having a boiling point of 120°C or less under atmospheric pressure is preferred, and a solvent having a low azeotropic point with water is more preferred from the viewpoint of facilitating the azeotropic removal of water generated during the reaction with a small amount of heat. When such a solvent capable of forming an azeotropic distillation with water is used, the amount thereof is preferably 300 times by mass or less, more preferably 0.5 to 200 times by mass, relative to the metal oxide or hydroxide. When the solvent capable of forming an azeotropic distillation with water is used in the above range, it can reduce the viscosity of the reaction mixture together with the carboxylic acid, making it easier to increase the dispersibility of the metal oxide or hydroxide in the mixture during the reaction by stirring or the like, and as a result, it also makes it easier to promote the reaction of producing the metal complex.

[0068] In the above method [i], the solvent added to the obtained mixture is preferably a solvent that can be used as the organic solvent used in step a1 of Production Method I and step a2 of Production Method II, and examples thereof include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, etc.; alcohols such as ethanol, methanol, n-propanol, isopropanol, etc.; aromatic hydrocarbons such as benzene, toluene, xylene, etc. When applied to Production Method I or Production Method II, ketones are preferred among the above solvents, and methyl ethyl ketone is more preferred, from the viewpoints of excellent solubility of the polysiloxane compound, the carbon source resin, and other optional additives and facilitating the solvent removal step described below. The amount of the solvent used is preferably 1 to 10 times by mass, more preferably 1 to 3 times by mass, relative to the amount of the mixture. When the solvent is used in the above range, it is easy to achieve both uniformity in mixing and stirring and a simple desolvation step when the prepared metal complex solution is applied to Production Method I or Production Method II.

[0069] [ii] A metal hydroxide of at least one metal selected from Li, Na, K, Rb, and Cs is mixed with a carboxylic acid having a hydrocarbon group having 2 to 20 carbon atoms in an amount of 100 to 500 times by mole relative to the metal hydroxide, and water in an amount of 300 times by mass or less relative to the metal hydroxide, and the mixture is heated. Subsequently, an inorganic salt of at least one metal selected from Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca is added and heated to carry out a metal exchange reaction. After separating the aqueous phase, a solvent is added to the mixture obtained by further dehydration, to prepare a metal complex solution.

[0070] The details of the carboxylic acid having a hydrocarbon group having 2 to 20 carbon atoms and the solvent in the above method [ii] are the same as those of the carboxylic acid having a hydrocarbon group having 2 to 20 carbon atoms and the solvent in the above method [i]. In the method [ii] above, the amount of water used is 300 times by mass or less, preferably 5 to 100 times by mass, relative to the metal hydroxide. Using water in this range facilitates homogenization of the reaction mixture together with the carboxylic acid having a hydrocarbon group with 2 to 20 carbon atoms, and facilitates the reaction of forming a salt between at least one metal selected from Li, Na, K, Rb, and Cs and the carboxylic acid. The heating temperature in this stage is preferably in the range of 30 to 90°C. The heating time varies depending on the scale of the reaction, but is usually preferably in the range of 0.5 to 3 hours. Next, an inorganic salt of at least one metal selected from Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca is added to the resulting mixture and heated to carry out a metal exchange reaction. The inorganic salt of the metal is preferably an inorganic salt of an acid stronger than the carboxylic acid, such as a sulfate, hydrochloride, or nitrate. The amount of the inorganic salt of the metal added is preferably 0.9 to 1.1 equivalents, more preferably 0.95 to 1.01 equivalents, calculated by multiplying the valence and the molar amount relative to the amount of at least one metal hydroxide selected from Li, Na, K, Rb, and Cs used. Adding the inorganic salt of the metal in this range facilitates the promotion of the metal exchange reaction, which in turn facilitates the promotion of the reaction for producing the metal complex. The heating temperature in this transmetallation reaction is preferably in the range of 30 to 90° C. The heating time varies depending on the scale of the reaction, but is usually preferably in the range of 0.5 to 3 hours.

[0071] The metal exchange reaction in method [ii] is the following reaction: The resulting salt of the carboxylic acid with at least one metal selected from Li, Na, K, Rb, and Cs, i.e., the salt of an alkali metal and a weak acid, is reacted with an inorganic salt of the metal, preferably an inorganic salt of a strong acid, to simultaneously liberate a weak acid (carboxylic acid) and a weak base (at least one metal selected from Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca), thereby producing a salt of the strong acid and the strong base, while the liberated weak acid and weak base are neutralized to form a metal complex. For example, reacting manganese sulfate with a mixture containing the sodium salt of the carboxylic acid produces sodium sulfate, while a manganese carboxylic acid complex is formed. Sodium sulfate is water-soluble and exists in the aqueous phase, while the manganese carboxylic acid complex is water-insoluble and exists in the organic phase. After separating the aqueous phase, the organic phase is further dehydrated to obtain a mixture. In the same manner as described above in method [i], a solvent is added to the mixture to prepare a solution in which a manganese carboxylate complex is dissolved, i.e., a metal complex solution.

[0072] In the precursor production method I, when a metal complex solution is used as the metal complex in step a1, it is believed that the excess free carboxylic acid first adsorbs onto the silicon particle surface, and the interaction between the hydrocarbon group of the adsorbed carboxylic acid and the organic anion of the metal complex, preferably the hydrocarbon group of the carboxylic acid anion, facilitates coordination and adsorption of the metal complex onto the silicon particle surface. Meanwhile, since Si-OH structures formed by the presence of trace amounts of moisture may also be present on the silicon particle surface, hydrogen bonding with the free carboxylic acid is also thought to occur. Therefore, the silicon particles contained in the resulting slurry 1, with the metal complex coordinated and adsorbed on their surfaces, are also dispersible in organic solvents due to the action of the dispersant. Mixing this slurry 1 with an organosilicon-based polymer material in step b1 facilitates the production of a mixture in which the silicon particles with the metal complex coordinated and adsorbed on their surfaces and the organosilicon-based polymer material are uniformly dispersed. Furthermore, in the precursor production method II, when an organosilicon-based polymer material and a metal complex solution as a metal complex are added to the slurry 2 containing silicon particles, dispersant, and organic solvent obtained in step a2 in step b2, a solution in which the organosilicon-based polymer material and the metal complex are uniformly dispersed is produced, and the resulting mixture is mixed with the silicon particles. In this case, too, it is presumed that the excess free carboxylic acid is adsorbed onto the silicon particle surface, and the hydrocarbon group moiety of the adsorbed carboxylic acid interacts with the organic anion of the metal complex, preferably the hydrocarbon group moiety of the carboxylic acid anion, in a manner similar to that described above, facilitating coordination and adsorption of the metal complex onto the silicon particle surface. Therefore, it is easy to obtain a mixture in which the silicon particles with the metal complex coordinately adsorbed onto their surfaces and the organosilicon-based polymer material are uniformly dispersed. Therefore, in both Process I and Process II, the precursor produced from the resulting mixture after further desolvation and drying tends to be in a state in which the silicon particles with metal complexes coordinated and adsorbed to their surfaces remain as primary particles without agglomerating, and are uniformly dispersed in the matrix of the organosilicon polymer material.

[0073] Furthermore, in Production Method I or Production Method II of this precursor, when a metal complex solution prepared by the above-mentioned method [i] or [ii] is used as the metal complex, desolvation and drying of the mixture of silicon particles, organosilicon-based polymer material, and metal complex can be carried out industrially advantageously in either Production Method I or Production Method II in a shorter time and with less heat. In addition, the miscibility and dispersibility of the silicon particle-containing slurry (Slurry 1 or Slurry 2) with the solution of organosilicon-based polymer material are improved. Therefore, it is presumed that the organic anion possessed by the metal complex, preferably the carboxylate anion, can easily link with the functional groups present on the silicon particle surface to modify the silicon particle surface while simultaneously protecting the silicon particle surface from oxidation. Furthermore, the metal complex solution contains the carboxylic acid, which is thought to promote the coordination of the metal complex to the silicon particles through the aforementioned interaction and prevent detachment. Therefore, the silicon particles are easily dispersed while maintaining the primary particle state with the metal complex adsorbed on their surface. This is thought to facilitate the formation of metal silicates on the surfaces of silicon particles contained in the present anode active material obtained from the present precursor, which is presumably why the present anode active material having the above-described properties defined in the present invention is more easily obtained. Incidentally, if the solvent used in the metal complex solution obtained by the present precursor production method I or II, or the above-mentioned method [i] or [ii], is the same, recovery and reuse of the solvent becomes easy.

[0074] In step b1 of Production Method I and step b2 of Production Method II, mixing can be carried out using a stirrer, an ultrasonic mixer, a premix disperser, or the like. In step b1 of Production Method I and step b2 of Production Method II, the conditions for removing the solvent and drying after mixing to obtain the precursor are not particularly limited. The solvent can be removed, for example, at a temperature in the range of 80 to 150°C under an inert gas atmosphere at atmospheric pressure or under reduced pressure. Drying can be carried out, for example, in an inert gas atmosphere at atmospheric pressure or under reduced pressure for 1 minute to 24 hours at a temperature in the range of 25 to 200° C. Such desolvent removal and drying can also be carried out using a known dryer, reduced pressure dryer, spray dryer, etc.

[0075] <Method of manufacturing negative electrode active material> The present precursor obtained by the above-described manufacturing method is calcined in an inert gas atmosphere and pulverized to obtain the present negative electrode active material. That is, the present invention encompasses a manufacturing method of the present negative electrode active material, which includes a step of calcining the present precursor in an inert gas atmosphere. The present invention also encompasses the present negative electrode active material obtained by calcining the present precursor, preferably the present precursor obtained by the above-described manufacturing method, in an inert gas atmosphere.

[0076] <Firing process> The firing process involves firing the precursor in an inert gas atmosphere at a maximum temperature of 900 to 1200°C to completely decompose the thermally decomposable organic components, and precisely controlling the firing conditions to turn the other main components into a fired product suitable for the active material. Specifically, the organosilicon-based polymer material (preferably a polysiloxane compound and a carbon source resin) contained in the present negative electrode active material is converted into a silicon-oxygen-carbon skeleton and free carbon by the energy of the high-temperature treatment in the baking step, thereby forming the above-mentioned silicon-based matrix in the present negative electrode active material. As described above, the compound that constitutes the silicon-based matrix phase may contain nitrogen in addition to silicon, oxygen, and carbon. Furthermore, due to the energy of the high-temperature treatment in the firing step, at least one of a lattice structure attributed to a metal silicate and a lattice structure attributed to silicon nitride is formed near the surface of the silicon particles contained in the negative electrode active material precursor, the silicon particles having a metal complex coordinated to at least a portion of the surface thereof.

[0077] The firing process is carried out according to a firing program that specifies the temperature rise rate, the holding time at a constant temperature, etc. The maximum temperature set in the firing program has a significant effect on the structure and performance of the fired product, which is the present negative electrode active material. In the present invention, by setting the maximum temperature to 900 to 1200°C, it is possible to precisely control the microstructure of the present negative electrode active material, which maintains the chemical bond state between silicon and carbon, and it is also possible to avoid oxidation of silicon particles due to firing at excessively high temperatures, which makes it easier to obtain better charge / discharge characteristics. The calcination method is not particularly limited, and any suitable calcination furnace having a heating function under an inert gas atmosphere, such as a fluidized bed reactor, a rotary furnace, a vertical moving bed reactor, a tunnel furnace, a batch furnace, or a rotary kiln, can be selected, and either a continuous method or a batch method calcination process can be used.

[0078] <Crushing process> The pulverization step is a step in which the sintered product obtained in the sintering step is pulverized and, if necessary, classified to obtain the present negative electrode active material. The pulverization to obtain the present negative electrode active material having the desired average particle size may be performed in one step or in several steps. For example, when preparing the present negative electrode active material of about 10 μm from a sintered product in the form of lumps or agglomerates of 10 mm or more, the sintered product can be coarsely pulverized to particles of about 1 mm using a jaw crusher, roll crusher, etc., and then pulverized to about 100 μm using a glow mill, ball mill, etc., and further pulverized to about 10 μm using a bead mill, jet mill, etc. The particles produced by pulverization may contain coarse particles, but fine powders also exist, so classification is preferably performed to remove these particles and adjust the particle size distribution of the present negative electrode active material. For example, when removing coarse particles, a classification method using a sieve is preferred from the viewpoint of ensuring the removal of coarse particles. Furthermore, a classifier such as an air classifier or a wet classifier may also be used depending on the purpose. In addition, if the shape of the precursor is controlled in advance by spray drying or the like before firing so that the average particle size of the negative electrode active material falls within a suitable range, and the firing step is carried out in that shape, it is possible to omit the pulverization step.

[0079] <Secondary battery> The negative electrode active material is excellent in charge / discharge capacity, initial coulombic efficiency, and capacity retention rate. Therefore, a secondary battery including the negative electrode active material, specifically a secondary battery having a negative electrode layer including the negative electrode active material, exhibits good charge / discharge characteristics and is excellent in initial coulombic efficiency and capacity retention rate. For example, the negative electrode active material and an organic binder are mixed together with a solvent using a dispersing device such as a stirrer, a ball mill, a super sand mill, or a pressure kneader to prepare a negative electrode material slurry. This negative electrode material slurry can be applied to a current collector (e.g., copper foil) to form a negative electrode layer.

[0080] Examples of the organic binder include styrene-butadiene rubber copolymers (hereinafter also referred to as "SBR"); unsaturated carboxylic acid copolymers such as ethylenically unsaturated carboxylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, (meth)acrylonitrile, and hydroxyethyl (meth)acrylate, and (meth)acrylic copolymers composed of ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid; and polymeric compounds such as polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polyimide, polyamideimide, and carboxymethylcellulose (hereinafter also referred to as "CMC"). Depending on their physical properties, these organic binders may be dispersed or dissolved in water or dissolved in an organic solvent such as N-methyl-2-pyrrolidone.

[0081] The content of the organic binder in the negative electrode layer of the lithium-ion secondary battery negative electrode is preferably 1 to 30% by mass, more preferably 2 to 20% by mass, and even more preferably 3 to 15% by mass. When the content of the organic binder is 1% by mass or more, adhesion is improved and destruction of the negative electrode structure due to expansion or contraction during charge and discharge is likely to be suppressed. On the other hand, when the content is 30% by mass or less, an increase in electrode resistance is more likely to be suppressed. Within this range, the present negative electrode active material has high chemical stability and can also employ an aqueous binder, making it easy to handle in practical terms.

[0082] The negative electrode material slurry may further contain a conductive additive, if necessary. Examples of conductive additives include carbon black, graphite, acetylene black, and conductive oxides and nitrides. When the negative electrode material slurry further contains a conductive additive, the amount thereof is preferably in the range of 1 to 15% by mass relative to the negative electrode active material.

[0083] Examples of materials for the current collector include copper, nickel, titanium, stainless steel, etc. The current collector is preferably in the form of a strip, such as a foil, perforated foil, or mesh. Porous materials such as porous metal (foamed metal), carbon paper, etc. can also be used as the current collector. Examples of methods for applying the negative electrode material slurry to the current collector include metal mask printing, electrostatic coating, dip coating, spray coating, roll coating, doctor blade coating, gravure coating, screen printing, etc. After application, it is preferable to perform a rolling treatment using a flat plate press, a calendar roll, or the like, as necessary.

[0084] Alternatively, the negative electrode layer may be obtained by forming the paste-like negative electrode material slurry into a sheet or pellet, and then integrating it with a current collector by rolling, pressing, or a combination thereof. Furthermore, a carbon material such as natural graphite, artificial graphite, or amorphous carbon such as hard carbon or soft carbon can be added to the negative electrode material slurry to prepare the negative electrode layer.

[0085] The negative electrode layer formed on the current collector or the negative electrode layer integrated with the current collector is preferably heat-treated depending on the type of organic binder, for example, at 100 to 130°C when an aqueous styrene-butadiene rubber copolymer (SBR) is used, or at 150 to 450°C when an organic binder having a polyimide or polyamideimide main skeleton is used. Such heat treatment can remove the solvent derived from the organic binder and also promotes strength increase due to hardening of the organic binder, thereby improving adhesion between particles and between the particles and the current collector. Note that the heat treatment is preferably carried out in an inert gas atmosphere such as helium, argon, or nitrogen, or in a vacuum atmosphere, from the viewpoint of preventing oxidation of the current collector during the heat treatment.

[0086] After the heat treatment, the negative electrode layer formed on the current collector or the negative electrode layer integrated with the current collector is preferably subjected to a pressure treatment in order to adjust the electrode density. In the negative electrode using this negative electrode active material, the electrode density is 1 to 1.8 g / cm. 3is preferably 1.1 to 1.7 g / cm 3 More preferably, it is 1.2 to 1.6 g / cm 3 It is more preferable that the electrode density is 100% or less. The higher the electrode density, the better the adhesion and the volumetric capacity density of the electrode tend to be. However, if the electrode density is too high, the voids in the electrode decrease, weakening the effect of suppressing the volumetric expansion of silicon and the like, which may result in a decrease in the capacity retention rate. Therefore, an optimal range of the electrode density is selected.

[0087] The secondary battery of the present invention contains the present negative electrode active material in the negative electrode. Secondary batteries having a negative electrode containing the present negative electrode active material are preferably nonaqueous electrolyte secondary batteries and solid electrolyte secondary batteries, and the present negative electrode active material exhibits excellent performance, particularly when used as the negative electrode of a nonaqueous electrolyte secondary battery. For example, when the secondary battery of the present invention is a wet electrolyte secondary battery, it can be constructed by disposing a positive electrode and a negative electrode containing the present negative electrode active material opposite each other via a separator and injecting an electrolyte solution.

[0088] The positive electrode can be obtained by forming a positive electrode layer on the surface of a current collector in the same manner as the negative electrode. In this case, the current collector can be made of a metal or alloy such as aluminum, titanium, or stainless steel, and can be in the form of a foil, a perforated foil, a mesh, or a strip.

[0089] The positive electrode material used in the positive electrode layer is not particularly limited, and when producing a nonaqueous electrolyte secondary battery, for example, a lithium ion secondary battery, examples of the positive electrode material include metal compounds, metal oxides, metal sulfides, and conductive polymers that can be doped or intercalated with lithium ions. Specifically, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2) and their composite oxides (LiCoxNiyMnzO2, x+y+z=1); lithium manganese spinel (LiMn2O4), lithium vanadium compounds, V2O5, VO 13, VO2, MnO2, TiO2, MoV2O8, TiS2, V2S5, VS2, MoS2, MoS3, Cr3O8, Cr2O5, olivine-type LiMPO4 (wherein M is Co, Ni, Mn, or Fe); conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, and polyacene, porous carbon, etc. These may be used alone or in combination of two or more.

[0090] The separator may be a nonwoven fabric, cloth, microporous film, or a combination thereof, whose main component is a polyolefin such as polyethylene or polypropylene. If the nonaqueous electrolyte secondary battery to be fabricated is configured so that the positive electrode and the negative electrode are not in direct contact with each other, it is not necessary to use a separator.

[0091] As the electrolyte, for example, a so-called organic electrolyte can be used, which is obtained by dissolving a lithium salt such as LiClO4, LiPF6, LiAsF6, LiBF4, or LiSO3CF3 in one or a mixture of two or more of a non-aqueous solvent such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, 3-methyl-1,3-oxazolidin-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, or ethyl acetate. The structure of the secondary battery of the present invention is not particularly limited, but typically, a positive electrode, a negative electrode, and an optional separator are wound into a flat spiral to form a wound electrode assembly, or these are stacked as flat plates to form a stacked electrode assembly, and these electrode assembly are sealed in an outer casing. Note that the half cells used in the examples of the present invention have a negative electrode mainly composed of the present negative electrode active material, and a simple evaluation was performed using metallic lithium as the counter electrode, in order to clearly compare the initial coulombic efficiency of the present negative electrode active material itself.

[0092] Secondary batteries using the present negative electrode active material are used as, for example, paper-type batteries, button-type batteries, coin-type batteries, laminated-type batteries, cylindrical batteries, square-type batteries, and the like. The present negative electrode active material can also be applied to electrochemical devices in general that use lithium ion insertion / extraction as a charge / discharge mechanism, such as hybrid capacitors and solid-state lithium secondary batteries.

[0093] The negative electrode active material, the negative electrode active material precursor and the method for producing the same, and the secondary battery having the negative electrode active material of the present invention have been described above, but the present invention is not limited to the configurations of the above-described embodiments. For example, the negative electrode active material, negative electrode active material precursor, and secondary battery having the negative electrode active material of the present invention may each have any other optional components in addition to the configurations of the above-mentioned embodiments, or may be replaced with any other components that exert the same function. Furthermore, the manufacturing method for the negative electrode active material precursor of the present invention may have any other optional step in the configurations of the above-mentioned embodiments, or may be replaced with any other step that exerts the same effect. [Example]

[0094] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the following examples. Unless otherwise specified, "parts" and "%" are by mass. The half cells used in the examples were configured so that the negative electrode was mainly made of the present negative electrode active material, and a simple evaluation was performed using metallic lithium as the counter electrode. This was done to more clearly compare the initial coulombic efficiency of the present negative electrode active material itself.

[0095] A. Example of preparing a solution of a metal complex (method [i]) Synthesis Example 1-1 A 0.5 L separable flask equipped with a thermometer, Dean-Stark tube, reflux condenser, and stirrer was charged with 312 molar equivalents (226 parts by mass) of 2-ethylhexanoic acid. While stirring at 250 rpm at 25 °C, 100 molar equivalents (29.1 parts by mass) of magnesium hydroxide, previously passed through a 1 mm mesh sieve, was gradually added. After the addition was complete, the temperature was raised to 130 °C and the mixture was stirred for 2 hours. After visually confirming the complete disappearance of the magnesium hydroxide powder, the mixture was heated to 130 °C under reduced pressure (40 hPa) and the generated water was removed. The resulting mixture (containing magnesium 2-ethylhexanoate and 2-ethylhexanoic acid) was cooled to 75 °C and remained liquid and stirrable. While stirring, 168 parts by mass of methyl ethyl ketone was added under atmospheric pressure to adjust the magnesium ion content to 3% by mass. The 2-ethylhexanoic acid content was 20% by mass. The mixture could be stirred without any problems even when cooled to 25°C. The resulting mixture was filtered using No. 5B filter paper and silica-containing diatomaceous earth to obtain approximately 400 parts by mass of a methyl ethyl ketone solution containing magnesium 2-ethylhexanoate and 2-ethylhexanoic acid (hereinafter referred to as "metal complex solution 1-1").

[0096] Synthesis Example 1-2 A 0.5 L separable flask equipped with a thermometer, Dean-Stark tube, reflux condenser, and stirrer was charged with 292 molar equivalents (256 parts by mass) of neodecanoic acid and 20 parts by mass of toluene. While stirring at 250 rpm at 25 °C, 100 molar equivalents (29.1 parts by mass) of magnesium hydroxide, previously passed through a 1 mm mesh sieve, was gradually added. After the addition was complete, the temperature was raised to 110 °C and the mixture was stirred for 0.5 hours. After visually confirming the complete disappearance of the magnesium hydroxide powder, the resulting water was distilled off via azeotropy with toluene. The pressure was then slowly reduced to 40 hPa at 110 °C to remove the toluene and residual water. The resulting mixture (containing magnesium neodecanoate and neodecanoic acid) was cooled to 75 °C and remained liquid and stirrable. While stirring, 138 parts by mass of methyl ethyl ketone was added under atmospheric pressure to adjust the magnesium ion content to 3% by mass. At this time, the content of neodecanoic acid was 20% by mass relative to the total amount of the mixed solution. The mixed solution could be stirred without any problems even after being cooled to 25°C. The resulting mixture was filtered using No. 5B filter paper and silica-containing diatomaceous earth to obtain approximately 400 parts by mass of a methyl ethyl ketone solution containing magnesium neodecanoate and neodecanoic acid (hereinafter referred to as "metal complex solution 1-2").

[0097] Synthesis Example 1-3 A methyl ethyl ketone solution containing magnesium 2-ethylhexanoate and 2-ethylhexanoic acid (hereinafter referred to as "metal complex solution 1-3") was obtained by performing the same operation as in Synthesis Example 1-2, except that 312 molar equivalents of 2-ethylhexanoic acid were used instead of 292 molar equivalents of neodecanoic acid.

[0098] Synthesis Example 1-4 A methyl ethyl ketone solution containing a magnesium complex in which 2-ethylhexanoic acid and neodecanoic acid were coordinated, neodecanoic acid, and 2-ethylhexanoic acid (hereinafter referred to as "metal complex solution 1-4") was obtained by performing the same operation as in Synthesis Example 1-2, except that a mixture of 145 molar equivalents of neodecanoic acid and 156 molar equivalents of 2-ethylhexanoic acid was used instead of 292 molar equivalents of neodecanoic acid in Synthesis Example 1-2.

[0099] Synthesis Example 1-5 A methyl ethyl ketone solution containing a magnesium complex in which 2-ethylhexanoic acid and isostearic acid were coordinated, isostearic acid, and 2-ethylhexanoic acid (hereinafter referred to as "metal complex solution 1-5") was obtained by performing the same operation as in Synthesis Example 1-2, except that a mixture of 106 molar equivalents of 2-ethylhexanoic acid and 78 molar equivalents of isostearic acid was used instead of 292 molar equivalents of neodecanoic acid.

[0100] Synthesis Examples 1-6 A methyl ethyl ketone solution containing magnesium n-hexanoate and n-hexanoic acid (hereinafter referred to as "metal complex solution 1-6") was obtained by performing the same operation as in Synthesis Example 1-2, except that 340 molar equivalents of n-hexanoic acid were used instead of 292 molar equivalents of neodecanoic acid.

[0101] Synthesis Example 1-7 A methyl ethyl ketone solution containing magnesium 2-methylpentanoate and 2-methylpentanoic acid (hereinafter referred to as "metal complex solution 1-7") was obtained by performing the same operation as in Synthesis Example 1-2, except that 340 molar equivalents of 2-methylpentanoic acid were used instead of 292 molar equivalents of neodecanoic acid.

[0102] Synthesis Example 1-8 A methyl ethyl ketone solution containing magnesium 2-ethylbutyrate and 2-ethylbutyric acid (hereinafter referred to as "metal complex solution 1-8") was obtained by performing the same operation as in Synthesis Example 1-2, except that 340 molar equivalents of 2-ethylbutyric acid were used instead of 292 molar equivalents of neodecanoic acid.

[0103] Synthesis Example 1-9 A methyl ethyl ketone solution containing magnesium n-valerate and n-valeric acid (hereinafter referred to as "metal complex solution 1-9") was obtained by performing the same operation as in Synthesis Example 1-2, except that 358 molar equivalents of n-valeric acid were used instead of 292 molar equivalents of neodecanoic acid, and the conditions for removing toluene and residual water were 100°C and 200 hPa.

[0104] Synthesis Example 1-10 A methyl ethyl ketone solution containing magnesium isovalerate and isovaleric acid (hereinafter referred to as "metal complex solution 1-10") was obtained by performing the same operation as in Synthesis Example 1-2, except that 358 molar equivalents of isovaleric acid were used instead of 292 molar equivalents of neodecanoic acid, and the conditions for removing toluene and residual water were 100°C and 300 hPa.

[0105] Synthesis Example 1-11 A methyl ethyl ketone solution containing magnesium DL-2-methylbutyrate and DL-2-methylbutyric acid (hereinafter referred to as "metal complex solution 1-11") was obtained by performing the same operation as in Synthesis Example 1-2, except that 358 molar equivalents of DL-2-methylbutyric acid were used instead of 292 molar equivalents of neodecanoic acid and that the conditions for removing toluene and residual water were changed to 100°C and 200 hPa.

[0106] Synthesis Example 1-12 A methyl ethyl ketone solution containing magnesium pivalate and pivalic acid (hereinafter referred to as "metal complex solution 1-12") was obtained by performing the same operation as in Synthesis Example 1-2, except that 358 molar equivalents of pivalic acid were used instead of 292 molar equivalents of neodecanoic acid and that the conditions for removing toluene and residual water were changed to 100°C and 200 hPa.

[0107] Synthesis Example 1-13 A methyl ethyl ketone solution containing magnesium n-butyrate and n-butyric acid (hereinafter referred to as "metal complex solution 1-13") was obtained by performing the same operation as in Synthesis Example 1-2, except that 384 molar equivalents of n-butyric acid were used instead of 292 molar equivalents of neodecanoic acid and that the conditions for removing toluene and residual water were changed to 100°C and 250 hPa.

[0108] Synthesis Example 1-14 A methyl ethyl ketone solution containing magnesium isobutyrate and isobutyric acid (hereinafter referred to as "metal complex solution 1-14") was obtained by performing the same operation as in Synthesis Example 1-2, except that 384 molar equivalents of isobutyric acid were used instead of 292 molar equivalents of neodecanoic acid and that the conditions for removing toluene and residual water were changed to 100°C and 300 hPa.

[0109] Comparative synthesis example 1 100 molar equivalents of magnesium hydroxide, 292 molar equivalents of neodecanoic acid, and 138 parts by mass of methyl ethyl ketone were placed in a 1 L separable flask equipped with a thermometer, a Dean-Stark tube, a reflux condenser, and a stirrer, and the temperature was raised from 25°C to 80°C while stirring at 250 rpm. Stirring was continued, but the magnesium hydroxide did not dissolve at all and the reaction did not proceed.

[0110] Comparative synthesis example 2 The same operation as in Comparative Synthesis Example 1 was carried out, except that 138 parts by mass of water was used instead of 138 parts by mass of methyl ethyl ketone in Comparative Synthesis Example 1 and the mixture was heated to 100°C. However, magnesium hydroxide did not dissolve at all and the reaction did not proceed.

[0111] Comparative synthesis example 3 A 1-L separable flask equipped with a thermometer, Dean-Stark tube, reflux condenser, and stirrer was charged with 100 molar equivalents of magnesium hydroxide and 292 molar equivalents of behenic acid. The mixture was heated from 25°C to 130°C while stirring at 250 rpm, and the resulting water was removed under reduced pressure to allow the reaction to proceed. The resulting mixture (containing behenic acid and magnesium behenate) was cooled to 25°C without further treatment; the mixture became too viscous during cooling and became unstirrable. Furthermore, the viscous mixture could not be removed from the separable flask at 25°C.

[0112] B. Example of preparation of metal complex solution (method [ii]) Synthesis Example 2-1 A 1 L separable flask equipped with a thermometer, a Dean-Stark tube, a reflux condenser, and a stirrer, and having a stopcock at the bottom, was charged with 100 parts by mass of ion-exchanged water and 230 molar equivalents (402 parts by mass) of neodecanoic acid, and while stirring at 250 rpm, a 20% by mass aqueous solution of sodium hydroxide (385 parts by mass), in an amount equivalent to 200 molar equivalents of sodium hydroxide, was slowly added dropwise at 25°C and mixed. After completion of the dropwise addition, the temperature was raised to 90°C and the mixture was stirred for 20 minutes. Next, 100 molar parts of manganese sulfate (165 parts by mass) was gradually added to the reaction mixture, which was an aqueous solution containing sodium neodecanoate, while stirring, to allow an ion exchange reaction. This resulted in separation into an oil layer consisting of neodecanoic acid and manganese neodecanoate, and an aqueous layer containing sodium sulfate. The aqueous layer was removed from the bottom of the flask, and the oil layer remaining in the flask was stirred at 130°C under reduced pressure (40 hPa) to remove the water dispersed in the oil layer. The oil layer was stirred without any problems. The resulting mixture (containing neodecanoic acid and manganese neodecanoate) was cooled to 75°C and stirred, and 360 parts by mass of methyl ethyl ketone was added under atmospheric pressure to prepare a mixed solution so that the manganese ion content was 6.5% by mass relative to the total amount. The mixed solution could be stirred without any problems even when cooled to 25°C. At this time, the neodecanoic acid content was 8% by mass relative to the total mixed solution. The resulting mixture was filtered using No. 5B filter paper and silica-containing diatomaceous earth to obtain approximately 815 parts by mass of a methyl ethyl ketone solution containing manganese neodecanoate and neodecanoic acid (hereinafter referred to as "metal complex solution 2-1").

[0113] Synthesis Example 2-2 A methyl ethyl ketone solution containing manganese 2-ethylhexanoate and 2-ethylhexanoic acid (hereinafter referred to as "metal complex solution 2-2") was obtained by performing the same operation as in Synthesis Example 2-1, except that 236 molar equivalents of 2-ethylhexanoic acid were used instead of 230 molar equivalents of neodecanoic acid.

[0114] Comparative Synthesis Example 4 A 1 L separable flask equipped with a thermometer, a Dean-Stark tube, a reflux condenser, and a stirrer, and having a stopcock at the bottom, was charged with 100 parts by mass of ion-exchanged water and 210 molar equivalents of neodecanoic acid (363 parts by mass). While stirring at 250 rpm, a 20% by mass aqueous solution of sodium hydroxide (385 parts by mass), in an amount equivalent to 200 molar equivalents of sodium hydroxide, was slowly added dropwise at 25°C and mixed. After the dropwise addition was completed, the temperature was raised to 90°C and the mixture was stirred for 20 minutes. Next, 100 molar parts (165 parts by mass) of manganese sulfate was gradually added to the reaction mixture, which was an aqueous solution containing sodium neodecanoate, while stirring, to cause an ion exchange reaction. The mixture separated into an oil layer consisting of neodecanoic acid and manganese neodecanoate, and an aqueous layer containing sodium sulfate. The aqueous layer was removed from the bottom of the flask, and the oil layer remaining in the flask was stirred at 130°C under reduced pressure to remove the water dispersed in the oil layer. The oil layer could be stirred without any problems. When the resulting mixture (containing neodecanoic acid and manganese neodecanoate) was cooled with stirring, it became highly viscous at around 90°C and became impossible to stir. Furthermore, the highly viscous mixture could not be removed from the separable flask at 25°C.

[0115] C. Example of preparing a silicon particle dispersion Synthesis Example 3-1 A 150 ml container of a small bead mill was charged with zirconia beads (Nikkato YTZ series) with a particle size of 0.1 to 0.2 mm and a 60% filling rate, and 100 ml of methyl ethyl ketone. 21 g of silicon powder ("SIE23PB" (product name, Kojundo Chemical Co., Ltd.) with an average particle size of 5 μm and 9 g of cationic dispersant ("BYK102" (product name, BYK Japan)) were then added and wet-milled in a bead mill to obtain a dark brown liquid dispersion of silicon particles with a solids concentration of 23% by mass (hereinafter referred to as "Dispersion 1"). TEM observation of the silicon particles in Dispersion 1 revealed flat flake-like shapes and an average particle size (D50) of 85 nm.

[0116] Synthesis Example 3-2 A 150 ml container of a small bead mill was charged with zirconia beads (Nikkato YTZ series) with a particle size of 0.1 to 0.2 mm and a 60% filling rate, and 100 ml of methyl ethyl ketone. Next, 21 g (747 mmol) of silicon powder ("SIE23PB" (product name, Kojundo Chemical Co., Ltd.) with an average particle size of 5 μm, 9 g of cationic dispersant liquid ("BYK102" (product name, BYK Japan)), and 30 g (37.3 mmol) of the metal complex solution 1-3 prepared by the method of Synthesis Example 1-3, adjusted so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon powder was 0.05, were added, and the mixture was wet-pulverized using a bead mill to obtain a dark brown liquid dispersion of silicon particles with a solids concentration of 32% by mass (hereinafter referred to as "Dispersion 2"). When the silicon particles in the resulting dispersion 2 were observed by TEM, they were found to have a flat flake shape and an average particle size (D50) of 90 nm.

[0117] Synthesis Example 3-3 In Synthesis Example 3-2, the same operations as in Synthesis Example 3-2 were performed, except that instead of Metal Complex Solution 1-3, Metal Complex Solution 2-2 prepared by the method of Synthesis Example 2-2 was added so that the atomic ratio (molar ratio) of manganese atoms to silicon atoms in the silicon powder was adjusted to 0.0005, and a dark brown liquid dispersion of silicon particles with a solid concentration of 23 mass% (hereinafter referred to as "Dispersion 3") was obtained.

[0118] D. Example of Polysiloxane Compound Production Synthesis Example 4-1: Synthesis of methyltrimethoxysilane condensate (a1) A reaction vessel equipped with a stirrer, thermometer, dropping funnel, condenser, and nitrogen gas inlet was charged with 1,421 parts by weight of methyltrimethoxysilane (MTMS) and heated to 60°C. Next, a mixture of 0.17 parts by weight of isopropyl acid phosphate (Phoslex A-3 (trade name), manufactured by SC Organic Chemicals) and 207 parts by weight of deionized water was added dropwise to the reaction vessel over 5 minutes, and the mixture was then heated to 80°C and stirred for 4 hours to carry out the hydrolysis and condensation reaction of MTMS. The resulting condensate was distilled at a temperature of 40°C to 60°C and under a reduced pressure of 40 kPa to 1.3 kPa to remove the methanol and water produced during the reaction, yielding 1,000 parts by weight of a liquid containing an MTMS condensate (a1) having a number average molecular weight of 1,000 to 5,000. The phrase "under a reduced pressure of 40 kPa to 1.3 kPa" means that the pressure is reduced to 40 kPa when the distillation of methanol begins and is reduced to 1.3 kPa eventually. The conversion rate in the above solution was calculated by dividing the theoretical yield (parts by mass) when all of the methoxy groups of MTMS had undergone condensation reaction by the actual yield (parts by mass) after the condensation reaction, and was found to be 70% by mass.

[0119] Synthesis Example 4-2: Synthesis of polysiloxane compound-1 A reaction vessel equipped with a stirrer, a thermometer, a dropping funnel, a condenser, and a nitrogen gas inlet was charged with 150 parts by mass of isopropanol (hereinafter also referred to as "IPA"), 105 parts by mass of phenyltrimethoxysilane (hereinafter also referred to as "PTMS"), and 277 parts by mass of dimethyldimethoxysilane (hereinafter also referred to as "DMDMS"), in that order, and the temperature was raised to 80°C. Next, a mixture containing 21 parts by mass of methyl methacrylate (hereinafter also referred to as "MMA"), 4 parts by mass of butyl methacrylate (hereinafter also referred to as "BMA"), 3 parts by mass of butyric acid (hereinafter also referred to as "BA"), 2 parts by mass of methacryloyloxypropyltrimethoxysilane (hereinafter also referred to as "MPTS"), 3 parts by mass of IPA, and 0.6 parts by mass of butylperoxy-2-ethylhexanoate (hereinafter also referred to as "TBPEH") was added dropwise to the reaction vessel over 6 hours at 80°C. After completion of the addition, the mixture was further reacted at 80°C for 20 hours to obtain an organic solvent solution of a vinyl polymer (a2) having a number average molecular weight of 10,000 and having hydrolyzable silyl groups. To the organic solvent solution of the vinyl polymer (a2) obtained above, a mixture of 0.04 parts by mass of isopropyl acid phosphate ("Phoslex A-3" (trade name), manufactured by SC Organic Chemical Industries, Ltd.) and 112 parts by mass of deionized water was added dropwise at 80°C over 5 minutes, and after the dropwise addition was completed, the mixture was stirred at 80°C for a further 10 hours to cause a hydrolysis and condensation reaction, thereby obtaining a liquid containing a composite resin in which the hydrolyzable silyl groups of the vinyl polymer (a2) were bonded to the hydrolyzable silyl groups and silanol groups of the polysiloxane derived from PTMS and DMDMS. Next, 472 parts by mass of the MTMS condensate (a1) obtained by the method of Synthesis Example 4-1 and 80 parts by mass of deionized water were added to this liquid, and the mixture was stirred for 10 hours at 80° C. to carry out a hydrolysis condensation reaction. The obtained condensate was distilled under the same conditions as in Synthesis Example 4-1 to remove the produced methanol and water, and then 250 parts by mass of IPA was added to obtain 1,000 parts by mass of polysiloxane compound-1 with a nonvolatile content of 60.1% by mass.

[0120] E. Example of negative electrode active material production Example 1-1 (a) Production process of negative electrode active material precursor A phenolic resin having an average molecular weight of 3000 ("HE100C-30 (trade name)" manufactured by Air Water Performance Chemicals Inc.), polysiloxane compound-1 obtained by the method of Synthesis Example 4-2, and melamine were added to methyl ethyl ketone as a solvent in a resin solid mass ratio of 79 / 20 / 1 to obtain a mixed solution. Next, silicon particle dispersion liquid 1 obtained by the method of Synthesis Example 3-1 was added to this mixed solution so that the silicon particle content of the total solid content of the negative electrode active material precursor was 50 mass%, to obtain a mixture. The metal complex solution 1-3 prepared by the method of Synthesis Example 1-3 was added to this mixture so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles in the mixture was 0.03, and the mixture was thoroughly mixed in a stirrer. As a result, a suspension of a negative electrode precursor mixture in which magnesium ions were uniformly dissolved was obtained. Thereafter, the solvent was removed at 120° C. under a nitrogen gas flow, and then the mixture was dried under reduced pressure at 110° C. for 10 hours using a vacuum dryer to obtain a dried product of a negative electrode active material precursor. (b) Firing process The dried negative electrode active material precursor obtained in the above step (a) was calcined at 1050° C. for 6 hours in a nitrogen atmosphere to obtain a black solid. (c) Grinding process The black solid obtained in the firing step (b) above was pulverized in a planetary ball mill to obtain a negative electrode active material (1-1).

[0121] Example 1-2 A negative electrode active material (1-2) was obtained by the same procedure as in Example 1-1, except that in step (a) of Example 1-1, metal complex solution 1-3 was added so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was 0.05.

[0122] Examples 1-3 A negative electrode active material (1-3) was obtained by the same procedure as in Example 1-1, except that in step (a) of Example 1-1, metal complex solution 1-3 was added so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was 0.07.

[0123] Example 2-1 A negative electrode active material (2-1) was obtained by the same procedure as in Example 1-1, except that in step (a) of Example 1-1, the metal complex solution 1-4 prepared by the method of Synthesis Example 1-4 was added so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was 0.03.

[0124] Example 2-2 A negative electrode active material (2-2) was obtained by the same procedure as in Example 2-1, except that in step (a) of Example 2-1, the metal complex solution 1-4 prepared by the method of Synthesis Example 1-4 was added so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was 0.05.

[0125] Example 3 A negative electrode active material (3) was obtained by the same procedure as in Example 1-1, except that in step (a) of Example 1-1, the metal complex solution 1-5 prepared by the method of Synthesis Example 1-5 was added so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was 0.05.

[0126] Example 4 A negative electrode active material (4) was obtained by the same procedure as in Example 1-1, except that in step (a) of Example 1-1, the metal complex solution 1-2 prepared by the method of Synthesis Example 1-2 was added so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was 0.05.

[0127] Example 5 A negative electrode active material (5) was obtained by the same procedure as in Example 1-1, except that in step (a) of Example 1-1, the metal complex solution 1-1 prepared by the method of Synthesis Example 1-1 was added so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was 0.05.

[0128] Example 6 A negative electrode active material (6) was obtained by the same procedure as in Example 1-1, except that in step (a) of Example 1-1, the metal complex solution 1-6 prepared by the method of Synthesis Example 1-6 was added so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was 0.05.

[0129] Example 7 A negative electrode active material (7) was obtained by the same procedure as in Example 1-1, except that in step (a) of Example 1-1, the metal complex solution 1-8 prepared by the method of Synthesis Example 1-8 was added so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was 0.05.

[0130] Example 8 A negative electrode active material (8) was obtained by the same procedure as in Example 1-1, except that in step (a) of Example 1-1, the metal complex solution 1-9 prepared by the method of Synthesis Example 1-9 was added so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was 0.05.

[0131] Example 9 A negative electrode active material (9) was obtained by the same operation as in Example 1-1, except that in step (a) of Example 1-1, the metal complex solution 1-11 prepared by the method of Synthesis Example 1-11 was added so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was 0.05.

[0132] Example 10 A negative electrode active material (10) was obtained by the same operation as in Example 1-1, except that in step (a) of Example 1-1, the metal complex solution 1-13 prepared by the method of Synthesis Example 1-13 was added so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was 0.05.

[0133] Example 11 (a) Production process of negative electrode active material precursor A phenolic resin having an average molecular weight of 3000 ("HE100C-30 (trade name)" manufactured by Air Water Performance Chemicals Inc.) and the polysiloxane compound-1 obtained by the method of Synthesis Example 4-2 were added to methyl ethyl ketone as a solvent in a resin solid mass ratio of 30 / 70 to obtain a mixed solution. Next, dispersion liquid 2 obtained by the method of Synthesis Example 3-2 was added to this mixed solution so that the silicon particle content of the total solid content of the negative electrode active material precursor was 50 mass% to obtain a mixture. As a result, a suspension of a negative electrode precursor mixture in which magnesium ions were uniformly dissolved was obtained. Thereafter, the solvent was removed at 120° C. under a nitrogen gas flow, and then the mixture was dried under reduced pressure at 110° C. for 10 hours using a vacuum dryer to obtain a dried product of a negative electrode active material precursor. (b) Firing process The dried negative electrode active material precursor obtained in the above step (a) was calcined at 1050° C. for 6 hours in a nitrogen atmosphere to obtain a black solid. (c) Grinding process The black solid obtained in the firing step (b) above was pulverized in a planetary ball mill to obtain a negative electrode active material (11).

[0134] Example 12-1 A negative electrode active material (12-1) was obtained by the same procedure as in Example 1-1, except that in step (a) of Example 1-1, instead of the metal complex solution 1-3 prepared by the method of Synthesis Example 1-3, the metal complex solution 2-1 prepared by the method of Synthesis Example 2-1 was added so that the atomic ratio (molar ratio) of manganese atoms to silicon atoms in the silicon particles was 0.0001.

[0135] Example 12-2 A negative electrode active material (12-2) was obtained by the same procedure as in Example 12-1, except that the metal complex solution 2-1 was added so that the atomic ratio (molar ratio) of manganese atoms to silicon atoms in the silicon particles was 0.0002.

[0136] Example 12-3 A negative electrode active material (12-3) was obtained in the same manner as in Example 12-1, except that the metal complex solution 2-1 was added so that the atomic ratio (molar ratio) of manganese atoms to silicon atoms in the silicon particles was 0.0005.

[0137] Example 13 A negative electrode active material (13) was obtained by the same procedure as in Example 12-1, except that in Example 12-1, metal complex solution 2-2 prepared by the method of Synthesis Example 2-2 was added instead of metal complex solution 2-1 so that the atomic ratio (molar ratio) of manganese atoms to silicon atoms in the silicon particles was 0.0001.

[0138] Example 14 A negative electrode active material (14) was obtained by the same procedure as in Example 11, except that in step (a) of Example 11, instead of the dispersion liquid 2 obtained by the method of Synthesis Example 3-2, the dispersion liquid 3 obtained by the method of Synthesis Example 3-3 was added so that the silicon particle content in the total solid content of the negative electrode active material precursor was 50 mass%.

[0139] Comparative Example 1 A negative electrode active material (C1) was obtained by the same procedure as in Example 1-1, except that in step (a) of Example 1-1, metal complex solution 1-3 was not added, i.e., the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was set to 0.

[0140] Comparative Example 2 A negative electrode active material (C2) was obtained by the same procedure as in Example 1-1, except that in step (a) of Example 1-1, instead of the metal complex solution 1-3, magnesium di(acetylacetonate) [Mg(acac)2] dissolved in methyl ethyl ketone in advance was added so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was 0.03.

[0141] Comparative Example 3 A negative electrode active material (C3) was obtained by the same procedure as in Example 1-1, except that in step (a) of Example 1-1, instead of the metal complex solution 1-3, magnesium chloride [MgCl] that had been suspended in methyl ethyl ketone in advance was added so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was 0.03.

[0142] Comparative Example 4 A negative electrode active material (C4) was obtained by the same procedure as in Example 12-1, except that in Example 12-1, manganese chloride (II) [MnCl] suspended in methyl ethyl ketone in advance was added instead of the metal complex solution 2-1 so that the atomic ratio (molar ratio) of manganese atoms to silicon atoms in the silicon particles was 0.0001.

[0143] F. Evaluation of negative electrode active materials The negative electrode active materials obtained in each of the Examples and Comparative Examples were measured for the following physical properties. The results are summarized in Table 1. (1) Average particle size (D50) Measurement was performed using a laser diffraction particle size distribution analyzer (Malvern Panalytical, Mastersizer 3000). The details of the device and measurement conditions are as follows: <Device details> Optical system: red light source (He-Ne laser, 632.8 nm), and blue light source (LED, 470nm) Parameters: Red laser; refractive index 3.0, absorption coefficient 0.2 Blue laser: refractive index 2.6, absorption coefficient 0.2 Powder density 2.3g / cm 3 <Measurement conditions> Particle Type: Non-Spherical Particle Mode: Yes Fraunhofer Type: No Background measurement time (red): 5.00 s, Sample measurement time (red): 5.00 s Background measurement time (blue): 5.00 s, Sample measurement time (blue): 5.00 s Measurement scattering intensity setting: Lower limit 1.00%, upper limit 20.00% of scattering intensity Dispersion unit: Hydro MV, ultrasonic rate 0% Analysis model: General purpose Light scattering model: Mie theory <Sample pretreatment and measurement parameter setting> (a) Dispersion of silicon particles: Diluted with methyl ethyl ketone. Material properties: Refractive index 3.800, absorption coefficient 0.200, particle density 1.00 g / cm 3 Dispersion medium characteristics: refractive index 1.379, level sensor threshold 85.000 (b) Negative electrode active material particles Mix with ion-exchanged water and suspend in an ultrasonic disperser for 1 minute. Material properties: refractive index 1.520, absorption coefficient 0.100, particle density 1.00 g / cm 3 Dispersion medium characteristics: refractive index 1.330, level sensor threshold 100.000

[0144] (2) Specific surface area The specific surface area was measured by the BET method using a specific surface area measurement device (BELSORP-mini, manufactured by BELJAPAN Co., Ltd.). Specifically, approximately 1.0 g of the negative electrode active material particles obtained in each example and comparative example was weighed out and placed in a sample tube (including an internal glass rod and a 2 μm filter cap for shatterproofing) and pre-dried under vacuum at 110°C for 6 hours. After cooling to 25°C under vacuum, the sample tube was purged with nitrogen, and the mass of the dried negative electrode active material sample was accurately measured. A blank sample tube was connected to one port of the specific surface area measurement device, and the sample tube containing the dried negative electrode active material was connected to the other port. Nitrogen gas adsorption measurement was performed at liquid nitrogen temperature, and the specific surface area was calculated by the BET method based on the measured sample mass using the software (BELMaster) provided with the device.

[0145] (3) Solid-state NMR ( 29 Si-NMR) Using a JNM-ECA600 manufactured by JEOL RESONANCE, the negative electrode active materials obtained in each Example and Comparative Example were collected in a solid-state NMR sample tube (made of ZrO, φ3.2 mm) and measured under the conditions below. The peak attributed to Si (peak A with a chemical shift value of approximately −80 ppm) and the peak attributed to SiO (peak B with a chemical shift value of approximately −110 ppm) were measured, and the ratio R of peak A to peak B was calculated. [Measurement conditions] Probe: S60HX32 / AM (3.2 mm) MAS rate: 5kHz, 29 Si(119MHz) single_pulse_solid, flip 30deg., RD ​​60s x_offset:0 ppm x_sweep:500ppm x_points:2k scans 1024 ca. 17hr

[0146] (4)X-ray structural analysis A sample of the particles of the negative electrode active material obtained in each example and comparative example was filled into a 0.5 mm deep glass sample plate manufactured by Rigaku Corporation, and measurement was carried out using a wide-angle X-ray diffraction (XRD) device ("Ultima IV" manufactured by Rigaku Corporation) under the following conditions. Optical system: Parallel beam method + scintillation counter detector on the incident side Cu / Kα rays: 40kV / 40mA Scan speed: 2° / min Step: 0.02° Scanning range: 5° to 70° The XRD profile was depicted, compared with the reference peak, and the crystallite size was calculated using XRD profile analysis software (PDXL Version 2) manufactured by Rigaku Corporation. The crystallite size (nm) was calculated from the half width of the peak at about 2θ=28.3°±0.5°, which was attributed to the (111) plane of Si in the negative electrode active material, using the following formula (A) as the basic formula (Scherrer analytical formula): L=Kλ / βcosθ (A) In the formula, K is the Scherrer constant, L is the crystallite size [m], λ is the measured X-ray wavelength of Cu / Kα rays [m], β is the half-width [rad], and θ is the Bragg angle of the diffraction line peak [rad]. NIST SRM660c [lanthanum boride (LaB6)] was used as an external width standard sample, and data measured under the same measurement conditions as above was converted into peak width correction data according to the method attached to Rigaku's Ultima IV, and width correction was performed using this. In addition, in order to eliminate values ​​specific to the XRD instrument and distortion of the crystal, β in the above formula (A) (Scherrer formula) was calculated by correcting the XRD peak width of the above external width standard sample (LaB6) with a sufficiently grown crystallite diameter using Rigaku software (PDXL 2) according to the following formulas (Y1) and (Y2). β=B×y(2θ<90°) (Y1) y=0.9991-0.01915Z-2.8205Z 2 +2.828Z 3 -1.0366Z 4 (Y2) Here, Z=b / B, where B is the integral half-width of the diffraction peak of the test sample Si, and b is the integral half-width of the external width standard sample LaB6.

[0147] In addition, in this specification, the Scherrer constant K is 0.94, which Scherrer estimated from a Gaussian function. If the Scherrer constant K is calculated from the (hkl) = (111) plane peak of cubic Si at around 28.45° using the following formula (X) described in Langford, JI & Wilson, aJC (1978), J. Appl. Cryst., 11, 102-113, and is K = 2 / √3 = 1.154, it should be noted that the calculated value is 1.154 / 0.94 = 1.227 times the crystallite size described in this specification. K=6h 3 / [√N{6h 2 -2(k+l)h+kl}] ···(X) where N=h 2 +k 2 +l 2

[0148] (5) Analysis of silicon particle surfaces The negative electrode active materials obtained in each example and comparative example were powdered and dispersed in a microgrid to prepare samples. The thickness of the metal silicate (e.g., MgSiO3) layer on the silicon particle surface was determined from the results of observations (accelerating voltage: 300 kV) by HR-TEM (High-Resolution Transmission Electron Microscopy) using a JEOL "JEM-ARM300F." FIG. 1 shows the results of HR-TEM observation of the periphery of the silicon particle surface in the negative electrode active material (1-2) prepared in Example 1-2 (FIG. 1(a)), and the results of calculation of the lattice spacing by fast discrete Fourier transform (FFT) (FIG. 1(b)). In Figure 1, numerous lattice spacings of d = 0.19 to 0.30 nm were observed. Furthermore, mapping images using STEM-EDS (Scanning Transmission Electron Microscope Energy-Dispersive Spectroscopy) revealed that Si, O, and Mg were detected near the surfaces of the silicon particles. While silicon particles themselves (i.e., silicon) do not have lattice spacings of d = 0.19 to 0.30 nm, MgSiO3 and Mg2SiO4 have numerous lattice spacings of d = 0.19 to 0.30 nm. Therefore, the above results confirmed that lattice structures belonging to magnesium silicates (MgSiO3 and Mg2SiO4) exist on the surfaces of the silicon particles in the negative electrode active material (1-2).

[0149] (6) Elemental composition ratio of silicon-based matrix The negative electrode active material film formed on copper foil, as described in (7) below, was subjected to cross-sectional milling with an Ar gas beam using a cross-section sample measurement device (JEOL "IB-19520CCP" cross-section polisher). This cross-section was observed using a JEOL "JSM-7900F" scanning electron microscopy (SEM)-EDS (energy dispersive X-ray spectroscopy) device. Several areas of the film cross-section, magnified approximately 3000-5000 times, that belonged to the matrix layer without silicon particles were selected, and composition analysis was performed using the attached EDS function to determine the elemental composition ratio of the silicon-based matrix phase after removing the added amount of silicon particles.

[0150] (7) Battery characteristic evaluation A slurry was prepared by mixing 80 parts by weight of the negative electrode active material obtained in each Example and Comparative Example, 10 parts by weight of acetylene black as a conductive additive, and 10 parts by weight of a mixture of CMC and SBR as a binder. The resulting slurry was formed into a film on copper foil. After drying under reduced pressure at 110°C, a coin-type lithium-ion battery was fabricated as a half-cell using a Li metal foil as the counter electrode. Using a secondary battery charge / discharge tester (Hokuto Denko Corporation), the charge / discharge characteristics of the fabricated half-cells were evaluated under the following conditions: constant current / constant voltage charge / constant current discharge, at 25°C, with a cutoff voltage range of 0.005 to 1.5 V, and a charge / discharge rate of 0.1 C (1 to 3 cycles) and 0.2 C (after 4 cycles). Between each charge / discharge cycle, the cells were left in an open circuit for 30 minutes. The initial coulombic efficiency was calculated according to the following formula: Initial coulombic efficiency (%) = Initial discharge capacity (mAh / g) / Initial charge capacity (mAh / g) Meanwhile, full-cell evaluation was performed as follows. A positive electrode film was fabricated using a single-layer sheet of LiCoO2 as the positive electrode active material and aluminum foil as the current collector. A negative electrode film was fabricated by mixing graphite powder with the negative electrode active material powder obtained in each Example and Comparative Example at a discharge capacity design value of 500 mAh / g. A nonaqueous electrolyte solution prepared by dissolving lithium hexafluorophosphate at a concentration of 1 mol / L in a 1 / 1 volumetric mixture of ethylene carbonate and diethyl carbonate was used as the nonaqueous electrolyte. A laminated lithium-ion secondary battery was fabricated using a 30 μm-thick microporous polyethylene film as the separator. The fabricated laminated lithium-ion secondary battery was charged at a constant current of 1.2 mA (0.25 c based on the positive electrode) at 25°C until the test cell voltage reached 4.2 V. After reaching 4.2 V, the current was reduced to maintain the cell voltage at 4.2 V, and the discharge capacity was calculated. The capacity retention rate after 300 cycles at 45°C was calculated according to the following formula. Capacity retention rate (%) = 300th discharge capacity (mAh / g) / initial discharge capacity (mAh / g)

[0151] [Table 1]

[0152] As can be seen from the results in Table 1, the negative electrode active material of the present invention has high initial coulombic efficiency and capacity retention, and has an excellent balance of these secondary battery properties. Furthermore, secondary batteries containing the negative electrode active material of the present invention have excellent battery properties. [Industrial Applicability]

[0153] The negative electrode active material of the present invention has excellent initial coulombic efficiency and capacity retention. Secondary batteries containing such negative electrode active materials have excellent battery properties such as charge / discharge characteristics, and can be effectively used in portable electronic devices, for example, as paper-type batteries, button-type batteries, coin-type batteries, laminated batteries, cylindrical batteries, and prismatic batteries. The negative electrode active material can also be used in general electrochemical devices that use lithium ion insertion / extraction as a charge / discharge mechanism, such as hybrid capacitors and solid-state lithium secondary batteries.

Claims

1. Contains a silicon-based matrix, silicon particles, and a metal silicate; the silicon particles are dispersed in a silicon-based matrix phase, In the solid-state NMR spectrum, the chemical shift value assigned to Si is peak A at about −80 ppm, and SiO ４ a chemical shift value attributed to the compound of formula (I) is detected as a peak B near −110 ppm, and a ratio R of the peak A to the peak B is in the range of 1.0 to 10.

0.

2. 2. The negative electrode active material according to claim 1, wherein the metal silicate is a silicate of at least one metal selected from Li, Na, K, Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca.

3. 2. The negative electrode active material according to claim 1, wherein the atomic ratio of metal atoms in said metal silicate to silicon atoms in said silicon particles is in the range of 0.00001 to 0.

2.

4. 2. The negative electrode active material according to claim 1, wherein the silicon particles have an average particle size of 150 nm or less and a crystallite size obtained from a half-width of the peak at 2θ=28.4° in an X-ray crystal structure diffraction spectrum of 35 nm or less.

5. 2. The negative electrode active material according to claim 1, wherein at least one of the lattice structure attributable to the metal silicate and the lattice structure attributable to silicon nitride is present near the surface of the silicon particles.

6. 2. The negative electrode active material according to claim 1, wherein the content of the silicon particles is in the range of 10 to 70 mass % based on the total amount of the negative electrode active material.

7. 2. The negative electrode active material according to claim 1, wherein the silicon-based matrix contains at least a compound represented by SiOxCyNz (wherein x, y, and z are positive numbers satisfying 1≦x≦2, 1≦y≦20, and 0≦z≦0.5, respectively).

8. The average particle size is 1 μm or more and 15 μm or less, and the specific surface area is 1 m ２ / g or more 30m ２ The negative electrode active material according to claim 1 , wherein the SiO 2 content is 1 / g or less.

9. A precursor of a negative electrode active material contains a metal complex containing a metal cation whose counter ion is an organic anion, silicon particles, and an organosilicon polymer material.

10. 10. The negative electrode active material precursor according to claim 9, wherein the metal cation is a cation of at least one metal selected from Li, Na, K, Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca.

11. The negative electrode active material precursor according to claim 9 , wherein the metal cation is at least one metal cation selected from Mg and Mn.

12. 10. The negative electrode active material precursor according to claim 9, wherein the organic anion comprises a carboxylate anion having a hydrocarbon group having 2 to 20 carbon atoms.

13. The negative electrode active material precursor according to claim 9 , wherein the silicon particles have an average particle size of 150 nm or less.

14. 10. The negative electrode active material precursor according to claim 9, wherein the organosilicon polymer material has a polymer structure containing silicon, carbon, and oxygen elements.

15. 10. The negative electrode active material precursor according to claim 9, wherein the organosilicon polymer material has a polymer structure consisting of a mixture of a polysiloxane compound and a carbon source resin, or a composite of a polysiloxane compound and a carbon source resin.

16. A method for producing a negative electrode active material precursor, comprising the following steps a1 and b1: Step a1: A step of adding an organic solvent, a dispersant, and a metal complex containing a metal cation and whose counter ion is an organic anion to silicon particles, followed by stirring or pulverizing the mixture to obtain a slurry 1. Step b1: A step of mixing an organosilicon polymer material with the slurry 1 obtained in step a1, followed by removing the solvent and drying to obtain a negative electrode active material precursor.

17. A method for producing a negative electrode active material precursor, comprising the following steps a2 and b2: Step a2: Adding an organic solvent and a dispersant to silicon particles and stirring or pulverizing the mixture to obtain a slurry 2 Step b2: A step of mixing an organosilicon polymer material, the slurry 2 obtained in step a2, and a metal complex containing a metal cation whose counter ion is an organic anion, followed by removing the solvent and drying to obtain a negative electrode active material precursor.

18. 18. The method for producing a negative electrode active material precursor according to claim 16 or 17, wherein the metal cation is a cation of at least one metal selected from Li, Na, K, Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca.

19. The method for producing a negative electrode active material precursor according to claim 16 or 17, wherein the metal cation is at least one metal cation selected from Mg and Mn.

20. 18. The method for producing a negative electrode active material precursor according to claim 16, wherein the organic anion includes a carboxylate anion having a hydrocarbon group having 2 to 20 carbon atoms.

21. The method for producing a negative electrode active material precursor according to claim 16 or 17, wherein the silicon particles have an average particle size of 150 nm or less.

22. 18. The method for producing a negative electrode active material precursor according to claim 16 or 17, wherein the organosilicon polymer material has a polymer structure containing silicon, carbon, and oxygen elements.

23. 18. The method for producing a negative electrode active material precursor according to claim 16 or 17, wherein the organosilicon-based polymer material has a polymer structure consisting of a mixture of a polysiloxane compound and a carbon source resin, or a composite of a polysiloxane compound and a carbon source resin.

24. The method for producing a negative electrode active material precursor according to claim 16 or 17, wherein the metal complex is used as a metal complex solution containing a solvent.

25. 25. The method for producing a negative electrode active material precursor according to claim 24, wherein the metal complex solution is prepared by mixing an oxide or hydroxide of at least one metal selected from Li, Na, K, Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca with a carboxylic acid having a hydrocarbon group having 2 to 20 carbon atoms in an amount of 100 to 500 times by mole relative to the oxide or hydroxide of the metal, heating the resulting mixture, and removing generated water while allowing the mixture to react.

26. 25. The method for producing a negative electrode active material precursor according to claim 24, comprising the steps of: mixing a hydroxide of at least one metal selected from Li, Na, K, Rb, and Cs with a carboxylic acid having a hydrocarbon group having 2 to 20 carbon atoms in an amount of 100 to 500 times by molar ratio relative to the metal hydroxide, and water in an amount of 300 times by mass or less relative to the metal hydroxide; heating the mixture; subsequently adding an inorganic salt of at least one metal selected from Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca and heating the mixture to carry out a metal exchange reaction; separating the aqueous phase; and further dehydrating the mixture; and adding a solvent to the resulting mixture to prepare the metal complex solution.

27. A method for producing a negative electrode active material, comprising a step of firing the negative electrode active material precursor according to any one of claims 9 to 15 in an inert gas atmosphere.

28. A secondary battery comprising the negative electrode active material according to any one of claims 1 to 8.

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