Metal complex and method for producing the same, negative electrode active material precursor containing metal complex and method for producing the same, negative electrode active material, and secondary battery having negative electrode active material

Abstract

To provide a metal complex which is useful for producing a negative electrode active material having superior initial coulombic efficiency and capacity retention and a method for producing the same, a negative electrode active material precursor containing the metal complex and a method for producing the same, a negative electrode active material, and a secondary battery having the negative electrode active material.SOLUTION: A metal complex contains a metal cation, the counterion of which includes a carboxylate anion having 2-20 carbon atoms and having a protected amino group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a metal complex and a method for producing the same, a negative electrode active material precursor containing the metal complex and a method for producing the same, a negative electrode active material, and a secondary battery having the negative electrode active material. In particular, the present invention relates to a metal complex useful for producing a negative electrode active material excellent in initial efficiency and capacity retention rate and a method for producing the same, a negative electrode active material precursor containing such a metal complex and a method for producing the same, a negative electrode active material that can be suitably used as a negative electrode active material for secondary batteries, and a secondary battery containing 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 to improve 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 initial coulombic efficiency by suppressing the formation of lithium silicate during the initial charge / discharge cycle in silicon-containing negative electrode active materials. As a result, they have found that a negative electrode active material obtained from a negative electrode active material precursor containing a specific metal complex, silicon particles, and an organosilicon-based polymer material contains a silicon matrix and a metal silicate, and the peak ratios attributable to Si and SiO4 in solid-state NMR spectroscopy have a specific relationship, which is effective in improving initial coulombic efficiency and capacity retention. They have also found an efficient method for producing such a specific metal complex, which has led to the completion of the present invention. An object of the present invention is to provide a metal complex useful for producing a negative electrode active material excellent in initial coulombic efficiency and capacity retention rate, and a method for producing the same. Another object of the present invention is to provide a metal complex-containing negative electrode active material precursor useful for producing such a negative electrode active material, and a method for producing the same. Another object of the present invention is to provide such a negative electrode active material and a secondary battery having such a negative electrode active material. [Means for solving the problem]

[0007] The present invention has the following aspects. [1] A metal complex containing a metal cation, the counter ion of which contains a carboxylate anion having 2 to 20 carbon atoms and a protected amino group. [2] The metal complex according to [1], 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. [3] The metal complex according to [1] or [2], wherein the metal cation is a cation of at least one metal selected from Li, Mg, and Mn. [4] The metal complex according to any one of [1] to [3], wherein the protecting group of the amino group in the protected amino group is at least one selected from a tert-butoxycarbonyl group, a benzyloxycarbonyl group, and a benzoyl group.

[0008] [5] A method for producing a metal complex according to any one of [1] to [4], comprising mixing at least one metal salt selected from Li, Na, K, Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca of an aliphatic carboxylic acid having 1 to 20 carbon atoms, a carboxylic acid having 2 to 20 carbon atoms and having a protected amino group, and a solvent, and heating the mixture. [6] A method for producing a metal complex containing a metal cation whose counter ion contains a carboxylate anion having 2 to 20 carbon atoms and a protected amino group, by mixing at least one metal hydroxide selected from Li, Na, K, Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca, a carboxylic acid having 2 to 20 carbon atoms and having a protected amino group, and a solvent, and heating the mixture.

[0009] [7] A negative electrode active material precursor comprising a metal complex containing a metal cation whose counter ion contains a carboxylic acid anion having 2 to 20 carbon atoms and a protected amino group, silicon particles, and an organosilicon polymer material. [8] The negative electrode active material precursor according to [7], 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. [9] The negative electrode active material precursor according to [7] or [8], wherein the metal cation is at least one metal cation selected from Li, Mg, and Mn.

[10] The negative electrode active material precursor according to any one of [7] to [9], wherein the protecting group of the amino group in the protected amino group is at least one selected from a tert-butoxycarbonyl group, a benzyloxycarbonyl group, and a benzoyl group.

[11] The negative electrode active material precursor according to any one of [7] to

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

[12] The negative electrode active material precursor according to any one of [7] to

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

[13] The negative electrode active material precursor according to any one of [7] to

[12] , 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.

[0010]

[14] 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 whose counter ion contains a carboxylic acid anion having 2 to 20 carbon atoms and having a protected amino group 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.

[15] 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 whose counter ion contains a carboxylic acid anion having 2 to 20 carbon atoms and having a protected amino group, followed by removing the solvent and drying to obtain a negative electrode active material precursor.

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

[14] or

[15] , 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.

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

[14] to

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

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

[14] to

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

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

[14] to

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

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

[14] to

[19] , 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.

[0011]

[21] A negative electrode active material obtained by firing the negative electrode active material precursor according to any one of [7] to

[13] in an inert gas atmosphere.

[22] The negative electrode active material according to

[21] , comprising a silicon-based matrix, silicon particles, and a metal silicate, wherein the silicon particles are dispersed in the silicon-based matrix phase, and wherein a chemical shift value attributable to Si in a solid-state NMR spectrum is detected as Peak A at approximately −80 ppm and a chemical shift value attributable to SiO4 is detected as Peak B at approximately −110 ppm, and the ratio R of Peak A to Peak B is in the range of 1.0 to 10.0.

[23] The negative electrode active material according to

[22] , 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.

[24] The negative electrode active material according to

[22] or

[23] , 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.

[25] The negative electrode active material according to any one of

[22] to

[24] , wherein the silicon particles have an average particle size of 150 nm or less and a crystallite size obtained from the half-width of the peak at 2θ=28.4° in an X-ray crystal structure diffraction spectrum of 35 nm or less.

[26] The negative electrode active material according to any one of

[22] to

[25] , 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.

[27] The negative electrode active material according to any one of

[22] to

[26] , 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.

[28] The negative electrode active material according to any one of

[22] to

[27] , 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).

[29] 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 of any one of

[21] to

[28] .

[30] A secondary battery having a negative electrode active material according to any one of

[21] to

[29] . [Effects of the Invention]

[0012] The present invention provides a metal complex and a method for producing the same, which are useful for producing a negative electrode active material having excellent initial coulombic efficiency and capacity retention. The present invention also provides a negative electrode active material precursor containing the metal complex and a method for producing the same, which are useful for producing such a negative electrode active material, such a negative electrode active material, and a secondary battery having such a negative electrode active material. [Brief explanation of the drawings]

[0013] [Figure 1] Figure 1(a) shows the results of HR-TEM observation of the surface of a silicon particle in the negative electrode active material (4), and Figure 1(b) shows the results of calculation of the lattice spacing by fast discrete Fourier transform (FFT). DETAILED DESCRIPTION OF THE INVENTION

[0014] <Metal complex and method for producing the same> The present invention is a metal complex (hereinafter also simply referred to as "the present metal complex") that contains a metal cation, the counter ion of which contains a carboxylate anion having 2 to 20 carbon atoms and having a protected amino group. The metal cation contained in the present 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 present 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 is usually either monovalent, divalent, or trivalent, which is preferable from the viewpoint that the present negative electrode active material obtained from the negative electrode active material precursor containing the present metal complex, as described below, tends to be excellent in 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. Among these, it is more preferable that the metal cation in the present metal complex is at least one metal cation selected from Li, Mg, and Mn, from the viewpoints of reactivity with the native oxide film on the surface of silicon particles, stability of the resulting Li silicate or Mg silicate, and production efficiency of silicon nitride produced by a Mn-catalyzed reaction, within the firing temperature range when the negative electrode active material of the present invention is obtained by firing the negative electrode active material precursor of the present invention containing the present metal complex. The negative electrode active material precursor of the present invention containing the present metal complex and the negative electrode active material of the present invention obtained by firing the negative electrode active material precursor in an inert gas atmosphere will be described in detail below.

[0015] In the present metal complex, the counter ion of the metal cation is a carboxylate anion having 2 to 20 carbon atoms and a protected amino group. Such a carboxylate anion is a carboxylate anion having 2 to 20 carbon atoms and having a protected amino group. In other words, it can be said to be a carboxylate anion of an aminocarboxylic acid having 2 to 20 carbon atoms and having a protected amino group, or a carboxylate anion of an amino acid having 2 to 20 carbon atoms and having a protected amino group. The position of the protected amino group is not limited to the α-position of the carbonyl group of the carboxylic acid (so-called α-amino acid), but can also be located in the middle of the carbon chain (so-called β-amino acid, γ-amino acid, etc.) or at the end (so-called ω-aminocarboxylic acid). Furthermore, the stereoisomerism of the carboxylate anion having 2 to 20 carbon atoms and having a protected amino group is not particularly limited, and it can be a D-form, an L-form, or a mixture thereof. The carboxylate anion having 2 to 20 carbon atoms and a protected amino group may be a monocarboxylate anion or a polycarboxylate anion. In the case of a carboxylate anion having multiple amino groups, the number of protected amino groups may be one or more, and in the case of multiple protected amino groups, the protecting groups described below on the protected amino groups may be the same or different. Furthermore, in the case of a polycarboxylate anion, it is sufficient that at least one of the multiple carboxyl groups is an anion, and the other carboxyl groups may be converted to an ester group. In addition, in this specification, even when an amide bond is formed by reaction of any one carboxyl group of a polycarboxylic acid with an amino group of a carboxylic acid or an ester thereof containing another amino group, this can also be considered as a carboxylate anion having a protected amino group. In the step of the method for producing a negative electrode active material precursor of the present invention, which will be described later, the carboxylic acid anion having 2 to 20 carbon atoms and a protected amino group is preferably a monocarboxylic acid anion, from the viewpoint of facilitating coordination or adsorption of the metal complex to the surface of silicon particles.

[0016] As used herein, the term "protected amino group" refers to an amino group protected with an amino-protecting group. Examples of the amino-protecting group include those widely known in the fields of organic synthetic chemistry or biochemistry. Among these, the amino-protecting group in the protected amino group is preferably at least one selected from the group consisting of a tert-butoxycarbonyl group, a benzyloxycarbonyl group, and a benzoyl group. That is, the protected amino group in the carboxylate anion can be deprotected by a known, commonly used method and is also a functional group that can enhance solubility in organic solvents.

[0017] Examples of the carboxylic acid having 2 to 20 carbon atoms and a protected amino group, which serves as a source of a carboxylic acid anion having 2 to 20 carbon atoms and a protected amino group (in other words, an aminocarboxylic acid having 2 to 20 carbon atoms and whose amino group is protected; or an amino acid having 2 to 20 carbon atoms and whose amino group is protected), include N-tert-butoxycarbonylalanine, N-tert-butoxycarbonylarginine, N(α)-tert-butoxycarbonylasparagine, N(α)-tert-butoxycarbonylglutamine, N-tert-butoxycarbonylglycine, N(α)-tert-butoxycarbonylhistidine, N-tert-butoxycarbonyl N-tert-butoxycarbonylisoleucine, N-tert-butoxycarbonylleucine, N(α)-tert-butoxycarbonyllysine, N(ε)-tert-butoxycarbonyllysine, N-tert-butoxycarbonylphenylalanine, N-tert-butoxycarbonylproline, N-tert-butoxycarbonylserine, N-tert-butoxycarbonylthreonine, N(α)-tert-butoxycarbonyltryptophan, N-tert-butoxycarbonyltyrosine, N-tert-butoxycarbonylvaline, N-tert-butoxycarbonyl-4-cyclohexyl-aspartic acid, N-tert-butoxycarbonyl-3-(3,4-dihydroxyphenyl)-alanine, N-benzyloxycarbonylalanine, N-benzyloxycarbonylarginine, N(α)-benzyloxycarbonylasparagine, N(α)-benzyloxycarbonylglutamine, N-benzyloxycarbonylglycine, N(α)-benzyloxycarbonylhistidine, N-benzyloxycarbonylisoleucine, N-benzyloxycarbonylleucine, N(α)-benzyloxycarbonyllysine , N(ε)-benzyloxycarbonyllysine, N-benzyloxycarbonylphenylalanine, N-benzyloxycarbonylproline, N-benzyloxycarbonylserine, N-benzyloxycarbonylthreonine, N(α)-benzyloxycarbonyltryptophan, N-benzyloxycarbonyltyrosine, N-benzyloxycarbonylvaline, N-benzyloxycarbonyl-4-cyclohexyl-aspartic acid, N-benzyloxycarbonyl N-benzoyl-3-(3,4-dihydroxyphenyl)-alanine, N-benzoylalanine, N-benzoylarginine, N(α)-benzoylasparagine, N(α)-benzoylglutamine, N-benzoylglycine, N(α)-benzoylhistidine, N-benzoylisoleucine, N-benzoylleucine, N(α)-benzoyllysine, N(ε)-benzoyllysine, N-benzoylphenylalanine, N-benzoylproline, N-benzoylserine, Examples include N-benzoylthreonine, N(α)-benzoyltryptophan, N-benzoyltyrosine, N-benzoylvaline, N-benzoyl-4-cyclohexyl-aspartic acid, N-benzoyl-3-(3,4-dihydroxyphenyl)-alanine, N(α)-tert-butoxycarbonyl-N(ε)-benzyloxycarbonyl-lysine, aspartame (L-α-aspartyl-L-phenylalanine methyl ester), and glycylglycine. In addition, compounds in which the amino group of an aminocarboxylic acid such as β-alanine, isoserine, 4-aminobutyric acid (GABA), 4-amino-3-hydroxybutyric acid, 6-aminohexanoic acid, or 12-aminolauric acid is protected with the above-mentioned amino-protecting group can also be used as a source of a carboxylic acid anion having 2 to 20 carbon atoms and a protected amino group.

[0018] The present metal complex is stable in the atmosphere and resistant to moisture and other factors, making it easy to handle. Furthermore, while conventional metal salts of fatty acids (fatty acid soaps) and metal salts of amino acids (amino acid soaps) are insoluble or have very low solubility in organic solvents, the present metal complex is soluble in various organic solvents, such as methyl ethyl ketone. Therefore, in the production of the negative electrode active material precursor of the present invention, described below, the present metal complex can be uniformly dissolved in an organic solvent and brought into contact with silicon particles. In the present metal complex, the metal cations presumably form chelate coordinate-type ionic bonds with carboxylic acid anions having 2 to 20 carbon atoms and a protected amino group, resulting in a small number of freely movable metal cations. On the other hand, the present metal complex modifies the surface of silicon particles, which have Lewis acidity, due to the presence of basic nitrogen atoms contained in the carboxylic acid anions. Therefore, when the present metal complex is uniformly dissolved in an organic solvent and brought into contact with silicon particles, the metal cations can be more uniformly dispersed on the silicon particle surface, making it easier to achieve both metal cation doping and silicon particle surface protection. Then, the negative electrode active material obtained by firing can be uniformly doped with a metal. The solubility of the metal complex in an organic solvent can be controlled by changing the structure of the carboxylic acid anion having 2 to 20 carbon atoms and a protected amino group. Furthermore, for example, by dissolving the present metal complex containing Li cations as the metal cation in an organic solvent, it is possible to prepare an easy-to-handle and stable solution containing Li cations. Therefore, by immersing silicon oxycarbide or silicon monoxide particles in such a solution, followed by drying and calcination, it is possible to obtain a lithium-doped silicon-based negative electrode active material more easily than when using, for example, a lithium naphthalenide solution.

[0019] The present metal complex can be preferably prepared by the following method [i] or [ii]. [i] The metal complex is obtained by mixing and heating at least one metal salt selected from Li, Na, K, Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca of an aliphatic carboxylic acid having 1 to 20 carbon atoms, a carboxylic acid having 2 to 20 carbon atoms and having a protected amino group, and a solvent.

[0020] In the method [i] above, examples of the aliphatic carboxylic acid having 1 to 20 carbon atoms include saturated or unsaturated monocarboxylic acids such as formic acid, 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 production of the present metal complex, stability of the produced present metal complex, and the charge / discharge characteristics of the present negative electrode active material obtained from the present negative electrode active material precursor containing the present metal complex, as described below. Furthermore, the aliphatic carboxylic acid having 1 to 20 carbon atoms preferably has a pKa of greater than 4, and more preferably a pKa in the range of 4 to 6. In the above method [i], the metal salt of an aliphatic carboxylic acid having 1 to 20 carbon atoms is preferably at least one metal salt selected from Li, Mg, and Mn, from the viewpoints of reactivity with the native oxide film on the surface of silicon particles, stability of the resulting Li silicate or Mg silicate, and production efficiency of silicon nitride produced by the Mn-catalyzed reaction, within the firing temperature range when the negative electrode active material of the present invention is obtained by firing the negative electrode active material precursor of the present invention containing the metal complex.

[0021] In the above method [i], the details of the carboxylic acid having 2 to 20 carbon atoms and having a protected amino group are the same as those of the carboxylic acid having 2 to 20 carbon atoms and having a protected amino group, which serves as the source of the carboxylic acid anion having 2 to 20 carbon atoms and having a protected amino group. The amount of the carboxylic acid having 2 to 20 carbon atoms and having a protected amino group used is preferably in the range of 1 to 5 times by mole, more preferably in the range of 1.9 to 2.5 times by mole, relative to the amount of the metal salt of the aliphatic carboxylic acid having 1 to 20 carbon atoms. Using the carboxylic acid having 2 to 20 carbon atoms and having a protected amino group in the above range facilitates the formation of the metal complex by reaction with the metal salt of the aliphatic carboxylic acid having 1 to 20 carbon atoms.

[0022] Examples of solvents that can be used in the above method [i] include water; 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. Among these, ethanol, methanol, and isopropanol are preferred from the viewpoints that they have high solubility for both metal salts of aliphatic carboxylic acids having 1 to 20 carbon atoms and carboxylic acids having 2 to 20 carbon atoms and a protected amino group, allowing for reduction in the amount used, and have low boiling points and are easy to remove the solvent. The amount of solvent used is preferably 1 to 100 times by mass, and more preferably 3 to 20 times by mass, the total amount of the metal salt of an aliphatic carboxylic acid having 1 to 20 carbon atoms and the carboxylic acid having 2 to 20 carbon atoms and having a protected amino group. When the solvent is used in the above range, the viscosity of the reaction mixture can be reduced together with the carboxylic acid having 2 to 20 carbon atoms that is liberated as the reaction proceeds, and this makes it easier to promote the reaction of producing the metal complex by stirring.

[0023] The above method [i] is positioned as a method in which a carboxylic acid having 2 to 20 carbon atoms and a protected amino group is brought into contact with a metal salt of a C1 to 20 aliphatic carboxylic acid (metal salt of a weak acid) in a solvent, the carboxylic acid having 2 to 20 carbon atoms and having a lower pKa than the C1 to 20 aliphatic carboxylic acid, which is the conjugate acid of the metal salt of the C1 to 20 aliphatic carboxylic acid (metal salt of a weak acid), thereby liberating the C1 to 20 aliphatic carboxylic acid as a weak acid, and promoting the formation of the metal complex by an anion exchange reaction. The assumed reaction mechanism for obtaining this metal complex by method [i] using a magnesium salt of an aliphatic carboxylic acid having 1 to 20 carbon atoms and N-tert-butoxycarbonyl-4-cyclohexyl-aspartic acid as the carboxylic acid having 2 to 20 carbon atoms and a protected amino group is shown in [Scheme 1].

[0024] [ka]

[0025] In method [i], when isolating the present metal complex after the reaction, the liberated aliphatic carboxylic acid having 1 to 20 carbon atoms may be distilled off together with the solvent, or at least a portion of it may remain. In the latter case, the present metal complex is obtained in the form of a mixture with the aliphatic carboxylic acid having 1 to 20 carbon atoms. When the present metal complex is used in the form of a mixture with the aliphatic carboxylic acid having 1 to 20 carbon atoms in the production of the negative electrode active material precursor described below, the aliphatic carboxylic acid having 1 to 20 carbon atoms is thought to be easily coordinated to or adsorbed on the surface of silicon particles. On the other hand, since Si—OH groups formed by the presence of trace amounts of moisture may also be present on the silicon particle surface, hydrogen bonds with the liberated aliphatic carboxylic acid having 1 to 20 carbon atoms are thought to also be formed. Therefore, it is presumed that the interaction between the aliphatic carboxylic acid having 1 to 20 carbon atoms coordinated to or adsorbed on the silicon particle surface and the present metal complex is further enhanced, and the carboxylate anion possessed by the present metal complex makes the present metal complex more likely to coordinate to or adsorb on the silicon particle surface.

[0026] [ii] At least one metal hydroxide selected from Li, Na, K, Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca, a carboxylic acid having 2 to 20 carbon atoms and having a protected amino group, and a solvent are mixed and heated to obtain the metal complex.

[0027] The details of the carboxylic acid having 2 to 20 carbon atoms and having a protected amino group and the solvent in the above method [ii] are the same as those of the carboxylic acid having 2 to 20 carbon atoms and having a protected amino group and the solvent in the above method [i]. In the above method [ii], from the viewpoint of smoothly proceeding with the reaction, an aliphatic carboxylic acid having 1 to 20 carbon atoms may be further coexisted as a catalyst in an amount of 0.1 to 10 mol % relative to the metal hydroxide. Details of such an aliphatic carboxylic acid having 1 to 20 carbon atoms are the same as those described in the above method [i]. Among them, in method [ii], octylic acid (2-ethylhexanoic acid) or acetic acid is preferred as the aliphatic carboxylic acid having 1 to 20 carbon atoms to be coexisted. In the method [ii] above, the amount of the solvent used is preferably 1 to 100 times by mass the total amount of the metal hydroxide and the carboxylic acid having 2 to 20 carbon atoms and a protected amino group. Using the solvent in this range makes it easier to make the reaction mixture uniform, and facilitates the reaction of producing the metal complex. The heating temperature in the above method [ii] is preferably in the range of 10 to 150° C., more preferably 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.

[0028] In the above method [ii], the present metal complex is obtained by reacting a metal hydroxide with a carboxylic acid having 2 to 20 carbon atoms and a protected amino group. When a carboxylic acid having 2 to 20 carbon atoms and a protected amino group has more carboxylic acid groups than protected amino groups, the molecule is acidic, and the reaction with a basic metal hydroxide is also a neutralization reaction, so the reaction proceeds relatively smoothly, even in solid and liquid phases. On the other hand, when the number of carboxylic acid groups is equal to or fewer than the number of amino groups, the molecule is neutral or basic, and the solid-liquid reaction with a basic metal hydroxide tends to require a very long time and be inefficient. When a C1 to C20 aliphatic carboxylic acid, which is an acidic substance with a relatively high (positively large) pKa, is coexisted in a small to equal amount, a metal salt of a C1 to C20 aliphatic carboxylic acid (metal salt of a weak acid) is first formed in the reaction system by a neutralization reaction with the metal hydroxide. The presence of a carboxylic acid having 2 to 20 carbon atoms and a protected amino group with a relatively low pKa (highly negative) in the reaction system is thought to induce the liberation of the weak acid mentioned in method [i] from the metal salt of such an aliphatic carboxylic acid having 1 to 20 carbon atoms, further promoting the formation of this metal complex. When a small amount of an aliphatic carboxylic acid having 1 to 20 carbon atoms is added, rather than an equivalent amount, the liberated aliphatic carboxylic acid reacts again with the metal hydroxide, thereby establishing a catalytic cycle in which the neutralization reaction and the weak acid liberation reaction can be repeated. In other words, in method [ii], a small amount of an aliphatic carboxylic acid having 1 to 20 carbon atoms is presumed to act as a catalyst in the reaction to form this metal complex, while an equivalent amount acts as a raw material for the reaction intermediate. The assumed reaction mechanism for obtaining this metal complex by method [ii] using magnesium hydroxide as the metal hydroxide and N-tert-butoxycarbonyl-4-cyclohexyl-aspartic acid as the carboxylic acid having 2 to 20 carbon atoms and a protected amino group is shown in [Scheme 2]. The assumed reaction mechanism for obtaining this metal complex by method [ii] in the coexistence of an aliphatic carboxylic acid having 1 to 20 carbon atoms as a catalyst is shown in [Scheme 3].

[0029] [ka]

[0030] [ka]

[0031] <Negative electrode active material precursor> The present invention also relates to a negative electrode active material precursor (hereinafter also referred to as "the present precursor") containing the present metal complex, silicon particles, and an organosilicon polymer material. The negative electrode active material of the present invention, which will be described later, is preferably obtained from the present precursor.

[0032] Details of the metal cation in the present metal complex contained in the present precursor are the same as those of the metal cation in the present metal complex described above. 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. Furthermore, in the present metal complex contained in the present precursor, the counter ion of the above-mentioned metal cation includes a carboxylate anion having 2 to 20 carbon atoms and having a protected amino group. Details of such a carboxylate anion having 2 to 20 carbon atoms and having a protected amino group are the same as those of the above-mentioned carboxylate anion having 2 to 20 carbon atoms and having a protected amino group in the present metal complex, and it is preferable that the protecting group of the amino group in the protected amino group is at least one selected from a tert-butoxycarbonyl group, a benzyloxycarbonyl group, and a benzoyl group. The precursor may contain one type of metal complex or a mixture of two or more types of metal complexes.

[0033] 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. When the average particle size of the silicon particles is within the above range, the charge / discharge performance of a secondary battery having a negative electrode active material obtained from this precursor is easily improved, and the capacity retention rate is easily maintained high for 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.

[0034] Silicon particles exceeding 300 nm tend to form large agglomerates, which can easily cause pulverization during charging and discharging in secondary batteries containing the resulting 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 resulting 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, resulting in 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 precursor be as small as possible.

[0035] The silicon particles may be granular, needle-like, or flake-like in shape. From the viewpoint of the charge-discharge performance of the negative electrode active material obtained from this precursor, 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. The average particle size of silicon particles can be measured by dynamic light scattering, but using a transmission electron microscope (TEM) or field emission scanning electron microscope (FE-SEM) makes it easier and more accurate to identify silicon particles with the above aspect ratios. In the case of negative electrode active materials, the sample to be measured can be cut with a focused ion beam (FIB) and the cross section can be observed with 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] [ka]

[0040] [ka]

[0041] (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 3 Examples 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 3Examples of the aralkyl group represented by each of the above include a benzyl group, a diphenylmethyl group, and a naphthylmethyl group.

[0042] 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.

[0043] The polysiloxane compound may be a composite resin in which polysiloxane segments and polymer segments are bonded together in a structure represented by the following structural formula (S-3), or may have a three-dimensional network polysiloxane structure.

[0044] [ka]

[0045] (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.

[0046] 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 thereof include groups represented by the following general formula (S-4):

[0047] [ka]

[0048] (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.

[0049] 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. R5 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.

[0050] 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.

[0051] [ka]

[0052] 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.).

[0053] 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, with a resol-type phenolic resin being more preferred. 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.).

[0054] 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.

[0055] The content of the present metal complex in the present precursor is preferably in the range of 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 Li or Mg, while it is preferably in the range of 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.

[0056] <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 the metal complex to silicon particles and 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 the metal complex, followed by desolvation and drying to obtain the precursor.

[0057] 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 this 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.

[0058] 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 grinding, a dispersant, which will be described later, may be present to promote dispersion of the silicon particles obtained by grinding. 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 %.

[0059] The organic solvent used in step a1 of Production Method I and step a2 of Production Method II is preferably a solvent that does not react with silicon particles, and examples thereof include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and diisobutyl ketone; alcohols such as ethanol, methanol, n-propanol, and isopropanol; and aromatic hydrocarbons such as benzene, toluene, and xylene. Among these, ketones are preferred.

[0060] 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.

[0061] 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.

[0062] The details of the metal cation in the present metal complex used in step a1 of production method I and step a2 of production method II are the same as those of the metal cation in the present metal complex described above. In particular, it is more preferable that the metal cation in the present 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 carboxylate anion having 2 to 20 carbon atoms and a protected amino group, which is the counter ion of the metal cation in the present metal complex, are the same as those of the carboxylate anion having 2 to 20 carbon atoms and a protected amino group in the present metal complex, and it is preferable that the protecting group of the amino group in the protected amino group is at least one selected from a tert-butoxycarbonyl group, a benzyloxycarbonyl group, and a benzoyl group. The inclusion of such a counter anion is more preferable from the viewpoint of facilitating coordination or adsorption of the metal complex to the silicon particle surface. The present metal complex used in step a1 of production method I and step a2 of production method II may be one type or a mixture of two or more types.

[0063] In step a1 of Production Method I and step b2 of Production Method II, the amount of the present 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 the metal anion contained in the present metal complex to the number of atoms (molar number) of Si contained in the silicon particles.

[0064] In producing the negative electrode active material precursor of the present invention, in step a1 of Production Method I and step b2 of Production Method II, it is particularly preferred to use the metal complex as a solution containing a solvent having a boiling point lower than that of water (hereinafter, also simply referred to as "metal complex solution"), taking advantage of the feature that the metal complex is soluble in various organic solvents.

[0065] In Process I for Preparing the Precursor, when a metal complex solution is used as the Metal Complex in Step a1, the Metal Complex's protected amino-group-containing carboxylic acid anion having 2 to 20 carbon atoms facilitates coordination or adsorption of the Metal Complex to the silicon particle surface. Therefore, the silicon particles contained in the resulting Slurry 1 are dispersed by the action of the dispersant with the Metal Complex coordinated or adsorbed to their surfaces, and mixing the Slurry 1 with an organosilicon-based polymer material in Step b1 makes it easy to obtain a mixture in which the silicon particles with the Metal Complex coordinated or adsorbed to their surfaces and the organosilicon-based polymer material are uniformly dispersed. Furthermore, in Process II for Producing the Precursor, when an organosilicon polymer material and a metal complex solution as the present metal complex are added in Step b2 to Slurry 2 containing silicon particles, a dispersant, and an organic solvent obtained in Step a2, a solution in which the organosilicon polymer material and the present metal complex are uniformly dispersed is produced, and the solution is mixed with the silicon particles. In this case, too, the present metal complex is easily coordinated or adsorbed to the silicon particle surface due to the carboxylic acid anion having 2 to 20 carbon atoms and a protected amino group possessed by the present metal complex, making it easy to obtain a mixture in which the silicon particles with the present metal complex coordinated or adsorbed to their surfaces and the organosilicon 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 the metal complex coordinated or adsorbed to their surfaces are uniformly dispersed in the matrix of the organosilicon polymer material without agglomerating as primary particles.

[0066] Furthermore, when the present metal complex is used as a metal complex solution, the mixability and dispersibility of the silicon particles, organosilicon-based polymer material, and present metal complex are improved in either Production Method I or Production Method II. Therefore, it is presumed that the carboxylic acid anion having 2 to 20 carbon atoms and a protected amino group contained in the present metal complex easily bonds with functional groups present on the silicon particle surface to modify the silicon particle surface while simultaneously protecting the silicon particle surface from oxidation. Furthermore, if the metal complex solution further contains a carboxylic acid due to the production method of the present metal complex, it is presumed that the carboxylic acid promotes coordination of the present metal complex to the silicon particles. Therefore, the silicon particles are more likely to be dispersed while maintaining their primary particle state with the present metal complex adsorbed on their surface. This is presumed to further promote the formation of metal silicate on the silicon particle surface contained in the present negative electrode active material obtained from the resulting precursor. For these reasons, it is presumed that the present negative electrode active material having the properties specified in the present invention described above is more likely to be obtained. In addition, when this metal complex is used as a metal complex solution in Process I or Process II of the present precursor, the miscibility of the silicon particle-containing slurry (Slurry 1 or Slurry 2) with the solution of the organosilicon polymer material is improved, and there is also the advantage that the solvent removal and drying of the mixture can be carried out industrially advantageously in a shorter time with less heat consumption. That is, compared to conventional methods for doping metals to improve the initial coulombic efficiency of silicon-containing negative electrode active materials, such as physical mixing with inorganic metal salts or contacting with organic metal compounds such as alkyl metal compounds, metal naphthalenides, and metal alkoxides, this method ensures flexibility in equipment, is easy to operate, and is highly safe. 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.

[0067] 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 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.

[0068] <Method of manufacturing negative electrode active material> The precursor obtained by the above-described production method is calcined in an inert gas atmosphere and pulverized to obtain a negative electrode active material. That is, the present invention encompasses a method for producing a negative electrode active material, which includes a step of calcining the precursor in an inert gas atmosphere.

[0069] <Firing process> The calcination process involves calcining this 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 calcination conditions to convert the other main components into a calcined product suitable for use as a negative electrode active material. Specifically, the organosilicon-based polymer material (preferably a polysiloxane compound and a carbon source resin) contained in this precursor is converted into a silicon-oxygen-carbon skeleton and free carbon by the energy of the high-temperature treatment in the baking step, forming a silicon-based matrix in the negative electrode active material, as described below. As mentioned 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 calcination step, at least one of a lattice structure attributable to a metal silicate and a lattice structure attributable to silicon nitride is formed near the surface of the silicon particles contained in the negative electrode active material precursor, at least a portion of whose surface is coordinated with the metal complex. The lattice structure attributable to a metal silicate is formed by the metal cation contained in the metal complex and silicon oxide present near the surface of the silicon particles, and therefore the irreversible capacity of the resulting negative electrode active material is reduced, leading to an increase in the initial coulombic efficiency.

[0070] 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 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 negative electrode active material, which maintains the chemical bonding state of silicon and carbon, and it is also possible to avoid oxidation of silicon particles due to firing at excessively high temperatures, making 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.

[0071] <Crushing process> The pulverization step is a step in which the sintered product obtained in the sintering step is pulverized and classified as necessary to obtain a negative electrode active material. The pulverization to obtain a negative electrode active material having a desired average particle size may be performed in one step or in several steps. For example, when preparing a negative electrode active material having a particle size 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 into particles of about 1 mm using a jaw crusher, roll crusher, or the like, and then pulverized to about 100 μm using a glow mill, ball mill, or the like, and further pulverized to about 10 μm using a bead mill, jet mill, or the like. 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 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.

[0072] <Negative electrode active material> The present invention also encompasses a negative electrode active material obtained by calcining the present precursor, preferably the present precursor obtained by the above-described production method, in an inert gas atmosphere. The negative electrode active material of the present invention (hereinafter also referred to as "the present negative electrode active material") preferably contains a silicon-based matrix, silicon particles, and a metal silicate, the silicon particles being dispersed in the silicon-based matrix phase, and a chemical shift value attributable to Si is detected as Peak A around -80 ppm and a chemical shift value attributable to SiO4 is detected as Peak B around -110 ppm in a solid-state NMR spectrum, with the ratio R of Peak A to Peak B being in the range of 1.0 to 10.0.

[0073] 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. Here, 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 precursor. 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. The details of the shape, length in the major axis direction, thickness, and aspect ratio of the silicon particles contained in the present negative electrode active material are the same as those described above for the silicon particles contained in the present precursor.

[0074] 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.

[0075] 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 and protected 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.

[0076] 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.

[0077] 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, and 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, while chemical reactions between the silicon and the electrolyte are avoided during charge / discharge, minimizing performance degradation of the silicon particles. 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.

[0078] 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, from the viewpoint of the balance between charge-discharge performance and initial Coulomb efficiency, 1 ≦ y ≦ 20 is preferable, and 1.2 ≦ y ≦ 15 is more preferable.

[0079] The compound constituting the silicon-based matrix phase may contain nitrogen in addition to silicon, oxygen, and carbon. Here, nitrogen is derived from a polysiloxane compound, a phenolic resin, a dispersant, a carboxylic acid anion having a protected amino group and having 2 to 20 carbon atoms, and other nitrogen compounds, etc., which are contained as constituent components in the negative electrode active material precursor in the method for producing the present negative electrode active material, and has an atomic group containing nitrogen as a functional group in its molecule, and nitrogen gas used in the firing process, etc., and can be introduced into the silicon-based matrix phase. 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.

[0080] 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 above 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. Note that 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 ICP emission spectrometer (ICP-OES).

[0081] Although it is preferable to measure x, y, and z by the above-mentioned method, the negative electrode active material may be locally analyzed, and the content ratio data obtained thereby may be obtained at many measurement points, and the content ratio of the entire negative electrode active material may be inferred from the data. Examples of local analysis include energy dispersive X-ray spectroscopy (SEM-EDX) and electron probe microanalyzer (EPMA).

[0082] 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).

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] It is believed that a silicon oxide film is always present on the surface of silicon particles due to natural oxidation unless the silicon particles are 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. Meanwhile, the present anode active material is obtained by calcining the present anode active material precursor, which is prepared by a process of uniformly dissolving the present metal complex during production. During calcination, the silicon oxide film on the silicon particle surface reacts with a specific metal cation contained in the present metal complex to convert it to metal silicate before the first charge operation. This conversion stabilizes lithium ions as the lithium silicate within the anode active material during the first charge operation, preventing them from returning to the positive electrode during discharge, 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.

[0088] Here, the nitrogen in the lattice structure attributable to silicon nitride is believed 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, the nitrogen is believed to be introduced due to the presence of nitrogen-containing atomic groups as functional groups in the polysiloxane compound, phenolic resin, dispersant, carboxylic acid anion having 2 to 20 carbon atoms and a protected amino group possessed by the present metal complex, other nitrogen compounds, and the like, which are contained as components of the negative electrode active material precursor, and due to the presence of nitrogen gas used in the calcination process. The lattice structure attributable 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 believed that the generation of lithium silicate during the initial charging operation of a secondary battery containing the present negative electrode active material can be reduced, improving the initial coulombic efficiency and capacity retention.

[0089] In the present negative electrode active material, the chemical shift value attributable to Si is detected as Peak A near -80 ppm and the chemical shift value attributable to SiO4 is detected as Peak B near -110 ppm in the solid-state NMR spectrum, and the ratio R of Peak A to Peak B is preferably 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 present 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 obtained from the above-mentioned negative electrode active material precursor, and is particularly preferably obtained from a negative electrode active material precursor produced using the present metal complex as a metal complex solution.

[0090] 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.

[0091] 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.

[0092] <Secondary battery> The present negative electrode active material is excellent in charge / discharge capacity, initial coulombic efficiency, and capacity retention rate. Therefore, a secondary battery including the present negative electrode active material, specifically a secondary battery having a negative electrode layer including the present 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] The metal complex and its manufacturing method, the negative electrode active material precursor and its manufacturing method, the negative electrode active material, 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 metal complex, negative electrode active material precursor, negative electrode active material, 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 substituted with any optional components that exhibit the same function. Furthermore, the method for producing a metal complex and the method for producing a 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 substituted with any optional step that exhibits the same effect. [Example]

[0107] 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.

[0108] A. Examples of metal complex production Example 1-1 A 500 mL separable flask equipped with a thermometer, reflux condenser, and stirrer was charged with 100 molar equivalents of magnesium acetate tetrahydrate (26.8 g (0.125 mol)), 200 molar equivalents of N-tert-butoxycarbonyl-4-cyclohexyl-L-aspartic acid (78.8 g (0.25 mol)), and 100 mL of ethanol, and mixed at 25°C. The mixture was then heated to 60°C while stirring at 250 rpm, and after stirring for 1 hour, the ethanol was distilled off under reduced pressure, yielding a viscous pale yellow liquid with a strong acetic acid odor. This liquid was dried in a vacuum dryer at 110°C and -0.1 MPa (gauge pressure) for 10 hours to remove water, acetic acid, and ethanol, thereby obtaining 77.5 g of N-tert-butoxycarbonyl-4-cyclohexyl-L-aspartic acid magnesium (hereinafter referred to as "Metal Complex 1-1") as a colorless powder (yield 95%).

[0109] Example 1-2 (1) N-tert-butoxycarbonyl-3-(3,4-dihydroxyphenyl)-L-alanine was synthesized with reference to the method described in Bioorganic & Medicinal Chemistry, 18 (2010), pp. 1834-1843. That is, 100 molar equivalents of 3-(3,4-dihydroxyphenyl)-L-alanine (23.7 g (0.12 mol)), 110 molar equivalents of triethylamine (13.3 g (0.132 mol)), and 250 mL of a mixture of water and dioxane (volume ratio 150:100) were placed in a 1 L separable flask equipped with a thermometer, a reflux condenser, and a stirrer under a nitrogen atmosphere, mixed and dissolved, and cooled to 0°C. 110 molar equivalents of di-tert-butyl dicarbonate (28.8 g (0.132 mol)) dissolved in 50 mL of dioxane was added dropwise to this solution over 6 hours, and after completion of the dropwise addition, the temperature was raised to 60°C and the mixture was stirred for an additional 18 hours. Water and ethyl acetate were added to the resulting reaction mixture, and the organic layer was separated. Ethyl acetate was added to the aqueous layer, and the aqueous layer was made weakly acidic with potassium hydrogen sulfate, taking care not to lower the pH below 3, and extracted three times with ethyl acetate. The resulting extract and the organic layer were mixed, dried over anhydrous sodium sulfate, and then the ethyl acetate was removed, yielding 26.4 g of N-tert-butoxycarbonyl-3-(3,4-dihydroxyphenyl)-L-alanine. (2) The magnesium salt of N-tert-butoxycarbonyl-3-(3,4-dihydroxyphenyl)-L-alanine (hereinafter referred to as "Metal Complex 1-2") was obtained as a brown solid by the same procedure as in Example 1-1, except that 200 molar equivalents of N-tert-butoxycarbonyl-4-cyclohexyl-L-aspartic acid was replaced with 200 molar equivalents of N-tert-butoxycarbonyl-3-(3,4-dihydroxyphenyl)-L-alanine obtained by the method described above.

[0110] Examples 1-3 The magnesium salt of N(α)-tert-butoxycarbonyl-L-asparagine (hereinafter referred to as "Metal Complex 1-3") was obtained as a colorless solid by the same procedure as in Example 1-1, except that 200 molar equivalents of N(α)-tert-butoxycarbonyl-4-cyclohexyl-L-aspartic acid was used instead of 200 molar equivalents of N(α)-tert-butoxycarbonyl-L-asparagine.

[0111] Examples 1-4 The magnesium salt of N(α)-carbobenzyloxy-L-arginine (hereinafter referred to as "Metal Complex 1-4") was obtained as a colorless solid by the same procedure as in Example 1-1, except that 200 molar equivalents of N(α)-carbobenzyloxy-L-arginine was used instead of 200 molar equivalents of N-tert-butoxycarbonyl-4-cyclohexyl-L-aspartic acid.

[0112] Examples 1-5 The magnesium salt of N-benzoyl-DL-alanine (hereinafter referred to as "Metal Complex 1-5") was obtained as a colorless solid by the same procedure as in Example 1-1, except that 200 molar equivalents of N-benzoyl-DL-alanine was used instead of 200 molar equivalents of N-tert-butoxycarbonyl-4-cyclohexyl-L-aspartic acid.

[0113] Examples 1-6 The magnesium salt of aspartame (hereinafter referred to as "Metal Complex 1-6") was obtained as a colorless solid by the same procedure as in Example 1-1, except that 200 molar equivalents of aspartame were used instead of 200 molar equivalents of N-tert-butoxycarbonyl-4-cyclohexyl-L-aspartic acid.

[0114] Examples 1-7 A 0.5 L separable flask equipped with a thermometer, Dean-Stark tube, reflux condenser, and stirrer was charged with 312 molar equivalents of 2-ethylhexanoic acid and 20 parts by weight of toluene. While stirring at 250 rpm, 100 molar equivalents (29.1 parts by weight) 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 2-ethylhexanoic acid and magnesium 2-ethylhexanoate) was cooled to 75 °C and remained liquid and stirrable. While stirring, 138 parts by weight of methyl ethyl ketone was added under atmospheric pressure to adjust the magnesium ion content to 3% by weight. At this time, the content of 2-ethylhexanoic acid was 20% by mass based on the total amount of the mixed liquid. The mixed liquid 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 a methyl ethyl ketone solution containing magnesium 2-ethylhexanoate and 2-ethylhexanoic acid. By mixing this solution with N-tert-butoxycarbonyl-4-cyclohexyl-aspartic acid in an amount twice the amount of magnesium contained in the magnesium 2-ethylhexanoate, magnesium N-tert-butoxycarbonyl-4-cyclohexyl-aspartate containing free 2-ethylhexanoate (hereinafter referred to as "Metal Complex 1-7") was obtained as a methyl ethyl ketone solution.

[0115] Examples 1-8 A 1 L separable flask equipped with a thermometer, a Dean-Stark tube, a reflux condenser, and a stirrer was charged with 100 molar equivalents of magnesium hydroxide (7.29 g (0.125 mol)), which had previously been passed through a 1 mm mesh sieve, 5 molar equivalents of 2-ethylhexanoic acid (0.9 g (6.25 mmol)), 200 molar equivalents of N-tert-butoxycarbonyl-4-cyclohexyl-aspartic acid (78.8 g (0.25 mol)), and 4 parts by mass of methyl ethyl ketone (300 g). The mixture was heated from 25°C to 70°C with stirring at 250 rpm. Stirring was continued for another 2 hours, at which point the magnesium hydroxide dissolved and disappeared. The reaction mixture was then placed under reduced pressure to remove water and methyl ethyl ketone, yielding 82 g of a mixture containing 2-ethylhexanoic acid and magnesium N-tert-butoxycarbonyl-4-cyclohexylaspartate (hereinafter referred to as "metal complex 1-8").

[0116] Examples 1-9 The same procedure as in Example 1-5 was carried out, except that 100 molar equivalents of manganese(II) acetate tetrahydrate was used instead of 100 molar equivalents of magnesium acetate tetrahydrate, to obtain manganese salt(II) of N-benzoyl-DL-alanine (hereinafter referred to as "Metal Complex 1-9") as a pale pink solid.

[0117] Examples 1-10 The same procedure as in Example 1-5 was carried out, except that 66 molar equivalents of manganese(III) acetate dihydrate was used instead of 100 molar equivalents of magnesium acetate tetrahydrate, to obtain manganese salt(III) of N-benzoyl-DL-alanine (hereinafter referred to as "Metal Complex 1-10") as a light brown solid.

[0118] Examples 1-11 In Example 1-1, except that 100 molar equivalents of lithium acetate dihydrate was used instead of 100 molar equivalents of magnesium acetate tetrahydrate, and the amount of N-tert-butoxycarbonyl-4-cyclohexyl-aspartic acid was changed from 200 molar equivalents to 100 molar equivalents, the same procedure as in Example 1-1 was carried out to obtain the lithium salt of N-tert-butoxycarbonyl-4-cyclohexyl-aspartic acid (hereinafter referred to as "Metal Complex 1-11") as a colorless solid.

[0119] Examples 1-12 The same procedure as in Example 1-1 was carried out, except that 100 molar equivalents of lithium acetate dihydrate was used instead of 100 molar equivalents of magnesium acetate tetrahydrate, and 100 molar equivalents of N-tert-butoxycarbonyl-L-leucine was used instead of 200 molar equivalents of N-tert-butoxycarbonyl-4-cyclohexyl-aspartic acid, to obtain the lithium salt of N-tert-butoxycarbonyl-L-leucine (hereinafter referred to as "Metal Complex 1-12") as a colorless solid.

[0120] Comparative Example 1 Magnesium aspartate was obtained by the same procedure as in Example 1-1, except that 200 molar equivalents of aspartic acid were used instead of 200 molar equivalents of N-tert-butoxycarbonyl-4-cyclohexyl-aspartic acid. However, the obtained magnesium aspartate was not soluble in methyl ethyl ketone.

[0121] Comparative Examples 2 to 4 In Comparative Example 1-1, the magnesium salt of GABA, the magnesium salt of 6-aminohexanoic acid, and the magnesium salt of asparagine were obtained by the same procedure as in Comparative Example 1, except that 200 molar equivalents of 4-aminobutyric acid (GABA), 6-aminohexanoic acid, and asparagine were used instead of aspartic acid. However, none of the obtained salts were soluble in methyl ethyl ketone.

[0122] B. Example of silicon particle dispersion (slurry) Synthesis Example 1-1 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.

[0123] C. Production examples of polysiloxane compounds Synthesis Example 1-2: 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.

[0124] Synthesis Example 1-3: 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 1-2 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 1-2 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.

[0125] D. Example of negative electrode active material production Example 2 (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 1-3, 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, the silicon particle dispersion obtained by the method of Synthesis Example 1-1 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 1-1 prepared in Example 1-1 was dissolved in methyl ethyl ketone to prepare a solution such that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles in this mixture was 0.014, and then added and 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 (2).

[0126] Example 3 A negative electrode active material (3) was obtained by the same procedure as in Example 2, except that in step (a) of Example 2, metal complex 1-1 was added as a methyl ethyl ketone solution so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was 0.028.

[0127] Example 4 A negative electrode active material (4) was obtained by the same procedure as in Example 2, except that in step (a) of Example 2, metal complex 1-1 was added as a methyl ethyl ketone solution so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was 0.07.

[0128] Example 5 A negative electrode active material (5) was obtained by the same procedure as in Example 2, except that in step (a) of Example 2, instead of metal complex 1-1, metal complex 1-3 prepared by the method of Example 1-3 was added as a methyl ethyl ketone solution so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was 0.028.

[0129] Example 6 A negative electrode active material (3) was obtained by the same procedure as in Example 2, except that in step (a) of Example 2, instead of metal complex 1-1, metal complex 1-2 prepared by the method of Example 1-2 was added as a methyl ethyl ketone solution so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was 0.028.

[0130] Example 7 A negative electrode active material (7) was obtained by the same procedure as in Example 2, except that in step (a) of Example 2, instead of metal complex 1-1, metal complex 1-4 prepared by the method of Example 1-4 was added as a methyl ethyl ketone solution so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was 0.028.

[0131] Example 8 A negative electrode active material (8) was obtained by the same procedure as in Example 2, except that in step (a) of Example 2, instead of metal complex 1-1, metal complex 1-5 prepared by the method of Example 1-5 was added as a methyl ethyl ketone solution so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was 0.028.

[0132] Example 9 A negative electrode active material (9) was obtained by the same procedure as in Example 2, except that in step (a) of Example 2, instead of metal complex 1-1, metal complex 1-6 prepared by the method of Example 1-6 was added as a methyl ethyl ketone solution so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was 0.028.

[0133] Example 10 A negative electrode active material (10) was obtained by the same procedure as in Example 2, except that in step (a) of Example 2, instead of metal complex 1-1, metal complex 1-9 prepared by the method of Example 1-9 was added as a methyl ethyl ketone solution so that the atomic ratio (molar ratio) of manganese atoms to silicon atoms in the silicon particles was 0.0001.

[0134] Example 11 A negative electrode active material (11) was obtained by the same procedure as in Example 10, except that in step (a) of Example 10, metal complex 1-9 was added as a methyl ethyl ketone solution so that the atomic ratio (molar ratio) of manganese atoms to silicon atoms in the silicon particles was 0.0002.

[0135] Example 12 A negative electrode active material (12) was obtained by the same procedure as in Example 2, except that in step (a) of Example 2, instead of metal complex 1-1, metal complex 1-10 prepared by the method of Example 1-10 was added as a methyl ethyl ketone solution so that the atomic ratio (molar ratio) of manganese atoms to silicon atoms in the silicon particles was 0.0001.

[0136] Example 13 (a) Production process of negative electrode active material precursor (1) A 150 ml container of a small bead mill was charged with zirconia beads (Nikkato Corporation, YTZ series) with a particle size of 0.1 mm to 0.2 mm and a 60% filling rate, and 100 ml of methyl ethyl ketone. Then, 21 g (747 mmol) of silicon powder ("SIE23PB" (trade name, manufactured by Kojundo Chemical Co., Ltd.) with an average particle size of 5 μm, 9 g of cationic dispersant liquid ("BYK102" (trade name, manufactured by BYK Japan KK), and 24.3 g (37.3 mmol) of metal complex 1-1 prepared by the method of Example 1-1, adjusted so that the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon powder was 0.028, were added, and wet-pulverized using a bead mill. As a result, a dark brown liquid dispersion of silicon particles with a solids concentration of 32% by mass and in which metal complex 1-1 had dissolved, was obtained. When the silicon particles in the resulting dispersion were observed by TEM, they were found to have a flat flake shape and an average particle size (D50) of 90 nm. (2) 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 1-3 were added to methyl ethyl ketone as a solvent in a resin solid mass ratio of 30 / 70 to obtain a mixed solution. Next, the silicon particle dispersion obtained in (1) above 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%, 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 baked at 1100° C. for 4 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 (13).

[0137] Comparative Example 5 A negative electrode active material (C5) was obtained by the same procedure as in Example 2, except that in step (a) of Example 2, metal complex 1-1 was not added, i.e., the atomic ratio (molar ratio) of magnesium atoms to silicon atoms in the silicon particles was set to 0.

[0138] Comparative Example 6 A negative electrode active material (C6) was obtained by the same procedure as in Example 2, except that in step (a) of Example 2, instead of the metal complex solution 1-1, 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.

[0139] Comparative Example 7 A negative electrode active material (C7) was obtained by the same procedure as in Example 2, except that in step (a) of Example 2, instead of the metal complex solution 1-1, 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.

[0140] Comparative Example 8 A negative electrode active material (C8) was obtained by the same procedure as in Example 2, except that in Example 2, manganese chloride (II) [MnCl] that had been suspended in methyl ethyl ketone in advance was added instead of the metal complex solution 1-1 so that the atomic ratio (molar ratio) of manganese atoms to silicon atoms in the silicon particles was 0.0001.

[0141] E. 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

[0142] (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.

[0143] (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

[0144] (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.

[0145] 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

[0146] (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 (4) prepared in Example 4 (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 (4).

[0147] (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.

[0148] (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)

[0149] [Table 1]

[0150] As can be seen from the results in Table 1, the negative electrode active material of the present invention has an initial coulombic efficiency of 82.4% or more and a capacity retention rate of 81.5% or more, which are all high, and the secondary battery properties are well-balanced. Furthermore, secondary batteries containing the negative electrode active material of the present invention have excellent battery properties. [Industrial Applicability]

[0151] 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. A metal complex comprising a metal cation, the counter ion of which comprises a carboxylate anion having 2 to 20 carbon atoms and having a protected amino group.

2. 2. The metal complex of claim 1, 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.

3. 2. The metal complex according to claim 1, wherein the metal cation is a cation of at least one metal selected from Li, Mg, and Mn.

4. 2. The metal complex according to claim 1, wherein the protecting group of the amino group in the protected amino group is at least one selected from a tert-butoxycarbonyl group, a benzyloxycarbonyl group, and a benzoyl group.

5. A method for producing a metal complex containing a metal cation whose counter ion contains a carboxylic acid anion having 2 to 20 carbon atoms and a protected amino group, the method comprising mixing at least one metal salt selected from Li, Na, K, Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca of an aliphatic carboxylic acid having 1 to 20 carbon atoms, a carboxylic acid having 2 to 20 carbon atoms and having a protected amino group, and a solvent, and heating the mixture.

6. A method for producing a metal complex containing a metal cation whose counter ion contains a carboxylic acid anion having 2 to 20 carbon atoms and a protected amino group, the method comprising mixing at least one metal hydroxide selected from Li, Na, K, Mg, Al, Mn, Co, Ni, Bi, Cu, Zn, Zr, and Ca, a carboxylic acid having 2 to 20 carbon atoms and having a protected amino group, and a solvent, and heating the mixture.

7. The negative electrode active material precursor comprises a metal complex containing a metal cation, the counter ion of which contains a carboxylic acid anion having 2 to 20 carbon atoms and having a protected amino group, silicon particles, and an organosilicon polymer material.

8. 8. The negative electrode active material precursor according to claim 7, 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.

9. The negative electrode active material precursor according to claim 7 , wherein the metal cation is at least one metal cation selected from the group consisting of Li, Mg, and Mn.

10. 8. The negative electrode active material precursor according to claim 7, wherein the protecting group of the amino group in the protected amino group is at least one selected from a tert-butoxycarbonyl group, a benzyloxycarbonyl group, and a benzoyl group.

11. The negative electrode active material precursor according to claim 7 , wherein the silicon particles have an average particle size of 150 nm or less.

12. 8. The negative electrode active material precursor according to claim 7, wherein the organosilicon polymer material has a polymer structure containing silicon, carbon, and oxygen elements.

13. 8. The negative electrode active material precursor according to claim 7, 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.

14. 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 whose counter ion contains a carboxylic acid anion having 2 to 20 carbon atoms and having a protected amino group 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.

15. 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 contains a carboxylic acid anion having 2 to 20 carbon atoms and having a protected amino group, followed by removing the solvent and drying to obtain a negative electrode active material precursor.

16. 16. The method for producing a negative electrode active material precursor according to claim 14 or 15, 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.

17. The method for producing a negative electrode active material precursor according to claim 14 or 15, wherein the metal cation is at least one metal cation selected from the group consisting of Li, Mg, and Mn.

18. 16. The method for producing a negative electrode active material precursor according to claim 14, wherein the organosilicon polymer material has a polymer structure containing silicon, carbon, and oxygen elements.

19. The method for producing a negative electrode active material precursor according to claim 14 or 15, wherein the silicon particles have an average particle size of 150 nm or less.

20. 16. The method for producing a negative electrode active material precursor according to claim 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.

21. A negative electrode active material obtained by firing the negative electrode active material precursor according to any one of claims 7 to 13 in an inert gas atmosphere.

22. 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 is detected as a peak B near −110 ppm, and the ratio R of the peak A to the peak B is in the range of 1.0 to 10.

0.

23. 23. The negative electrode active material according to claim 22, 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.

24. 23. The negative electrode active material according to claim 22, 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.

25. 23. The negative electrode active material according to claim 22, 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.

26. 23. The negative electrode active material according to claim 22, 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.

27. The negative electrode active material according to claim 22, wherein the content of the silicon particles is in the range of 10 to 70 mass% with respect to the entire negative electrode active material.

28. 23. The negative electrode active material according to claim 22, 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).

29. 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 21 , wherein the SiO 2 content is 1 / g or less.

30. A secondary battery comprising the negative electrode active material according to claim 21.

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