Porous silicon material, method for producing same, negative electrode active material containing porous silicon material, composition for secondary battery negative electrode, secondary battery negative electrode, and secondary battery

Abstract

This porous silicon material comprises elemental N and at least one metal element selected from the group consisting of Al, Zn, Mg, Fe, Sn, Sc, Ti, V, Cr, Mn, Cu, Co, Ni and Mo.

Description

Porous silicon material and method for producing the same, as well as a negative electrode active material having a porous silicon material, a composition for a secondary battery negative electrode, a secondary battery negative electrode and secondary battery

[0001] The present invention relates to a porous silicon material and a method for producing the same, as well as a negative electrode active material having the porous silicon material, a composition for a secondary battery negative electrode, a secondary battery negative electrode, and a secondary battery. More specifically, the present invention relates to a porous silicon material suitably applicable as a negative electrode active material for a secondary battery, a method for producing the same, and a secondary battery containing the porous silicon material as a negative electrode.

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

[0003] However, silicon and silicon-containing negative electrode active materials undergo significant volume expansion and contraction with the intercalation and release of lithium ions. Repeated charging and discharging pulverizes the active material, leading to delamination and disintegration of the electrode material and deterioration of electronic conductivity, thus resulting in poor charge-discharge cycle characteristics. As one attempt to improve the charge-discharge cycle characteristics and expansion characteristics of such silicon-containing negative electrode active materials, the development of porous silicon materials is progressing. Patent document 1 discloses a negative electrode active material containing porous silicon particles, preferably obtained by an electrochemical etching method, having a specific 50% particle diameter, and furthermore, the difference between the 90% particle diameter and the 10% particle diameter being within a specific range, and whose surface may be coated with a conductive agent. This material is said to have excellent cycle characteristics and output characteristics.

[0004] Furthermore, a technique for creating porous silicon materials by creating alloys of silicon (Si) with metal elements that form a eutectic composition, and then using an acid or alkali de-alloying reaction, is attracting attention. For example, Patent Document 2 discloses a negative electrode active material for lithium secondary batteries, which is an aggregate of porous particles made only of Si, in which numerous voids of a specific pore size range are formed internally, and in which part of the structure is an amorphous phase of Si and the remainder is a crystalline phase of Si, and a method for manufacturing the same. When the Si constituting the porous particles alloys with lithium and expands in volume, it expands while compressing the volume of the voids, so the volume of the porous particles does not change much in appearance, preventing pulverization, and lithium ion diffusion can be performed efficiently, enabling high-rate charging and discharging, and the amorphous phase of Si is said to improve cycle characteristics. Patent Document 3 discloses a method for producing porous silicon particles, comprising the steps of particleizing a silicon alloy containing 50% or more by mass of aluminum (Al) and 50% or less by mass of silicon (Si), and then removing the Al. Preferably, using a silicon alloy in which the Al and Si are in a blending ratio near the eutectic composition, porous silicon particles can be obtained that contain a three-dimensional network structure of silicon with voids and have an average porosity of 50% by volume or more and 95% by volume or less. It is said that an all-solid-state lithium-ion secondary battery having a negative electrode containing such porous silicon particles as a negative electrode active material can suppress the deterioration of charge-discharge characteristics (cycle characteristics). Patent Document 4 discloses a method for producing a porous silicon material, comprising the steps of particleizing a silicon alloy containing specific mass percent of Al and Si, removing the Al to obtain a porous material, and then heating the porous material to diffuse elements other than Si onto the surface. It is said that such a porous silicon material has a small pore size and a large porosity, which reduces volume expansion and contraction and improves charge-discharge cycle characteristics, and has a purer silicon skeleton, thus having superior charge-discharge capacity.

[0005] Furthermore, attempts have been made to form composites of silicon and carbon-based materials, and composites composed of silicon and a carbon matrix having a porous structure. For example, Patent Document 5 discloses a method for producing an Si / C composite in which an active material containing silicon is brought into contact with a carbon precursor containing lignin, and the lignin is converted to inorganic carbon at a temperature of 400°C or higher under an inert gas atmosphere. The carbon structure formed by the carbonization of lignin is said to be able to withstand the extreme volume expansion of silicon during charging, has a carbon matrix with high strength and elasticity, and exhibits excellent cycle stability. Patent Document 6 discloses a method for producing Si / C particles in which silicon particles coated with a sacrificial organic or inorganic material are coated with an organic carbon precursor to form a pre-composite, the pre-composite is heat-treated to obtain a porous composite, and then carbon-coated. Such Si / C particles have a structure in which silicon particles are embedded in the pores within the carbon matrix, which is said to reduce the abscission of the passivation protective layer (solid electrolyte interface: SEI), and to provide a high-capacity lithium-ion battery. Patent Document 7 discloses a negative electrode active material comprising a silicon-based composite having a bimodal pore structure including mesopores and giant pores, represented as SiOa (0 ≤ a < 1), and having a carbon coating layer on its surface. It is said that this can improve initial efficiency and lifetime characteristics, and that the specific surface area can be controlled to prevent side reactions with the electrolyte. Patent Document 8 discloses a silicon-silicon oxide-carbon composite in which silicon particles are uniformly distributed within a silicon oxide-carbon structure containing numerous fine pores, in which carbon is coated onto silicon oxide. It is said that this reduces volume expansion due to lithium ion insertion, improves electrical conductivity, and allows the electrolyte to easily penetrate into the porous structure, thus improving output characteristics.

[0006] Japanese Patent Publication No. 2016-51622, Japanese Patent Publication No. 2004-214054, Japanese Patent Publication No. 2021-123517, Japanese Patent Publication No. 2023-001963, Japanese Patent Publication No. 2014-183043, Japanese Patent Publication No. 2019-511444, Japanese Patent Publication No. 2018-523898, Japanese Patent Publication No. 2018-513098

[0007] While Patent Document 1 specifies the distribution of the average particle size of the porous silicon particles, it does not disclose any details regarding the porosity of the "pores" that contribute to improving charge-discharge characteristics by suppressing degradation due to the expansion and contraction of silicon (Si). Furthermore, the electrochemical etching method (in other words, the anodic oxidation method) and ultrasonic crushing method mentioned as methods for obtaining porous silicon particles are difficult to mass-produce from an industrial standpoint and have productivity issues. Patent Document 2 describes a negative electrode active material for lithium secondary batteries which is formed by rapidly cooling an alloy molten metal containing a specific metal element and silicon, and then completely dissolving and removing the specific element from the rapidly cooled alloy. The content of the specific metal element in the alloy molten metal is preferably 0.01% by mass or more and 70% by mass or less, but appropriate surface treatment is necessary to suppress the decrease in initial charge-discharge efficiency due to surface oxidation. The porous silicon particles disclosed in Patent Document 3 are obtained using a silicon alloy in which Al and Si are in a composition ratio near that of a eutectic composition. However, using an alloy with a eutectic composition as a raw material limits the silicon content, resulting in high manufacturing costs for porous silicon particles when calculated on a silicon-only basis, posing a challenge from a productivity standpoint. On the other hand, increasing the Si composition in a silicon alloy usually makes Si segregation more likely, leading to problems such as expansion and a decrease in cycle characteristics. There is still room for improvement in the charge-discharge capacity and cycle characteristics of porous silicon materials obtained by the method of Patent Document 4.

[0008] The Si / C composite obtained by the method described in Patent Document 5 shows its specific surface area, but makes no mention of the pore size or pore distribution in the carbon structure formed by the carbonization of lignin, leaving room for further investigation in suppressing degradation due to Si expansion and contraction and improving battery characteristics. The Si / C particles obtained by the method described in Patent Document 6 have a complicated manufacturing process, and only the theoretical capacity of the obtained Si / C particles is shown, without mentioning the effects such as suppressing expansion during charging and discharging as a negative electrode or the extent to which charge-discharge cycle characteristics can be improved. The negative electrode using a silicon-based composite negative electrode active material disclosed in Patent Document 7 still shows a large thickness change (Swelling) of 190% after repeated charging and discharging as shown in Example 1, and there is still room for improvement in terms of lifespan characteristics. The secondary battery using a silicon-silicon oxide carbon composite as the negative electrode active material in Patent Document 8 has large irreversible characteristics in the first cycle, and still has problems in terms of battery capacity. Therefore, there is still a need for a silicon-based anode active material that can be manufactured economically, has high capacity, improves battery characteristics such as cycle performance, and suppresses expansion and contraction during charging and discharging.

[0009] The inventors focused on the elemental species constituting porous silicon materials and conducted research. As a result, they found that a porous silicon material containing nitrogen (N), preferably containing N on or near its surface, can improve charge-discharge characteristics. They also found that such a porous silicon material containing N can suppress Si expansion and contraction associated with charge-discharge due to its voids, thereby improving cycle characteristics. Furthermore, they found that a porous silicon material containing N can be efficiently manufactured by forming a porous portion through a de-alloying reaction with acid or alkali using a silicon-based alloy (e.g., Al-Si alloy) as a raw material, and then firing it in a nitrogen gas atmosphere in the presence of specific metal elements. They also found that using such a porous silicon material containing N as a negative electrode active material suppresses expansion and contraction associated with repeated charge-discharge cycles, allowing for the mass production of a negative electrode with excellent cycle characteristics. Moreover, they found that using such a porous silicon material containing N and a matrix phase containing carbon as the negative electrode active material further enhances the suppression of expansion and contraction associated with repeated charge-discharge cycles and improves cycle characteristics even more significantly.

[0010] The object of the present invention is to provide a porous silicon material useful as a negative electrode active material and a method for producing the same, which can create a negative electrode that suppresses expansion and contraction associated with repeated charging and discharging and has excellent initial discharge capacity and cycle characteristics. The object of the present invention is also to provide a negative electrode active material containing such porous silicon material and a secondary battery having such negative electrode active material.

[0011] The present invention has the following embodiments: [1] A porous silicon material comprising N and one or more metallic elements selected from the group consisting of Al, Zn, Mg, Fe, Sn, Sc, Ti, V, Cr, Mn, Cu, Co, Ni, and Mo. [2] The porous silicon material of [1] wherein the metallic element comprises Al. [3] The porous silicon material of [1] or [2] having one or more peaks at a binding energy of 396 eV to 400 eV in XPS (X-ray photoelectron spectroscopy) measurements. [4] Any porous silicon material of [1] to [3] wherein the content of N is 0.1% by mass or more and 15.0% by mass or less based on the total mass of the porous silicon material. [5] Any porous silicon material of [1] to [4] wherein the content of O is 1.0% by mass or more and 50.0% by mass or less based on the total mass of the porous silicon material. [6] A porous silicon material according to any of [1] to [5], wherein the content of the metal element is 1% by mass or more and 15% by mass or less with respect to the total mass of the porous silicon material. [7] The porosity Q calculated by the following formula (1) １ A porous silicon material of any of [1] to [6], wherein the content is more than 20% but less than 95%. Q １ (%) = 100 × P / (V + P) (1) P: Pore volume of porous silicon material V: Volume of porous silicon material [8] A porous silicon material of any of [1] to [7] having silicon domain particles with an average particle size in the range of 5 nm to 1 μm. [9] A porous silicon material of any of [1] to [8] containing crystalline silicon and having a crystallite size of the Si(111) plane calculated by the fundamental parameter (FP) method by X-ray diffraction analysis of 1 nm or more and 30 nm or less.

[10] In the Raman spectrum obtained by Raman spectroscopy, at 480 cm⁻¹ －１ Super 520cm －１ The region has one or more peaks, and the full width at half maximum of the peaks is 5 cm. －１ Super 60cm －１[1] to [9] any porous silicon material less than [1].

[11] A porous silicon material from any of [1] to

[10] containing N element near the interface between the silicon domain particles and the voids.

[12] A method for producing a porous silicon material from any of [1] to

[11] , comprising the following steps: (i) a step of preparing an alloy containing Si; (ii) a step of obtaining a porous material by treating the alloy prepared in step (i) with an acid or alkali; (iii) a step of obtaining a porous silicon material by heat-treating the porous material obtained in step (ii) at 700°C to 1100°C in an inert gas atmosphere containing nitrogen gas.

[13] A method for producing a porous silicon material from any of [1] to

[11] , comprising the following steps. (i) A step of preparing an alloy containing Si. (ii) A step of obtaining a porous material by treating the alloy prepared in step (i) with an acid or alkali. (ii') A step of adding a metal to the porous material obtained in step (ii). (iii) A step of obtaining a porous silicon material by heat-treating the metal-added porous material obtained in step (ii') in an inert gas atmosphere containing nitrogen gas at 700°C to 1100°C.

[0012]

[14] A negative electrode active material comprising any of the porous silicon materials from [1] to

[11] .

[15] The negative electrode active material of

[14] comprising any of the porous silicon materials from [1] to

[11] and a matrix phase containing element C.

[16] The negative electrode active material of

[15] wherein the matrix phase contains one or more elements from the group consisting of Si, O, and C.

[17] The negative electrode active material of

[15] or

[16] wherein the matrix phase contains at least silicon oxycarbide and a carbonaceous phase.

[18] The negative electrode active material of any of

[15] to

[17] wherein the content of element N relative to the total mass is 5% by mass or less.

[19] The negative electrode active material of any of

[15] to

[18] wherein the content of the porous silicon material relative to the total mass is 20% by mass or more and 80% by mass or less.

[20] Particles having an average particle size (D50) of 1 μm or more and a specific surface area of ​​1 m² ２ / g or more 50m ２The negative electrode active material according to any one of

[15] to

[19] , which is 0.1 g or less.

[21] Void ratio Q calculated by the following formula (2) based on voids that may exist inside the porous silicon material or at the interface between the porous silicon material and the matrix phase ２ The negative electrode active material according to any one of

[15] to

[20] , which is 1% or more and 70% or less. Q ２ = 100 × (1 - W / ρ) (2) W: Apparent density of particles (g / cm ３ ) ρ: True density of particles (g / cm ３ )

[22] A composition for a secondary battery negative electrode containing the negative electrode active material according to any one of

[14] to

[21] .

[23] A secondary battery negative electrode including a negative electrode material layer formed using the composition for a secondary battery negative electrode of

[22] .

[24] A secondary battery including the secondary battery negative electrode of

[23] , a positive electrode, an electrolytic solution, and a separator.

[0013] According to the present invention, it is possible to provide a porous silicon material useful as a negative electrode active material and a method for producing the same, which can suppress expansion and contraction accompanying repeated charge and discharge and can create a negative electrode excellent in initial discharge capacity and cycle characteristics. Further, according to the present invention, it is possible to provide a negative electrode active material containing such a porous silicon material and a secondary battery excellent in battery characteristics such as charge and discharge characteristics having such a negative electrode active material.

[0014] <Porous silicon material> The porous silicon material of the present invention is a porous silicon material containing an N element and one or more metal elements selected from the group consisting of Al, Zn, Mg, Fe, Sn, Sc, Ti, V, Cr, Mn, Cu, Co, Ni, and Mo. The porous silicon material of the present invention preferably contains Al among the metal elements.

[0015] Among the aforementioned metal elements, Al, Zn, Mg, Fe, and Sn (hereinafter also referred to as "element group A") can form alloys with Si. Therefore, in the method for producing the porous silicon material of the present invention described later, for example, by adding one or more metal elements belonging to element group A in the step of preparing an alloy containing Si, an alloy containing element group A and Si can be prepared, and the porous silicon material of the present invention can be prepared from such an alloy. Alternatively, a porous material can be obtained by treating an alloy containing Si with an acid or alkali, one or more metal elements belonging to element group A can be added to the obtained porous material, and then the porous silicon material of the present invention containing element group A can be prepared by heat treatment in an inert gas atmosphere containing nitrogen gas.

[0016] The porous silicon material of the present invention, which contains Sc, Ti, V, Cr, Mn, Cu, Co, Ni, and Mo (hereinafter also referred to as "element group B") among the aforementioned metal elements, can be prepared in the method for producing the porous silicon material of the present invention described later, by treating an alloy containing Si, preferably an Al-Si alloy, with acid or alkali to obtain a porous material, adding one or more metal elements belonging to element group B to the obtained porous material, and then heat-treating it in an inert gas atmosphere containing nitrogen gas.

[0017] The metal elements (i.e., element group A and element group B) contained in the porous silicon material of the present invention are presumed to play a role in adjusting the content of element N contained in the porous silicon material of the present invention during the heat treatment step in an inert gas atmosphere containing nitrogen gas, which is a step in the method for manufacturing the porous silicon material of the present invention described later.

[0018] The porous silicon material of the present invention contains an element N, and it is presumed that this element is contained as one or more nitrogen-containing compounds of silicon nitride represented by the following formula (α) SiNx (α) (wherein 0 < x ≤ 1.33) or aluminum nitride represented by the following formula (β) AlNy (β) (wherein 0 < y ≤ 1.00). In other words, the porous silicon material of the present invention preferably has one or more peaks at a binding energy of 396 eV to 400 eV in XPS (X-ray photoelectron spectroscopy) measurements.

[0019] The nitrogen content in the porous silicon material of the present invention is preferably 0.1% by mass or more and 15.0% by mass or less, and more preferably 0.5% by mass or more and 10% by mass or less, relative to the total mass of the porous silicon material. When the nitrogen content is within the above range, the nitrogen-containing compound is preferably present near the surface of the porous silicon material, which is thought to suppress contact between silicon (Si) and oxidizing substances such as oxygen gas, thereby suppressing the growth and increase of the silicon oxide film. Therefore, the initial efficiency during charging and discharging when used as a negative electrode active material is likely to be improved. Furthermore, the presence of the nitrogen-containing compound in addition to the voids in the porous silicon material is thought to suppress structural damage due to the expansion and contraction of Si, thereby suppressing the expansion of the negative electrode and improving cycle characteristics.

[0020] The oxygen (O) content in the porous silicon material of the present invention is preferably 1.0% by mass or more and 50.0% by mass or less, and more preferably 3.0% by mass or more and 30.0% by mass or less, relative to the total mass of the porous silicon material. If the oxygen (O) content is less than 1.0% by mass, the Si in the material is easily oxidized, forming an oxide film on the surface, which tends to reduce the initial charge-discharge efficiency. On the other hand, if the oxygen (O) content is within the above range, in other words, if a certain amount of oxidized Si is present near the surface of the material due to oxidation caused by oxygen gas in the air or oxidation due to contact with oxidizing substances such as oxygen gas for the purpose of adjusting the oxygen (O) content, the surface of the porous silicon material of the present invention tends to have a continuous three-dimensional network structure of Si, which makes alloying and de-alloying with lithium easier. Therefore, battery characteristics such as cycle characteristics of a secondary battery equipped with a negative electrode containing the porous silicon material of the present invention tend to improve. In general, the oxygen (O) element is preferably included in the form of an oxide of Si and a metal element that constitutes the porous silicon material of the present invention.

[0021] In the porous silicon material of the present invention, the content of metal elements is preferably 1% by mass or more and 15% by mass or less relative to the total mass of the porous silicon material. Here, the content of metal elements belonging to element group A is preferably 1% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 5% by mass or less, relative to the total mass of the porous silicon material. The content of metal elements belonging to element group B is preferably 1% by mass or more and 15% by mass or less, and more preferably 1% by mass or more and 5% by mass or less, relative to the total mass of the porous silicon material. Furthermore, the total content of element group A and element group B is preferably 1% by mass or more and 15% by mass or less, relative to the total mass of the porous silicon material.

[0022] The porous silicon material of the present invention has a porosity Q calculated by the following formula (1). １ It is preferable that it is between 20% and less than 95%. Q １ (%) = 100 × P / (V + P) (1) P: Pore volume of porous silicon material V: Porosity Q multiplied by volume of porous silicon material １ The porosity Q is preferably 25% or more, and more preferably 30% or more. １ A porosity of Q is preferably 90% or less, and more preferably 85% or less. １ When the range is within the aforementioned range, the porous silicon material of the present invention, when used as a negative electrode active material, can adequately buffer both the volume expansion due to alloying of silicon (Si) and lithium during charging and the volume contraction when lithium is released during discharge, thereby suppressing volume changes. Furthermore, the strength of the porous silicon material of the present invention is less likely to decrease, and pulverization due to volume changes can be prevented. Therefore, the expansion of the negative electrode containing the porous silicon material of the present invention is suppressed, and the battery characteristics of a secondary battery equipped with such a negative electrode are easily improved.

[0023] The porous silicon material of the present invention preferably has particles with an average particle size (D50) in the range of 50 nm to 30 μm, and more preferably in the range of 100 nm to 25 μm. The shape of the particles is not particularly limited, but is generally preferably spherical. When the D50 of the porous silicon material of the present invention is within the above range, the capacity and cycle characteristics when used as a secondary battery are more easily improved, and expansion and contraction are more easily suppressed.

[0024] The porous silicon material of the present invention preferably has silicon domain particles with an average particle size in the range of 5 nm to 1 μm. The average particle size of such silicon domain particles is preferably in the range of 10 nm to 750 nm, and more preferably in the range of 20 nm to 500 nm. In other words, the porous silicon material of the present invention preferably contains crystalline silicon, and the crystallite size of the Si(111) plane calculated by the fundamental parameter (FP) method by X-ray diffraction analysis is preferably 1 nm or more and 30 nm or less. Having such a crystallite size within the above range is preferable from the viewpoint of battery characteristics such as capacity and cycle characteristics when used as a secondary battery. Details of the X-ray diffraction analysis and FP method are as described in the examples below. The porous silicon material of the present invention may also contain amorphous silicon components in at least a part.

[0025] The porous silicon material of the present invention exhibits a Raman spectrum of 480 cm⁻¹ in Raman spectroscopy. －１ Super 520cm －１ Preferably, it has one or more peaks in the region less than 490 cm. －１ Super 520cm －１ It is more preferable to have one or more peaks in the region less than 5 cm. Also, the full width at half maximum of the peaks should be 5 cm. －１ Super 60cm －１ Preferably less than 5 cm －１ Super 40cm －１ It is more preferable that it be less than 5 cm. －１ Super 30cm －１It is even more preferable that the value is less than the specified value. If the porous silicon material of the present invention has the aforementioned peak in the Raman spectrum, it means that structural defects and strains occur within the silicon, irregularities are created in the bonding, and it is likely to exhibit amorphous silicon behavior. Therefore, the expansion of the negative electrode containing the porous silicon material of the present invention is suppressed, and the battery characteristics of a secondary battery equipped with such a negative electrode are likely to be improved.

[0026] The porous silicon material of the present invention preferably contains nitrogen (N) near the interface between the silicon domain particles and the voids. Here, in this specification, "near" the interface between the silicon domain particles and the voids means a depth of, for example, within 10 nm from the interface, preferably within 5 nm, and more preferably within 3 nm. The nitrogen (N) contained in the porous silicon material of the present invention is presumed to be contained as one or more nitrogen-containing compounds of silicon nitride represented by formula (α) or aluminum nitride represented by formula (β) as described above. Furthermore, in the method for producing the porous silicon material of the present invention, which will be described later, heat treatment is performed under an inert gas atmosphere containing nitrogen gas, so it is considered that these nitrogen-containing compounds tend to be generated from the surface side of the porous silicon material that comes into contact with nitrogen gas and tend to be unevenly distributed.

[0027] The specific surface area of ​​the porous silicon material of the present invention is 1 m². ２ / g or more 30m ２ It is preferable that it is less than or equal to / g, and 2m ２ / g or more 15m ２ It is more preferable that the specific surface area is less than or equal to / g. When the specific surface area is within the above range, it is easier to maintain an appropriate amount of solvent absorption during electrode fabrication, and it is also easier to maintain an appropriate amount of binder used to maintain bonding properties.

[0028] <Method for Manufacturing Porous Silicon Material> The porous silicon material of the present invention can be manufactured by a manufacturing method (hereinafter also referred to as "Method 1") which includes the following steps: (i) a step of preparing an alloy containing Si; (ii) a step of obtaining a porous material by treating the alloy prepared in step (i) with an acid or alkali; (iii) a step of obtaining a porous silicon material by heat-treating the porous material obtained in step (ii) at a temperature of 700°C to 1100°C in an inert gas atmosphere containing nitrogen gas. In Method 1, one or more metal elements selected from element group A can be introduced in step (i) as metal elements contained in the porous silicon material of the present invention. The metal elements are thought to act as catalysts for the reaction that forms nitrogen-containing compounds such as silicon nitride when heat-treated in an inert gas atmosphere containing nitrogen gas in step (iii).

[0029] [Step (i)] The Si-containing alloy is preferably an alloy containing silicon and a metal of element group A, and more preferably an alloy containing Si and Al. Such a Si-containing alloy may be a commercially available product manufactured industrially, or it can be obtained by melting silicon and a metal of element group A in an inert gas atmosphere such as argon, using a melting method such as a high-frequency crucible. The composition of the Si-containing alloy is preferably such that the Si content is in the range of 5 to 30 atoms, and more preferably 10 to 25 atoms, when the total Si-containing alloy is considered to be 100 atoms. The content of the metal of element group A is preferably 70 to 95 atoms, and more preferably 75 to 90 atoms. The silicon and element group A (e.g., aluminum) used as raw materials for the alloy may contain small amounts of impurities that inevitably remain during their refining, but it is preferable that the impurity content be as low as possible. For example, when the total amount of Si and Al is 100 atom%, it is preferable that it be 2 atom% or less, and more preferably 1.5 atom% or less.

[0030] Alloys containing Si are preferably molten and used as alloy particles. Methods for particle formation include the single-roll liquid rapid cooling method using a single-roll casting machine, and methods using water atomizers or gas atomizers. Among these, particle formation using a gas atomizer is preferred from the viewpoint of obtaining spherical particles. The advantages of spherical particles will be described later. The cooling rate when particle formation with a gas atomizer is 10 ２ Preferably it is k / second or higher, 10 ６ A cooling rate of 10 K / sec or higher is more preferable. ８ A cooling rate of K / sec or less is preferred. Furthermore, when molten an alloy containing Si, it is preferable to do so under an inert gas atmosphere such as nitrogen, helium, or argon, and more preferably under a helium or argon atmosphere. In addition, particle formation using a gas atomizer is preferably carried out under a helium or argon atmosphere. By controlling the cooling rate within the above range, the crystalline phase of the Si component in the resulting alloy particles does not become excessively enlarged, making it easier to control the domain size to 1 nm to 100 nm, and at least a portion of the silicon phase is more likely to contain amorphous silicon components.

[0031] The average particle size (D50) of the alloy particles is preferably in the range of greater than 0.1 μm and less than 20 μm. More preferably, the D50 of the alloy particles is 0.2 μm or more, and more preferably 18 μm or less. More preferably, the D50 of the alloy particles is 0.5 μm or more, and even more preferably 15 μm or less. Furthermore, the particle shape of the alloy particles is preferably spherical. When the D50 of the alloy particles is within the above range and is spherical, it becomes easier to maintain the strength of the particles of the porous silicon material of the present invention obtained from such alloy particles, and it is easier to suppress the volume change of the porous silicon material itself during charging and discharging. As a result, the electrical properties such as the cycle characteristics of a secondary battery equipped with a negative electrode containing the porous silicon material of the present invention are easily improved. Since the D50 of the alloy particles becomes the D50 of the obtained porous silicon material, it is preferable to adjust the average particle size of the alloy particles to the range of greater than 0.1 μm and less than 20 μm. The D50 of the alloy particles and the porous silicon material of the present invention is the particle size (D50) at which the cumulative volume distribution curve reaches 50% when plotted from the smallest diameter side, as measured by dynamic light scattering using a laser diffraction particle size analyzer or the like. This measurement was performed using a laser diffraction particle size analyzer (Malvern Panalytical, "Mastersizer 3000"). Note that commercially available alloy particles may be used for atomizing Si-containing alloys using a gas atomizer.

[0032] [Step (ii)] A porous material is obtained by treating the Si-containing alloy, preferably alloy particles, prepared in Step (i) with an acid or alkali. The acid or alkali is preferably one that dissolves elements and / or compounds other than Si in the Si-containing alloy, but does not dissolve Si, and examples include hydrochloric acid, sulfuric acid, sodium hydroxide, potassium hydroxide, etc. The acid or alkali is preferably used as an aqueous solution. When used as an aqueous solution, the concentration of the acid or alkali is not particularly limited as long as it is within a range that can dissolve elements and / or compounds other than Si in the alloy particles, and can be in the range of 1 to 5 mol / L, for example. Dealloying can be performed, for example, by immersing the Si-containing alloy, preferably alloy particles, in an acid or alkali solution, heating it to room temperature (25°C) or 30°C to 80°C, and stirring for 1 to 24 hours. The obtained porous material is preferably further washed with distilled water and dried. Drying can be carried out using a known dryer, vacuum dryer, etc., at a temperature range of, for example, 25 to 200°C, under an inert gas atmosphere, at atmospheric pressure, or under reduced pressure conditions, for a period of 1 minute to 24 hours.

[0033] [Step (iii)] The porous material obtained in Step (ii) is heat-treated at 700°C to 1100°C in an inert gas atmosphere containing nitrogen gas to obtain the porous silicon material of the present invention. The inert gas containing nitrogen gas may be nitrogen gas alone, or a mixture of nitrogen gas and an inert gas such as nitrogen gas and argon gas, or nitrogen gas and helium gas. The purity of the nitrogen gas is preferably 95% by volume or higher, more preferably 98% by volume or higher, and even more preferably 99% by volume or higher. A small amount of oxygen gas may or may not be present in the inert gas containing nitrogen gas. When a small amount of oxygen gas is present in the inert gas containing nitrogen gas, the oxygen gas content is preferably 0.5% by volume or less relative to the total inert gas. The heat treatment temperature is preferably in the range of 600°C to 1200°C, and more preferably in the range of 700°C to 1100°C. While there are no particular restrictions on the heat treatment time, a range of 1 to 24 hours is preferred from the viewpoint of producing the porous silicon material of the present invention containing element N by sufficiently generating the nitrogen-containing compound described above from the surface side where the porous material comes into contact with nitrogen gas.

[0034] The porous silicon material of the present invention can also be manufactured by a manufacturing method (hereinafter also referred to as "manufacturing method 2") which includes the following steps: (i) a step of preparing an alloy containing Si; (ii) a step of obtaining a porous material by treating the alloy prepared in step (i) with an acid or alkali; (ii') a step of adding a metal to the porous material obtained in step (ii); (iii') a step of obtaining a porous silicon material by heat-treating the porous material with the metal added obtained in step (ii') at a temperature of 700°C to 1100°C in an inert gas atmosphere containing nitrogen gas. The details of steps (i) and (ii) in manufacturing method 2 are the same as those of steps (i) and (ii) in manufacturing method 1 described above. In manufacturing method 2, a metal element selected from element group A can be introduced in step (i) as a metal element contained in the porous silicon material of the present invention. Furthermore, in step (ii'), one or more metallic elements selected from element group A or element group B can be introduced into the porous material as metallic elements contained in the porous silicon material of the present invention. That is, in manufacturing method 2, one or more metallic elements selected from element group A and element group B can be introduced as metallic elements contained in the porous silicon material of the present invention. The metallic elements are thought to act as catalysts for the reaction that forms nitrogen-containing compounds such as silicon nitride when heat-treated in an inert gas atmosphere containing nitrogen gas in step (iii').

[0035] One method for adding metal to the porous material in step (ii') is to mix the porous material with a metal complex (hereinafter also referred to as "metal complex") which contains a cation of one or more metal elements selected from element group A and element group B, and whose counterion is an organic anion. The valency of the metal cation in the metal complex can be any valency that each of the above-mentioned metals can take, and is usually preferred to be monovalent, divalent, or trivalent from the viewpoint that the porous silicon material of the present invention will be able to easily achieve excellent initial Coulomb efficiency and capacity retention rate. However, for example, Mn also has valencies of 4 to 6, and metal cations having these valencies may also be used. Examples of organic anions in the metal complex include alkoxy anions, aryloxy anions, carboxylic acid anions, phosphate anions having an organic group, phosphite anions having an organic group, and sulfonic acid anions having an organic group. Among these, carboxylic acid anions are preferred, and it is more preferable to include carboxylic acid anions having a hydrocarbon group with 2 to 20 carbon atoms from the viewpoint that the metal complex will easily coordinate adsorb onto the porous material surface. Examples of hydrocarbon groups having 2 to 20 carbon atoms include linear or branched alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, undecyl, and dodecyl groups; cycloalkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, methylcyclohexyl, and cyclooctyl groups; aryl groups such as phenyl, methylphenyl, ethylphenyl, and naphthyl groups; and aralkyl groups such as benzyl groups. Among these, n-pentyl, isopentyl, 2-ethylhexyl, and decyl groups are preferred. These groups may also be in the form of structural isomers. Carboxylate anions having hydrocarbon groups having 2 to 20 carbon atoms may be monocarboxylic acid anions or polycarboxylic acid anions, but monocarboxylic acid anions are preferred from the viewpoint of facilitating coordination adsorption of metal complexes to the porous surface. These organic anions may have further substituents. If such substituents have a nitrogen-containing atomic group as a functional group, they can also serve as a source of nitrogen for the porous silicon material of the present invention.Metal complexes may be used individually or in combination of two or more.

[0036] The amount of metal complex added is preferably in the range of 0.01 to 5 mol%, and more preferably in the range of 0.05 to 3 mol%, as the ratio (molar ratio) of the number of metal anions contained in the metal complex to the number of Si atoms (moles) in the porous material. Furthermore, it is preferable to use the metal complex as a metal complex solution containing a solvent (hereinafter simply referred to as "metal complex solution"). Examples of solvents 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. Mixing of the porous material and the metal complex can be done using a stirrer, ultrasonic mixer, premix disperser, etc. When the metal complex solution is mixed with the porous material, it is preferable to obtain a porous material with the metal added by desolvation and drying after mixing. The conditions for desolvation and drying are not particularly limited. Desolvent removal can be carried out, for example, in a range of 80 to 150°C under atmospheric pressure or reduced pressure in an inert gas atmosphere. Drying can be carried out, for example, in a range of 25 to 200°C under atmospheric pressure or reduced pressure in an inert gas atmosphere for a range of 1 minute to 24 hours. Such desolvent removal and drying can also be carried out using known dryers, vacuum dryers, spray dryers, etc.

[0037] A porous silicon material is obtained by heat-treating the metal-added porous material obtained in step (ii') of manufacturing method 2 at a temperature of 700°C to 1100°C under an inert gas atmosphere containing nitrogen gas (iii'). The details of the inert gas containing nitrogen gas and the heat treatment in step (iii') of manufacturing method 2 are the same as those of step (iii) in manufacturing method 1 described above.

[0038] The porous silicon material of the present invention obtained as described above has voids that can mitigate volume changes due to the expansion and contraction of Si during charging and discharging. Therefore, expansion can be suppressed in the negative electrode of a secondary battery containing the porous silicon material of the present invention, and pulverization of the porous silicon material can be suppressed. When spherical alloy particles atomized in a gas atomizing device are used as the Si-containing alloy, the resulting porous silicon material of the present invention tends to have improved cycle characteristics and expansion is easily suppressed when used as the negative electrode active material. Furthermore, alloys with a higher Si content than the eutectic composition of Si and aluminum can also be used as raw materials. Even when the Si composition ratio is increased, amorphous silicon components tend to be present in at least a portion of the silicon phase, which suppresses expansion and further improves cycle characteristics. In addition, the mass productivity of the porous silicon material of the present invention is improved, making it economically advantageous.

[0039] <Negative Electrode Active Material> The present invention also relates to a negative electrode active material comprising the porous silicon material of the present invention as described above. The negative electrode active material of the present invention may consist of the porous silicon material of the present invention alone, or it may contain the porous silicon material of the present invention and an active material such as a carbonaceous material. It may also contain other necessary third components. The negative electrode active material of the present invention may also consist of the porous silicon material described above and a matrix phase containing C element (carbon element). In particular, it is preferable that the matrix phase contains one or more elements from the group consisting of Si, O, and C.

[0040] The negative electrode active material of the present invention preferably contains 20% to 80% by mass of the above-mentioned porous silicon material relative to its total mass, and more preferably 30% to 70% by mass. When the content of the above-mentioned porous silicon material in the negative electrode active material of the present invention is within the above range, a sufficient protective effect on the matrix phase is achieved, and it is easy to achieve both charge / discharge capacity and cycle characteristics. The negative electrode active material of the present invention has particles with an average particle size (D50) of 1 μm to 10 μm and a specific surface area of ​​1 m². ２ / g or more 50m ２It is preferable that the value is less than or equal to / g. The negative electrode active material of the present invention has a porosity Q calculated by the following formula (2), based on the voids that may exist inside the porous silicon material or at the interface between the porous silicon material and the matrix phase. ２ However, it is preferable that it be between 1% and 70%. Q ２ = 100 × (1 - W / ρ) (2) W: Apparent density of particles (g / cm³) ３ ρ: True density of particles (g / cm³) ３ In the anode active material of the present invention, any voids that may exist inside the porous silicon material or at the interface between the porous silicon material and the matrix phase are all contained within the matrix phase, and these voids are closed off within the anode active material. Therefore, the porosity Q of the anode active material of the present invention can be determined from the apparent true density value measured with the voids inside and the true density value without considering the internal voids. ２ The following is calculated. Note that the matrix phase may have voids, but it is preferable that there are no voids in the matrix phase.

[0041] In the negative electrode active material of the present invention, the content of element N relative to the total mass is preferably 5% by mass or less, and more preferably 4% by mass or less. On the other hand, the content of element N in the negative electrode active material of the present invention is preferably 1% or more from the viewpoint of suppressing oxidation due to the presence of element N and improving cycle characteristics by strengthening the framework of the Si surface.

[0042] When the negative electrode active material of the present invention has a matrix phase containing element C (carbon), the porous silicon material described above is dispersed in the matrix phase. The matrix phase preferably contains one or more elements from the group consisting of Si, O, and C, and more preferably contains at least silicon oxycarbide (SiOC) and a carbonaceous phase. In other words, the negative electrode active material of the present invention is more preferably a negative electrode active material (hereinafter also referred to as "this negative electrode active material") which is composed of the porous silicon material described above and a matrix phase containing element C, wherein the matrix phase contains at least silicon oxycarbide and a carbonaceous phase.

[0043] The matrix phase in this negative electrode active material is preferably composed of a compound containing silicon, oxygen, and carbon. The compound containing silicon, oxygen, and carbon preferably has a structure that includes a three-dimensional network structure of the silicon-oxygen-carbon skeleton of SiOC (silicon oxycarbide) and free carbon. Here, free carbon refers to carbon that is not included in the three-dimensional silicon-oxygen-carbon skeleton of SiOC, and includes carbon that exists as a carbon phase, carbon that is bonded to other carbon in the carbon phase, and carbon that is bonded to the silicon-oxygen-carbon skeleton and the carbon phase.

[0044] When the matrix phase is composed of compounds containing silicon, oxygen, and carbon, and the structure includes a three-dimensional network structure of the silicon-oxygen-carbon skeleton of SiOC and free carbon, the silicon-oxygen-carbon skeleton in the matrix phase has high chemical stability, and by forming a composite structure with free carbon, the diffusion of lithium ions becomes easier as the electron transition resistance is reduced. The porous silicon material described above is densely enclosed in a composite structure of the silicon-oxygen-carbon skeleton and free carbon, thereby preventing direct contact between the porous silicon material and the electrolyte. As a result, when this negative electrode active material is used as the negative electrode, the porous silicon material in the negative electrode plays a major role in the manifestation of charge and discharge performance, while chemical reactions between the surface of the porous silicon material and the electrolyte during charge and discharge are avoided, thereby minimizing performance degradation of the porous silicon material itself. Furthermore, if the compounds constituting the matrix phase have 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 fluctuations in the electron distribution inside the silicon-oxygen-carbon skeleton, leading to the formation of electrostatic bonds and coordination bonds between the silicon-oxygen-carbon skeleton and the lithium ions. These electrostatic and coordination bonds allow lithium ions to be stored within the silicon-oxygen-carbon skeleton. On the other hand, because the coordination bond energy is relatively low, lithium ion desorption reactions occur easily. In other words, it is thought that the silicon-oxygen-carbon skeleton can reversibly undergo lithium ion insertion and desorption reactions during charging and discharging.

[0045] When the compounds constituting the matrix phase contain silicon, oxygen, and carbon, the matrix phase preferably contains a compound represented by the formula SiOxCy (wherein x represents the molar ratio (atomic ratio) of oxygen to silicon, and y represents the molar ratio (atomic ratio) of carbon to silicon). When this negative electrode active material is used in a secondary battery, from the viewpoint of achieving a superior balance between charge / discharge performance and capacity retention, 1 ≤ x < 2 is preferred, 1 ≤ x ≤ 1.9 is more preferred, and 1 ≤ x ≤ 1.8 is even more preferred. Furthermore, when this negative electrode active material is used in a secondary battery, from the viewpoint of balancing charge / discharge performance and initial Coulomb efficiency, 1 ≤ y ≤ 20 is preferred, and 1.2 ≤ y ≤ 15 is more preferred.

[0046] The matrix phase may contain nitrogen in addition to silicon, oxygen, and carbon. Here, nitrogen can be introduced into the matrix phase from nitrogen derived from polysiloxane compounds, phenolic resins, dispersants, and other nitrogen compounds that serve as precursors to the matrix phase and have nitrogen-containing atomic groups as functional groups within their molecules, as well as from nitrogen gas used in the calcination process. When the matrix phase contains nitrogen, the charge-discharge performance and capacity retention rate of the negative electrode active material tend to be better. When the compounds constituting the matrix phase contain silicon, oxygen, carbon, and nitrogen, it is preferable that the matrix phase contains a compound represented by the formula SiOxCyNz (wherein x and y have the same meanings as described above, and z represents the molar ratio (atomic ratio) of nitrogen to silicon). When the matrix phase contains a compound represented by the formula SiOxCyNz, from the viewpoint of charge / discharge performance and capacity retention rate when this negative electrode active material is used in a secondary battery, 1 ≤ x ≤ 2, 1 ≤ y ≤ 20, and 0 < z ≤ 0.5 are preferred, and 1 ≤ x ≤ 1.9, 1.2 ≤ y ≤ 15, and 0 < z ≤ 0.4 are more preferred. Note that x, y, and z are all positive numbers. x, y, and z can be determined by measuring the mass content of each element and then converting it to a molar ratio (atomic ratio). In this case, the oxygen and carbon content can be quantified using an inorganic element analyzer, and the silicon content can be quantified using an ICP emission spectrometer (ICP-OES).

[0047] While it is preferable to measure x, y, and z using the method described above, it is also possible to determine the total content ratio of the negative electrode active material by performing a localized analysis of the negative electrode active material, obtaining a large number of measurement points for the content ratio data obtained therefrom, and then inferring the total content ratio of the negative electrode active material. Examples of localized analysis include energy-dispersive X-ray spectroscopy (SEM-EDX) and electron probe microanalyzer (EPMA).

[0048] The anode active material can be suitably produced by, for example, obtaining an anode active material precursor containing the porous silicon material and the organosilicon polymer material through the following steps, and then calcining the precursor in an inert gas atmosphere. (i) Add an organic solvent to the porous silicon material and stir to obtain a slurry. (ii) Mix the slurry with the organosilicon polymer material, then desolvent and dry to obtain an anode active material precursor. (iii) Calcine the anode active material precursor obtained in (ii) in an inert gas atmosphere.

[0049] Examples of organic solvents to be added to porous silicon materials 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. When adding an organic solvent to a porous silicon material and stirring to obtain a slurry, a dispersant may be included, and is preferable, from the viewpoint of improving dispersibility. Both aqueous and non-aqueous dispersants can be used as dispersants, but non-aqueous dispersants are preferred from the viewpoint of suppressing the progression of oxidation on the surface of the porous silicon material. Examples of non-aqueous dispersants include high molecular weight non-aqueous dispersants such as polyether-based, polyalkylene polyamine-based, and polycarboxylic acid partial alkyl ester-based dispersants; low molecular weight non-aqueous dispersants such as polyhydric alcohol ester-based and alkyl polyamine-based dispersants; and polyphosphate-based dispersants.

[0050] Next, the slurry and the organosilicon polymer material are mixed, and then desolvated and dried to obtain a negative electrode active material precursor. The organosilicon polymer material contained in the negative electrode active material precursor preferably has a polymer structure containing silicon, carbon, and oxygen elements. In particular, 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. The content of porous silicon material in the negative electrode active material precursor is preferably in the range of 10 to 40% by mass, and more preferably in the range of 15 to 35% by mass. The content of organosilicon polymer material in the negative electrode active material precursor is preferably in the range of 60 to 90% by mass, and more preferably in the range of 65 to 85% by mass. Furthermore, when 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, it is preferable that the content of the polysiloxane compound relative to the total amount of the organosilicon polymer material is in the range of 1 to 50% by mass, and the content of the carbon source resin is in the range of 50 to 99% by mass.

[0051] The polysiloxane compound constituting the organosilicon polymer material is preferably a resin containing at least one of the following structures: polycarbosilane, polysilazane, polysilane, and polysiloxane. It may also 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 composite forms include graft copolymerization, block copolymerization, random copolymerization, and alternating copolymerization. Examples of composite resins include composite resins having a graft structure in which polysiloxane segments are chemically bonded to the side chains of polymer segments, and composite resins having a block structure in which polysiloxane segments are chemically bonded to the ends of polymer segments. The polysiloxane segment is preferably one having at least one of the structural units represented by the following general formula (S-1) or the following general formula (S-2). In particular, it is more preferable that the polysiloxane compound has a carboxyl group, epoxy group, amino group, or polyether group at the side chain or terminal of the siloxane bond (Si-O-Si) main skeleton.

[0052]

[0053]

[0054] (In the formula, R １ R represents alkyl, aryl, epoxy, and carboxyl groups. ２ and R ３ Each of these independently represents an alkyl group, a cycloalkyl group, an aryl group, an aralkyl group, an epoxy group, and a carboxyl group. １ , R ２ and R ３ Examples of alkyl groups represented by each include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, isopentyl group, neopentyl group, tert-pentyl group, 1-methylbutyl group, 2-methylbutyl group, 1,2-dimethylpropyl group, 1-ethylpropyl group, hexyl group, isohexyl group, 1-methylpentyl group, 2-methylpentyl group, 3-methylpentyl group, 1,1-dimethylbutyl group, 1,2-dimethylbutyl group, 2,2-dimethylbutyl group, 1-ethylbutyl group, 1,1,2-trimethylpropyl group, 1,2,2-trimethylpropyl group, 1-ethyl-2-methylpropyl group, and 1-ethyl-1-methylpropyl group. １ , R ２ and R ３ Examples of aryl groups represented by each include phenyl group, naphthyl group, 2-methylphenyl group, 3-methylphenyl group, 4-methylphenyl group, 4-vinylphenyl group, and 3-isopropylphenyl group. ２ and R ３ Examples of cycloalkyl groups represented by each include cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl groups. ２ and R ３ Examples of aralkyl groups represented by each include benzyl group, diphenylmethyl group, and naphthylmethyl group.

[0055] Examples of polymer segments other than the polysiloxane segment of a 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. Among these, vinyl polymer segments are preferred.

[0056] The polysiloxane compound may be a composite resin in which polysiloxane segments and polymer segments are bonded together in the structure shown in the following structural formula (S-3), or it may have a three-dimensional network polysiloxane structure.

[0057]

[0058] (In the formula, the carbon atoms are carbon atoms constituting the polymer segment, and the two silicon atoms are silicon atoms constituting the polysiloxane segment.) The polysiloxane segment of the polysiloxane compound may have functional groups that react upon heating, such as polymerizable double bonds. In this case, the crosslinking reaction can proceed by heat-treating the polysiloxane compound before firing, making it solid, thus facilitating the firing process. Examples of such polymerizable double bonds include vinyl groups and (meth)acryloyl groups. It is preferable that there are two or more polymerizable double bonds in the polysiloxane segment, more preferably 3 to 200, and even more preferably 3 to 50. Using a composite resin in which two or more polymerizable double bonds are present as the polysiloxane compound allows the crosslinking reaction to proceed easily.

[0059] The polysiloxane segment may have at least one silanol group or a hydrolyzable silyl group. Here, examples of hydrolyzable groups in the hydrolyzable silyl group include halogen atoms, alkoxy groups, substituted alkoxy groups, asiloxy groups, phenoxy groups, mercapto groups, amino groups, amide groups, aminooxy groups, iminooxy groups, alkenyloxy groups, etc. When these groups are hydrolyzed, the hydrolyzable silyl group becomes a silanol group. In parallel with the crosslinking reaction by the heat treatment described above, a hydrolysis condensation reaction proceeds between the hydroxyl group in the silanol group and the hydrolyzable group in the hydrolyzable silyl group, thereby obtaining a solid polysiloxane compound. In this specification, a silanol group is a silicon-containing group having a hydroxyl group directly bonded to a silicon atom. Also, in this specification, a hydrolyzable silyl group is a silicon-containing group having a hydrolyzable group directly bonded to a silicon atom, and specifically, for example, a group represented by the following general formula (S-4) can be mentioned.

[0060]

[0061] (In the formula, R ４ represents a monovalent organic group, R ５ (where b represents a halogen atom, alkoxy group, acyloxy group, aryloxy group, mercapto group, amino group, amide group, aminooxy group, iminooxy group, or alkenyloxy group. b is an integer from 0 to 2.)

[0062] R ４ Examples of monovalent organic groups represented by include alkyl groups, aryl groups, or aralkyl groups. Specific examples of alkyl groups, aryl groups, or aralkyl groups are shown in the general formula (S-2) where R ２ and R ３ These are equivalent to alkyl, aryl, or aralkyl groups, respectively. ５ Examples of halogen atoms represented by R include fluorine, chlorine, bromine, and iodine atoms. ５ Examples of alkoxy groups represented by include methoxy, ethoxy, propoxy, isopropoxy, butoxy, sec-butoxy, and tert-butoxy groups. ５Examples of acyloxy groups represented by include formyloxy group, acetoxy group, propanoyloxy group, butanoyloxy group, pivaloyloxy group, pentanoyloxy group, phenylacetoxy group, acetoacetoxy group, benzoyloxy group, naphthoyloxy group, etc. ５ Examples of aryloxy groups represented by R include phenyloxy groups and naphthyloxy groups. ５ Examples of alkenyloxy groups represented by include vinyloxy group, 1-propenyloxy group, isopropenyloxy group, 2-butenyloxy group, 3-butenyloxy group, 2-pentenyloxy group, 3-methyl-3-butenyloxy group, and 2-hexenyloxy group.

[0063] The polymer segment may optionally have various functional groups, as long as they do not impede the effects of the present invention. Examples of such functional groups include carboxyl groups, protected carboxyl groups, carboxylic acid anhydrides, tertiary amino groups, hydroxyl groups, protected hydroxyl groups, cyclocarbonate groups, epoxy groups, carbonyl groups, primary amide groups, secondary amide groups, carbamate groups, and functional groups represented by the following structural formula (S-5). The polymer segment may also have polymerizable double bonds such as vinyl groups and (meth)acryloyl groups.

[0064]

[0065] Polysiloxane compounds can be produced, for example, by the following methods (1) to (3): (1) A polymer segment containing at least one silanol group or 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 silanol group or hydrolyzable silyl group and a polymerizable double bond, and a hydrolysis condensation reaction is carried out. (2) A polymer segment containing at least one silanol group or hydrolyzable silyl group is prepared in advance as a raw material for the polymer segment. Polysiloxane is also prepared in advance by hydrolysis condensation reaction of a silane compound having at least one silanol group or hydrolyzable silyl group and a polymerizable double bond. Then, the polymer segment and the polysiloxane are mixed and a hydrolysis condensation reaction is carried out. (3) A method of mixing a polymer segment with a silane compound having at least one silanol group or hydrolyzable silyl group and a polymerizable double bond, and carrying out a hydrolysis condensation reaction with a polysiloxane. Alternatively, commercially available products may be used as the polysiloxane compound, such as the "Ceranet®" series (organic-inorganic hybrid coating resin; manufactured by DIC Corporation) and the "CompoCeran® SQ" series (organic-inorganic hybrid material that is a silsesquioxane; manufactured by Arakawa Chemical Industries, Ltd.).

[0066] As the carbon source resin constituting the organosilicon polymer material, synthetic resins and natural chemical raw materials that have good miscibility with polysiloxane compounds and are easily carbonized by high-temperature firing under an inert gas atmosphere are preferred. Examples of synthetic resins include thermoplastic resins such as polyvinyl alcohol and polyacrylic acid, and thermosetting resins such as phenolic resins and furan resins. Examples of natural chemical raw materials include heavy oils, particularly tar pitches such as coal tar, tar light oil, tar medium oil, tar heavy oil, naphthalene oil, anthracene oil, coal tar pitch, pitch oil, mesophase pitch, oxygen-crosslinked petroleum pitch, and heavy oil. Among these, from the viewpoint of price, availability, and impurity exclusion, it is preferable that the carbon source resin is a synthetic resin containing aromatic hydrocarbon moieties, preferably a phenolic resin, epoxy resin, or thermosetting resin, and more preferably a resol-type phenolic resin. Commercially available phenolic resins can be used, for example, the "Sumilight Resin (registered trademark)" series (resol-type phenolic resin, manufactured by Sumitomo Bakelite Co., Ltd.).

[0067] The polysiloxane compound and the carbon source resin may be used as a mixture, or 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 covalent bonds. For example, a silane compound having an epoxy group and a hydrolyzable silyl group (hereinafter also referred to as "epoxysilane compound") or a silane compound having an isocyanate group and a hydrolyzable silyl group (hereinafter also referred to as "isocyanate silane compound") can be used as part of the raw materials for the polysiloxane compound, and the silane compound containing the epoxysilane compound or isocyanate silane compound can be produced by polycondensation in the presence of a carbon source resin having a substituent (hydroxyl group, amino group, carboxyl group, thiol group, etc.) that can react with the epoxy group or isocyanate group. Furthermore, a composite in which a polysiloxane compound and a carbon source resin are bonded together can also be produced by polymerizing a polymer segment containing at least one epoxy group or isocyanate group and a hydrolyzable silyl group, preferably a monomer having substituents reactive with epoxy groups or isocyanate groups, in the presence of a polysiloxane compound having constituent units derived from an epoxysilane compound or isocyanatesilane compound, and which can form a carbon source resin; or by polycondensing a silane compound containing an epoxysilane compound or isocyanatesilane compound and a monomer having substituents reactive with epoxy groups or isocyanate groups, which can form a carbon source resin, in a single process. The covalent bonds in the composite of the polysiloxane compound and the carbon source resin are not limited to bonds derived from the epoxy groups or isocyanate groups as described above, but may also be ester bonds, ether bonds, etc.

[0068] Mixing of the slurry and the organosilicon polymer material can be performed using a stirrer, ultrasonic mixer, premix disperser, etc. The conditions for desolvation and drying after mixing are not particularly limited. Desolvation can be performed, for example, in the range of 80 to 150°C under atmospheric pressure or reduced pressure in an inert gas atmosphere. Drying can be performed, for example, in the range of 25 to 200°C under atmospheric pressure or reduced pressure in an inert gas atmosphere for a range of 1 minute to 24 hours. Such desolvation and drying can also be performed using known dryers, vacuum dryers, spray dryers, etc.

[0069] The negative electrode active material is obtained by calcining the negative electrode active material precursor, which has been obtained through desolvation and drying, in an inert gas atmosphere. From the viewpoint of easily completely decomposing thermally decomposable organic components, the maximum temperature reached during calcination is preferably in the range of 900 to 1200°C. When the maximum temperature reached is within the above range, it is easier to precisely control the fine structure of silicon and carbon in the matrix phase, and oxidation of silicon due to calcination at excessively high temperatures can be avoided, thus making it easier to obtain better charge-discharge characteristics. Specifically, the organosilicon polymer material (preferably polysiloxane compound and carbon source resin) contained in the negative electrode active material precursor is converted into a silicon-oxygen-carbon skeleton and free carbon by the energy of the high-temperature treatment during calcination, forming the matrix phase in the negative electrode active material described above. As described above, the compounds constituting the matrix phase may contain nitrogen in addition to silicon, oxygen, and carbon. The firing method is not particularly limited, and any fluidized bed reactor, rotary furnace, vertical moving bed reactor, tunnel furnace, batch furnace, rotary kiln, etc., that have a heating function under an inert gas atmosphere can be appropriately selected, and both continuous and batch methods are possible.

[0070] The negative electrode active material of the present invention may have its surface coated with a coating material. The coating material is preferably a substance that exhibits electronic conductivity, lithium ion conductivity, and an effect of suppressing the decomposition of the electrolyte, and examples include electronically conductive materials such as carbon, titanium, and nickel. When the negative electrode active material of the present invention is coated with a coating material, the method is not particularly limited, and examples include methods using CVD (Chemical Vapor Deposition).

[0071] <Composition for secondary battery negative electrode, secondary battery negative electrode, secondary battery> The present invention also includes a composition for secondary battery negative electrode containing the negative electrode active material of the present invention, and a secondary battery negative electrode comprising a negative electrode material layer formed using such secondary battery negative electrode composition. The present invention further includes a secondary battery comprising the above secondary battery negative electrode, a positive electrode, an electrolyte, and a separator.

[0072] The negative electrode active material of the present invention exhibits excellent capacity and cycle characteristics, and furthermore, expansion and contraction associated with charging and discharging are suppressed. Therefore, a secondary battery containing the negative electrode active material of the present invention, and more specifically a secondary battery having a negative electrode comprising a negative electrode material layer containing the negative electrode active material of the present invention, exhibits good charge-discharge characteristics and excellent cycle characteristics. For example, a composition for a secondary battery negative electrode can be prepared by kneading the negative electrode active material of the present invention and an organic binder together with a solvent using a dispersion device such as a stirrer, ball mill, super sand mill, or pressurized kneader. This composition for a secondary battery negative electrode can be applied to a current collector (e.g., copper foil) to form a negative electrode material layer. The solvent is preferably one that does not react with the negative electrode active material of the present invention. Examples include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, and cyclohexanone; alcohols such as ethanol, methanol, n-propanol, isopropanol, benzyl alcohol, and diacetone alcohol; aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as hexane, cyclohexane, octane, and nonane; ethers such as tetrahydrofuran, diethyl ether, and glyme; and esters such as ethyl acetate and butyl acetate. When preparing the negative electrode composition for secondary batteries, polymeric non-aqueous dispersants such as polyether-based, polyalkylene polyamine-based, and polycarboxylic acid partial alkyl ester-based dispersants; low molecular weight non-aqueous dispersants such as polyhydric alcohol ester-based and alkyl polyamine-based dispersants; and dispersants such as polyphosphate-based dispersants may be present as needed.

[0073] Examples of the organic binders include styrene-butadiene rubber copolymers (hereinafter also referred to as "SBR"); ethylenically unsaturated carboxylic acid copolymers such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, (meth)acrylonitrile, and hydroxyethyl (meth)acrylate, and unsaturated carboxylic acid copolymers such as (meth)acrylic copolymers made from ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid; and polymer 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.

[0074] The content of organic binder in the negative electrode material layer of the lithium-ion secondary battery negative electrode is preferably 0.1 to 30% by mass, more preferably 0.5 to 20% by mass, and even more preferably 1 to 15% by mass. When the organic binder content is 1% by mass or more, adhesion is improved, and the destruction of the negative electrode structure due to expansion or contraction during charging and discharging is more easily suppressed. On the other hand, when it is 30% by mass or less, the increase in electrode resistance is more easily suppressed. Within this range, the negative electrode active material of the present invention has high chemical stability and can also use an aqueous binder, making it easy to handle in practical terms.

[0075] The secondary battery negative electrode composition may further contain conductive additives as needed. Examples of conductive additives include carbon black, graphite, acetylene black, conductive oxides, and nitrides. When the secondary battery negative electrode composition further contains a conductive additive, the amount is preferably in the range of 1 to 15% by mass relative to the negative electrode active material of the present invention.

[0076] Examples of materials for the current collector include copper, nickel, titanium, and stainless steel. The shape of the current collector is preferably a strip shape such as foil, perforated foil, or mesh. In addition, porous materials such as porous metal (foamed metal) and carbon paper can also be used as current collectors. Examples of methods for applying the secondary battery negative electrode composition to the current collector include metal mask printing, electrostatic painting, dip coating, spray coating, roll coating, doctor blade method, gravure coating, and screen printing. After application, it is preferable to perform rolling treatment using a flat plate press, calender roll, etc., as needed.

[0077] Alternatively, a negative electrode layer may be obtained by forming a paste-like negative electrode composition for secondary batteries into a sheet or pellet, and then integrating it with a current collector using a roll, press, or a combination thereof. Furthermore, a negative electrode layer can also be prepared by adding carbon materials such as natural graphite, artificial graphite, hard carbon, or amorphous carbon such as soft carbon to the negative electrode composition for secondary batteries.

[0078] The negative electrode material layer formed on the current collector or the negative electrode material layer integrated with the current collector is preferably heat-treated according to the type of organic binder used. For example, when using a water-based styrene-butadiene rubber copolymer (SBR), heat treatment is preferably performed at 100 to 130°C, and when using an organic binder with polyimide or polyamide-imide as the main backbone, heat treatment is preferably performed at 150 to 450°C. Such heat treatment removes solvents derived from the organic binder and promotes increased strength due to the hardening of the organic binder, thereby improving adhesion between particles and between particles and the current collector. It is preferable to perform the heat treatment under an inert gas atmosphere such as helium, argon, or nitrogen, or under a vacuum atmosphere, from the viewpoint of preventing oxidation of the current collector during heat treatment.

[0079] Furthermore, after heat treatment, the negative electrode consisting of a negative electrode material layer formed on the current collector or a negative electrode material layer integrated with the current collector, in other words, the negative electrode of a secondary battery using the negative electrode active material of the present invention, is preferably subjected to pressurization from the viewpoint of adjusting the electrode density. In such a negative electrode, the electrode density is 1 to 1.8 g / cm³. ３ Preferably, it is 1.1 to 1.7 g / cm³. ３It is more preferable that the concentration be 1.2 to 1.6 g / cm³. ３ It is even more preferable that the electrode density is as follows: While higher electrode density tends to improve adhesion and electrode volumetric density, if it is too high, the voids in the electrode decrease, weakening the effect of suppressing silicon volume expansion and potentially reducing the capacity retention rate. Therefore, an optimal range for electrode density is selected.

[0080] The secondary battery of the present invention comprises a secondary battery negative electrode having a negative electrode material layer formed using the secondary battery negative electrode composition, a positive electrode, an electrolyte, and a separator. In other words, the secondary battery of the present invention contains the negative electrode active material of the present invention in the negative electrode. As secondary batteries having a negative electrode containing the negative electrode active material of the present invention, non-aqueous electrolyte secondary batteries and solid electrolyte secondary batteries are preferred. For example, if the secondary battery of the present invention is a wet electrolyte secondary battery, it can be constructed by arranging the positive electrode and the negative electrode containing the negative electrode active material of the present invention opposite each other via a separator, and injecting the electrolyte.

[0081] The positive electrode is obtained by forming a positive electrode layer on the surface of the current collector, similar to the negative electrode. In this case, the current collector can be made of a metal or alloy such as aluminum, titanium, or stainless steel, in the form of a foil, perforated foil, mesh, or other strip.

[0082] The cathode material used in the cathode layer is not particularly limited. In the case of non-aqueous electrolyte secondary batteries, for example, when manufacturing lithium-ion secondary batteries, examples include metal compounds, metal oxides, metal sulfides, and conductive polymers that can dope or intercalate lithium ions. Specifically, lithium cobalt oxide (LiCoO) ２ ), lithium nickelate (LiNiO ２ ), lithium manganese (LiMnO ２ ) and their composite oxides (LiCoxNiyMnzo ２ (x + y + z = 1); Lithium manganese spinel (LiMn ２ O ４ ), lithium vanadium compound, V ２ O ５ , V ６ O １３ , VO ２ MnO ２, TiO ２ , MoV ２ O ８ , TiS ２ , V ２ S ５ , VS ２ , MoS ２ , MoS ３ , Cr ３ O ８ , Cr ２ O ５ , Olivine-type LiMPO ４ (where M is Co, Ni, Mn, or Fe); conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, porous carbon, etc. These can be used alone or in combination of two or more kinds.

[0083] As the separator, for example, non-woven fabrics, cloths, microporous films mainly composed of polyolefins such as polyethylene and polypropylene, or combinations thereof can be used. Note that when the structure is such that the positive and negative electrodes of the non-aqueous electrolyte secondary battery to be manufactured do not directly contact each other, it is not necessary to use a separator.

[0084] As the electrolyte, for example, lithium salts such as LiClO ４ , LiPF ６ , LiAsF ６ , LiBF ４ , LiSO ３ CF ３ etc., dissolved in a single type or a mixture of two or more kinds of non-aqueous solvents 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, ethyl acetate, etc., so-called organic electrolytes can be used.

[0085] The structure of the secondary battery of the present invention is not particularly limited, but generally, the positive electrode, the negative electrode, and a separator provided as needed are wound in a flat spiral shape to form a wound electrode plate group, or these are stacked as flat plates to form a stacked electrode plate group, and these electrode plate groups are enclosed in an outer casing. In the half-cell used in the embodiment of the present invention, the negative electrode is mainly composed of a negative electrode active material containing the porous silicon material of the present invention, and a simple evaluation is performed using metallic lithium as the counter electrode. This is to more clearly compare the initial discharge capacity and cycle characteristics of the porous silicon material of the present invention itself.

[0086] When the secondary battery of the present invention is a solid electrolyte secondary battery, it can be configured, for example, by comprising the positive electrode described above, the negative electrode described above containing the negative electrode active material of the present invention, and a solid electrolyte interposed between the positive electrode and the negative electrode that conducts lithium ions. As the solid electrolyte, for example, oxide-based lithium ion conductors such as LISICON-type ion conductors, perovskite-type ion conductors, garnet-type ion conductors, NASICON-type ion conductors; β-Li ３ PS ４ Examples include sulfide-based lithium-ion conductors, glass-based inorganic solid electrolytes, and thiolysicone-based solid electrolytes. These solid electrolytes may be formed in a plate shape and placed between the positive and negative electrodes. The solid electrolyte secondary battery may also include a restraining member that constrains the laminate, which is a stack of the positive electrode, solid electrolyte, and negative electrode, in the stacking direction.

[0087] A secondary battery equipped with a negative electrode using the porous silicon material of the present invention is suitably used as, for example, a paper-type battery, a button-type battery, a coin-type battery, a stacked battery, a cylindrical battery, a prismatic battery, and the like. The porous silicon material of the present invention is also applicable to electrochemical devices in general that use the insertion and deinsertion of lithium ions as a charge and discharge mechanism, such as hybrid capacitors and solid lithium secondary batteries. The porous silicon material of the present invention is not limited to negative electrode materials for lithium-ion batteries, but can also be used as thermoelectric materials, solar cells, electronic device components, filter materials, and optical materials.

[0088] The porous silicon material and its manufacturing method of the present invention, a negative electrode active material containing the porous silicon material of the present invention, a secondary battery negative electrode composition containing the negative electrode active material, a secondary battery negative electrode comprising a negative electrode material layer formed using the secondary battery negative electrode composition, and a secondary battery comprising the secondary battery negative electrode have been described above. However, the present invention is not limited to the configurations of the embodiments described above. For example, the porous silicon material, the negative electrode active material containing the porous silicon material, the secondary battery negative electrode composition containing the negative electrode active material, the secondary battery negative electrode comprising a negative electrode material layer formed using the secondary battery negative electrode composition, and the secondary battery comprising the secondary battery negative electrode may each have additional configurations in the configurations of the embodiments described above, or may be replaced with any configuration that exhibits similar functions. Furthermore, the manufacturing method of the porous silicon material of the present invention may have additional steps for any other purpose in the configurations of the embodiments described above, or may be replaced with any steps that exhibit similar effects.

[0089] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the examples below. Unless otherwise specified, "parts" and "%" are based on mass. In the examples, the half-cells used have a negative electrode mainly composed of a negative electrode active material containing the porous silicon material of the present invention, and a simple evaluation is performed using metallic lithium as the counter electrode. This is to more clearly compare the initial discharge capacity of the porous silicon material of the present invention itself. The raw materials used in the examples and comparative examples are shown below. <Particles of alloy containing Si> • Alloy particle 1: Spherical particles of Al-Si alloy (Al / Si = 88 / 12; mass ratio), D50 = 5 μm, manufactured by Skyspring • Alloy particle 2: Spherical particles of Al-Si alloy (Al / Si = 88 / 12; mass ratio), D50 = 1 μm, manufactured by Skyspring • Alloy particle 3: Spherical particles of Al-Si alloy (Al / Si = 88 / 12; mass ratio), D50 = 20 μm, manufactured by XIANtech • Alloy particle 4: Spherical particles of Al-Si alloy (Al / Si = 70 / 30; mass ratio), D50 = 20 μm, manufactured by the Ultra-High Temperature Materials Research Center Co., Ltd. - Alloy particle 5: Spherical particles of Al-Si alloy (Al / Si = 88 / 12; mass ratio), D50 = 40 μm, manufactured by High Purity Chemicals Co., Ltd. - Alloy particle 6: Spherical particles of Al-Si alloy (Al / Si = 60 / 40; mass ratio), D50 = 20 μm, manufactured by the Ultra-High Temperature Materials Research Center Co., Ltd. - Alloy particle 7: Al-Si １０ - Spherical particles of Mg alloy (Al / Si / Mg = 88 / 11.5 / 0.5; mass ratio), D50 = 20 μm, manufactured by Toyo Aluminum Co., Ltd. - Alloy particles 8: ADC12 (aluminum alloy die-cast, Al-Si-Cu alloy, manufactured by Toyosaka Shoji Co., Ltd.) were used as raw materials and prepared using a gas atomization device (N ２ Spherical particles (D50 = 20 μm) produced by gas (10 MPa, outlet temperature 950°C) and alloy particles 9: Made using a gas atomizing device with ADC1 (aluminum alloy die-cast, Al-Si alloy, manufactured by Toyoei Shoji Co., Ltd.) as the raw material (N ２Spherical particles (D50 = 20 μm) and alloy particles (10 MPa, outlet temperature 950°C) were subjected to a gas-induced reaction. Silicon nanoparticles (manufactured by NER Corporation, D50 = 100 nm) were immersed in ethanol and subjected to ultrasonic treatment (ultrasonic homogenizer "LUH150", manufactured by Yamato Scientific Co., Ltd.) for 5 minutes at room temperature (25°C). Next, a solution of 5 μmol / L silver nitrate mixed with a 0.02 M hydrofluoric acid aqueous solution was added to form silver nanoparticles on the surface of the silicon nanoparticles. Then, an aqueous solution containing hydrofluoric acid and hydrogen peroxide in a ratio of 25:1 (mass ratio) (total content of hydrofluoric acid and hydrogen peroxide: 5 mass%) was added and stirred for 5 minutes at room temperature (25°C) to form micropores in the silicon nanoparticles. The silicon nanoparticles were separated from the mixture, washed with distilled water, dried, and then stirred in a 1 M nitric acid aqueous solution before being separated and dried to obtain silicon nanoparticles with a porous structure. Alloy particles 11: Silicon powder (manufactured by NER Corporation Japan), D50 = 3 μm

[0090] <Metal Salts> ・Metal salt 1: Mn-OCTOATE 8% (Trade name, manufactured by DIC Corporation) ・Metal salt 2: DICNATE Al-100 (Trade name, manufactured by DIC Corporation) ・Metal salt 3: Tetraisopropyl orthotitanate (manufactured by TCI Corporation) ・Metal salt 4: DICNATE 285T (Trade name, manufactured by DIC Corporation) ・Metal salt 5: Zn-OCTOATE 20%T (Trade name, manufactured by DIC Corporation) ・Metal salt 6: Ni-OCTOATE 10%H (Trade name, manufactured by DIC Corporation)

[0091] <Matrix> - Resin 1: "Sumilight Resin (registered trademark) PR-53570" (product name, phenolic resin, manufactured by Sumitomo Bakelite Co., Ltd.) - Resin 2: "SSA-500" (product name, polysiloxane resin, manufactured by DIC Corporation)

[0092] A-1. Examples of Manufacturing Porous Silicon Materials Example 1 Alloying was performed by immersing alloy particles 1 in 3M hydrochloric acid and reacting at room temperature (25°C) for 24 hours. The reaction mixture was filtered by suction through a 1 μm filter, washed with distilled water, dried under reduced pressure at 60°C for 10 hours, and then calcined at 700°C for 2 hours under a nitrogen atmosphere to obtain porous silicon material 1. Examples 2-12, Comparative Examples 1-4 The same procedure as in Example 1 was performed except that the type of alloy particles and calcination conditions (atmosphere gas type, temperature, and time) were changed as shown in Table 1 to obtain porous silicon materials 2-12, C1-C4. In Example 8, alloy particles 2 were obtained by first passing the material through a filter and then recovering it by centrifugation. In Examples 9 and 10, dealloying was performed by immersing in 0.5M hydrochloric acid and reacting at 60°C for 30 minutes.

[0093] Example 13 Alloying was performed by immersing alloy particles 1 in 3M hydrochloric acid and reacting at room temperature (25°C) for 24 hours. The reaction mixture was filtered by suction through a 1 μm filter and washed with distilled water. To the resulting solid, metal salt 1 dispersed in methyl ethyl ketone was added so that the atomic ratio of Mn to Si was 0.2 mol%, and the mixture was mixed with a homodisperser at 1000 rpm for 5 minutes. Then, it was dried under reduced pressure at 60°C for 10 hours, and further fired at 700°C for 2 hours under a nitrogen atmosphere to obtain porous silicon material 13.

[0094] Examples 14-26 and Comparative Examples 5-6: The same procedure as in Example 13 was followed, except that the type of alloy particles, the type and amount of metal salt added, and the firing conditions (atmosphere gas, temperature, and time) were changed as shown in Table 1, to obtain porous silicon materials 14-26 and C5-C6.

[0095] A-2. Example of Production of Negative Electrode Active Material Example 27 Alloy particles 1 were immersed in 3M hydrochloric acid and reacted at room temperature (25°C) for 24 hours to remove the alloy. The reaction mixture was filtered by suction through a 1 μm filter, washed with distilled water, and then dried under reduced pressure at 60°C for 10 hours. 40% by mass of a dispersant (DISPERBYK® 9077: manufactured by BYK Additionals & Instruments) was added to the obtained dried particles and left to stand for 1 day. Next, methyl ethyl ketone was added and stirred to obtain a slurry so that the dry particle concentration was 70% by mass. Resin 1, as a raw material for the matrix phase, was mixed into this slurry so that the Si content after calcination was 50% by mass. The solvent was removed under a nitrogen atmosphere at 120°C, then dried under reduced pressure at 110°C for 10 hours, and then calcined under a nitrogen atmosphere at 1100°C for 2 hours. The resulting calcined material was pulverized in a planetary ball mill loaded with 5 mm diameter zirconia beads as a medium. Subsequently, the pulverized material was placed in a rotary kiln-type reactor and, in a nitrogen atmosphere, using LPG (liquid propane gas) as the carbon source, carbon was adsorbed onto the surface of the pulverized material by CVD (Chemical Vapor Deposition) at 850°C and 1 atm for 120 minutes. After that, the material was crushed and passed through a 20 μm mesh to obtain the negative electrode active material 27.

[0096] Examples 28-36, Comparative Example 7, and Comparative Example 9 were performed in the same manner as in Example 27, except that the type of alloy particles, the type of resin used as the raw material for the matrix phase and the mixing ratio with the slurry, and the firing conditions (atmospheric gas type, temperature, and time) were changed as shown in Table 2, to obtain negative electrode active materials 28-36, C7, and C9.

[0097] Example 37 Alloy particles 1 were dealloyed by immersing them in 3M hydrochloric acid and reacting them at room temperature (25°C) for 24 hours. The reaction mixture was filtered by suction through a 1 μm filter, washed with distilled water, and then dried under reduced pressure at 60°C for 10 hours. 40% by mass of a dispersant (DISPERBYK® 9077: manufactured by BYK Additionals & Instruments) was added to the resulting dried particles and allowed to stand for 1 day. Next, methyl ethyl ketone was added and stirred to obtain a slurry, resulting in a dry particle concentration of 70% by mass. To this slurry, a metal salt 1 dispersed in methyl ethyl ketone was mixed so that the atomic ratio of Mn to Si contained in the alloy particles 1 was 0.2 mol%, and resin 2 as the raw material for the matrix phase was mixed so that the Si content after firing was 50 mass%, the solvent was removed at 120°C under a nitrogen atmosphere, then dried under reduced pressure at 110°C for 10 hours, and then fired at 1100°C for 2 hours under a nitrogen atmosphere. The resulting fired product was pulverized in a planetary ball mill loaded with zirconia beads with a diameter of 5 mm as the medium. The resulting pulverized product was subjected to the same procedure as in Example 27 (CVD) to adsorb carbon onto its surface, then crushed and passed through a 20 μm mesh passerby to obtain the negative electrode active material 37.

[0098] Examples 38-46, Comparative Example 8, and Comparative Example 10 were performed in the same manner as in Example 37, except that the type of alloy particles, the type and amount of metal salt added, the type of resin used as the raw material for the matrix phase and the mixing ratio with the slurry, and the firing conditions (atmosphere gas, temperature, and time) were changed as shown in Table 2 to obtain negative electrode active materials 37-46, C8, and C10. In Examples 41-42, the following further changes were made. In Example 41, zirconia beads with a diameter of 2 mm were used as a medium when crushing the obtained fired product. In Example 42, zirconia beads with a diameter of 10 mm were used as a medium when crushing the obtained fired product.

[0099] B. Evaluation of Porous Silicon Materials and Anode Active Materials The following physical properties were measured for the porous silicon materials and anode active materials obtained in each example and comparative example.

[0100] (1) Elemental Analysis (1-1) Oxygen and Nitrogen Atom Content (mass%) For the porous silicon materials obtained in Examples 1 to 26 and Comparative Examples 1 to 6, the oxygen and nitrogen atom content (mass%) was measured using an ONH analyzer (LECO "ONH836"). For the negative electrode active materials obtained in Examples 27 to 46 and Comparative Examples 7 to 10, the nitrogen atom content (mass%) was measured using an ICP-OES analyzer (Agilent Technologies "Agilent 5110 ICP-OES"). (1-2) Quantitative Analysis of Metallic Elements For the porous silicon materials obtained in Examples 1 to 26 and Comparative Examples 1 to 6, the metallic elements were measured using an EDS analyzer (JEOL "JED-2300").

[0101] (2) Average particle size (D50) was measured using a laser diffraction particle size distribution analyzer (Malvern Panalytical, Mastersizer 3000).

[0102] (3) Porosity For the porous silicon materials obtained in Examples 1 to 26 and Comparative Examples 1 to 6, a fully automated pore distribution analyzer (Quanta Chrome "pore Master 60-GT") was used to measure the pore distribution in the measurement range of pore diameter 400 μm to 0.0036 μm by placing the sample in a sample cell, and the porosity was calculated as follows: Porosity = 100 × P / R P: Pore volume = Cumulative pore volume calculated by pore distribution measurement × Mass of sample R: Bulk volume = Total cell volume - Cell volume excluding sample For the negative electrode active materials obtained in Examples 27 to 46 and Comparative Examples 7 to 10, apparent density W (g / cm³) ３ The true density ρ (g / cm³) was measured using a true density meter (Anton Paar "Ultrapyc 5000"). On the other hand, the negative electrode active material was pulverized in a ball mill until the D50 was 1 μm or less, eliminating internal voids, and then the true density ρ (g / cm³) was measured using a true density meter (Anton Paar). ３ The void ratio was calculated using the following formula (2): Void ratio (%) = 100 × (1 - W / ρ) (2)

[0103] (4) Analysis of the silicon portion (4-1) Silicon domain diameter For the porous silicon materials obtained in Examples 1 to 26 and Comparative Examples 1 to 6, each porous silicon material was fixed onto copper foil, and the cross section cut out using a cross-section polisher (registered trademark; JEOL Ltd. "IB-19520CCP") was observed at an arbitrary magnification (5,000 to 50,000 times) using a scanning electron microscope (SEM (Scanning Electron Microscope): JEOL Ltd. "FEM-7900F"). The SEM images were analyzed using image analysis software (Image J) to measure the short axis of 100 arbitrary silicon domains, and the average value was calculated to determine the silicon domain diameter. (4-2) Crystallite Size For the negative electrode active materials obtained in Examples 27-46 and Comparative Examples 7-10, the peak intensity of the Si(111) plane was measured using the fundamental parameter (FP) method with a wide-angle X-ray diffraction (XRD) apparatus (Rigaku Corporation's "Ultima IV"). The crystallite size (nm) was determined from the peak full width at half maximum (FMAX) around 2θ = 28.3° ± 0.5°, which is attributed to the Si(111) plane, using the following equation (A) as the basic equation (Scherrer's analytical equation): L = Kλ / βcosθ ... (A) In the equation, K is Scherrer's constant, L is the crystallite size [m], λ is the measured X-ray wavelength of the Cu / Kα line [m], β is the FMAX [rad], and θ is the Bragg angle of the diffraction line peak [rad]. The measurement conditions were as follows: Cu / Kα line: 40kV / 40mA Scan speed: 2° / min Step: 0.02° Scanning range: 5° to 70°

[0104] (5) Raman analysis: The Raman spectrum is measured using a micro-Raman spectrometer (JASCO Corporation "NRS5500"), and the peak wavelength and full width at half maximum (cm) derived from Si are determined. －１ ) was determined. Meanwhile, the Raman spectrum of the Si crystal used as a reference sample was measured, and the obtained peak wavelength (520 cm) was determined. －１ ) and peak half-width (6 cm) －１These values ​​were used as reference values. The greater the strain within the Si-Si bond structure, the greater the shift in the Si-derived peak wavelength obtained from the measurement of each porous silicon material or each negative electrode active material from the reference peak wavelength of the Si crystal. Peak full width at half maximum (FWHM) is also an indicator of the uniformity of the Si-Si bond structure state, and the peak FWHM broadens due to crystallinity, defects in the structure, etc. In other words, a wide peak FWHM indicates the existence of diverse Si-Si bond structure states.

[0105] (6) Specific surface area The specific surface area of ​​the negative electrode active materials obtained in Examples 27 to 46 and Comparative Examples 7 to 10 was calculated by BET method analysis using nitrogen gas adsorption measurement with a specific surface area measuring device (BELsorb miniX manufactured by Microtrac-Bel).

[0106] (7) Surface analysis (X-ray photoelectron spectroscopy) Nitrogen-derived peaks were observed using an X-ray photoelectron spectrometer (FEI Japan, "Thermo Scientific K-Alpha XPS System"), and the peak values ​​(eV) were measured.

[0107] C. Evaluation of Battery Characteristics in Half Cells (1-1) A slurry was prepared by mixing 6.9 parts by mass of porous silicon material obtained in Examples 1 to 26 and Comparative Examples 1 to 6 with 1 part by mass of acetylene black and 0.1 parts by mass of carbon nanotubes as conductive additives and a mixture of 0.25 parts by mass of CMC and 0.75 parts by mass of SBR (total 1 part by mass) as a binder, and stirring for 10 minutes in a rotation-orbit mixer (Thinky Co., Ltd. "Awatori Rentaro"). (1-2) For the negative electrode active materials obtained in Examples 27 to 46 and Comparative Examples 7 to 10, the same procedure as in (1-1) above was performed to prepare a slurry, except that carbon nanotubes were not added as conductive additives. (2) Each slurry obtained in (1-1) and (1-2) above was deposited as a film on a copper foil with a thickness of 20 μm. After drying under reduced pressure at 110°C, it was punched out into a circular shape with a diameter of 14 mm and weighed approximately 1.0 g / cm ３ The negative electrode was obtained as a thin film by pressing it using a tablet molding machine. The thickness of the obtained negative electrode was measured at five points using a thickness gauge (Nikon "MF-501"), and the average value was L ０Next, in a dry room with a moisture dew point of -40°C or lower, a Li metal foil was used as the counter electrode, and the negative electrode obtained above was placed opposite it via a polypropylene separator (25 μm thick). A non-aqueous electrolyte solution, in which lithium hexafluoride phosphate was dissolved at a concentration of 1 mol / L in a mixture of ethylene carbonate and diethyl carbonate in a 1:1 volume ratio, was adsorbed onto the Li metal foil, and a coin-type lithium-ion battery (CR2032 type) was fabricated as a half-cell.

[0108] (3) Using a secondary battery charge / discharge test apparatus (manufactured by Hokuto Denko Co., Ltd.), the charge / discharge characteristics of the fabricated half-cells were evaluated at 25°C, with a cutoff voltage range of 0.005 to 1.5V, and charge / discharge rates of 0.1C (1 to 3 cycles) and 0.2C (after 4 cycles), under constant current / constant voltage charging / constant current discharging conditions. During each charge / discharge transition, the circuit was left open for 30 minutes. For the negative electrodes formed from the porous silicon material obtained in Examples 1 to 26 and Comparative Examples 1 to 6, the cycle characteristics were measured after 10 charge / discharge cycles. For the negative electrodes formed from the negative electrode active materials obtained in Examples 27 to 46 and Comparative Examples 7 to 10, the cycle characteristics were measured after 20 charge / discharge cycles. In addition, the coin-type lithium-ion batteries created above were disassembled in their initial fully charged state, the negative electrodes were removed, washed with dimethyl carbonate, and air-dried. The thickness of this negative electrode was measured at five locations using a thickness gauge, and the average value was taken. １ The expansion rate of the negative electrode was calculated using the following formula: Expansion rate (%) = 100 × L １ / L ０

[0109] Table 1 summarizes the preparation conditions and detailed physical properties of the porous silicon materials obtained in Examples 1 to 26 and Comparative Examples 1 to 6, as well as the evaluation results in half-cells. Table 2 summarizes the preparation conditions and detailed physical properties of the negative electrode active materials obtained in Examples 27 to 46 and Comparative Examples 7 to 10, as well as the evaluation results in half-cells.

[0110]

[0111]

[0112] D. Evaluation of battery characteristics in an all-solid-state battery using porous silicon material Example 47 60 parts by mass of the porous silicon material 2 obtained in Example 2 and β-Li as the solid electrolyte３ PS ４ 35 parts by mass of (NEI Corporation) and 5 parts by mass of VGCF (Vapor Grown Carbon Fiber; manufactured by Resonaq Corporation) as a conductive material were mixed in a mortar while being crushed to obtain a negative electrode composite. The obtained negative electrode composite was pressed at 20 MPa to produce a negative electrode composite layer. Meanwhile, the above solid electrolyte was pressed at 30 MPa to produce a solid electrolytic layer. Furthermore, Li foil (manufactured by Honjo Metal Co., Ltd.) and In foil (manufactured by Nihon Handa Co., Ltd.) were pressed at 30 MPa to obtain a Li-In alloy foil as a positive electrode. Then, the negative electrode composite layer, solid electrolytic layer, and Li-In alloy foil prepared above were stacked in this order and a surface pressure of 5 t / cm was applied. ２ All-solid-state batteries for evaluation were fabricated by tightly sealing them with tabbed laminate and pressing them at 60 MPa to create a laminate. Using a secondary battery charge / discharge test apparatus (manufactured by Hokuto Denko Co., Ltd.), the charge / discharge characteristics (cycle characteristics) of the fabricated all-solid-state batteries were evaluated at 45°C under the conditions of constant current / constant voltage charging at 0.3 mA to -0.57 V on the first attempt, followed by constant current discharge at 0.3 mA to 0.88 V. The results are shown in Table 3.

[0113] Example 48 An all-solid-state battery was fabricated in the same manner as in Example 47, except that the porous silicon material 13 obtained in Example 13 was used instead of the porous silicon material 2, and the cycle characteristics were evaluated. The results are shown in Table 3. Comparative Example 11 An all-solid-state battery was fabricated in the same manner as in Example 47, except that the porous silicon material C1 obtained in Comparative Example 1 was used instead of the porous silicon material 2, and the cycle characteristics were evaluated. The results are shown in Table 3.

[0114]

[0115] The results from Tables 1 to 3 show that the negative electrode active material containing the porous silicon material of the present invention can suppress the expansion and contraction of the negative electrode containing such negative electrode active material, and exhibits excellent initial discharge capacity and cycle characteristics. Furthermore, secondary batteries containing the porous silicon material of the present invention as a negative electrode active material exhibit excellent battery characteristics such as charge and discharge characteristics.

[0116] The negative electrode formed using the negative electrode active material containing the porous silicon material of the present invention suppresses expansion and contraction associated with repeated charging and discharging, and exhibits excellent initial discharge capacity and cycle characteristics. Secondary batteries having such a negative electrode have excellent battery characteristics such as charge and discharge characteristics, and can be effectively used in portable electronic devices, for example, as paper type batteries, button type batteries, coin type batteries, stacked type batteries, cylindrical batteries, prismatic batteries, etc. The negative electrode active material containing the porous silicon material of the present invention can also be applied to electrochemical devices in general that use the insertion and deinsertion of lithium ions as a charge and discharge mechanism, such as hybrid capacitors and solid lithium secondary batteries.

Claims

1. A porous silicon material comprising N and one or more metallic elements selected from the group consisting of Al, Zn, Mg, Fe, Sn, Sc, Ti, V, Cr, Mn, Cu, Co, Ni, and Mo.

2. The porous silicon material according to claim 1, wherein the metal element comprises Al.

3. The porous silicon material according to claim 1, wherein, in XPS (X-ray photoelectron spectroscopy) measurements, it has one or more peaks at a binding energy of 396 eV to 400 eV.

4. The porous silicon material according to claim 1, wherein the content of element N is 0.1% by mass or more and 15.0% by mass or less, relative to the total mass of the porous silicon material.

5. The porous silicon material according to claim 1, wherein the content of element O is 1.0% by mass or more and 50.0% by mass or less, relative to the total mass of the porous silicon material.

6. The porous silicon material according to claim 1, wherein the content of the metal element is 1% by mass or more and 15% by mass or less with respect to the total mass of the porous silicon material.

7. The void ratio Q calculated using the following formula (1) １ The porous silicon material according to claim 1, wherein the amount is more than 20% and less than 95%. １ (%) = 100 × P / (V + P) (1) P: Pore volume of porous silicon material V: Volume of porous silicon material 8. The porous silicon material according to claim 1, having silicon domain particles having an average particle size in the range of 5 nm to 1 μm.

9. The porous silicon material according to claim 1, comprising crystalline silicon, wherein the crystallite size of the Si(111) plane, as calculated by the fundamental parameter (FP) method by X-ray diffraction analysis, is 1 nm or more and 30 nm or less.

10. In the Raman spectrum obtained by Raman spectroscopy, 480 cm⁻¹ －１ Super 520cm －１ The region has one or more peaks, and the full width at half maximum of the peaks is 5 cm. －１ Super 60cm －１ A porous silicon material according to claim 1, wherein the material is less than [amount missing].

11. The porous silicon material according to claim 1, wherein the element N is contained near the interface between the silicon domain particles and the voids.

12. A method for producing a porous silicon material according to any one of claims 1 to 11, comprising the following steps: (i) a step of preparing an alloy containing Si; (ii) a step of obtaining a porous material by treating the alloy prepared in step (i) with an acid or alkali; (iii) a step of obtaining a porous silicon material by heat-treating the porous material obtained in step (ii) at a temperature of 700°C to 1100°C in an inert gas atmosphere containing nitrogen gas.

13. A method for producing a porous silicon material according to any one of claims 1 to 11, comprising the following steps: (i) preparing an alloy containing Si; (ii) obtaining a porous material by treating the alloy prepared in step (i) with an acid or alkali; (iii') adding a metal to the porous material obtained in step (ii); (iii) obtaining a porous silicon material by heat-treating the metal-added porous material obtained in step (iii') at a temperature of 700°C to 1100°C in an inert gas atmosphere containing nitrogen gas.

14. A negative electrode active material comprising the porous silicon material described in any one of claims 1 to 11.

15. The negative electrode active material according to claim 14, comprising a porous silicon material according to any one of claims 1 to 11 and a matrix phase containing element C.

16. The negative electrode active material according to claim 15, wherein the matrix phase contains one or more elements from the group consisting of Si, O, and C.

17. The negative electrode active material according to claim 15, wherein the matrix phase comprises at least silicon oxycarbide and a carbonaceous phase.

18. The negative electrode active material according to claim 15, wherein the content of element N relative to the total mass is 5% by mass or less.

19. The negative electrode active material according to claim 15, wherein the content of the porous silicon material relative to the total mass is 20% by mass or more and 80% by mass or less.

20. Particles with an average particle size (D50) of 1 μm or more and 10 μm or less, and a specific surface area of ​​1 m² ２ / g or more 50m ２ The negative electrode active material according to claim 15, wherein the amount is less than or equal to / g.

21. The porosity Q calculated by the following formula (2) based on the voids that may exist inside the porous silicon material or at the interface between the porous silicon material and the matrix phase ２ is 1% or more and 70% or less. The negative electrode active material according to claim 15. Q ２ = 100 × (1 - W / ρ) (2) W: apparent density of particles (g / cm ３ ) ρ: true density of particles (g / cm ３ ) 22. A composition for a secondary battery negative electrode, comprising the negative electrode active material described in claim 14.

23. A secondary battery negative electrode comprising a negative electrode material layer formed using the secondary battery negative electrode composition described in claim 22.

24. A secondary battery comprising a negative electrode, a positive electrode, an electrolyte, and a separator as described in claim 23.

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