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

Abstract

The present invention provides a porous silicon material useful as a negative electrode active material that suppresses expansion and contraction associated with repeated charging and discharging, and can create a negative electrode with excellent initial discharge capacity and cycle characteristics, a negative electrode active material containing such porous silicon material, and a secondary battery having such a negative electrode active material. [Solution] 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.

Description

[Technical Field]

[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. [Background technology]

[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 rapidly being 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 primarily use graphite as the negative electrode material. However, graphite has a low theoretical capacity density (372 mAh / g), which limits the development of lithium-ion batteries with even higher energy densities. To compensate for the limited theoretical capacity density of graphite, negative electrode materials using elements capable of intercalating and releasing lithium ions, such as silicon (Si), metals like tin, or alloys and oxides of other elements, are being investigated. Among these, silicon has a theoretical capacity more than 10 times that of graphite (4200 mAh / g), making silicon and silicon-containing negative electrode active materials noteworthy as next-generation negative electrode materials capable of achieving higher 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 causes the active material to be pulverized, 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 silicon-containing negative electrode active materials, the development of porous silicon materials is underway. Patent Document 1 discloses a negative electrode active material containing porous silicon particles, preferably obtained by an electrochemical etching method, in which a specific 50% particle size, and furthermore, the difference between the 90% particle size and the 10% particle size, is within a specific range, and the surface may be coated with a conductive agent, and which is said to have excellent cycle characteristics and output characteristics.

[0004] Furthermore, there is growing interest in techniques for creating porous silicon materials by preparing alloys of silicon (Si) with metal elements that form a eutectic composition, and then using de-alloying reactions with acids or alkalis. For example, Patent Document 2 discloses a negative electrode active material for lithium secondary batteries, which is an aggregate of porous particles made solely 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, as well as a method for producing 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 allowing for efficient diffusion of lithium ions, enabling high-rate charging and discharging. It is also said that the amorphous phase of Si improves cycle characteristics. Patent Document 3 discloses a method for producing porous silicon particles, comprising the steps of atomizing 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, a silicon alloy in which the Al and Si are in a blending ratio near the eutectic composition can be used to obtain porous silicon particles containing a three-dimensional network structure of silicon with voids, and having 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, which includes the steps of atomizing a silicon alloy containing Al and Si in specific mass percentages, removing Al to obtain a porous material, and heating such a porous material to diffuse elements other than Si to the surface. Such a porous silicon material is said to have improved charge-discharge cycle characteristics due to its small pore size and large porosity, which mitigate volume expansion and contraction, and to have excellent charge-discharge capacity because it has a purer silicon skeleton.

[0005] Furthermore, attempts have also been made to form composites of silicon and carbon-based substances, and composites composed of silicon and a carbon matrix and having a porous structure. For example, Patent Document 5 discloses a method for producing a 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 into inorganic carbon at 400 °C or higher in an inert gas atmosphere. The carbon structure formed by the carbonization of lignin can cope with the extreme volume expansion of silicon during charging, has a carbon matrix with great strength and elasticity, and is said to have 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 further carbon-coated. Such Si / C particles are said to be able to reduce the delamination of the passivation protection layer (solid electrolyte interface: SEI) and provide a high-capacity lithium-ion battery because the silicon particles are embedded in the pores in the carbon matrix. Patent Document 7 discloses a negative electrode active material including a silicon-based composite represented by SiOa (0 ≦ a < 1) and having a bimodal pore structure including mesopores and macropores, and including a carbon coating layer on the surface, which can improve the initial efficiency and life characteristics and can prevent side reactions with the electrolyte by controlling the specific surface area. Patent Document 8 discloses a silicon-silicon oxide carbon composite in which silicon particles are uniformly distributed in a silicon oxide-carbon structure containing a large number of fine pores, where carbon coats silicon oxide. It is said that volume expansion due to the insertion of lithium ions is reduced, electrical conductivity is improved, and electrolyte easily penetrates into the interior of the porous structure, making it easy to improve output characteristics.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Summary of the Invention

Problems to be Solved by the Invention

[0007] Although the porous silicon particles of Patent Document 1 are defined in terms of the distribution of their average particle size, there is no disclosure regarding details such as the porosity of "pores" that suppress deterioration due to the expansion and contraction of silicon (Si) and contribute to the improvement of charge-discharge characteristics. Also, methods mentioned for obtaining porous silicon particles, such as the method of electrochemically etching (in other words, the method by anodic oxidation) or the method of crushing with ultrasonic waves, are difficult to mass-produce from an industrial perspective and have problems with productivity. The negative electrode active material for lithium secondary batteries described in Patent Document 2 is formed by rapidly cooling a molten alloy containing a specific metal element and silicon, and then completely dissolving and removing the specific element from the resulting quenched alloy. The content of the specific metal element in the molten alloy is preferably 0.01% by mass or more and 70% by mass or less. However, 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 the 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 described in 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. Therefore, there is still room for further investigation into suppressing degradation due to the expansion and contraction of Si 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 effects such as suppression of expansion when charged and discharged as a negative electrode, or the extent to which the charge-discharge cycle characteristics can be improved. The negative electrode using the silicon-based composite negative electrode active material disclosed in Patent Document 7 still exhibits a significant thickness change (swelling) of 190% after repeated charge-discharge cycles, as shown in Example 1, and also has room for improvement in terms of lifespan characteristics. The secondary battery described in Patent Document 8, which uses a silicon-silicon oxide carbon composite as the negative electrode active material, exhibits significant irreversible characteristics in the first cycle, and still presents challenges 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 the porous silicon material 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, and 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, we discovered that porous silicon materials containing N element can be efficiently produced by forming a porous region 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. We also found that when such porous silicon materials containing N element are used as a negative electrode active material, expansion and contraction associated with repeated charging and discharging are suppressed, and negative electrodes with excellent cycle characteristics can be mass-produced. Furthermore, we found that using a negative electrode active material composed of a porous silicon material containing N elements and a matrix phase containing carbon elements can further enhance the suppression of expansion and contraction associated with repeated charging and discharging, as well as improve cycle characteristics.

[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 exhibits excellent initial discharge capacity and cycle characteristics. Another object of the present invention is to provide a negative electrode active material containing such porous silicon material, and a secondary battery having such negative electrode active material. [Means for solving the problem]

[0011] The present invention has the following aspects. [1] A porous silicon material comprising the element 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] A porous silicon material of [1], wherein the metal element comprises Al. [3] A porous silicon material according to [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] A porous silicon material according to any of [1] to [3], wherein the content of element N is 0.1% by mass or more and 15.0% by mass or less with respect to the total mass of the porous silicon material. [5] A porous silicon material according to any of [1] to [4], wherein the element O content 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] A porous silicon material of any of the following types [1] to [6], wherein the porosity Q1 calculated by the following formula (1) is greater than 20% and less than 95%. Q1(%) = 100 × P / (V + P) (1) P: Pore volume of porous silicon material V: Volume of porous silicon material [8] A porous silicon material having silicon domain particles with an average particle size in the range of 5 nm to 1 μm, any of [1] to [7]. [9] A porous silicon material of any of the following types [1] to [8], which contains crystalline silicon and has a crystallite size of the Si(111) plane calculated by the fundamental parameter (FP) method by X-ray diffraction analysis of 1 nm to 30 nm.

[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 less than [1] to [9].

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

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

[12] A method for producing any of the porous silicon materials described in [1] to

[11] , comprising the following steps. (i) Steps to prepare 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 process to obtain a porous silicon material by heat-treating the porous material obtained in step (ii) in an inert gas atmosphere containing nitrogen gas at a temperature of 700°C to 1100°C.

[13] A method for producing any of the porous silicon materials described in [1] to

[11] , comprising the following steps: (i) Steps to prepare 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) above. (iii) A process to obtain 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 a temperature of 700°C to 1100°C.

[0012]

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

[11] .

[15] A negative electrode active material of

[14] , comprising one of the porous silicon materials of [1] to

[11] and a matrix phase containing element C.

[16] The negative electrode active material of

[15] , wherein the matrix phase comprises 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 comprises at least silicon oxycarbide and a carbonaceous phase.

[18] A 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] A 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 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 A negative electrode active material of any of

[15] to

[19] that is less than or equal to / g.

[21] A negative electrode active material of any of

[15] to

[20] , wherein the porosity Q2 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, is 1% or more and 70% or less. Q2 = 100 × (1 - W / ρ) (2) W: Apparent density of particles (g / cm³) 3 ρ: true density of particles (g / cm³) 3 ) A composition for the negative electrode of a secondary battery, containing any of the negative electrode active materials

[22]

[14] to

[21] . A secondary battery negative electrode comprising a negative electrode material layer formed using the secondary battery negative electrode composition of

[23]

[22] . A secondary battery comprising a negative electrode, a positive electrode, an electrolyte, and a separator, as described in

[24]

[23] . [Effects of the Invention]

[0013] According to the present invention, a porous silicon material useful as a negative electrode active material and a method for producing the same can be provided, 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. Furthermore, according to the present invention, a negative electrode active material containing such porous silicon material and a secondary battery having such a negative electrode active material that has excellent battery characteristics such as charge-discharge characteristics can be provided. [Modes for carrying out the invention]

[0014] <Porous Silicone Material> The porous silicon material of the present invention is a porous silicon material comprising the element 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. The porous silicon material of the present invention preferably contains Al among the aforementioned 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 by obtaining a porous material by treating an alloy containing Si, preferably an Al-Si alloy, with an acid or alkali in the method for producing the porous silicon material of the present invention described later, 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 N element, and its embodiment is, for example, the following formula (α). SiNx (α) (where 0 < x ≤ 1.33.) It is presumed to be included as one or more nitrogen-containing compounds of silicon nitride represented by the following formula (β). AlNy (β) (where 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) measurement.

[0019] The content of N element 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, based on the total mass of the porous silicon material. When the content of N element is within the above range, the above-mentioned nitrogen-containing compound is preferably present in the vicinity of the surface of the porous silicon material, so that the contact between silicon (Si) and oxidizing substances such as oxygen gas can be suppressed, and the growth and increase of the silicon oxide film can be suppressed. Therefore, the initial efficiency in charge and discharge when used as a negative electrode active material is likely to be improved. In addition, the presence of the above-mentioned nitrogen-containing compound in addition to the voids of the porous silicon material is considered to be able to suppress the structural destruction due to the expansion and contraction of Si, suppress the expansion of the negative electrode, and improve the 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, an oxide film is formed on the surface, and the initial charge-discharge efficiency tends to decrease. 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, making 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 addition, element O is usually included in the form of oxides of Si and metal elements that constitute 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 metallic 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 metallic 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, it is preferable that the total content of element group A and element group B is between 1% by mass and 15% by mass relative to the total mass of the porous silicon material.

[0022] The porous silicon material of the present invention preferably has a porosity Q1 calculated by the following formula (1) that is greater than 20% and less than 95%. Q1(%) = 100 × P / (V + P) (1) P: Pore volume of porous silicon material V: Volume of porous silicon material The porosity Q1 is preferably 25% or more, and more preferably 30% or more. Furthermore, the porosity Q1 is preferably 90% or less, and more preferably 85% or less. When the porosity Q1 is within the range described above, 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 preferred to be spherical. When the D50 of the porous silicon material of the present invention falls within the aforementioned 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 having 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 using X-ray diffraction analysis, is preferably between 1 nm and 30 nm. Having such a crystallite size within the aforementioned 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 described in the examples below. Incidentally, the porous silicon material of the present invention may contain an amorphous silicon component at least in part.

[0025] The porous silicon material of the present invention preferably has one or more peaks in a region of less than 480 cm -1 and more than 520 cm -1 in the Raman spectrum obtained by Raman spectroscopy, and more preferably has one or more peaks in a region of less than 490 cm -1 and more than 520 cm -1 in the Raman spectrum obtained by Raman spectroscopy. Also, it is preferable that the full width at half maximum of the peak is less than 60 cm -1 and more than 5 cm -1 more preferably less than 40 cm -1 and more than 5 cm -1 even more preferably less than 30 cm -1 and more than 5 cm -1 in the Raman spectrum obtained by Raman spectroscopy. When the porous silicon material of the present invention has the above-described peak in the Raman spectrum, it means that structural defects and strains occur in the silicon, irregularities occur in the bonding, and the behavior of amorphous silicon is likely to be shown. Therefore, the expansion of the negative electrode containing the porous silicon material of the present invention is suppressed, and the battery characteristics of the secondary battery provided with such a negative electrode are likely to be improved.

[0026] The porous silicon material of the present invention preferably contains N element in the vicinity of the interface between the silicon domain particles and the voids. Here, in this specification, the "vicinity" of the interface between the silicon domain particles and the voids means a depth within, for example, 10 nm from the interface, preferably within 5 nm, and more preferably within 3 nm. The N element 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 the above formula (α) or aluminum nitride represented by formula (β). Further, in the method for producing the porous silicon material of the present invention, which will be described later, heat treatment is performed in an inert gas atmosphere containing nitrogen gas. Therefore, these nitrogen-containing compounds are likely to be generated from the surface side where the porous silicon material comes into contact with nitrogen gas and are likely 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 Preferably, it should be 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 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 "Manufacturing Method 1") which includes, for example, the following steps. (i) Steps to prepare 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 process to obtain a porous silicon material by heat-treating the porous material obtained in step (ii) in an inert gas atmosphere containing nitrogen gas at a temperature of 700°C to 1100°C. In this manufacturing method 1, one or more metallic elements selected from element group A can be introduced in step (i) as metallic elements contained in the porous silicon material of the present invention. It is thought that the metal elements act as catalysts in the reaction that forms nitrogen-containing compounds such as silicon nitride when heat-treated in an inert gas atmosphere containing nitrogen gas in process (iii).

[0029] [Process (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 atom%, and more preferably 10 to 25 atom%, when the total Si-containing alloy is considered to be 100 atom%. The content of metals of element group A is preferably 70 to 95 atom%, and more preferably 75 to 90 atom%. Furthermore, 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 the impurity content 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 quenching method using a single-roll casting machine, and methods using water atomization or gas atomization equipment. Among these, particle formation using a gas atomization equipment is preferred from the viewpoint of obtaining spherical particles. The advantages of spherical particles will be described later. The cooling rate when atomizing 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, it is preferable that the alloy particles have a spherical shape. When the D50 of the alloy particles is within the aforementioned 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 also becomes easier to suppress volume changes 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 tend to improve. Since the D50 of the alloy particles becomes the D50 of the resulting porous silicon material, it is preferable to adjust the average particle size of the alloy particles to a range of more 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, based on the particle size distribution measured by dynamic light scattering using a laser diffraction particle size analyzer, etc., and was measured using a laser diffraction particle size distribution analyzer (Malvern Panalytical, "Mastersizer 3000"). Furthermore, commercially available alloy particles may be used when the Si-containing alloy is atomized using a gas atomizing device.

[0032] [Step (ii)] A porous material is obtained by treating the Si-containing alloy, preferably alloy particles, prepared in step (i) above, 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 itself. Examples include hydrochloric acid, sulfuric acid, sodium hydroxide, and potassium hydroxide. 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, for example, in the range of 1 to 5 mol / L. De-alloying can be carried out, for example, by immersing an alloy containing Si, preferably alloy particles, in an acid or alkaline solution, and stirring it at room temperature (25°C) or 30°C to 80°C for a period of 1 to 24 hours. The resulting 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) above 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. The inert gas containing nitrogen gas may or may not contain a small amount of oxygen 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. There are no particular restrictions on the heat treatment time, but from the viewpoint of producing the porous silicon material of the present invention containing element N by sufficiently generating the above-mentioned nitrogen-containing compound from the surface side where the porous material comes into contact with nitrogen gas, a range of 1 to 24 hours is preferred.

[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) Steps to prepare 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) above. (iii') A process to obtain 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 a temperature of 700°C to 1100°C. 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 this 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 metal elements selected from element group A or element group B can be introduced into the porous material as a metal element contained in the porous silicon material of the present invention. In other words, 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. It is thought that the metal elements act as catalysts in the reaction that forms nitrogen-containing compounds such as silicon nitride when heat-treated in an inert gas atmosphere containing nitrogen gas during process (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 of the valencies that each of the above-mentioned metals can take, and is usually preferred to be monovalent, divalent, or trivalent from the viewpoint of the porous silicon material of the present invention exhibiting excellent initial Coulombic efficiency and capacity retention. 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 metal complexes include alkoxy anions, aryloxy anions, carboxylic acid anions, phosphate anions with organic groups, phosphite anions with organic groups, and sulfonic acid anions with organic groups. Among these, carboxylate anions are preferred, and those containing carboxylate anions having a hydrocarbon group with 2 to 20 carbon atoms are more preferred from the viewpoint of facilitating coordination adsorption of the metal complex onto the porous 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 isomer mixtures. The carboxylate anion having a hydrocarbon group with 2 to 20 carbon atoms may be a monocarboxylic acid anion or a polyvalent carboxylic acid anion, but from the viewpoint of facilitating coordination adsorption of the metal complex to the porous surface, a monocarboxylic acid anion is preferred. 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 in 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) contained in the porous material. Furthermore, it is preferable to use the metal complex as a metal complex solution containing a solvent (hereinafter also 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. The porous material and the metal complex can be mixed using a stirrer, ultrasonic mixer, premix disperser, etc. When the metal complex solution is mixed with the porous material, it is preferable to desolvent and dry the mixture after mixing to obtain the porous material with the metal added. The conditions for desolvation and drying are not particularly limited. Desolvation can be carried out, for example, in the 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 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 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 in step (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 associated with 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 the pulverization of the porous silicon material can be suppressed. When spherical alloy particles, atomized using a gas atomization device, are used as the Si-containing alloy, the resulting porous silicon material of the present invention, when used as the negative electrode active material, tends to improve cycle characteristics and suppress expansion. Furthermore, alloys with a higher Si content than the eutectic composition of Si and aluminum can also be used as raw materials. Even with a higher Si composition ratio, amorphous silicon components tend to be present in at least a portion of the silicon phase, suppressing expansion and further improving cycle characteristics. Additionally, 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 be 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 porous silicon material relative to its total mass, and more preferably 30% to 70% by mass. When the content of the 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, making it easier 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 or more and 10 μm or less, and a specific surface area of ​​1 m². 2 / g or more 50m 2 It is preferable that the amount is less than or equal to / g. The negative electrode active material of the present invention preferably has a porosity Q2 calculated by the following formula (2), which is based on voids that may exist inside the porous silicon material or at the interface between the porous silicon material and the matrix phase, and is between 1% and 70%. Q2 = 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 Q2 of the anode active material of the present invention is calculated from the apparent true density value measured with the voids inside and the true density value without considering the internal voids. 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 inclusion 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 C element (carbon element), 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 anode active material of the present invention is more preferably anode active material (hereinafter also referred to as "this anode 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 the 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 compound constituting the matrix phase is a compound 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 such a 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 the degradation of the performance of the porous silicon material itself. Furthermore, if the compounds constituting the matrix phase have a three-dimensional network structure of silicon-oxygen-carbon skeletons 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 compound constituting the matrix phase contains silicon, oxygen, and carbon, the matrix phase preferably contains a compound represented by the formula SiOxCy (where 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 an excellent balance between charge-discharge performance and capacity retention rate, 1≦x<2 is preferable, 1≦x≦1.9 is more preferable, and 1≦x≦1.8 is even more preferable. Further, when this negative electrode active material is used in a secondary battery, from the viewpoint of achieving an excellent balance between charge-discharge performance and the balance of the initial Coulomb efficiency, 1≦y≦20 is preferable, and 1.2≦y≦15 is more preferable.

[0046] The matrix phase may contain nitrogen in addition to silicon, oxygen, and carbon. Here, the nitrogen is derived from a polysiloxane compound, a phenol resin, a dispersant, or other nitrogen compounds that serve as precursors of the matrix phase and have an atomic group containing nitrogen as a functional group within their molecules, and can be introduced into the matrix phase due to nitrogen gas used in the firing process, etc. When the matrix phase contains nitrogen, the charge-discharge performance and capacity retention rate of this negative electrode active material tend to be more excellent. When the compound constituting the matrix phase contains silicon, oxygen, carbon, and nitrogen, the matrix phase preferably contains a compound represented by the formula SiOxCyNz (where 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 viewpoints 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 preferable, and 1≦x≦1.9, 1.2≦y≦15, and 0<z≦0.4 are more preferable. Note that x, y, and z are all positive numbers. x, y, and z can be determined by converting the mass content of each element to a molar ratio (atomic ratio) after measuring the mass content. At this time, the content of oxygen and carbon can be quantified by using an inorganic element analyzer, and the content of silicon can be quantified by using an ICP emission analyzer (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] This negative electrode active material can be suitably manufactured, for example, by obtaining a negative electrode active material precursor containing the above-mentioned porous silicon material and organosilicon polymer material through the following process, and then firing this precursor in an inert gas atmosphere. (i) Add an organic solvent to the porous silicon material and stir to obtain a slurry. (ii) After mixing the slurry with an organosilicon polymer material, a negative electrode active material precursor is obtained by desolvent removal and drying. (iii) The negative electrode active material precursor obtained in (ii) above is calcined 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 it is preferable to include a dispersant, 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 porous silicon materials. 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 is mixed with an organosilicon polymer material, and then desolvent 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-based polymer material has a polymer structure consisting of a mixture of a polysiloxane compound and a carbon source resin, or a composite of a polysiloxane compound and a carbon source resin. 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 the 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. 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 polycarbosilane structure, polysilazane structure, polysilane structure, and polysiloxane structure. 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 with other polymer segments. Examples of composite polymers 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 structural unit represented by the following general formula (S-1) or the following general formula (S-2). In particular, the polysiloxane compound is more preferably one having 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] [ka]

[0053] [ka]

[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, cycloalkyl group, aryl group, aralkyl group, epoxy group, and carboxyl group. R 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. R 1 , R 2 and R 3Examples 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. R 2 and R 3 Examples of cycloalkyl groups that each represents include cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl groups. R 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] [ka]

[0058] (In the formula, the carbon atoms are carbon atoms that make up the polymer segment, and the two silicon atoms are silicon atoms that make up the polysiloxane segment.) The polysiloxane segments of a polysiloxane compound may contain functional groups that react upon heating, such as polymerizable double bonds. In this case, the crosslinking reaction can be promoted by heat-treating the polysiloxane compound before calcination, thereby solidifying it and facilitating the calcination 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 containing two or more polymerizable double bonds 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. 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 groups in the silanol group and the hydrolyzable groups in the hydrolyzable silyl group, thereby obtaining a solid polysiloxane compound. In this specification, a silanol group refers to a silicon-containing group having a hydroxyl group directly bonded to a silicon atom. Furthermore, in this specification, a hydrolyzable silyl group refers to a silicon-containing group having a hydrolyzable group directly bonded to a silicon atom, specifically, for example, a group represented by the following general formula (S-4).

[0060] [ka]

[0061] (In the formula, R 4 represents a monovalent organic group, R5 (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 the alkyl, aryl, or aralkyl groups represented by each of these terms. R 5 Examples of halogen atoms represented by this include fluorine, chlorine, bromine, and iodine atoms. R 5 Examples of alkoxy groups represented by include methoxy, ethoxy, propoxy, isopropoxy, butoxy, sec-butoxy, and tert-butoxy groups. R 5 Examples of acyloxy groups represented by include formyloxy group, acetoxy group, propanoyloxy group, butanoyloxy group, pivaloyloxy group, pentanyloxy group, phenylacetoxy group, acetoacetoxy group, benzoyloxy group, naphthoyloxy group, and others. R 5 Examples of aryloxy groups represented by this include phenyloxy groups and naphthyloxy groups. R 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] [ka]

[0065] Polysiloxane compounds can be produced, for example, by the methods shown in (1) to (3) below. (1) A method of preparing polymer segments containing at least one silanol group or hydrolyzable silyl group as raw materials for polymer segments, mixing these polymer segments 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. (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. A 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 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. Furthermore, commercially available polysiloxane compounds may be used, such as the "Ceranate®" 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 or 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 exclusion of impurities, the carbon source resin is preferably 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, such as 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 a silane compound containing the epoxysilane compound or isocyanate silane compound can be produced by polycondensation in the presence of a carbon source resin having substituents (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 that can react 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 that can react with epoxy groups or isocyanate groups, which can form a carbon source resin, in a single process. The covalent bonds in the composite of polysiloxane compounds and carbon source resins are not limited to those derived from epoxy groups or isocyanate groups as described above, but may also be ester bonds, ether bonds, etc.

[0068] Mixing of the slurry with 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 solvent removal and drying, in an inert gas atmosphere. From the viewpoint of easily decomposing thermally decomposable organic components, the maximum temperature reached during firing is preferably in the range of 900 to 1200°C. When the maximum temperature is within this range, it is easier to precisely control the microstructure of silicon and carbon in the matrix phase, and oxidation of silicon due to firing at excessively high temperatures can be avoided, thus making it easier to obtain better charge and discharge characteristics. Specifically, the organosilicon polymer material (preferably a polysiloxane compound and a 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 firing, forming the matrix phase described above in the negative electrode active material. As described above, the compounds constituting the matrix phase may also 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 is expected to have electronic conductivity, lithium ion conductivity, and an effect of suppressing the decomposition of the electrolyte, and examples of electronically conductive substances include 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 secondary battery negative electrode composition 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-mentioned negative electrode, positive electrode, electrolyte, and separator.

[0072] The negative electrode active material of the present invention exhibits excellent capacity and cycle characteristics, and furthermore, expansion and contraction during 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 negative electrode composition for a secondary battery 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 negative electrode composition for a secondary battery can be applied to a current collector (e.g., copper foil) to form a negative electrode layer. The solvent is preferably one that does not react with the negative electrode active material of the present invention, and 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 a composition for the negative electrode of a secondary battery, if necessary, high-molecular-weight non-aqueous dispersants such as polyethers, polyalkylene polyamines, and polycarboxylic acid partial alkyl esters; low-molecular-weight non-aqueous dispersants such as polyhydric alcohol esters and alkyl polyamines; and dispersants such as polyphosphates may be included in the presence of these materials.

[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 current collector is preferably in the form of a strip, such as foil, perforated foil, or mesh. Porous materials such as porous metal (foamed metal) and carbon paper can also be used as current collectors. Methods for applying the secondary battery negative electrode composition to the current collector include, for example, metal mask printing, electrostatic coating, dip coating, spray coating, roll coating, doctor blade coating, 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 fabricated by adding carbon materials such as natural graphite, artificial graphite, hard carbon, or amorphous carbon such as soft carbon to the composition for the negative electrode of a secondary battery.

[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 at 100 to 130°C is preferable, and when using an organic binder with polyimide or polyamide-imide as the main backbone, heat treatment at 150 to 450°C is preferable. This 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 the 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. 3 It 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. Preferred secondary batteries having a negative electrode containing the negative electrode active material of the present invention include non-aqueous electrolyte secondary batteries and solid electrolyte secondary batteries. For example, if the secondary battery of the present invention is a wet electrolyte secondary battery, it can be constructed by arranging a positive electrode and a negative electrode containing the negative electrode active material of the present invention opposite each other via a separator, and injecting an 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 manufacturing lithium-ion secondary batteries, among non-aqueous electrolyte secondary batteries, examples include metal compounds, metal oxides, metal sulfides, and conductive polymers that can dope or intercalate lithium ions. Specifically, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2) and their composite oxides (LiCoxNiyMnzO2, x+y+z=1); lithium manganese spinel (LiMn2O4), lithium vanadium compounds, V2O5, V6O 13 Examples include VO2, MnO2, TiO2, MoV2O8, TiS2, V2S5, VS2, MoS2, MoS3, Cr3O8, Cr2O5, olivine-type LiMPO4 (where M is Co, Ni, Mn, or Fe); conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, and polyacene; and porous carbon. These may be used individually or in combination of two or more types.

[0083] As a separator, nonwoven fabrics, cloths, microporous films, or combinations thereof, mainly composed of polyolefins such as polyethylene and polypropylene can be used. However, if the structure of the non-aqueous electrolyte secondary battery being manufactured is such that the positive and negative electrodes do not come into direct contact, a separator is not required.

[0084] As the electrolyte, a so-called organic electrolyte can be used, which is obtained by dissolving lithium salts such as LiClO4, LiPF6, LiAsF6, LiBF4, and LiSO3CF3 in one or more 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-oxazolidine-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, and ethyl acetate.

[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. Examples of solid electrolytes include oxide-based lithium ion conductors such as LISICON-type ion conductors, perovskite-type ion conductors, garnet-type ion conductors, and NASICON-type ion conductors; sulfide-based lithium ion conductors such as β-Li3PS4; glass-based inorganic solid electrolytes; and thiolysicone-based solid electrolytes. These solid electrolytes may be formed into plates and placed between the positive and negative electrodes. A solid-state electrolyte secondary battery may also include a restraining member that constrains the laminate, which comprises a positive electrode, a solid electrolyte, and a negative electrode, in the direction of stacking.

[0087] The 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-type 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 can be used not only as a negative electrode material for lithium-ion batteries, but also as a thermoelectric material, solar cell, electronic device component, filter material, and optical material.

[0088] The porous silicon material and method for producing the same according to 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 of the present invention, the negative electrode active material containing the porous silicon material, the composition for a secondary battery negative electrode containing the negative electrode active material, the secondary battery negative electrode provided with a negative electrode material layer formed using the composition for a secondary battery negative electrode, and the secondary battery provided with the secondary battery negative electrode may each have any other arbitrary configuration added in the configuration of the above-described embodiment, or may be replaced with any configuration that exhibits the same function. Further, the method for producing the porous silicon material of the present invention may have any other arbitrary purpose steps in the configuration of the above-described embodiment, or may be replaced with any steps that exhibit the same effect.

Examples

[0089] Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited only to the following examples. Unless otherwise specified, "parts" and "%" are based on mass. Note that the half-cell used in the examples has 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 for more clearly comparing the initial discharge capacity of the porous silicon material itself of the present invention. The raw materials used in the examples and comparative examples are shown. <Particles of an alloy containing Si> · Alloy particle 1: Spherical particles of an Al—Si alloy (Al / Si = 88 / 12; mass ratio), D50 = 5 μm, manufactured by Skyspring · Alloy particle 2: Spherical particles of an Al—Si alloy (Al / Si = 88 / 12; mass ratio), D50 = 1 μm, manufactured by Skyspring · Alloy particle 3: Spherical particles of an Al—Si alloy (Al / Si = 88 / 12; mass ratio), D50 = 20 μm, manufactured by XIANtech · Alloy particle 4: Spherical particles of an Al—Si alloy (Al / Si = 70 / 30; mass ratio), D50 = 20 μm, manufactured by the Ultra-High Temperature Materials Research Center · Alloy particle 5: Spherical particles of an Al—Si alloy (Al / Si = 88 / 12; mass ratio), D50 = 40 μm, manufactured by High-Purity Chemical 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: Spherical particles with a D50 of 20 μm were created using a gas atomization device (N2 gas, 10 MPa, outlet temperature 950°C) with ADC12 (aluminum alloy die-cast, Al-Si-Cu alloy, manufactured by Toyoei Shoji Co., Ltd.) as the raw material. ·Alloy particles 9: Spherical particles with a D50 of 20 μm were created using a gas atomization device (N2 gas, 10 MPa, outlet temperature 950°C) with ADC1 (aluminum alloy die-cast, Al-Si alloy, manufactured by Toyoei Shoji Co., Ltd.) as the raw material. ·Alloy particles 10: Silicon nanoparticles (manufactured by NER Corporation, D50 = 100 nm) were immersed in ethanol and subjected to sonication (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:hydrogen peroxide = 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. Silicon nanoparticles with a porous structure were obtained by separating them from the mixture, washing them with distilled water, drying them, stirring them in a 1M aqueous nitric acid solution, separating them again, and drying them. • Alloy particle 11: Silicon powder (manufactured by NER Corporation, Japan), D50 = 3 μm

[0090] <metal salts> • Metal salt 1: Mn-OCTOATE 8% (product name, manufactured by DIC Corporation) • Metal salt 2: DICNATE Al-100 (product name, manufactured by DIC Corporation) • Metal salt 3: Tetraisopropyl orthotitanate (manufactured by TCI) • Metal salt 4: DICNATE 285T (product name, manufactured by DIC Corporation) • Metal salt 5: Zn-OCTOATE 20%T (product name, manufactured by DIC Corporation) • Metal salt 6: Ni-OCTOATE 10%H (product 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 Dealloying 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 under a nitrogen atmosphere at 700°C for 2 hours to obtain porous silicon material 1. Examples 2-12, Comparative Examples 1-4 The same procedure as in Example 1 was followed, except that the type of alloy particles and the firing conditions (atmospheric gas type, temperature, and time) were changed as shown in Table 1, to obtain porous silicon materials 2-12 and C1-C4. In Example 8, alloy particles 2 were obtained by first passing the material through a filter and then recovering it by centrifugal force. In Examples 9 and 10, dealloying was performed by immersion in 0.5 M hydrochloric acid and reacting at 60°C for 30 minutes.

[0093] Example 13 Dealloying 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 homodisper at 1000 rpm for 5 minutes. Subsequently, it was dried under reduced pressure at 60°C for 10 hours, and then calcined under a nitrogen atmosphere at 700°C for 2 hours to obtain porous silicon material 13.

[0094] Examples 14-26, Comparative Examples 5-6 The same procedure as in Example 13 was performed, 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] A2. Examples of manufacturing negative electrode active materials Example 27 Dealloying was performed by immersing alloy particles 1 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. To the obtained dry particles, 40% by mass of dispersant (DISPERBYK® 9077: manufactured by BYK Additives & Instruments) was added and left 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. Resin 1, used as the 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, followed by vacuum drying at 110°C for 10 hours, and then calcination under a nitrogen atmosphere at 1100°C for 2 hours. The resulting calcined product was pulverized in a planetary ball mill loaded with 5 mm diameter zirconia beads as the medium. Next, the obtained pulverized material was placed in a rotary kiln-type reactor, and under a nitrogen atmosphere, LPG (liquid propane gas) was used as a 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, Comparative Example 9 Except for changing 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) as shown in Table 2, the same procedure as in Example 27 was performed to obtain negative electrode active materials 28-36, C7, and C9.

[0097] Example 37 Dealloying 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, and then dried under reduced pressure at 60°C for 10 hours. To the obtained dry particles, 40% by mass of dispersant (DISPERBYK® 9077: manufactured by BYK Additives & Instruments) was added and left 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, metal salt 1 dispersed in methyl ethyl ketone was mixed so that the atomic ratio of Mn to Si contained in 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 calcination 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 calcined at 1100°C for 2 hours under a nitrogen atmosphere. The resulting calcined product was pulverized in a planetary ball mill loaded with zirconia beads with a diameter of 5 mm as the medium. The obtained pulverized material was subjected to the same procedure (CVD) as in Example 27 to adsorb carbon onto its surface, and then crushed and passed through a 20 μm mesh to obtain the negative electrode active material 37.

[0098] Examples 38-46, Comparative Example 8, Comparative Example 10 Except for changing 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) as shown in Table 2, the same procedure as in Example 37 was performed to obtain negative electrode active materials 37-46, C8, and C10. Furthermore, the following modifications were made in Examples 41 and 42. In Example 41, 2 mm diameter zirconia beads were used as a medium when crushing the resulting calcined product. In Example 42, 10 mm diameter zirconia beads were used as a medium when crushing the resulting calcined product.

[0099] B. Evaluation of porous silicon materials and negative electrode active materials The following physical properties were measured for the porous silicon material and negative electrode active material 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 1-26 and Comparative Examples 1-6, the oxygen and nitrogen atom content (mass%) was measured using an ONH analyzer (LECO "ONH836"). The nitrogen atom content (mass%) of the negative electrode active materials obtained in Examples 27-46 and Comparative Examples 7-10 was measured using an ICP-OES analyzer (Agilent 5110 ICP-OES, manufactured by Agilent Technologies). (1-2) Determination of metallic elements The porous silicon materials obtained in Examples 1-26 and Comparative Examples 1-6 were measured using an EDS analyzer (JEOL Ltd. "JED-2300").

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

[0102] (3) Porosity For the porous silicon materials obtained in Examples 1-26 and Comparative Examples 1-6, a fully automated pore distribution analyzer ("pore Master 60-GT" manufactured by Quanta Chrome) was used to measure the pore distribution in the measurement range of pore diameters from 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 The negative electrode active materials obtained in Examples 27-46 and Comparative Examples 7-10 have an 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). Porosity (%)=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 1-26 and Comparative Examples 1-6, each porous silicon material was fixed onto copper foil, and cross-sections cut using a cross-section polisher (registered trademark; JEOL Ltd. "IB-19520CCP") were observed at arbitrary magnifications (5000 to 50000x) using a scanning electron microscope (SEM (SEM): 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 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 formula, 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 full width at half maximum [rad], and θ is the Bragg angle of the diffraction line peak [rad]. Furthermore, the measurement conditions are 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 was measured using a micro-Raman spectrometer (JASCO Corporation "NRS5500"), and the peak wavelength and its full width at half maximum (cm) derived from Si were 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 (6cm) -1 These 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. The 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 broad peak FWHM indicates the existence of diverse Si-Si bond structure states.

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

[0106] (7) Surface analysis (X-ray photoelectron spectroscopy) We observed the nitrogen atom-derived peak using an X-ray photoelectron spectrometer (FEI Japan, "Thermo Scientific K-Alpha XPS System") and measured the peak value (eV).

[0107] C. Battery characteristics evaluation using half-cells (1-1) A slurry was prepared by mixing 6.9 parts by mass of porous silicon material obtained in Examples 1-26 and Comparative Examples 1-6 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-and-revolution type mixer (Thinky Co., Ltd. "Awatori Rentaro"). (1-2) For the negative electrode active materials obtained in Examples 27-46 and Comparative Examples 7-10, the same procedure as in (1-1) above was performed to prepare a slurry, except that carbon nanotubes were not added as a conductive additive. (2) The slurries obtained in (1-1) and (1-2) above were each deposited as films on copper foil with a thickness of 20 μm. After drying under reduced pressure at 110°C, they were punched out into circles with a diameter of 14 mm, weighing approximately 1.0 g / cm². 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 defined as L0. Next, 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. The open circuit was left for 30 minutes between each charge / discharge cycle. For the negative electrodes formed from porous silicon materials 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 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. Furthermore, the coin-type lithium-ion battery created above was disassembled in its initial fully charged state, the negative electrode was removed, washed with dimethyl carbonate, and air-dried. The thickness of this negative electrode was measured at five points using a thickness gauge, and the average value was taken as L1. The expansion rate of the negative electrode was then calculated using the following formula. Expansion rate (%) = 100 × L1 / L0

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

[0110] [Table 1]

[0111] [Table 2]

[0112] D. Evaluation of battery characteristics in all-solid-state batteries using porous silicon materials. Example 47 In Example 2, 60 parts by mass of porous silicon material 2, 35 parts by mass of β-Li3PS4 (manufactured by NEI Corporation) as a solid electrolyte, 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 material. The obtained negative electrode composite material was pressed at 20 MPa to produce a negative electrode composite material layer. On the other hand, a solid electrolytic layer was fabricated by pressing the above solid electrolyte at 30 MPa. Furthermore, by pressing Li foil (manufactured by Honjo Metal Co., Ltd.) and In foil (manufactured by Nihon Handa Co., Ltd.) at 30 MPa, a Li-In alloy foil was obtained to serve as the positive electrode. Then, the negative electrode mixture layer, solid electrolytic layer, and Li-In alloy foil prepared as described above are stacked in this order to create a surface pressure of 5 t / cm². 2 All-solid-state batteries for evaluation were fabricated by tightly bonding the layers together, sealing them with tabbed laminate, and pressing them at 60 MPa to create a laminated structure. 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 battery were evaluated at 45°C under the conditions of initial constant-current / constant-voltage charging at 0.3mA down to -0.57V, followed by constant-current discharge at 0.3mA down to 0.88V. The results are shown in Table 3.

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

[0114] [Table 3]

[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. [Industrial applicability]

[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 includes 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 with respect 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, based on 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 is calculated using the following formula (1) １ The porous silicon material according to claim 1, wherein the percentage is more than 20% and less than 95%. Q 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 with 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 vicinity of the interface between the silicon domain particles and the voids contains an element N.

12. A method for producing a porous silicon material according to any one of claims 1 to 11, comprising the following steps. (i) Steps to prepare 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 to obtain a porous silicon material by heat-treating the porous material obtained in step (ii) in an inert gas atmosphere containing nitrogen gas at a temperature of 700°C to 1100°C.

13. A method for producing a porous silicon material according to any one of claims 1 to 11, comprising the following steps. (i) Steps to prepare 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) above. (iii) A step to obtain a porous silicon material by heat-treating the metal-added porous material obtained in step (iii') in an inert gas atmosphere containing nitrogen gas at a temperature of 700°C to 1100°C.

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 composed 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 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, and the negative electrode active material according to claim 15. Q ２ = 100 × (1-W / r) (2) W: Apparent density of particles (g / cm³) ３ ρ: True density of particles (g / cm³) 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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