Porous silicon-based particles and a method for producing the same, composite particles containing porous silicon-based particles and a method for producing the same, a negative electrode active material having the composite particles, a composition for a secondary battery negative electrode, a secondary battery negative electrode and secondary battery

Abstract

The present invention provides porous silicon-based particles useful as raw materials for negative electrode active materials, which suppress expansion and contraction associated with repeated charging and discharging, and enable the creation of negative electrodes with excellent initial discharge capacity and cycle characteristics; composite particles having a matrix phase containing such porous silicon-based particles; a negative electrode active material containing such composite particles; and a secondary battery having such negative electrode active material. [Solution] Porous silicon-based particles having internal voids, comprising a silicon phase and a non-silicon phase, wherein the content of the silicon phase is 60% by mass or more of the total mass; and composite particles comprising the porous silicon-based particles and a matrix phase enclosing the porous silicon-based particles.

Description

[Technical Field]

[0001] The present invention relates to porous silicon-based particles and a method for producing the same, as well as composite particles containing such porous silicon-based particles and a method for producing the same, a negative electrode active material having the composite particles, a composition for a secondary battery negative electrode, a secondary battery negative electrode, and a secondary battery. More specifically, the present invention relates to composite particles containing porous silicon-based particles and a method for producing the same, which can be suitably applied as a negative electrode active material for a secondary battery, and a secondary battery containing such composite particles in the 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, 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, a technique for creating porous silicon materials by producing alloys of silicon (Si) with metal elements that form a eutectic composition, and then using de-alloying reactions with acids or alkalis, is attracting attention. Patent Document 2 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).

[0005] Furthermore, attempts have been made to form composites of silicon and carbon-based materials, as well as composites composed of silicon and a carbon matrix, which have a porous structure. For example, Patent Document 3 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 to inorganic carbon at a temperature of 400°C or higher under an inert gas atmosphere. The carbon structure formed by the carbonization of lignin is said to have a carbon matrix that can withstand the extreme volume expansion of silicon during charging, has high strength and elasticity, and exhibits excellent cycle stability. Patent Document 4 discloses a particulate material containing a porous carbon skeleton including specific pores and a plurality of nanoscale silicon domains located within the pores, and including a plurality of composite particles having a mass ratio of Si to the porous carbon skeleton within a specific range. By including a space portion within the porous carbon skeleton, it is said that a sufficient capacity retention rate can be achieved. Patent Document 5 discloses a porous electrode active material containing a silicon-based oxide represented by SiOx (0.5 ≤ x ≤ 1.2), having a predetermined BET specific surface area, including honeycomb-shaped pores on the surface and also having pores inside, with a porosity of 5 to 90%. By physically controlling the crystal structure without changing the crystal structure and forming pores on the surface and inside of the silicon-based oxide, the volume change that occurs during charge and discharge can be efficiently controlled, and it is said to have excellent life characteristics. Patent Document 6 discloses a negative electrode active material containing a silicon-based composite having a bimodal pore structure including mesopores and macropores, represented by SiOa (0 ≤ a < 1), and including a carbon coating layer on the surface. It is said that the initial efficiency and life characteristics can be improved, and the specific surface area is controlled to prevent side reactions with the electrolyte.

Prior Art Documents

Patent Documents

[0006] <​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​While Patent Document 1 specifies the distribution of the average particle size of the porous silicon particles, it does not disclose any details regarding the porosity of the "pores" that contribute to improving charge-discharge characteristics by suppressing degradation due to the expansion and contraction of silicon (Si). Furthermore, the electrochemical etching method (in other words, the anodic oxidation method) and ultrasonic crushing method mentioned as methods for obtaining porous silicon particles are difficult to mass-produce from an industrial standpoint and have challenges in terms of productivity. The porous silicon particles disclosed in Patent Document 2 are obtained using a silicon alloy in which Al and Si are in a composition ratio near that of a eutectic composition. While they exhibit excellent charge-discharge characteristics, their large average pore size makes them less effective as a relaxation phase against Si expansion. Furthermore, using an alloy with a eutectic composition as a raw material limits the Si content, resulting in high manufacturing costs for porous silicon particles when calculated on a silicon-only basis, posing challenges from a productivity standpoint. The Si / C composite obtained by the method described in Patent Document 3 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 particulate material disclosed in Patent Document 4 has problems with its mechanical properties, such as durability against press pressure during negative electrode fabrication, because nanoscale silicon domains are deposited in the voids inside the porous carbon skeleton. The porous electrode active material disclosed in Patent Document 5 inevitably has a high specific surface area of ​​the pores formed, making it easier for lithium ions adsorbed into the electrode active material to be incorporated into the surface film formed by surface side reactions, which tends to reduce the initial charge-discharge efficiency. The negative electrode using the silicon-based composite negative electrode active material disclosed in Patent Document 6 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. 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.

[0008] The inventors investigated the phase composition of porous silicon materials and the pore size of porous silicon materials. As a result, they found that composite particles having porous silicon-based particles having a silicon phase and a non-silicon phase in a specific ratio, preferably in which the non-silicon phase contains silicon dioxide and the porosity and pore volume ratio are within a predetermined range, and a matrix phase enclosing such porous silicon-based particles, can improve charge-discharge characteristics. They also found that such composite particles can suppress Si expansion and contraction associated with charge-discharge due to their voids, thereby improving cycle characteristics. Furthermore, they found that such porous silicon-based particles can be suitably manufactured from specific silicon oxide particles.

[0009] The object of the present invention is to provide porous silicon-based particles useful as raw materials for negative electrode active materials, 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. The object of the present invention is also to provide composite particles having a matrix phase containing such porous silicon-based particles, a method for producing the same, a negative electrode active material containing such composite particles, and a secondary battery having such negative electrode active material. [Means for solving the problem]

[0010] The present invention has the following aspects. [1] A porous silicon-based particle having internal voids, comprising a silicon phase and a non-silicon phase, wherein the content of the silicon phase is 60% by mass or more of the total mass. [2] The porous silicon-based particles of [1], wherein the non-silicon phase contains silicon dioxide as a constituent component. [3] The porous silicon-based particle of [1] or [2], wherein the non-silicon phase contains one or more elements selected from the group consisting of Ag, Al, Bi, C, Cu, Li, Mg, Ni, Sn, Ti, and Zn. [4] A porous silicon-based particle of any of the following types [1] to [3], wherein the porosity calculated by the following formula (I) is between 10 and 90%. Porosity (%)=100×(Vp / (ν+Vp)) (I) Vp: Total pore volume (cm³) in the pore size range of porous silicon-based particles from 0.4 nm to 400 μm. 3 / g) ν: Specific volume (cm³) of porous silicon-based particles 3 / g) [5] A porous silicon-based particle of any of the following types [1] to [4], wherein the mesopore volume fraction calculated by the following formula (II) is 50 to 90%. Mesopore volume percentage (%) = 100 × (Vpm / Vp) (II) Vpm: Total pore volume (cm³) in the pore size range of porous silicon-based particles from 2 nm to 50 nm. 3 / g) Vp: Total pore volume (cm³) in the pore size range of porous silicon-based particles from 0.4 nm to 400 μm. 3 / g) [6] A porous silicon-based particle of any of the following types [1] to [5], in which the average pore size, most frequent pore size, and median pore size are all in the pore size range of 2 nm to 50 nm. [7] A porous silicon particle of any of [1] to [6], wherein the void is formed throughout the entire particle.

[0011] [8] A composite particle comprising porous silicon-based particles of any of [1] to [7] and a matrix phase containing the porous silicon-based particles. [9] The composite particle according to [8], wherein the content of the porous silicon-based particles is 5 to 90% by mass of the total mass of the composite particle.

[10] A composite particle of [8] or [9] in which the porosity of the matrix phase is lower than the porosity of the porous silicon-based particles.

[11] A composite particle having closed pores inside, one of the [8] to

[10] .

[12] A composite particle of any of the following [8] to

[11] , having a closed porosity of 15 to 85% calculated by the following formula (III). Closed porosity (%)=100×(1-ρb / ρt) (III) ρb: Apparent density of composite particles measured by gas displacement method (g / cm³) 3 ) ρt: True density of composite particles (g / cm³) 3 ) Here, the true density ρt of the composite particles is calculated from equation (IV) below. ρt=(ws+wm) / (ws / ρs+wm / ρm) (IV) ws: Mass percentage of porous silicon-based particles in the entire composite particle system wm: Mass percentage of the matrix phase in the entire composite particle ρs: True density of porous silicon-based particles (g / cm³) 3 ) ρm: True density of the matrix phase (g / cm³) 3 )

[13] The matrix phase is a composite particle of any of [8] to

[12] containing the element carbon.

[14] A composite particle of any of [8] to

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

[15] A composite particle of any of [8] to

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

[0012]

[16] A method for producing porous silicon-based particles according to any of [1] to [7], comprising the following steps: (i) A process of heat-treating silicon oxide particles represented by the formula SiOx (wherein x is a positive number greater than or equal to 0 and less than 2) in an inert gas atmosphere at a temperature in the range of 800°C to 1350°C. (ii) A step of etching the heat-treated silicon oxide by contacting it with an etching solution to obtain porous silicon-based particles.

[17] A method for producing porous silicon-based particles according to any of [1] to [7], comprising the following steps: (i) A process of heat-treating silicon oxide particles represented by the formula SiOx (wherein x is a positive number greater than or equal to 0 and less than 2) in an inert gas atmosphere at a temperature in the range of 800°C to 1350°C. (i') A step of contacting the heat-treated silicon oxide with a solution containing a fluorine-based compound and a metal precursor to deposit metal particles on the surface of the heat-treated silicon oxide. (ii) A step of etching the silicon oxide to which the metal particles are attached by contacting it with an etching solution to obtain porous silicon-based particles.

[0013] A method for producing composite particles according to any of [8] to

[15] , comprising the step of forming a matrix phase that contains porous silicon-based particles according to any of [1] to [7].

[19] A negative electrode active material containing any composite particles from [8] to

[15] . A composition for secondary battery negative electrodes, containing the negative electrode active material

[20]

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

[21]

[20] .

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

[21] . [Effects of the Invention]

[0014] According to the present invention, it is possible to provide porous silicon-based particles useful as raw materials for negative electrode active materials and a method for producing the same, which can be used to create a negative electrode that has excellent initial discharge capacity and cycle characteristics, by suppressing expansion and contraction associated with repeated charging and discharging. Furthermore, according to the present invention, it is possible to provide composite particles having a matrix phase containing such porous silicon-based particles and a method for producing the same, a negative electrode active material containing such composite particles, and a secondary battery having such negative electrode active material that has excellent battery characteristics such as charge and discharge characteristics. [Modes for carrying out the invention]

[0015] <Porous silicon-based particles> The porous silicon-based particles of the present invention consist of a silicon phase and a non-silicon phase, wherein the content of the silicon phase is 60% by mass or more of the total mass, and the porous silicon-based particles have voids inside. The silicon phase content in the porous silicon-based particles of the present invention is preferably 65% ​​by mass or more, and more preferably 70% by mass or more. Furthermore, the silicon phase content is preferably 99% by mass or less, and more preferably 95% by mass or less. Having the silicon phase content within the above range makes it easier to improve the capacity during charging and discharging and the cycle characteristics when the composite particles of the present invention, described later, are used as a negative electrode active material. The porous silicon-based particles of the present invention preferably have the non-silicon phase containing silicon dioxide as a constituent component. When the non-silicon phase contains silicon dioxide, it tends to act as a sufficient restraint phase in Si expansion during charging, while imparting a certain mechanical strength against the shrinkage during discharging. Therefore, it is easy to improve the cycle characteristics of a secondary battery using, as a negative electrode active material, the composite particles of the present invention having a matrix phase encapsulating the porous silicon-based particles of the present invention.

[0016] Further, in the porous silicon-based particles of the present invention, the non-silicon phase may contain one or more elements selected from the group consisting of Ag, Al, Bi, C, Cu, Li, Mg, Ni, Sn, Ti, and Zn. When the non-silicon phase contains the one or more elements, the content of such elements is preferably more than 0.5% by mass and less than 10% by mass, and more preferably more than 1% by mass and less than 5% by mass, based on the total mass of the porous silicon-based particles of the present invention. When the non-silicon phase contains the one or more elements within the above range, it is easy to sufficiently form micropores in the porous silicon-based particles of the present invention and to act as a restraint phase against the expansion of Si. Also, it is preferable from the viewpoint that the ionic conductivity is improved to facilitate the effective diffusion of lithium ions and that a large amount of impurities does not remain in the porous silicon-based particles of the present invention.

[0017] The porous silicon-based particles of the present invention preferably have a porosity calculated by the following formula (I) of 10 to 90%. The porosity of the porous silicon-based particles of the present invention is more preferably 15% or more, and even more preferably 20% or more. The porosity of the porous silicon-based particles of the present invention is more preferably 80% or less, and even more preferably 70% or less. Porosity (%) = 100×(Vp / (ν + Vp)) (I) Vp: Total pore volume (cm 3 / g) in the pore diameter range of 0.4 nm to 400 μm of the porous silicon-based particles ν: Specific volume (cm 3 / g) of the porous silicon-based particles When the porosity is within the aforementioned range, and the composite particles of the present invention, described later, which have a matrix phase containing the porous silicon-based particles of the present invention, are used as the negative electrode active material, both the volume expansion due to alloying of silicon and lithium during charging and the volume contraction when lithium is released during discharge can be sufficiently buffered, thereby suppressing volume changes. Furthermore, the strength of the porous silicon-based particles of the present invention within such composite particles does not easily decrease, and pulverization due to volume changes can be prevented. Therefore, the expansion of the negative electrode containing the porous silicon-based particles of the present invention is suppressed, and the battery characteristics of a secondary battery equipped with such a negative electrode are easily improved.

[0018] Furthermore, the porous silicon-based particles of the present invention preferably have a mesopore volume ratio of 50 to 90%, calculated by the following formula (II). Mesopore volume percentage (%) = 100 × (Vpm / Vp) (II) Vpm: Total pore volume (cm³) in the pore size range of porous silicon-based particles from 2 nm to 50 nm. 3 / g) Vp: Total pore volume (cm³) in the pore size range of porous silicon-based particles from 0.4 nm to 400 μm. 3 / g) In this specification, the pore size region of 2 nm to 50 nm is also referred to as the "mesopore region," and the pore size region of 0.4 nm to 400 μm is also referred to as the "total pore size region." In other words, the mesopore volume ratio calculated by formula (II) is the ratio of the total pore volume of the pores in the mesopore region to the total pore volume of the total pore region of the porous silicon-based particles of the present invention. Because the mesopore volume ratio of the porous silicon-based particles of the present invention falls within the aforementioned range, the pores are easily maintained even when the matrix phase is formed in the composite particles of the present invention, which have a matrix phase containing the porous silicon-based particles of the present invention, as described later. As a result, when the composite particles of the present invention are used as a negative electrode active material, the expansion and contraction of the negative electrode during charging and discharging can be effectively suppressed, making it easier to improve cycle characteristics. Preferably, the porous silicon-based particles of the present invention have average pore diameter, most frequent pore diameter, and median pore diameter all within the pore diameter range of 2 nm to 50 nm (mesopore region). Because the average pore diameter, most frequent pore diameter, and median pore diameter of the porous silicon-based particles of the present invention are within this range, the pores are easily maintained even when a matrix phase is formed in the composite particles of the present invention, as described later. As a result, when the composite particles of the present invention are used as a negative electrode active material, expansion and contraction of the negative electrode during charging and discharging can be effectively suppressed, making it easier to improve cycle characteristics. In the porous silicon-based particles of the present invention, it is preferable that the voids are formed throughout the entire porous silicon-based particle. The porous silicon-based particles of the present invention, in which the mesopore volume fraction, average pore diameter, most frequent pore diameter, and median pore diameter are within the ranges described above, are preferably obtained by the manufacturing method described later.

[0019] The porous silicon-based particles of the present invention preferably have an average particle size (D50) in the range of 50 nm to 30 μm, and more preferably in the range of 100 nm to 20 μm. The shape of the particles is not particularly limited, but is generally preferred to be spherical. When the D50 of the porous silicon-based particles of the present invention is within the range described above, the capacity and cycle characteristics of a secondary battery using the composite particles of the present invention, described later, which have a matrix phase containing the porous silicon-based particles of the present invention, as the negative electrode active material are more easily improved, and expansion and contraction at the negative electrode are more easily suppressed.

[0020] The porous silicon-based particles of the present invention preferably contain 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. 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. Furthermore, the porous silicon-based particles of the present invention may contain at least a portion of an amorphous silicon component.

[0021] <Method for manufacturing porous silicon-based particles> The porous silicon-based particles 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) A process of heat-treating silicon oxide particles represented by the formula SiOx (wherein x is a positive number greater than or equal to 0 and less than 2) in an inert gas atmosphere at a temperature in the range of 800°C to 1350°C. (ii) A step of etching the heat-treated silicon oxide by contacting it with an etching solution to obtain porous silicon-based particles.

[0022] [Process (i)] In silicon oxide particles represented by the formula SiOx (wherein x is a positive number greater than or equal to 0 and less than 2), (hereinafter also simply referred to as "silicon oxide particles"), x is preferably 0.4 or greater, more preferably 0.5 or greater. Furthermore, x is preferably 1.9 or less, and more preferably 1.8 or less. When x of the silicon oxide particles is within the above range, it is easy to adjust the content and size of silicon dioxide (SiO2) in the silicon oxide particles, and it is easy to control the porosity and pore size of the porous silicon-based particles of the present invention obtained. Note that commercially available silicon oxide particles may be used.

[0023] The average particle size (D50) of the silicon oxide particles is preferably in the range of greater than 0.1 μm and less than 20 μm. More preferably, the D50 of the silicon oxide particles is 0.2 μm or more, and even more preferably 0.5 μm or more. More preferably, the D50 of the silicon oxide particles is 15 μm or less, and even more preferably 10 μm or less. When the D50 of silicon oxide particles is within the aforementioned range, it becomes easier to maintain the strength of the porous silicon-based particles of the present invention obtained from such silicon oxide particles, and it becomes easier to suppress the volume change during charging and discharging of the composite particles of the present invention, which are described later and contain the porous silicon-based particles of the present invention as a constituent component. As a result, the electrical properties such as the cycle characteristics of a secondary battery equipped with a negative electrode containing the composite particles of the present invention tend to improve. Since the D50 of the silicon oxide particles becomes the D50 of the resulting porous silicon-based particles, it is preferable to adjust the average particle size of the silicon oxide particles to a range of 0.1 μm to 10 μm. The D50 of silicon oxide particles and porous silicon-based particles of the present invention is the particle diameter (D50) at which the cumulative volume distribution curve reaches 50% when plotted from the smallest diameter side in 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").

[0024] In step (i), the silicon oxide particles described above are heat-treated in an inert gas atmosphere at a temperature in the range of 800°C to 1350°C. Examples of inert gases include nitrogen gas, helium gas, and argon gas. The heat treatment temperature is preferably 850°C or higher, more preferably 900°C or higher. The heat treatment temperature is preferably 1200°C or lower, more preferably 1100°C or lower. There are no particular restrictions on the heat treatment time, but it is usually preferably between 1 and 12 hours. This heat treatment can disproportionate silicon oxide particles into a silicon phase (Si phase) and a silicon dioxide phase (SiO2 phase), i.e., a silicon phase and a non-silicon phase.

[0025] [Step (ii)] The heat-treated silicon oxide obtained in step (i) above is brought into contact with an etching solution and etched to obtain the porous silicon-based particles of the present invention. As the etching solution, hydrofluoric acid (an aqueous solution of hydrogen fluoride) can be used alone, or a mixture of hydrofluoric acid and hydrogen peroxide can be suitably used. The concentration of hydrogen fluoride in the hydrofluoric acid is not particularly limited and can usually be appropriately selected in the range of 1 to 50% by mass. Similarly, the concentration and amount of hydrogen peroxide used when mixed with hydrofluoric acid are not particularly limited, but it is generally preferable to mix them so that hydrogen peroxide is present in the range of 1 to 10% by mass relative to the hydrogen fluoride, and use this mixture as the etching solution. According to this method, further pores can be formed inside pores (macropores) with a diameter of 50 nm or more that have formed in the silicon oxide, and the mesopore volume ratio of the porous silicon-based particles obtained according to the present invention can be easily controlled to the range defined in the present invention by these internally formed pores. Pores in the so-called nanopore region, with a pore diameter of less than 2 nm, are prone to clogging due to surface oxidation of the silicon oxide particles themselves or sintering during firing. On the other hand, in the case of pores with a pore diameter of 50 nm or more (macropores), the organosilicon polymer material, which is suitably used to form the matrix phase containing the porous silicon-based particles of the present invention as described later, tends to penetrate into the interior of such macropores and form the matrix phase, making it difficult to maintain such pores. As a result, the resulting porous silicon-based particles have fewer voids, and the suppression of silicon expansion and contraction when used as a negative electrode active material tends to be insufficient. The porous silicon-based particles obtained in step (ii) are preferably further washed with distilled water or an aliphatic alcohol having 1 to 5 carbon atoms, such as ethanol or isopropanol, and then dried. Drying can be carried out using a known dryer, vacuum dryer, etc., at a temperature in the range of 25 to 200°C, under atmospheric pressure in an inert gas atmosphere, or under reduced pressure for a period of 1 minute to 24 hours.

[0026] The porous silicon-based particles of the present invention can also be produced by a manufacturing method (hereinafter also referred to as "Manufacturing Method 2") which includes the following steps. (i) A process of heat-treating silicon oxide particles represented by the formula SiOx (wherein x is a positive number greater than or equal to 0 and less than 2) in an inert gas atmosphere at a temperature in the range of 800°C to 1350°C. (i') A step of contacting the heat-treated silicon oxide with a solution containing a fluorine-based compound and a metal precursor to deposit metal particles on the surface of the heat-treated silicon oxide. (ii) A step of etching the silicon oxide to which the metal particles are attached by contacting it with an etching solution to obtain porous silicon-based particles. 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.

[0027] In step (i') of manufacturing method 2, the heat-treated silicon oxide obtained in step (i) is brought into contact with a solution containing a fluorine-based compound and a metal precursor, thereby electrolessly depositing metal particles onto the surface of the heat-treated silicon oxide. Solutions containing fluorinated compounds and metal precursors can be prepared by mixing an aqueous solution of a fluorinated compound such as hydrogen fluoride, fluorosilicic acid (H2SiF6), or ammonium fluoride (NH4F) with an aqueous solution of a metal salt of one or more elements selected from the group consisting of Ag, Al, Bi, C, Cu, Li, Mg, Ni, Sn, Ti, and Zn. Examples of such metal salts include inorganic metal salts such as hydrochloride, nitrate, and sulfate; and metal salts having organic anions such as alkoxy anions, aryloxy anions, carboxylic acid anions, phosphate anions with organic groups, phosphite anions with organic groups, and sulfonate anions with organic groups. The mixing ratio of the fluorine compound to the metal salt is not particularly limited. The mass ratio of the metal salt to the fluorine compound is usually preferably in the range of 0.01 to 50, and more preferably in the range of 0.05 to 10. In manufacturing method 2, a metal element can be introduced into the porous silicon-based particles of the present invention in step (i'). That is, in manufacturing method 2, one or more of the above-mentioned metal elements can be introduced as metal elements contained in the porous silicon-based particles of the present invention. It is presumed that the metal element will adhere to the surface of the silicon oxide particles and readily exhibit the effects described above. In manufacturing method 2, if necessary, the process may further include a step of removing metal fine particles adhering to the heat-treated silicon oxide surface using an acidic solution after etching.

[0028] The porous silicon material of the present invention can also be manufactured by a manufacturing method (hereinafter also referred to as "manufacturing method 3") which includes the steps of (a1) preparing an alloy containing Si, and (a2) treating the alloy prepared in step (a1) with an acid or alkali to obtain a porous material. In step (a1), the metal element used as the raw material for the alloy is preferably one or more selected from the group consisting of Al, Mg, Sn, and Zn, with Al being more preferred. The silicon and metal element used as the raw material 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. For alloys containing Si, it is preferable to atomize the molten metal and use it as alloy particles. Methods for atomization include the single-roll liquid quenching method using a single-roll casting machine, and methods using water atomization equipment or gas atomization equipment. A porous material is obtained by a step (a2) in which an alloy containing Si is treated 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 60°C for a period of 1 to 5 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 of, for example, 25 to 200°C, in an air or inert gas atmosphere, under atmospheric pressure or reduced pressure conditions, for a period of 1 minute to 24 hours. Examples of inert gases include nitrogen gas, helium gas, and argon gas. Furthermore, if drying is carried out in an air atmosphere, silicon dioxide can be formed as a non-silicon phase near the surface of the resulting porous material. Alternatively, silicon dioxide may be formed near the surface of the porous material by further calcining the porous material dried in an inert gas atmosphere under an oxygen-containing gas atmosphere.

[0029] The porous silicon-based particles of the present invention obtained as described above have voids that can mitigate volume changes associated with the expansion and contraction of silicon (Si) during charging and discharging. Therefore, in the negative electrode of a secondary battery containing the composite particles of the present invention, as described later, expansion can be suppressed and pulverization can be suppressed.

[0030] <Composite particles> The present invention also relates to composite particles composed of the porous silicon-based particles of the present invention described above and a matrix phase enclosing the porous silicon-based particles. In the composite particles of the present invention, the content of the porous silicon-based particles is preferably 5 to 90% by mass of the total mass of the composite particles of the present invention, and more preferably 10 to 85% by mass, from the viewpoint of improving the capacity and cycle characteristics when used as a negative electrode active material. The composite particles of the present invention have voids in the porous silicon-based particles of the present invention described above, and the matrix phase may also have voids. In other words, the composite particles of the present invention can be said to be porous particles. When the matrix phase has voids, the porosity of the matrix phase is preferably in the range of 0.1 to 75%, more preferably in the range of 0.2 to 50%, and even more preferably in the range of 0.3 to 30%. In the composite particles of the present invention, it is preferable that the porosity of the matrix phase is lower than that of the porous silicon-based particles. In other words, the matrix phase in the composite particles of the present invention may have voids, but it is particularly preferable that the matrix phase has no voids, or, if voids exist, that the porosity of the matrix phase is in the range of 0.1 to 10%, from the viewpoint of easily functioning as a relaxation phase that suppresses Si expansion. The porosity of the matrix phase in the composite particles of the present invention can be determined, for example, by observation using a scanning electron microscope (SEM).

[0031] The composite particles of the present invention preferably have closed pores inside. Since the composite particles of the present invention have a structure in which porous silicon-based particles are encapsulated in a matrix phase, any voids that may exist inside the porous silicon-based particles or at the interface between the porous silicon particles and the matrix phase are all contained within the matrix phase. Furthermore, even with the presence of the matrix phase, the mesopore volume ratio in the porous silicon-based particles is easily maintained, so Si expansion can be suppressed in a secondary battery using the composite particles of the present invention as the negative electrode active material, and the cycle characteristics can also be improved. In this specification, these voids that are closed within the composite particles are referred to as "closed pores." The composite particles of the present invention preferably have a closed porosity of 15 to 85%, calculated from the following formula (III). Closed porosity (%)=100×(1-ρb / ρt) (III) ρb: Apparent density of composite particles measured by gas displacement method (g / cm³) 3 ) ρt: True density of composite particles (g / cm³) 3 ) Here, the true density ρt of the composite particles is calculated from equation (IV) below. ρt=(ws+wm) / (ws / ρs+wm / ρm) (IV) ws: Mass percentage of porous silicon-based particles in the entire composite particle system wm: Mass percentage of the matrix phase in the entire composite particle ρs: True density of porous silicon-based particles (g / cm³) 3 ) ρm: True density of the matrix phase (g / cm³) 3 )

[0032] The composite particles of the present invention preferably have an average particle size (D50) in the range of 50 nm to 30 μm, and more preferably in the range of 100 nm to 20 μm. The shape of the particles is not particularly limited, but is generally preferably spherical. When the D50 of the composite particles of the present invention is within the range described above, the capacity and cycle characteristics of a secondary battery using the composite particles of the present invention as the negative electrode active material are more easily improved, and expansion and contraction at the negative electrode are more easily suppressed.

[0033] The specific surface area of ​​the composite particles of the present invention is 0.1 m². 2 / g or more 30m 2 Preferably, it should be less than or equal to / g, and 0.5m 2 / g or more 15m 2 It is more preferable that the specific surface area is less than or equal to / g. When the specific surface area is within the above range, it is easier to maintain an appropriate amount of solvent absorption during electrode fabrication, and it is also easier to maintain an appropriate amount of binder used to maintain bonding properties. Furthermore, an improvement in initial efficiency can be expected by suppressing side reactions with the electrolyte.

[0034] In the composite particles of the present invention, the matrix phase preferably contains carbon. In this case, a carbon layer may be formed on at least a part or the entire surface of the porous silicon-based particles of the present invention, and such carbon layer may be the matrix phase. There are no particular restrictions on the method of forming the carbon layer, but for example, the CVD method described later is preferred. When the composite particles of the present invention have a matrix phase containing element C (carbon), the porous silicon material described above is dispersed in the matrix phase. The matrix phase preferably contains one or more elements from the group consisting of Si, O, and C, and more preferably contains at least silicon oxycarbide (SiOC) and a carbonaceous phase. In other words, the composite particles of the present invention are preferably composed of the porous silicon-based particles of the present invention described above and a matrix phase containing carbon elements, and more preferably composite particles (hereinafter also referred to as "the composite particles") in which the matrix phase contains at least silicon oxycarbide and a carbonaceous phase.

[0035] The matrix phase in these composite particles is preferably composed of a compound containing silicon, oxygen, and carbon. Such a compound containing silicon, oxygen, and carbon preferably has a three-dimensional network structure of the silicon-oxygen-carbon skeleton of SiOC (silicon oxycarbide) and a structure containing 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.

[0036] When the matrix phase is composed of compounds containing silicon, oxygen, and carbon, and the structure includes a three-dimensional network structure of the silicon-oxygen-carbon skeleton of SiOC and free carbon, the silicon-oxygen-carbon skeleton in the matrix phase has high chemical stability, and by forming a composite structure with free carbon, the diffusion of lithium ions becomes easier as the electron transition resistance is reduced. The porous silicon-based particles described above are enclosed within the composite structure of the silicon-oxygen-carbon skeleton and free carbon, in other words, tightly enclosed, thereby preventing direct contact between the porous silicon-based particles and the electrolyte. As a result, when these composite particles are used as the negative electrode active material, the porous silicon-based particles in the negative electrode play a major role in the manifestation of charge and discharge performance, while chemical reactions between the surface of the porous silicon-based particles and the electrolyte during charge and discharge are avoided. This is thought to minimize the degradation of the performance of the porous silicon-based particles themselves that constitute the composite particles. 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.

[0037] When the compounds constituting the matrix phase contain silicon, oxygen, and carbon, it is preferable that the matrix phase contains a compound represented by the formula SiOxCy (wherein x represents the molar ratio (atomic ratio) of oxygen to silicon, and y represents the molar ratio (atomic ratio) of carbon to silicon). When these composite particles are used as a negative electrode active material in a secondary battery, from the viewpoint of achieving a superior balance between charge / discharge performance and capacity retention, 1 ≤ x < 2 is preferred, 1 ≤ x ≤ 1.9 is more preferred, and 1 ≤ x ≤ 1.8 is even more preferred. When the composite particles are used as a negative electrode active material in a secondary battery, from the viewpoint of the balance between charge-discharge performance and initial Coulomb efficiency, 1 ≦ y ≦ 20 is preferable, and 1.2 ≦ y ≦ 15 is more preferable.

[0038] 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 are precursors of the matrix phase and have an atomic group containing nitrogen as a functional group in their molecules, and nitrogen gas used in the firing process, etc., and can be introduced into the matrix phase. When the matrix phase contains nitrogen, the charge-discharge performance and capacity retention rate of the composite particles 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 the composite particles are used as a negative electrode active material in a secondary battery, 1 ≦ x ≦ 2, 1 ≦ y ≦ 20, 0 < z ≦ 0.5 are preferable, and 1 ≦ x ≦ 1.9, 1.2 ≦ y ≦ 15, 0 < z ≦ 0.4 are more preferable. Note that x, y, and z are all positive numbers. x, y, and z can be obtained by measuring the mass content of each element and then converting it to a molar ratio (atomic ratio). At this time, the contents of oxygen and carbon can be quantified by using an inorganic element analyzer, and the content of silicon can be quantified by using an ICP emission spectrometer (ICP-OES).

[0039] Although the measurement of x, y, and z is preferably performed by the above method, it may also be obtained by performing a local analysis of the composite particles, acquiring a large number of measurement points of the content ratio data obtained thereby, and extrapolating the content ratio of the entire composite particles. Examples of the local analysis include energy dispersive X-ray spectroscopy (SEM-EDX) and electron probe microanalyzer (EPMA).

[0040] These composite particles can be suitably obtained by a manufacturing method that includes a step of forming a matrix phase containing the porous silicon particles described above. The process of forming the matrix phase includes, for example, a process of forming a matrix phase consisting of carbon elements on at least part or all of the surface of porous silicon-based particles by CVD (Chemical Vapor Deposition) or coating using a spray drying device. In the case of CVD, there are no particular restrictions on the carbon source, such as LPG (liquid propane gas). The detailed conditions for the CVD method vary depending on the thickness of the matrix phase to be formed, but it can usually be carried out in an inert gas atmosphere such as nitrogen gas, helium gas, or argon gas, in a pressure range of 0.8 to 1 atm, a temperature range of 750 to 950°C, and for 10 to 360 minutes.

[0041] Furthermore, for example, a precursor containing the above-mentioned porous silicon-based particles and an organosilicon-based polymer material can be obtained by the following process, and by calcining this precursor in an inert gas atmosphere, a matrix phase containing porous silicon particles can be formed, thereby enabling the suitable production of the composite particles. (i) Add an organic solvent to porous silicon particles and stir to obtain a slurry. (ii) After mixing the slurry with an organosilicon polymer material, a precursor is obtained by desolvation and drying. (iii) The precursor obtained in (ii) above is calcined in an inert gas atmosphere.

[0042] Examples of organic solvents to be added to porous silicon particles 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 porous silicon-based particles 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 particles. Examples of non-aqueous dispersants include 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 polyphosphates.

[0043] Next, the slurry is mixed with an organosilicon polymer material, and then desolvated and dried to obtain a precursor. The organosilicon polymer material contained in the 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 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 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.

[0044] 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.

[0045] [ka]

[0046] [ka]

[0047] (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 3Examples 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 3 Examples of aryl groups represented by each include phenyl group, naphthyl group, 2-methylphenyl group, 3-methylphenyl group, 4-methylphenyl group, 4-vinylphenyl group, and 3-isopropylphenyl group. 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.

[0048] 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.

[0049] 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.

[0050] [ka]

[0051] (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.

[0052] 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).

[0053] [ka]

[0054] (In the formula, R 4 represents a monovalent organic group, R 5 (where b represents a halogen atom, alkoxy group, acyloxy group, aryloxy group, mercapto group, amino group, amide group, aminooxy group, iminooxy group, or alkenyloxy group. b is an integer from 0 to 2.)

[0055] 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.

[0056] 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.

[0057] [ka]

[0058] 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.).

[0059] 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.).

[0060] 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.

[0061] 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.

[0062] The composite particles are obtained by calcining the 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 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 composite particles. 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.

[0063] The composite particles of the present invention may have their surfaces coated with a coating material. The coating material is preferably a substance that exhibits electronic conductivity, lithium ion conductivity, and an effect of suppressing the decomposition of the electrolyte, and examples of electronically conductive substances include carbon, titanium, and nickel. When coating the composite particles of the present invention with a coating material, the method is not particularly limited and examples include methods using CVD (Chemical Vapor Deposition) and spray drying.

[0064] <Negative electrode active material> The present invention also relates to a negative electrode active material containing the composite particles of the present invention as described above. The negative electrode active material of the present invention may consist of the composite particles of the present invention alone, or it may contain the composite particles of the present invention and an active material such as a carbonaceous material. It may also contain other necessary third components.

[0065] When the negative electrode active material of the present invention contains an active material such as a carbonaceous material or other necessary third components, the content of the composite particles of the present invention relative to the total mass of the negative electrode active material of the present invention is preferably 10% by mass or more and 90% by mass or less, and more preferably 20% by mass or more and 80% by mass or less. When the content of the composite particles of the present invention is within the above range, the discharge capacity and cycle characteristics during the initial charge tend to be excellent. 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 ​​0.1 m². 2 / g or more 50m 2 It is preferable that the amount is less than or equal to / g.

[0066] <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.

[0067] 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.

[0068] 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.

[0069] The content of organic binder in the negative electrode material layer of the lithium-ion secondary battery negative electrode is preferably 1 to 30% by mass, more preferably 2 to 20% by mass, and even more preferably 3 to 15% by mass. When the 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] The present invention has described porous silicon-based particles and a method for producing the same, composite particles having a matrix phase containing the porous silicon-based particles and a method for producing the same, a negative electrode active material containing the composite particles, 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. However, the present invention is not limited to the configurations of the embodiments described above. For example, the porous silicon-based particles of the present invention, composite particles having a matrix phase containing the porous silicon-based particles, a negative electrode active material containing the composite particles, 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 may each have additional configurations in the above-described embodiments, or may be replaced with any configuration that exhibits similar functions. Furthermore, the method for producing porous silicon-based particles and the method for producing composite particles of the present invention may have additional steps for any other purpose in the above-described embodiments, or may be replaced with any steps that exhibit similar effects. [Examples]

[0084] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the following examples. Unless otherwise specified, "parts" and "%" are based on mass. In the examples, the half-cells used have a negative electrode mainly composed of a negative electrode active material containing the porous silicon material of the present invention, and a simple evaluation was performed using metallic lithium as the counter electrode. This was done to more clearly compare the initial discharge capacity of the porous silicon material of the present invention itself. The raw materials used in the examples and comparative examples are shown below. <Silicon oxide particles> • Silicon oxide particles 1: Spherical particles represented by the formula SiOx (where x is 1.6), D50 = 5 μm, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. • Silicon oxide particles 2: Silicon oxide particles 1 were ground using a ball mill (Frecce Classic Line P-5) at 300 rpm for 30 minutes, and then subjected to a 20 μm mesh pass, resulting in particles with a D50 of 1.9 μm. • Silicon oxide particles 3: Silicon oxide particles 1 were subjected to CVD treatment at 900°C for 90 minutes in a nitrogen gas atmosphere at 1 atom (at atmospheric pressure) using LPG (liquid propane gas) as the carbon source, and a 20 μm mesh pass was applied to the resulting particles, with a D50 of 6.1 μm. • Silicon oxide particles 4: Spherical particles of disproportionated SiO obtained by calcining silicon oxide particles 1 at 1100°C for 12 hours under a nitrogen atmosphere.

[0085] <matrix> • Resin 1: "TD-141-40" (product name, phenolic resin, manufactured by DIC Corporation) • Resin 2: "SSA-500" (product name, polysiloxane resin, manufactured by DIC Corporation)

[0086] A-1. Examples of production methods for porous silicon-based particles Example 1 Silicon oxide particles 1 were dried under reduced pressure at 110°C for 6 hours, then placed in an alumina crucible and calcined under a nitrogen atmosphere at 1100°C for 6 hours. After passing the calcined material through a 20 μm mesh, 10 g of it was added little by little to 300 ml of hydrofluoric acid aqueous solution (HF concentration 5% by mass), while maintaining the internal temperature below 50°C. After the addition was complete, the mixture was allowed to react for 2 hours. The reaction mixture was filtered by suction through a 1 μm filter, washed sequentially with distilled water and ethanol, and then dried under reduced pressure at 60°C for 10 hours to obtain porous silicon-based particles 1 as a brown powder.

[0087] Example 2 In Example 1, the same procedure as in Example 1 was followed, except that a hydrofluoric acid-isopropanol mixed solution (HF concentration 5% by mass, water:isopropanol = 75:25 (mass ratio)) was used instead of an aqueous hydrofluoric acid solution (HF concentration 5% by mass), to obtain porous silicon-based particles 2.

[0088] Example 3 In Example 1, the same procedure was followed except that the HF concentration of the hydrofluoric acid aqueous solution was changed from 5% by mass to 10% by mass, and the reaction time was changed from 2 hours to 30 minutes, to obtain porous silicon-based particles 3.

[0089] Example 4 In Example 1, the same procedure as in Example 1 was followed, except that silicon oxide particles 1 were used as is without vacuum drying and calcination, to obtain porous silicon-based particles 4.

[0090] Example 5 In Example 1, the HF concentration of the hydrofluoric acid aqueous solution was changed from 5% by mass to 3% by mass, and the post-reaction washing was performed using only ethanol. The same procedure as in Example 1 was followed to obtain porous silicon-based particles 5.

[0091] Example 6 In Example 1, the same procedure was performed as in Example 1, except that silicon oxide particle 3 was used instead of silicon oxide particle 1, to obtain porous silicon-based particle 6.

[0092] Example 7 In Example 1, the same procedure was followed as in Example 1, except that silicon oxide particle 3 was used instead of silicon oxide particle 1, and a hydrofluoric acid-ethanol mixed solution (HF concentration 5% by mass, water:ethanol = 75:25 (mass ratio)) was used instead of an aqueous hydrofluoric acid solution (HF concentration 5% by mass). Porous silicon-based particle 7 was obtained.

[0093] Example 8 Silicon oxide particles 2 were added to a solution prepared by mixing 1 mmol / L silver nitrate (manufactured by Kanto Chemical Co., Ltd.) with a 10% by mass hydrofluoric acid aqueous solution, and stirred at 25°C for 10 minutes to form silver nanoparticles on the surface of silicon oxide particles 2. Next, an aqueous solution containing hydrofluoric acid and hydrogen peroxide in a ratio of 10:1 (by mass) (total content of hydrofluoric acid and hydrogen peroxide: 5% by mass) was added, and the mixture was stirred at 25°C for 15 minutes to form micropores in the silicon oxide particles 2. After separating the particles from the mixture, washing them with distilled water, drying them, stirring them in a 1M aqueous nitric acid solution, separating them again, washing them with distilled water, and drying them under reduced pressure at 60°C for 10 hours, porous silicon-based particles 8 were obtained.

[0094] Example 9 In Example 1, the same procedure as in Example 1 was followed, except that a hydrofluoric acid-ethanol mixed solution (HF concentration 5% by mass, water:ethanol = 75:25 (mass ratio)) was used instead of an aqueous hydrofluoric acid solution (HF concentration 5% by mass) to obtain porous silicon-based particles 9.

[0095] Example 10 In Example 8, the same procedure was followed except that silicon oxide particles 3 were used instead of silicon oxide particles 2, a 1 mmol / L copper nitrate aqueous solution was used instead of a 1 mmol / L silver nitrate aqueous solution, and the reaction time was changed to 30 minutes, to obtain porous silicon-based particles 10.

[0096] Example 11 In Example 10, the same procedure as in Example 1 was followed, except that a hydrofluoric acid-ethanol mixed solution (HF concentration 5% by mass, water:ethanol = 75:25 (mass ratio)) was used instead of an aqueous hydrofluoric acid solution (HF concentration 5% by mass), to obtain porous silicon-based particles 11.

[0097] Example 12 Aluminum (manufactured by Kojun Kagaku Kenkyusho Co., Ltd.) and silicon (manufactured by Kojun Kagaku Kenkyusho Co., Ltd.) were mixed in a ratio of 90 atom% aluminum to 10 atom% silicon and melted using a miniature arc melting furnace (Daiya Vacuum Co., Ltd. "ACM-M01"). Subsequently, a 20 μm thick foil-like Al-Si alloy was obtained by a single-roll method under an argon gas atmosphere using a liquid quenching device (Nisshin Giken Co., Ltd. "NEV-A05"). The obtained Al-Si alloy was de-alloyed by immersing it in 2M hydrochloric acid in a box with a nitrogen gas atmosphere and stirring at 60°C for 30 minutes. The reaction mixture was filtered by suction using a 1 μm filter, washed sequentially with distilled water and dehydrated ethanol, and then dried under air at 60°C for 10 hours to oxidize at least a portion of the Si. The amount of Al remaining in the obtained porous silicon-based particles was analyzed by Rietveld analysis of X-ray diffraction (XRD) measurement data. If more than 45% by mass of Al remained, the above-described de-alloying operation was repeated until the amount of Al remaining was 20% or less, thereby obtaining porous silicon-based particles 12.

[0098] Example 13 In Example 12, porous silicon-based particles 13 were obtained by performing the same procedure as in Example 12, except that a foil-like Al-Si alloy with a thickness of 10 μm was obtained by a single-roll method under an argon gas atmosphere.

[0099] Comparative Example 1 In Example 1, the same procedure as in Example 1 was performed except that silicon oxide particle 5 was used instead of silicon oxide particle 1 to obtain porous silicon-based particle C1.

[0100] A-2. Examples of composite particle manufacturing Example 14 The porous silicon-based particles 1 obtained in Example 1 were subjected to CVD treatment in a rotary kiln using LPG (liquid propane gas) as the carbon source, in a nitrogen gas atmosphere, at 1 atom, at 950°C for 120 minutes, to obtain composite particles 1, which are carbon-coated porous silicon-based particles 1.

[0101] Example 15 In Example 14, the same procedure as in Example 14 was followed, except that the CVD treatment conditions were 900°C for 180 minutes, to obtain composite particle 2.

[0102] Example 16 In Example 14, porous silicon-based particles 2 obtained in Example 2 were used instead of porous silicon-based particles 1 obtained in Example 1, and the same procedure as in Example 14 was performed except that the CVD treatment conditions were 900°C for 150 minutes, to obtain composite particles 3.

[0103] Example 17 In Example 14, porous silicon-based particles 5 obtained in Example 5 were used instead of porous silicon-based particles 1 obtained in Example 1, and the same procedure as in Example 14 was performed except that the CVD treatment conditions were 900°C for 150 minutes, to obtain composite particles 4.

[0104] Example 18 In Example 2, methyl ethyl ketone was added to the porous silicon-based particles 2 so that the solid content was 20% by mass, and the mixture was thoroughly mixed with a stirrer. Then, resin 1 was added so that the silicon element content in the solid after firing was 40% by mass. The prepared mixture was spray-dried using a spray-drying apparatus (Okawara Chemical Machinery Co., Ltd. "CPL-2") under a nitrogen atmosphere at a spray pressure of 0.2 MPa, an inlet temperature of 140°C, and an outlet temperature of 80°C to obtain a dried product. This dried product was calcined under a nitrogen atmosphere at 1000°C for 6 hours to obtain a calcined product. Furthermore, the calcined product was subjected to CVD treatment in a rotary kiln using LPG (liquid propane gas) as the carbon source, under a nitrogen gas atmosphere at 1 atom (at atmospheric pressure), at 850°C for 90 minutes to obtain composite particles 5, which are carbon-coated porous silicon-based particles 2.

[0105] Example 19 In Example 18, the same procedure as in Example 18 was performed except that porous silicon-based particles 8 obtained in Example 8 were used instead of porous silicon-based particles 2 obtained in Example 2, and a mixture of resin 1 and resin 2 (mass ratio 50:50) was mixed instead of resin 1 so that the silicon element content in the solid after firing was 40% by mass. A composite particle 6 was obtained, which consisted of a matrix phase containing silicon oxycarbide and a carbonaceous phase as a matrix phase containing Si, O, and C, and porous silicon-based particles 8 whose outside was further coated with carbon.

[0106] Example 20 In Example 19, a mixture of resin 1 and resin 2 (mass ratio 50:50) was mixed so that the silicon element content in the solid after firing was 20% by mass. Furthermore, phenylalanine (Tokyo Chemical Industries) at 25% by mass relative to the silicon content of the porous silicon-based particles 8 was added. The same procedure as in Example 19 was followed to obtain composite particles 7.

[0107] B. Evaluation of porous silicon-based particles and composite particles The following physical properties were measured for the porous silicon-based particles and composite particles obtained in each example and comparative example.

[0108] (1) Abundance ratio of non-silicon phase in porous silicon-based particles The molar ratio of the non-silicon phase to the total porous silicon-based particles was quantified using an ICP-OES analyzer (Agilent 5110 ICP-OES, Agilent Technologies) and an XRD instrument (Smart Lab IV, Rigaku). It was assumed that all present oxygen elements originated from silicon oxide, and that all elements other than silicon and oxygen were contained in the non-silicon phase, and this was used to determine the composition ratio of the non-silicon phase.

[0109] (2) Average particle size (D50) The D50 of porous silicon-based particles and composite particles was measured using a laser diffraction particle size distribution analyzer (Malvern Panalytical, Mastersizer 3000).

[0110] (3) Porosity of porous silicon-based particles Nitrogen gas adsorption measurements using a specific surface area measuring device (Microtrac-Bel "BELsorp miniX") were used to determine the BET specific surface area (cm²) of porous silicon-based particles obtained by BET method analysis. 2 The true density (cm³) of porous silicon particles was measured using a true density meter (Anton Parl "Ultrapyc 5000") ( / g), and the true density (cm³) of porous silicon particles was measured using a true density meter (Anton Parl "Ultrapyc 5000"). 3 From ( / g), the total pore volume Vp (cm 3 ( / g) and specific volume ν(cm³) 3 The void ratio ( / g) was calculated, and the void ratio was calculated using the following formula (I). Porosity (%)=100×(Vp / (ν+Vp)) (I) Vp: Total pore volume (cm³) in the pore size range of porous silicon-based particles from 0.4 nm to 400 μm. 3 / g) ν: Specific volume (cm³) of porous silicon-based particles 3 / g)

[0111] (4) Particle average pore size, most frequent pore size, median pore size, and mesopore volume fraction of porous silicon-based particles Based on the values ​​obtained from the specific surface area measurement described in (3) above, the average pore size, most frequent pore size, and median pore size of the porous silicon-based particles were determined. Furthermore, the mesopore volume fraction of porous silicon-based particles was calculated using the following formula (II). Mesopore volume percentage (%) = 100 × (Vpm / Vp) (II) Vpm: Total pore volume (cm³) in the pore size range of porous silicon-based particles from 2 nm to 50 nm. 3 / g) Vp: Total pore volume (cm³) in the pore size range of porous silicon-based particles from 0.4 nm to 400 μm. 3 / g)

[0112] (5) Crystallite size of porous silicon-based particles and composite particles Using a wide-angle X-ray diffraction (XRD) instrument (Rigaku Corporation's "Ultima IV"), the peak intensity of the Si(111) plane was measured by the fundamental parameter (FP) method. From the peak full width at half maximum (FMAX) around 2θ = 28.3° ± 0.5°, which is attributed to the Si(111) plane, the following equation (A) was used as the basic equation (Scherrer's analytical equation) to determine the crystallite size (nm). 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°

[0113] (6) Specific surface area of ​​composite particles The BET specific surface area was calculated using BET method analysis based on nitrogen gas adsorption measurements performed with a specific surface area measuring device (Microtrac-Bel "BELsorp miniX").

[0114] (7) Porosity of composite particles The porosity of the composite particles was calculated using the specific surface area measurements from (6) above and the measurements taken with a true density meter (Anton Parl's "Ultrapyc 5000"), using the following equations (III) and (IV). Closed porosity (%)=100×(1-ρb / ρt) (III) ρb: Apparent density of composite particles measured by gas displacement method (g / cm³) 3 ) ρt: True density of composite particles (g / cm³) 3 ) Here, the true density ρt of the composite particles is calculated from equation (IV) below. ρt=(ws+wm) / (ws / ρs+wm / ρm) (IV) ws: Mass percentage of porous silicon-based particles in the entire composite particle system wm: Mass percentage of the matrix phase in the entire composite particle ρs: True density of porous silicon-based particles (g / cm³) 3 ) ρm: True density of the matrix phase (g / cm³) 3 )

[0115] (8) Porosity of the matrix phase of composite particles The composite particles were fixed onto a copper foil and cut using a cross-section polisher (registered trademark; JEOL Ltd. "IB-19520CCP"), and the cross-section was observed with a scanning electron microscope (SEM: JEOL Ltd. "FEM-7900F") at arbitrary magnifications (5000 to 50000x). The percentage of clear areas in five arbitrary regions of the obtained SEM image was binarized using image analysis software (Image J) to calculate the porosity within the matrix phase.

[0116] C. Battery characteristics evaluation using half-cells The composite particles 1 to 7 obtained in Examples 14 to 20 and the porous silicon-based particle C1 obtained in Comparative Example 1 were evaluated. (1) A slurry was prepared by mixing 8 parts by mass of composite particles or porous silicon-based particles, 1 part by mass of acetylene black as a conductive additive, 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"). (2) Each slurry obtained in (1) above was deposited as a film on a copper foil with a thickness of 20 μm. After drying under reduced pressure at 110°C, it was punched out in a circular shape with a diameter of 14 mm and pressed using a tablet molder to obtain a negative electrode as a thin film with a thickness of approximately 40 μm. 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.

[0117] (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 (4 cycles and beyond), under constant current / constant voltage charging / constant current discharging conditions. The open circuit state was maintained for 30 minutes during each charge / discharge switching. The cycle characteristics after 30 charge / discharge cycles are shown in Table 2. Also, the carp created above A lithium-ion battery of type N was disassembled in its initial fully charged state, the negative electrode was removed, cleaned 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

[0118] Table 1 summarizes the details of the porous silicon-based particles and their physical properties obtained in Examples 1-13 and Comparative Example 1. The detailed physical properties of the composite particles obtained in Examples 14-20 and the evaluation results in half-cells are summarized in Table 2, along with the evaluation results in half-cells of the porous silicon particle C1 obtained in Comparative Example 1.

[0119] [Table 1]

[0120] [Table 2]

[0121] D. Evaluation of battery characteristics in all-solid-state batteries using porous silicon materials. Example 21 60 parts by mass of the composite particles 1 obtained in Example 14, 35 parts by mass of β-Li3PS4 (manufactured by NEI) as a solid electrolyte, and 5 parts by mass of VGCF (Vapor Grown Carbon Fiber; manufactured by Resonaq) as a conductive material were mixed in a mortar while being crushed to obtain a negative electrode composite material. A negative electrode composite material layer was fabricated by pressing the obtained negative electrode composite material at 20 MPa. 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.

[0122] Example 22 In Example 21, an all-solid-state battery was fabricated in the same manner as in Example 21, except that composite particle 6 obtained in Example 19 was used instead of composite particle 1, and the cycle characteristics were evaluated. The results are shown in Table 3.

[0123] Comparative Example 2 In Example 21, an all-solid-state battery was fabricated in the same manner as in Example 21, except that porous silicon-based particles C1 obtained in Comparative Example 1 were used instead of composite particles 1, and the cycle characteristics were evaluated. The results are shown in Table 3.

[0124] [Table 3]

[0125] The results from Tables 1 to 3 show that the negative electrode active material containing the composite particles of the present invention, which has a matrix phase containing porous silicon-based particles, 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 composite particles of the present invention as a negative electrode active material exhibit excellent battery characteristics such as charge and discharge characteristics. [Industrial applicability]

[0126] The negative electrode formed using the negative electrode active material containing the composite particles 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 composite particles 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. Porous silicon-based particles having internal voids, comprising a silicon phase and a non-silicon phase, wherein the content of the silicon phase is 60% by mass or more of the total mass.

2. The porous silicon-based particle according to claim 1, wherein the non-silicon phase contains silicon dioxide as a constituent component.

3. The porous silicon-based particle according to claim 1, wherein the non-silicon phase contains one or more elements selected from the group consisting of Ag, Al, Bi, C, Cu, Li, Mg, Ni, Sn, Ti, and Zn.

4. The porous silicon-based particle according to claim 1, wherein the porosity calculated by the following formula (I) is 10 to 90%. Porosity (%) = 100 x (Vp / (ν+Vp)) (I) Vp: Total pore volume (cm³) in the pore size range of porous silicon-based particles from 0.4 nm to 400 μm. ３ / g) ν: Specific volume of porous silicon-based particles (cm³) ３ / g)

5. The porous silicon-based particle according to claim 1, wherein the mesopore volume fraction calculated by the following formula (II) is 50 to 90%. Mesopore volume percentage (%) = 100 × (Vpm / Vp) (II) Vpm: Total pore volume (cm³) in the pore size range of porous silicon-based particles from 2 nm to 50 nm. ３ / g) Vp: Total pore volume (cm³) in the pore size range of porous silicon-based particles from 0.4 nm to 400 μm. ３ / g)

6. The porous silicon-based particle according to claim 1, wherein the average pore diameter, most frequent pore diameter, and median pore diameter are all in the pore diameter range of 2 nm to 50 nm.

7. The porous silicon-based particle according to claim 1, wherein the voids are formed throughout the entire particle.

8. A composite particle comprising porous silicon-based particles according to any one of claims 1 to 7 and a matrix phase containing the porous silicon-based particles.

9. The composite particle according to claim 8, wherein the content of the porous silicon-based particles is 5 to 90% by mass of the total mass of the composite particle.

10. The composite particle according to claim 8, wherein the porosity of the matrix phase is lower than that of the porous silicon-based particles.

11. The composite particle according to claim 8, having closed pores inside.

12. The composite particle according to claim 11, wherein the closed porosity calculated from the following formula (III) is 15 to 85%. Closed porosity (%) = 100 x (1-ρb / ρt) (III) ρb: Apparent density of composite particles measured by gas displacement method (g / cm³) ３ ) ρt: True density of composite particles (g / cm³) ３ ) Here, the true density ρt of the composite particles is calculated using the following formula (IV). ρt=(ws+wm) / (ws / ρs+wm / ρm) (IV) ws: Mass percentage of porous silicon-based particles in the entire composite particle system wm: Mass percentage of the matrix phase in the entire composite particle ρs: True density of porous silicon-based particles (g / cm³) ３ ) ρm: True density of the matrix phase (g / cm³) ３ )

13. The composite particle according to claim 8, wherein the matrix phase contains a carbon element.

14. The composite particle according to claim 8, wherein the matrix phase contains one or more elements composed of Si, O, and C.

15. The composite particle according to claim 14, wherein the matrix phase comprises at least silicon oxycarbide and a carbonaceous phase.

16. A method for producing porous silicon-based particles according to any one of claims 1 to 7, comprising the following steps. (i) A process of heat-treating silicon oxide particles represented by formula SiOx (wherein x is a positive number greater than or equal to 0 and less than 2) in an inert gas atmosphere at a temperature in the range of 800°C to 1350°C. (ii) A step of etching the heat-treated silicon oxide by contacting it with an etching solution to obtain porous silicon-based particles.

17. A method for producing porous silicon-based particles according to any one of claims 1 to 7, comprising the following steps. (i) A process of heat-treating silicon oxide particles represented by formula SiOx (wherein x is a positive number greater than or equal to 0 and less than 2) in an inert gas atmosphere at a temperature in the range of 800°C to 1350°C. (i') A step of contacting the heat-treated silicon oxide with a solution containing a fluorine-based compound and a metal precursor to deposit metal particles on the surface of the heat-treated silicon oxide. (ii) A step of etching the silicon oxide to which the metal particles are attached by contacting it with an etching solution to obtain porous silicon-based particles.

18. A method for producing composite particles according to claim 8, comprising the step of forming a matrix phase that contains porous silicon-based particles according to any one of claims 1 to 7.

19. A negative electrode active material comprising the composite particles described in claim 8.

20. A composition for a secondary battery negative electrode, comprising the negative electrode active material described in claim 19.

21. A secondary battery negative electrode comprising a negative electrode material layer formed using the secondary battery negative electrode composition described in claim 20.

22. A secondary battery comprising a negative electrode, a positive electrode, an electrolyte, and a separator as described in claim 21.

Images