Composite active material for secondary battery, and secondary battery

Abstract

The present invention relates to a composite active material for a secondary battery, comprising a silicon material having at least one structure selected from the group consisting of A and B, a: A has a metal ion silicate phase and a silicon nitride phase and / or a silicon carbide phase that are integrated outside the silicon particles, and also has a matrix phase that encloses the metal ion silicate phase and the silicon nitride phase and / or the silicon carbide phase; B: A has a matrix phase that contains a metal ion silicate and silicon nitride and / or silicon carbide outside the silicon particles.

Description

Technical Field

[0001] The present invention relates to a composite active material for a secondary battery and a secondary battery comprising the composite active material for a secondary battery. Background Art

[0002] In terms of environmental responses to energy demand, the move toward electric vehicles (EVs) is rapidly advancing, expanding the scope of lithium-ion batteries (LIBs). Graphite, the mainstream negative electrode material for LIBs, has a low theoretical capacity density (372 mAh / g). To increase battery capacity, the development of high-capacity active materials using silicon, tin, and oxides is actively underway. However, these materials experience significant volume expansion and contraction with the absorption and release of lithium ions. Consequently, repeated charge and discharge can cause the active material to pulverize, leading to deterioration in charge and discharge characteristics.

[0003] Patent Document 1 describes a negative electrode active material comprising a silicon oxide complex containing Si, SiO x Silicon oxide represented by (0<x≦2), magnesium silicate containing Si and Mg; and a carbon coating layer, located on the surface of the silicon oxide complex and containing a carbon-based substance, having a specific peak by X-ray diffraction analysis, and having a water content below a certain level.

[0004] Patent Document 2 describes a silicon composite oxide for a negative electrode material of a secondary battery, characterized in that silicon oxide (SiO x , 0<x<2) contains silicon particles and MgSiO3 (enstatite) crystals with a crystal size of 1nm to 25nm, and contains a carbon film on the surface.

[0005] Patent Document 3 describes a silicon negative electrode active material comprising a silicon core composed of silicon particles and a double cladding having a silicon carbide layer on the silicon core and a silicon oxide layer between the silicon core and the silicon carbide layer.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application No. 2020-529709

[0009] Patent Document 2: Japanese Patent Application Publication No. 2018-156922

[0010] Patent Document 3: Japanese Patent Application Laid-Open No. 2020-181820 Summary of the Invention

[0011] Problems to be solved by the invention

[0012] However, the silicon particles or active materials containing them described in Patent Documents 1 to 3 suffer from insufficient control over the surface layer structure of the silicon particles (either through metal ion silicate control or through the use of a silicon nitride or silicon carbide coating). This results in a decrease in both the initial coulombic efficiency and charge / discharge capacity. Therefore, further improvements are required in terms of battery cycle characteristics and initial coulombic efficiency.

[0013] An object of the present invention is to provide a composite active material for a secondary battery and a secondary battery comprising the composite active material in a negative electrode, wherein the composite active material for a secondary battery can maintain high charge and discharge performance such as capacity retention rate and initial coulombic efficiency when the secondary battery is manufactured.

[0014] Technical means to solve the problem

[0015] The present inventors investigated methods for treating the oxide film on the surface of silicon particles, aiming to increase the initial Coulombic efficiency and improve the cycling characteristics of silicon materials used in negative electrode active materials. Their findings revealed that a metal ion silicate phase forms on the exterior of the silicon particles through a solid-phase reaction between metal ions, such as alkali metal ions or alkaline earth metal ions, and silicon oxide, forming a passivating oxide film.

[0016] It was further discovered that there is Mn in silicon materials 2+ In the case of transition metal ions such as silicon ions, the catalytic effect of the transition metal ions is utilized to promote the formation of silicon nitride phase or silicon carbide phase on the silicon particles, thereby greatly suppressing the oxidation of the silicon particles during high-temperature calcination, and further improving the charge and discharge performance through the formation of the oxide film and silicon nitride phase or silicon carbide phase on the outside of the silicon particles.

[0017] The present invention has the following aspects.

[0018] [1] A composite active material for a secondary battery, comprising a silicon material having at least one structure selected from the group consisting of A and B below.

[0019] A: The silicon particles have a metal ion silicate phase and a silicon nitride phase and / or a silicon carbide phase integrated on the outside, and a matrix phase enclosing them.

[0020] B: The silicon particles have a matrix phase containing metal ion silicate and silicon nitride and / or silicon carbide.

[0021] [2] The composite active material for a secondary battery according to [1], comprising a silicon material having the structure of A.

[0022] [3] The composite active material for a secondary battery according to [1] or [2], wherein the metal ion silicate phase and one or more of the silicon nitride phase and the silicon carbide phase are present in a layered form on the silicon particles.

[0023] [4] The composite active material for a secondary battery according to any one of [1] to [3], wherein the metal ions in the metal ion silicate phase are ions of at least one element selected from the group consisting of alkali metal elements and alkaline earth metal elements.

[0024] [5] The composite active material for a secondary battery according to [4], wherein the alkali metal element is Li.

[0025] [6] The composite active material for a secondary battery according to [4], wherein the alkaline earth metal is Mg.

[0026] [7] The composite active material for a secondary battery according to any one of [1] to [6], wherein the silicon material further contains a transition metal element.

[0027] [8] The composite active material for secondary batteries according to [7], characterized in that the transition metal element is at least one selected from the group consisting of Fe, Mn, Ni, Cr, Cu, Nb, Mo, Ru, Rh, Pd and La.

[0028] [9] The composite active material for a secondary battery according to [4], wherein the metal ions are contained in an amount within a range of 0.2 atm% to 10.0 atm% relative to silicon in the silicon particles.

[0029]

[10] The composite active material for secondary batteries according to [7], wherein the content of the transition metal element is 0.01 atm% to 5.0 atm% relative to the total amount of silicon present in the silicon particles.

[0030]

[11] The composite active material for a secondary battery according to any one of [1] to

[10] , comprising carbonaceous matter as a component of the matrix phase.

[0031]

[12] The composite active material for a secondary battery according to any one of [1] to

[11] , wherein the matrix phase has a composition represented by SiOy (1<y≦2).

[0032]

[13] The composite active material for a secondary battery according to any one of [1] to

[12] , wherein the matrix phase contains silicon oxycarbide.

[0033]

[14] The composite active material for a secondary battery according to any one of [1] to

[13] , wherein the average particle size of the silicon particles is in the range of 10 nm to 300 nm.

[0034]

[15] The composite active material for secondary batteries according to [7], wherein the transition metal element is in a range of 0.001 atm% to 5 atm% relative to the total amount of silicon in the composite active material for secondary batteries.

[0035]

[16] The composite active material for a secondary battery according to any one of [1] to

[15] , wherein a carbon layer is present on the surface.

[0036]

[17] A secondary battery comprising the composite active material for a secondary battery according to any one of [1] to

[16] in a negative electrode.

[0037] Effects of the Invention

[0038] The composite active material for secondary batteries of the present invention can cleverly process the oxide film on silicon particles by obtaining a synergistic effect of passivation of the oxide film and oxidation inhibition during high-temperature calcination in the silicon material, thereby maintaining high charge and discharge performance such as the capacity retention rate or first coulomb efficiency of the secondary battery. DETAILED DESCRIPTION

[0039] Hereinafter, embodiments of the present invention will be described in detail.

[0040] In addition, in this specification, "mass" and "weight" have the same meaning. In addition, in this specification, "to" indicating a numerical range is used to include the numerical values ​​described before and after as the lower limit and upper limit unless otherwise specified.

[0041] [Composite active material for secondary batteries]

[0042] The composite active material for secondary batteries of this embodiment includes a silicon material having at least one structure selected from the group consisting of A and B below.

[0043] A: The silicon particles have a metal ion silicate phase and a silicon nitride phase and / or a silicon carbide phase integrated on the outside, and a matrix phase enclosing them.

[0044] B: The silicon particles have a matrix phase containing metal ion silicate and silicon nitride and / or silicon carbide.

[0045] The composite active material for a secondary battery in this embodiment only needs to include a silicon material having any one of the structures A and B, preferably a silicon material having the structure A. In B, the metal ion silicate phase component in A, i.e., the metal ion silicate, is present in the matrix phase. Similarly, the silicon nitride phase and / or silicon carbide phase component in A, i.e., silicon nitride and / or silicon carbide, is present in the matrix phase. Furthermore, "silicon nitride phase and / or silicon carbide phase" refers to either or both of the silicon nitride phase and the silicon carbide phase.

[0046] The silicon material A has a structure in which a metal ion silicate phase and a silicon nitride phase and / or a silicon carbide phase are integrated and present outside the silicon particles. The term "integrated" as used in this specification refers to either a state in which the two phases are tightly connected with no gaps or inclusions at the boundary between the two phases, or a composite state in which the two phases diffuse into each other and the boundary is blurred.

[0047] In the silicon material of A, it is preferred that the metal ion silicate phase and the silicon nitride phase and / or the silicon carbide phase are present in layers on the silicon particles. In A, the layer structure outside the silicon particles is not particularly limited, and the metal ion silicate phase and the silicon nitride phase and / or the silicon carbide phase may also be present in layers alternately on the silicon particles. In this case, the silicon nitride phase and / or the silicon carbide phase may be present on the metal ion silicate phase, and the metal ion silicate phase may also be present on the silicon nitride phase and / or the silicon carbide phase. The metal ion silicate phase is present in layers to form a passivated silicon surface oxide film. In addition, the silicon nitride phase and / or the silicon carbide phase is present in layers to significantly suppress the oxidation of the silicon particles during high-temperature calcination.

[0048] From the viewpoint of enhancing the passivation effect of the oxide film on the silicon particles, the metal ions in the metal ion silicate (phase) are preferably ions of at least one element selected from the group consisting of alkali metal elements and alkaline earth metal elements.

[0049] In addition, it is particularly preferable that Li is used as the alkali metal element, and Mg is used as the alkaline earth metal element.

[0050] The metal ion silicate phase is preferably a lithium silicate compound or a magnesium silicate compound, more preferably lithium metasilicate (Li2SiO3) or magnesium metasilicate (MgSiO3), and particularly preferably magnesium metasilicate (MgSiO3).

[0051] The content of the metal ions relative to the total amount of silicon (Si element) in the silicon particles is preferably 0.2 atm% to 10.0 atm%, more preferably 0.3 atm% to 9.0 atm%, and even more preferably 0.5 atm% to 8.0 atm%. When the content of the metal ions is within this range, a high passivation effect of the oxide film on the silicon particles can be achieved.

[0052] The composite active material for a secondary battery in this embodiment preferably comprises the metal ion silicate phase in the silicon material, near the surface of the silicon particles. Specifically, the metal ion silicate (phase) may be directly chemically or physically bonded to the surface of the silicon particles, or the metal ion silicate (phase) may be present near the surface of the silicon particles. Furthermore, "near the surface of the silicon particles" refers to within a few nanometers, preferably within 5 nanometers, of the surface.

[0053] The presence of the metal ion silicate (phase) near the surface of the silicon particles can be confirmed using a high-resolution transmission electron microscope (HR-TEM). Specifically, the sample can be sliced ​​using a focused ion beam (FIB) and then observed using HR-TEM.

[0054] When the metal ion silicate phase in the structure of A is in a crystalline state, the lattice structure of the present silicate phase crystallites is observed in the HR-TEM measurement. Therefore, the thickness of the metal ion silicate phase near the surface of the present silicon particle is measured within the observation field of 1,000,000 magnification of the HR-TEM.

[0055] Furthermore, scanning transmission electron microscope energy-dispersive spectroscopy (STEM-EDS) and X-ray photoelectron spectroscopy (XPS) can be used to detect the presence of metal elements near silicon particles. Furthermore, the thickness of the metal silicate phase can be determined in conjunction with the metal elements.

[0056] When the metal ion silicate (phase) is a magnesium silicate compound, the magnesium silicate compound preferably forms a crystalline film that covers at least a portion of the surface of the silicon particles. When the magnesium silicate compound covers at least a portion of the surface of the silicon particles, the coverage is more preferably 50% or greater, and particularly preferably 80% or greater. The upper limit of the coverage is not particularly limited and is, for example, 100%.

[0057] When the magnesium silicate compound is a crystalline film and further covers at least a portion of the surface of the silicon particles, the thickness of the crystalline film is preferably 0.2 nm to 10 nm, more preferably 1 nm to 8 nm.

[0058] The coverage and the thickness of the crystalline film can be measured by the HR-TEM.

[0059] When the metal element is Li and / or Mg, the total content (molar ratio) of Li and Mg relative to the total amount of silicon (Si element) in the composite active material for a secondary battery is preferably 0.5 mol% to 10.0 mol%, more preferably 1.0 mol% to 7.0 mol%, and even more preferably 2.0 mol% to 6.0 mol%.

[0060] In addition, it is considered that Li or Mg exists in the composite active material for secondary batteries as metal ions (Li + Mg 2+ ) in the form of .

[0061] In the composite active material for secondary batteries of this embodiment, the silicon material preferably further includes a transition metal element. The transition metal element may be present in the silicon nitride (phase) or silicon carbide (phase), may be present in the silicon particles themselves, or may be present in the matrix phase external thereto. By including the transition metal element in the silicon material, the formation of silicon nitride (phase) or silicon carbide (phase) on the silicon particles is promoted by the catalytic action of the transition metal ions.

[0062] In order to more effectively generate silicon nitride (phase) or silicon carbide (phase) on silicon particles, the transition metal element is preferably at least one selected from the group consisting of Fe, Mn, Ni, Cr, Cu, Nb, Mo, Ru, Rh, Pd, and La, and more preferably at least one selected from the group consisting of Fe, Mn, Ni, Cu, and La. In this embodiment, the transition metal element is considered to be present in the form of metal ions in the metal ion silicate (phase) or silicon nitride (phase) and / or silicon carbide (phase) on the silicon particles.

[0063] The content of the transition metal element relative to the total amount of silicon (Si element) in the silicon particles constituting the composite active material for a secondary battery is preferably 0.01 atm% to 5.0 atm%, more preferably 0.02 atm% to 4.0 atm%, and even more preferably 0.05 atm% to 3.0 atm%. Furthermore, the content of the transition metal element relative to the total amount of silicon (Si element conversion) in the composite active material for a secondary battery of this embodiment is preferably 0.001 atm% to 5 atm%, more preferably 0.003 atm% to 4 atm%, and even more preferably 0.005 atm% to 3 atm%.

[0064] If the content of the transition metal element is within the above range, a silicon nitride phase or a silicon carbide phase can be formed on the silicon particles to maintain high charge and discharge performance. The content of the transition metal element can be measured by quantitative analysis of the content of various elements, such as inductively coupled plasma (ICP) mass spectrometry (ICP-MS), energy dispersive X-ray spectroscopy (EDX) analysis, X-ray fluorescence (XRF) analysis, and electron probe X-ray microanalyzer (EPMA) analysis.

[0065] The silicon nitride in the silicon nitride phase has a chemical formula of SiN x The inorganic compound represented by (0.1<x<1.33) has electrochemical reactivity with lithium ions and very excellent fracture toughness, high temperature characteristics, and thermal shock resistance. Silicon nitride can be either α phase or β phase. In addition, the silicon nitride phase is a structure generated by a solid phase reaction at a high temperature (for example, above 1200°C), but due to the catalytic effect of transition metal ions, it can be easily formed even at low temperatures. By changing the type and addition amount of transition metal ions or the conditions of the solid phase reaction, the composition or crystal state of the silicon nitride phase can be appropriately controlled.

[0066] Furthermore, the silicon carbide in the silicon carbide phase, represented by the chemical formula SiC, is a 1:1 compound of carbon and silicon. It exhibits properties intermediate between diamond and silicon, boasting exceptional hardness, heat resistance, and chemical stability. The composition and crystallization state of the silicon carbide phase can also be appropriately controlled by varying the solid-phase reaction conditions.

[0067] In this embodiment, there is no particular limitation on the structure of silicon nitride (phase) or silicon carbide (phase), and both crystalline and amorphous structures are applicable. The presence of the silicon nitride (phase) or silicon carbide (phase), whether crystalline or amorphous, can be determined by solid 29 Si-NMR ( 29 Si-Nuclear Magnetic Resonance, 29 Si-NMR) spectroscopy was used to confirm.

[0068] In the silicon material of this embodiment, it is preferable that the solid 29In the Si-NMR spectrum, peak D was detected, whose chemical shift was in the range of 0ppm to -20ppm, which was attributed to the silicon carbide phase; peak E was detected, whose chemical shift was in the range of -30ppm to -60ppm, which was attributed to the silicon nitride phase; and peak F was detected, whose chemical shift was in the range of -70ppm to -120ppm, which was attributed to silicon. The area ratio R of each peak calculated by the following formula was in the range of 0.1 to 1.0.

[0069] R=(D+E) / F

[0070] Peaks D and E represent Si elements other than zero-valent elements, such as SiO4 or SiO2, and Peak C represents zero-valent Si. The area ratio R of each peak calculated by the formula is within the range described above, indicating that the proportion of Si (zero-valent) is greater than that of Si (other than zero-valent), indicating that oxidation of the silicon particles constituting the silicon material of this embodiment has not progressed (they are in a low-oxidation state). By lowering the oxidation state of the silicon particles as described above, the initial Coulombic efficiency when the active material is prepared can be effectively improved. The presence of silicon nitride (phase) or silicon carbide (phase) outside the silicon particles can improve the chemical stability of the silicon particles and also improve the cycle characteristics during charge and discharge.

[0071] If silicon nitride (phase) or silicon carbide (phase) is crystalline, it can be confirmed by XRD (X-ray diffraction, CuKα light source) measurement. For example, if X-ray diffraction peaks consistent with α-Si3N4 (PDF#41-0360), β-Si3N4 (PDF#33-1160), α-SiC (PDF#49-1430), or β-SiC (PDF#29-1129) are detected within the range of 2θ = 10° to 80°, it is determined that various crystalline structures of the silicon nitride (phase) or silicon carbide (phase) are present.

[0072] The thickness of the silicon nitride phase and / or silicon carbide phase present on the silicon particles is preferably 0.1nm to 10nm, more preferably 0.3nm to 8nm, and even more preferably 0.5nm to 6nm, based on the total thickness of the silicon nitride phase and the silicon carbide phase. If the total thickness of the silicon nitride phase and the silicon carbide phase is within the above range, very excellent fracture toughness, high temperature properties, thermal shock resistance and chemical stability can be imparted, and oxidation of the silicon particles during high temperature calcination can be greatly suppressed. The thickness of the silicon nitride phase and the silicon carbide phase can be measured by cutting with a focused ion beam (FIB) and observing the cross section with a field emission scanning electron microscope (FE-SEM), or by slicing the sample and observing the cross section of the silicon particles with a transmission electron microscope (TEM).

[0073] The SiN can be easily controlled by adjusting the amount of transition metal elements added as catalysts or the high temperature reaction conditions (temperature, time, atmosphere). x The range of x in the SiN x (0.1<x<1.33) Since it readily reacts with lithium ions, it has a certain degree of electrochemical reactivity. Meanwhile, silicon nitride phases are widely used as gas barriers, blocking oxygen diffusion. In this embodiment, when a silicon nitride phase forms on the silicon particles during high-temperature calcination of the active material, it prevents oxygen from diffusing into the silicon particles, effectively suppressing silicon oxidation reactions.

[0074] Furthermore, silicon materials typically have a natural oxide film on silicon particles. During high-temperature calcination, transition metal ions can diffuse through this film, significantly accelerating the silicon nitridation reaction through a catalytic effect. Consequently, silicon nitride crystals form between the surface oxide film and the silicon crystals at the center of the particles, blocking contact between the silicon crystals and oxygen from external or peripheral sources, thereby suppressing the oxidation reaction of the silicon particles.

[0075] The silicon particles in the silicon material preferably exhibit a peak near 2θ = 28.4° in XRD (X-ray diffraction) measurement. Detection of this peak indicates the presence of Si crystals having a (111) primary crystal plane. Si crystals have properties that contribute significantly to the charge and discharge performance of secondary batteries, such as the charge and discharge capacity and initial coulombic efficiency.

[0076] The average particle size of the silicon particles constituting the silicon material is preferably in the range of 10 nm to 300 nm, more preferably 20 nm to 250 nm, and even more preferably 50 nm to 200 nm. When the average particle size of the silicon particles is within this range, the charge and discharge performance of the secondary battery, such as the capacity retention rate and initial coulombic efficiency, can be maintained at a high level.

[0077] The average particle size of silicon particles constituting the silicon material can be measured by observing a cross section of the silicon material using a transmission electron image.

[0078] From the viewpoints of charge-discharge capacity, initial coulombic efficiency, and cycle characteristics, the specific surface area of ​​the silicon particles constituting the silicon material is preferably 50 m 2 / g~400m 2 / g, more preferably 100m 2 / g~300m 2 / g, more preferably 150m 2 / g~230m 2 / g. Specific surface area is determined by the Brunauer-Emmett-Teller (BET) method and can be determined by nitrogen adsorption measurement, for example, using a specific surface area measuring instrument. Furthermore, to remove organic matter adhering to the silicon particles, it is preferred to heat treat them in a nitrogen atmosphere at 500°C for 2 hours before measuring the specific surface area.

[0079] The shape of the silicon particles constituting the silicon material may be any of granular, needle-shaped, and flaky. However, the crystal state is not particularly limited and may be crystalline or amorphous. When the silicon particles are crystalline, from the perspective of initial Coulomb efficiency and cycle characteristics, the crystallite diameter obtained from the diffraction peak attributed to Si(111) in X-ray diffraction is preferably in the range of 5 nm to 14 nm. The crystallite diameter is preferably 12 nm or less, and more preferably 10 nm or less.

[0080] From the perspective of charge and discharge performance when a secondary battery is made, the length of the silicon particles constituting the silicon material in the long axis direction is preferably 30nm to 300nm, and the thickness is preferably 1nm to 60nm. From the perspective of charge and discharge performance when a secondary battery is made, it is preferably a needle-like or flake-like shape in which the ratio of thickness to length, i.e., the so-called aspect ratio, is 0.5 or less. The morphology of the silicon particles can be determined by a dynamic light scattering method to determine the average particle size, but by using an analysis method using a transmission electron microscope (TEM) or a field emission scanning electron microscope (FE-SEM), it is easier and more precise to identify samples of aspect ratio. In the case of silicon particles, the sample can be cut using a focused ion beam (FIB) and the cross section can be observed by FE-SEM, or the sample can be sliced ​​and observed using TEM to identify the state. In addition, the aspect ratio of the silicon particles is a calculation result based on the main part 50 particles of the sample in the field of view reflected in the TEM image.

[0081] The general state of the silicon particles constituting the silicon material is that an amorphous oxide film (silicon oxide) is present on the outer surface in the atmosphere. If there is such an amorphous oxide film, as long as it does not have a large adverse effect on the charge and discharge performance (capacity, first coulomb efficiency), then from the perspective of giving the silicon particles more excellent fracture toughness, high temperature characteristics, thermal shock resistance and chemical stability, an amorphous oxide film may also be present in small amounts on the surface of the silicon particles. In addition, from the perspective of making the balance of the influence (positive and negative) of the amorphous oxide film source good, the thickness of the oxide film is preferably less than 8nm, more preferably less than 7nm, and particularly preferably less than 6nm. If the thickness of the oxide film is within the range, the charge and discharge performance decline (capacity and first coulomb efficiency) of the silicon material can be minimized, and the cycle characteristics can be improved.

[0082] The matrix phase in the composite active material for secondary batteries of this embodiment preferably has a composition represented by SiOy (1 < y ≦ 2), and preferably also contains carbonaceous materials. In addition, the matrix phase preferably contains silicon elements, carbon elements and oxygen elements, and is a three-dimensional network structure of a silicon-oxygen-carbon skeleton. The three-dimensional network structure of the silicon-oxygen-carbon skeleton has relatively high chemical stability, and adopts a composite structure with carbon (carbonaceous phase), and the volume change is small relative to the absorption and release of lithium. The three-dimensional network structure of the matrix phase is preferably a structure containing silicon oxide carbide (SiOC). In addition to silicon elements, carbon elements and oxygen elements, the three-dimensional network structure may also have nitrogen elements.

[0083] The composite active material for a secondary battery preferably has a carbon layer on its surface, i.e., a carbon film on at least a portion of its surface. The carbon layer (carbon film) is preferably a film comprising low-crystalline carbon. The term "low-crystalline carbon" refers to an amorphous carbon material in which, unlike graphite carbon materials, a regular lattice structure is almost invisible, or a short-periodic structure is present only in trace amounts.

[0084] From the perspective of improving chemical stability or thermal stability, the mass of the composite active material for secondary batteries is set to 100 mass %, and the amount of the carbon layer (carbon film) is preferably 0.1 mass % or more and 30 mass % or less, more preferably 1 mass % or more and 25 mass % or less, and further preferably 5 mass % or more and 20 mass % or less. The composite active material for secondary batteries may have a carbon layer (carbon film) continuously or intermittently on its surface. The carbon layer (carbon film) is preferably present on the surface of the active material by chemical vapor growth method.

[0085] The true density of the composite active material for secondary batteries is preferably 1.6 g / cm 3 Above and 2.6g / cm 3 From the viewpoint of increasing the energy density of the secondary battery obtained, the true density is more preferably 1.75 g / cm 3 More than, more preferably 1.80g / cm 3 The true density is a value measured using a true density measuring device.

[0086] The average particle size of the composite active material for secondary batteries is preferably greater than or equal to 2 μm and less than or equal to 15 μm. If the average particle size of the composite active material for secondary batteries is greater than or equal to 2 μm, a substantial increase in specific surface area can be suppressed, the amount of solid electrolyte interface (SEI) generated during charging and discharging when the secondary battery is made can be reduced, and the reversible charge and discharge capacity per unit volume can be increased. In addition, if the average particle size of the composite active material for secondary batteries is less than or equal to 15 μm, the adhesion strength with the current collector can be fully guaranteed, and peeling from the current collector can be suppressed. The average particle size of the composite active material for secondary batteries is more preferably greater than or equal to 2.5 μm, and further preferably greater than or equal to 3.0 μm. In addition, the average particle size of the composite active material for secondary batteries is more preferably less than or equal to 12 μm, and further preferably less than or equal to 10 μm.

[0087] The specific surface area of ​​the composite active material for secondary batteries is preferably 0.3 m 2 / g or more and 10m 2 / g or less. The specific surface area is more preferably 0.5m 2 / g or more, particularly preferably 1m 2 / g or more. If the specific surface area is within the above range, the amount of solvent absorbed during electrode production can be appropriately maintained, and the amount of binder used to maintain adhesion can also be appropriately maintained. In addition, the specific surface area is a value obtained by the BET method and can be obtained by nitrogen adsorption measurement, for example, using a specific surface area measuring device for measurement.

[0088] [Method for producing composite active material for secondary batteries]

[0089] The silicon material in the composite active material for secondary batteries of this embodiment is manufactured by the following method, which at least includes: a process of wet-pulverizing the raw silicon (wet-pulverizing process); a process of loading a compound containing a metal element on silicon particles (metal element loading process); a process of uniformly mixing the polysiloxane compound, the carbon source resin, and the silicon slurry obtained by the wet-pulverizing process, and then removing the solvent and drying it (homogenizing process); a process of performing a high-temperature treatment after the homogenizing process (high-temperature treatment process). The homogenizing process can be either before or after the metal element loading process. In addition, the composite active material for secondary batteries of the embodiment is not limited to the material obtained by the manufacturing method.

[0090] In the wet pulverization process, the raw silicon is dispersed in a solvent such as an organic solvent to obtain a silicon slurry as a nano-silicon dispersion. The silicon slurry can be adjusted while the raw silicon is pulverized using a wet pulverization device. In order to promote the pulverization of the raw silicon, a dispersant is preferably added to the organic solvent. Examples of wet pulverization devices include a roller mill, a high-speed rotary pulverizer, a container-driven mill, a bead mill, and the like. In addition, the preferred range of the average particle size of the silicon particles in the obtained silicon slurry is as described above. The average particle size of the silicon particles after the raw silicon is pulverized is obtained by measuring using a laser diffraction particle size analyzer or the like, and determining the particle size when the cumulative volume reaches 50% when a volume cumulative distribution curve is drawn from the smaller diameter side in the particle size distribution.

[0091] Examples of the organic solvent include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and diisobutyl ketone; alcohols such as ethanol, methanol, n-propanol, and isopropanol; and aromatics such as benzene, toluene, and xylene.

[0092] The type of dispersant can be aqueous or non-aqueous, preferably non-aqueous. Examples of non-aqueous dispersants include: polymers such as polyethers, alcohols, polyalkylene polyamines, and polycarboxylic acid partial alkyl esters, low-molecular weights such as polyol esters and alkyl polyamines, and inorganic types such as polyphosphates. The concentration of the solid components of the silicon particles and the dispersant in the silicon slurry is not particularly limited. The total amount of the solvent, dispersant, and silicon particles is set to 100% by mass, preferably in the range of 5% to 40% by mass, and more preferably in the range of 10% to 30% by mass. The amount of the dispersant added relative to the weight of the silicon particles is preferably in the range of 2% to 60% by mass, and more preferably in the range of 5% to 50% by mass.

[0093] In the metal element loading process, a compound containing a metal element is added to the silicon slurry obtained in the wet pulverization process and stirred, and the solvent is removed and then dried. As a result, after high-temperature treatment, silicon particles having a metal ion silicate phase are obtained. In terms of a high passivation effect of the oxide film on the silicon particles, the metal ion is preferably an ion of at least one element selected from the group consisting of alkali metal elements and alkaline earth metal elements. In addition, it is particularly preferred that the alkali metal element is Li and the alkaline earth metal is Mg. As the compound containing the metal element, for example, anhydrous lithium acetate can be cited in the case of Li, and anhydrous magnesium acetate can be cited in the case of Mg. These metal element-containing compounds can be dispersed in an appropriate organic solvent (polar or non-polar) such as ethanol or methyl ethyl ketone (MEK).

[0094] By adding a compound containing a transition metal element such as Fe, Mn, Ni, Cr, Cu, Nb, Mo, Ru, Rh, Pd, or La in the same manner as described above and stirring, these transition metal ions can be supported on the silicon material. Examples of the compound containing a transition metal element, for example, when the transition metal element is manganese (Mn), include manganese (II) chloride, anhydrous manganese (II) acetate, manganese (II) sulfate, manganese (II) acetate tetrahydrate, and manganese (II, III) acetylacetonate.

[0095] The stirring can be carried out using a stirrer including a stirring blade, and the stirring time is, for example, 5 minutes to 2 hours, preferably 10 minutes to 1 hour. The stirring can be carried out at room temperature, for example, while being heated to 30°C to 50°C. The desolventizing agent can be carried out by a common method such as filtration. The drying is carried out, for example, using a dryer, a reduced pressure dryer, a spray dryer, etc. The drying temperature is preferably 80°C or higher, preferably 120°C or lower. The drying can also be carried out while reducing pressure.

[0096] In the homogenization step, a matrix phase having a three-dimensional network structure of a silicon-oxygen-carbon skeleton is mixed with silicon particles and homogenized, followed by solvent removal and drying to obtain an active material precursor. The matrix phase is formed of a polysiloxane compound and a carbon source resin.

[0097] Examples of the polysiloxane compound include resins containing at least one of a polycarbosilane structure, a polysilazane structure, a polysilane structure, and a polysiloxane structure. These resins may be resins containing only these structures, or they may be composite resins comprising at least one of these structures as a segment chemically bonded to other polymer segments. Composite forms include graft copolymerization, end-capped copolymerization, random copolymerization, and alternating copolymerization. Examples include composite resins having a graft structure chemically bonded between a polysiloxane segment and a side chain of a polymer segment, and composite resins having an end-capped structure chemically bonded to a polysiloxane segment at the end of a polymer segment.

[0098] The polysiloxane segment is preferably a polysiloxane compound having a structural unit represented by the following general formula (S-1) and / or the following general formula (S-2). More preferably, the polysiloxane compound has a carboxyl group, epoxy group, amino group, or polyether group on a side chain or at a terminal of the siloxane bond (Si—O—Si) main skeleton.

[0099] [Chemistry 1]

[0100]

[0101] [Chemistry 2]

[0102]

[0103] In the general formula (S-1) and the general formula (S-2), R 1 represents an aromatic hydrocarbon group or an alkyl group, an epoxy group, a carboxyl group, etc. which may have a substituent. 2 and R 3 Each represents an alkyl group, a cycloalkyl group, an aryl group or an aralkyl group, an epoxy group, a carboxyl group, etc.

[0104] Examples of the alkyl group include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, tert-pentyl, 1-methylbutyl, 2-methylbutyl, 1,2-dimethylpropyl, 1-ethylpropyl, hexyl, isohexyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 2,2-dimethylbutyl, 1-ethylbutyl, 1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethyl-2-methylpropyl, and 1-ethyl-1-methylpropyl. Examples of the cycloalkyl group include cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl.

[0105] Examples of the aryl group include a phenyl group, a naphthyl group, a 2-methylphenyl group, a 3-methylphenyl group, a 4-methylphenyl group, a 4-vinylphenyl group, and a 3-isopropylphenyl group.

[0106] Examples of the aralkyl group include a benzyl group, a diphenylmethyl group, and a naphthylmethyl group.

[0107] Examples of polymer segments other than the polysiloxane segment in the polysiloxane compound include vinyl polymer segments such as acrylic polymers, fluoroolefin polymers, vinyl ester polymers, aromatic vinyl polymers, and olefin polymers, and polymer segments such as polyurethane polymer segments, ester polymer segments, and ether polymer segments. Among these, the vinyl polymer segment is preferred.

[0108] The polysiloxane compound may be a composite resin in which a polysiloxane segment and a polymer segment are bonded via a structure represented by the following structural formula (S-3), or may have a three-dimensional network-like polysiloxane structure.

[0109] [Chemistry 3]

[0110]

[0111] In the formula, the carbon atom is a carbon atom constituting a polymer segment, and the two silicon atoms are silicon atoms constituting a polysiloxane segment.

[0112] The polysiloxane segments of the polysiloxane compound may contain functional groups that react upon heating, such as polymerizable double bonds. Heat-treating the polysiloxane compound before thermal decomposition allows for crosslinking reactions and solidification, making thermal decomposition easier.

[0113] Examples of polymerizable double bonds include vinyl groups and (meth)acryloyl groups. The polysiloxane segment preferably contains two or more polymerizable double bonds, more preferably 3 to 200, and even more preferably 3 to 50. Furthermore, the use of a composite resin containing two or more polymerizable double bonds as the polysiloxane compound facilitates crosslinking reactions.

[0114] The polysiloxane segment may contain silanol groups and / or hydrolyzable silyl groups. Examples of the hydrolyzable groups in the hydrolyzable silyl groups include halogen atoms, alkoxy groups, substituted alkoxy groups, acyloxy groups, phenoxy groups, mercapto groups, amino groups, amide groups, aminooxy groups, iminooxy groups, and alkenyloxy groups. These groups are hydrolyzed to convert the hydrolyzable silyl groups into silanol groups. In parallel with the thermal curing reaction, a hydrolysis-condensation reaction occurs between the hydroxyl groups in the silanol groups or the hydrolyzable groups in the hydrolyzable silyl groups to obtain a solid polysiloxane compound.

[0115] The so-called silanol group in this specification is a silicon-containing group having a hydroxyl group directly bonded to a silicon atom. In addition, the so-called hydrolyzable silyl group in this specification is a silicon-containing group having a hydrolyzable group directly bonded to a silicon atom. Specifically, for example, the group represented by the following general formula (S-4) can be mentioned.

[0116] [Chemistry 4]

[0117]

[0118] In addition, in the formula (S-4), R 4 is a monovalent organic group such as an alkyl group, an aryl group or an aralkyl group, R 5 is a halogen atom, an alkoxy group, an acyloxy group, an allyloxy group, a mercapto group, an amino group, an amide group, an aminooxy group, an iminooxy group or an alkenyloxy group. In addition, b is an integer from 0 to 2.

[0119] Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 1,2-dimethylpropyl group, a 1-ethylpropyl group, a hexyl group, an isohexyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 1,1-dimethylbutyl group, a 1,2-dimethylbutyl group, a 2,2-dimethylbutyl group, a 1-ethylbutyl group, a 1,1,2-trimethylpropyl group, a 1,2,2-trimethylpropyl group, a 1-ethyl-2-methylpropyl group, and a 1-ethyl-1-methylpropyl group.

[0120] Examples of the aryl group include a phenyl group, a naphthyl group, a 2-methylphenyl group, a 3-methylphenyl group, a 4-methylphenyl group, a 4-vinylphenyl group, and a 3-isopropylphenyl group.

[0121] Examples of the aralkyl group include a benzyl group, a diphenylmethyl group, and a naphthylmethyl group.

[0122] Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

[0123] Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, a sec-butoxy group, and a tert-butoxy group.

[0124] Examples of the acyloxy group include a formyloxy group, an acetyloxy group, a propionyloxy group, a butyryloxy group, a pivaloyloxy group, a valeryloxy group, a phenylacetyloxy group, an acetoacetyloxy group, a benzoyloxy group, and a naphthoyloxy group.

[0125] Examples of the allyloxy group include a phenyloxy group and a naphthyloxy group.

[0126] Examples of the alkenyloxy group include vinyloxy, allyloxy, 1-propenyloxy, isopropenyloxy, 2-butenyloxy, 3-butenyloxy, 2-pentenyloxy, 3-methyl-3-butenyloxy, and 2-hexenyloxy.

[0127] Examples of the polysiloxane segment having the structural unit represented by the general formula (S-1) and / or the general formula (S-2) include polysiloxane segments having the following structures.

[0128] [Chemistry 5]

[0129]

[0130] [Chemistry 6]

[0131]

[0132] [Chemistry 7]

[0133]

[0134] R in the structural formula (1) to the structural formula (3) 6 Indicates that the R 1 In addition, R in the above structural formulas (4) to (8) 7 With R 8 Respectively represent the R 2 and R 3 Same meaning.

[0135] The polymer segments may optionally have various functional groups within a range that does not hinder the effects of the present invention. Examples of such functional groups include carboxyl groups, blocked carboxyl groups, carboxylic anhydride groups, tertiary amino groups, hydroxyl groups, blocked 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).

[0136] [Chemistry 8]

[0137]

[0138] Furthermore, the polymer segment may have a polymerizable double bond such as a vinyl group or a (meth)acryloyl group.

[0139] The polysiloxane compound is preferably produced by, for example, the methods shown in the following (1) to (3).

[0140] (1) A method in which a polymer segment containing a silanol group and / or a hydrolyzable silyl group is prepared in advance as a raw material for a polymer segment, and the polymer segment is mixed with a silane compound having both a silanol group and / or a hydrolyzable silyl group and a polymerizable double bond, followed by a hydrolysis-condensation reaction.

[0141] (2) A polymer segment containing a silanol group and / or a hydrolyzable silyl group is prepared in advance as a raw material for the polymer segment. Alternatively, a silane compound having both a silanol group and / or a hydrolyzable silyl group and a polymerizable double bond is subjected to a hydrolysis-condensation reaction to prepare polysiloxane in advance. The polymer segment and the polysiloxane are then mixed and subjected to a hydrolysis-condensation reaction.

[0142] (3) A method in which a polymer segment, a silane compound having a silanol group and / or a hydrolyzable silyl group and a polymerizable double bond are mixed with polysiloxane to carry out a hydrolysis-condensation reaction. A polysiloxane compound is obtained by the above method.

[0143] Commercially available polysiloxane compounds include, for example, the CERANATE (registered trademark) series (organic / inorganic hybrid coating resins; manufactured by DIC Corporation) and the COMPOCERAN SQ series (silsesquioxane hybrids; manufactured by Arakawa Chemical Industries, Ltd.).

[0144] The carbon source resin has good miscibility with the polysiloxane compound and is carbonized by high-temperature calcination in an inert non-oxidizing atmosphere, effectively forming a carbonaceous phase in the matrix phase. The carbon source resin or the resin contained in the carbon source resin composition is not particularly limited, as long as it contains a molecular structure having a benzene ring or an aromatic functional group. Examples include: thermosetting resins; thermoplastic resins; petroleum-based or carbonaceous tars or asphalts such as by-products of petroleum-based tars or asphalts during the production of ethylene, coal tars produced during the dry distillation of coal, heavy components or asphalts obtained by distilling off low-boiling components of coal tar, tars or asphalts obtained by liquefying coal, etc.; and those obtained by cross-linking the tars or asphalts, etc. One or more of these can be used in combination.

[0145] Thermosetting resins are not particularly limited, and examples include: phenolic resins such as novolac-type phenolic resins and cresol-type phenolic resins; epoxy resins such as bisphenol-type epoxy resins and novolac-type epoxy resins; melamine resins; urea-formaldehyde resins; aniline resins; cyanate ester resins; furan resins; ketone resins; unsaturated polyester resins; and polyurethane resins. Modified versions of these resins with various components may also be used. When using a thermosetting resin, the aforementioned hardener may be used in combination.

[0146] In addition, the thermoplastic resin is not particularly limited, and examples thereof include polyethylene, polystyrene, polyacrylonitrile, acrylonitrile-styrene (AS) resin, acrylonitrile-butadiene-styrene (ABS) resin, polypropylene, vinyl chloride, methacrylic resin, polyethylene terephthalate, polyamide, polycarbonate, polyacetal, polyphenylene ether, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyetherimide, polyamideimide, polyimide, and polyphthalamide.

[0147] As the resin or resin composition of the raw material of carbonaceous phase in the composite active material for secondary battery of the present embodiment, with regard to the viewpoint of promoting the generation of silicon nitride, it is preferably to include nitrogen-containing resin as main component resin. By carbonizing this resin, the catalytic effect of transition metal ions on the generation of nitrogen substances is improved, and a carbonaceous phase containing nitrogen can also be obtained. If nitrogen is included in carbon, due to the electronegativity of nitrogen, suitable electrical characteristics can be given to carbon (carbon material for lithium ion secondary battery). Thus, the occlusion and release of lithium ions can be promoted, giving high charge and discharge characteristics.

[0148] Examples of the nitrogen-containing resins include the following: thermosetting resins include melamine resins, urea resins, aniline resins, cyanate resins, and polyurethane resins, as well as phenol resins and epoxy resins modified with nitrogen-containing components such as amines.

[0149] When a nitrogen-containing compound is used as a component other than the main component resin, the type thereof is not particularly limited. For example, in addition to hexamethylenetetramine as a hardener for novolac-type phenolic resins, aliphatic polyamines, aromatic polyamines, dicyandiamide, etc. as hardeners for epoxy resins, nitrogen-containing compounds such as amine compounds, ammonium salts, nitrates, and nitro compounds that do not function as hardeners other than hardener components can also be used.

[0150] As the nitrogen-containing compound, either one kind may be used or two or more kinds may be used in combination, regardless of whether the main component resin contains nitrogen-containing resins or not.

[0151] In this embodiment, the preparation method of the resin composition used as the raw material of the carbonaceous phase is not particularly limited. For example, the main component resin and other components can be mixed in a specified ratio, and these components can be dissolved in a solvent and mixed, or the precursor of the active material can be prepared by mixing these components with the silicon slurry.

[0152] When the composite active material for a secondary battery further comprises carbon (carbon coating) on ​​its surface, the resulting active material is coated with the carbon coating in a chemical vapor deposition apparatus in a flow of a pyrolytic carbon source gas and a carrier inert gas at a temperature range of 700°C to 1000°C. Examples of pyrolytic carbon source gases include acetylene, ethylene, acetone, alcohols, propane, methane, and ethane. Examples of inert gases include nitrogen, helium, and argon, with nitrogen being commonly used.

[0153] Next, in the high-temperature treatment step, the active material precursor dried in the homogenization step is calcined in a non-oxidizing atmosphere. The apparatus used for the high-temperature treatment can be appropriately selected, depending on the intended purpose, from a fluidized bed reactor, rotary kiln, vertical moving bed reactor, tunnel furnace, batch furnace, rotary kiln, and the like. High-temperature treatment is performed according to a calcination schedule defined by factors such as the heating rate and the time it is held at a constant temperature. The calcination temperature preferably reaches a maximum temperature within a range of 900°C to 1300°C, for example. This results in the silicon material of this embodiment.

[0154] The non-oxidizing atmosphere during the high-temperature calcination is not particularly limited to the type of gas used, and examples thereof include nitrogen, argon, hydrogen, and nitrogen / hydrogen mixed gases. Of these, nitrogen is preferably used from the viewpoint of promoting the formation of silicon nitride.

[0155] Furthermore, the calcined product obtained in the high-temperature treatment step can be crushed and classified as needed to obtain a silicon material with a desired particle size. The crushing can be performed in one stage until the target particle size is reached, or it can be performed in multiple stages. In the case where the particle size of the calcined silicon material is a lump or agglomerated particles of 10 mm or more, it can be coarsely crushed using a jaw crusher, a roller crusher, etc., and then crushed using a glow mill, a ball mill, etc., and then crushed using a bead mill, a jet mill, etc. In addition, the particle size is the volume average particle size and is the D50 value.

[0156] Furthermore, if the silicon material produced by pulverization contains coarse particles, classification is preferably performed to remove the coarse particles and to adjust the particle size distribution by removing fine powder. The classifier used can be a pneumatic classifier, a wet classifier, or the like, depending on the intended purpose. However, in order to reliably achieve the desired removal of coarse particles, classification by sieving is preferred.

[0157] [Secondary battery]

[0158] The secondary battery of this embodiment is not particularly limited as long as it contains the composite active material for secondary batteries in the negative electrode, but may also contain components such as an organic binder or a conductive additive. The secondary battery of this embodiment can be made by applying a slurry containing an organic binder and other components such as conductive additives as needed in a thin film on the collector copper foil. In addition, a carbon material such as graphite can be added to the slurry to make the negative electrode. Examples of the carbon material include natural graphite, artificial graphite, amorphous carbon such as hard carbon or soft carbon, and the like.

[0159] For example, the negative electrode layer can be obtained by mixing a composite active material for a secondary battery and a binder as an organic binder with a solvent using a dispersing device such as a blender, a ball mill, a super sand mill, or a pressure kneader to prepare a negative electrode material slurry, which is then applied to a current collector to form a negative electrode layer. Alternatively, the negative electrode material slurry can be formed into a sheet, granules, or other form, and then integrated with the current collector to obtain the negative electrode layer.

[0160] Examples of the organic binder include styrene-butadiene rubber copolymers (hereinafter also referred to as "SBR (Styrene Butadiene Rubber)"); unsaturated carboxylic acid copolymers such as ethylenically unsaturated carboxylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, (meth)acrylonitrile, and hydroxyethyl (meth)acrylate; and (meth)acrylic acid copolymers containing 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, polyamide-imide, and carboxymethyl cellulose (hereinafter also referred to as "CMC (Carboxymethyl Cellulose)").

[0161] These organic binders include those dispersed or dissolved in water, and those dissolved in organic solvents such as N-methyl-2-pyrrolidone (NMP), depending on their physical properties. The content of the organic binder in the negative electrode layer of the negative electrode of the lithium ion secondary battery is preferably 1% to 30% by mass, more preferably 2% to 20% by mass, and further preferably 3% to 15% by mass.

[0162] By having an organic binder content of 1% by mass or more, adhesion is improved, and the expansion and contraction during charge and discharge further suppress the destruction of the negative electrode structure. On the other hand, by having an organic binder content of 30% by mass or less, the increase in electrode resistance can be further suppressed.

[0163] A conductive additive may also be mixed into the negative electrode material slurry as needed. Examples of conductive additives include carbon black, graphite, acetylene black, and conductive oxides or nitrides. The amount of conductive additive used relative to the negative electrode active material of this embodiment can be, for example, 1% to 15% by mass.

[0164] In addition, about the material and shape of the collector, for example, copper, nickel, titanium, stainless steel, etc. can be made into a strip-shaped collector in the form of foil, perforated foil, mesh, etc. In addition, porous materials such as porous metal (foam metal) or carbon paper can also be used.

[0165] Examples of methods for coating the negative electrode material slurry on the current collector include metal mask printing, electrostatic coating, dip coating, spray coating, roll coating, doctor blade coating, gravure coating, and screen printing. After coating, the slurry is preferably subjected to rolling treatment using a flat press, calendar rolls, or the like, as needed.

[0166] Furthermore, the negative electrode material slurry is formed into a sheet or pellet shape, and the sheet or pellet shape and the current collector can be integrated with a roller, a press, or a combination thereof.

[0167] The negative electrode layer formed on the current collector or the negative electrode layer integrated with the current collector is preferably heat-treated according to the organic binder used. For example, when using an aqueous styrene-butadiene rubber copolymer (SBR) or the like, it is sufficient to heat-treat at 100°C to 130°C. When using an organic binder having a polyimide or polyamide-imide as the main skeleton, it is preferably heat-treated at 150°C to 450°C.

[0168] By described heat treatment, the removal of solvent, the high strength caused by the hardening of adhesive are carried out, and the adhesion between particle and current collector can be improved. In addition, in order to prevent the oxidation of the current collector in the process, these heat treatments are preferably carried out under inert atmospheres such as helium, argon, nitrogen, vacuum atmosphere.

[0169] In addition, it is preferable to perform a pressure treatment on the negative electrode after the heat treatment. In the negative electrode, the electrode density is preferably 1 g / cm 3 to 1.8g / cm 3 , more preferably 1.1 g / cm 3 to 1.7g / cm 3 , and more preferably 1.2 g / cm 3 Up to 1.6g / cm 3 Regarding electrode density, higher electrode density tends to improve adhesion and the volumetric capacity density of the electrode. On the other hand, if the electrode density is too high, the voids in the electrode decrease, which may weaken the effect of suppressing the volume expansion of silicon and other components, and reduce the capacity retention rate. Therefore, the optimal range of electrode density is selected.

[0170] The secondary battery of this embodiment includes the composite active material for a secondary battery of this embodiment. As a secondary battery including the composite active material for a secondary battery, a non-aqueous electrolyte secondary battery and a solid electrolyte secondary battery are preferred, and particularly when used as the negative electrode of a non-aqueous electrolyte secondary battery, excellent performance is achieved.

[0171] When used in a wet electrolyte secondary battery, for example, the secondary battery of this embodiment can be constructed by placing a positive electrode and a negative electrode separator containing the negative electrode active material of this embodiment facing each other and injecting an electrolyte solution.

[0172] The positive electrode can be obtained by forming a positive electrode layer on the surface of a current collector in the same manner as the negative electrode. The current collector can be a strip-shaped current collector made of a metal or alloy such as aluminum, titanium, stainless steel, etc. in the form of foil, perforated foil, mesh, etc.

[0173] There is no particular limitation on the positive electrode material used for the positive electrode layer. In the case of a non-aqueous electrolyte secondary battery, when a lithium ion secondary battery is produced, for example, a metal compound, metal oxide, metal sulfide or conductive polymer material that can be doped or intercalated with lithium ions can be used. For example, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2) and their composite oxides (LiCoO2) can be used alone or in combination. x Ni y Mn z O2, x+y+z=1), lithium manganese spinel (LiMn2O4), lithium vanadium compounds, V2O5, V6O 13 , VO2, MnO2, TiO2, MoV2O8, TiS2, V2S5, VS2, MoS2, MoS3, Cr3O8, Cr2O5, olivine-type LiMPO4 (wherein M is Co, Ni, Mn or Fe), polyacetylene, polyaniline, polypyrrole, polythiophene, polybenzone and other conductive polymers, porous carbon, etc.

[0174] As a separator, for example, a nonwoven fabric, a cloth, a microporous membrane or a combination thereof based on polyolefins such as polyethylene and polypropylene can be used. In addition, in the case where the positive electrode of the nonaqueous electrolyte secondary battery produced is not in direct contact with the negative electrode, there is no need to use a separator.

[0175] As the electrolyte, for example, a so-called organic electrolyte can be used, which is obtained by dissolving a lithium salt such as LiClO4, LiPF6, LiAsF6, LiBF4, LiSO3CF3 in a non-aqueous solvent such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, 3-methyl-1,3-oxazolidin-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, butyl methyl carbonate, ethylpropyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, or a mixture of two or more components.

[0176] The structure of the secondary battery of this embodiment is not particularly limited. Generally, the following structure is employed: the positive electrode, negative electrode, and optionally, a separator are wound into a flat spiral to form a wound electrode plate assembly, or stacked into flat plates to form a stacked electrode plate assembly, and these electrode plate assemblies are enclosed in an outer casing. Furthermore, the half-cells used in the examples of the present invention have a structure in which the negative electrode is primarily composed of the negative electrode active material of this embodiment, and a simplified evaluation using metallic lithium is performed on the opposite electrode. This allows for a more precise comparison of the cycling characteristics of the active material itself.

[0177] The secondary battery of this embodiment is not particularly limited and can be used as a paper battery, button battery, coin battery, laminated battery, cylindrical battery, prismatic battery, etc. The negative electrode active material of this embodiment can also be used in an entire electrochemical device that uses lithium ion insertion / desorption as a charging and discharging mechanism, such as a hybrid capacitor, a solid lithium secondary battery, etc.

[0178] Example

[0179] The present invention is described in detail below using examples, but the present invention is not limited to these. [%] and [parts] in these examples represent "mass %" and "mass parts" unless otherwise specified. Silicon slurries, polysiloxane compounds, and curable resin compositions were prepared by the following method. Secondary battery evaluations were performed using the composite active materials for secondary batteries prepared in Examples 1 to 24 and Comparative Examples 1 and 2.

[0180] Synthesis Example 1: Preparation of Silicon Particles (Silicon Slurry; Si1 to Si5)

[0181] Zirconia beads (particle size range: 0.1 mm to 0.2 mm) and 100 ml of methyl ethyl ketone (MEK) solvent were placed in a 150 ml container of a small bead mill at a filling rate of 60%. Then, raw silicon (average particle size 5 μm) and a cationic dispersant solution (BYK-Chemie Japan Co., Ltd., BYK145) were added as shown in Table 1 below. Wet milling was performed in a bead mill under the various conditions shown in Table 1 below to obtain a dark brown liquid silicon slurry (solids concentration 30% by mass; Si1 to Si5). The average particle size (D50) of the pulverized silicon particles was measured using a laser diffraction particle size analyzer (Mastersizer 3000, manufactured by Malvern Panalytical). Furthermore, the size of the pulverized silicon particles was confirmed by TEM observation. The average particle size (D50) of the silicon particles is shown in Table 1.

[0182] [Table 1]

[0183]

[0184] "Synthesis Example 2: Preparation of polysiloxane compounds"

[0185] (Synthesis of Condensate (a1) of Methyltrimethoxysilane)

[0186] First, a reaction vessel equipped with a stirrer, a thermometer, a dropping funnel, a cooling tube, and a nitrogen inlet was charged with 1,421 parts of methyltrimethoxysilane (hereinafter referred to as MTMS), and the temperature was raised to 60°C. Next, a mixture of 0.17 parts of isopropyl acid phosphate ("Phoslex A-3" manufactured by SC Organic Chemical Co., Ltd.) and 207 parts of deionized water was added dropwise to the reaction vessel over 5 minutes, and then stirred at 80°C for 4 hours to carry out a hydrolysis-condensation reaction. The condensation product obtained by the hydrolysis condensation reaction is distilled at a temperature of 40°C to 60°C and a reduced pressure of 40kPa to 1.3kPa (meaning that the reduced pressure condition at the beginning of methanol distillation is 40kPa and the final pressure is reduced to 1.3kPa) to remove the methanol and water generated during the reaction, thereby obtaining 1,000 parts by mass of a liquid containing a condensation product of MTMS with a number average molecular weight of 1,000 to 5000 (70% by mass of the active ingredient).

[0187] The effective component is a component calculated by dividing the theoretical yield (parts by mass) when all methoxy groups of silane monomers such as MTMS undergo condensation reaction by the actual yield (parts by mass) after the condensation reaction [theoretical yield (parts by mass) when all methoxy groups of silane monomers undergo condensation reaction / actual yield (parts by mass) after the condensation reaction].

[0188] (Production of Curable Resin Composition (1))

[0189] First, a reaction vessel equipped with a stirrer, a thermometer, a dropping funnel, a cooling tube, and a nitrogen inlet was charged with 150 parts by mass of butanol (hereinafter referred to as BuOH), 105 parts by mass of polytetramethoxysilane (hereinafter referred to as PTMS), and 277 parts by mass of dimethoxydimethylsilane (hereinafter referred to as DMDMS), and the temperature was raised to 80°C. Next, a mixture containing 21 parts by mass of methyl methacrylate (hereinafter referred to as MMA), 4 parts by mass of butyl methacrylate (hereinafter referred to as BMA), 3 parts by mass of butyl acrylate (hereinafter referred to as BA), 2 parts by mass of (3-mercaptopropyl)triethoxysilane (hereinafter referred to as MPTS), 3 parts by mass of BuOH, and 0.6 parts by mass of tert-butylperoxy-2-ethylhexanoate (hereinafter referred to as TBPEH) was added dropwise to the reaction vessel over 6 hours at the above temperature. After the completion of the dropwise addition, the mixture was reacted at the above temperature for a further 20 hours to obtain an organic solvent solution of a vinyl polymer (a2-1) having a number average molecular weight of 10,000 and having a hydrolyzable silyl group.

[0190] Next, a mixture of 0.04 parts by mass of Phoslex A-3 and 112 parts by mass of deionized water was added dropwise over 5 minutes, and the mixture was stirred at the temperature for 10 hours to carry out a hydrolysis condensation reaction, thereby obtaining a liquid of a composite resin composed of the hydrolyzable silyl group possessed by the vinyl polymer (a2-1) and the hydrolyzable silyl group and silanol group possessed by the polysiloxane derived from the PTMS and DMDMS.

[0191] Then, 472 parts by mass of the MTMS condensate (a1) obtained above and 80 parts by mass of deionized water were added to the liquid, and the mixture was stirred at the temperature for 10 hours to carry out a hydrolysis-condensation reaction. The generated methanol and water were removed by distillation under the same conditions as in Synthesis Example 1, and 250 parts by mass of BuOH were added to obtain 1,000 parts by mass of a curable resin composition (1) having a non-volatile content of 60.1% by mass.

[0192] (Production of Curable Resin Composition (2))

[0193] First, 150 parts by mass of BuOH, 249 parts by mass of PTMS, and 263 parts by mass of DMDMS were placed in a reaction vessel equipped with a stirrer, a thermometer, a dropping funnel, a cooling tube, and a nitrogen inlet, and the temperature was raised to 80°C.

[0194] Next, a mixture containing 18 parts by mass of MMA, 14 parts by mass of BMA, 7 parts by mass of BA, 1 part by mass of acrylic acid (AA), 2 parts by mass of MPTS, 6 parts by mass of BuOH, and 0.9 parts by mass of TBPEH was added dropwise to the reaction vessel at the above temperature over 5 hours. After the completion of the dropwise addition, the mixture was reacted at the above temperature for a further 10 hours to obtain an organic solvent solution of a vinyl polymer (a2-2) having a number average molecular weight of 20,100 and having a hydrolyzable silyl group.

[0195] Next, a mixture of 0.05 parts by mass of Phoslex A-3 and 147 parts by mass of deionized water was added dropwise over 5 minutes, and then stirred at the temperature for 10 hours to carry out a hydrolysis condensation reaction, thereby obtaining a liquid of a composite resin composed of hydrolyzable silyl groups possessed by the vinyl polymer (a2-2) and hydrolyzable silyl groups and silanol groups possessed by the polysiloxane derived from PTMS and DMDMS.

[0196] Then, 76 parts by mass of 3-glycidyloxypropyltrimethoxysilane, 231 parts by mass of the MTMS condensate (a1) obtained above, and 56 parts by mass of deionized water were added to the liquid, and the mixture was stirred at the above temperature for 15 hours to carry out a hydrolysis-condensation reaction. The generated methanol and water were then removed by distillation under the same conditions as in Synthesis Example 1, and 250 parts by mass of BuOH were added to obtain 1,000 parts by mass of a curable resin composition (2) having a non-volatile content of 60.0% by mass.

[0197] Example 1

[0198] To 100 g of a slurry containing silicon particles (Si2 of Synthesis Example 1, average particle size D50 = 100 nm, Si content = 16.7 mass %), an appropriate amount of anhydrous magnesium acetate solution (concentration 5 mass %; solvent ethanol) was added to achieve a Mg / Si (molar ratio) of 2.0 / 100 and an appropriate amount of manganese (III) acetylacetonate solution (concentration 5 mass %; solvent MEK) was added to achieve a Mn / Si (molar ratio) of 0.02 / 100. After stirring at room temperature for 1 hour, the polysiloxane compound (curable resin composition (1): average molecular weight 3500) and phenol resin (average molecular weight 3000) prepared in Synthesis Example 2 were added to the product after high-temperature calcination to achieve a composition mass ratio of Si / SiOC / C of 50 / 20 / 30. After being thoroughly mixed in a stirrer, the mixture was dried under reduced pressure at 110°C. The dried product was calcined at 1100°C for 2 hours in a nitrogen atmosphere, and then pulverized and classified (average particle size D50 = about 5 μm) to obtain a powder of active material for silicon material. The measurement results of Fourier-Transform Infrared Spectrophotometer (FT-IR) showed that Si-N bonds (900 cm -1 ) and Si-C(800cm -1 ) bond stretching absorption peak. According to the results of TEM observation and STEM-EDS element mapping analysis of the cross section of the active material particles after FIB processing, it is believed that magnesium silicate lattice and SiN x / SiC microcrystal structure, and also detected the Mg and Mn elements added during the material production.

[0199] 80 parts by mass of the powder of the active material obtained in the above-mentioned method were mixed with 10 parts of acetylene black as a conductive aid and 10 parts of a mixture of CMC and SBR as a binder to prepare a slurry. The obtained slurry was formed into a film on a copper foil. After drying under reduced pressure at 110°C, a coin-type lithium-ion battery was prepared as a half-cell using Li metal foil as the opposite electrode. The charge and discharge characteristics of the prepared half-cell were evaluated at 25°C using a secondary battery charge and discharge test device (manufactured by Beidou Co., Ltd.). The cut-off voltage range was set to 0.005V to 1.5V. The charge and discharge measurement results showed that the initial charge / discharge capacity was 1720mAhg -1 / 1500mAhg -1, the first coulombic efficiency was 87.2%. For the evaluation of the full battery, a single-layer sheet was used to make the positive electrode film. The single-layer sheet used LiCoO2 as the positive electrode material and aluminum foil as the current collector. The negative electrode film was made by mixing graphite powder and active material powder with a discharge capacity design value of 450mAh / g. The following coin-type lithium-ion secondary battery was made: the non-aqueous electrolyte used was a non-aqueous electrolyte solution obtained by dissolving lithium hexafluorophosphate at a concentration of 1 mol / L in a 1 / 1 (volume ratio) mixture of ethylene carbonate and diethyl carbonate, and the separator used a polyethylene microporous film with a thickness of 30μm. The laminated lithium-ion secondary battery was charged at room temperature at a constant current of 1.2mA (0.25C based on the positive electrode) until the voltage of the test battery reached 4.2V. After reaching 4.2V, the current was reduced and charged in a manner to maintain the battery voltage at 4.2V to obtain the discharge capacity. The capacity retention rate after 100 cycles at 45° C. was 88% (shown in Table 2 below).

[0200] Example 2 to Example 6

[0201] To 100 g of a slurry containing silicon particles (Si2 from Synthesis Example 1, average particle size D50 = 100 nm, Si content = 16.7 mass%), under the same conditions as in Example 1, an appropriate amount of manganese (III) acetylacetonate solution (5 mass% concentration; solvent MEK) was added, maintaining a constant Mg / Si (molar ratio) of 2.0 / 100, to achieve Mn / Si (molar ratios) of 0.05 / 100 (Example 2); 0.1 / 100 (Example 3); 0.5 / 100 (Example 4); 1.0 / 100 (Example 5); and 4.5 / 100 (Example 6). The mixture was stirred at room temperature for 1 hour. All other operations were performed under the same conditions as in Example 1. The obtained analytical results and charge and discharge evaluation results of half cells and full cells are shown in Table 2.

[0202] Example 7 to Example 11

[0203] To 100 g of a slurry containing silicon particles (Si2 from Synthesis Example 1, average particle size D50 = 100 nm, Si content = 16.7 mass%), under the same conditions as in Example 1, an appropriate amount of manganese(III) acetylacetonate solution (5 mass% concentration; solvent MEK) was added, maintaining a constant Mn / Si (molar ratio) of 0.5 / 100, to adjust the Mg / Si (molar ratio) to 0.1 / 100 (Example 7); 0.5 / 100 (Example 8); 1.0 / 100 (Example 9); 5.0 / 100 (Example 10); and 9.5 / 100 (Example 11). The mixture was stirred at room temperature for 1 hour. All other operations were performed under the same conditions as in Example 1. The obtained analytical results and charge and discharge evaluation results of half cells and full cells are shown in Table 2.

[0204] Example 12

[0205] In 100 g of a slurry containing silicon particles (Si2 of Synthesis Example 1, average particle size D50 = 100 nm, Si content = 16.7 mass %), under the same conditions as in Example 1, an appropriate amount of anhydrous lithium acetate solution (concentration 5 mass %; solvent ethanol) was added to a constant Mn / Si (molar ratio) of 0.5 / 100 to meet a Li / Si (molar ratio) of 4.0 / 100, and the mixture was stirred at room temperature for 1 hour. The dried precursor was calcined at a high temperature of 1000°C for 2 hours in a nitrogen atmosphere. Other operations were carried out under the same conditions as in Example 1. By cross-sectional HR-TEM analysis of the obtained silicon material, i.e., the active material, a lattice structure of lithium silicate and silicon nitride microcrystals was observed near the surface of the silicon particles, and the presence of Li element was also detected on the surface of the silicon particles by XPS elemental analysis. In addition, the charge and discharge evaluation results of the half-cell and full-cell are shown in Table 2.

[0206] Example 13 to Example 16

[0207] To 100 g of a slurry containing silicon particles (Si2 of Synthesis Example 1, average particle size D50 = 100 nm, Si content = 16.7 mass %), under the same conditions as in Example 1, various metal ion solutions (Fe 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3+ 、Ni + 、Cu 2+ 、La 3+ ), and stirred at room temperature for 1 hour.

[0208] Example 13: Fe / Si (molar ratio) = 0.1 / 100 (5 mass% anhydrous iron (II) acetate ethanol solution)

[0209] Example 14: Ni / Si (molar ratio) = 0.1 / 100 (5 mass% anhydrous nickel acetate ethanol solution)

[0210] Example 15: Cu / Si (molar ratio) = 0.1 / 100 (5 mass% anhydrous copper (II) acetate ethanol solution)

[0211] Example 16: La / Si (molar ratio) = 0.1 / 100 (5 mass% anhydrous lanthanum (III) acetate ethanol solution)

[0212] Other operations were performed under the same conditions as in Example 1. Table 2 shows the obtained analysis results and the charge and discharge evaluation results of the half cell and the full cell.

[0213] Example 17 to Example 18

[0214] To 100 g of a slurry containing silicon particles (Si2 of Synthesis Example 1, average particle size D50 = 100 nm, Si content = 16.7 mass %), anhydrous magnesium acetate (concentration 5 mass %; solvent ethanol) and a manganese (III) acetylacetonate solution (concentration 5 mass %; solvent MEK) were added under the same conditions as in Example 1 to achieve a Mg / Si (molar ratio) of 2.0 / 100 and a Mn / Si (molar ratio) of 0.5 / 100, and the mixture was stirred at room temperature for 1 hour. Subsequently, the polysiloxane resin (curable resin composition (1): average molecular weight 3500) and phenol resin (average molecular weight 3000) prepared in Synthesis Example 2 were added to the resultant after high-temperature calcination to achieve a compositional mass ratio of Si / SiOC / C of 50 / 10 / 40 (Example 17) and 50 / 2 / 48 (Example 18), respectively. The mixture was thoroughly mixed in a stirrer and then dried under reduced pressure at 110°C. The dried product was calcined at 1100°C for 2 hours in a nitrogen atmosphere, and then crushed and classified (average particle size D50 = about 5 μm) to obtain a powder of the active material as a silicon material. Then, 25 g of the sample powder was placed in a reaction vessel of a chemical vapor deposition device (Chemical Vapor Deposition (CVD), disc rotary kiln, Takasago Industrial Co., Ltd.), and a carbon film was formed on the active material in a mixed flow of acetylene (flow rate: 0.3 L / min) and nitrogen (flow rate: 0.7 L / min) at 850°C for 1 hour. According to the thermal analysis results of the active material as a silicon material, the amount of carbon film was 5%. The obtained analysis results and the charge and discharge evaluation results of half cells and full cells are shown in Table 2.

[0215] Example 19

[0216] In 100 g of a slurry containing silicon particles (Si2 of Synthesis Example 1, average particle size D50 = 100 nm, Si content = 16.7 mass %), under the same conditions as in Example 1, anhydrous magnesium acetate (concentration 5 mass %; solvent ethanol) and acetylacetonate manganese (III) solution (concentration 5 mass %; solvent MEK) were added to achieve a Mg / Si (molar ratio) = 2.0 / 100 and a Mn / Si (molar ratio) = 0.5 / 100, and the mixture was stirred at room temperature for 1 hour. Then, methyl polysilicate silane (M Silicate 51, Tama Chemical Industry Co., Ltd.) was added to the resultant after high temperature calcination to achieve a composition mass ratio Si / SiO x After being thoroughly mixed in a blender with a mixture of 50 / 10 / 40, the mixture was dried under reduced pressure at 110°C. The dried mixture was calcined at 1100°C for 2 hours in a nitrogen atmosphere, and then pulverized and classified (average particle size D50 = approximately 5 μm) to obtain a powder of the active material, which serves as the silicon material. The obtained analytical results and charge-discharge evaluation results of half cells and full cells are shown in Table 2.

[0217] Example 20

[0218] To 100 g of a slurry containing silicon particles (Si2 of Synthesis Example 1, average particle size D50 = 100 nm, Si content = 16.7 mass %), anhydrous magnesium acetate (concentration 5 mass %; solvent ethanol) and a manganese (III) acetylacetonate solution (concentration 5 mass %; solvent MEK) were added under the same conditions as in Example 1 to achieve a Mg / Si (molar ratio) of 2.0 / 100 and a Mn / Si (molar ratio) of 0.5 / 100, and the mixture was stirred at room temperature for 1 hour. Subsequently, a polysiloxane resin (curable resin composition (2): average molecular weight 3500) and a phenol resin (average molecular weight 3000) prepared in the same manner as in Synthesis Example 2 were added to the resultant after high-temperature calcination to achieve a compositional mass ratio of Si / SiOC / C of 40 / 30 / 30. The mixture was thoroughly mixed in a stirrer and then dried under reduced pressure at 110°C. The dried product was calcined at 1100°C for 2 hours in a nitrogen atmosphere, then pulverized and classified (average particle size D50 = approximately 5 μm) to obtain a powder of the active material, serving as the silicon material. The analytical results and charge-discharge evaluation results of half-cells and full-cells are shown in Table 2.

[0219] Example 21 to Example 24

[0220] In 100 g of a slurry containing silicon particles (Example 21: Si5 of Synthesis Example 1 / average particle size D50 = 15 nm; Example 22: Si1 of Synthesis Example 1 / average particle size D50 = 57 nm; Example 23: Si3 of Synthesis Example 1 / average particle size D50 = 250 nm; Example 24: Si4 of Synthesis Example 1 / average particle size D50 = 400 nm), anhydrous magnesium acetate (concentration 5% by mass; solvent ethanol) and manganese (III) acetylacetonate solution (concentration 5% by mass; solvent MEK) were added under the same conditions as in Example 1 so as to achieve a Mg / Si (molar ratio) of 2.0 / 100 and a Mn / Si (molar ratio) of 0.5 / 100, and the mixture was stirred at room temperature for 1 hour. Then, a polysiloxane resin (curable resin composition (1): average molecular weight 3500) and a phenol resin (average molecular weight 3000) prepared in the same manner as in Synthesis Example 2 were added to the resultant after high-temperature calcination to achieve a composition weight ratio of 2.0 / 100.

[0221] Si / SiOC / C=50 / 10 / 40, after being thoroughly mixed in a blender, was dried under reduced pressure at 110°C. The dried product was calcined at high temperature at 1100°C for 2 hours in a nitrogen atmosphere, and then crushed and classified (average particle size D50=about 5μm) to obtain a powder of the active material as a silicon material. Then, 25g of the active material powder was placed in a reaction vessel of a chemical vapor deposition device (CVD, disc rotary kiln, Takasago Industrial Co., Ltd.), and a carbon film was formed on the active material in a mixed flow of acetylene (flow rate: 0.3L / min) and nitrogen (flow rate: 0.7L / min) at 850°C for 1 hour. According to the thermal analysis results of the active material as the silicon material, the amount of carbon film was 5%. The obtained analysis results or the charge and discharge evaluation results of half cells and full cells are shown in Table 2.

[0222] Comparative Example 1

[0223] 100 g of a slurry containing silicon particles (Si2 of Synthesis Example 1, average particle size D50 = 100 nm, Si content = 16.7% by mass) was mixed with the polysiloxane resin of Synthesis Example 2 (curable resin composition (1): average molecular weight 3500) and phenol resin (average molecular weight 3000) so that the composition mass ratio of the product after high-temperature calcination was Si / SiOC / C = 50 / 10 / 40. After sufficient stirring, the product was dried under reduced pressure at 110°C. The dried product was calcined at 1100°C for 2 hours in a nitrogen atmosphere, and then pulverized and classified (average particle size D50 = about 5 μm) to obtain a powder of an active material as a silicon material. The measurement result of Fourier transform infrared spectrophotometer (FT-IR) was that no Si-N bond was detected (900 cm -1 ) and Si-C(800cm-1 ) bond stretching absorption peak. According to TEM observation of the cross section of the active material particles processed by FIB, no SiN x / SiC microcrystal structure. Other operations were carried out under the same conditions as in Example 1. Table 2 shows the charge and discharge evaluation results of the half cell and the full cell.

[0224] Comparative Example 2

[0225] Commercially available nano-silicon particles (average particle size of 100 nm or less, Sigma-Aldrich), the polysiloxane resin of Synthesis Example 2 (curable resin composition (1): average molecular weight 3500) and phenol resin (average molecular weight 3000) were mixed so that the composition mass ratio of the product after high-temperature calcination was Si / SiOC / C = 50 / 10 / 40. After sufficient stirring, the mixture was dried under reduced pressure at 110°C. The dried product was calcined at 1100°C for 2 hours in a nitrogen atmosphere, and then pulverized and classified (average particle size D50 = about 5 μm) to obtain a powder of active material as a silicon material. The measurement result of Fourier transform infrared spectrophotometer (FT-IR) was that no Si-N bond was detected (900 cm -1 ) and Si-C(800cm -1 ) bond expansion and contraction absorption peak. Other operations were carried out under the same conditions as in Example 1. The charge and discharge evaluation results of the half cell and the full cell are shown in Table 2.

[0226]

[0227] Table 2 shows that the composite active materials for secondary batteries according to this embodiment (Examples 1 to 24) exhibit higher capacity retention and initial coulombic efficiency when fabricated into secondary batteries than active materials containing no metal elements (Comparative Examples 1 and 2). This demonstrates that the composite active materials for secondary batteries according to this embodiment can maintain high charge and discharge performance, such as capacity retention and initial coulombic efficiency, in secondary batteries.

[0228] Although the present invention has been described in detail with reference to specific embodiments, it is clear to those skilled in the art that various changes or modifications may be made without departing from the spirit and scope of the present invention. This application is based on Japanese patent application (Japanese Patent Application No. 2023-029515) filed on February 28, 2023, the contents of which are incorporated herein by reference.

Claims

1. A composite active material for a secondary battery, comprising a silicon material having at least one structure selected from the group consisting of A and B below: A: The silicon particles have a metal ion silicate phase and a silicon nitride phase and / or a silicon carbide phase integrated on the outside, and a matrix phase enclosing them. B: A matrix phase containing metal ion silicate and silicon nitride and / or silicon carbide is present on the outside of the silicon particles. 2 . The composite active material for a secondary battery according to claim 1 , comprising a silicon material having the structure of A. 3 .

3. The composite active material for secondary batteries according to claim 1, wherein The metal ion silicate phase and the silicon nitride phase and / or the silicon carbide phase exist in a layered form on the silicon particles.

4. The composite active material for secondary batteries according to claim 1, wherein The metal ions in the metal ion silicate phase are ions of at least one element selected from the group consisting of alkali metal elements and alkaline earth metal elements.

5. The composite active material for secondary batteries according to claim 4, wherein The alkali metal element is Li.

6. The composite active material for secondary batteries according to claim 4, wherein The alkaline earth metal is Mg.

7. The composite active material for secondary batteries according to claim 1, wherein The silicon material further contains a transition metal element.

8. The composite active material for secondary batteries according to claim 7, wherein The transition metal element is at least one selected from the group consisting of Fe, Mn, Ni, Cr, Cu, Nb, Mo, Ru, Rh, Pd and La.

9. The composite active material for secondary batteries according to claim 4, wherein The metal ions are contained in an amount within a range of 0.2 atm % to 10.0 atm % relative to silicon in the silicon particles.

10. The composite active material for secondary batteries according to claim 7, wherein The content of the transition metal element is 0.01 atm% to 5.0 atm% relative to the total amount of silicon in the silicon particles.

11. The composite active material for secondary batteries according to claim 1, wherein Carbonaceous matter is contained as a component of the matrix phase.

12. The composite active material for secondary batteries according to claim 1, wherein The matrix phase has a composition represented by SiOy (1<y≦2).

13. The composite active material for secondary batteries according to claim 1, wherein The matrix phase contains silicon oxycarbide.

14. The composite active material for secondary batteries according to claim 1, wherein The average particle size of the silicon particles is in the range of 10 nm to 300 nm.

15. The composite active material for secondary batteries according to claim 7, wherein The transition metal element is contained in an amount of 0.001 atm% to 5 atm% relative to the total amount of silicon in the composite active material for a secondary battery.

16. The composite active material for secondary batteries according to claim 1, wherein There is a carbon layer on the surface. 17 . A secondary battery comprising the composite active material for a secondary battery according to claim 1 in a negative electrode.

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