Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates

Definitions

• the present invention relates to a composite active material for secondary batteries and a secondary battery containing the composite active material for secondary batteries.
• LIBs lithium-ion batteries
• EVs electric vehicles
• Patent Document 1 describes a negative electrode active material that includes a silicon oxide complex containing Si, silicon oxide represented by SiOx (0 ⁇ x ⁇ 2), and magnesium silicate containing Si and Mg, and a carbon coating layer that is located on the surface of the silicon oxide complex and contains a carbon-based material, has a specific peak in X-ray diffraction analysis, and has a moisture content below a certain level.
• Patent Document 2 describes a silicon composite oxide for use as a secondary battery negative electrode material, which is characterized in that it contains silicon particles with a crystal size of 1 to 25 nm and MgSiO 3 (enstatite) crystals in a silicon oxide (SiO x , 0 ⁇ x ⁇ 2) and has a carbon coating on the surface.
• Patent document 3 describes a silicon anode active material that includes a double clamping layer having a silicon core containing silicon particles, a silicon carbide layer on the silicon core, and a silicon oxide layer between the silicon core and the silicon carbide layer.
• the object of the present invention is to provide a composite active material for secondary batteries that can maintain high charge/discharge performance, such as capacity retention rate and initial coulombic efficiency, when used as a secondary battery, and a secondary battery that contains the composite active material for secondary batteries in the negative electrode.
• the present inventors have investigated a method for treating the surface oxide film of silicon particles, aiming to improve the initial coulombic efficiency and cycle characteristics of silicon materials in negative electrode active materials.
• a metal ion silicate phase is generated on the outside of silicon particles by a solid-phase reaction between metal ions such as alkali metal ions and alkaline earth metal ions and silicon oxide, forming an inactive oxide film.
• transition metal ions such as Mn2 + are present in a silicon material
• the catalytic action of the transition metal ions promotes the formation of a silicon nitride phase or silicon carbide phase on the silicon particles, thereby significantly suppressing the oxidation of the silicon particles during high-temperature sintering, and further that the formation of an oxide film and a silicon nitride phase or silicon carbide phase on the exterior of the silicon particles leads to improved charge/discharge performance.
• 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:
• B A silicon material having a matrix phase containing a metal ion silicate and silicon nitride and/or silicon carbide outside the silicon particles.
• 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.
• the metal ion is contained in a range of 0.2 atm % to 10.0 atm % relative to the silicon in the silicon particles.
• the composite active material for secondary batteries of the present invention achieves a synergistic effect between inactivating the oxide film on the silicon material and inhibiting oxidation during high-temperature firing, allowing the oxide film on the silicon particles to be skillfully processed, and high charge/discharge performance such as the capacity retention rate and initial coulombic efficiency in secondary batteries to be maintained.
• mass is synonymous with “weight.”
• weight is synonymous with “weight.”
• to indicating a range of values is used to mean that the values before and after the range are included as the lower and upper limits, unless otherwise specified.
• the composite active material for a secondary battery of the present embodiment contains a silicon material having at least one structure selected from the group consisting of A and B below.
• A A silicon particle having a metal ion silicate phase and a silicon nitride phase and/or a silicon carbide phase integrated therewith, and further having a matrix phase that contains these phases.
• B A silicon particle having a metal ion silicate phase and a silicon nitride phase and/or a silicon carbide phase integrated therewith, and further having a matrix phase that contains these phases.
• the matrix phase includes silicate and silicon nitride and/or silicon carbide.
• the composite active material for secondary batteries of this embodiment may contain a silicon material having either one of the structures A and B above, and preferably contains a silicon material having the structure A above.
• metal ion silicate which is a component of the metal ion silicate phase in A
• silicon nitride and/or silicon carbide which are components of the silicon nitride phase and/or silicon carbide phase in A
• silicon nitride phase and/or silicon carbide phase means either one or both of the silicon nitride phase and silicon carbide phase.
• the silicon material A has a structure in which a metal ion silicate phase and a silicon nitride phase and/or silicon carbide phase are integrated and exist outside the silicon particle.
• integrated refers to either a state in which the two are in close contact with each other with no gaps or inclusions at the boundary between them, or a composite state in which the two have diffused into each other and the boundary is unclear.
• the metal ion silicate phase and the silicon nitride phase and/or silicon carbide phase exist in layers on the silicon particles.
• the layer structure outside the silicon particles is not particularly limited, and the metal ion silicate phase and the silicon nitride phase and/or silicon carbide phase may exist in alternating layers on the silicon particles.
• the silicon nitride phase and/or silicon carbide phase may exist on the metal ion silicate phase
• the metal ion silicate phase may exist on the silicon nitride phase and/or silicon carbide phase.
• the presence of the metal ion silicate phase in layers forms an inactive silicon surface oxide film, and the presence of the silicon nitride phase and/or silicon carbide phase in layers significantly suppresses the oxidation of the silicon particles during high-temperature firing.
• the metal ion in the metal ion silicate (phase) is preferably an ion of at least one element selected from the group consisting of alkali metal elements and alkaline earth metal elements. Moreover, it is particularly preferable that the alkali metal element is Li, and that the alkaline earth metal is Mg.
• the metal ion silicate phase is preferably a lithium silicate compound or a magnesium silicate compound, more preferably lithium metasilicate (Li 2 SiO 3 ) or magnesium metasilicate (MgSiO 3 ), especially magnesium metasilicate (MgSiO 3 ).
• the content of the above metal ions 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%, relative to the total amount of silicon (Si element) in the silicon particles.
• Si element silicon
• the silicon material preferably has the metal ion silicate phase in the vicinity of the surface of the silicon particles. That is, the metal ion silicate (phase) may be chemically or physically directly attached to the surface of the silicon particles, or the metal ion silicate (phase) may be present in the vicinity of the surface of the silicon particles. Note that the vicinity of the surface of the silicon particles is within a few nm from the surface, preferably within 5 nm.
• HR-TEM high-resolution transmission electron microscope
• a sample can be sliced using a focused ion beam (FIB) and observed with an HR-TEM.
• the thickness of the metal ion silicate phase in the vicinity of the surface of the silicon particle is measured in a 1,000,000 times magnification field of view of the HR-TEM.
• the presence of metal elements in the vicinity of silicon particles can be detected using STEM-EDS (Scanning Transmission Electron Microscope Energy-Dispersive-Spectroscopy) and XPS (X-ray Photoelectron Spectroscopy), and the thickness of the metal silicate phase can be determined by combining the metal elements.
• the metal ion silicate (phase) is a magnesium silicate compound
• the magnesium silicate compound is a crystalline film and covers at least a portion of the surface of the silicon particle.
• the coverage is more preferably 50% or more, and particularly preferably 80% or more.
• the upper limit of the coverage is not particularly limited, but is, for example, 100%.
• the thickness of the crystalline film is preferably 0.2 nm to 10 nm, more preferably 1 nm to 8 nm.
• the coverage and the thickness of the crystalline film can be measured by the HR-TEM.
• the total content (molar ratio) of Li and Mg 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 %, based on the amount of silicon (Si element) in the entire composite active material for a secondary battery. It is believed that Li and Mg exist as metal ions (Li + , Mg 2+ ) in the composite active material for secondary batteries.
• the silicon material further contains a transition metal element.
• This transition metal element may be present in silicon nitride (phase) or silicon carbide (phase), may be present in the internal silicon particles, or may be present in the external matrix phase.
• the silicon material contains a transition metal element, the catalytic action of the transition metal ions promotes the formation of silicon nitride (phase) or silicon carbide (phase) on the 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, in order to more effectively generate silicon nitride (phase) and silicon carbide (phase) on the silicon particles, and more preferably at least one selected from the group consisting of Fe, Mn, Ni, Cu, and La.
• the transition metal element is considered to be present in the form of metal ions in the metal ion silicate (phase), silicon nitride (phase), and/or silicon carbide (phase) on the silicon particles.
• the content of the transition metal element 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%, based on the total amount of silicon (Si element) in the entire silicon particles constituting the secondary battery composite active material.
• the content of the transition metal element 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%, based on the total amount of silicon (Si element equivalent) in the secondary battery composite active material of this embodiment.
• a silicon nitride phase or a silicon carbide phase can be formed on the silicon particles to such an extent that high charge/discharge performance can be maintained.
• the content of the transition metal element can be measured by quantitative analysis of the content of various elements, such as ICP mass (inductively coupled plasma mass) analysis, energy dispersive X-ray fluorescence (EDX) analysis, X-ray fluorescence (XRF) analysis, and EPMA (electron probe microanalyzer) analysis.
• the silicon nitride in the silicon nitride phase is an inorganic compound represented by the chemical formula SiNx (0.1 ⁇ x ⁇ 1.33), and has electrochemical reactivity with lithium ions, as well as excellent fracture toughness, high-temperature properties, and thermal shock resistance.
• the silicon nitride may be in either the ⁇ or ⁇ phase.
• the silicon nitride phase is a structure formed by a solid-phase reaction at high temperatures (e.g., 1200°C or higher), but can be easily formed at low temperatures due to the catalytic effect of transition metal ions.
• the components and crystalline state of the silicon nitride phase can be appropriately controlled by changing the type and amount of transition metal ion added and the conditions of the solid-phase reaction.
• the silicon carbide in the silicon carbide phase is represented by the chemical formula SiC and is a 1:1 compound of carbon and silicon, with properties intermediate between diamond and silicon, and excellent hardness characteristics, heat resistance, and chemical stability.
• the composition and crystalline state of the silicon carbide phase can also be appropriately controlled by changing the conditions of the solid-phase reaction.
• silicon nitride (phase) or silicon carbide (phase) 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) can be confirmed by solid-state 29Si -NMR spectrum, regardless of whether it is crystalline or amorphous.
• a peak D in the chemical shift range of 0 ppm to ⁇ 20 ppm, which is assigned to a silicon carbide phase, a peak E in the chemical shift range of ⁇ 30 ppm to ⁇ 60 ppm, which is assigned to a silicon nitride phase, and a peak F in the chemical shift range of ⁇ 70 ppm to ⁇ 120 ppm, which is assigned to silicon, are detected in the solid-state 29 Si-NMR spectrum, and it is preferable that the area ratio R of the above peaks calculated by the following formula is in the range of 0.1 to 1.0.
• R (D + E)/F
• the peaks D and E are Si elements other than zero valence such as SiO 4 and SiO 2 , and the peak C is zero valence Si.
• the area ratio R of each peak calculated by the above formula is in this range, which means that the proportion of Si (zero valence) is greater than Si (other than zero valence), which indicates that the oxidation of the silicon particles constituting the silicon material of this embodiment is not advanced (low oxidation state).
• the silicon particles are in a low oxygen state, which can effectively improve the initial Coulomb efficiency when used as an active material, and the presence of silicon nitride (phase) or silicon carbide (phase) outside the silicon particles can increase the chemical stability of the silicon particles and improve the cycle characteristics during charging and discharging.
• Crystalline silicon nitride (phase) or silicon carbide (phase) can be confirmed by XRD (X-ray diffraction, CuK ⁇ light source) measurement.
• XRD X-ray diffraction, CuK ⁇ light source
• ⁇ -Si 3 N 4 PDF#41-0360
• ⁇ -Si 3 N 4 PDF#33-1160
• ⁇ -SiC PDF#49-1430
• ⁇ -SiC PDF#29-1129
• the thickness of the silicon nitride phase and/or silicon carbide phase present on the silicon particles is the sum of the thicknesses of the silicon nitride phase and silicon carbide phase, and is preferably 0.1 nm to 10 nm, more preferably 0.3 nm to 8 nm, and even more preferably 0.5 nm to 6 nm.
• the sum of the thicknesses of the silicon nitride phase and silicon carbide phase is within this range, it is possible to impart very excellent fracture toughness, high-temperature characteristics, thermal shock resistance, and chemical stability, and oxidation of the silicon particles during high-temperature sintering can be significantly suppressed.
• the thickness of the silicon nitride phase and silicon carbide phase can be measured by cutting with a focused ion beam (FIB) and observing the cross section with an FE-SEM, or by slicing the sample and observing the cross section of the silicon particles with a TEM.
• FIB focused ion beam
• SiNx The range of x in SiNx can be easily controlled by adjusting the amount of transition metal element added that acts as a catalyst and the high-temperature reaction conditions (temperature, time, atmosphere), etc.
• This SiNx (0.1 ⁇ x ⁇ 1.33) can easily react with Li ions, and therefore has a certain electrochemical reaction activity.
• silicon nitride phases are widely used as gas barrier materials and have the function of blocking oxygen diffusion. In this embodiment, when a silicon nitride phase is formed on silicon particles during high-temperature sintering of the active material, oxygen diffusion into the silicon particles is prevented, and the oxidation reaction of silicon is effectively suppressed.
• silicon materials it is common for a natural oxide film to exist on the silicon particles, and during high-temperature firing, transition metal ions can diffuse through this natural oxide film, causing a catalytic effect that greatly promotes the nitridation reaction of silicon.
• silicon nitride crystals can be formed between the surface oxide film and the silicon crystals in the center of the particles, blocking contact between the silicon crystals and oxygen from outside the silicon or the surrounding area, suppressing the oxidation reaction of the silicon particles.
• the Si crystal has the property of being able to highly express charge/discharge performance, particularly in secondary batteries, such as charge/discharge capacity and initial coulombic efficiency.
• 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.
• the charge/discharge performance such as the capacity retention rate and the initial coulombic efficiency, of the secondary battery can be maintained at a high level.
• the average particle size of the silicon particles constituting the silicon material can be measured by observing a cross section of the silicon material using a transmission electron image.
• the specific surface area of the silicon particles constituting the silicon material is preferably 50 m 2 /g to 400 m 2 /g, more preferably 100 m 2 /g to 300 m 2 /g, and even more preferably 150 m 2 /g to 230 m 2 /g, from the viewpoints of charge/discharge capacity, initial coulombic efficiency, and cycle characteristics.
• the specific surface area is a value determined by the BET method, and can be determined by nitrogen gas adsorption measurement, for example, by using a specific surface area measuring device.
• the shape of the silicon particles constituting the silicon material may be granular, needle-like, or flake-like, but there is no particular limitation on the crystal state, and either crystalline or amorphous can be used.
• a crystallite diameter obtained from the diffraction peak assigned to Si(111) in X-ray diffraction is preferably in the range of 5 nm to 14 nm from the viewpoint of initial Coulombic efficiency and cycle characteristics.
• the crystallite diameter is preferably 12 nm or less, and more preferably 10 nm or less.
• the silicon particles constituting the silicon material preferably have a length in the long axis direction of 30 nm to 300 nm and a thickness of 1 nm to 60 nm from the viewpoint of charge/discharge performance when used as a secondary battery. From the viewpoint of charge/discharge performance when used as a secondary battery, a needle-like or flake-like shape with an aspect ratio, which is the ratio of thickness to length, of 0.5 or less is preferable.
• the shape of the silicon particles can be measured by dynamic light scattering to measure the average particle size, but the aspect ratio of a sample can be more easily and precisely identified by using analytical means such as a transmission electron microscope (TEM) or a field emission scanning electron microscope (FE-SEM).
• the sample can be cut with a focused ion beam (FIB) and the cross section can be observed with an FE-SEM, or the sample can be sliced and the state can be identified by TEM observation.
• the aspect ratio of silicon particles is a calculation result based on the main part of 50 particles of the sample within the field of view of the TEM image.
• the silicon particles constituting the silicon material generally have an amorphous oxide film (silicon oxide) on the outer surface in the atmosphere.
• amorphous oxide film silicon oxide
• the presence of such an amorphous oxide film can impart superior fracture toughness, high-temperature characteristics, thermal shock resistance, and chemical stability to the silicon particles, so long as it does not have a significant adverse effect on the charge/discharge performance (capacity, initial coulombic efficiency).
• a small amount of the amorphous oxide film may be present on the surface of the silicon particles.
• the thickness of the oxide film is preferably 8 nm or less, more preferably 7 nm or less, and particularly preferably 6 nm or less. If the thickness of the oxide film is within this range, the extent of the decrease in the charge/discharge performance of the silicon material (capacity and initial coulombic efficiency) can be minimized, and the cycle characteristics can be improved.
• 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 also preferably contains carbonaceous matter.
• the matrix phase preferably contains silicon, carbon, and oxygen elements, and has a three-dimensional network structure of a silicon-oxygen-carbon skeleton.
• This three-dimensional network structure of a silicon-oxygen-carbon skeleton has relatively high chemical stability, has a composite structure with carbon (carbonaceous phase), and exhibits small volumetric changes in response to the absorption and release of lithium.
• the three-dimensional network structure of the matrix phase preferably contains a silicon oxycarbide (SiOC) structure. This three-dimensional network structure may contain nitrogen elements in addition to silicon, carbon, and oxygen elements.
• the above-mentioned composite active material for secondary batteries preferably has a carbon layer on the surface, that is, has a carbon coating on at least a part of the surface.
• the carbon layer (carbon coating) is preferably a coating made of low-crystalline carbon.
• Low-crystalline carbon refers to a carbon material that is in an amorphous state in which, unlike graphitic carbon materials, there is little evidence of a regular lattice period structure, or only a small amount of a short-period structure is present.
• the amount of the carbon layer (carbon coating) is preferably 0.1% by mass to 30% by mass, more preferably 1% by mass to 25% by mass, and even more preferably 5% by mass to 20% by mass, based on 100% by mass of the composite active material for secondary batteries.
• the composite active material for secondary batteries may have a carbon layer (carbon coating) on its surface, either continuously or intermittently.
• the carbon layer (carbon coating) is preferably formed on the surface of the active material by chemical vapor deposition.
• the true density of the composite active material for secondary batteries is preferably 1.6 g/cm 3 or more and 2.6 g/cm 3 or less. From the viewpoint of improving the energy density of the resulting secondary battery, the true density is more preferably 1.75 g/cm 3 or more, and further preferably 1.80 g/cm 3 or more.
• the true density is a value measured using a true density measuring device.
• the average particle size of the composite active material for secondary batteries is preferably 2 ⁇ m or more and 15 ⁇ m or less. If the average particle size of the composite active material for secondary batteries is 2 ⁇ m or more, a significant increase in the specific surface area can be suppressed, and the amount of SEI generated during charging and discharging when used as a secondary battery can be reduced, thereby improving the reversible charge and discharge capacity per unit volume. Furthermore, if the average particle size of the composite active material for secondary batteries is 15 ⁇ m or less, the adhesive strength with the current collector can be sufficiently ensured, and peeling from the current collector can be suppressed.
• the average particle size of the composite active material for secondary batteries is more preferably 2.5 ⁇ m or more, and even more preferably 3.0 ⁇ m or more. Furthermore, the average particle size of the composite active material for secondary batteries is more preferably 12 ⁇ m or less, and even more preferably 10 ⁇ m or less.
• the specific surface area of the composite active material for secondary batteries is preferably 0.3 m 2 /g or more and 10 m 2 /g or less.
• the specific surface area is more preferably 0.5 m 2 /g or more, and particularly preferably 1 m 2 /g or more.
• the specific surface area is a value determined by the BET method, and can be determined by nitrogen gas adsorption measurement, for example, using a specific surface area measurement device.
• the silicon material in the composite active material for secondary batteries of this embodiment can be manufactured by a method including at least a step of wet-grinding raw silicon (wet grinding step), a step of supporting a metal element-containing compound on silicon particles (metal element supporting step), a step of uniformly mixing a polysiloxane compound, a carbon source resin, and the silicon slurry obtained in the wet grinding step, followed by desolvation and drying (homogenization step), and a step of performing high-temperature treatment after the homogenization step (high-temperature treatment step).
• the homogenization step may be performed either before or after the metal element supporting step.
• the composite active material for secondary batteries of the above embodiment is not limited to that obtained by this manufacturing method.
• the raw silicon is dispersed in a solvent such as an organic solvent to obtain a silicon slurry, which is a nanosilicon dispersion liquid.
• the silicon slurry can be prepared while grinding the raw silicon in a wet grinding device. It is preferable to add a dispersant to the organic solvent to promote grinding of the raw silicon.
• wet grinding devices include roller mills, high-speed rotary grinders, container-driven mills, and bead mills.
• 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 grinding the raw silicon is measured using a laser diffraction particle size analyzer or the like, and is obtained by determining the particle size at which the cumulative volume distribution curve is 50% when the particle size distribution is plotted from the small diameter side.
• organic solvent examples include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and diisobutyl ketone; alcohols such as ethanol, methanol, normal propyl alcohol, and isopropyl alcohol; and aromatics such as benzene, toluene, and xylene.
• ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and diisobutyl ketone
• alcohols such as ethanol, methanol, normal propyl alcohol, and isopropyl alcohol
• aromatics such as benzene, toluene, and xylene.
• the above-mentioned dispersants include aqueous and non-aqueous dispersants, with non-aqueous dispersants being preferred.
• non-aqueous dispersants include polymeric types such as polyethers, alcohols, polyalkylene polyamines, and polycarboxylic acid partial alkyl esters, low molecular weight types such as polyhydric alcohol esters and alkyl polyamines, and inorganic types such as polyphosphates.
• the solids concentration of the silicon particles and dispersant in the silicon slurry is not particularly limited, but is preferably in the range of 5% to 40% by mass, and more preferably 10% to 30% by mass, with the total amount of the solvent, dispersant, and silicon particles being 100% by mass.
• the amount of dispersant added is preferably in the range of 2% to 60% by mass, and more preferably 5% to 50% by mass, relative to the weight of the silicon particles.
• a metal element-containing compound is added to the silicon slurry obtained in the wet grinding process, and the mixture is stirred, and the solvent is removed and then dried. This results in silicon particles having a metal ion silicate phase after high-temperature treatment.
• 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, since it has a high inactivation effect on the oxide film on the silicon particles.
• the alkali metal element is Li
• the alkaline earth metal element is Mg.
• metal element-containing compounds include lithium acetate anhydride when Li is used, and magnesium acetate anhydride when Mg is used. These metal element-containing compounds may be added by dispersing them in an appropriate organic solvent (polar or non-polar), such as ethanol or MEK.
• transition metal element-containing compound such as Fe, Mn, Ni, Cr, Cu, Nb, Mo, Ru, Rh, Pd, or La
• examples of the transition metal element-containing compound include manganese(II) chloride, manganese(II) acetate anhydride, manganese(II) sulfate, manganese(II) acetate tetrahydrate, and manganese(II,III) acetylacetonate.
• the above stirring can be performed with a stirrer equipped with stirring blades, and the stirring time is, for example, 5 minutes to 2 hours, preferably 10 minutes to 1 hour.
• the stirring can be performed at room temperature, or while heating, for example, to 30 to 50°C.
• the above solvent can be removed by a common method such as filtration.
• the above drying is performed, for example, with a dryer, a reduced pressure dryer, a spray dryer, or the like.
• the drying temperature is preferably 80°C or higher, and 120°C or lower. Drying can be performed while applying a reduced pressure.
• the matrix phase which is a three-dimensional network structure of silicon-oxygen-carbon skeleton, is mixed with silicon particles and homogenized, and then the solvent is removed and dried to obtain the active material precursor.
• This matrix phase is formed from a polysiloxane compound and a carbon source resin.
• the polysiloxane compound may be a resin containing at least one of a polycarbosilane structure, a polysilazane structure, a polysilane structure, and a polysiloxane structure. It may be a resin containing only these structures, or a composite resin having at least one of these structures as a segment and chemically bonded to other polymer segments.
• the form of the composite may be graft copolymerization, block copolymerization, random copolymerization, alternating copolymerization, etc.
• Examples include a composite resin having a graft structure in which a polysiloxane segment is chemically bonded to the side chain of a polymer segment, and a composite resin having a block structure in which a polysiloxane segment is chemically bonded to the end of a polymer segment.
• 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).
• the polysiloxane compound has a carboxy group, an epoxy group, an amino group, or a polyether group on the side chain or terminal of the main siloxane bond (Si-O-Si) skeleton.
• R1 represents an aromatic hydrocarbon group or an alkyl group which may have a substituent, an epoxy group, a carboxy group, etc.
• R2 and R3 each represent an alkyl group, a cycloalkyl group, an aryl group or an aralkyl group, an epoxy group, a carboxy group, etc.
• alkyl group examples 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.
• cycloalkyl group examples include cyclopropyl, cyclobutyl, cyclopentyl,
• aryl groups include phenyl, naphthyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 4-vinylphenyl, and 3-isopropylphenyl groups.
• aralkyl groups examples include benzyl groups, diphenylmethyl groups, and naphthylmethyl groups.
• polymer segments other than polysiloxane segments contained in polysiloxane compounds include vinyl polymer segments such as acrylic polymers, fluoroolefin polymers, vinyl ester polymers, aromatic vinyl polymers, and olefin polymers, as well as polymer segments such as urethane polymer segments, ester polymer segments, and ether polymer segments. Among these, vinyl polymer segments are preferred.
• the polysiloxane compound may be a composite resin in which polysiloxane segments and polymer segments are bonded in a structure shown in the following structural formula (S-3), or may have a three-dimensional network-like polysiloxane structure.
• the carbon atom is a carbon atom that constitutes a polymer segment
• the two silicon atoms are silicon atoms that constitute a polysiloxane segment.
• the polysiloxane segment of the polysiloxane compound may have a functional group capable of reacting by heating, such as a polymerizable double bond, in the polysiloxane segment.
• a functional group capable of reacting by heating such as a polymerizable double bond
• the crosslinking reaction proceeds, and the compound becomes solid, making it easier to carry out the thermal decomposition treatment.
• polymerizable double bonds examples include vinyl groups and (meth)acryloyl groups.
• two or more polymerizable double bonds are present in the polysiloxane segment, more preferably 3 to 200, and even more preferably 3 to 50.
• the crosslinking reaction can be easily promoted.
• the polysiloxane segment may have a silanol group and/or a hydrolyzable silyl group.
• the hydrolyzable group in the hydrolyzable silyl group include a halogen atom, an alkoxy group, a substituted alkoxy group, an acyloxy group, a phenoxy group, a mercapto group, an amino group, an amide group, an aminooxy group, an iminoxy group, and an alkenyloxy group.
• the hydrolyzable silyl group becomes a silanol group.
• a hydrolysis condensation reaction proceeds between the hydroxyl group in the silanol group and the hydrolyzable group in the hydrolyzable silyl group, thereby obtaining a solid polysiloxane compound.
• silyl group refers to a silicon-containing group having a hydroxyl group directly bonded to a silicon atom.
• hydrolyzable silyl group refers to a silicon-containing group having a hydrolyzable group directly bonded to a silicon atom, and specific examples include groups represented by the following general formula (S-4).
• R4 is a monovalent organic group such as an alkyl group, an aryl group, or an aralkyl group
• R5 is a halogen atom, an alkoxy group, an acyloxy group, an allyloxy group, a mercapto group, an amino group, an amido group, an aminooxy group, an iminoxy group, or an alkenyloxy group
• b is an integer of 0 to 2.
• alkyl groups 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 groups.
• aryl groups include phenyl, naphthyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 4-vinylphenyl, and 3-isopropylphenyl groups.
• aralkyl groups examples include benzyl groups, diphenylmethyl groups, and naphthylmethyl groups.
• Halogen atoms include, for example, fluorine atoms, chlorine atoms, bromine atoms, iodine atoms, etc.
• alkoxy groups include methoxy groups, ethoxy groups, propoxy groups, isopropoxy groups, butoxy groups, sec-butoxy groups, and tert-butoxy groups.
• acyloxy groups include formyloxy groups, acetoxy groups, propanoyloxy groups, butanoyloxy groups, pivaloyloxy groups, pentanoyloxy groups, phenylacetoxy groups, acetoacetoxy groups, benzoyloxy groups, and naphthoyloxy groups.
• allyloxy group examples include a phenyloxy group and a naphthyloxy group.
• alkenyloxy groups include vinyloxy groups, allyloxy groups, 1-propenyloxy groups, isopropenyloxy groups, 2-butenyloxy groups, 3-butenyloxy groups, 2-pentenyloxy groups, 3-methyl-3-butenyloxy groups, and 2-hexenyloxy groups.
• polysiloxane segments having structural units represented by the above general formula (S-1) and/or the above general formula (S-2) include those having the following structures.
• R6 in the structural formulae (1) to (3) above has the same meaning as R1 above.
• R7 and R8 in the structural formulae (4) to (8) above have the same meaning as R2 and R3 above, respectively.
• the polymer segment may have various functional groups as necessary, as long as they do not impair the effects of the present invention.
• functional groups that can be used include a carboxyl group, a blocked carboxyl group, a carboxylic anhydride group, a tertiary amino group, a hydroxyl group, a blocked hydroxyl group, a cyclocarbonate group, an epoxy group, a carbonyl group, a primary amide group, a secondary amide, a carbamate group, and the functional group represented by the following structural formula (S-5).
• the polymer segment may also have a polymerizable double bond such as a vinyl group or a (meth)acryloyl group.
• the polysiloxane compound is preferably produced, for example, by the methods shown in (1) to (3) below.
• a polymer segment containing a silanol group and/or a hydrolyzable silyl group is prepared in advance as the raw material for the polymer segment.
• a polysiloxane is also prepared in advance by subjecting a silane compound having both a silanol group and/or a hydrolyzable silyl group and a polymerizable double bond to a hydrolysis and condensation reaction. The polymer segment and the polysiloxane are then mixed together to carry out a hydrolysis and condensation reaction.
• polysiloxane compounds include, for example, the Ceranate (registered trademark) series (organic-inorganic hybrid coating resin; manufactured by DIC Corporation) and the Compoceran SQ series (silsesquioxane hybrid; manufactured by Arakawa Chemical Industries, Ltd.).
• the carbon source resin has good compatibility with polysiloxane compounds, and is carbonized by high-temperature baking in an inert, non-oxidizing atmosphere to effectively form 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, and may include a molecular structure having a benzene ring or an aromatic functional group.
• thermosetting resins examples include thermosetting resins; thermoplastic resins; petroleum-based or coal-based tar or pitch, such as petroleum-based tar or pitch produced as a by-product during ethylene production, coal tar produced during coal carbonization, heavy components or pitch obtained by distilling off low-boiling components of coal tar, and tar or pitch obtained by liquefying coal; and further, the above tar or pitch that has been crosslinked.
• thermosetting resins such as thermoplastic resins; petroleum-based or coal-based tar or pitch, such as petroleum-based tar or pitch produced as a by-product during ethylene production, coal tar produced during coal carbonization, heavy components or pitch obtained by distilling off low-boiling components of coal tar, and tar or pitch obtained by liquefying coal; and further, the above tar or pitch that has been crosslinked.
• thermosetting resins such as petroleum-based tar or pitch produced as a by-product during ethylene production, coal tar produced during coal carbonization, heavy components or pitch obtained by distill
• Thermosetting resins are not particularly limited, and examples include phenolic resins such as novolac-type phenolic resins and resol-type phenolic resins; epoxy resins such as bisphenol-type epoxy resins and novolac-type epoxy resins; melamine resins; urea resins; aniline resins; cyanate resins; furan resins; ketone resins; unsaturated polyester resins; urethane resins; and the like. Modified versions of these resins modified with various components can also be used. When using a thermosetting resin, a curing agent for it can be used in combination.
• Thermoplastic resins are not particularly limited, and examples 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, polyphthalamide, etc.
• the resin or resin composition used as the raw material for the carbonaceous phase in the composite active material for secondary batteries of this embodiment preferably contains nitrogen-containing resins as the main resin component from the viewpoint of promoting silicon nitride formation.
• nitrogen-containing resins as the main resin component from the viewpoint of promoting silicon nitride formation.
• Thermosetting resins include melamine resin, urea resin, aniline resin, cyanate resin, urethane resin, as well as phenolic resin and epoxy resin modified with nitrogen-containing components such as amines.
• the type is not particularly limited, but examples include hexamethylenetetramine, which is a hardener for novolac-type phenolic resins, aliphatic polyamines, aromatic polyamines, and dicyandiamide, which are hardeners for epoxy resins, as well as nitrogen-containing compounds such as amine compounds, ammonium salts, nitrates, and nitro compounds that do not function as hardeners, other than the hardener components.
• hexamethylenetetramine which is a hardener for novolac-type phenolic resins
• aliphatic polyamines aliphatic polyamines
• aromatic polyamines aromatic polyamines
• dicyandiamide which are 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 the hardener components.
• the nitrogen-containing compound may be used alone or in combination of two or more kinds, whether or not the main component resin contains nitrogen-containing resins.
• the method for preparing the resin composition used as the raw material for the carbonaceous phase is not particularly limited, and for example, the above-mentioned main component resin and other components are blended in a predetermined ratio, and these components are dissolved in a solvent and mixed, or a precursor of the active material can be prepared by mixing these components with the above-mentioned silicon slurry.
• the obtained active material is coated with a carbon coating in a chemical vapor deposition apparatus at a temperature range of 700°C to 1000°C in a flow of pyrolytic carbon source gas and carrier inert gas.
• pyrolytic carbon source gas include acetylene, ethylene, acetone, alcohol, propane, methane, and ethane.
• inert gas include nitrogen, helium, and argon, with nitrogen being usually used.
• the active material precursor dried in the homogenization step is fired in a non-oxidizing atmosphere.
• the equipment used for the high-temperature treatment can be appropriately selected from among a fluidized bed reactor, a rotary furnace, a vertical moving bed reactor, a tunnel furnace, a batch furnace, a rotary kiln, etc. depending on the purpose.
• the high-temperature treatment is carried out according to a firing program that is defined by the heating rate, the holding time at a constant temperature, etc.
• the firing temperature is preferably, for example, in the range of 900°C to 1300°C, with the maximum temperature reached. In this way, the silicon material of this embodiment is obtained.
• the non-oxidizing atmosphere during the high-temperature firing is not particularly limited in terms of the type of gas used, and examples include nitrogen, argon, hydrogen, and nitrogen/hydrogen mixed gas. Of these, the use of nitrogen gas is preferred from the standpoint of promoting the formation of silicon nitride.
• the sintered product obtained in the high-temperature treatment step may be pulverized and classified as necessary to obtain a silicon material of the desired particle size.
• the pulverization may be performed in one step until the desired particle size is reached, or may be performed in several steps. If the particle size of the sintered silicon material is a mass or agglomerate of 10 mm or more, it may be coarsely pulverized using a jaw crusher, roll crusher, etc., and then pulverized using a glow mill, ball mill, etc., and further pulverized using a bead mill, jet mill, etc.
• the particle size is the volume average particle size, which is the D50 value.
• the silicon material produced by pulverization contains coarse particles, it is preferable to carry out classification in order to remove these and to adjust the particle size distribution by removing fine powder.
• the classifier used will vary depending on the purpose, such as an air classifier or a wet classifier, but when removing coarse particles, a classification method that passes the material through a sieve is preferable as this will ensure that the purpose is achieved.
• the secondary battery of this embodiment is not particularly limited as long as the negative electrode contains the composite active material for secondary batteries, but may contain other components such as an organic binder and a conductive assistant.
• the secondary battery of this embodiment can be produced by applying a slurry containing an organic binder and, if necessary, other components such as a conductive assistant, in the form of a thin film onto a copper foil collector.
• a carbon material such as graphite can be added to the slurry to produce a negative electrode. Examples of carbon materials include natural graphite, artificial graphite, and amorphous carbon such as hard carbon or soft carbon.
• the negative electrode material can be obtained by kneading the composite active material for secondary batteries and the organic binder together with a solvent using a dispersing device such as a stirrer, ball mill, super sand mill, or pressure kneader to prepare a negative electrode material slurry, which is then applied to a current collector to form a negative electrode layer. It can also be obtained by forming the paste-like negative electrode material slurry into a sheet, pellet, or other shape and integrating it with the current collector.
• a dispersing device such as a stirrer, ball mill, super sand mill, or pressure kneader
• organic binder examples include styrene-butadiene rubber copolymers (hereinafter also referred to as "SBR”); ethylenically unsaturated carboxylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, (meth)acrylonitrile, and hydroxyethyl (meth)acrylate, and unsaturated carboxylic acid copolymers such as (meth)acrylic copolymers consisting of ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid; and polymeric compounds such as polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polyimide, polyamideimide, and carboxymethylcellulose (hereinafter also referred to as "CMC").
• SBR styren
• these organic binders may be dispersed or dissolved in water, or dissolved in an organic solvent such as N-methyl-2-pyrrolidone (NMP).
• NMP N-methyl-2-pyrrolidone
• the content of the organic binder in the negative electrode layer of the lithium ion secondary battery negative electrode is preferably 1% by mass to 30% by mass, more preferably 2% by mass to 20% by mass, and even more preferably 3% by mass to 15% by mass.
• the organic binder content is 1% by mass or more, adhesion is better, and damage to the negative electrode structure caused by expansion and contraction during charging and discharging is more suppressed.
• the organic binder content is 30% by mass or less, an increase in electrode resistance is more suppressed.
• a conductive additive may be mixed into the negative electrode material slurry as necessary.
• conductive additives include carbon black, graphite, acetylene black, and oxides and nitrides that exhibit electrical conductivity.
• the amount of conductive additive used may be, for example, 1% by mass to 15% by mass with respect to the negative electrode active material of this embodiment.
• the material and shape of the current collector can be, for example, a strip of copper, nickel, titanium, stainless steel, or the like in foil, perforated foil, mesh, or the like. Porous materials such as porous metal (foamed metal) and carbon paper can also be used.
• Methods for applying the negative electrode material slurry to the current collector include, for example, metal mask printing, electrostatic painting, dip coating, spray coating, roll coating, doctor blade, gravure coating, and screen printing. After application, it is preferable to carry out a rolling process using a flat plate press, calendar roll, etc., as necessary.
• the negative electrode material slurry can also be made into a sheet or pellet shape, and integrated with the current collector by, for example, rolling, pressing, or a combination of these.
• 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.
• the organic binder used For example, when using a water-based styrene-butadiene rubber copolymer (SBR), heat treatment at 100 to 130°C is sufficient, and when using an organic binder with a polyimide or polyamideimide as the main skeleton, heat treatment at 150 to 450°C is preferable.
• SBR water-based styrene-butadiene rubber copolymer
• This heat treatment removes the solvent and hardens the binder, increasing strength and improving adhesion between particles and between the particles and the current collector. It is preferable to carry out these heat treatments in an inert atmosphere such as helium, argon, or nitrogen, or in a vacuum atmosphere, to prevent oxidation of the current collector during treatment.
• an inert atmosphere such as helium, argon, or nitrogen
• the negative electrode is preferably subjected to pressure treatment.
• the electrode density is preferably 1 g/cm 3 to 1.8 g/cm 3 , more preferably 1.1 g/cm 3 to 1.7 g/cm 3 , and even more preferably 1.2 g/cm 3 to 1.6 g/cm 3.
• the higher the electrode density the more the adhesion and the volume capacity density of the electrode tend to improve.
• the electrode density is too high, the voids in the electrode are reduced, which weakens the effect of suppressing the volume expansion of silicon, etc., and the capacity retention rate may decrease. Therefore, the optimal range of the electrode density is selected.
• the secondary battery of this embodiment includes the composite active material for secondary batteries of this embodiment.
• secondary batteries including the composite active material for secondary batteries non-aqueous electrolyte secondary batteries and solid electrolyte secondary batteries are preferred, and excellent performance is exhibited particularly when used as the negative electrode of a non-aqueous electrolyte secondary battery.
• the secondary battery of this embodiment When the secondary battery of this embodiment is used as a wet electrolyte secondary battery, for example, it can be constructed by arranging a positive electrode and a negative electrode containing the negative electrode active material of this embodiment facing each other with a separator interposed therebetween and injecting an electrolyte.
• 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 of metal or alloy such as aluminum, titanium, or stainless steel in the form of foil, perforated foil, mesh, or the like.
• the positive electrode material used in the positive electrode layer is not particularly limited.
• a lithium ion secondary battery is produced among nonaqueous electrolyte secondary batteries, for example, a metal compound, a metal oxide, a metal sulfide, or a conductive polymer material capable of doping or intercalating lithium ions may be used.
• lithium cobalt oxide LiCoO2
• lithium nickel oxide LiNiO2
• lithium manganese oxide LiMnO2
• lithium manganese spinel LiMn2O4
• lithium vanadium compounds V2O5 , V6O13 , VO2 , MnO2
• TiO2 , MoV2O8 TiS2 , V2S5 , VS2
• MoS2 , MoS3 , Cr3O8 , Cr2O5 olivine type LiMPO4 (wherein M is Co, Ni, Mn or Fe)
• conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene and polyacene, porous carbon, etc. can be used alone or in combination.
• separator for example, a nonwoven fabric, cloth, microporous film, or a combination of these, whose main component is a polyolefin such as polyethylene or polypropylene, can be used. Note that if the positive and negative electrodes of the nonaqueous electrolyte secondary battery to be fabricated are not in direct contact with each other, there is no need to use a separator.
• electrolyte examples include LiClO 4 , LiPF 6 , LiAsF 6 , LiBF 4 , and LiSO 3 CF
• a so-called organic electrolyte solution can be used in which a lithium salt such as 3 is dissolved 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, ⁇ -butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetra
• the structure of the secondary battery of this embodiment is not particularly limited, but typically, the positive and negative electrodes, and a separator that is provided as necessary, are wound into a flat spiral shape to form a wound electrode plate group, or these are stacked in a flat plate shape to form a stacked electrode plate group, and these electrode plate groups are sealed in an exterior body.
• the half cells used in the examples of the present invention are mainly composed of the negative electrode active material of this embodiment in the negative electrode, and a simple evaluation was performed using metallic lithium as the counter electrode, in order to more clearly compare the cycle characteristics of the active material itself.
• the secondary battery of this embodiment is not particularly limited, but may be used as a paper battery, a button battery, a coin battery, a laminated battery, a cylindrical battery, a square battery, or the like.
• the negative electrode active material of this embodiment described above can also be applied to electrochemical devices in general that use the insertion and removal of lithium ions as a charging and discharging mechanism, such as hybrid capacitors and solid-state lithium secondary batteries.
• Synthesis Example 1 Preparation of silicon particles (silicon slurry; Si1 to Si5)"
• a container (150 ml) of a small bead mill device zirconia beads (particle size range: 0.1 mm to 0.2 mm) and 100 ml of methyl ethyl ketone solvent (MEK) were placed at a filling rate of 60%, and then raw silicon (average particle size 5 ⁇ m) and a cationic dispersant liquid (BYK Japan Co., Ltd., BYK145) were placed as shown in Table 1 below, and wet milling was performed under the conditions shown in Table 1 below to obtain a dark brown liquid silicon slurry (solid concentration 30 mass%; Si1 to Si5).
• MK methyl ethyl ketone solvent
• the average particle size (D50) of the silicon particles after milling was measured using a laser diffraction particle size distribution measuring device (Malvern Panalytical, Mastersizer 3000), and the size of the silicon particles after milling was confirmed by TEM observation.
• the average particle size (D50) of the silicon particles is shown in Table 1.
• Synthesis Example 2 Preparation of polysiloxane compound
• Synthesis of methyltrimethoxysilane condensate (a1) First, 1,421 parts of methyltrimethoxysilane (hereinafter referred to as MTMS) was charged into a reaction vessel equipped with a stirrer, a thermometer, a dropping funnel, a cooling tube, and a nitrogen gas inlet, and the temperature was raised to 60° C.
• the effective component is calculated by dividing the theoretical yield (parts by mass) when all methoxy groups of a silane monomer such as MTMS undergo a condensation reaction by the actual yield (parts by mass) after the condensation reaction [theoretical yield (parts by mass) when all methoxy groups of a silane monomer undergo a condensation reaction/actual yield (parts by mass)].
• MMA methyl methacrylate
• BMA butyl methacrylate
• BA butyl acrylate
• MPTS 3-mercaptopropyl)triethoxysilane
• BuOH tert-butylperoxy-2-ethylhexanoate
• TBPEH tert-butylperoxy-2-ethylhexanoate
• 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 into the reaction vessel over a period of 5 hours, and after completion of the dropwise addition, the mixture was allowed to react at the same temperature for a further 10 hours to obtain an organic solvent solution of a vinyl polymer (a2-2) having a hydrolyzable silyl group and a number average molecular weight of 20,100.
• anhydrous magnesium acetate solution concentration 5 mass%; solvent ethanol
• Mg/Si (molar ratio) 2.0/100
• manganese (III) acetylacetonate solution Concentration 5 mass%; solvent MEK
• a slurry was prepared by mixing 80 parts by mass of the powder of the active material obtained above, 10 parts of acetylene black as a conductive assistant, and 10 parts of a mixture of CMC and SBR as a binder. 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 with Li metal foil as a counter electrode. The charge and discharge characteristics of the prepared half cell were evaluated at 25°C using a secondary battery charge and discharge tester (manufactured by Hokuto Co., Ltd.). The cutoff voltage range was 0.005 to 1.5V.
• a positive electrode film was prepared using a single-layer sheet using LiCoO2 as the positive electrode active material and aluminum foil as the current collector, and a negative electrode film was prepared by mixing graphite powder and active material powder with a discharge capacity design value of 450 mAh / g.
• a non-aqueous electrolyte solution in which lithium hexafluorophosphate was dissolved at a concentration of 1 mol / L in a 1 / 1 (volume ratio) mixture of ethylene carbonate and diethyl carbonate was used as the non-aqueous electrolyte, and a coin-type lithium ion secondary battery was prepared using a polyethylene microporous film with a thickness of 30 ⁇ m as the separator.
• the laminated lithium ion secondary battery was charged at a constant current of 1.2 mA (0.25c based on the positive electrode) at room temperature until the voltage of the test cell reached 4.2 V, and after reaching 4.2 V, the current was reduced to keep the cell voltage at 4.2 V and charging was performed, and the discharge capacity was obtained.
• the capacity retention rate after 100 cycles at 45° C. was 88% (see Table 2 below).
• Table 2 The obtained analytical results and the results of charge/discharge evaluation of the half cell and full cell are shown in Table 2.
• anhydrous magnesium acetate concentration 5 mass%; solvent ethanol
• manganese (III) acetylacetonate solution Concentration 5 mass%; solvent MEK
• the analytical results and the charge/discharge evaluation results of the half cell and full cell are shown in Table 2.
• anhydrous magnesium acetate concentration 5 mass%; solvent ethanol
• manganese (III) acetylacetonate solution Concentration 5 mass%; solvent MEK
• the obtained analysis results and the charge/discharge evaluation results of the half cell and full cell are shown in Table 2.
• the composite active material for secondary batteries of this embodiment (Examples 1 to 24) had higher capacity retention and initial (coulombic) efficiency when used in secondary batteries than the active material not containing metal elements (Comparative Examples 1 and 2). Therefore, it was shown that the composite active material for secondary batteries of this embodiment can maintain high charge/discharge performance such as capacity retention and initial coulombic efficiency in secondary batteries.

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