Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/02—Silicon
• • 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
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the present invention relates to nanosilicon, nanosilicon slurry, and a method for producing the nanosilicon.
• the present invention also relates to a secondary battery active material containing the nanosilicon, a negative electrode containing the secondary battery active material, and a secondary battery containing the negative electrode.
• Non-aqueous electrolyte secondary batteries are used in mobile devices, hybrid vehicles, electric vehicles, household storage batteries, etc., and are required to have well-balanced characteristics such as electrical capacity, safety, and operational stability. ing. Furthermore, in recent years, with the downsizing of various electronic devices and communication devices and the rapid spread of hybrid vehicles, etc., batteries with higher capacity and various battery characteristics such as cycle characteristics and discharge rate characteristics are required as power sources for driving these devices. There is a strong demand for the development of lithium-ion secondary batteries with further improved performance.
• silicon Since silicon has a large theoretical electrical capacity, the use of silicon as a negative electrode active material is being investigated with the aim of increasing the capacity of lithium-ion secondary batteries. However, silicon has a large difference in volume expansion and contraction when it is repeatedly charged and discharged, and the silicon particles are destroyed during repeated charging and discharging. As a result, the cycle characteristics of the secondary battery using silicon as the negative electrode active material were poor.
• Non-Patent Document 1 describes that such breakage of silicon particles is suppressed in silicon particles having a particle size of 150 nm or less. Further, Patent Document 1 describes a negative electrode active material for a secondary battery using silicon particles having nano-order particle diameters.
• the present inventors paid attention to the particle size of silicon particles and the degree of surface oxidation of silicon particles, and studied active materials for secondary batteries that are excellent in cycle characteristics, electrical capacity, and initial coulombic efficiency. As a result, the present inventors have found an active material for a secondary battery that is excellent in the cyclability, electrical capacity and initial coulombic efficiency of a lithium secondary battery. That is, the present invention relates to a secondary battery active material used in a lithium-ion secondary battery and a secondary battery containing the above-mentioned secondary battery active material as a negative electrode active material.
• An object of the present invention is to provide silicon particles used as an active material for secondary batteries that provide excellent secondary batteries.
• a further object of the present invention is to provide a method for producing silicon particles used in the active material for secondary batteries.
• the present invention has the following aspects.
• Nano-silicon having a specific surface area of 100 to 400 m 2 /g and oxygen atoms of 5 to 45 atom % relative to silicon atoms.
• the present invention also has the following aspects.
• [4] A nanosilicon slurry containing the nanosilicon according to [1] to [3], a dispersant and a solvent.
• the present invention has the following aspects.
• [5] A method for producing nano-silicon by wet pulverizing silicon powder in a non-aqueous solvent having a dew point temperature of -60°C or less, a temperature of 60°C or less, and a water concentration of 10000 ppm or less.
• [6] The above [5], wherein the wet pulverization is performed in a non-aqueous solvent containing at least one surfactant selected from the group consisting of cationic surfactants, anionic surfactants and amphoteric surfactants.
• nano-silicon manufacturing method is described in a non-aqueous solvent having a dew point temperature of -60°C or less, a temperature of 60°C or less, and a water concentration of 10000 ppm or less.
• the silicon powder having a volume average particle diameter of 1 to 20 ⁇ m and an oxygen atom content of 10 atom % or less with respect to silicon atoms is wet pulverized in a non-aqueous solvent [5] or [6] 3.
• the present invention has the following aspects.
• the nanosilicon obtained by the method for producing nanosilicon according to any one of [5] to [8] is mixed with a resin, dried, and then fired in an inert gas atmosphere.
• a method for producing an active material [10] A secondary battery active material containing the nanosilicon according to any one of [1] to [3].
• a secondary battery comprising the negative electrode for a secondary battery according to [11].
• the present invention relates to a secondary battery active material used in a lithium ion secondary battery and a secondary battery containing the secondary battery active material as a negative electrode active material.
• an active material for a secondary battery that provides a secondary battery with excellent performance.
• the present invention provides a method for producing silicon particles used in the active material for secondary batteries.
• the nanosilicon of the present invention (hereinafter also referred to as "present nanosilicon”) has a specific surface area of 100 to 400 m 2 /g and oxygen atoms of 5 to 45 atom % relative to silicon atoms.
• the oxygen atom is 5 to 45 atom% with respect to the silicon atom
• the value obtained by dividing the number of oxygen atoms in the present nanosilicon by the number of silicon atoms and expressed in atom% is 5 to 45 atom%. 45, and so on.
• silicon particles with a small particle size are considered to be prevented from being broken even if their volume changes due to repeated charging and discharging.
• silicon particles with a small particle size have a large surface area, which is considered to increase the surface oxidation rate of the silicon particles.
• the active material for secondary batteries containing silicon particles with a small particle size can suppress deterioration in cycle characteristics due to repeated charging and discharging, but results in poor electrical capacity and initial coulombic efficiency.
• This nanosilicon has a volume average particle size of nano-order, and the small particle size improves the cycle characteristics.
• the surface area is comparable to or higher than that of conventional silicon particles, it is thought that the electrical capacity and initial coulombic efficiency are improved because the content of oxygen atoms is kept low.
• the volume-average particle size of nano-order means that the volume-average particle size is in units of nanometers, and the volume-average particle size is usually 1 to 999 nm. If the silicon particles exceed 1000 nm, the dispersibility of the silicon slurry will deteriorate, the pressure during stirring will increase, and there is a possibility that the productivity will decrease. From these points of view, the volume average particle diameter of the present nanosilicon is preferably 10 to 200 nm, more preferably 10 to 100 nm, still more preferably 20 to 70 nm.
• the volume average particle diameter is a D50 value that can be measured using a laser diffraction particle size analyzer or the like. D50 can be measured by a dynamic light scattering method using a laser particle size analyzer or the like.
• the volume average particle diameter of the present nanosilicon is the particle diameter when the volume cumulative distribution curve is drawn from the small diameter side in the particle diameter distribution, and the particle diameter reaches 50%.
• the specific surface area of this nanosilicon is 100 to 400 m 2 /g.
• the specific surface area is a value determined by the BET method, can be determined by nitrogen gas adsorption measurement, and can be measured using, for example, a specific surface area measuring device.
• the specific surface area of the present nanosilicon is more preferably 100 to 300 m 2 /g, still more preferably 100 to 230 m 2 /g, from the viewpoint of electric capacity and initial coulombic efficiency.
• the amount of oxygen atoms in this nanosilicon is 5 to 45 atm % with respect to silicon atoms as described above. Even if the average particle diameter of the present nanosilicon is small as in the above range, by using the present nanosilicon having the amount of oxygen atoms in the above range as the negative electrode active material of the secondary battery, cycle performance, initial coulomb efficiency and It is considered that a secondary battery having an excellent capacity retention rate can be obtained.
• the amount of oxygen atoms in the present nanosilicon is preferably 5 to 30 atm %, more preferably 5 to 25 atm %, still more preferably 5 to 15 %, from the viewpoint of initial coulombic efficiency and capacity retention rate.
• the amount of oxygen atoms was obtained by sintering nanosilicon at a temperature of 300 to 800° C. to volatilize the additive, and then performing composition analysis using SEM-EDS (manufactured by JEOL, JSM-7900F).
• the present nanosilicon may contain carbon atoms and nitrogen atoms in addition to silicon atoms and oxygen atoms. When it contains nitrogen atoms, it is preferably 5% by mass or less from the viewpoint of capacity reduction due to silicon nitride formation.
• the shape of the present nanosilicon may be granular, needle-like, or flake-like as long as the present nanosilicon satisfies the above-mentioned specific surface area and oxygen atomic weight, but is preferably crystalline.
• the present nanosilicon is crystalline, if the crystallite diameter obtained from the diffraction peak attributed to Si (111) in X-ray diffraction (hereinafter also referred to as “crystallite diameter”) is in the range of 5 to 14 nm , is preferable from the viewpoint of initial coulombic efficiency and capacity retention rate.
• the crystallite size is more preferably 12 nm or less, still more preferably 10 nm or less.
• the present nanosilicon preferably has a length in the longitudinal direction of 30 to 300 nm and a thickness of 1 to 60 nm.
• a needle-like or flake-like shape having a so-called aspect ratio of 0.5 or less, which is a ratio of thickness to length, is preferable.
• the form of this nano-silicon can be measured by the dynamic light scattering method, but it is possible to measure the average particle size by using a transmission electron microscope (TEM) or a field emission scanning electron microscope (FE-SEM). , samples of said aspect ratio can be more easily and precisely identified.
• TEM transmission electron microscope
• FE-SEM field emission scanning electron microscope
• the sample can be cut with a focused ion beam (FIB) and the cross section can be observed with FE-SEM, or the sample can be sliced and observed with TEM. can identify the state of the present nanosilicon.
• the aspect ratio of the present nanosilicon is a result of calculation based on 50 grains of the main portion of the sample within the field of view shown in the TEM image.
• the present nanosilicon When used as a secondary battery active material, the present nanosilicon may be used as it is as an active material, or may be used as a secondary battery active material in which the matrix phase contains the present nanosilicon. From the viewpoint of the stability of the secondary battery active material, it is preferable to use an active material in which the matrix phase contains the present nanosilicon as the secondary battery active material.
• the matrix phase is a material capable of intercalating and deintercalating lithium ions.
• a substance capable of intercalating and deintercalating is a substance that can intercalate lithium ions into the matrix phase during charging of the battery and release lithium ions from the matrix phase during discharging. In the lithium secondary battery, the cycle of absorption and desorption is repeated.
• Substances capable of intercalating and deintercalating lithium ions include graphite, silicon dioxide, titanium oxide, and compounds containing silicon, oxygen, and carbon.
• the matrix phase is preferably composed of these substances. From the viewpoint of improving the initial efficiency and the capacity retention rate, it is more preferable to use a compound containing carbon.
• Compounds containing silicon, oxygen and carbon include silicon oxycarbide.
• Silicon oxycarbide is composed of a compound containing silicon, oxygen, and carbon. Among them, a three-dimensional network structure of silicon-oxygen-carbon skeleton and a structure containing free carbon are preferable. Here, free carbon is carbon that is not contained in the three-dimensional skeleton of silicon-oxygen-carbon. Free carbon includes carbon present as a carbon phase, carbon bonded between carbon phase carbons, and carbon bonded between a silicon-oxygen-carbon skeleton and a carbon phase.
• Silicon oxycarbide is preferably represented by the following formula (1).
• SiOx Cy (1) x represents the molar ratio of oxygen to silicon, and y represents the molar ratio of carbon to silicon.
• x represents the molar ratio of oxygen to silicon
• y represents the molar ratio of carbon to silicon.
• 1 ⁇ x ⁇ 2 is preferable, and 1 ⁇ x ⁇ 1, from the viewpoint that the balance between the charge/discharge performance and the capacity retention ratio is superior. 0.9 is more preferred, and 1 ⁇ x ⁇ 1.8 is even more preferred.
• the active material containing the present nanosilicon and matrix phase is used in a secondary battery, 1 ⁇ y ⁇ 20 is preferable, and 1.2 ⁇ y ⁇ 15 from the viewpoint of the balance between charge/discharge performance and initial coulomb efficiency. is more preferred.
• the above x and y can be obtained by measuring the mass content of each element and then converting to a molar ratio (atomic number ratio).
• the content of oxygen and carbon can be quantified by using an inorganic elemental analyzer, and the content of silicon can be quantified by using an ICP optical emission spectrometer (ICP-OES).
• ICP-OES ICP optical emission spectrometer
• the active material is locally analyzed, and a large number of measurement points for the content ratio data obtained thereby is obtained, and the entire active material
• the content ratio of Local analysis includes, for example, Energy Dispersive X-ray Spectroscopy (SEM-EDX) and Electron Probe Microanalyzer (EPMA).
• the matrix phase is a silicon oxycarbide phase composed of silicon oxycarbide and the structure contains a three-dimensional network structure of silicon-oxygen-carbon skeleton and free carbon
• the silicon-oxygen-carbon skeleton in the silicon oxycarbide phase is chemically stable. It has a high strength, has a composite structure with free carbon, and has a small volume change with respect to lithium absorption and release.
• this nanosilicon in the negative electrode plays a role as a main component for manifesting charge-discharge performance, while the silicon oxycarbide phase
• the breakage of the nanosilicon particles due to the volume change is further suppressed, and the cycle performance of the lithium secondary battery is further improved.
• the silicon-oxygen-carbon skeleton is converted into silicon-oxygen by the approach of lithium ions.
• - Electron distribution inside the carbon skeleton is changed, and electrostatic bonds and coordinate bonds are formed between the silicon-oxygen-carbon skeleton and lithium ions.
• Lithium ions are stored in the silicon-oxygen-carbon skeleton by this electrostatic bond and coordinate bond.
• the coordination bond energy is relatively low, the desorption reaction of lithium ions easily occurs. In other words, it is considered that the silicon-oxygen-carbon skeleton can reversibly cause intercalation and deintercalation reactions of lithium ions during charging and discharging.
• the silicon oxycarbide may contain nitrogen in addition to silicon, oxygen and carbon.
• nitrogen contained in raw materials used such as phenolic resins or polysiloxane compounds, nitrogen compounds such as other dispersants, and nitrogen gas used in the firing process
• Nitrogen atoms can be introduced into the silicon oxycarbide phase as atomic groups containing atoms as functional groups in the molecule. Since the silicon oxycarbide phase contains nitrogen, the charge/discharge performance and the capacity retention rate tend to be excellent when the active material containing the present nanosilicon and matrix phase is used as the negative electrode active material.
• the silicon oxycarbide phase When the compound constituting the silicon oxycarbide phase is a compound containing silicon, oxygen, carbon and nitrogen, the silicon oxycarbide phase preferably contains a compound represented by the following formula (2). SiOaCbNc (2) In formula (2), a and b have the same meanings as above, and c represents the molar ratio of nitrogen to silicon. When the silicon oxycarbide phase contains the compound represented by the formula (2), 1 ⁇ a ⁇ 2, 1 ⁇ b ⁇ 20 and 0 ⁇ c ⁇ 0.5 are preferable, and 1 ⁇ a ⁇ 1.9, 1.2 ⁇ b ⁇ 15 and 0 ⁇ c ⁇ 0.4 are more preferable.
• a, b and c can be obtained by measuring the mass content of the elements and then converting them into molar ratios (atomic number ratios). As with x and y, it is preferable to measure a, b and c by the method described above. It is also possible to acquire and analogize the content ratio of the entire active material. Local analysis includes, for example, Energy Dispersive X-ray Spectroscopy (SEM-EDX) and Electron Probe Microanalyzer (EPMA).
• SEM-EDX Energy Dispersive X-ray Spectroscopy
• EPMA Electron Probe Microanalyzer
• the volume average particle size of the active material containing the nanosilicon and the matrix phase is preferably 2 ⁇ m or more and 15 ⁇ m or less.
• the volume average particle size of the active material whose matrix phase contains the present nanosilicon is more preferably 2.5 ⁇ m or more, particularly preferably 3.0 ⁇ m or more. Moreover, the volume average particle size of the active material is more preferably 12 ⁇ m or less, and particularly preferably 10 ⁇ m or less. The volume average particle diameter is the value of D50.
• the specific surface area of the active material whose matrix phase contains the present nanosilicon is preferably 0.3 m 2 /g or more and 10 m 2 /g or less.
• the specific surface area of the active material whose matrix phase contains the present nanosilicon is more preferably 0.5 m 2 /g or more, and particularly preferably 1.0 m 2 /g or more. Further, the specific surface area of the active material is more preferably 9.0 m 2 /g or less, particularly preferably 8.0 m 2 /g or less.
• the specific surface area is a value determined by the BET method as described above, and can be determined by nitrogen gas adsorption measurement, and can be measured using, for example, a specific surface area measuring device.
• the silicon oxycarbide When the matrix phase is an active material containing silicon oxycarbide, the silicon oxycarbide preferably has a silicon-oxygen-carbon skeleton structure and free carbon composed only of carbon elements.
• silicon oxycarbide has free carbon, in the Raman spectrum of the active material, 1590 cm ⁇ 1 assigned to the G band of the graphite long-period carbon lattice structure and the D band of the graphite short-period carbon lattice structure with disorder and defects.
• An assigned scattering peak near 1330 cm ⁇ 1 is observed.
• the intensity ratio, I (G band)/I (D band), of the D band scattering peak intensity, I (G band), to the D band scattering intensity, I (D band) is 0.7 or more and 2 or less. preferable.
• the scattering peak intensity ratio, I (G band)/I (D band), is more preferably 0.7 or more and 1.8 or less.
• the fact that the scattering peak intensity ratio, I (G band)/I (D band), is within the above range means that the free carbon in the matrix has the following properties.
• Free carbon is mainly formed in the silicon-oxygen-carbon skeleton composed of SiO 2 C 2 , SiO 3 C, and SiO 4 , and some silicon atoms of the silicon-oxygen-carbon skeleton , electron transfer within the silicon-oxygen-carbon framework and between surface silicon atoms and free carbon is facilitated. Therefore, when an active material containing the present nanosilicon in the matrix phase is used as a negative electrode active material in a secondary battery, the lithium ion insertion and desorption reactions during charging and discharging proceed rapidly, and the charging and discharging characteristics are improved.
• the active material may expand and contract due to the lithium ion insertion and extraction reactions, but the presence of free carbon in the vicinity of the active material mitigates the expansion and contraction of the entire active material, increasing the capacity retention rate. It is considered that there is an effect to improve.
• Free carbon is formed during the thermal decomposition of the silicon-containing compound and carbon source resin in an inert gas atmosphere during the production of the silicon oxycarbide phase.
• the carbonizable sites in the molecular structures of the silicon-containing compound and the carbon source resin become carbon components by high-temperature pyrolysis in an inert atmosphere, and some of these carbons form a silicon-oxygen-carbon skeleton.
• the carbonizable component is preferably a hydrocarbon, more preferably alkyls, alkylenes, alkenes, alkynes, aromatics, and more preferably aromatics.
• the presence of free carbon is expected to reduce the resistance of the active material. It is considered that a secondary battery active material having an excellent balance of retention rates can be obtained.
• free carbon can be introduced only from a silicon-containing compound, the combined use of a carbon source resin is expected to increase the abundance of free carbon and increase its effect.
• the type of carbon source resin is not particularly limited, but a carbon compound containing a six-membered ring of carbon is preferred.
• the existence state of the free carbon can be identified by thermogravimetric differential thermal analysis (TG-DTA) as well as Raman spectrum. Unlike the carbon atoms in the silicon-oxygen-carbon skeleton, free carbon is easily thermally decomposed in the atmosphere, and the amount of carbon present can be determined from the amount of thermogravimetric loss measured in the presence of air. That is, the carbon content can be quantified using TG-DTA.
• TG-DTA thermogravimetric differential thermal analysis
• changes in thermal decomposition temperature behavior such as decomposition reaction start temperature, decomposition reaction end temperature, number of thermal decomposition reaction species, temperature of maximum weight loss for each thermal decomposition reaction species can be easily grasped. .
• the temperature values of these behaviors can be used to determine the state of the carbon.
• the carbon atoms in the silicon-oxygen-carbon skeleton that is, the carbon atoms bonded to the silicon atoms constituting the SiO 2 C 2 , SiO 3 C, and SiO 4 have very strong chemical bonds. It has high thermal stability, and it is thought that it will not be thermally decomposed in the air within the temperature range measured by thermal analysis equipment.
• the carbon in the silicon oxycarbide phase of the active material has properties similar to those of amorphous carbon, so that it is thermally decomposed in the atmosphere within a temperature range of about 550°C to 900°C. As a result, rapid weight loss occurs.
• the maximum temperature of the TG-DTA measurement conditions is not particularly limited, but TG-DTA measurement is performed in the air under conditions from about 25° C. to about 1000° C. or higher in order to completely complete the thermal decomposition reaction of carbon. is preferred.
• the surface of the active material may be coated with a coating material.
• a coating material a substance that can be expected to have electronic conductivity, lithium ion conductivity, and an effect of suppressing decomposition of the electrolytic solution is preferable.
• the coating material include electron conductive substances such as carbon, titanium, and nickel. Among these, from the viewpoint of improving the chemical stability and thermal stability of the negative electrode active material, carbon is preferable, and low-crystalline carbon is more preferable.
• the average thickness of the coating layer is preferably 10 nm or more and 300 nm or less.
• the content of low-crystalline carbon is preferably 1 to 30% by mass based on the total amount of the active material being 100% by mass.
• the carbon coating is preferably formed on the surface of the active material by vapor phase deposition.
• the amount of the carbon coating is preferably 1% by mass or more and 10% by mass or less, where the total amount of the active material and the carbon coating is 100% by mass, from the viewpoint of improving the chemical stability and thermal stability of the active material. .
• the mass of the active material is the mass of the nanosilicon when the active material is composed only of the nanosilicon, or the total amount of both when the active material is composed of the nanosilicon and the matrix phase.
• the matrix phase consists of silicon oxycarbide
• silicon oxycarbide contains nitrogen
• the active material contains another third component described later, it is the total amount including the third component.
• the active material may contain other necessary third components in addition to the above.
• the third component includes at least one metal silicate compound selected from the group consisting of Li, K, Na, Ca, Mg and Al (hereinafter also referred to as "metal silicate compound").
• a silicate compound is generally a compound containing an anion having a structure in which one or several silicon atoms are centered and surrounded by electronegative ligands.
• Metal silicate compounds include Li, K, Na, Ca, It is a salt of at least one metal selected from the group consisting of Mg and Al and a compound containing the anion.
• Examples of compounds containing anions include orthosilicate ion (SiO 4 4- ), metasilicate ion (SiO 3 2- ), pyrosilicate ion (Si 2 O 7 6- ), cyclic silicate ion (Si 3 O 9 6- or Si 6 O 18 12- ) are known.
• the present silicate compound is preferably a silicate compound which is a salt of metasilicate ion and at least one metal selected from the group consisting of Li, K, Na, Ca, Mg and Al. Li or Mg is preferred among the metals.
• the metal silicate compound contains at least one metal selected from the group consisting of Li, K, Na, Ca, Mg and Al, and may contain two or more of these metals. When having two or more kinds of metals, one silicate ion may have a plurality of kinds of metals, or may be a mixture of silicate compounds having different metals. Also, the metal silicate compound may contain other metals as long as it contains at least one metal selected from the group consisting of Li, K, Na, Ca, Mg and Al.
• the metal silicate compound is preferably a lithium silicate compound or a magnesium silicate compound, more preferably lithium metasilicate (Li 2 SiO 3 ) or magnesium metasilicate (MgSiO 3 ), and particularly preferably magnesium metasilicate (MgSiO 3 ).
• This nanosilicon production method involves wet pulverizing silicon powder in a non-aqueous solvent with a dew point temperature of -60°C or less, a temperature of 60°C or less, and a water concentration of 10000 ppm or less (hereinafter referred to as “this method. (also referred to as “manufacturing method”).
• the dew point temperature is the temperature at which dew condensation occurs when the gas is cooled, and it is an index representing the humidity in the gas.
• "Under a gas atmosphere with a dew point temperature of -60°C or lower” means a gas atmosphere in which dew condensation occurs for the first time when the gas is cooled to -60°C, and indicates a state in which the amount of water in the gas is low. If the dew point temperature exceeds ⁇ 60° C., a large amount of water is mixed into the solvent during wet pulverization, resulting in poor dispersion and gelation of the silicon particles, resulting in a decrease in productivity.
• the dew point temperature can be calculated approximately using, for example, the saturated water vapor pressure table of JIS Z 8806 “Humidity—Measurement method”.
• the gas atmosphere is usually an inert gas atmosphere, preferably a nitrogen atmosphere from the viewpoint of handling.
• a dew point temperature of ⁇ 60° C. or less means that the water content in nitrogen is 10.67 ppm.
• the silicon powder is wet-ground in a non-aqueous solvent having a temperature of 60° C. or less and a water concentration of 10000 ppm or less under the gas atmosphere. From the viewpoint of suppressing evaporation of the solvent and gelation of the silicon particles, the temperature is preferably 40° C. or less.
• the temperature of the non-aqueous solvent is preferably 40° C. or less.
• non-aqueous solvents 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; aromatic benzene, toluene and xylene.
• the water concentration of the non-aqueous solvent is preferably 10000 ppm or less, more preferably 5000 ppm or less, still more preferably 1000 ppm or less, and most preferably 600 ppm or less, from the viewpoint of reduction in initial efficiency due to oxidation of silicon.
• the moisture concentration of the non-aqueous solvent is controlled by the dew point of the atmosphere, for example, by adding a dehydrating agent to the non-aqueous solvent before use and filtering off the dehydrating agent after a certain period of time, or by distilling the non-aqueous solvent before use. can be controlled within the above range by a method such as
• the concentration of silicon particles is preferably 5 to 50% by mass in the non-aqueous solvent.
• Silicon particles are wet pulverized in a non-aqueous solvent at the above temperature and water concentration.
• the silicon particles used are composed of zero-valent silicon. If the volume average particle diameter of the silicon particles is too small, the dispersibility may deteriorate and the productivity may decrease. Therefore, the volume average particle diameter of the silicon particles is preferably 1 ⁇ m or more, more preferably 3 ⁇ m or more. Even if the volume average particle diameter of the silicon particles is too large, the productivity may decrease, so the volume average particle diameter is preferably 20 ⁇ m or less, preferably 10 ⁇ m or less, and more preferably 5 ⁇ m or less.
• the volume average particle diameter is the same as D50, and the measurement method is also the same as the above.
• the oxygen atoms in the silicon particles used are preferably 10 atm% or less, more preferably 5 atm% or less, and even more preferably 2 atm% or less, relative to the silicon atoms. is.
• the purity of the silicon particles to be used is less than 99% by mass, the metal may be easily eluted when this nanosilicon is used as the negative electrode active material, making it difficult to handle as a battery. Therefore, the purity of the silicon particles used is preferably 99% by mass or more, more preferably 99.9% by mass, and still more preferably 99.99% by mass.
• Pulverizers used for wet pulverization include, for example, ball mills, bead mills, and jet mills.
• the crushing conditions are controlled such as a bead particle size of 0.5 mm or less, a bead filling rate of 50 to 95 vol%, a rotor peripheral speed of 2 to 14 m / s, or a crushing time of 0.5 to 24 h, etc., and classified.
• the present nanosilicon having an average particle size of nano-order can be obtained.
• the bead particle size is preferably 0.2 mm or less.
• the peripheral speed of the bead mill rotor is preferably 4 to 12 m/s, more preferably 6 to 12 m/s.
• a dispersant may be added to facilitate pulverization of the silicon particles.
• dispersants include aqueous and non-aqueous dispersants, and non-aqueous dispersants are preferred.
• non-aqueous dispersants include polymer types such as polyether, alcohol, polyalkylene polyamine, and polycarboxylic acid partial alkyl esters; low molecular types such as polyhydric alcohol esters and alkyl polyamines; Inorganic types such as salts are exemplified.
• the dispersant is added, it is preferably in the range of 5% to 60% by mass, more preferably 5% to 30% by mass, relative to the mass of the silicon particles.
• cationic surfactants include aliphatic amine salts, aliphatic quaternary ammonium salts, aromatic quaternary ammonium salts and heterocyclic quaternary ammonium salts.
• the amine value of the cationic surfactant is, for example, 1 to 100 mgKOH/g, preferably 5 to 80 mgKOH/g, more preferably 10 to 48 mgKOH/g, particularly preferably 35 to 48 mgKOH/g.
• DISPERBYK9077 manufactured by BYK Additives & Instruments, DISPERBYK is a registered trademark
• DISPERBYK is a registered trademark
• Anionic surfactants include carboxylates, sulfonates, sulfates and phosphates.
• the anionic surfactant has an acid value of, for example, 1 to 200 mgKOH/g, preferably 10 to 180 mgKOH/g, more preferably 50 to 150 mgKOH/g.
• the acid value is within the above range, so that the viscosity of the slurry can be suppressed, resulting in excellent cycle characteristics, charge/discharge capacity, and initial coulombic efficiency of the battery.
• DISPERBYK111 manufactured by BYK Additives & Instruments
• the surfactant may be an amphoteric surfactant having an amine value and an acid value as described above, or a cationic surfactant and an anionic surfactant having an amine value and an acid value as described above may be used in combination.
• Amphoteric surfactants are surfactants that exhibit the properties of anionic surfactants in the alkaline region and the properties of cationic surfactants in the acidic region, and include, for example, compounds containing carboxylates, amino acids and betaine.
• ANTI-TERRA registered trademark
• U100 manufactured by BYK Additives & Instruments
• the amount added is preferably 5 to 60% by mass, more preferably 5 to 40% by mass, still more preferably 5 to 20% by mass, based on the mass of the silicon particles.
• the present active material is, for example, the present nanosilicon and resin are mixed and dried. , can be produced by firing in an inert gas atmosphere.
• the resin to be mixed with the present nanosilicon should be a resin capable of intercalating and deintercalating lithium ions by firing.
• substances capable of intercalating and deintercalating lithium ions include graphite, silicon dioxide, titanium oxide, and compounds containing silicon, oxygen, and carbon. and carbon source resins.
• the nanosilicon slurry is preferably a nanosilicon slurry containing the present nanosilicon, a dispersant and a solvent (hereinafter also referred to as "present nanosilicon slurry").
• the dispersant contained in the present nanosilicon slurry is the same as described above, and the solvent is water or the same nonaqueous solvent as the nonaqueous solvent described above. Preferred dispersants and non-aqueous solvents are also the same as above.
• the nanosilicon slurry may also contain a surfactant.
• the nanosilicon slurry preferably comprises the nanosilicon, a dispersant and a non-aqueous solvent.
• the present nanosilicon slurry is more preferably a slurry in which the present nanosilicon is dispersed in the nonaqueous solvent without separating the obtained present nanosilicon using the dispersant in the present manufacturing method.
• the non-aqueous solvent and optionally a dispersant are included, the total amount of the dispersant and the present nanosilicon is 100% by mass, and the amount of the present nanosilicon is in the range of 5% by mass to 40% by mass.
• 10% by mass to 30% by mass is more preferable.
• the matrix phase of the present active material contains the silicon oxycarbide
• the mixture of the polysiloxane compound and the carbon source resin is mixed with the present nanosilicon
• the nanosilicon slurry is mixed with a mixture of a polysiloxane compound and a carbon source resin, the solvent is removed to obtain a precursor, the obtained precursor is calcined to obtain a calcined product, and if necessary, the mixture is pulverized.
• the present active material having a desired average particle size or specific surface area can be obtained.
• polysiloxane compound examples include resins containing at least one of a polycarbosilane structure, a polysilazane structure, a polysilane structure and a polysiloxane structure.
• a resin containing only these structures may be used, or a composite resin having at least one of these structures as a segment and chemically bonded to another polymer segment may be used.
• Forms of composite include graft copolymerization, block copolymerization, random copolymerization, alternating copolymerization, and the like.
• Examples include composite resins having a graft structure in which polysiloxane segments are chemically bonded to the side chains of polymer segments, composite resins having a block structure in which polysiloxane segments are chemically bonded to the ends of polymer segments, and the like. .
• a polysiloxane compound in which the polysiloxane segment has a structural unit represented by the following general formula (S-1) and/or the following general formula (S-2) is preferred.
• the polysiloxane compound more preferably has a carboxy group, an epoxy group, an amino group, or a polyether group at the side chain or end of the siloxane bond (Si--O--Si) main skeleton.
• R 1 represents an optionally substituted aromatic hydrocarbon group, alkyl group, epoxy group, carboxy group, or the like.
• R2 and R3 each represent an alkyl group, a cycloalkyl group, an aryl group or an aralkyl group, an epoxy group, a carboxy group, or the like.
• Alkyl groups include, for example, methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, isopentyl group, neopentyl group, tert-pentyl group, 1 -methylbutyl group, 2-methylbutyl group, 1,2-dimethylpropyl group, 1-ethylpropyl group, hexyl group, isohesyl group, 1-methylpentyl group, 2-methylpentyl group, 3-methylpentyl group, 1,1 -dimethylbutyl group, 1,2-dimethylbutyl group, 2,2-dimethylbutyl group, 1-ethylbutyl group, 1,1,2-trimethylpropyl group, 1,2,2-trimethylpropyl group, 1-ethyl- 2-methylpropyl group, 1-ethyl-1-methylpropyl group
• aryl groups include phenyl, naphthyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 4-vinylphenyl, and 3-isopropylphenyl groups.
• the aralkyl group includes, for example, a benzyl group, a diphenylmethyl group, a naphthylmethyl group and the like.
• polymer segments other than the polysiloxane segment possessed by the polysiloxane compound include vinyl polymer segments such as acrylic polymers, fluoroolefin polymers, vinyl ester polymers, aromatic vinyl polymers, and polyolefin polymers, Examples include polymer segments such as polyurethane polymer segments, polyester polymer segments, and polyether polymer segments. Among them, a vinyl polymer segment is preferred.
• the polysiloxane compound may be a composite resin in which polysiloxane segments and polymer segments are bonded in a structure represented by the following structural formula (S-3), or may have a three-dimensional network-like polysiloxane structure.
• the carbon atom is the carbon atom that constitutes the polymer segment
• the two silicon atoms are the silicon atoms that constitute the 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 cross-linking reaction proceeds and the polysiloxane compound becomes solid, thereby facilitating the thermal decomposition treatment.
• polymerizable double bonds examples include vinyl groups and (meth)acryloyl groups. Two or more polymerizable double bonds are preferably present in the polysiloxane segment, more preferably 3 to 200, and even more preferably 3 to 50. In addition, by using a composite resin having two or more polymerizable double bonds as the polysiloxane compound, the cross-linking reaction can be facilitated.
• the polysiloxane segment may have silanol groups and/or hydrolyzable silyl groups.
• Hydrolyzable groups in hydrolyzable silyl groups include, for example, halogen atoms, alkoxy groups, substituted alkoxy groups, acyloxy groups, phenoxy groups, mercapto groups, amino groups, amido groups, aminooxy groups, iminooxy groups, alkenyloxy and the like, and the hydrolyzable silyl group becomes a silanol group by hydrolysis of these groups.
• a hydrolytic 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. can.
• a silanol group as used in the present invention is a silicon-containing group having a hydroxyl group directly bonded to a silicon atom.
• the hydrolyzable silyl group referred to in the present invention is a silicon-containing group having a hydrolyzable group directly bonded to a silicon atom, specifically, for example, a group represented by the following general formula (S-4) is mentioned.
• R4 is a monovalent organic group such as an alkyl group, an aryl group or an aralkyl group; group, iminooxy group or alkenyloxy group.
• b is an integer of 0 to 2;
• Alkyl groups include, for example, methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, isopentyl group, neopentyl group, tert-pentyl group, 1 -methylbutyl group, 2-methylbutyl group, 1,2-dimethylpropyl group, 1-ethylpropyl group, hexyl group, isohesyl group, 1-methylpentyl group, 2-methylpentyl group, 3-methylpentyl group, 1,1 -dimethylbutyl group, 1,2-dimethylbutyl group, 2,2-dimethylbutyl group, 1-ethylbutyl group, 1,1,2-trimethylpropyl group, 1,2,2-trimethylpropyl group, 1-ethyl- 2-methylpropyl group, 1-ethyl-1-methylpropyl group
• aryl groups include phenyl, naphthyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 4-vinylphenyl, and 3-isopropylphenyl groups.
• the aralkyl group includes, for example, a benzyl group, a diphenylmethyl group, a naphthylmethyl group and the like.
• the halogen atom includes, for example, fluorine atom, chlorine atom, bromine atom, iodine atom and the like.
• alkoxy groups include methoxy, ethoxy, propoxy, isopropoxy, butoxy, sec-butoxy, and tert-butoxy groups.
• acyloxy groups include formyloxy, acetoxy, propanoyloxy, butanoyloxy, pivaloyloxy, pentanoyloxy, phenylacetoxy, acetoacetoxy, benzoyloxy, and naphthoyloxy groups. mentioned.
• allyloxy groups include phenyloxy groups and naphthyloxy groups.
• alkenyloxy groups include vinyloxy, allyloxy, 1-propenyloxy, isopropenyloxy, 2-butenyloxy, 3-butenyloxy, 2-petenyloxy, 3-methyl-3-butenyloxy, 2 -hexenyloxy group and the like.
• polysiloxane segments having structural units represented by general formula (S-1) and/or general formula (S-2) include those having the following structures.
• the polymer segment may have various functional groups as necessary to the extent that the effects of the present invention are not impaired.
• Such functional groups include, for example, carboxyl group, blocked carboxyl group, carboxylic anhydride group, tertiary amino group, hydroxyl group, blocked hydroxyl group, cyclocarbonate group, epoxy group, carbonyl group, primary amide group, secondary Amide, carbamate groups, functional groups represented by the following structural formula (S-5), and the like can be used.
• polymer segment may have polymerizable double bonds such as vinyl groups and (meth)acryloyl groups.
• 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, and the polymer segment and the silanol group and/or the hydrolyzable silyl group are and a method of mixing with a silane compound having a polymerizable double bond and carrying out a hydrolytic condensation reaction.
• a polymer segment containing a silanol group and/or a hydrolyzable silyl group is prepared in advance.
• 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 hydrolytic condensation reaction. Then, a method of mixing the polymer segment and polysiloxane and performing a hydrolytic condensation reaction.
• a polysiloxane compound is obtained by the method described above.
• Examples of the polysiloxane compound include the Ceranate (registered trademark) series (organic/inorganic hybrid type coating resin; manufactured by DIC Corporation) and the Compoceran SQ series (silsesquioxane type hybrid; manufactured by Arakawa Chemical Industries, Ltd.). .
• the carbon source resin is preferably a synthetic resin or a natural chemical raw material that has good miscibility with the polysiloxane compound, is carbonized by high-temperature baking in an inert atmosphere, and has an aromatic functional group.
• Synthetic resins include thermoplastic resins such as polyvinyl alcohol and polyacrylic acid, and thermosetting resins such as phenol resin and furan resin.
• Natural chemical raw materials include heavy oils, especially tar pitches such as coal tar, light tar oil, medium tar oil, heavy tar oil, naphthalene oil, anthracene oil, coal tar pitch, pitch oil, mesophase pitch, and oxygen-crosslinked petroleum pitch. , heavy oil, etc., but the use of phenolic resin is more preferable from the viewpoint of inexpensive availability and removal of impurities.
• the carbon source resin is preferably a resin containing an aromatic hydrocarbon moiety
• the resin containing an aromatic hydrocarbon moiety is preferably a phenol resin, an epoxy resin, or a thermosetting resin
• the phenol resin is preferably a resol type.
• phenolic resins include the Sumilite Resin series (resol-type phenolic resin, manufactured by Sumitomo Bakelite Co., Ltd.).
• the present nanosilicon slurry preferably the present nanosilicon slurry, is mixed with the mixture of the polysiloxane compound and the carbon source resin, and the solvent is removed to obtain a precursor.
• the mixture containing the polysiloxane compound and the carbon source resin is preferably in a state in which the polysiloxane compound and the carbon source resin are uniformly mixed.
• Said mixing is carried out using a device having the function of dispersing and mixing. Apparatuses having dispersing and mixing functions include, for example, stirrers, ultrasonic mixers, premix dispersers, and the like.
• a dryer, a reduced-pressure dryer, a spray dryer, or the like can be used for solvent removal and drying for the purpose of distilling off the organic solvent.
• the precursor preferably contains 3% to 50% by mass of the present nanosilicon, 15% to 85% by mass of the solid content of the polysiloxane compound, and 3% to 70% by mass of the solid content of the carbon source resin.
• the solid content of the silicon oxide particles is preferably 8% to 40% by mass
• the solid content of the polysiloxane compound is 20% to 70% by mass
• the solid content of the carbon source resin is preferably 3% to 60% by mass. preferable.
• the precursor obtained above is fired in an inert gas atmosphere to completely decompose the thermally decomposable organic component to obtain a fired product.
• the firing temperature for example, by firing at a temperature in which the maximum reaching temperature is in the range of 900° C. to 1200° C., the thermally decomposable organic component can be completely decomposed.
• the polysiloxane compound and the carbon source resin are converted into a silicon oxycarbide phase having a silicon-oxygen-carbon skeleton and free carbon by the energy of the high temperature treatment.
• Firing is carried out according to a firing program that is defined by the rate of temperature increase, the holding time at a certain temperature, etc.
• the maximum attainable temperature is the maximum temperature to be set, and strongly affects the structure and performance of the fired product.
• the fine structure of the present active material which possesses the chemical bonding state of silicon and carbon in the silicon oxycarbide phase, can be precisely controlled, and better charge-discharge characteristics can be obtained.
• the calcination method is not particularly limited, but it is sufficient to use a reaction apparatus having a heating function in an inert gas atmosphere, and continuous and batch processes are possible.
• a fluidized bed reactor, a rotary furnace, a vertical moving bed reactor, a tunnel furnace, a batch furnace, a rotary kiln, or the like can be appropriately selected as the firing apparatus according to the purpose.
• This active material can be obtained by pulverizing the obtained fired product and classifying it as necessary.
• the pulverization may be carried out in one step to the desired particle size, or may be carried out in several steps. For example, when producing an active material of about 10 ⁇ m from a sintered mass or agglomerated particles of 10 mm or more, it is roughly pulverized with a jaw crusher, a roll crusher, etc. to particles of about 1 mm, and then pulverized to about 100 ⁇ m with a glow mill, ball mill, etc. , a bead mill, a jet mill, or the like to a size of about 10 ⁇ m.
• Particles produced by pulverization may contain coarse particles, and in order to remove them, or to adjust the particle size distribution by removing fine powder, classification is performed.
• the classifier to be used may be a wind classifier, a wet classifier, or the like depending on the purpose, but when removing coarse particles, the classification method through a sieve is preferable because the purpose can be reliably achieved.
• the pulverization step can be omitted when the precursor mixture is controlled to have a shape near the target particle size by spray drying or the like before firing, and firing is performed in that shape.
• the present active material has at least one metal silicate compound selected from the group consisting of Li, K, Na, Ca, Mg and Al
• a slurry of the present silicon oxide particles is mixed with a mixture of a polysiloxane compound and a carbon source resin.
• at least one metal salt selected from the group consisting of is added, and then the same operation as described above is performed to obtain the silicate.
• a present active material having a compound is obtained.
• Salts of at least one metal selected from the group consisting of Li, K, Na, Ca, Mg and Al include halides such as fluorides, chlorides and bromides of these metals, hydroxides and carbonates. mentioned.
• the metal salt may be a salt of two or more metals, one salt may contain a plurality of metals, or a mixture of salts containing different metals.
• the amount of the metal salt to be added is preferably 0.01 to 0.4 in molar ratio with respect to the number of moles of the silicon oxide particles.
• the metal salt When the metal salt is soluble in an organic solvent, the metal salt may be dissolved in the organic solvent, added to the suspension, and mixed. When the metal salt is insoluble in the organic solvent, the metal salt particles may be dispersed in the organic solvent and then added to the suspension and mixed.
• the metal salt is preferably nanoparticles having an average particle size of 100 nm or less from the viewpoint of improving the dispersion effect. Alcohols, ketones and the like can be suitably used as the organic solvent, but aromatic hydrocarbon solvents such as toluene, xylene, naphthalene and methylnaphthalene can also be used.
• the metal salt molecules and the present nanosilicon can be brought into sufficient contact.
• silicon oxide exists on the surface or around the nano-silicon
• the metal salt molecules and the nano-silicon are sufficiently brought into contact with each other under the condition that the metal salt molecules and the nano-silicon are solid-phase reacted.
• the silicate compound can be present near the surface of nanosilicon.
• concentration of the silicate compound near the surface of the nanosilicon higher than the concentration of silicon oxycarbide, it is important to improve the contact state between the metal salt and the silicon oxide particles.
• by surface-modifying the metal salt molecules using an organic additive they can be attached to the vicinity of the present nanosilicon surface.
• the molecular structure of the organic additive is not particularly limited, but a molecular structure that allows physical or chemical bonding with the dispersant present on the surface of the present nanosilicon is preferred.
• the physical or chemical bond includes electrostatic action, hydrogen bond, intermolecular Van der Waals force, ionic bond, covalent bond and the like.
• the surface of the nanosilicon can be coated with the silicate compound by the solid phase reaction of the metal salt molecules with the silicon oxide on the surface of the nanosilicon.
• the present active material is excellent in cyclability, initial coulombic efficiency and capacity retention rate, and a secondary battery using the present active material as a negative electrode exhibits good characteristics.
• a slurry containing the present active material, an organic binder, and, if necessary, other components such as a conductive aid is applied in the form of a thin film onto a current collector copper foil to form a negative electrode.
• a negative electrode can also be produced by adding a carbon material such as graphite to the slurry.
• Carbon materials include natural graphite, artificial graphite, amorphous carbon such as hard carbon or soft carbon, and the like.
• the present active material and a binder that is an organic binder are kneaded 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 used as a current collector. It can be obtained by applying it to the body to form a negative electrode layer. It can also be obtained by forming a paste-like negative electrode material slurry into a sheet-like or pellet-like shape and integrating this with a current collector.
• a dispersing device such as a stirrer, ball mill, super sand mill, or pressure kneader
• organic binder examples include styrene-butadiene rubber copolymer (hereinafter also referred to as "SBR"); methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (meth) acrylonitrile , and ethylenically unsaturated carboxylic acid esters such as hydroxyethyl (meth)acrylate, and ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid (meth)acrylic copolymerization Unsaturated carboxylic acid copolymers such as coalesced; A high molecular compound is mentioned.
• SBR styrene-butadiene rubber copolymer
• these organic binders can 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 ratio 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 3% by mass. to 15% by mass is more preferable.
• the present active material has high chemical stability and is easy to handle in terms of practical use in that an aqueous binder can also be used.
• the negative electrode material slurry may be mixed with a conductive aid, if necessary.
• conductive aids include carbon black, graphite, acetylene black, oxides and nitrides exhibiting conductivity, and the like.
• the amount of the conductive aid used may be about 1% by mass to 15% by mass with respect to the negative electrode active material of the present invention.
• the material and shape of the current collector for example, copper, nickel, titanium, stainless steel, etc. may be used in the form of a foil, a perforated foil, a mesh, or the like in a strip shape.
• Porous materials such as porous metal (foamed metal) and carbon paper can also be used.
• Examples of the method for applying the negative electrode material slurry to the current collector include a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, and a screen printing method. etc. After coating, it is preferable to carry out a rolling treatment using a flat plate press, calendar rolls, or the like, if necessary.
• the negative electrode material slurry can be made into a sheet or pellet form, and integrated with the current collector by, for example, rolling, pressing, or a combination thereof.
• 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 a water-based styrene-butadiene rubber copolymer (SBR) or the like is used, heat treatment at 100 to 130° C. is sufficient, and when an organic binder having a main skeleton of polyimide or polyamideimide is used, Heat treatment at 150 to 450° C. is preferred.
• SBR styrene-butadiene rubber copolymer
• This heat treatment removes the solvent and hardens the binder to increase the strength, improving the adhesion between particles and between the particles and the current collector.
• These heat treatments are preferably performed in an inert atmosphere such as helium, argon, or nitrogen, or in a vacuum atmosphere in order to prevent oxidation of the current collector during the treatment.
• the negative electrode using the present active material preferably has an electrode density of 1 g/cm 3 to 1.8 g/cm 3 , more preferably 1.1 g/cm 3 to 1.7 g/cm 3 . More preferably from 0.2 g/cm 3 to 1.6 g/cm 3 .
• the electrode density there is a tendency that the higher the electrode density, the higher the adhesion and the volume capacity density of the electrode.
• the electrode density is too high, the voids in the electrode are reduced, which weakens the effect of suppressing the volume expansion of silicon or the like, and the capacity retention rate may decrease. Therefore, an optimum range of electrode densities is selected.
• the secondary battery of the present invention contains the present active material in the negative electrode.
• a secondary battery having a negative electrode containing the present active material a non-aqueous electrolyte secondary battery and a solid electrolyte secondary battery are preferable, and excellent performance is exhibited particularly when used as a negative electrode of a non-aqueous electrolyte secondary battery. It is.
• a positive electrode and a negative electrode containing the negative electrode active material of the present invention are placed facing each other with a separator interposed therebetween, and an electrolytic solution is injected. It can be configured by
• the positive electrode can be obtained by forming a positive electrode layer on the surface of the current collector in the same manner as the negative electrode.
• the current collector may be a strip-shaped one made of a metal or alloy such as aluminum, titanium, or stainless steel in the form of foil, foil with holes, mesh, or the like.
• the positive electrode material used for the positive electrode layer is not particularly limited.
• a metal compound, a metal oxide, a metal sulfide, or a conductive polymer material capable of doping or intercalating lithium ions should be used.
• lithium cobalt oxide LiCoO 2
• lithium nickel oxide LiNiO 2
• lithium manganate LiMnO 2
• lithium manganese spinel LiMn 2 O 4
• lithium vanadium compounds V2O5 , V6O13 , VO2 , MnO2 , TiO2 , MoV2O8 , TiS2 , V2S5 , VS2 , MoS2 , MoS3 , Cr3O8 , Cr 2 O 5
• olivine-type LiMPO 4 (where M is Co, Ni, Mn or Fe), conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene and polyacene, porous carbon, etc. can be used.
• the separator for example, a non-woven fabric, cloth, microporous film, or a combination of them can be used, the main component of which is polyolefin such as polyethylene or polypropylene.
• the positive electrode and the negative electrode of the non-aqueous electrolyte secondary battery to be manufactured are structured such that they do not come into direct contact with each other, there is no need to use a separator.
• electrolytes examples include lithium salts such as LiClO 4 , LiPF 6 , LiAsF 6 , LiBF 4 and LiSO 3 CF 3 , ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, cyclopentanone, sulfolane.
• the structure of the secondary battery of the present invention is not particularly limited, but usually, a positive electrode, a negative electrode, and an optional separator are wound into a flat spiral to form a wound electrode plate group. It is common to have a structure in which flat plates are laminated to form a laminated electrode plate group, and these electrode plate groups are enclosed in an outer package.
• the active material is mainly used for the negative electrode, and a simple evaluation is performed using metallic lithium for the counter electrode. for comparison.
• Secondary batteries using this active material are not particularly limited, but are used as paper-type batteries, button-type batteries, coin-type batteries, laminate-type batteries, cylindrical batteries, prismatic batteries, and the like.
• the negative electrode active material of the present invention described above can also be applied to general electrochemical devices having a charging/discharging mechanism of intercalating and deintercalating lithium ions, such as hybrid capacitors and solid lithium secondary batteries.
• this active material when used as a negative electrode active material for a secondary battery, it provides a secondary battery that is excellent in cyclability, initial coulombic efficiency, and capacity retention rate.
• the present active material can be used as a negative electrode by the method described above to form a secondary battery having the negative electrode.
• the present nanosilicon, the present nanosilicon slurry containing the present nanosilicon, the method for producing the present nanosilicon, the present active material containing the present nanosilicon, and the secondary battery containing the present active material in the negative electrode have been described above. It is not limited to the configuration of the above embodiment.
• the present nanosilicon, the present nanosilicon slurry, the present active material, and the secondary battery containing the present active material in the negative electrode may be added with any other configuration to the configuration of the above-described embodiment, and exhibit the same function. Any configuration may be substituted.
• the present nanosilicon production method and the present active material production method may be added with other arbitrary steps, or may be replaced with arbitrary steps exhibiting similar functions. good.
• the present invention will be described in detail below with reference to Examples, but the present invention is not limited to these.
• the active material is mainly used for the negative electrode, and a simple evaluation is performed using metallic lithium for the counter electrode. for comparison.
• Synthesis Example 1 Preparation of Polysiloxane Compound (Synthesis of Condensate (a1) of Methyltrimethoxysilane) 1,421 parts by mass of methyltrimethoxysilane (hereinafter referred to as "MTMS”) was charged into a reaction vessel equipped with a stirrer, thermometer, dropping funnel, cooling tube and nitrogen gas inlet, and heated to 60°C. I warmed up. Then, a mixture of 0.17 parts by mass of iso-propyl acid phosphate ("Phoslex A-3" manufactured by SC Organic Chemical Co., Ltd.) and 207 parts by mass of deionized water was dropped into the reaction vessel over 5 minutes. , and stirred at a temperature of 80° C.
• MTMS methyltrimethoxysilane
• the active ingredient content of the obtained liquid was 70% by mass.
• the effective ingredient is the value obtained by dividing the theoretical yield (parts by mass) when all the methoxy groups of the silane monomer such as MTMS are condensed by the actual yield (parts by mass) after the condensation reaction. Theoretical yield when all methoxy groups are condensed (parts by mass)/Actual yield after condensation reaction (parts by mass)].
• MMA methyl methacrylate
• BMA butyl methacrylate
• BA butyric acid
• MPTS methacryloyloxypropyltrimethoxysilane
• BuOH butylperoxy-2-ethylhexanoate
• Example 1 70 g of commercially available silicon powder (manufactured by Kojundo Chemical Co., Ltd.) having a silicon purity of 99.9% by mass, a volume average particle diameter of 3.2 ⁇ m, and an oxygen content of 3.5 atom % with respect to silicon, DISPERBYK9077 (manufactured by BYK Additives & Instruments, DISPERBYK is a registered trademark) and 280 g of methyl ethyl ketone (hereinafter also referred to as "MEK”) were mixed in a stirring tank and stirred well. The stirring tank was covered with a lid, and nitrogen gas with a dew point of -70°C was supplied to create an inert gas atmosphere in the tank.
• DISPERBYK9077 manufactured by BYK Additives & Instruments, DISPERBYK is a registered trademark
• MEK methyl ethyl ketone
• the initial water concentration was 0.058% by mass.
• This mixed solution was subjected to wet pulverization for 1.5 hours using a bead mill (Ultra Apec Mill UAM-015 manufactured by Hiroshima Metal & Machinery Co., Ltd.) to obtain nanosilicon uniformly dispersed in the dispersion medium.
• the beads in the bead mill had a diameter of 0.2 mm, and the temperature of the mixture during wet grinding was 40°C or less.
• Nanosilicon having a specific surface area of 105 m 2 /g, a crystallite size of 13.5 nm, an oxygen content of 12.5 atom % relative to silicon, and a volume average particle size of 180 nm was obtained.
• the dried resin material which is a calcined precursor, was calcined in a nitrogen atmosphere at a temperature of 1050° C. for 6 hours to obtain a black solid.
• the resulting black solid was pulverized with a planetary ball mill to obtain a negative electrode active material powder.
• a mixed slurry containing 80% by mass of the negative electrode active material powder, 10% by mass of acetylene black as a conductive aid, and 10% by mass of a mixture of CMC and SBR as a binder was prepared and formed into a film on a copper foil. After that, it was dried under reduced pressure at 110° C., and a Li metal foil was used as a counter electrode to prepare a half cell.
• the charge/discharge characteristics of this half cell were evaluated using a second battery charge/discharge measuring device (manufactured by Hokuto Co., Ltd.) with a cutoff voltage range of 0.005 to 1.5V.
• the initial discharge capacity was 1630 mAh/g
• the initial efficiency was 86%
• the retention rate after 5 cycles was 91%.
• a single-layer sheet using LiCoO 2 as a positive electrode active material and aluminum foil as a current collector was used to prepare a positive electrode film, and graphite powder was used at a discharge capacity design value of 450 mAh / g. and the active material powder were mixed to prepare a negative electrode film.
• lithium hexafluorophosphate was added to a mixture of ethylene carbonate (hereinafter also referred to as “EC”) and diethyl carbonate (hereinafter also referred to as “DEC”) at a volume ratio of 1/1 at a concentration of 1 mol/mol.
• a laminated lithium ion secondary battery was fabricated using a non-aqueous electrolyte solution dissolved at a concentration of L and using a polyethylene microporous film having a thickness of 30 ⁇ m as a separator.
• a laminated lithium ion secondary battery was charged at 25°C at a constant current of 1.2mA (0.25c based on the positive electrode) until the voltage of the test cell reached 4.2V, and after reaching 4.2V, Cell voltage is 4. The battery was charged while the current was decreased so as to keep the voltage at 2 V, and the discharge capacity was obtained.
• the capacity retention rate was 90% after 300 cycles, where charging and discharging within a voltage range of 2.5 V to 4.2 V was defined as one cycle.
• the laminate cell was dismantled in an argon atmosphere in a glove box, the negative electrode was taken out, washed with an EC/DEC mixed solution, allowed to stand and dried, and then the thickness of the electrode film was measured. The rate of change in the thickness of the negative electrode film before and after charging/discharging was taken as the negative electrode expansion rate. The expansion rate of the negative electrode was 19%. Table 1 shows the results.
• Examples 2 to 12 Nanosilicon produced by wet pulverization with a bead mill in the same manner as in Example 1 except that the weight percentage of the additive in the mixed liquid during wet pulverization with a bead mill and the pulverization time of the wet pulverization are set to the conditions shown in Table 1. was used to prepare a negative electrode active material. Using this, a half cell was produced in the same manner as in Example 1, and charge/discharge characteristics were evaluated. Table 1 shows the results.
• Example 13 Wet pulverization with a bead mill was performed in the same manner as in Example 1, except that the initial moisture concentration of the mixed liquid during wet pulverization with a bead mill was 0.49% by mass, and a negative electrode active material was produced using the produced nanosilicon. Using this, a half cell was produced in the same manner as in Example 1, and charge/discharge characteristics were evaluated. Table 1 shows the results.
• Example 14 and 18 Wet pulverization with a bead mill was performed in the same manner as in Example 1, except that the volume average particle size of the raw silicon powder during wet pulverization with a bead mill) and the amount of oxygen relative to silicon in the raw silicon powder were different, and nanosilicon prepared was used. to prepare a negative electrode active material. Using this, a half cell was produced in the same manner as in Example 1, and charge/discharge characteristics were evaluated. Table 1 shows the results.
• Example 19 Wet pulverization with a bead mill was carried out in the same manner as in Example 1, except that the raw material silicon powder during wet pulverization with a bead mill had a silicon purity of 99% by weight, a volume average particle diameter of 4.6 ⁇ m, and an oxygen content relative to silicon of 1.5 atom %. was performed, and a negative electrode active material was produced using the produced nanosilicon. Using this, a half cell was produced in the same manner as in Example 1, and charge/discharge characteristics were evaluated. Table 1 shows the results.
• Comparative example 1 Wet pulverization with a bead mill was carried out in the same manner as in Example 1, except that no additive was added. The thickening was intense, gelation occurred during pulverization, and the operation of the bead mill was stopped. Gelation of the nano-silicon-containing slurry made it unsuitable for the next step, making it impossible to continue.
• Comparative example 2 Wet pulverization with a bead mill was carried out in the same manner as in Example 1, except that the wet pulverization was performed at an initial water content of 2.51% by mass and a liquid temperature of 60° C. or higher. The thickening was intense, gelation occurred during pulverization, and the operation of the bead mill was stopped. Gelation of the nano-silicon-containing slurry made it unsuitable for the next step, making it impossible to continue.
• Comparative example 3 Wet pulverization by a bead mill was carried out in the same manner as in Example 1 except that the dew point of the nitrogen gas supplied to the stirring vessel was ⁇ 40° C. or higher. The thickening was intense, gelation occurred during pulverization, and the operation of the bead mill was stopped. Gelation of the nano-silicon-containing slurry made it unsuitable for the next step, making it impossible to continue.
• Comparative example 4 After preparing the negative electrode active material in the same manner as in Example 1, except that the precursor of the negative electrode active material was baked in air, a half cell was prepared. The measurement results of charge-discharge characteristics were an initial discharge capacity of 1090 mAh/g and an initial efficiency of 61.2%. Table 1 shows the results.
• Comparative example 5 Wet pulverization, preparation of a negative electrode active material, and preparation of a half cell were performed in the same manner as in Example 1, except that a silicon powder having a volume average particle size of 0.5 ⁇ m and an oxygen content of 16 atom % relative to silicon was used as a raw material. . The clumps could not be loosened, the separator (screen) was clogged, the pressure inside the bead mill increased, and the operation of the bead mill stopped. It was impossible to continue grinding.
• Comparative example 6 Wet pulverization was carried out in the same manner as in Example 1, except that silicon powder having a volume average particle size of 30 ⁇ m and an oxygen content of 0.3 atom % relative to silicon was used as the raw material. Coarse particles could not be pulverized and the separator of the bead mill was clogged, resulting in screen blockage. A pressure rise in the bead mill occurred and the bead mill stopped operating. It was impossible to continue.
• Each evaluation method is as follows. Volume average particle size: Measured using a laser diffraction particle size distribution analyzer (Mastersizer 3000, manufactured by Malvern Panalytical). Specific surface area: Measured by BET method from nitrogen adsorption measurement using a specific surface area measuring device (BELSORP-mini manufactured by BEL JAPAN). 29 Si-NMR: JNM-ECA600 manufactured by JEOL RESONANCE was used.
• Battery characteristics evaluation Battery characteristics are measured using a secondary battery charge-discharge test device (manufactured by Hokuto Denko Co., Ltd.), room temperature 25 ° C., cutoff voltage range from 0.005 to 1.5 V, charge / discharge rate is 0 The charging/discharging characteristics were evaluated under constant current/constant voltage charging/constant current discharging conditions at 0.2 C (from 1 to 3 cycles) and 0.2 C (after 4 cycles). At the time of switching between charging and discharging, the battery was left in an open circuit for 30 minutes.
• Discharge capacity, charge capacity, initial coulombic efficiency and cyclability (in the present application, refers to the capacity retention rate after charging and discharging a full cell for 5 cycles at 25° C.), and negative electrode expansion rate were determined as follows.
• Charge capacity and discharge capacity of active material Obtained by half-cell charge/discharge measurement.
• a secondary battery containing the present active material as a negative electrode active material has excellent battery characteristics.

Landscapes

• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Battery Electrode And Active Subsutance (AREA)
• Silicon Compounds (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=87765683

Family Applications (1)

Country Status (3)

Cited By (1)

Citations (5)

Family Cites Families (2)

• 2023
  • 2023-02-09 WO PCT/JP2023/004279 patent/WO2023162692A1/ja not_active Ceased
  • 2023-02-09 JP JP2023547255A patent/JP7485230B2/ja active Active
  • 2023-02-16 TW TW112105563A patent/TW202346205A/zh unknown

Patent Citations (5)

Also Published As

Similar Documents

Legal Events