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
  • C01B33/113—Silicon oxides; Hydrates thereof
• • 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
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
• • 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
• • 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 an active material for secondary batteries and a method for producing the same.
• the present invention also relates to a secondary battery containing the active material for a secondary battery in a 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.
• Patent Document 1 describes porous silicon obtained by carbonizing metallic silicon or a silicon-containing compound and an organic compound containing no silicon having a softening point or melting point together in an inert gas or in a vacuum at a specific temperature. containing carbon-based composite materials have been proposed.
• silicon oxide contains many oxygen atoms that generate irreversible lithium silicate during charging, and has the problem of low initial efficiency. Therefore, when a battery was actually produced, an excessive battery capacity of the positive electrode was required, and an increase in battery capacity corresponding to the increase in capacity of the active material was not observed.
• Patent Document 2 describes a silicon crystal for non-aqueous electrolyte secondary battery negative electrode material having a structure in which silicon crystallites are dispersed through siloxane bonds and have fine spaces between silicon crystallites. Oxides have been proposed. However, when silicon oxide is used as the negative electrode active material for lithium-ion secondary batteries, the rapid decrease in charge-discharge capacity after many charge-discharge cycles is due to the large volume change caused by the absorption and release of large amounts of lithium. It is believed that this is due to the occurrence of particle destruction.
• Patent Document 3 has a coat layer containing silicon, oxygen and carbon even without silicon nanoparticles, and has a specific BET specific surface area and particle size under specific conditions. A structure is disclosed that satisfies
• the present inventors have investigated a secondary battery active material using silicon oxide, which suppresses the destruction of particles due to volume change of silicon oxide, improves the cycle performance of lithium secondary batteries, and has a high electric capacity. As a result, the present inventors have found a composite active material for secondary batteries that improves the cyclability, initial coulombic efficiency and capacity retention rate of lithium secondary batteries. 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 an active material for a secondary battery that provides an excellent secondary battery.
• the present invention has the following aspects.
• the Raman spectrum has scattering peaks near 1590 cm ⁇ 1 and 1330 cm ⁇ 1 attributed to the G band and D band of the carbon structure, and the intensity ratio of the scattering peaks I (G band)/I (D band ) is from 0.7 to 2, the active material for a secondary battery according to any one of [1] to [6].
• the core-shell composite structure has a carbon coating on its surface, and the carbon coating amount is 1% by mass or more and 10% by mass or less when the total mass of the core-shell composite structure is 100% by mass.
• (1) Step of obtaining the precursor for forming a shell layer (2) Step of coating and drying the precursor for forming a shell layer on the surface of the silicon oxide-containing particles (3) Firing in an inert gas atmosphere at a temperature of 900°C
• a secondary battery comprising the secondary battery active material according to any one of [1] to [9] in a negative electrode.
• 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.
• a secondary battery active material that provides an excellent secondary battery is provided.
• the active material for a secondary battery of the present invention (hereinafter also referred to as “this active material”) has a silicon oxide-containing particle as a core (hereinafter also referred to as “this core”), and a silicon oxycarbide-containing phase as a shell layer ( It has a core-shell composite structure hereinafter also referred to as “this shell layer”).
• this core silicon oxide-containing particle
• this shell layer silicon oxycarbide-containing phase
• silicon oxide has a high capacity, but when it absorbs and releases a large amount of lithium, it undergoes a large change in volume, and as a result, it is considered to be inferior in cycleability.
• the silicon oxycarbide phase has a relatively low capacity, it has a small volume change with respect to lithium absorption and desorption, and is excellent in cycle characteristics. It is considered that this active material has the former as the core and the latter as the shell layer, thereby obtaining an active material for a secondary battery that maintains a high capacity and provides a secondary battery with
• Silicon oxide is generally a general term for amorphous silicon oxides obtained by heating a mixture of silicon dioxide and metal silicon to generate silicon monoxide gas, which is then cooled and precipitated, and is represented by the following general formula ( 1).
• SiOn (1) SiOn (1) However, in the formula (1), n is 0.4 or more and 1.8 or less, preferably 0.5 or more and 1.6 or less.
• the silicon oxide-containing particles may contain components other than the silicon oxide, such as metal tin, tin oxide, germanium, and germanium oxide.
• silicon oxide may generate zero-valent silicon by a disproportionation reaction.
• the silicon oxide-containing particles contain zero-valent silicon, when the present active material is subjected to X-ray diffraction analysis, a peak attributed to the Si (111) plane near 28.4° in 2 ⁇ is detected in the X-ray diffraction pattern. be.
• Zero-valent silicon may be added separately to the silicon oxide-containing particles, and the zero-valent silicon contained in the silicon oxide-containing particles is zero-valent silicon generated by the disproportionation reaction. is preferred because the crystallites of are relatively small.
• the silicon oxide-containing particles form large lumps, and when this active material is used as a negative electrode active material, the silicon oxide-containing particles cause large expansion and contraction of the negative electrode active material during charging and discharging. . As a result, the stress concentrates on a part of the matrix, so that the structure of the active material tends to collapse, and the capacity retention rate of the negative electrode active material tends to decrease. On the other hand, if the average particle size of the silicon oxide-containing particles is too small, the silicon oxide-containing particles tend to agglomerate. Therefore, the dispersibility of the silicon oxide-containing particles in the negative electrode active material may deteriorate.
• the silicon oxide-containing particles are too fine, the specific surface area tends to increase, and by-products tend to increase on the surfaces of the silicon oxide-containing particles when the negative electrode active material is baked at high temperatures. These may lead to deterioration in charge/discharge performance.
• the average particle size of the silicon oxide-containing particles that form the core is preferably 20 ⁇ m or less, more preferably 15 ⁇ m or less, from the above-mentioned viewpoint. From the viewpoint of particle dispersibility and specific surface area, the average particle size of the silicon oxide-containing particles is preferably 1 ⁇ m or more, more preferably 2 ⁇ m or more.
• the average particle size 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 average particle diameter of the present silicon oxide particles is the particle diameter at which the volume cumulative distribution curve is drawn from the small diameter side to 50% in the particle diameter distribution.
• the silicon oxide-containing particles can be made into particles by pulverizing silicon oxide, for example, so that the average particle diameter falls within the above range.
• pulverizers used for pulverization include pulverizers such as ball mills, bead mills, and jet mills.
• the pulverization may be wet pulverization using an organic solvent, and as the organic solvent, for example, alcohols, ketones, etc. can be preferably used. Group hydrocarbon solvents can also be used.
• the obtained silicon oxide-containing particles can be classified by controlling the bead mill conditions such as the bead particle size, blending ratio, number of revolutions, or pulverization time, and the average particle size of the silicon oxide-containing particles can be controlled within the above range. can.
• the shape of the silicon oxide-containing particles may be granular, needle-like, or flake-like.
• the average particle diameter can be measured by a dynamic light scattering method, but it is possible to use an analysis means such as a transmission electron microscope (TEM) or a field emission scanning electron microscope (FE-SEM).
• TEM transmission electron microscope
• FE-SEM field emission scanning electron microscope
• the aspect ratio of the sample can be more easily and precisely identified.
• 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 silicon oxide particles.
• the aspect ratio of the present silicon oxide particles can be obtained by calculation from 50 particles of the main portion of the sample within the field of view shown in the TEM image.
• the shell layer consists of a silicon oxycarbide-containing phase.
• Silicon oxycarbide is composed of a compound containing silicon, oxygen and carbon, and preferably has a three-dimensional network structure of silicon-oxygen-carbon skeleton and a structure containing free carbon.
• 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.
• the silicon oxycarbide-containing phase may contain titanium oxide, lithium titanate, aluminum oxide, transition metal oxides, etc., in addition to the silicon oxycarbide.
• Silicon oxycarbide is preferably represented by the following formula (2).
• SiOx Cy (2) In formula (2), 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, 1 ⁇ x ⁇ 1.9 is more preferable, and 1 ⁇ x ⁇ 1.8 is more preferred.
• 1 ⁇ y ⁇ 20 is preferable, and 1.2 ⁇ y ⁇ 15 is more preferable, from the viewpoint of the balance between charge/discharge performance and initial coulombic efficiency.
• the above x and y can be obtained by measuring the content mass of each element and then converting it into 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 present active material is locally analyzed, and a large number of measurement points for the content ratio data obtained thereby is obtained. It is also possible to analogize the content ratio of the entire substance. Local analysis includes, for example, Energy Dispersive X-ray Spectroscopy (SEM-EDX) and Electron Probe Microanalyzer (EPMA).
• the silicon oxycarbide-containing phase has a structure containing a three-dimensional network of silicon-oxygen-carbon skeleton and free carbon
• the silicon-oxygen-carbon skeleton in the silicon oxycarbide phase has high chemical stability, and the structure containing free carbon , the volume change is small with respect to lithium absorption and desorption.
• At least a portion of the silicon oxide-containing particles is covered with a structure containing a silicon-oxygen-carbon skeleton and free carbon, thereby suppressing a volume change of the silicon oxide-containing particles due to lithium intercalation and deintercalation.
• the silicon oxide-containing particles in the negative electrode play the role of being the main component for the expression of charge-discharge performance, and the silicon oxycarbide-containing phase changes the volume of the silicon oxide-containing particles during charge-discharge.
• the cyclability of the lithium secondary battery is improved by suppressing the destruction of the particles associated with the
• the silicon-oxygen-carbon skeleton becomes silicon- A change occurs in the electron distribution inside the oxygen-carbon skeleton, 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 contains nitrogen as a functional group in the molecule of raw materials used in the manufacturing method of the active material described later, such as phenolic resins, dispersants, polysiloxane compounds, other nitrogen compounds, and nitrogen gas used in the firing process. By forming an atomic group, it can be introduced into silicon oxycarbide. Since the silicon oxycarbide-containing phase contains nitrogen, the charge/discharge performance and the capacity retention rate tend to be excellent when the present active material is used as a negative electrode active material.
• the silicon oxycarbide-containing phase preferably contains a compound represented by the following formula (3).
• SiOxCyNz (3) In formula (3), x and y have the same meanings as above, and z represents the molar ratio of nitrogen to silicon.
• the silicon oxycarbide-containing phase contains the compound represented by the above formula (3), 1 ⁇ x ⁇ 2, 1 ⁇ y ⁇ 20 and 0 ⁇ z ⁇ 0.5 are preferable, and 1 ⁇ x ⁇ 1.9, 1.2 ⁇ y ⁇ 15 and 0 ⁇ z ⁇ 0.4 are more preferable.
• z can be obtained by measuring the mass of the element contained and then converting it into a molar ratio (atomic number ratio). As with x and y, it is preferable to measure z by the method described above. It is also possible to 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 present active material has a core-shell composite structure having the present core and the present shell layer.
• a core-shell composite structure is a structure in which the surface of the core is covered with the shell.
• the shell layer need not cover the entire surface of the core, and may cover at least a portion of the core.
• the coverage of the shell layer is preferably 70% or more, more preferably 80% or more, and particularly preferably 100%. The coverage is determined by SEM observation and EDS elemental mapping.
• the thickness of the shell layer is preferably 5 nm to 500 nm, more preferably 10 nm to 400 nm, from the viewpoint of the balance between charge/discharge capacity/initial coulomb efficiency and cycle characteristics.
• the average particle size of the active material is preferably 1 ⁇ m or more and 30 ⁇ m or less.
• the average particle diameter of the present active material is more preferably 2 ⁇ m or more, particularly preferably 3 ⁇ m or more. Further, the average particle diameter of the present active material is more preferably 25 ⁇ m or less, particularly preferably 20 ⁇ m or less.
• the average particle size is the value of D50.
• the specific surface area of the present active material is preferably 0.3 m 2 /g or more and 10 m 2 /g or less.
• the specific surface area of the active material is more preferably 0.5 m 2 /g or more, particularly preferably 1.0 m 2 /g or more. Further, the specific surface area of the present 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, and can be determined by nitrogen gas adsorption measurement, for example, using a specific surface area measuring device.
• the present active material preferably has a silicon-oxygen-carbon skeleton structure and free carbon composed only of carbon elements in the silicon oxycarbide-containing phase.
• the Raman spectrum of the present active material shows 1590 cm ⁇ 1 attributed to the G band of the graphite long-period carbon lattice structure, A scattering peak is observed near 1330 cm ⁇ 1 attributed to the D band of the periodic carbon lattice structure.
• 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 preferably 0.7 to 2. .
• 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. For this reason, it is thought that the lithium ion intercalation and deintercalation reactions at the time of charging and discharging when the present active material is used in a secondary battery proceed rapidly, and the charging and discharging characteristics are improved.
• the negative electrode active material may slightly expand and contract due to the insertion and extraction reactions of lithium ions, the presence of free carbon in the vicinity of the expansion and contraction of the active material as a whole mitigates the expansion and contraction. It is considered that there is an effect of greatly improving the capacity retention rate.
• Free carbon is formed along with the thermal decomposition of the silicon-containing compound and carbon source resin in an inert gas atmosphere during the production of the silicon oxycarbide-containing 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 this active material, and when this active material is used as the negative electrode of a secondary battery, the reaction inside this active material occurs uniformly and smoothly, resulting in charging and discharging. It is considered that a secondary battery active material having an excellent balance between performance and capacity retention 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-containing phase of the active material has properties similar to those of amorphous carbon, 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 present active material preferably has a film on the surface of the core-shell composite structure.
• the film it is preferable to use a film of a substance that can be expected to have electronic conductivity, lithium ion conductivity, and an effect of suppressing the decomposition of the electrolytic solution.
• the coating include coatings of 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, a carbon coating is preferable, and an amorphous carbon coating is more preferable.
• the average thickness of the coating is 10 nm or more and 300 nm or less, or the amount of carbon coating is 100 masses of the total mass of the core-shell composite structure. As %, 1 to 10% by mass is preferable.
• the carbon coating is preferably applied to the surface of the core-shell composite structure by vapor deposition.
• the total mass of the core-shell composite structure is the total amount of the core and the shell layers that constitute the active material. In the case of the present shell layer in which the silicon oxycarbide-containing layer phase contains nitrogen, it is the total amount including nitrogen, and in the case of the core-shell composite structure including the third component described later, it is the total amount including the third component.
• the silicon-containing active material When the silicon-containing active material is used as the negative electrode active material, lithium reacts with silicon oxide present in the silicon-containing active material during initial charging to produce lithium oxide. The produced lithium oxide cannot reversibly return to the positive electrode during discharge. It is believed that lithium is lost due to such an irreversible reaction, resulting in a decrease in initial charge/discharge efficiency.
• the present active material may contain a third component other than the silicon oxide-containing particles and the silicon oxycarbide-containing phase.
• Examples of such a third component include 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 an ABO-type oxide of at least one metal selected from the group consisting of Mg and Al and a compound containing the anion.
• Examples of compounds containing the anion 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.
• This silicate compound is preferably a silicate compound which is an ABO type oxide 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 ( Li2SiO3 , Li2Si2O5 , Li4SiO4 ) or magnesium metasilicate (MgSiO3 , Mg2SiO4 ) .
• lithium metasilicate Li2SiO3 , Li2Si2O5 , Li4SiO4
• MgSiO3 , Mg2SiO4 magnesium metasilicate
• Magnesium metasilicate MgSiO 3 , Mg 2 SiO 4
• the metal silicate compound is preferably distributed throughout the core-shell structure, and more preferably uniformly distributed.
• the presence of the metal silicate compound in the core-shell structure can be confirmed by a high-resolution transmission electron microscope (hereinafter also referred to as "HR-TEM").
• HR-TEM high-resolution transmission electron microscope
• this active material can be sliced by a focused ion beam (FIB) and confirmed by HR-TEM observation.
• the metal silicate compound can be detected by powder X-ray diffraction measurement (XRD) when it is in a crystalline state, and can be confirmed by solid 29 Si-NMR measurement when it is amorphous.
• the active material contains the metal silicate compound and has a surface coating
• the active material consists of the core composed of silicon oxide and the metal silicate compound, the shell layer, and the surface coating in this order from the inside. Multilayer composite structures are preferred.
• the surface coating is preferably an amorphous carbon coating.
• the present active material can be obtained, for example, by a manufacturing method (hereinafter also referred to as “the present manufacturing method”) including the following steps (1) to (3).
• a manufacturing method hereinafter also referred to as “the present manufacturing method” including the following steps (1) to (3).
• a step of obtaining the precursor for forming the shell layer hereinafter also referred to as “this precursor”) (hereinafter also referred to as “this precursor forming step”)
• On the surface of the silicon oxide-containing particles A step of applying and drying the present precursor (hereinafter also referred to as a “main coating and drying step”)
• a step of obtaining the present active material by high temperature firing at a firing temperature of 900 ° C. to 1300 ° C. in an inert atmosphere hereinafter, it is also referred to as “main firing process”.
• the present precursor is a compound that becomes the above-mentioned main shell layer by being coated on the surface of the silicon oxide-containing particles, dried, and then baked, and is a compound containing the above-mentioned silicon oxycarbide.
• this precursor include a mixture of a polysiloxane compound and a carbon source resin.
• the present precursor may optionally contain components contained in the silicon oxycarbide-containing phase other than the polysiloxane compound and the carbon source resin.
• 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.
• composite resins that have a graft structure in which polysiloxane segments and side chains of polymer segments are chemically bonded
• composite resins that have a block structure in which polysiloxane segments are chemically bonded to the ends of polymer segments. mentioned.
• 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 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 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
• R5 is a halogen atom, an alkoxy group, an acyloxy group, an allyloxy group, a mercapto group, an amino group; amido group, aminooxy 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 (a) to (c) below.
• a polymer segment containing a silanol group and/or a hydrolyzable silyl group is prepared in advance as a raw material for the polymer segment; 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 polysiloxane compound and the carbon source resin are mixed to form the precursor.
• a stirrer, an ultrasonic mixer, a premix disperser, or the like is used for mixing.
• the present precursor may be a slurry or a solution in which the mixture of the polysiloxane compound and the carbon source resin is dispersed in a solvent. Water or an organic solvent is used as the solvent.
• organic solvents 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; aromatic benzene, toluene, and xylene.
• a dispersant When slurrying the mixture of the polysiloxane compound and the carbon source resin, a dispersant may be added to the slurry.
• 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 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.
• concentration of the mixture of the polysiloxane compound and the carbon source resin in the slurry or solution of the mixture of the polysiloxane compound and the carbon source resin is not particularly limited.
• the amount of the mixture of the polysiloxane compound and the carbon source resin is preferably in the range of 70% by mass to 99% by mass, more preferably 80% by mass to 95% by mass. preferable.
• the main precursor obtained in the main precursor forming step is first applied to the surfaces of the silicon oxide-containing particles.
• the silicon oxide-containing particles can be produced by heating a mixture of silicon dioxide and metal silicon and then cooling and precipitating silicon monoxide gas produced. Alternatively, commercially available silicon oxide may be used. Silicon oxide may be pulverized, classified, or the like to obtain silicon oxide-containing particles having a desired average particle size. The pulverization and classification methods are as described above.
• the method of application may be a method of spraying the present precursor and the silicon oxide-containing particles, a method of applying with a roll, a brush, or the like, or immersing in the present precursor. method and the like.
• a method of immersing the present precursor in a slurry or solution of the silicon oxide-containing particles, or a method of applying the present precursor to the silicon oxide-containing particles by vapor deposition, or the like can be mentioned. be done.
• a method of using a slurry as the present precursor and immersing and mixing the silicon oxide-containing particles in the slurry-like present precursor, or a method of mixing a slurry of the silicon oxide-containing particles and the slurry-like present precursor. is preferred.
• These mixings are preferably carried out using a device having the functions of dispersing and mixing.
• Apparatuses having dispersing and mixing functions include, for example, stirrers, ultrasonic mixers, premix dispersers, and the like.
• the slurry of silicon oxide-containing particles can be prepared by using an organic solvent and pulverizing the silicon oxide particles with a wet powder pulverizer.
• a dispersant may be added to the organic solvent in order to accelerate the pulverization of the silicon oxide-containing particles.
• wet pulverizers include roller mills, high-speed rotary pulverizers, container-driven mills, and bead mills.
• 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; aromatic benzene, toluene, xylene, and the like. mentioned.
• a dispersant may be added.
• dispersants include aqueous and non-aqueous dispersants as in the previous term, 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 concentration of the solid content of the silicon oxide-containing particles in the slurry of the silicon oxide-containing particles is not particularly limited.
• the amount of silicon oxide is preferably in the range of 5% to 40% by mass, more preferably 10% to 30% by mass.
• the surface of the silicon oxide-containing particles is coated with the present precursor by the method described above, and the silicon oxide-containing particles coated with the present precursor are dried.
• a slurry of silicon oxide-containing particles or a slurry of the present precursor it is preferable to dry until the solvent used is removed. Drying for the purpose of removing the solvent can be performed using a dryer, a vacuum dryer, a spray dryer, or the like. When the solvent is removed by drying, the solvent may be completely removed, or a small amount of the solvent may remain in the main baking step described below.
• the dried product obtained in the main coating and drying step contains 20% to 90% by mass of the silicon oxide-containing particles, 5% to 30% by mass of the solid content of the polysiloxane compound, and 0% by mass of the solid content of the carbon source resin. % to 20% by mass, the solid content of the silicon oxide-containing particles is 30% to 85% by mass, the solid content of the polysiloxane compound is 10 to 25% by mass, and the solid content of the carbon source resin is 0%. It is more preferable to contain from mass % to 10 mass %.
• the dried product obtained in the main coating and drying step is baked at a high temperature of 900°C to 1300°C in an inert atmosphere.
• the thermally decomposable organic component is completely decomposed to obtain the main active material.
• the thermally decomposable organic component can be completely decomposed.
• the polysiloxane compound and the carbon source resin are converted into a silicon oxycarbide-containing 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 sintering temperature is the maximum temperature set in the main sintering process, and strongly affects the structure and performance of the sintered product.
• the calcination method is not particularly limited, but a reaction apparatus having a heating function may be used in an inert atmosphere, and treatment can be performed by a continuous method or a batch method.
• 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.
• inert gas include gases such as nitrogen, helium, and argon.
• the active material obtained in the main firing step may be pulverized and classified 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 lumps or agglomerated particles of 10 mm or more are reduced to about 10 ⁇ m, they are roughly pulverized with a jaw crusher, roll crusher, etc. to particles of about 1 mm, and then made to about 100 ⁇ m with a glow mill, ball mill, etc., and then with a bead mill, jet mill, etc. Pulverize to 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 dried product obtained in the main coating and drying step is controlled to a shape near the target particle size by spray drying or the like before the main baking step and subjected to the main baking step in that shape, the pulverization step is omitted. is also possible.
• the present active material contains the metal silicate compound
• at least one selected from the group consisting of Li, K, Na, Ca, Mg and Al is added to the slurry obtained by mixing the slurry of silicon oxide particles and the present precursor. After adding a seed metal salt and drying, the present active material having the silicate compound is obtained in the main firing step.
• 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 0.01 to 0 in terms of molar ratio with respect to the number of moles of silicon oxide in the silicon oxide-containing particles. Up to 0.5 is preferred.
• the metal salt When the metal salt is soluble in an organic solvent, the metal salt may be dissolved in the organic solvent and added to the slurry of the silicon oxide-containing particles and the present precursor and mixed.
• the metal salt particles 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 and mixed with the slurry of the silicon oxide-containing particles and the present precursor.
• 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 core-shell composite containing the present silicate compound can be obtained by uniformly dispersing the metal salt in the slurry of the silicon oxide-containing particles and the present precursor. Bringing the molecules of the metal salt into sufficient contact with the silicon oxide particles and the silicon oxycarbide under the condition that the slurry of the present precursor and the slurry of the silicon oxide-containing particles and the metal salt undergo a solid phase reaction.
• the silicate compound can be present in the composite structure.
• by surface-modifying the metal salt molecules with an organic additive they can adhere to the vicinity of the surface of the silicon oxide-containing particles.
• 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 silicon oxide-containing particles 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 metal salt molecules undergo a solid phase reaction with the SiO 2 phase in the silicon oxide, thereby forming a metal silicate compound in the silicon oxide-containing particles.
• the present production method includes (4) heat in a chemical vapor deposition apparatus after the main firing step.
• a step of coating with a carbon coating at a temperature in the range of 700° C. to 1000° C. in a decomposable carbon source gas and carrier inert gas flow to obtain a negative electrode active material may be included.
• Thermally decomposable carbon source gases include propane, acetylene, ethylene, acetone, and the like.
• the inert gas include nitrogen, helium, argon, etc. Nitrogen is usually used.
• 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.
• the present active material may be used alone, or a mixed active material of the present active material and another active material may be used, or the present active material may be used as a matrix phase. It may be used with a dispersed composite active material.
• the matrix phase is a substance 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 oxide, titanium oxide, tin oxide, and compounds containing silicon, oxygen, and carbon.
• the matrix phase is preferably composed of these substances. , oxygen and carbon.
• silicon oxycarbide contained in the silicon oxycarbide-containing phase, and preferred silicon oxycarbides are also the same as above.
• Silicon oxycarbide may also contain nitrogen atoms, and preferred compounds in the case of containing nitrogen are the same as those described above.
• a slurry composed of the present active material, a mixed active material or composite active material containing the present active material, an organic binder, and, if necessary, other ingredients such as a conductive agent is applied onto a current collector copper foil. It can be applied in the form of a thin film to form a negative electrode. Also, a negative electrode can be produced by adding a carbon material such as graphite to a slurry containing the present active material. 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 coalescence; A high molecular compound is mentioned.
• 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 active material, the secondary battery including the present active material in the negative electrode, and the method for producing the present active material have been described above, the present invention is not limited to the configurations of the above embodiments.
• any other configuration may be added, or any configuration that exhibits the same function may be substituted. good.
• any other step may be added, or may be replaced with any step that exhibits a similar function.
• the present invention will be described in detail below with reference to Examples, but the present invention is not limited to these.
• the negative electrode is composed mainly of the silicon-containing active material of the present invention, and the counter electrode is metallic lithium. This is to clearly compare the cycle characteristics.
• Synthesis example Preparation of polysiloxane compound Synthesis example 1 (synthesis of condensate (a1) of methyltrimethoxysilane) 1,421 parts by mass of methyltrimethoxysilane (hereinafter abbreviated 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. heated 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)].
• Synthesis Example 2 (Production of curable resin composition (1)) 150 parts by mass of butanol (hereinafter also referred to as “BuOH”) and 105 parts by mass of phenyltrimethoxysilane (hereinafter, hereinafter referred to as Also referred to as “PTMS”.) and 277 parts by mass of dimethyldimethoxysilane (hereinafter also referred to as “DMDMS”) were charged, and the temperature was raised to 80.degree.
• BuOH butanol
• PTMS phenyltrimethoxysilane
• DDMS dimethyldimethoxysilane
• MMA methyl methacrylate
• BMA butyl methacrylate
• BA butyric acid
• MPTS methacryloyloxypropyltrimethoxysilane
• BuOH butylperoxy-2-ethylhexanoate
• Example 1 The polysiloxane resin (curable resin composition (1)) having an average molecular weight of 3500 prepared in Synthesis Example 2 and the phenolic resin having an average molecular weight of 3000 were mixed with an isopropyl alcohol solvent so that the weight ratio of the resin solids was 90/10. The mixture was mixed and stirred to prepare 100 parts of a mixed liquid having a solid concentration of 3% by mass. After preparation, 100 parts of silicon oxide particles (commercially available) having an average particle size of 3 ⁇ m were added and thoroughly mixed in a stirrer. The resulting resin-mixed slurry containing silicon oxide particles was spray-dried with a small spray dryer (nitrogen circulation). A black solid was obtained by high-temperature firing at 950° C.
• the active material particles had an average particle size of 3.0 ⁇ m, a specific surface area of 3.4 m 2 /g, and a carbon thermal analysis result of the carbon coating amount of 2.1%.
• a slurry was prepared by mixing 80 parts by mass of the active material particles obtained above, 10 parts by mass of acetylene black as a conductive additive, and 10 parts by mass of a mixture of CMC and SBR as a binder.
• the obtained slurry was formed into a film on a copper foil.
• a coin-type lithium ion battery was produced as a half cell using a Li metal foil as a counter electrode.
• a secondary battery charge/discharge test device manufactured by Hokuto Co., Ltd.
• the cutoff voltage range was 0.005 to 1.5V.
• the charge/discharge measurement results were an initial discharge capacity of 1587 mAh/g and an initial coulombic efficiency of 74.9%.
• 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 a constant current of 1.2mA (0.25c based on the positive electrode) at 45°C until the voltage of the test cell reached 4.2V, and after reaching 4.2V, Charging was performed by decreasing the current so as to keep the cell voltage at 4.2 V, and the discharge capacity was determined.
• the capacity retention rate was 91% after 300 cycles, where charging and discharging within the voltage range of 2.5 V to 4.2 V was one cycle. The results are shown in Table 1.
• Examples 2 to 5 In the same manner as in Example 1, the polysiloxane resin (curable resin composition (1)) having an average molecular weight of 3500 prepared in Synthesis Example 2 and the phenolic resin having an average molecular weight of 3000 were mixed so that the weight ratio of the resin solids was 90/10. Then, it was mixed with an isopropyl alcohol solvent and stirred to make the solid concentration 6% by mass in Example 2, 12% by mass in Example 3, 30% by mass in Example 4, and 50% by mass in Example 5. A modified mixture was used. After preparing the mixture to 100 parts, 100 parts of silicon oxide (commercially available) having an average particle size of 3 ⁇ m was added to prepare a slurry, which was then spray-dried.
• silicon oxide commercially available
• Example 1 the same conditions as in Example 1 were used to obtain an active material powder having a carbon coating.
• the particle size and specific surface area were measured, and the obtained active material powder was used to evaluate charge/discharge performance in half-cell and full-cell.
• Various evaluation results are shown in Table 1.
• Example 6 The weight ratio of the polysiloxane resin (curable resin composition (1)) shown in Example 1 and the phenolic resin was adjusted so that the thickness of the silicon oxide covered phase on the surface of the silicon oxide particles after high-temperature baking was 103 nm.
• a mixed solution was prepared by mixing with an isopropyl alcohol solvent and stirring so that the ratio was 90/10. 100 parts of silicon oxide particles having an average particle size of 1.5 ⁇ m in Example 6, 5 ⁇ m in Example 7, 11 ⁇ m in Example 8, and 16 ⁇ m in Example 9 are added to 100 parts of the prepared mixture to prepare a slurry. did.
• an active material powder having a carbon coating was obtained under the same conditions as in Example 1. The particle size and specific surface area were measured, and the obtained active material powder was used to evaluate charge/discharge performance in half-cell and full-cell.
• Various evaluation results are shown in Table 1.
• Example 9 In the same manner as in Example 3, the weight ratio of the polysiloxane resin (curable resin composition (1)) having an average molecular weight of 3500 prepared in Synthesis Example 2 and the phenolic resin having an average molecular weight of 3000 was 100/0, 50/50 in Example 11, and 30/70 in Example 12, were mixed with an isopropyl alcohol solvent and stirred to prepare a mixture with a solid concentration of 12% by mass. 100 parts of silicon oxide (commercially available) having an average particle size of 3 ⁇ m was added to 100 parts of the prepared mixed liquid to prepare a slurry, which was then spray-dried. Other than that, the same operation as in Example 1 was performed to obtain an active material powder having a carbon coating. The particle size and specific surface area were measured, and the obtained active material powder was used to evaluate charge/discharge performance in half-cell and full-cell. Various evaluation results are shown in Table 1.
• Examples 13 and 14 The polysiloxane resin having an average molecular weight of 3500 (curable resin composition (2)) prepared in Synthesis Example 3 and the phenolic resin having an average molecular weight of 3000 were added to an isopropyl alcohol solvent so that the weight ratio of the resin solids was 90/10. The mixture was mixed and stirred to prepare a mixed liquid having a solid concentration of 12% by mass. 100 parts of silicon oxide particles (commercially available) having an average particle diameter of 3 ⁇ m were added to 100 parts of the prepared mixed solution and thoroughly mixed in a stirrer. The obtained resin mixed slurry containing silicon oxide particles was spray-dried with a small spray dryer (nitrogen circulation). In a nitrogen atmosphere, high-temperature firing was performed at 1050° C.
• Example 14 Example 14
• the obtained black solid matter was pulverized with a planetary ball mill to prepare a black powder.
• Example 1 the same operation as in Example 1 was performed to obtain an active material powder having a carbon coating.
• the particle size and specific surface area were measured, and the obtained active material powder was used to evaluate charge/discharge performance in half-cell and full-cell.
• Table 1 Various evaluation results are shown in Table 1.
• Examples 15 and 16 After preparing a slurry containing silicon oxide particles in the same manner as in Example 3, the molar ratio of Li + /silicon oxide to the amount of silicon oxide particles was 30/100 in Example 15 and 50/100 in Example 16. LiCl as a raw material was added to the slurry containing the silicon oxide particles and spray-dried. Subsequent conditions were the same as in Example 1, and an active material powder having a carbon coating was produced. The Li element content in the obtained active material particles was 2.5% by mass for Example 15 and 5.1% by mass for Example 16. The particle size and specific surface area of the obtained active material particles were measured, and the obtained active material particles were used to evaluate charge/discharge performance in half-cell and full-cell. Various evaluation results are shown in Table 1.
• Comparative example 1 20 g of silicon oxide powder with an average particle size of 5 ⁇ m is put into a CVD apparatus (desktop rotary kiln: manufactured by Takasago Kogyo Co., Ltd.), and a mixed gas of 0.2 L/min of ethylene gas and 0.8 L/min of nitrogen gas is introduced. Meanwhile, the surface of the black powder was coated with carbon by a chemical vapor deposition method at 850° C. for 1 hour to prepare active material particles. The amount of carbon coating after treatment was measured by a thermal analyzer and found to be 2.0% higher than the weight before treatment.
• Comparative example 2 The curable resin composition (1) prepared in Synthesis Example 1 was dried at 110° C. under reduced pressure and then baked at a high temperature of 1100° C. for 4 hours in a nitrogen atmosphere to obtain a black solid. The resulting black solid was pulverized in a planetary ball mill to produce a black powder, which was subjected to carbon coating treatment under the same CVD conditions as in Comparative Example 1. The particle size and specific surface area of the black powder obtained after the carbon coating treatment were measured, and the half-cell and full-cell charging/discharging performances were evaluated using the black powder after the carbon coating treatment. Various evaluation results are shown in Table 1.
• XRD powder X-ray diffraction
• each evaluation method is as follows. D50: 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.
• Raman scattering spectrum measurement NRS-5500 (manufactured by JASCO Corporation) was used as a measuring instrument. The measurement conditions were an excitation laser wavelength of 532 nm, an objective lens magnification of 100, and a measurement wavenumber range of 3500 to 100 cm ⁇ 1 .
• Measurement of nitrogen content An oxygen/nitrogen analyzer (EMGA-920) was used. Measurement of the thickness of the silicon oxycarbide-containing phase: The cross-sectional structure of the particles was processed with a cross-section polisher (CP method) and measured by FE-SEM observation. Measurement of carbon film amount: Weight loss was measured and calculated in the atmosphere using a thermal analysis device (manufactured by Rigaku, Thermo Plus EVO2).
• 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 conditions of constant current/constant voltage charging/constant current discharging at 0.2 C (after 4 cycles) and 1 C (1 to 3 times). 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 300 cycles of charging and discharging a full cell at 25° C.), and negative electrode expansion rate were obtained as follows.
• Charge capacity and discharge capacity of active material Obtained by half-cell charge/discharge measurement.
• the initial discharge capacity (mAh/g) was obtained by measuring a full cell (laminate cell).
• Negative electrode expansion rate After charging and discharging the full cell for 300 cycles, the negative electrode was taken out, washed with an EC/DEC mixed solution, left 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 present active material when used as a negative electrode active material, the expansion rate of the negative electrode is low while maintaining a high capacity, and both the cyclability (or capacity retention rate) and the initial coulomb efficiency are high. In addition, the characteristics of these secondary batteries are well balanced.
• a secondary battery containing the present active material as a negative electrode active material has excellent battery characteristics.

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• 2023
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