Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
• • 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
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
• • 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
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/139—Processes of manufacture
  • H01M4/1397—Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
• • 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
  • H01M4/58—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 a positive electrode material, a paste, and a sodium ion battery.
• This application claims priority based on Japanese Patent Application No. 2014-91866 for which it applied to Japan on April 25, 2014, and uses the content here.
• a positive electrode active material Na 2 M 2 (SO 4 ) 3 (where M is a transition metal element such as Fe, Mn, Co, Ni)) containing a sulfate compound has been proposed (for example, see Non-Patent Document 1).
• This positive electrode active material differs from the conventional monoclinic structure or Nasicon type sodium sulfate compound, when used as a positive electrode material, 3.6 V vs. A discharge reaction occurs when the Na content is exceeded.
• it is a low-cost material composed of abundant elements such as Na, Fe, S, and O, it is expected as a very promising material as a positive electrode active material for sodium ion batteries.
• a positive electrode active material containing a sodium sulfate compound having a novel crystal structure has a low electronic conductivity and has a problem in solubility in water. Therefore, in order to improve battery characteristics such as discharge capacity and cycle characteristics at a high-speed charge / discharge rate, it is necessary to uniformly coat the surface of sodium sulfate compound particles with a carbonaceous material. Conventionally, the surface of positive electrode active material particles is uniformly coated with a carbonaceous material by pyrolysis of organic matter. However, since the positive electrode active material containing sodium sulfate compound has low thermal stability, It is necessary to coat the carbonaceous material.
• the present invention has been made in view of the above circumstances, and provides a positive electrode material, a paste, and a sodium ion battery that are excellent in water resistance, have high electron conductivity, and are suitably used for sodium ion secondary batteries. Objective.
• the positive electrode material of the present invention has a Na x M y (SO 4 ) y (where M is the M 2 O 10 dimer crystal structure in which two MO 6 in the structure share a ridge to form a dimer).
• M is the M 2 O 10 dimer crystal structure in which two MO 6 in the structure share a ridge to form a dimer.
• the paste of the present invention is characterized by containing the positive electrode material of the present invention, a conductive auxiliary agent, and a binder.
• the sodium ion battery of the present invention comprises an electrode plate having a positive electrode formed on one main surface of a current collector using the paste of the present invention.
• Na x M y (SO 4 ) having two M 2 MO 6 were formed edge-sharing to dimers O 10 dimeric crystal structure in the structure represented by y
• the coverage of the carbonaceous film on the surface of the primary particles of the positive electrode active material particles containing the sodium sulfate compound is high. Therefore, since it is excellent in water resistance and has high electron conductivity, it can be suitably used for a sodium ion secondary battery. Thereby, the cycle deterioration of the battery capacity can be greatly improved.
• the paste of the present invention since it contains the positive electrode material of the present invention, when this paste is applied to one main surface of a current collector to form a positive electrode to form an electrode plate, a high capacity and high An electrode plate having an energy density can be provided.
• the positive electrode is formed on one main surface of the current collector using the paste containing the positive electrode material of the present invention. Therefore, a sodium ion battery having a high capacity and a high energy density can be provided.
• the positive electrode material of the present embodiment Na x M y (SO 4 ) having two M 2 MO 6 were formed edge-sharing to dimers O 10 dimeric crystal structure in the structure y (where, M Is one or more selected from the group of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag 1.6 ⁇ x ⁇ 2.4, 1.6 ⁇ y ⁇ 2.4, 2.4 ⁇ z ⁇ 3.6), and positive electrode active material particles comprising a sodium sulfate compound represented by: It includes carbonaceous electrode active material composite particles comprising a carbonaceous film covering the surface of the positive electrode active material particles.
• Na x M y (SO 4 ) particles of sodium sulfate compounds represented by y the non-patent document 3 (https://ecs.confex.com/ecs/imlb2014/webprogram/Paper34514.html ), which is described based on the manufacturing method (synthesis method) using Na 2 SO 4 and FeSO 4 (anhydrous) as raw materials.
• Na x M y (SO 4 ) y is preferably Na 2 M 2 (SO 4 ) 3 , and more preferably Na 2 Fe 2 (SO 4 ) 3 .
• the carbonaceous film is formed by a low-temperature process of 500 ° C. or lower, which will be described later. Since the carbonaceous film is formed by a low temperature process of 500 ° C. or less, the positive electrode active material particles containing the above-mentioned sodium sulfate compound having low thermal stability can be carbonized at a high coverage without being deteriorated by heat. A quality film can be formed.
• carbonaceous is a carbon material containing carbon alone or carbon as a main component.
• “the surface of the positive electrode active material particles is coated with a carbonaceous film” means one or more of the following states.
• the surface of the positive electrode active material particles is a particle composed of simple carbon or a particle composed of a carbon material mainly composed of carbon.
• the average particle diameter of primary particles of positive electrode active material particles (carbonaceous electrode active material composite particles) coated with a carbonaceous film is preferably 0.05 ⁇ m or more and 20 ⁇ m or less, more preferably 0.1 ⁇ m or more and 5 ⁇ m or less. is there.
• the reason why the average particle diameter of the primary particles of the carbonaceous electrode active material composite particles is preferably 0.05 ⁇ m or more and 20 ⁇ m or less is as follows. When the average particle diameter of the primary particles of the carbonaceous electrode active material composite particles is less than 0.05 ⁇ m, the specific surface area of the carbonaceous electrode active material composite particles increases, so the mass of carbon required increases and the charge / discharge capacity decreases. .
• the carbonaceous electrode active material composite particles are composed of aggregated particles obtained by aggregating a plurality of primary particles of the positive electrode active material particles coated with the carbonaceous film, and the carbonaceous material is between the primary particles. It is preferable to interpose a film. This is because the carbonaceous film suppresses the elution of transition metal ions from the positive electrode material to the electrolytic solution, and enhances ion conductivity between the positive electrode active material particles.
• the carbonaceous electrode active material composite particles are aggregated particles obtained by aggregating a plurality of primary particles of positive electrode active material particles coated with a carbonaceous film, the average aggregated particle diameter of the aggregated particles is 0.5 ⁇ m or more and 100 ⁇ m. The following is preferable, and more preferably 1 ⁇ m or more and 20 ⁇ m or less.
• the reason why the average aggregated particle diameter of the aggregated particles is in the above range is that when the average aggregated particle diameter is less than 0.5 ⁇ m, the aggregated particles are too fine to bend easily, and when producing a positive electrode forming paste. This is because handling becomes difficult.
• the average aggregated particle diameter exceeds 100 ⁇ m when a positive electrode for a battery is produced, there is a high possibility that aggregated particles having a size exceeding the thickness of the positive electrode after drying are present, and the thickness of the positive electrode is uniform. This is because it becomes impossible to maintain the sex.
• the average agglomerated particle diameter of the agglomerated particles may be observed using an SEM or the like, as in the method for measuring the average particle diameter of the positive electrode active material particles coated with the carbonaceous film, or dispersed in water or the like and lasered. You may measure a number average particle diameter using a diffraction scattering type particle size distribution measuring apparatus.
• the volume density of the aggregate can be measured using a mercury porosimeter.
• the volume density is preferably 40% by volume to 95% by volume, and more preferably 60% by volume to 90% by volume.
• the aggregated particles are densified to increase the strength of the aggregated particles.
• the aggregated particles are not easily broken.
• the increase in the viscosity of the electrode slurry is suppressed and the fluidity is maintained, so that the coating property is improved and the filling property of the electrode material in the coating film of the electrode slurry can be improved.
• the coverage of the carbonaceous film on the surface of the positive electrode active material particles can be measured using a transmission electron microscope (TEM), an energy dispersive X-ray spectrometer (EDX), or the like.
• TEM transmission electron microscope
• EDX energy dispersive X-ray spectrometer
• 60% or more, more preferably 80% or more, and still more preferably 90% or more of the surface of the positive electrode active material particle is covered with the carbonaceous film.
• the reason why the coverage of the carbonaceous film on the surface of the positive electrode active material particles is 60% or more is that when the coverage is less than 60%, the surface of the positive electrode active material particles is exposed and moisture is easily adsorbed. As a result, the hydrofluoric acid produced by the adsorbed moisture deteriorates the battery components, and gas generation occurs due to water decomposition due to charge / discharge, which increases the internal pressure in the battery and may damage the battery. This is because it is not preferable.
• the coverage of the carbonaceous film on the surface of the positive electrode active material particles is determined as follows. That is, the ratio of the surface length covered with the carbonaceous film to the particle surface length of the cross section of the positive electrode active material particles obtained using a transmission electron microscope (TEM) was measured, and for 50 particles Similarly, measure and average the values.
• TEM transmission electron microscope
• the amount of oxygen in the carbonaceous material is oxygen containing at least one of a hydroxyl group (—OH), a carbonyl group (> C ⁇ O), a carboxyl group (—COOH), an ether bond, and an ester bond at or near the terminal.
• the oxygen content in the carbon is preferably 5.0% by mass or less, more preferably 3.0% by mass or less.
• the reason why the oxygen content in the carbonaceous material is 5.0% by mass or less is that when the oxygen content in the carbonaceous material exceeds 5.0% by mass, the oxygen-containing functionalities present in the carbonaceous material at the time of charging.
• the gas generated by the oxidation of the group increases the internal pressure in the sodium ion battery. As a result, the sodium ion battery may be destroyed, which is not preferable.
• the oxygen content in the carbonaceous substance exceeds 5.0% by mass, the amount of moisture adsorbed on the oxygen-containing functional group in the carbonaceous substance increases, and the electrolyte is due to the residual moisture when the sodium ion battery is formed. NaPF 6 decomposes. This is because hydrofluoric acid generated by this decomposition is not preferable because there is a possibility of deteriorating battery constituent members.
• the thickness (average value) of the carbonaceous film is preferably 0.1 nm or more and 20 nm or less.
• the reason why the thickness of the carbonaceous film is in the above range is that if the thickness of the carbonaceous film is less than 0.1 nm, the film having a desired resistance value is formed because the thickness of the carbonaceous film is too thin. become unable. And as a result, electroconductivity falls and it becomes because it becomes impossible to ensure the electroconductivity as a positive electrode material.
• the thickness of the carbonaceous film exceeds 20 nm, battery activity, for example, battery capacity per unit mass of the positive electrode material decreases.
• the carbonaceous electrode active material composite particles are composed of aggregated particles obtained by aggregating a plurality of primary particles of the positive electrode active material particles coated with the carbonaceous film, and the carbonaceous material is between the primary particles. It is preferable to interpose a film. This is because the carbonaceous film suppresses the elution of transition metal ions from the positive electrode material to the electrolytic solution, and enhances ion conductivity between the positive electrode active material particles.
• the specific surface area of the carbonaceous electrode active material composite particles is preferably 0.1 m 2 / g or more and 30 m 2 / g or less, more preferably 0.2 m 2 / g or more and 20 m 2 / g or less.
• the reason for limiting the specific surface area of the carbonaceous electrode active material composite particles 0.1 m 2 / g or more and a 30 m 2 / g or less, a specific surface area of the carbonaceous electrode active material composite particles 0.1 m 2 / g If it is less than that, it takes time to move sodium ions or electrons within the carbonaceous electrode active material composite particles. For this reason, the internal resistance increases and the output characteristics deteriorate, which is not preferable.
• the specific surface area of the carbonaceous electrode active material composite particles exceeds 30 m 2 / g, the specific surface area of the carbonaceous electrode active material composite particles increases, resulting in an increase in the required carbon mass and a reduction in charge / discharge capacity. This is because it is not preferable.
• the “internal resistance” is mainly a sum of an electronic resistance and a sodium ion movement resistance.
• Electronic resistance is proportional to carbon content, carbon density and crystallinity
• sodium ion transfer resistance is inversely proportional to carbon content, carbon density and crystallinity.
• a method for evaluating the internal resistance for example, a current pause method or the like is used.
• the internal resistance is the wiring resistance, contact resistance, charge transfer resistance, sodium ion transfer resistance, sodium reaction resistance at the positive and negative electrodes, interelectrode resistance determined by the distance between the positive and negative electrodes, solvation of sodium ions, desolvation It is measured as the sum of resistance related to the sum and SEI (Solid Electrolyte Interface) movement resistance of sodium ions.
• the water content of the carbonaceous electrode active material composite particles is preferably 5% by mass or less, more preferably 2.5% by mass or less.
• the reason why the moisture content of the carbonaceous electrode active material composite particles is 5% by mass or less is that when the moisture content exceeds 5% by mass, the carbonaceous electrode active material composite particles are used as a sodium ion battery.
• NaPF 6 that is an electrolyte is decomposed by the remaining water. This is because hydrofluoric acid generated by this decomposition is not preferable because it deteriorates the battery component.
• the carbon content of the carbonaceous electrode active material composite particles is preferably 0.3% by mass or more and 8.0% by mass or less, more preferably 0.5% by mass or more and 5.0% by mass or less. is there.
• the reason why the carbon content of the carbonaceous electrode active material composite particles is 0.3 mass% or more and 8.0 mass% or less is as follows. That is, when the carbon content of the carbonaceous electrode active material composite particles is less than 0.3% by mass, the discharge capacity at a high-speed charge / discharge rate is lowered when a battery is formed, and sufficient charge / discharge rate performance is realized. Is not preferable because it becomes difficult.
• the manufacturing method of the electrode material of this embodiment is not specifically limited. For example, the 500 ° C. or less of a low-temperature process, and a method having a step of coating with carbonaceous coating the Na x M y (SO 4) y surface of the particles (primary particles).
• Na x M y (SO 4 ) y particles are obtained from Na 2 SO 4 and FeSO described in Non-Patent Document 3 (https://ecs.confex.com/ecs/imlb2014/webprogram/Paper34514.html). 4 (anhydrous) and a production method (synthesis method) using as a raw material.
• the 500 ° C. or less of a low temperature process to form a carbonaceous coating on the surface of the Na x M y (SO 4) y particles There is no particular limitation as long as it is possible.
• Examples of the carbon source used in CVD include alcohols such as methanol, ethanol and propanol, and gases such as methane and acetylene.
• Examples of the carbon source used in PVD and sputtering include graphite and a graphite target material.
• Examples of the carbon source used in the method using a bead mill or planetary mill and the hybridization method include the following. Examples thereof include carbon powders such as acetylene black, conductive furnace, ketjen black, graphite, graphene, graphene oxide, fullerene, and carbon nanotube.
• Examples of the carbon source used in the method of heating and carbonizing a mixture of Na x M y (SO 4 ) y particles and a carbon source include the following.
• sugars such as glucose, lactose and sucrose
• organic solvents such as glycerin and ethylene glycol
• polymers such as polyvinyl pyrrolidone, polyvinyl alcohol and polyacrylic acid
• monomers such as vinyl pyrrolidone and vinyl alcohol
• the positive electrode active material particles containing the above-mentioned sodium sulfate compound with low thermal stability can be formed with a high coverage without being deteriorated by heat. Can do.
• the paste of this embodiment contains the positive electrode material of this embodiment, a conductive additive, and a binder.
• the positive electrode material is preferably contained in an amount of 70% by mass to 98% by mass when the total mass of the positive electrode material, the conductive additive and the binder is 100% by mass, and is 85% by mass to 95% by mass. More preferably, it is contained below. When the positive electrode material is contained within the above range, a positive electrode having excellent battery characteristics can be obtained.
• the conductive auxiliary agent is not particularly limited.
• one or more selected from the group of fibrous carbon such as acetylene black, ketjen black, furnace black, vapor grown carbon fiber (VGCF), and carbon nanotube can be used.
• the conductive auxiliary agent is preferably contained in an amount of 0.5% by mass or more and 15% by mass or less, when the total mass of the positive electrode material, the conductive auxiliary agent, and the binder is 100% by mass.
• the content is more preferably 10% by mass or less, and further preferably 2% by mass or more and 8% by mass or less.
• the reason why the content of the conductive auxiliary agent is in the above range is as follows. That is, when the content of the conductive assistant is less than 0.5% by mass, when the positive electrode is formed using the paste of this embodiment, the electron conductivity is not sufficient, and the battery capacity and the charge / discharge rate are reduced. It is because it is not preferable. On the other hand, when the content of the conductive auxiliary agent exceeds 15% by mass, the positive electrode material in the positive electrode is relatively reduced, which is not preferable because the battery capacity of the sodium ion battery per unit volume is reduced.
• the binder is not particularly limited. Examples thereof include one or more selected from the group of polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber, polyethylene, polypropylene and the like.
• PVdF polyvinylidene fluoride
• PTFE polytetrafluoroethylene
• styrene-butadiene rubber polyethylene, polypropylene and the like.
• the binder is preferably contained in an amount of 0.5% by mass or more and 10% by mass or less, when the total mass of the positive electrode material, the conductive additive, and the binder is 100% by mass. It is more preferable to contain 7 mass% or less.
• the reason why the content of the binder is within the above range is that when the content of the binder is less than 0.5% by mass, a coating film is formed using the paste of this embodiment. This is because the binding property between the film and the current collector is not sufficient, and the coating film may be cracked or dropped off during rolling of the positive electrode.
• the solvent may be mixed as appropriate to facilitate the application of the paste.
• the kind of solvent is not specifically limited.
• alcohols such as water, methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol: IPA), butanol, pentanol, hexanol, octanol, diacetone alcohol; ethyl acetate, butyl acetate, ethyl lactate, propylene glycol Esters such as monomethyl ether acetate, propylene glycol monoethyl ether acetate, ⁇ -butyrolactone; diethyl ether, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (ethyl cellosolve), ethylene glycol monobutyl ether (butyl cellosolve) ), Ethers such as diethylene glycol monomethyl ether and diethylene glycol monoethyl ether; acetone,
• the solvent is preferably mixed in the paste so as to be 30% by mass or more and 70% by mass or less.
• the total mass of the positive electrode material, the conductive additive and the binder is preferably contained in the paste so as to be 30% by mass or more and 70% by mass or less, and 40% by mass or more and 60% by mass. More preferably, it is contained below.
• the manufacturing method of the paste of the present embodiment is not particularly limited as long as it is a method capable of uniformly mixing the positive electrode material, the conductive additive, the binder, and the solvent.
• Examples thereof include a method using a kneading machine such as a ball mill, a sand mill, a planetary (planetary) mixer, a paint shaker, or a homogenizer.
• the electrode plate of this embodiment is obtained by forming a positive electrode on one main surface of a current collector using the paste of this embodiment. This electrode plate is used for the positive electrode of a sodium ion battery.
• the manufacturing method of the electrode plate of this embodiment will not be specifically limited if it is a method which can form a positive electrode in one surface of a collector using the positive electrode material of this embodiment.
• the paste of this embodiment is applied to one surface of the current collector to form a coating film, the coating film is dried, and then pressure-bonded to one surface of the current collector.
• An electrode plate on which a positive electrode is formed can be obtained.
• the sodium ion battery according to the present embodiment includes the electrode plate according to the present embodiment.
• the sodium ion battery of this embodiment is composed of a positive electrode made of the electrode plate of this embodiment, a negative electrode, a separator, and an electrolytic solution.
• the negative electrode, the electrolytic solution, the separator, and the like are not particularly limited.
• a negative electrode material such as metal Na, carbon material, Na alloy, Li 4 Ti 5 O 12 , Na 4 Ti 5 O 12 , Na 2 Ti 3 O 7 , tin-based alloy, or silicon compound may be used. it can.
• the electrolytic solution is, for example, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) mixed at a volume ratio of 1: 1, and sodium hexafluorophosphate (NaPF 6 ) is added to the obtained mixed solvent.
• EC ethylene carbonate
• EMC ethyl methyl carbonate
• NaPF 6 sodium hexafluorophosphate
• porous propylene can be used as the separator.
• the electrode plate of this embodiment since the electrode plate of this embodiment is used as the positive electrode, it has a high capacity and a high energy density.
• Na x M y with two M MO 6 was formed edge-sharing to dimer 2 O 10 dimer crystal structure in the structure (
• the coverage of the carbonaceous film on the surface of the primary particles of the positive electrode active material particles containing the sodium sulfate compound represented by SO 4 ) y is high.
• it since it is excellent in water resistance and has high electron conductivity, it can be suitably used for a sodium ion secondary battery.
• the area where Na x M y (SO 4 ) y and the electrolytic solution directly contact with each other can be reduced, and the transition metal ions can be prevented from being eluted into the electrolytic solution.
• transition metal ions eluted from Na x M y (SO 4 ) y are captured by the carbonaceous film, and migration of the transition metal ions to the negative electrode can be suppressed. With these effects, the amount of transition metal ions reaching the negative electrode can be reduced, and the cycle deterioration of the battery capacity can be greatly improved.
• the positive electrode material of the present embodiment is contained, when the paste is applied to one main surface of the current collector to form the positive electrode to obtain an electrode plate, a high capacity In addition, an electrode plate having a high energy density can be provided.
• an electrode plate having a high capacity and a high energy density can be provided.
• the high capacity and high A sodium ion battery having an energy density can be provided.
• Non-patent Document 3 by the method described in (https://ecs.confex.com/ecs/imlb2014/webprogram/Paper34514.html), an average primary particle diameter of 5.84 ⁇ m Na 2 Fe 2 (SO 4 ) 3 was produced.
• Na 2 SO 4 as a raw material and FeSO 4 (anhydrous) were put in a pot together with zirconia beads having a diameter of 5 mm, and mixed at a rotation speed of 300 rpm for 1 hour using a ball mill apparatus.
• the mixed powder thus obtained is placed in an alumina board, and heated in an argon (Ar) gas stream at 350 ° C.
• Example 1 including carbonaceous electrode active material composite particles composed of a carbonaceous film covering the surface of three particles was obtained. The coverage of the carbonaceous film on the surface of the carbonaceous electrode active material composite particles was 93%. In the obtained positive electrode material, the carbon content of the carbonaceous electrode active material composite particles was 0.71% by mass.
• a sodium metal was disposed as a negative electrode with respect to the positive electrode of the sodium ion battery, and a separator made of porous polypropylene was disposed between the positive electrode and the negative electrode to obtain a battery member.
• ethylene carbonate and diethyl carbonate were mixed at 1: 1 (mass ratio), and a 1M NaPF 6 solution was further added to prepare an electrolyte solution having sodium ion conductivity.
• the battery member was immersed in the electrolyte solution, and a sodium ion battery of Example 1 was produced.
• Example 2 In the same manner as in Example 1, Na 2 Fe 2 (SO 4 ) 3 having an average primary particle size of 7.63 ⁇ m was produced. A carbonaceous film having an average thickness of 5.9 nm is formed on the surface of the Na 2 Fe 2 (SO 4 ) 3 by a thermal CVD method to obtain the positive electrode material of Example 2 including carbonaceous electrode active material composite particles. It was. The coverage of the carbonaceous film on the surface of the carbonaceous electrode active material composite particles was 85%. In the obtained positive electrode material, the carbon content of the carbonaceous electrode active material composite particles was 1.34% by mass.
• the average primary particle size of Na 2 Fe 2 (SO 4 ) 3 in the positive electrode material of Example 2 shows the carbon content of the active material composite particles. Moreover, it carried out similarly to Example 1, using the positive electrode material of Example 2, the sodium ion battery was produced, and the sodium ion battery was evaluated. The evaluation results are shown in Table 2.
• Example 3 In the same manner as in Example 1, Na 2 Fe 2 (SO 4 ) 3 having an average primary particle size of 12.73 ⁇ m was produced. This Na 2 Fe 2 (SO 4) 3 of the surface, by sputtering, to form a carbonaceous coating having an average thickness of 7.1 nm, to obtain a positive electrode material of Example 3 containing carbonaceous electrode active material composite particles . The coverage of the carbonaceous film on the surface of the carbonaceous electrode active material composite particles was 96%. In the obtained positive electrode material, the carbon content of the carbonaceous electrode active material composite particles was 2.98% by mass.
• the average primary particle diameter of Na 2 Fe 2 (SO 4 ) 3 in the positive electrode material of Example 3 the average thickness of the carbonaceous coating, the coverage of the carbonaceous coating on the surface of the carbonaceous electrode active material composite particles, the carbonaceous electrode Tables 1 and 2 show the carbon content of the active material composite particles. Moreover, it carried out similarly to Example 1, using the positive electrode material of Example 3, the sodium ion battery was produced, and the sodium ion battery was evaluated. The evaluation results are shown in Table 2.
• Example 4 In the same manner as in Example 1, Na 2 Fe 2 (SO 4 ) 3 having an average primary particle size of 18.76 ⁇ m was produced. Next, Na 2 Fe 2 (SO 4 ) 3 particles and sodium carboxymethylcellulose powder as a carbon source were mixed so that the mass ratio was 96.5: 3.5. Next, this mixture was treated with a planetary ball mill apparatus for 2 hours to obtain a precursor of a positive electrode material. Next, this precursor was heat-treated at 450 ° C. for 12 hours in an argon (Ar) stream to carbonize sodium carboxymethylcellulose powder, and an average thickness of 12 was formed on the surface of Na 2 Fe 2 (SO 4 ) 3.
• a carbonaceous film having a thickness of 6 nm was formed to obtain a positive electrode material of Example 4 containing carbonaceous electrode active material composite particles.
• the coverage of the carbonaceous film on the surface of the carbonaceous electrode active material composite particles was 76%.
• the carbon content of the carbonaceous electrode active material composite particles was 4.33 mass%.
• the average primary particle size of Na 2 Fe 2 (SO 4) 3 in the positive electrode material of Example 4 the average thickness of the carbonaceous film, the coverage of the carbonaceous coating on the surface of the carbonaceous electrode active material composite particles, carbonaceous electrode Tables 1 and 2 show the carbon content of the active material composite particles.
• Example 5 In the same manner as in Example 1, Na 2 Fe 2 (SO 4 ) 3 having an average primary particle size of 14.92 ⁇ m was produced. Then, a Na 2 Fe 2 (SO 4) 3 particles and acetylene black powder as a carbon source, 96.5 in a weight ratio were mixed so that 3.5. Next, this mixture was treated with a planetary ball mill apparatus for 2 hours to obtain a precursor of a positive electrode material. Next, this precursor is heat-treated at 450 ° C. for 12 hours in an argon (Ar) stream to form a carbonaceous film having an average thickness of 8.7 nm on the surface of Na 2 Fe 2 (SO 4 ) 3.
• Example 5 a positive electrode material of Example 5 containing carbonaceous electrode active material composite particles was obtained.
• the coverage of the carbonaceous film on the surface of the carbonaceous electrode active material composite particles was 64%.
• the carbon content of the carbonaceous electrode active material composite particles was 2.26% by mass.
• the average primary particle diameter of Na 2 Fe 2 (SO 4 ) 3 in the positive electrode material of Example 5 the average thickness of the carbonaceous coating, the coverage of the carbonaceous coating on the surface of the carbonaceous electrode active material composite particles, the carbonaceous electrode Tables 1 and 2 show the carbon content of the active material composite particles.
• Example 6 In the same manner as in Example 1, Na 2 Fe 2 (SO 4 ) 3 having an average primary particle size of 9.96 ⁇ m was produced. Next, Na 2 Fe 2 (SO 4 ) 3 particles were mixed with sodium carboxymethylcellulose powder and acetylene black powder as a carbon source so that the mass ratio was 96: 2.5: 1.5. Next, this mixture was treated with a planetary ball mill apparatus for 2 hours to obtain a precursor of a positive electrode material. Next, this precursor was heat-treated at 450 ° C. for 12 hours in an argon (Ar) stream to carbonize sodium carboxymethylcellulose powder, and an average thickness of 16 was formed on the surface of Na 2 Fe 2 (SO 4 ) 3.
• a carbonaceous film having a thickness of 3 nm was formed, and a positive electrode material of Example 6 including carbonaceous electrode active material composite particles was obtained.
• the coverage of the carbonaceous film on the surface of the carbonaceous electrode active material composite particles was 87%.
• the carbon content of the carbonaceous electrode active material composite particles was 7.12% by mass.
• the average primary particle size of Na 2 Fe 2 (SO 4 ) 3 in the positive electrode material of Example 6, the average thickness of the carbonaceous coating, the coverage of the carbonaceous coating on the surface of the carbonaceous electrode active material composite particles, the carbonaceous electrode Tables 1 and 2 show the carbon content of the active material composite particles.
• Example 1 The surface of Na 2 Fe 2 (SO 4 ) 3 particles obtained in the same manner as in Example 1 and having an average primary particle size of 5.84 ⁇ m was used as it was without being covered with a carbonaceous film. In the same manner, a sodium ion battery was produced, and the sodium ion battery was evaluated. The evaluation results are shown in Table 2. Tables 1 and 2 show the average primary particle size of Na 2 Fe 2 (SO 4 ) 3 in the positive electrode material of Comparative Example 1, the carbon content of the carbonaceous electrode active material composite particles, and the like.
• Example 2 In the same manner as in Example 1, Na 2 Fe 2 (SO 4 ) 3 having an average primary particle size of 5.99 ⁇ m was produced. Next, Na 2 Fe 2 (SO 4 ) 3 particles and sodium carboxymethylcellulose powder as a carbon source were mixed so that the mass ratio was 96.5: 3.5. Next, this mixture was treated with a planetary ball mill apparatus for 2 hours to obtain a precursor of a positive electrode material. The precursor was then heat treated at 550 ° C. for 12 hours in an argon (Ar) stream. Then, the crystal structure changed from Na 2 Fe 2 (SO 4 ) 3 , and a desired positive electrode material could not be obtained.
• Na 2 Fe 2 (SO 4 ) 3 particles are coated with a carbonaceous film by a low temperature process of 500 ° C. or lower, so the coverage of the carbonaceous film is high, and the water resistance is excellent. Since the electron conductivity is high, the high capacity and high energy effect possessed by the Na 2 Fe 2 (SO 4 ) 3 particles can be sufficiently exerted, so that higher voltage, higher energy density, higher load characteristics and faster chargeability can be achieved.
• the present invention can also be applied to a next-generation secondary battery that is expected to have a discharge characteristic. In the case of a next-generation secondary battery, the effect is very large.

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