WO2014174952A1 - 電極材料および電極並びにリチウムイオン電池 - Google Patents
電極材料および電極並びにリチウムイオン電池 Download PDFInfo
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- WO2014174952A1 WO2014174952A1 PCT/JP2014/057790 JP2014057790W WO2014174952A1 WO 2014174952 A1 WO2014174952 A1 WO 2014174952A1 JP 2014057790 W JP2014057790 W JP 2014057790W WO 2014174952 A1 WO2014174952 A1 WO 2014174952A1
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- H—ELECTRICITY
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- 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
- H01M4/362—Composites
- H01M4/366—Composites as layered products
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- 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
- H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- 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
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- 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
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- 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
- H01M4/581—Chalcogenides or intercalation compounds thereof
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- 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
- H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
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- H—ELECTRICITY
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- 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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
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- 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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/626—Metals
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- 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
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- 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
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
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- 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 electrode material, an electrode, and a lithium ion battery.
- non-aqueous electrolyte secondary batteries such as lithium ion batteries have been proposed and put into practical use as small, light, and high capacity batteries.
- a lithium ion battery is composed of a positive electrode and a negative electrode having a property capable of reversibly removing and inserting lithium ions, and a non-aqueous electrolyte.
- Lithium ion batteries are lighter and smaller than secondary batteries such as conventional lead batteries, nickel cadmium batteries, and nickel metal hydride batteries, and have high energy. Therefore, the lithium ion battery is used as a power source for portable electronic devices such as a portable telephone, a notebook personal computer, and a portable information terminal.
- lithium ion batteries have been studied as high-output power sources for electric vehicles, hybrid vehicles, electric tools, and the like. High-speed charge / discharge characteristics are required for the electrode active materials of batteries used as these high-output power supplies. In addition to smoothing the power generation load, application to large batteries such as stationary power sources and backup power sources is also being studied, and it is also important that there is no problem of resource amount as well as long-term safety and reliability.
- the positive electrode of the lithium ion battery is composed of an electrode material including a lithium-containing metal oxide, a positive electrode active material, and a lithium-containing metal oxide having a property capable of reversibly removing and inserting lithium ions, a conductive additive, and a binder. Moreover, the positive electrode of a lithium ion battery is formed by apply
- lithium (Li) compounds such as lithium nickelate (LiNiO 2 ), lithium manganate (LiMn 2 O 4 ), and lithium iron phosphate (LiFePO 4 ) are also used.
- lithium cobaltate and lithium nickelate have problems such as instability of charge state, in addition to problems of element toxicity and resource amount.
- lithium manganate has a problem of dissolution in an electrolytic solution at a high temperature. Therefore, in recent years, phosphate-based electrode materials having an olivine structure typified by lithium iron phosphate have attracted attention as electrode materials that are excellent in long-term safety and reliability.
- phosphate-based electrode materials do not have sufficient electron conductivity. Therefore, in order to charge and discharge a large current, various devices such as finer particles and composite with a conductive material are required, and many efforts have been made so far.
- a method for increasing the electron conductivity of the phosphate-based electrode material for example, a method of adding and dissolving a second and third elements has been proposed (see, for example, Patent Document 1). Further, it is known that elements such as chromium and nickel contained in the electrode material are dissolved in the electrolytic solution at the time of charging and discharging, and re-deposited and grown on the negative electrode.
- Elements such as manganese, iron, and cobalt used in the electrode material are similar in nature to elements such as chromium and nickel, which are elements of the same period (fourth period) in the periodic table. Therefore, elements such as chromium and nickel are easily mixed into the electrode material from the raw materials and the environment. Elements such as chromium and nickel mixed in the electrode material cause defects in the crystal structure and are likely to be the starting point of dissolution described above. As a result, there is a problem that not only does the negative electrode damage due to dissolution and the safety decrease due to a short circuit occur, but also the amount of active species in the electrode active material is reduced and the capacity of the lithium ion battery is reduced.
- the present invention has been made to solve the above-described problems, and an object of the present invention is to provide an electrode material, an electrode, and a lithium ion battery excellent in electronic conductivity, load characteristics, and cycle characteristics.
- the present inventors have a high oxidation-reduction potential, so by adding a small amount of nickel that is inactive in the reaction potential range of elements such as manganese, iron, and cobalt, The present inventors have found that a good phosphate-based electrode material excellent in electron conductivity and load characteristics can be realized, and have completed the present invention.
- the electrode material of the present invention is [1] Li x Fe y A z BO 4 (where A is one or more selected from the group consisting of Mn and Co, and B is one or more selected from the group consisting of P, Si and S, or An electrode material comprising two or more types, an electrode active material represented by 0 ⁇ x ⁇ 4, 0 ⁇ y ⁇ 1.5, 0 ⁇ z ⁇ 1.5) as a main component and containing nickel, A surface of particles of the electrode active material is coated with a carbonaceous film, and the nickel content is 1 ppm or more and 100 ppm or less.
- the electrode material of the present invention is the electrode material according to [1], wherein the manganese content is 5000 ppm or less.
- the electrode of the present invention is an electrode characterized by being formed using the electrode material according to any one of [1] to [3].
- a lithium ion battery of the present invention is a lithium ion battery comprising a positive electrode comprising the electrode according to [4].
- the electrode material excellent in electronic conductivity, load characteristics, and cycling characteristics, an electrode, and a lithium ion battery can be provided.
- the electrode material of this embodiment is Li x Fe y A z BO 4 (where A is one or more selected from the group consisting of Mn and Co, and B is selected from the group consisting of P, Si and S) 1 or 2 or more, 0 ⁇ x ⁇ 4, 0 ⁇ y ⁇ 1.5, 0 ⁇ z ⁇ 1.5), and an electrode comprising nickel as a main component
- the electrode active material particle surface is covered with a carbonaceous film, and the nickel content is 1 ppm or more and 100 ppm or less.
- the manganese content is preferably 5000 ppm or less, and more preferably 1 ppm or more and 5000 ppm or less.
- the cobalt content is preferably 80 ppm or less, and more preferably 1 ppm or more and 80 ppm or less.
- the electrode material of the present embodiment is Li x Fe y A z BO 4 (where A is one or more selected from the group consisting of Mn and Co, B is P, The particle surface of the electrode active material represented by one or more selected from the group consisting of Si and S, 0 ⁇ x ⁇ 4, 0 ⁇ y ⁇ 1.5, 0 ⁇ z ⁇ 1.5) It is covered with a carbonaceous film.
- the content of nickel with respect to the entire electrode material is 1 ppm or more and 100 ppm or less, preferably 1 ppm or more and 85 ppm or less, more preferably 1 ppm or more and 60 ppm or less.
- the reason why the nickel content is preferably within the above range is that the following phenomenon occurs when the nickel content is outside the above range.
- the content of nickel in the electrode material mainly composed of an electrode active material containing iron (Li x Fe y A z BO 4 ) is less than 1 ppm, the electron conductivity of the electrode material cannot be increased.
- the content of nickel with respect to the entire electrode material is 1 ppm or more and 100 ppm or less, so that a lithium ion battery including an electrode formed using this electrode material as a positive electrode can be used for a long time. Even in the charge / discharge cycle, damage to the negative electrode and influence on safety can be virtually ignored. That is, when the electrode material containing an electrode active material containing iron (Li x Fe y A z BO 4 ) as a main component contains nickel in an amount of 1 ppm to 100 ppm, electron conductivity and stability (dissolution resistance) An electrode material excellent in both of these can be obtained.
- the nickel content in the electrode material is controlled to 1 ppm or more and 100 ppm without performing performance evaluation on the battery, thereby adversely affecting the electronic conductivity and stability (dissolution resistance).
- the manufacturing cost of the electrode material can be reduced.
- nickel is contained in ordinary stainless steel, in the synthesis of electrode materials including a heating step with reaction, stainless steel is used as the material of the member that comes into contact with the raw material such as a container during heating and in the previous step. By using it, nickel can be added to the electrode material. Therefore, not only can the manufacturing equipment be reduced in price, and thus the cost of the product can be reduced, but also improvement in performance can be expected.
- nickel is easily dissolved in an electrode material mainly composed of an electrode active material containing iron (Li x Fe y A z BO 4 ), but 100 ppm is included in the crystal structure. If nickel is present in excess, the elution of iron as well as nickel is accelerated. This is presumably because the lattice strain caused by nickel dissolved in the lattice becomes the starting point of dissolution.
- a trace amount of nickel can be added.
- a mixture in which an organic substance, which is a precursor of a carbonaceous film, is further mixed is heat-treated in a non-oxidizing atmosphere.
- An electrode active material having excellent characteristics can be obtained. In this case, for example, it is possible to omit the addition of a new nickel source by using stainless steel for the mixing facility of the organic substance and the phosphate electrode active material and adjusting the mixing conditions.
- the electrode material of this embodiment is an iron polyanion-based electrode material containing a trace amount of nickel, particularly a lithium-ion battery electrode material made of a phosphate-based electrode active material having an olivine structure. That is, the electrode material of the present embodiment is an electrode material such as lithium iron phosphate (LiFePO 4 ) or Li [MnFe] PO 4 , and a small amount of nickel is used to impart good electron conductivity and cycle stability. In addition, by controlling the nickel content to 1 ppm or more and 100 ppm or less, the electrode material is excellent in electronic conductivity and has virtually no adverse effects due to elution starting from lattice strain caused by nickel. It is.
- the electrode material of the present embodiment is mainly composed of an electrode active material represented by Li x Fe y A z BO 4 containing iron, contains nickel, and the nickel content is 1 ppm or more and 100 ppm or less. It was. Thereby, the electrode material of this embodiment can improve electronic conductivity.
- nickel dissolves in the electrolyte during charge and discharge, and reprecipitates and grows on the negative electrode, whereby the activity of the negative electrode is increased. It can be prevented from lowering.
- a lithium ion battery equipped with an electrode formed using the electrode material of the present embodiment as a positive electrode it has excellent electronic conductivity, and even during a long charge / discharge cycle, damage to the negative electrode and impact on safety are prevented. Lithium ion batteries can be virtually ignored.
- a lithium ion battery having high voltage, high energy density, high load characteristics, and high-speed charge / discharge characteristics can be realized. Therefore, a lithium ion battery having long-term cycle stability and reliability can be realized.
- the electrode material of the present embodiment can be obtained by mixing an electrode active material, a nickel source, and an organic substance serving as a carbon source, and then performing a heat treatment in a non-oxidizing atmosphere.
- the electrode active material of the present embodiment can be produced by a solid phase reaction method, a hydrothermal synthesis method, or the like, but if synthesized under a high pressure using a hydrothermal synthesis method, it is compared with a solid phase reaction method.
- the desired substance can be obtained at a low temperature, and fine particles excellent in monodispersibility can be obtained, which is preferable.
- an electrode active material, a nickel source, and an organic substance serving as a carbon source are dissolved or dispersed in a solvent to form a uniform slurry.
- a dispersant may be added.
- a nickel source is added to a raw material such as an electrode active material so that the nickel content with respect to the entire electrode material finally obtained is 1 ppm or more and 100 ppm or less.
- a raw material containing nickel as an impurity as a part of the raw material is used.
- combination of an electrode material the material containing nickel, such as stainless steel, is applied to the equipment used in the process before heating and before.
- Li x Fe y A z BO 4 (where A is one or more selected from the group consisting of Mn and Co, and B is one or more selected from the group consisting of P, Si and S)
- the electrode active material represented by 0 ⁇ x ⁇ 4, 0 ⁇ y ⁇ 1.5, 0 ⁇ z ⁇ 1.5) is a conventional method such as a solid phase method, a liquid phase method, or a gas phase method.
- the produced electrode active material is used.
- the electrode active material (Li x Fe y A z BO 4 ) was selected from the group consisting of lithium salts such as lithium acetate (LiCH 3 COO), lithium chloride (LiCl), or lithium hydroxide (LiOH), for example.
- lithium salts such as lithium acetate (LiCH 3 COO), lithium chloride (LiCl), or lithium hydroxide (LiOH), for example.
- Li source divalent iron salt such as iron (II) chloride (FeCl 2 ), iron (II) acetate (Fe (CH 3 COO) 2 ), iron (II) sulfate (FeSO 4 ), and phosphoric acid ( Phosphate compounds such as H 3 PO 4 ), ammonium dihydrogen phosphate (NH 4 H 2 PO 4 ), diammonium hydrogen phosphate ((NH 4 ) 2 HPO 4 ), and a small amount of nickel raw material (for example, nickel chloride) (II) (NiCl 2), nickel acetate (II) (Ni (CH 3 COO) 2), manganese sulphate optionally nickel sulfate (II) (NiSO 4) nickel salt, etc.) MnSO 4), A source such as cobalt sulfate (CoSO 4) and (raw material A in the general formula Li x Fe y A z BO 4 ), a slurry-like mixture obtained by mixing the water,
- the above raw materials use high-purity reagent grades, and a small amount of nickel raw material is added.
- industrial grades and recycled materials can be used.
- the Li x Fe y A z BO 4 particles may be crystalline particles or amorphous particles, or may be mixed crystal particles in which crystalline particles and amorphous particles coexist.
- the reason that the Li x Fe y A z BO 4 particles may be amorphous particles is that the amorphous Li x Fe y A z BO 4 particles are non-oxidized at 500 ° C. or more and 1000 ° C. or less. This is because crystallization occurs when heat treatment is performed in a neutral atmosphere. Therefore, in the case of forming a carbonaceous film for further enhancing electronic conductivity, amorphous Li x Fe y A z BO 4 powder is preferably used.
- the size of Li x Fe y A z BO 4 particles is not particularly limited, but the average particle size is preferably 0.01 ⁇ m or more and 20 ⁇ m or less, more preferably 0.02 ⁇ m or more and 5 ⁇ m or less. .
- the reason why the average particle size of the primary particles of the electrode active material is preferably within the above range is as follows when the average particle size of the primary particles of the electrode active material is outside the above range. This is because a different phenomenon occurs.
- the average particle size of the primary particles of the electrode active material is less than 0.01 ⁇ m, a large amount of binder resin for binding the electrode material is required, and the ratio of the electrode active material in the electrode plate is reduced. As a result, not only the capacity decreases, but it becomes difficult to form a good carbonaceous film for further enhancing the electron conductivity, and the discharge capacity in high-speed charge / discharge is reduced. Therefore, it becomes difficult to realize sufficient charge / discharge rate performance.
- the average particle diameter of the primary particles of the electrode active material exceeds 20 ⁇ m, the internal resistance of the primary particles increases, and the discharge capacity in high-speed charge / discharge becomes insufficient.
- the average particle diameter in this embodiment is a number average particle diameter.
- the average particle size of the primary particles of the electrode active material can be measured using a laser diffraction scattering type particle size distribution measuring device or the like.
- the shape of the electrode active material is not particularly limited, but it is easy to produce an electrode material composed of spherical, particularly spherical, secondary particles. Therefore, the shape of the primary particles composed of the electrode active material is also spherical, particularly true spherical. preferable.
- the reason why the shape of the primary particles of the electrode active material is preferably spherical, and particularly true spherical, is that the electrode active material, the binder resin (binder), and the solvent are mixed to produce an electrode (positive electrode). This is because, when preparing the paste, the amount of the solvent can be reduced, and the electrode (positive electrode) preparation paste can be easily applied to the current collector.
- the average molecular weight of the organic substance serving as the carbon source is preferably 200,000 or less, more preferably 100,000 or less.
- the solubility of the organic substance in water decreases.
- the viscosity of the obtained solution becomes high, and this high viscosity may cause a decrease in workability, which is not preferable.
- examples of such organic substances include glucose, sucrose, polyvinyl alcohol, polyacrylic acid, and hydroxy acid. These organic substances may be used alone or in combination of two or more.
- the solvent is preferably water, but in addition to water, alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol: IPA), butanol, pentanol, hexanol, octanol, diacetone alcohol, Ethyl acetate, butyl acetate, ethyl lactate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, esters such as ⁇ -butyrolactone, diethyl ether, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether ( Ethyl cellosolve), ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monomethyl ether, diethylene glycol monoethyl ether Ethers such as tellurium, ketones such as acetone, methyl ethyl ketone (MEK
- the electrode active material or the precursor of the electrode active material is uniformly dispersed, and the organic substance is dissolved or dispersed. If there is, it will not be specifically limited.
- a method for dissolving or dispersing the raw material of the electrode material in a solvent for example, a method using a medium stirring type dispersing device such as a planetary ball mill, a vibration ball mill, a bead mill, a paint shaker, or an attritor that stirs medium particles at high speed is preferable.
- a uniform slurry can be prepared by dispersing the electrode active material as primary particles and then stirring so as to dissolve the organic substance, which is preferable. By doing so, the surface of the primary particles of the electrode active material is coated with the organic substance, and as a result, the carbon derived from the organic substance is uniformly interposed between the primary particles of the electrode active material.
- this slurry is sprayed in a high-temperature atmosphere, for example, in the air of 70 ° C. or more and 250 ° C. or less and dried.
- the conditions at the time of spraying for example, the concentration of the electrode active material or its precursor in the slurry, the concentration of the organic compound, the spraying pressure, the speed, and the conditions at the time of drying after spraying, for example, the atmospheric temperature, residence Adjust time etc. as appropriate.
- a dried product having an average particle size of 0.5 ⁇ m or more and 100 ⁇ m or less, preferably 0.5 ⁇ m or more and 20 ⁇ m or less is obtained.
- the dried product is heat-treated at a temperature of 400 ° C. or higher and 1000 ° C. or lower, preferably 550 ° C. or higher and 850 ° C. or lower in a non-oxidizing atmosphere, that is, in an inert atmosphere or a reducing atmosphere.
- a non-oxidizing atmosphere that is, in an inert atmosphere or a reducing atmosphere.
- an atmosphere made of an inert gas such as nitrogen (N 2 ) or argon (Ar) is preferable, and when it is desired to suppress oxidation, a reducing atmosphere containing a reducing gas such as hydrogen (H 2 ). Is preferred.
- the reason why the heat treatment temperature is set to 400 ° C. or more and 1000 ° C. or less is that the following phenomenon occurs when the heat treatment temperature is out of the above range.
- the heat treatment temperature is less than 400 ° C.
- the decomposition / reaction of the organic substance serving as the carbon source does not proceed sufficiently, and if the carbonization of the organic substance serving as the carbon source becomes insufficient, the generated decomposition / reaction product is high resistance carbon. It becomes a thin layer made of an electron-conductive material.
- the heat treatment temperature exceeds 1000 ° C. components of Li x Fe y A z BO particles constituting the electrode active material, for example, lithium (Li) evaporate, resulting in a shift in composition.
- the heat treatment time is not particularly limited as long as the organic substance serving as the carbon source is sufficiently carbonized, and examples thereof include a time of 0.5 hours or more and 48 hours or less.
- the electrode material of the present embodiment can be obtained.
- an electrode material of the present embodiment after mixing an electrode active material, a nickel source, and an organic substance serving as a carbon source, heat treatment is performed in a non-oxidizing atmosphere, thereby improving electron conductivity.
- an electrode material excellent in electronic conductivity, load characteristics, and cycle characteristics can be easily realized at lower cost, lower environmental load, and lower device damage.
- the electrode of this embodiment is an electrode formed using the electrode material of this embodiment.
- the electrode material, a binder composed of a binder resin, and a solvent are mixed to prepare an electrode-forming paint or an electrode-forming paste.
- a conductive aid such as carbon black may be added as necessary.
- the binder resin for example, polytetrafluoroethylene (PTFE) resin, polyvinylidene fluoride (PVdF) resin, fluororubber, and the like are preferably used.
- PTFE polytetrafluoroethylene
- PVdF polyvinylidene fluoride
- fluororubber fluororubber
- the mixing ratio of the electrode material and the binder resin is not particularly limited.
- the binder resin is 1 part by mass or more and 30 parts by mass or less, preferably 3 parts by mass or more and 20 parts by mass with respect to 100 parts by mass of the electrode material. Part or less.
- the solvent used in the electrode-forming paint or electrode-forming paste may be appropriately selected according to the properties of the binder resin.
- water methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol: IPA)
- Alcohols such as butanol, pentanol, hexanol, octanol, diacetone alcohol, ethyl acetate, butyl acetate, ethyl lactate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, esters such as ⁇ -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
- the electrode-forming paint or electrode-forming paste was applied to one surface of the metal foil, and then dried, and a coating film composed of a mixture of the electrode material and the binder resin was formed on one surface. Obtain a metal foil. Next, this coating film is pressure-bonded and dried to produce an electrode having an electrode material layer on one surface of the metal foil. In this way, the electrode of this embodiment can be produced.
- the electrode of the present embodiment since it is formed using the electrode material of the present embodiment, the electron conductivity can be enhanced, and nickel is dissolved in the electrolyte during charging and discharging, and re-deposited and grown on the negative electrode. And it can prevent that the activity of a negative electrode falls. Therefore, an electrode having excellent electron conductivity, high voltage, high energy density, high load characteristics, and high-speed charge / discharge characteristics can be realized. As a result, an electrode having long-term cycle stability and reliability can be realized.
- the lithium ion battery of this embodiment includes a positive electrode made of the electrode of this embodiment, a negative electrode made of metal Li, Li alloy, Li 4 Ti 5 O 12 , a carbon material, etc., and an electrolyte solution and a separator or a solid electrolyte. Yes.
- the positive electrode comprising the electrode of this embodiment since the positive electrode comprising the electrode of this embodiment is provided, the electronic conductivity, load characteristics, and cycle characteristics can be improved. Therefore, it is possible to provide a lithium ion battery having durability, high discharge capacity, sufficient charge / discharge rate performance, and having long-term cycle stability and reliability.
- Electrode active materials and carbonization catalyst solutions used in common with the examples and comparative examples were prepared.
- this precursor slurry was put into a pressure vessel and hydrothermal synthesis was performed at 170 ° C. for 24 hours. After this reaction, the mixture was naturally cooled to room temperature (25 ° C.) to obtain a precipitated cake-like reaction product. This precipitate was sufficiently washed with distilled water several times and kept at a water content of 30% so as not to be dried to obtain a cake-like substance. A small amount of a sample for measurement was collected from this cake-like substance, vacuum-dried at 70 ° C. for 2 hours, and the obtained powder was identified by X-ray diffraction. As a result, it was found that single-phase LiFePO 4 was formed. confirmed.
- LiOH Lithium hydroxide
- H 3 PO 4 phosphoric acid
- FeSO 4 ⁇ 7H 2 O iron sulfate heptahydrate
- Mn source manganese sulfate pentahydrate
- LiOH Lithium hydroxide
- H 3 PO 4 phosphoric acid
- FeSO 4 ⁇ 7H 2 O iron sulfate heptahydrate
- CoSO 4 ⁇ 7H 2 O cobalt sulfate heptahydrate as the Co source
- Carbonization catalyst solution A carbonization catalyst solution for coating carbon on Li [MnFe] PO 4 active material containing Mn and Li [CoFe] PO 4 active material containing Co, which are organic carbonization negative catalysts, was prepared. Here, 1 mol each of lithium carbonate, iron (III) nitrate and phosphoric acid was added to water to prepare a total amount of 1 kg, and then stirred and dissolved to obtain a carbonization catalyst solution. The concentration in terms of LiFePO 4 in this carbonization catalyst solution was 15.78% by mass, and the molar concentration was 1 mol / kg.
- Example 1 In the above LiFePO 4 synthesis step, iron sulfate heptahydrate (FeSO 4 ⁇ 7H 2 O) was used as a raw material, and a small amount of nickel sulfate (NiSO 4 ) was added (corresponding to a nickel content of 10 ppm in the electrode active material). A positive electrode active material made of LiFePO 4 was obtained. 20 g of the above LiFePO 4 and 1 g of the carbonization catalyst solution in terms of LiFePO 4 were mixed. Then, 4.0 g of polyvinyl alcohol was added to the mixture, and water was further added to make the total amount 100 g.
- Electrode material A1 was obtained.
- Example 2 A positive electrode active material made of LiFePO 4 was obtained in the same manner as in Example 1 except that nickel sulfate (NiSO 4 ) was added so as to correspond to a nickel content of 80 ppm in the electrode active material. Using the obtained positive electrode active material, an electrode material A2 coated with the carbon coating of Example 2 was obtained in the same manner as Example 1.
- Example 3 A positive electrode active material made of LiFePO 4 was obtained in the same manner as in Example 1 except that nickel sulfate (NiSO 4 ) was added so as to correspond to a nickel content of 50 ppm in the electrode active material. Using the obtained positive electrode active material, an electrode material A3 coated with the carbon coating of Example 3 was obtained in the same manner as Example 1.
- Example 4 A positive electrode active material made of LiFePO 4 was obtained in the same manner as in Example 1 except that nickel sulfate (NiSO 4 ) was added so as to correspond to a nickel content of 1 ppm in the electrode active material. Using the obtained positive electrode active material, an electrode material A4 coated with the carbon coating of Example 4 was obtained in the same manner as in Example 1.
- Example 5 A part of iron sulfate heptahydrate (FeSO 4 ⁇ 7H 2 O) , to correspond to a manganese content 4500ppm in the electrode active material is replaced with manganese sulfate pentahydrate (MnSO 4 ⁇ 5H 2 O)
- a positive electrode active material made of Li [MnFe] PO 4 was obtained in the same manner as in Example 1 except that. Using the obtained positive electrode active material, an electrode material A5 coated with the carbon coating of Example 5 was obtained in the same manner as in Example 1.
- Example 6 A part of iron sulfate heptahydrate (FeSO 4 ⁇ 7H 2 O) , to correspond to the cobalt content 80ppm in the electrode active material, replaced with cobalt sulfate heptahydrate (CoSO 4 ⁇ 7H 2 O)
- a positive electrode active material made of Li [CoFe] PO 4 was obtained in the same manner as Example 1 except for the above.
- an electrode material A6 coated with the carbon coating of Example 6 was obtained in the same manner as Example 1.
- Example 7 In the synthesis process of LiFePO 4 , iron sulfate heptahydrate (FeSO 4 ⁇ 7H 2 O) was used as a raw material, and a small amount of nickel sulfate (NiSO 4 ) was added (corresponding to a nickel content of 10 ppm in the electrode active material). A positive electrode active material made of LiFePO 4 was obtained. 20 g of the above LiFePO 4 and 4.0 g of polyvinyl alcohol were added, water was further added to make the total amount 100 g, and this mixture was pulverized and mixed together with 150 g of zirconia balls having a diameter of 5 mm in a ball mill to obtain a slurry. . The obtained slurry was dried and granulated using a spray dryer, and then heat-treated at 700 ° C. for 5 hours in a nitrogen (N 2 ) atmosphere, and coated with the carbon coating of Example 7. Electrode material A7 was obtained.
- Example 2 A positive electrode active material made of LiFePO 4 was obtained in the same manner as in Example 1 except that nickel sulfate (NiSO 4 ) was added in an amount equivalent to a nickel content of 120 ppm in the electrode active material. Using the obtained positive electrode active material, an electrode material B2 coated with the carbon coating of Comparative Example 2 was obtained in the same manner as in Example 1.
- Example 3 In the same manner as in Example 1, a positive electrode active material made of LiFePO 4 was obtained. The obtained positive electrode active material was heat-treated at 700 ° C. for 5 hours under a nitrogen (N 2 ) atmosphere to obtain an electrode material B3 not covered with the carbon coating of Comparative Example 3.
- this positive electrode material paste was applied onto an aluminum (Al) foil having a thickness of 30 ⁇ m and dried. Then, it crimped
- a counter electrode (negative electrode) made of metallic lithium was used for load characteristic evaluation.
- the counter electrode (negative electrode) which consists of artificial graphite was used for cycle characteristic evaluation.
- NMP N-methyl-2-pyrrolidinone
- this counter electrode material paste was applied onto an aluminum (Al) foil having a thickness of 30 ⁇ m and dried. Then, it crimped
- a porous polypropylene film was used as the separator.
- LiPF 6 was used a solution of 1 mol / L.
- the solvent used in this LiPF 6 solution 1 ethylene carbonate and diethyl carbonate at a volume ratio of: using a mixture to 1.
- the test electrode (positive electrode), counter electrode (negative electrode), and nonaqueous electrolyte solution prepared as described above, and a 2016 type coin cell lithium ions of each of Examples 1 to 7 and Comparative Examples 1 to 3 were used.
- a battery was produced.
- the lithium ion batteries using the electrode materials A1 to 7 of Examples 1 to 7 all showed good load characteristics and cycle characteristics.
- the load characteristics of the lithium ion battery using the electrode material B1 containing almost no nickel of Comparative Example 1 were inferior to those of Examples 1-7.
- the cycle characteristics were inferior to those in Examples 1-7.
- Examples 1 to 7 and Comparative Examples 1 to 3 acetylene black was used as a conductive additive, but the present invention is not limited to this. Carbon black, graphite, ketjen black, natural graphite, artificial graphite, etc. The carbon material may be used.
- a counter electrode made of lithium metal was used for load characteristic evaluation, and a counter electrode made of artificial graphite was used for cycle characteristic evaluation.
- the present invention is not limited to this. Instead, other carbon materials such as natural graphite and coke, and negative electrode materials such as Li 4 Ti 5 O 12 and Li alloys may be used as the counter electrode.
- Examples 1 to 7 and Comparative Examples 1 to 3 ethylene carbonate containing 1 mol / L LiPF 6 solution and diethyl carbonate were mixed at a volume ratio of 1: 1 as a non-aqueous electrolyte solution that is a non-aqueous electrolyte.
- the electrolytic solution and the separator are used.
- the present invention is not limited to this, and a solid electrolyte may be used instead of the electrolytic solution and the separator.
- the electrode material of the present invention comprises an electrode active material represented by Li x Fe y A z BO 4 as a main component, contains nickel, the particle surface of the electrode active material is covered with a carbonaceous film, and nickel In the lithium ion battery provided with an electrode formed using this electrode material, nickel is contained in the electrolyte during charging / discharging.
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Abstract
Description
本願は、2013年4月24日に、日本に出願された特願2013-091117号に基づき優先権を主張し、その内容をここに援用する。
リチウムイオン電池は、従来の鉛電池、ニッケルカドミウム電池、ニッケル水素電池等の二次電池と比べて、軽量かつ小型であるとともに、高エネルギーを有している。そのため、リチウムイオン電池は、携帯用電話機、ノート型パーソナルコンピュータ、携帯用情報端末等の携帯用電子機器の電源として用いられている。また、リチウムイオン電池は、近年、電気自動車、ハイブリッド自動車、電動工具等の高出力電源としても検討されている。これらの高出力電源として用いられる電池の電極活物質には、高速の充放電特性が求められている。
また、発電負荷の平滑化と共に、定置用電源、バックアップ電源等の大型電池への応用も検討されており、長期の安全性、信頼性と共に資源量の問題がないことも重要視されている。
そこで、近年、長期の安全性、信頼性に優れた電極材料として、リン酸鉄リチウムに代表されるオリビン構造を有するリン酸塩系電極材料が注目を浴びている。
また、電極材料中に含まれる、クロム、ニッケルといった元素は、充放電時に電解液中に溶解し、負極上に再析出、成長することが知られている。このような元素の再析出や成長は、負極の活性を低下させるばかりではなく、遂には正極と負極の間に導電経路を形成し、短絡を引き起こし、安全性に深刻な影響を与えることが知られている。このように、電極材料に過剰な異種元素を導入することは、必ずしも電極材料の電子伝導性を高めるための有効な方法とは言い難い。そのため、より純度の高い電極材料を得るための検討も多くなされている。
[1]LixFeyAzBO4(但し、AはMnおよびCoからなる群から選択される1種または2種以上、BはP、SiおよびSからなる群から選択される1種または2種以上、0≦x<4、0<y<1.5、0≦z<1.5)で表される電極活物質を主成分とし、ニッケルを含有してなる電極材料であって、前記電極活物質の粒子表面が炭素質膜で被覆されており、かつ、前記ニッケルの含有量が1ppm以上かつ100ppm以下であることを特徴とする電極材料である。
本実施形態の電極材料は、LixFeyAzBO4(但し、AはMnおよびCoからなる群から選択される1種または2種以上、BはP、SiおよびSからなる群から選択される1種または2種以上、0≦x<4、0<y<1.5、0≦z<1.5)で表される電極活物質を主成分とし、ニッケルを含有してなる電極材料であって、電極活物質の粒子表面が炭素質膜で被覆されており、かつ、ニッケルの含有量が1ppm以上かつ100ppm以下である。
本実施形態の電極材料は、マンガンの含有量が5000ppm以下が好ましく、1ppm以上かつ5000ppm以下がより好ましい。
また、本実施形態の電極材料は、コバルトの含有量が80ppm以下が好ましく、1ppm以上かつ80ppm以下がより好ましい。
ここで、ニッケルの含有量が上記の範囲内であるのが好ましい理由は、ニッケルの含有量が上記の範囲外であると、次のような現象が生じるからである。鉄を含有する電極活物質(LixFeyAzBO4)を主成分とする電極材料におけるニッケルの含有量が1ppm未満では、電極材料の電子伝導性を高められない。一方、ニッケルの含有量が100ppmを超えると、結晶構造中に欠陥を生じ、充放電時に電解液中にニッケルが溶解し、負極上に再析出、成長する。そのため、負極の活性を低下させるばかりではなく、正極と負極の間に導電経路を形成し、短絡を引き起こす。
本実施形態の電極材料では、電池における性能評価を行うことなく、電極材料中のニッケル含有量を1ppm以上かつ100ppmに管理することにより、電子伝導性と安定性(溶解耐性)に悪影響を与えることのない工業グレードや再生原料の鉄原料を用いることができる。また、電極材料の製造コストを低減することもできる。
また、ニッケルは通常のステンレス鋼に含まれるから、反応を伴う加熱工程を含む電極材料の合成においては、加熱時およびそれ以前の工程において、容器等の原料に接触する部材の材質にステンレス鋼を用いることにより、電極材料にニッケルを添加できる。よって、製造設備の低価格化、ひいては、製品の低コスト化に繋がるばかりでなく、それによる性能の向上も期待できる。
この場合、例えば、有機物とリン酸塩系電極活物質の混合設備にステンレス鋼を用い、混合条件を調整することにより、新たなニッケル源の追加を省略することも可能である。
本実施形態の電極材料は、電極活物質と、ニッケル源と、炭素源となる有機物とを混合した後、非酸化性雰囲気下にて熱処理することにより、得られる。
なお、本実施形態の電極活物質は、固相反応法、水熱合成法等により作製することができるが、水熱合成法を用いて高圧下で合成すれば、固相反応法と比べて低温で目的の物質を得ることができ、単分散性に優れた微粒子を得ることができるので、好ましい。
まず、電極活物質と、ニッケル源と、炭素源となる有機物とを、溶媒に溶解あるいは分散させて、均一なスラリーとする。この溶解あるいは分散の際には、分散剤を加えてもよい。
本実施形態の電極材料を製造するには、電極活物質等の原料に、最終的に得られる電極材料の全体に対するニッケルの含有量が1ppm以上かつ100ppm以下となるように、ニッケル源を加えるか、原料の一部にニッケルを不純物として含む原料を用いる。あるいは、電極材料の合成において、加熱時およびそれ以前の工程において用いられる設備にステンレス鋼等のニッケルを含む材料を適用する。
最終的に得られる電極材料の全体に対するニッケルの含有量が1ppm以上かつ100ppm以下となるように管理することにより、上記の各原料は純度の高い試薬グレードを使用し、微量のニッケル原料を添加してもよく、また、工業グレードや再生原料を使用することができる。
ここで、電極活物質の1次粒子の形状として球状、特に真球状が好ましいさらなる理由は、電極活物質と、バインダー樹脂(結着剤)と、溶媒とを混合して電極(正極)作製用ペーストを調製する際に、溶媒の量を低減できるとともに、この電極(正極)作製用ペーストの集電体への塗工も容易となるからである。
ここで、炭素源となる有機物の平均分子量が20万を超えると、この有機物の水に対する溶解度が小さくなる。また、この有機物を水に溶解させたとしても、得られた溶液の粘度が高くなり、この高粘度が作業性の低下を招く虞があるので好ましくない。
このような有機物としては、グルコース、スクロース、ポリビニルアルコール、ポリアクリル酸、ヒドロキシ酸等が挙げられる。これらの有機物は、1種のみを単独で用いてもよく、2種以上を混合して用いてもよい。
ここで、噴霧の際の条件、例えば、スラリー中の電極活物質またはその前駆体の濃度、有機化合物の濃度、噴霧圧力、速度、更に、噴霧後に乾燥させる際の条件、例えば、雰囲気温度、滞留時間等を適宜調整する。これにより、平均粒径が0.5μm以上かつ100μm以下、好ましくは0.5μm以上かつ20μm以下の乾燥物が得られる。
不活性雰囲気としては、窒素(N2)、アルゴン(Ar)等の不活性ガスからなる雰囲気が好ましく、より酸化を抑えたい場合には水素(H2)等の還元性ガスを含む還元性雰囲気が好ましい。
また、熱処理時間は、炭素源となる有機物が充分に炭化される時間であればよく、特に制限はないが、例えば、0.5時間以上かつ48時間以下の時間が挙げられる。
以上により、本実施形態の電極材料を得ることができる。
本実施形態の電極は、本実施形態の電極材料を用いて形成された電極である。
本実施形態の電極を作製するには、上記の電極材料と、バインダー樹脂からなる結着剤と、溶媒とを混合して、電極形成用塗料または電極形成用ペーストを調製する。この際、必要に応じてカーボンブラック等の導電助剤を添加してもよい。
上記の電極材料とバインダー樹脂との配合比は、特に限定されないが、例えば、電極材料100質量部に対してバインダー樹脂を1質量部以上かつ30質量部以下、好ましくは3質量部以上かつ20質量部以下とする。
次いで、この塗膜を加圧圧着し、乾燥して、金属箔の一方の面に電極材料層を有する電極を作製する。
このようにして、本実施形態の電極を作製することができる。
本実施形態のリチウムイオン電池は、本実施形態の電極からなる正極と、金属Li、Li合金、Li4Ti5O12、炭素材料等からなる負極と、電解液とセパレータあるいは固体電解質を備えている。
(電極活物質)
(1)LiFePO4は、水熱合成法にて作製した。
まず、Li源として水酸化リチウム(LiOH)、P源としてリン酸(H3PO4)、Fe源として硫酸鉄7水和物(FeSO4・7H2O)を用い、これらをモル比でLi:Fe:P=2:1:1となるように純水中に投入して混合し、200mlの前駆体スラリーを作製した。
このケーキ状物質から測定用試料を若干量採取し、70℃にて2時間真空乾燥させ、得られた粉体をX線回折で同定したところ、単相のLiFePO4が生成していることが確認された。
Li源として水酸化リチウム(LiOH)、P源としてリン酸(H3PO4)、Fe源として硫酸鉄7水和物(FeSO4・7H2O)、Mn源として硫酸マンガン5水和物(MnSO4・5H2O)を用い、これらをモル比でLi:Fe:Mn:P=2:1:1:1となるように純水中に投入して混合した以外は、LiFePO4の場合と同様にして、ケーキ状物質を得た。
Li源として水酸化リチウム(LiOH)、P源としてリン酸(H3PO4)、Fe源として硫酸鉄7水和物(FeSO4・7H2O)、Co源として硫酸コバルト7水和物(CoSO4・7H2O)を用い、これらをモル比でLi:Fe:Co:P=2:1:1:1となるように純水中に投入して混合した以外は、LiFePO4の場合と同様にして、ケーキ状物質を得た。
有機物の炭化負触媒であるMnを含むLi[MnFe]PO4活物質およびCoを含むLi[CoFe]PO4活物質に炭素被覆するための炭化触媒溶液を調製した。
ここでは、炭酸リチウム、硝酸鉄(III)、リン酸をそれぞれ水に1molずつ加え、全体量が1kgとなるように調製し、次いで、撹拌・溶解し、炭化触媒溶液を得た。
この炭化触媒溶液中のLiFePO4に換算した濃度は15.78質量%、モル濃度で1mol/kgであった。
上記のLiFePO4の合成工程において、原料に硫酸鉄7水和物(FeSO4・7H2O)を用い、硫酸ニッケル(NiSO4)を微量(電極活物質中ニッケル含有量10ppm相当)添加して、LiFePO4からなる正極活物質を得た。
上記のLiFePO420gと、炭化触媒溶液をLiFePO4換算で1gとを混合し、次いで、この混合液にポリビニルアルコール4.0gを添加し、さらに水を添加して全体量を100gとし、この混合物を、直径5mmのジルコニアボール150gとともにボールミルにて粉砕混合し、スラリーを得た。
得られたスラリーを、スプレードライヤーを用いて乾燥、造粒し、その後、窒素(N2)雰囲気下にて、700℃にて5時間、熱処理を行い、実施例1の炭素被覆で被覆された電極材料A1を得た。
硫酸ニッケル(NiSO4)を、電極活物質中のニッケル含有量80ppmに相当するように添加した以外は実施例1と同様にして、LiFePO4からなる正極活物質を得た。
得られた正極活物質を用い、実施例1と同様にして、実施例2の炭素被覆で被覆された電極材料A2を得た。
硫酸ニッケル(NiSO4)を、電極活物質中のニッケル含有量50ppmに相当するように添加した以外は実施例1と同様にして、LiFePO4からなる正極活物質を得た。
得られた正極活物質を用い、実施例1と同様にして、実施例3の炭素被覆で被覆された電極材料A3を得た。
硫酸ニッケル(NiSO4)を、電極活物質中のニッケル含有量1ppmに相当するように添加した以外は実施例1と同様にして、LiFePO4からなる正極活物質を得た。
得られた正極活物質を用い、実施例1と同様にして、実施例4の炭素被覆で被覆された電極材料A4を得た。
硫酸鉄7水和物(FeSO4・7H2O)の一部を、電極活物質中のマンガン含有量4500ppmに相当するように、硫酸マンガン5水和物(MnSO4・5H2O)に置き換えた以外は実施例1と同様にして、Li[MnFe]PO4からなる正極活物質を得た。
得られた正極活物質を用い、実施例1と同様にして、実施例5の炭素被覆で被覆された電極材料A5を得た。
硫酸鉄7水和物(FeSO4・7H2O)の一部を、電極活物質中のコバルト含有量80ppmに相当するように、硫酸コバルト7水和物(CoSO4・7H2O)に置き換えた以外は実施例1と同様にして、Li[CoFe]PO4からなる正極活物質を得た。
得られた正極活物質を用い、実施例1と同様にして、実施例6の炭素被覆で被覆された電極材料A6を得た。
LiFePO4の合成工程において、原料に硫酸鉄7水和物(FeSO4・7H2O)を用い、硫酸ニッケル(NiSO4)を微量(電極活物質中のニッケル含有量10ppmに相当)添加して、LiFePO4からなる正極活物質を得た。
上記のLiFePO420gと、ポリビニルアルコール4.0gを添加し、さらに水を添加して全体量を100gとし、この混合物を、直径5mmのジルコニアボール150gとともにボールミルにて粉砕混合し、スラリーを得た。
得られたスラリーを、スプレードライヤーを用いて乾燥、造粒し、その後、窒素(N2)雰囲気下にて、700℃にて5時間、熱処理を行い、実施例7の炭素被覆で被覆された電極材料A7を得た。
硫酸鉄7水和物(FeSO4・7H2O)を純水に溶解した後、再結晶させて、不純物を取り除いた。
この不純物を取り除いた硫酸鉄7水和物(FeSO4・7H2O)を用い、硫酸ニッケル(NiSO4)を添加しなかった以外は実施例1と同様にして、LiFePO4からなる正極活物質を得た。
得られた正極活物質を用い、実施例1と同様にして、比較例1の炭素被覆で被覆された電極材料B1を得た。
硫酸ニッケル(NiSO4)を電極活物質中ニッケル含有量120ppm相当添加した以外は実施例1と同様にして、LiFePO4からなる正極活物質を得た。
得られた正極活物質を用い、実施例1と同様にして、比較例2の炭素被覆で被覆された電極材料B2を得た。
実施例1と同様にして、LiFePO4からなる正極活物質を得た。
得られた正極活物質を窒素(N2)雰囲気下にて、700℃にて5時間、熱処理を行い、比較例3の炭素被覆で被覆されてない電極材料B3を得た。
実施例1~7および比較例1~3にて得られた各々の電極材料を用いて、実施例1~7および比較例1~3各々のリチウムイオン電池を作製した。
まず、上記の電極材料と、導電助剤としてアセチレンブラック(AB)と、結着材(バインダー)としてポリフッ化ビニリデン(PVdF)とを、質量比が電極材料:AB:PVdF=90:5:5となるように混合し、さらに溶媒としてN-メチル-2-ピロリジノン(NMP)を加えて流動性を付与し、正極材料ペーストとした。
次いで、得られた各電極板を、直径16mmの円板状に打ち抜き、実施例1~7および比較例1~3各々の試験電極(正極)を作製した。
また、サイクル特性評価用として、人造黒鉛からなる対極(負極)を用いた。この人造黒鉛からなる対極を以下のように作製した。
人造黒鉛と、導電助剤としてアセチレンブラック(AB)と、結着材(バインダー)としてポリフッ化ビニリデン(PVdF)とを、質量比が電極材料:AB:PVdF=93:2:5となるように混合し、さらに溶媒としてN-メチル-2-ピロリジノン(NMP)を加えて流動性を付与し、対極材料ペーストとした。
次いで、この対極材料ペーストを厚み30μmのアルミニウム(Al)箔上に塗布し、乾燥した。その後、所定の密度となるように圧着し、電極板とした。
次いで、得られた各電極板を、直径16mmの円板状に打ち抜き、実施例1~7および比較例1~3各々のサイクル特性評価用の対極(負極)を作製した。
また、非水電解質である非水電解質溶液として、1mol/LのLiPF6溶液を用いた。なお、このLiPF6溶液に用いられる溶媒としては、炭酸エチレンと炭酸ジエチルを体積比で1:1に混合したものを用いた。
そして、以上の様にして作製された試験電極(正極)、対極(負極)および非水電解質溶液と、2016型のコインセルを用いて、実施例1~7および比較例1~3各々のリチウムイオン電池を作製した。
実施例1~7および比較例1~3にて得られた各々の電極材料を、大気中、750℃にて5時間、熱処理を行った後、熱処理後の電極材料を塩酸で全量溶解した溶液を、ICP原子発光分光分析により定量し、電極材料のニッケル、マンガン、コバルト含有量を定量した。
また、サイクル試験後のリチウムイオン電池を解体し、対極(負極)を構成する人造黒鉛を、大気中、750℃にて5時間、熱処理を行った後、熱処理後の残渣を塩酸で全量溶解した溶液を、ICP原子発光分光分析により定量し、人造黒鉛のニッケル含有量および鉄含有量を定量した。
これらの測定結果を表1に示す。表1中、「tr.」は、検出下限未満の極微量であることを示す。
実施例1~7および比較例1~3各々のリチウムイオン電池について、充放電試験を実施した。それぞれのリチウムイオン電池について、0.1Cの電流で定電流充電を行い、各電流で放電容量を測定した。
電圧範囲は、正極活物質がLiFePO4の場合2-4.2V、正極活物質がLi[MnFe]PO4の場合2-4.5V、正極活物質がLi[CoFe]PO4の場合2-4.8Vとした。
サイクル試験は、1Cの電流で2-4.2Vで行った。1000サイクル後の放電容量を、5サイクル目の放電容量で除して、容量維持率を求めた。
これらの測定結果を表1に示す。
一方、比較例1のニッケルをほとんど含まない電極材料B1を用いたリチウムイオン電池では、実施例1~7よりも負荷特性が劣っていた。また、比較例2のニッケルの含有量が100ppmを超える電極材料B2を用いたリチウムイオン電池では、実施例1~7よりもサイクル特性が劣っていた。
また、実施例1~7および比較例1~3では、負荷特性評価用として、金属リチウムからなる対極を用い、サイクル特性評価用として、人造黒鉛からなる対極を用いたが、これに限定されるものではなく、対極として、天然黒鉛、コークスのような他の炭素材料、Li4Ti5O12やLi合金等の負極材料を用いてもよい。
また、実施例1~7および比較例1~3では、電解液とセパレータを用いたが、これに限定されるものではなく、電解液とセパレータの代わりに固体電解質を用いてもよい。
Claims (5)
- LixFeyAzBO4(但し、AはMnおよびCoからなる群から選択される1種または2種以上、BはP、SiおよびSからなる群から選択される1種または2種以上、0≦x<4、0<y<1.5、0≦z<1.5)で表される電極活物質を主成分とし、ニッケルを含有してなる電極材料であって、前記電極活物質の粒子表面が炭素質膜で被覆されており、かつ、前記ニッケルの含有量が1ppm以上かつ100ppm以下であることを特徴とする電極材料。
- 前記マンガンの含有量が5000ppm以下であることを特徴とする請求項1に記載の電極材料。
- 前記コバルトの含有量が80ppm以下であることを特徴とする請求項1に記載の電極材料。
- 請求項1~3のいずれか1項に記載の電極材料を用いて形成されていることを特徴とする電極。
- 請求項4に記載の電極からなる正極を備えてなることを特徴とするリチウムイオン電池。
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