WO2016175186A1 - ジフルオロリン酸塩の精製方法 - Google Patents
ジフルオロリン酸塩の精製方法 Download PDFInfo
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- WO2016175186A1 WO2016175186A1 PCT/JP2016/062982 JP2016062982W WO2016175186A1 WO 2016175186 A1 WO2016175186 A1 WO 2016175186A1 JP 2016062982 W JP2016062982 W JP 2016062982W WO 2016175186 A1 WO2016175186 A1 WO 2016175186A1
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- difluorophosphate
- lithium
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- carbonate
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B25/00—Phosphorus; Compounds thereof
- C01B25/16—Oxyacids of phosphorus; Salts thereof
- C01B25/26—Phosphates
- C01B25/455—Phosphates containing halogen
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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
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0566—Liquid materials
- H01M10/0567—Liquid materials characterised by the additives
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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
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0566—Liquid materials
- H01M10/0568—Liquid materials characterised by the solutes
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/40—Electric properties
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/80—Compositional purity
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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
- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/0025—Organic electrolyte
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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
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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
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/60—Other road transportation technologies with climate change mitigation effect
- Y02T10/70—Energy storage systems for electromobility, e.g. batteries
Definitions
- the present invention is a technique capable of easily and easily purifying difluorophosphate expected to be used in an electrolyte solution solvent and additive of a lithium ion secondary battery, a functional material intermediate, a pharmaceutical intermediate, and the like. About.
- lithium-ion secondary batteries have a wide range of applications, from the power sources of relatively small electronic devices such as mobile phones, digital cameras, and personal computers to large-sized devices such as electric vehicles and power tools.
- the diversified performance requirements for these lithium ion secondary batteries are increasing day by day, and studies on adaptation to various fields are being actively conducted.
- in-vehicle use is a field in which achievement of performance on the assumption of use in a harsh environment is required.
- the non-aqueous electrolyte for a lithium ion secondary battery can suppress degradation and degradation of the electrolyte depending on the combination and blending ratio of the above members. This effect is a factor that greatly improves the performance and reliability of the lithium ion secondary battery.
- Patent Document 1 when a non-aqueous electrolyte solution to which at least one selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate is used as an additive, this additive is used as an electrode. It reacts with the lithium used to form a good-quality film at the interface between the positive electrode and the negative electrode, and this film suppresses the contact between the charged active material and the organic solvent, and the active material and the electrolyte solution. That the decomposition of the non-aqueous electrolyte caused by contact with the battery is suppressed, and the storage characteristics of the battery are improved.
- this additive reacts with the lithium used to form a good-quality film at the interface between the positive electrode and the negative electrode, and this film suppresses the contact between the charged active material and the organic solvent, and the active material and the electrolyte solution. That the decomposition of the non-aqueous electrolyte caused by contact with the battery is suppressed, and the storage characteristics of the battery are improved.
- Patent Document 2 discloses a method of reacting borate with lithium hexafluorophosphate
- Patent Document 3 discloses a method of adding a halide to lithium hexafluorophosphate and reacting with water in a non-aqueous solvent
- Patent Document 4 discloses a process for producing difluorophosphate by reacting phosphorus oxoacid, hexafluorophosphate and alkali salt in the presence of hydrogen fluoride.
- Patent Document 6 describes a method of bringing difluorophosphate into contact with hydrogen fluoride.
- hexafluorophosphate may be by-produced and decomposed in the system, and this decomposition leads to coloring of crystals of difluorophosphate.
- the effect of reducing the free acid content (acidic impurities) and the effect of reducing the insoluble residue are small, it is difficult to obtain a high-purity difluorophosphate, which is not an efficient method.
- methods for efficiently producing and purifying other difluorophosphates such as sodium difluorophosphate, potassium difluorophosphate, and ammonium difluorophosphate on an industrial scale are also required.
- An object of the present invention is to solve the above-described problems, and is to provide a method for purifying difluorophosphate that is highly purified without requiring complicated operations.
- the inventors of the present invention diligently studied to solve the above problems.
- at least one treatment agent selected from the group consisting of carbonates, hydroxides, halides or amines of alkali metals or alkaline earth metals is added to the difluorophosphate containing impurities.
- impurities can be separated, and the present invention has been completed. That is, the present invention provides the following.
- Impurities can be obtained by adding at least one treatment agent selected from the group consisting of carbonates, hydroxides, halides or amines of alkali metals or alkaline earth metals to difluorophosphate containing impurities.
- a process for purifying difluorophosphate characterized in that
- the non-aqueous solvent contains at least hexafluorophosphate as an electrolyte salt, and further contains difluorophosphate, and at least a part of the difluorophosphate is
- a nonaqueous electrolytic solution for a secondary battery which is a difluorophosphate purified by the purification method according to any one of [1] to [5] so that the impurity content is 1 wt% or less.
- the free acid content (acidic impurities) described above depends on the production method, but hydrogen salts (acidic) such as monofluorophosphoric acid, hydrogen monofluorophosphate, dihydrogen phosphate, monohydrogen phosphate, etc. Salt), acidic oxides such as CO 2 , P 2 O 5 , P 2 O 3 , and SiO 2 , and acidic gases such as HF, HCl, and HBr.
- hydrogen salts such as monofluorophosphoric acid, hydrogen monofluorophosphate, dihydrogen phosphate, monohydrogen phosphate, etc. Salt
- acidic oxides such as CO 2 , P 2 O 5 , P 2 O 3 , and SiO 2
- acidic gases such as HF, HCl, and HBr.
- the insoluble residue mentioned above depends on the production method, it is mainly a salt such as halide salt, phosphate salt, carbonate salt, hydroxide salt, sulfide salt, SiO 2 , P 2 O. Crystalline oxides such as 5 and polymer compounds such as polyphosphoric acid are conceivable.
- the method for purifying a difluorophosphate of the present invention includes a step of mixing and reacting a difluorophosphate containing an impurity and a treating agent to separate the impurity.
- the difluorophosphate used in the present invention can be produced by a known method.
- a treating agent used for purification of difluorophosphate 1) Salts 2) At least one selected from amines can be used.
- the treating agent can be used without particular limitation as long as it is of a commercially available grade.
- salts include carbonates, hydroxides or halides of alkali metals or alkaline earth metals.
- alkali metal examples include lithium, sodium, potassium, rubidium, and cesium. Lithium, sodium, or potassium is preferable from the viewpoint of availability and cost advantages.
- alkaline earth metal examples include beryllium, magnesium, calcium, strontium, and barium.
- Magnesium or calcium is preferable if it is selected from the viewpoint of availability, cost advantage, and safety.
- amines examples include poly (4-vinylpyridine), triethylamine, or N, N, N ′, N ′,-tetramethylethylenediamine.
- halide examples include fluoride, chloride, bromide, and iodide. If it selects from the ease of removal of a by-product, a fluoride or a chloride is preferable.
- the treating agent is preferably an alkali metal carbonate, hydroxide, or halide, and more preferably lithium metal carbonate, hydroxide, or halide.
- alkali metal carbonate, hydroxide, or halide preferably an alkali metal carbonate, hydroxide, or halide.
- mixing (contact) with the difluorophosphate and the treatment agent may be performed under solvent-free conditions or in the presence of a suitable solvent.
- the difluorophosphate and the treating agent may be in an undissolved state, in a dissolved state, or in a state in which only one is dissolved. From the viewpoint of uniformity and processing operation, it is preferable to use a solvent that dissolves only difluorophosphate.
- the solvent is not particularly limited as long as it does not participate in the reaction.
- organic solvents such as carbonate esters, esters, phosphate esters, ethers, nitriles, amide compounds, alcohols, or alkanes. Is mentioned. More specifically, the following are mentioned.
- Examples of the carbonic acid esters include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, and preferably dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, or propylene carbonate. It is done.
- Examples of the esters include alkyl esters of acetic acid such as methyl acetate, ethyl acetate, and butyl acetate.
- the number of carbon atoms in the alkyl group is preferably 1 or more and 8 or less, more preferably 1 or more and 6 or less, and still more preferably 1 or more and 4 or less.
- ethyl acetate and butyl acetate are particularly preferred.
- phosphoric acid esters include trialkyl esters of phosphoric acid such as trimethyl phosphate and triethyl phosphate, and trialkyl esters of phosphorous acid such as trimethyl phosphite or diethylmethyl phosphite.
- the number of carbon atoms in the alkyl group of phosphoric acid and phosphorous acid is preferably 1 or more and 5 or less, more preferably 1 or more and 3 or less.
- the structure of the alkyl group of phosphoric acid and phosphorous acid may be a combination of the same alkyl group, or a combination of different alkyl groups.
- Examples of the combination of the same alkyl group include a combination that is all methyl groups, a combination that is all ethyl groups, and a combination that is all propyl groups.
- the combination of different alkyl groups includes a combination of one methyl group and two ethyl groups, a combination of one ethyl group and two methyl groups, a combination of one methyl group and two propyl groups, one propyl group, A combination of two methyl groups, a combination of one ethyl group and two propyl groups, a combination of one propyl group and two ethyl groups, and the like.
- Examples of ethers include diethyl ether, dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, and the like, preferably dimethoxyethane.
- Examples of the nitrile compound include acetonitrile.
- Examples of the amide compound include dimethylformamide.
- Examples of alcohols include alkyl alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, and butyl alcohol. The number of carbon atoms in the alkyl group is preferably 1 or more and 8 or less, more preferably 1 or more and 6 or less, and still more preferably 1 or more and 4 or less.
- alkanes include chain saturated hydrocarbons such as n-hexane and n-heptane.
- the number of carbon atoms in the saturated hydrocarbon is preferably 5 or more and 12 or less, more preferably 5 or more and 10 or less, and even more preferably 6 or more and 8 or less.
- organic solvents from the viewpoint of use as an electrolyte additive for batteries, particularly as an additive for electrolyte solutions for secondary batteries, and the possibility of remaining in the solvent, carbonates, esters, Or ethers are preferred.
- the organic solvent may be used alone or in combination of two or more. When using 2 or more types, it is preferable to mix the good solvent and poor solvent of difluorophosphate in arbitrary ratios, or make it the same composition as the electrolyte solution used with a battery.
- the method of adding the treatment agent is not particularly limited, and it may be added all at once, sequentially, or dividedly, or mixed and added with any organic solvent. May be. Among them, batch addition or mixed addition is preferable from the viewpoint of simplification and ease of operation.
- the charged amounts of the difluorophosphate containing impurities and the treatment agent depend on the content of free acid (acidic impurities) in the impurities, but can be arbitrarily set.
- the treating agent is not particularly limited since an excess amount remaining after the reaction can be easily removed by an operation such as filtration or decantation, but an addition amount of 1 to 300 wt% with respect to the difluorophosphate is preferable. From the viewpoint of ease of purification operation, it is preferably 1 to 100 wt%, particularly preferably 1 to 50 wt%.
- the reaction temperature between the difluorophosphate and the treating agent can be arbitrarily set and is not particularly limited, but is preferably ⁇ 50 to 150 ° C. Furthermore, 0 to 100 ° C. is preferable, and 20 to 80 ° C. is particularly preferable.
- the control temperature at the bottom of the reflux tower is preferably ⁇ 50 to 20 ° C., more preferably ⁇ 40 to 10 ° C., and particularly preferably ⁇ 30 to 5 ° C.
- the contact between the difluorophosphate and the treatment agent may be performed under atmospheric pressure, under reduced pressure, or under pressure, and among them from the viewpoint of ease of operation. It is preferable to carry out under atmospheric pressure conditions.
- the reaction time of the difluorophosphate and the treating agent can be arbitrarily set, and is not particularly limited, but is preferably 5 minutes to 100 hours. Furthermore, it is preferably 30 minutes to 50 hours, particularly preferably 1 to 24 hours.
- a salt or complex is formed by mixing the impurity, particularly a free acid content (acidic impurity) in the impurity and the treatment agent, and then the salt or complex is subjected to a further purification step.
- the purification method is not particularly limited. For example, a method of removing precipitated salts or complexes such as filtration or decantation, a method of separation by interaction such as chromatography, or an excess of carbonates or hydroxides are removed. A method of neutralizing by reaction with an acid such as hydrogen fluoride can be used.
- the difluorophosphate obtained by the purification method of the present invention can be used as a non-aqueous electrolyte additive for lithium ion secondary batteries, a functional material intermediate, a pharmaceutical intermediate, and the like.
- a non-aqueous electrolyte additive for a lithium ion secondary battery which is one embodiment of a difluorophosphate obtained by the purification method of the present invention, and a lithium ion secondary battery using the same will be described.
- the non-aqueous electrolyte for secondary battery of the present invention contains at least hexafluorophosphate and difluorophosphate in a non-aqueous solvent, and at least a part of the difluorophosphate is purified by the purification method of the present invention. It is a difluorophosphate (hereinafter also referred to as a difluorophosphate of the present invention). Hexafluorophosphate is used as an electrolyte salt.
- the proportion of the difluorophosphate of the present invention is preferably 5 to 100 wt%, more preferably 50 to 100 wt%.
- the difluorophosphate of the present invention is refined so that the impurity content is 1 wt% or less, preferably 0.8 wt% or less, more preferably 0.5 wt% or less.
- the free acid content (acidic impurities) is preferably 0.5 wt% or less, more preferably 0.2 wt% or less, and most preferably 0.1 wt% or less.
- the insoluble residue is preferably 1 wt% or less, more preferably 0.5 wt% or less, and most preferably 0.3 wt% or less.
- the content of difluorophosphate is preferably 0.01 to 20.0 wt%, more preferably 0.05 to 15.0 wt%, and 0.10 in the nonaqueous electrolytic solution. ⁇ 10.0 wt% is most preferred.
- the non-aqueous solvent used in the non-aqueous electrolyte of the present invention is not particularly limited as long as it is a solvent capable of dissolving difluorophosphate.
- a solvent capable of dissolving difluorophosphate for example, carbonates, esters, ethers, lactones, nitriles , Amides, sulfones and the like can be used, but ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferred.
- it may be two or more types of mixed solvents instead of single.
- the electrolyte salt dissolved in the non-aqueous solvent may contain at least hexafluorophosphate and LiPF 6 in the case of a lithium ion secondary battery.
- LiPO 2 F 2 , LiBF 4 , LiClO 4 , LiN (CF 3 SO 2 ) 2 , LiN (FSO 2 ) 2 , LiCF 3 SO 3 , LiC (CF 3 SO 2 ) 3 , LiC (FSO) 2 ) 3 , LiCF 3 CO 2 , LiB (CF 3 SO 3 ) 4 , LiB (FSO 3 ) 4 , LiB (C 2 O 4 ) 2 , LiBF 2 (C 2 O 4 ), or the like can be used.
- the content of the electrolyte salt in the non-aqueous solvent is preferably in the range of 20.0 to 80.0 wt%, more preferably in the range of 40.0 to 60.0 wt%.
- the nonaqueous electrolytic solution of the present invention can be used as a nonaqueous electrolytic solution for either a primary battery or a secondary battery, but is preferably used as a nonaqueous electrolytic solution constituting a lithium ion secondary battery.
- a lithium ion secondary battery using the non-aqueous electrolyte of the present invention (hereinafter also referred to as the non-aqueous electrolyte secondary battery of the present invention) will be described.
- a positive electrode active material, a binder, a conductive material or the like that is slurried with a solvent is applied to a current collector, dried and pressed.
- the positive electrode active material is not particularly limited as long as it is a material that can occlude and release lithium ions and has a noble potential, and a commonly used known positive electrode active material can be used. Examples thereof include metal compounds such as metal oxides, metal hydroxides, metal sulfides, metal halides, and metal phosphate compounds. Further, a lithium transition metal composite oxide having a layered structure such as a metal intercalation compound, a spinel structure, or an olivine structure can be used. The transition metal element preferably contains at least one metal selected from nickel, cobalt, manganese, titanium, iron, and the like. Furthermore, a transition metal composite oxide obtained by adding or replacing lithium, magnesium, aluminum, or titanium to these transition metal elements may be used.
- the positive electrode active material in order to obtain a high energy density non-aqueous electrolyte secondary battery, it is preferable to use a lithium transition metal composite oxide having a layered structure, specifically, a lithium-cobalt composite oxide, Preferred examples include lithium / cobalt / nickel / manganese composite oxide and lithium / cobalt / nickel / aluminum composite oxide.
- the content of the positive electrode active material with respect to the total amount of the positive electrode active material, the conductive material, and the binder is preferably 10.0 to 99.9 wt%, more preferably 50.0 to 98.0 wt%.
- Examples of the conductive material include acetylene black, ketjen black, furnace black, needle coke, and graphite. Among them, acetylene black and graphite are preferable.
- the content of the conductive material with respect to the total amount of the positive electrode active material, the conductive material, and the binder is preferably 0.05 to 50.0 wt%, more preferably 1.0 to 30.0 wt%.
- binder for example, polyvinylidene fluoride (PVDF), strong ruruboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), polyvinyl alcohol (PVA), polyvinyl chloride (PVC), polypropylene (PP), polybutadiene ( BR) and the like.
- PVDF polyvinylidene fluoride
- CMC strong ruruboxymethyl cellulose
- SBR styrene butadiene rubber
- the content of the binder with respect to the total amount of the positive electrode active material, the conductive material, and the binder is preferably 0.05 to 50.0 wt%, more preferably 1.0 to 30.0 wt%.
- Examples of the solvent to be slurried include water-based solvents such as water and alcohol, and organic solvents such as N-methyl-2-pyrrolidone (NMP), dimethylformamide, methyl acetate, and N, N-dimethylaminopropylamine.
- the aqueous solvent is preferably water, and the organic solvent is preferably NMP.
- the amount of the solvent used is preferably 20.0 to 90.0 parts by mass, more preferably 30.0 to 80.0 parts by mass with respect to 100 parts by mass of the positive electrode active material.
- the positive electrode current collector can be made of aluminum, stainless steel, nickel or copper steel.
- the negative electrode of the non-aqueous electrolyte secondary battery of the present invention is a negative electrode active material, a binder, a conductive material, etc., slurryed with a solvent, applied to a current collector, dried, and pressed, as with the positive electrode Etc. are used.
- the negative electrode active material is not particularly limited as long as it is a material that can occlude and release lithium ions, and a commonly used negative electrode active material can be used.
- metallic lithium lithium alloy such as lithium-silicon alloy, lithium-tin alloy, tin-silicon alloy, lithium-titanium alloy, tin-titanium alloy, tin-based titanium compound such as titanium oxide, carbon material, conductive A functional polymer or the like can be used.
- the carbon material include carbon materials such as graphite (natural, artificial), coke (petroleum, coal), fullerene, carbon nanotube, carbon fiber, and organic fired body.
- tin-based or titanium-based compound a metal oxide having a potential lower than that of the positive electrode active material such as SnO 2 , SnO, or TiO 2 can be used.
- the negative electrode active material it is particularly preferable to use a carbon material such as crystalline graphite which has a small volume change accompanying insertion and extraction of lithium and is excellent in reversibility.
- the binder for the negative electrode, the conductive material, and the solvent to be slurried the same materials as those mentioned above for the positive electrode (content, etc.) can be used in the same manner.
- the negative electrode current collector copper, nickel, stainless steel, nickel-plated steel or the like can be used.
- a separator for preventing a short circuit between the positive electrode and the negative electrode.
- the non-aqueous electrolyte is used by impregnating the separator.
- the material and shape of the porous film are not particularly limited as long as it is stable with respect to the electrolytic solution and has excellent liquid retention, and a porous sheet or nonwoven fabric made of polyolefin such as polypropylene or polyethylene is preferable.
- porous sheet examples include polyethylene, polypropylene, polyvinylidene fluoride, polyvinylidene chloride, polyacrylonitrile, polyacrylamide, polycarbonate, polyamide, polyimide, polytetrafluoroethylene, poly (meth) acrylic acid, and copolymers thereof. And mixtures thereof.
- the shape of the nonaqueous electrolyte secondary battery of the present invention having the above configuration is not particularly limited, and can be various shapes such as a coin shape, a cylindrical shape, a square shape, and a pouch shape.
- a coin shape a coin shape
- a cylindrical shape a cylindrical shape
- a square shape a pouch shape.
- a pouch shape a shape shown in FIG.
- the purity of the product was analyzed by anion analysis by ion chromatography and quantified by the relative area ratio of difluorophosphate ions.
- the free acid content (acidic impurities) was quantified in terms of HF by neutralization titration with NaOH.
- the insoluble residue was dissolved in 1,2-dimethoxyethane, filtered through a polytetrafluoroethylene membrane filter, and the amount of insoluble residue was measured.
- the amount of insoluble residue for [Example 6] and [Example 7] was determined by making up a predetermined amount of the filtrate or supernatant with 1,2-dimethoxyethane and filtering with a polytetrafluoroethylene membrane filter. The remaining amount was measured.
- Example 1 ⁇ Synthesis of lithium difluorophosphate> Difluorophosphate was synthesized as follows with reference to the method of Example 2 described in JP-A-2015-044701. A 500 mL PFA bottle containing 100.1 g (0.66 mol) of granular lithium hexafluorophosphate is placed in a shaker while being sealed with nitrogen gas, and then 27.4 g of pure water ( 1.52 mol) and 259.7 g (2.18 mol) of thionyl chloride were introduced at a rate of 0.2 g / min and 1.7 g / min, respectively, and reacted at 25 ° C. for 22 hours. The obtained crystals were dried in a 120 ° C.
- the purified lithium difluorophosphate was analyzed by ion chromatography, the purity of the lithium difluorophosphate was 99% or more in terms of relative area.
- the free acid content (acidic impurities) was 55 ppm, and the insoluble residue was 849 ppm.
- Example 2 ⁇ Synthesis of lithium difluorophosphate> In the same manner as in Example 1, 58.9 g of white crystalline lithium difluorophosphate was obtained. When the obtained crystal was analyzed by ion chromatography, the purity of lithium difluorophosphate was 85% in relative area. The free acid content (acidic impurities) was 3.70 wt%, and the insoluble residue was 5.15 wt%.
- the purified lithium difluorophosphate was analyzed by ion chromatography, the purity of the lithium difluorophosphate was 99% or more in terms of relative area.
- the free acid content (acidic impurities) was 60 ppm, and the insoluble residue was 337 ppm.
- Example 3 ⁇ Synthesis of lithium difluorophosphate> In the same manner as in Example 1, 63 g of lithium difluorophosphate was obtained. When the obtained crystal was analyzed by ion chromatography, the purity of lithium difluorophosphate was 84% in relative area. The free acid content (acidic impurities) was 0.155 wt%, and the insoluble residue was 5.48 wt%.
- the purified lithium difluorophosphate was analyzed by ion chromatography, the purity of the lithium difluorophosphate was 99% or more in terms of relative area.
- the free acid content (acidic impurities) was 884 ppm, and the insoluble residue was 1209 ppm.
- Example 4 ⁇ Synthesis of lithium difluorophosphate> In the same manner as in Example 1, 59 g of lithium difluorophosphate was obtained. When the obtained crystal was analyzed by ion chromatography, the purity of lithium difluorophosphate was 89% in relative area. The free acid content (acidic impurities) was 0.128 wt%, and the insoluble residue was 4.73 wt%.
- the purified lithium difluorophosphate was analyzed by ion chromatography, the purity of the lithium difluorophosphate was 99% or more in terms of relative area.
- the free acid content (acidic impurities) was 675 ppm, and the insoluble residue was 823 ppm.
- Example 5 ⁇ Synthesis of lithium difluorophosphate> In the same manner as in Example 1, 62 g of lithium difluorophosphate was obtained. When the obtained crystal was analyzed by ion chromatography, the purity of lithium difluorophosphate was 91% in relative area. The free acid content (acidic impurities) was 0.238 wt%, and the insoluble residue was 5.28 wt%.
- the purified lithium difluorophosphate was analyzed by ion chromatography, the purity of the lithium difluorophosphate was 99% or more in terms of relative area.
- the free acid content (acidic impurities) was 267 ppm, and the insoluble residue was 918 ppm.
- Example 6 ⁇ Synthesis of lithium difluorophosphate> In the same manner as in Example 1, 58 g of lithium difluorophosphate was obtained. When the obtained crystal was analyzed by ion chromatography, the purity of lithium difluorophosphate was 87% in relative area. The free acid content (acidic impurities) was 4.72 wt%, and the insoluble residue was 6.89 wt%.
- Example 7 ⁇ Synthesis of lithium difluorophosphate> In the same manner as in Example 1, 61 g of lithium difluorophosphate was obtained. When the obtained crystal was analyzed by ion chromatography, the purity of lithium difluorophosphate was 82% in relative area. The free acid content (acidic impurities) was 0.182 wt%, and the insoluble residue was 4.64 wt%.
- Example 8 ⁇ Preparation of lithium difluorophosphate> When 0.04 g of lithium dihydrogen phosphate was added to 6 g of the lithium difluorophosphate after purification described in Example 2, and the free acid content (acidic impurities) was measured, it was 0.014 wt%.
- the purified lithium difluorophosphate was analyzed by ion chromatography, the purity of the lithium difluorophosphate was 99% or more in terms of relative area.
- the free acid content (acidic impurities) was 24 ppm, and the insoluble residue was 510 ppm.
- the difluorophosphate was purified as described below with reference to the method of Example 1 described in JP-A-2015-013795.
- 100 g of the lithium difluorophosphate was placed in a PFA container having an internal volume of 250 mL and held in a thermostat set at 130 ° C. for 1 hour while flowing nitrogen at 1 L / min.
- the aeration gas was switched from nitrogen alone to nitrogen gas containing 40% by volume of HF while being kept in a constant temperature bath at 130 ° C., and the flow rate was set to 10 L / min.
- Aeration of nitrogen gas containing HF was performed for 1 hour. Further, the aeration gas was switched again to nitrogen gas at a flow rate of 1 L / min.
- a non-aqueous electrolyte secondary battery of a pouch-type cell was produced using an electrolyte containing lithium difluorophosphate. This will be specifically described below.
- Example 9 ⁇ Preparation of LiCoO 2 positive electrode> 93 parts by mass of LiCoO 2 as a positive electrode active material, 4 parts by mass of acetylene black as a conductive material, and 3 parts by mass of polyvinylidene fluoride (PVDF) as a binder were mixed to obtain a positive electrode material.
- This positive electrode material was dispersed in N-methyl-2-pyrrolidone (NMP) to form a slurry. This slurry was applied to one side of a positive electrode current collector made of aluminum, dried, and press-molded to produce a LiCoO 2 positive electrode.
- NMP N-methyl-2-pyrrolidone
- This negative electrode material was dispersed in water to form a slurry. This slurry was applied to one side of a copper negative electrode current collector, dried, and press molded to produce a graphite negative electrode.
- a battery element was fabricated by laminating the positive electrode, the negative electrode, and the polyethylene separator in the order of the negative electrode, the separator, and the positive electrode.
- This battery element was inserted into a bag made of a laminate film in which both surfaces of aluminum were covered with a resin layer while projecting positive and negative terminals, and then the electrolyte was poured into the bag and vacuum sealed. A pouch-type battery was produced.
- LiPF 6 lithium hexafluorophosphate
- EMC ethyl methyl carbonate
- Example 2 A non-aqueous electrolyte secondary battery of a pouch-type cell was prepared in the same manner as in Example 8, except that a non-aqueous electrolyte was prepared using lithium difluorophosphate before purification in Example 1.
- the method for purifying difluorophosphate of the present invention it is possible to easily purify high-purity difluorophosphate using only inexpensive raw materials.
- the by-product forms a low-solubility salt or complex, which can be easily removed by filtration or decantation.
- it is the method of this invention it is possible to make a free acid content (acidic impurity) and an insoluble residue low as much as possible.
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Abstract
Description
また、リチウム塩に加えて、ジフルオロリン酸ナトリウム、ジフルオロリン酸カリウム、ジフルオロリン酸アンモニウム、といった他のジフルオロリン酸塩を効率よく工業スケールで製造し、精製する方法も同様に求められている。
不純物を含むジフルオロリン酸塩に対し、アルカリ金属又はアルカリ土類金属の炭酸塩、水酸化物、ハロゲン化物ないしはアミン類からなる群より選択される少なくとも1種類以上の処理剤を加えることで、不純物を分離することを特徴とするジフルオロリン酸塩の精製方法。
前記精製方法において、不純物を処理剤により塩若しくは錯体形成させた後、ろ過によりこの塩若しくは錯体をろ別することを特徴とする[1]に記載のジフルオロリン酸塩の精製方法。
前記処理剤がアルカリ金属の炭酸塩、水酸化物ないしはハロゲン化物である[1]~[2]に記載のジフルオロリン酸塩の精製方法。
前記処理剤がリチウムの炭酸塩、水酸化物ないしはハロゲン化物である[1]~[3]に記載のジフルオロリン酸塩の精製方法。
不純物と処理剤との反応が溶媒中で行われる[1]~[4]に記載のジフルオロリン酸塩の精製方法。
二次電池用非水電解液において、非水溶媒中に少なくともヘキサフルオロリン酸塩を電解質塩として含有し、更にはジフルオロリン酸塩を含むものにおいて、当該ジフルオロリン酸塩の少なくとも一部が、[1]~[5]に記載の精製方法によって不純物の含有量が1wt%以下となるように精製されたジフルオロリン酸塩であることを特徴とする二次電池用非水電解液。
遊離酸分(酸性不純物)としてモノフルオロリン酸一水素リチウムが含まれているジフルオロリン酸リチウムに対して処理剤として炭酸リチウムを用いた場合を例に取ると以下のような反応が進行していると考えられる。
2LiHPO3F + Li2CO3 → 2Li2PO3F + H2O + CO2
Li2PO3FはLiHPO3Fに比べ溶解度が下がりろ過やデカンテーション等により除去が可能である。また、副生するH2Oは加熱により簡便に留去でき、CO2についてはガスとして容易に取り除くことが可能である。
本発明のジフルオロリン酸塩の精製方法は、不純物を含むジフルオロリン酸塩と処理剤とを混合して反応させ、該不純物を分離する工程を有する。
1)塩類
2)アミン類
より選択される少なくとも1種を使用することができる。
処理剤は、市販されているグレードのものであれば特に制限無く使用することができる。
エステル類(すなわち炭酸エステル類以外のエステル類)としては、酢酸メチル、酢酸エチル、酢酸ブチル等の酢酸のアルキルエステルが挙げられる。アルキル基中の炭素原子数は、1以上8以下が好ましく、1以上6以下が更に好ましく、1以上4以下が一層好ましい。特に酢酸エチル及び酢酸ブチルが好ましく挙げられる。
リン酸エステルとしては、リン酸トリメチル及びリン酸トリエチル等のリン酸のトリアルキルエステルや、亜リン酸トリメチル又は亜リン酸ジエチルメチル等の亜リン酸のトリアルキルエステルが挙げられる。リン酸及び亜リン酸のアルキル基中の炭素原子数は、1以上5以下が好ましく、1以上3以下が更に好ましい。また、リン酸及び亜リン酸のアルキル基の構成は、同じアルキル基の組み合わせでもよく、異なるアルキル基の組み合わせでもよい。同じアルキル基の組み合わせとしては、例えば、全てメチル基である組み合わせ、全てエチル基である組み合わせ、全てプロピル基である組み合わせが挙げられる。また異なるアルキル基の組み合わせとしては、1つのメチル基と2つのエチル基の組み合わせ、1つのエチル基と2つのメチル基の組み合わせ、1つのメチル基と2つのプロピル基の組み合わせ、1つのプロピル基と2つのメチル基の組み合わせ、1つのエチル基と2つのプロピル基の組み合わせ、1つのプロピル基と2つのエチル基の組み合わせ等が挙げられる。 エーテル類としては、ジエチルエーテル、ジメトキシエタン、テトラヒドロフラン、又は2-メチルテトラヒドロフラン等が挙げられ、好ましくはジメトキシエタンが挙げられる。
ニトリル化合物としては、アセトニトリル等が挙げられる。
アミド化合物としては、ジメチルホルムアミド等が挙げられる。
アルコール類としては、メチルアルコール、エチルアルコール、プロピルアルコール、ブチルアルコール等のアルキルアルコールが挙げられる。アルキル基中の炭素原子数は、1以上8以下が好ましく、1以上6以下が更に好ましく、1以上4以下が一層好ましい。
アルカン類としては、n-ヘキサン、n-ヘプタン等の鎖式飽和炭化水素が挙げられる。飽和炭化水素中の炭素原子数は、5以上12以下が好ましく、5以上10以下が更に好ましく、6以上8以下が一層好ましい。
また、本発明のジフルオロリン酸塩は、不純物の含有量が、1wt%以下であり、好ましくは0.8wt%以下、より好ましくは0.5wt%以下となるように精製されている。
より具体的には、遊離酸分(酸性不純物)が、好ましくは0.5wt%以下であり、より好ましくは0.2wt%以下であり、最も好ましくは0.1wt%以下である。また、不溶解残分が、好ましくは1wt%以下であり、より好ましくは0.5wt%以下であり、最も好ましくは0.3wt%以下である。
また、金属層間化合物等の層状構造や、スピネル型構造や、オリビン型構造を有するリチウム遷移金属複合酸化物を使用することができる。
遷移金属元素としては、ニッケル、コバルト、マンガン、チタン、及び鉄等から選択される少なくとも1種の金属を含有するものが好ましい。
更に、これらの遷移金属元素に、リチウム、マグネシウム、アルミニウム、チタンを添加又は置換した遷移金属複合酸化物であってもよい。
正極活物質としては、高エネルギー密度の非水電解液二次電池を得るために、層状構造を有するリチウム遷移金属複合酸化物を用いることが好ましく、具体的には、リチウム・コバルト複合酸化物、リチウム・コバルト・ニッケル・マンガン複合酸化物、リチウム・コバルト・ニッケル・アルミニウム複合酸化物等を好ましいものとして挙げることができる。正極活物質、導電材、及び結着材の合計量に対する、正極活物質の含有量は、好ましくは10.0~99.9wt%、より好ましくは50.0~98.0wt%である。
正極活物質、導電材、及び結着材の合計量に対する、導電材の含有量は、好ましくは0.05~50.0wt%、より好ましくは1.0~30.0wt%である。
正極活物質、導電材、及び結着材の合計量に対する、結着材の含有量は、好ましくは0.05~50.0wt%、より好ましくは1.0~30.0wt%である。
例えば、金属リチウム、リチウム-シリコン合金、リチウム-スズ合金等のリチウム合金、スズ-シリコン合金、リチウム-チタン合金、スズ-チタン合金、チタン酸化物等のスズ系若しくはチタン系化合物、炭素材料、導電性ポリマー等を用いることができる。
炭素材料としては、黒鉛(天然、人造)、コークス(石油性、石炭性)、フラーレン、カーボンナノチューブ、炭素繊維、有機物焼成体等の炭素材料を挙げることができる。
スズ系若しくはチタン系化合物としては、SnO2、SnO、TiO2等の電位が正極活物質に比べて卑な金属酸化物を用いることができる。
負極活物質としては、特に、リチウムの吸蔵及び放出に伴う体積変化が少なくて可逆性に優れる結晶性黒鉛等の炭素材料を用いることが好ましい。
<ジフルオロリン酸リチウムの合成>
ジフルオロリン酸塩を特開2015-044701号公報記載の実施例2の方法を参考として、以下のように合成を行った。
500mLのPFA製ボトルに顆粒状のヘキサフルオロリン酸リチウム100.1g(0.66mol)を入れたものを、窒素ガスでシールしながら振とう機にセットし、その上で純水27.4g(1.52mol)と塩化チオニル259.7g(2.18mol)をそれぞれ0.2g/min、1.7g/minの速度で導入し、25℃で22時間反応を行った。得られた結晶を120℃の乾燥機中で窒素気流下乾燥し、粗ジフルオロリン酸リチウムを60.2g得た。得られた結晶をイオンクロマトグラフィーにて分析したところジフルオロリン酸リチウムの純度は相対面積で88%であった。また、遊離酸分(酸性不純物)は0.161wt%、不溶解残分は5.56wt%であった。
前記ジフルオロリン酸リチウム50g、酢酸エチル650gを内容積1Lのナスフラスコに容れ、1L/minで窒素シールしながら60℃に設定した恒温槽内に30min保持した。その後、炭酸リチウム5gをナスフラスコ内に添加し、撹拌した。1時間後、室温まで冷却し、続いて得られた混合液をメンブレンフィルターでろ過した。その後、ロータリーエバポレーターを用いてろ液から溶媒を留去したところ、42gの白色結晶のジフルオロリン酸リチウムが得られた。精製後のジフルオロリン酸リチウムをイオンクロマトグラフィーで分析したところジフルオロリン酸リチウムの純度は相対面積で99%以上であった。また、遊離酸分(酸性不純物)は55ppm、不溶解残分は849ppmであった。
<ジフルオロリン酸リチウムの合成>
前記実施例1と同様にして58.9gの白色結晶のジフルオロリン酸リチウムを得た。得られた結晶をイオンクロマトグラフィーにて分析したところジフルオロリン酸リチウムの純度は相対面積で85%であった。また、遊離酸分(酸性不純物)は3.70wt%、不溶解残分は5.15wt%であった。
前記ジフルオロリン酸リチウム50g、1,2-ジメトキシエタン200gを内容積500mlのナスフラスコに容れ、1L/minで窒素シールしながら60℃に設定した恒温槽内に30min保持した。その後、炭酸リチウム10gをナスフラスコ内に添加し、撹拌した。1時間後、室温まで冷却し、続いて得られた混合液をメンブレンフィルターでろ過した。その後、ロータリーエバポレーターを用いてろ液から溶媒を留去したところ、45gの白色結晶のジフルオロリン酸リチウムが得られた。精製後のジフルオロリン酸リチウムをイオンクロマトグラフィーで分析したところジフルオロリン酸リチウムの純度は相対面積で99%以上であった。また、遊離酸分(酸性不純物)は60ppm、不溶解残分は337ppmであった。
<ジフルオロリン酸リチウムの合成>
前記実施例1と同様にしてジフルオロリン酸リチウム63gを得た。得られた結晶をイオンクロマトグラフィーにて分析したところジフルオロリン酸リチウムの純度は相対面積で84%であった。また、遊離酸分(酸性不純物)は0.155wt%、不溶解残分は5.48wt%であった。
前記ジフルオロリン酸リチウム50g、1,2-ジメトキシエタン200gを内容積500mlのナスフラスコに容れ、1L/minで窒素シールしながら60℃に設定した恒温槽内に30min保持した。その後、水酸化リチウム2gをナスフラスコ内に添加し、撹拌した。1時間後、室温まで冷却し、続いて得られた混合液をメンブレンフィルターでろ過した。その後、ロータリーエバポレーターを用いてろ液から溶媒を留去したところ、45gの白色結晶のジフルオロリン酸リチウムが得られた。精製後のジフルオロリン酸リチウムをイオンクロマトグラフィーで分析したところジフルオロリン酸リチウムの純度は相対面積で99%以上であった。また、遊離酸分(酸性不純物)は884ppm、不溶解残分は1209ppmであった。
<ジフルオロリン酸リチウムの合成>
前記実施例1と同様にしてジフルオロリン酸リチウム59gを得た。得られた結晶をイオンクロマトグラフィーにて分析したところジフルオロリン酸リチウムの純度は相対面積で89%であった。また、遊離酸分(酸性不純物)は0.128wt%、不溶解残分は4.73wt%であった。
前記ジフルオロリン酸リチウム50g、1,2-ジメトキシエタン200gを内容積500mlのナスフラスコに容れ、1L/minで窒素シールしながら60℃に設定した恒温槽内に30min保持した。その後、フッ化リチウム20gをナスフラスコ内に添加し、撹拌した。1時間後、室温まで冷却し、続いて得られた混合液をメンブレンフィルターでろ過した。その後、ロータリーエバポレーターを用いてろ液から溶媒を留去したところ、45gの白色結晶のジフルオロリン酸リチウムが得られた。精製後のジフルオロリン酸リチウムをイオンクロマトグラフィーで分析したところジフルオロリン酸リチウムの純度は相対面積で99%以上であった。また、遊離酸分(酸性不純物)は675ppm、不溶解残分は823ppmであった。
<ジフルオロリン酸リチウムの合成>
前記実施例1と同様にしてジフルオロリン酸リチウム62gを得た。得られた結晶をイオンクロマトグラフィーにて分析したところジフルオロリン酸リチウムの純度は相対面積で91%であった。また、遊離酸分(酸性不純物)は0.238wt%、不溶解残分は5.28wt%であった。
前記ジフルオロリン酸リチウム50g、1,2-ジメトキシエタン200gを内容積500mlのナスフラスコに容れ、1L/minで窒素シールしながら60℃に設定した恒温槽内に30min保持した。その後、ポリ(4-ビニルピリジン)20gをナスフラスコ内に添加し、撹拌した。1時間後、室温まで冷却し、続いて得られた混合液をメンブレンフィルターでろ過した。その後、ロータリーエバポレーターを用いてろ液から溶媒を留去したところ、45gの白色結晶のジフルオロリン酸リチウムが得られた。精製後のジフルオロリン酸リチウムをイオンクロマトグラフィーで分析したところジフルオロリン酸リチウムの純度は相対面積で99%以上であった。また、遊離酸分(酸性不純物)は267ppm、不溶解残分は918ppmであった。
<ジフルオロリン酸リチウムの合成>
前記実施例1と同様にしてジフルオロリン酸リチウム58gを得た。得られた結晶をイオンクロマトグラフィーにて分析したところジフルオロリン酸リチウムの純度は相対面積で87%であった。また、遊離酸分(酸性不純物)は4.72wt%、不溶解残分は6.89wt%であった。
前記ジフルオロリン酸リチウム50g、1,2-ジメトキシエタン200gを内容積500mlのナスフラスコに容れ、1L/minで窒素シールしながら60℃に設定した恒温槽内に30min保持した。その後、炭酸リチウム10gをナスフラスコ内に添加し、撹拌した。1時間後、室温まで冷却し、続いて得られた混合液をメンブレンフィルターでろ過した。得られたろ液(ジフルオロリン酸リチウムを20wt%含有)を分析したところ遊離酸分(酸性不純物)はジフルオロリン酸リチウムに対して34ppmであった。また、不溶解残分は430ppmであった。
<ジフルオロリン酸リチウムの合成>
前記実施例1と同様にしてジフルオロリン酸リチウム61gを得た。得られた結晶をイオンクロマトグラフィーにて分析したところジフルオロリン酸リチウムの純度は相対面積で82%であった。また、遊離酸分(酸性不純物)は0.182wt%、不溶解残分は4.64wt%であった。
前記ジフルオロリン酸リチウム50g、1,2-ジメトキシエタン200gを内容積500mlのナスフラスコに容れ、1L/minで窒素シールしながら60℃に設定した恒温槽内に30min保持した。その後、炭酸リチウム10gをナスフラスコ内に添加し、撹拌した。1時間後、室温まで冷却し、続いて得られた混合液を静置することで炭酸リチウムを沈降させた。炭酸リチウムを含まない上澄み液を分取し、得られた液(ジフルオロリン酸リチウムを20wt%含有)を分析したところ遊離酸分(酸性不純物)は観測されず、不溶解残分は2790ppであった。
<ジフルオロリン酸リチウムの調製>
前記実施例2に記載の精製後のジフルオロリン酸リチウム6gに対してリン酸二水素リチウムを0.04g添加して遊離酸分(酸性不純物)を測定したところ0.014wt%であった。
前記調製ジフルオロリン酸リチウム5g、1,2-ジメトキシエタン20gを内容積100mlのナスフラスコに容れ、1L/minで窒素シールしながら60℃に設定した恒温槽内に30min保持した。その後、炭酸リチウム1gをナスフラスコ内に添加し、撹拌した。1時間後、室温まで冷却し、続いて得られた混合液をメンブレンフィルターでろ過した。その後、ロータリーエバポレーターを用いてろ液から溶媒を留去したところ、4gの白色結晶のジフルオロリン酸リチウムが得られた。精製後のジフルオロリン酸リチウムをイオンクロマトグラフィーで分析したところジフルオロリン酸リチウムの純度は相対面積で99%以上であった。また、遊離酸分(酸性不純物)は24ppm、不溶解残分は510ppmであった。
<ジフルオロリン酸リチウムの合成>
前記実施例1と同様にしてジフルオロリン酸リチウム120gを得た。得られた結晶をイオンクロマトグラフィーにて分析したところジフルオロリン酸リチウムの純度は相対面積で88%であった。また、遊離酸分(酸性不純物)は0.566wt%、不溶解残分は6.25wt%であった。
前記ジフルオロリン酸リチウム100gを内容積250mLのPFA容器に容れ、1L/minで窒素フローさせながら130℃設定した恒温槽内に1時間保持した。その後、130℃の恒温槽内に保持したまま、通気ガスを窒素のみから40体積%のHFを含む窒素ガスに切り替え、その流量を10L/minとした。HFを含む窒素ガスの通気は1時間行った。更に、通気ガスを再び流量1L/minの窒素ガスに切り替えた。窒素ガスの通気は130℃に保持したまま10時間行った。その後、室温まで冷却した。これにより白色結晶のジフルオロリン酸リチウム93gを得た。精製後のジフルオロリン酸リチウムをイオンクロマトグラフィーで分析したところジフルオロリン酸リチウムの純度は相対面積で79%であった。また、遊離酸分(酸性不純物)は3979ppm、不溶解残分は121149ppmであった。
ジフルオロリン酸塩を含む非水電解液を用いた非水電解液二次電池について、添加効果を確認するための評価試験を実施した。
<LiCoO2正極の作製>
正極活物質としてLiCoO2 93質量部、導電材としてアセチレンブラック 4質量部、及び結着剤としてポリフッ化ビニリデン(PVDF)3質量部を混合して、正極材料とした。この正極材料をN-メチル-2-ピロリドン(NMP)に分散させてスラリー状とした。このスラリーをアルミニウム製の正極集電体の片面に塗布し、乾燥後、プレス成型してLiCoO2正極を作製した。
負極活物質として人造黒鉛97.0質量部、結着剤としてスチレンブタジエンゴム(SBR)2.0質量部、及びカルボキシメチルセルロース(CMC)1.0質量部を混合して、負極材料とした。この負極材料を水に分散させてスラリー状とした。このスラリーを銅製の負極集電体の片面に塗布し、乾燥後、プレス成型して黒鉛負極を作製した。
ここで、前記のパウチ型セルにおいて、上記の正極、負極、及びポリエチレン製のセパレーターを負極、セパレーター、正極の順に積層して電池要素を作製した。この電池要素をアルミニウムの両面を樹脂層で被覆したラミネートフィルムからなる袋内に、正極と負極の端子を突設させながら挿入した後、上記電解液を袋内に注入し、真空封止を行い、パウチ型電池を作製した。
エチレンカーボネート(EC)とエチルメチルカーボネート(EMC)をEC:EMC=3:7の体積比で混合した非水溶媒に、電解質としてヘキサフルオロリン酸リチウム(LiPF6)を1.1mol/Lの割合で溶解させた溶液に、実施例1で精製したジフルオロリン酸リチウムを溶液に対して1wt%添加し、非水電解液を調製し、前記の手順にてパウチ型セルの非水電解液二次電池を作製した。
実施例1で精製前のジフルオロリン酸リチウムを用いて非水電解液を調製した以外は実施例8と同様の方法で、パウチ型セルの非水電解液二次電池を作成した。
作製した各非水電解液二次電池を、それぞれ25℃において0.2Cに相当する定電流で4.2Vまで充電し、さらに4.2Vの定電圧で電流値が0.02Cになるまで定電圧充電させた後、0.2Cの定電流で2.7Vになるまで放電させて、初期放電容量を求めた。その後、同条件で、もう2サイクル充放電を行い、電池を安定させた。ここで、1Cとは電池の基準容量を1時間で放電する電流値を表し、5Cとはその5倍の電流値を、0.1Cとはその1/10の電流値を、また0.2Cとはその1/5の電流値を表す。
初期放電容量を評価し、安定化させた電池を25℃にて0.2Cの定電流で4.2Vまで充電し、さらに4.2Vの定電圧で電流値が0.02Cになるまで定電圧充電させた後、0.2Cの定電流で初期放電容量の半分の容量となるように放電した。これを-10℃において10mVの交流電圧振幅を印加することで電池のインピーダンスを測定し、0.03Hzの実軸抵抗を求めた。評価結果を表2に示す。
Claims (8)
- 不純物を含むジフルオロリン酸塩と、アルカリ金属又はアルカリ土類金属の炭酸塩、水酸化物及びハロゲン化物並びにアミン類からなる群より選択される少なくとも1種類の処理剤とを混合し、該不純物を分離する工程を有するジフルオロリン酸塩の精製方法。
- 前記精製方法において、前記不純物と前記処理剤とを混合して塩又は錯体を形成させた後、ろ過によりこの塩又は錯体をろ別する請求項1に記載のジフルオロリン酸塩の精製方法。
- 前記処理剤がアルカリ金属の炭酸塩、水酸化物又はハロゲン化物である請求項1又は2に記載のジフルオロリン酸塩の精製方法。
- 前記処理剤がリチウムの炭酸塩、水酸化物又はハロゲン化物である請求項1~3のいずれか1項に記載のジフルオロリン酸塩の精製方法。
- 前記不純物と前記処理剤との反応が溶媒中で行われる請求項1~4のいずれか1項に記載のジフルオロリン酸塩の精製方法。
- 前記処理剤がアミン類である請求項1、2又は5に記載のジフルオロリン酸塩の精製方法。
- 前記溶媒が酢酸エステル、リン酸エステル、ニトリル化合物、アミド化合物、アルコール類又はアルカン類である請求項5に記載のジフルオロリン酸塩の精製方法。
- 二次電池用非水電解液において、非水溶媒中に少なくともヘキサフルオロリン酸塩及びジフルオロリン酸塩を含み、該ジフルオロリン酸塩の少なくとも一部が、請求項1~7のいずれか1項に記載の精製方法によって不純物の含有量が1wt%以下となるように精製されたジフルオロリン酸塩である二次電池用非水電解液。
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