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  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
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  • C01B17/00—Sulfur; Compounds thereof
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  • C01D5/00—Sulfates or sulfites of sodium, potassium or alkali metals in general
  • C01D5/02—Preparation of sulfates from alkali metal salts and sulfuric acid or bisulfates; Preparation of bisulfates
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  • C01G49/14—Sulfates
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  • H01M4/04—Processes of manufacture in general
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  • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
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  • H01M4/04—Processes of manufacture in general
  • H01M4/0438—Processes of manufacture in general by electrochemical processing
  • H01M4/044—Activating, forming or electrochemical attack of the supporting material
  • H01M4/0445—Forming after manufacture of the electrode, e.g. first charge, cycling
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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
  • H01M4/04—Processes of manufacture in general
  • H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
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  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/139—Processes of manufacture
  • H01M4/1397—Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
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  • 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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  • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
  • H01M4/621—Binders
  • H01M4/622—Binders being polymers
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  • 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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  • C01—INORGANIC CHEMISTRY
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  • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
  • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
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  • C01P2002/80—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70
  • C01P2002/88—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70 by thermal analysis data, e.g. TGA, DTA, DSC
• • 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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  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
• • H—ELECTRICITY
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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
  • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
  • H01M2004/028—Positive electrodes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the present invention relates to a sulphate-containing electrode material as an active ingredient, as well as to a process for its production.
• Lithium batteries using an insertion compound are known as the operating basis of the positive electrode, such as Li x CoO 2 (0.4 ⁇ x ⁇ 1) which is used pure or in solid solution with nickel, manganese and / or aluminum.
• the main obstacles to the generalization of this type of electrochemistry are the scarcity of cobalt and the excessively positive potential of the transition oxides, with consequent safety problems for the battery.
• the carbon deposition is carried out at high temperature, under reducing conditions.
• transition elements other than Fe 11 and Mn 11 , the elements Co 11 and Ni 11 being easily reduced to the metallic state. It is the same for Fe m , Mn 111 , Cr m , V m , which are interesting dopants to increase the ionic or electronic conductivity.
• patent application US-2005/0163699 describes the ceramic preparation of compounds A to M b (SO 4 ) c Z d cited above.
• M is Ni, Fe, Co, Mn, (MnMg), (FeZn), or (FeCo).
• M is Ni, Fe, Co, Mn, (MnMg), (FeZn), or (FeCo).
• These compounds are prepared by ceramic means from LiF precursor of Li and sulfate of the element or elements M.
• the most interesting are the compounds which contain Fe, because in addition to their relatively low cost, they are susceptible on the basis of structural and chemical considerations (especially ionocovalence of bonds) to exhibit valuable electrochemical properties in a desirable range of potential to ensure reliable use for high volume applications.
• the red color found in the compounds obtained at different temperatures is due to the O 2+ / Fe 3+ combination in a crystalline mesh such as oxide Fe 2 O 3 . It is also known that the Fe 11 compounds oxidize in air at 200 ° C giving Fe m , and the preparation of Example 2 at 400 ° C in air confirms it.
• the iron-containing compounds which are prepared by ceramics from LiF and iron sulphate according to US-2005/0163699 are therefore not constituted by LiFeSO 4 F. Similarly, it appears that the compounds in which M is Co, Nor are not stable at the temperatures used during the preparation recommended by the ceramic route. It is therefore not plausible that the compounds described in US-2005/0163699 have actually been obtained.
• the international application WO 2010/046608 describes the ionothermal preparation of various polyanionic fluorinated compounds of alkali metal (Li or Na) and of transition metal, said compounds being useful as electrode active material.
• the transition metal is Fe are particularly interesting, because of the high abundance of sources and the non-toxicity of Fe, in particular LiFeSO 4 F with a tavorite structure, NaFeSO 4 F, LiFePO 4 , LiFePO F 4, LiFePO 4 Na 2 Feo.95Mn 0. 5 o F P0 4, LiFe 1-y Mn y SO 4 F. M.
• Ati, et al. [Electrochemistry Communications 13, (201 1) 1280-1283] describe the preparation of a pure compound of formula LiFeSO 4 F with a triplite structure.
• U.S. Patent 5,908,716 discloses sulfate and at least one transition metal compounds and their use as a positive electrode active material. These compounds have the formula A x M y (SO 4 ) z wherein x, y and z are> 0, A is selected from alkali metals, M is a metal, preferably a transition metal.
• the iron-based compounds specifically mentioned herein are as follows: Li 3 Fe (SO 4), L ⁇ Fe ⁇ SO ⁇ , Na Fe (SO 4), and the intermediate compositions Li xl Na x2 V y IFE y2 (SO 4) 2 and Li Na xl x2 y2 IFE V y (SO 4). US Pat. No.
• the Li-ion or Na-ion battery technologies are initially assembled in the discharged state, that is to say using an active material at the negative electrode that can not initially release ions.
• alkaline eg electrodes based on graphite, amorphous carbon, Li 4 Ti 5 Oi 2 , etc.
• the active material at the positive electrode must therefore be the alkaline ion source material, i.e. it must be able to release alkaline ions when oxidized.
• the chemical formula of a positive electrode material must therefore initially contain lithium atoms in its structure as well as iron atoms in the +11 oxidation state.
• iron in the +11 oxidation state oxidizes very easily to iron + III.
• the compounds based on iron + III are indeed very stable compounds. It is therefore more difficult to stabilize +11 iron-based phases than iron-based III + phases. It is necessary for this to work in very special conditions and difficult to implement, for example in acidic medium or reducing medium.
• an important criterion for selecting a compound as a cathode active material for a battery operated by alkaline ion (Li or Na) circulation is a high operating potential.
• the reported operating potentials are 3.4 V. Li ° / Li + for LiFePO 4 , 3.6 V vs. Li ° / Li + for Fe 2 (SO 4 ) 3 , 3.6 V vs. Li ° / Li + for LiFeSO 4 F with a tavorite structure, and 3.9V vs. Li ° / Li + for LiFeSO 4 F with triplite structure.
• a sulphate-containing material has an electrochemical potential greater than the phosphate-like material
• a material containing two (SO 4 ) 2 - groups has an electrochemical potential greater than an analogous material containing only a sulfate group
• a material containing a group (SO 4 ) " and an anion F " has an electrochemical potential greater than a similar material containing two groups (SO 4 ) 2 " .
• the inventors have been able to stabilize polyanionic compounds based on sulfate, iron in the +11 oxidation state and alkali metal, and which, surprisingly, make it possible to reach high potentials, even though they do not contain fluorine, which can pose safety problems both in the production and in the use of electrochemical devices.
• the object of the present invention is to provide a new electrode material containing alkali metals and iron in the +11 oxidation state, free of fluorine and which nonetheless has a high operating potential, as well as a process which makes it possible to produce said material reliably, quickly and economically.
• An electrode material according to the present invention is characterized in that it contains, as positive electrode active material, at least one iron sulphate in the +11 oxidation state and the alkali corresponding to the formula (Nai -a b Li) x Fe y (sO 4) z (I) wherein the subscripts a, b, x, y and z are selected so as to ensure the electroneutrality of the compound, where 0 ⁇ a ⁇ l , 0 ⁇ b ⁇ l, l ⁇ x ⁇ 3, l ⁇ y ⁇ 2, l ⁇ z ⁇ 3, and 2 ⁇ (2z-x) / y ⁇ 3 so that at least some of the iron is in the oxidation state +11, excluding the Li 2 Fe 2 (SO 4 ) 3 compound whose use as a positive electrode active ingredient has already been described, in particular in the patent application EP 0 743 692.
• the compounds of formula (I) not containing iron in the +11 oxidation state such as for example NaFe (SO 4 ) 2 and Na Fe (SO 4 ).
• An electrode material of the invention preferably contains at least 50% by weight of compound of formula (I), more preferably at least 80% by weight.
• the electrode material further contains an electronic conduction agent, and optionally a binder.
• the proportion of electronic conduction agent is preferably less than 15% by weight.
• the proportion of binder is preferably less than 10%.
• the sulphates of formula (I) used as active material in an electrode material according to the invention are new, with the exception of the compound Li 2 Fe 2 (SO 4 ), which however has never been obtained by direct synthesis (that is to say other than by reduction of the compound Fe 2 (SO 4 )). They constitute in this respect another object of the invention.
• a sulphate of formula (I) according to the present invention may be prepared by the ceramic route from precursor sulphates, in particular from lithium sulphate, sodium sulphate and iron sulphate.
• the precursors are mixed using amounts corresponding to the stoichiometry of the sulfate of formula (I).
• the precursors may be mixed for example in a mill to promote intimate contact between the precursors.
• the mixture is then subjected to a heat treatment at a temperature between 100 and 350 ° C.
• the sulfate of formula (I) containing iron in the +11 oxidation state, the heat treatment must be carried out under an inert or reducing atmosphere in order to prevent the oxidation of Fe II + to Fe III + .
• the synthesis may for example be carried out under vacuum or in an inert gas atmosphere (argon for example).
• a sulphate of formula (I) according to the present invention may also be prepared ionothermally, from the same precursor sulphates mentioned for the ceramic route, in particular from lithium sulphate, sodium sulphate and sulphate of sulphate. iron.
• the precursors are mixed, using amounts corresponding to the stoichiometry of the sulfate of formula (I).
• the mixture of the precursors is then dispersed in an ionic liquid.
• the suspension thus formed is introduced into a reactor, in which it is subjected to a heat treatment for a few hours at a temperature above 100 ° C.
• the maximum temperature is determined by the stability of the ionic liquid used (for example by its decomposition temperature).
• ionic liquid is meant a compound which contains only anions and cations which compensate for their charges, and which is liquid at the temperature of the formation reaction of the compounds of the invention, either pure or in admixture with an additive. .
• the use of an ionic liquid is an inert reaction medium, which prevents the oxidation of iron +11.
• EMI-TFSI 1,3-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide
• a sulphate of formula (I) according to the present invention can also be prepared by "flash sintering", also known under the name SPS which is the acronym for the English expression “Spark Plasma Sintering”, from the same precursor sulphates than those mentioned for the ceramic route, in particular from lithium sulphate, sodium sulphate and iron sulphate.
• the precursors are mixed, using amounts corresponding to the stoichiometry of the sulfate of formula (I).
• the mixture of the precursor sulfates is then placed in a carbon matrix in a flash sintering apparatus (SPS) and the mixture is subjected to rapid heating at temperatures between 100 and 400 ° C for a duration of a few minutes to a few hours. while it is pressed at a pressure above 1 bar.
• SPS flash sintering apparatus
• the precursor sulphates may be hydrated sulphates or dehydrated sulphates.
• the dehydrated sulphates are obtained by simple heat treatment of commercial hydrated sulphates to the dehydration temperature specific to each of them.
• a sulphate of formula (I) in which at least a portion of the iron is in the Fe III + state can also be obtained by chemical or electrochemical oxidation of the analogous sulfate containing only Fe II + according to the general reaction:
• Suitable oxidizing agents mention may in particular be made of NO 2 BF 4 .
• the compound Li 2 Fe II + (SO 4 ) 2 is preferably prepared from Li 2 SO 4 and dehydrated FeSO 4 .
• the dehydrated sulphates are obtained from the commercial products FeSO 4 7H 2 O and Li 2 SO 4 -H 2 O.
• the two precursors, dehydrated or not, are mixed under an inert atmosphere, using amounts corresponding to the stoichiometry of the final material. .
• the mixture is then placed in an inert atmosphere and then subjected to heat treatment at a temperature between 200 ° C and 350 ° C.
• the mixture of the precursors can be carried out using an SPEX type mill, for example for two times 30 minutes.
• the inert atmosphere may be an argon atmosphere or a primary vacuum enclosure.
• the primary vacuum chamber may be a quartz or Pyrex® bulb.
• the heat treatment is carried out at a temperature preferably above 300 ° C.
• the duration of the heat treatment is preferably greater than 12 hours.
• the mixture of precursors subjected to the heat treatment can be in the form of pellets, which promotes the contact between the precursors, the possibility for the species to migrate, and thus obtaining a complete reaction and pure products.
• the compound Na 2 Fe II + (SO 4 ) 2 can be prepared from Na 2 SO 4 and FeSO 4 -7H 2 O.
• the precursors in stoichiometric quantities are mixed under an inert atmosphere.
• the mixture is then placed under an inert atmosphere and then subjected to heat treatment at a temperature between 140 and 300 ° C.
• the inert atmosphere may be nitrogen or argon, for example.
• the heat treatment can be carried out directly on the mixture of precursors in the form of powders.
• the precursors may be mixed by mechanical grinding, for example using an SPEX type mill for 20 minutes.
• the precursors can also be mixed by dissolving the precursors in water and evaporation between 20 ° C. and 100 ° C. with stirring. In this embodiment, it is preferable to work under anoxic conditions, in order to avoid the oxidation of Fe 11+ to Fe III +.
• the process is carried out in an electrochemical cell in which the active material of the positive electrode is the compound Na x > Fe y (SO 4 ) z , the anode is an anode containing lithium, and the electrolyte contains a salt. of lithium.
• the electrochemical cell is subjected to a charge / discharge cycle in the appropriate potential range, for example between 2.0 and 4.2V. Li + / Li °.
• This electrochemically is particularly advantageous to access the mixed sulfates of formula ( ⁇ ) (Nai -a b Li) x Fe (SO 4) 2 as described above.
• the process is carried out in an electrochemical cell in which the active material of the positive electrode is the compound Li x > Fe y (SO 4 ) z , the anode is an anode containing sodium, and the electrolyte contains a sodium salt.
• the electrochemical cell is subjected to a charge / discharge cycle in the appropriate potential range, for example, between 2.8 and 4.5V. Na + / Na °.
• This electrochemically is particularly advantageous to access the mixed sulfates of formula ( ⁇ ) (Nai -a b Li) x Fe (SO 4) 2 as described above.
• An electrode material containing the compound (I) according to the invention can be used in various electrochemical devices.
• an electrode material of the invention may be used for the manufacture of electrodes in electrochemical devices operating by circulation of alkaline ions (Li + or Na + ) in the electrolyte, such as in particular batteries, supercapacitors and electrochromic systems.
• An electrode containing an electrode material according to the invention can be prepared by depositing on a current collector a positive electrode composition containing a sulfate of formula (I).
• Said composition preferably further contains an electronic conduction agent, and optionally a binder.
• the sulfate content in said composition is preferably at least equal to 50% by weight, more preferably at least 80% by weight.
• the content of electronic conduction agent is less than 15% by weight, and the binder content is less than 10%.
• Said electrode composition is obtained by mixing the constituents in the appropriate proportions.
• the mixing can be carried out in particular by mechanical grinding.
• the electronic conduction agent may be, for example, a carbon black, an acetylene black, natural or synthetic graphite or carbon nanotubes.
• the optional binder of the positive electrode is preferably a polymer which has a high modulus of elasticity (of the order of several hundred MPa), and which is stable under the temperature and voltage conditions in which the electrode is intended to work.
• a polymer which has a high modulus of elasticity (of the order of several hundred MPa), and which is stable under the temperature and voltage conditions in which the electrode is intended to work.
• fluorinated polymers such as polyvinyl fluoride or polyethylene tetrafluoride
• CMC carboxymethylcelluloses
• copolymers of ethylene and propylene or a mixture of at least two of these polymers.
• the material of the working electrode contains a polymeric binder
• a composition containing the sulfate of formula (I), the binder, a volatile solvent, and optionally an ionic conductive agent to apply said composition on a current collector, and to remove the volatile solvent by drying.
• the volatile solvent may be chosen for example from acetone, tetrahydrofuran, diethyl ether, hexane, and N-methylpyrrolidone.
• the amount of material deposited on the current collector is preferably such that the amount of compound according to the invention is between 0.1 and 200 mg per cm 2 , preferably from 1 to 50 mg per cm 2 .
• the current collector may consist of a grid or sheet of aluminum, titanium, graphite paper or stainless steel.
• An electrode according to the invention can be used in an electrochemical cell comprising a positive electrode and a negative electrode separated by an electrolyte.
• the electrode according to the invention constitutes the positive electrode.
• the negative electrode may consist of lithium metal or a lithium alloy, sodium metal or a sodium alloy, a transition metal oxide forming by reduction a nanometric dispersion in lithium oxide, or a double nitride of lithium and a transition metal.
• the negative electrode may also be constituted by a material capable of reversibly inserting Li + ions at lower potentials than the positive electrode, preferably less than 1.6 V.
• Examples of such materials are low potential oxides having the general formula Li 1 + y + x / 3 Ti 2-x / 3O 4 (0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1), Li 4+ x Ti 5 Oi 2 (0 ⁇ x ' ⁇ 3), carbon and carbon products from the pyrolysis of organic materials, as well as dicarboxylates.
• Examples of elements that can form alloys with lithium include, for example, Sn and Si.
• Examples of elements that can form alloys with sodium include, for example, Pb.
• the electrolyte advantageously comprises at least one lithium or sodium salt in solution in a polar aprotic liquid solvent, in a solvating polymer optionally plasticized with a liquid solvent or an ionic liquid, or in a gel consisting of an addition-gelled liquid solvent. a solvating or non-solvating polymer.
• the salt of the electrolyte may be chosen from the salts conventionally used in the technical field, in particular the salts of strong acids, such as, for example, the salts having an anion ClO 4 " , BF 4 " , PF 6 " , and salts having an anion perfluoroalkanesulfonate, bis (perfluoroalkylsulfonyl) imide, bis (perfluoroalkylsulfonyl) methane or tris (perfluoroalkylsulfonyl) methane.
• the salts having an anion ClO 4 " , BF 4 " , PF 6 " and salts having an anion perfluoroalkanesulfonate, bis (perfluoroalkylsulfonyl) imide, bis (perfluoroalkylsulfonyl) methane or tris (perfluoroalkylsulfonyl) methane.
• the salt of the electrolyte is a lithium salt. LiClO 4 is particularly preferred.
• the salt of the electrolyte is a sodium salt. NaClO 4 is particularly preferred.
• the liquid solvent is preferably a polar aprotic liquid organic solvent chosen, for example, from linear ethers and cyclic ethers, esters, nitriles, nitro derivatives, amides, sulphones, sulfolanes, alkylsulfamides and partially hydrogenated hydrocarbons.
• Particularly preferred solvents are diethyl ether, dimethoxyethane, glyme, tetrahydrofuran, dioxane, dimethyltetrahydrofuran, methyl or ethyl formate, propylene or ethylene carbonate, alkyl carbonates, and the like.
• the electrolyte when it is a polar polymer solvent, it may be chosen from solvating polymers, crosslinked or otherwise, with or without grafted ionic groups.
• a solvating polymer is a polymer which comprises solvating units containing at least one heteroatom selected from sulfur, oxygen, nitrogen and fluorine.
• solvating polymers examples include polyethers of linear structure, comb or block, forming or not a network, based on poly (ethylene oxide), or copolymers containing the ethylene oxide unit or propylene oxide or allylglycidylether, polyphosphazenes, crosslinked networks based on polyethylene glycol crosslinked by isocyanates or networks obtained by polycondensation and carrying groups that allow the incorporation of crosslinkable groups.
• Block copolymers in which certain blocks carry functions which have redox properties can also be mentioned.
• the above list is not limiting, and all polymers having solvating properties can be used.
• the solvent of the electrolyte may simultaneously comprise an aprotic liquid solvent chosen from the aprotic liquid solvents mentioned above and a polar polymer solvent comprising units containing at least one heteroatom chosen from sulfur, nitrogen, oxygen and fluorine.
• a polar polymer By way of example of such a polar polymer, mention may be made of polymers which mainly contain units derived from acrylonitrile, vinylidene fluoride, N-vinylpyrrolidone or methyl methacrylate.
• the proportion of aprotic liquid in the solvent can vary from 2% (corresponding to a plasticized solvent) to 98% (corresponding to a gelled solvent).
• the present invention is illustrated by the following exemplary embodiments, to which it is however not limited.
• the synthesis was carried out using dehydrated lithium sulfate and dehydrated Fe sulfate.
• the dehydrated iron sulphate FeSO 4 was obtained by heating in a primary vacuum at 280 ° C. the compound FeSO 4 .H 2 O, itself prepared by dehydration of the commercial compound FeSO 4 .7H 2 O in an ionic liquid EMI-TFSI at 160 ° C.
• the dehydrated lithium sulfate Li 2 SO 4 was obtained by heating in air at 300 ° C. the commercial compound Li 2 SO 4 .H 2 O.
• Li 2 SO 4 and FeSO 4 were mixed and the mixture was subjected to two successive grindings of 30 minutes in an SPEX® mill.
• the mixture of powders thus obtained was then pelletized using a unixial press.
• the pellet was then placed in a quart ampoule, which was sealed under vacuum.
• the ampoule was then placed in an oven and heat treated at 320 ° C for 12 hours.
• the synthesis was carried out using hydrated lithium sulfate and Fe sulfate monohydrate.
• the iron sulfate monohydrate FeSO 4 .H 2 O was obtained by mixing the commercial compound FeSO 4 .7H 2 O with the ionic liquid EMI-TFSI, and bringing this suspension to 140 ° C for two hours. The iron sulphate monohydrate FeSO 4 .H 2 O was then recovered by centrifugation of the suspension, then washed three times with ethyl acetate before being dried under vacuum.
• Li 2 SO 4 .H 2 O is a commercial compound.
• SPS synthesis was performed using dehydrated lithium sulfate and dehydrated iron sulfate.
• the iron sulfate monohydrate FeSO 4 .H 2 O was obtained by mixing the commercial compound FeSO 4 .7H 2 O with the ionic liquid EMI-TFSI, and bringing this suspension to 140 ° C for two hours.
• the iron sulphate monohydrate FeSO 4 .H 2 O was then recovered by centrifugation of the suspension, then washed three times with ethyl acetate before being dried under vacuum.
• This iron sulphate monohydrate FeSO 4 .H 2 O was then dehydrated by heating the powder at 280 ° C. for 8 hours under primary vacuum to obtain anhydrous iron sulphate FeSO 4 .
• Dehydrated lithium sulfate Li 2 SO 4 was prepared by heating commercial lithium sulfate monohydrate at 350 ° C for 5 hours.
• Li 2 SO 4 and FeSO 4 were mixed and the mixture was subjected to three grindings of 45 minutes in a SPEX® mill. About 300 mg of this mixture was then introduced into a carbon matrix (Mersen 2333) of internal diameter 10 mm, between two carbon sheets (Papyex®). The set was installed in a SPS HPD 10 FCT unit connected to an argon glove box. The powder was then pressed at 50 MPa and subjected to a heat treatment of 20 minutes at 320 ° C. (heating rate 75 ° C./min via a sequence of 1 tap of 1 ms in continuous polarization) under vacuum.
• Example 1 The compound obtained in Example 1 above was characterized by X-ray diffraction (XRD) with Ka radiation from Cobalt. The diagram is shown in Figure 1 attached.
• XRD X-ray diffraction
• the Li 2 Fe (SO 4 ) 2 compound of Example 1 above was tested as a positive electrode material in a Swagelok® cell in which the negative electrode is a lithium film, and the two electrodes are separated by a fiberglass separator impregnated with a 1M solution of LiClO 4 in propylene carbonate carbonate PC.
• 100 mg of Li 2 Fe (SO 4 ) 2 compound and 25 mg of Super P® carbon were mixed by mechanical grinding in an SPEX 8000® mill for 19 minutes. A quantity of mixture corresponding to 8 mg of Li 2 Fe (SO 4 ) 2 per cm 2 was applied to a stainless steel current collector.
• the electrochemical cell was cycled between 3.2 and 4.5V vs. Li + / Li ° at a rate of C / 20.
• the appended FIG. 2 represents the variation of the potential V (in Volts vs. Li + / Li °) as a function of the insertion rate T of lithium in Li T Fe (SO 4 ) 2 , during the cycling of the cell at a steady state. of C / 20.
• Figures 2 and 3 show that the potential of the Fe 3+ / Fe 2+ couple in Li 2 Fe (SO 4 ) 2 is 3.83 V. Li + / Li °. This potential is greater than the potential of the LiFe compound (SO 4 ) F of tavorite structure (whose Fe 3+ / Fe 2+ pair potential is 3.6 V vs. Li + / Li °) even though Li 2 Fe (SO 4 ) 2 does not contain fluorine. In addition, this potential of 3.83 V vs. Li + / Li ° corresponds to the highest potential ever reported for the Fe 2+ / Fe 3+ redox couple in an inorganic compound containing no fluorine.
• FIG. 4 represents the variation of the capacitance CP (mAh / g) as a function of the cycling regime C, a regime n C representing the regime allowing to achieve a complete charge in 1 / n hour.
• Example 3 The compound obtained above in Example 3 was characterized by X-ray diffraction (XRD) with Ka radiation from Cobalt. The diagram is shown in the appended FIG.
• FIG. 5 shows the brightness of the DRX pattern recorded for the sample prepared in Example 3.
• the star signals a diffraction line attributed to graphite from the graphite matrix used for the synthesis; the pound sign (#) indicates a very small amount of the FeSO 4 precursor that has not completely reacted.
• FIG. 5 The comparison of FIG. 5 with FIG. 1 clearly shows that the same Li 2 Fe (SO 4 ) 2 phase is obtained by SPS as that prepared by the ceramic route.
• the Li 2 Fe (SO 4 ) 2 compound of Example 3 above was tested as a positive electrode material in a Swagelok® cell in which the negative electrode is a lithium film, and the two electrodes are separated by a fiberglass separator impregnated with a 1M solution of LiClO 4 in the propylene carbonate carbonate PC.
• 100 mg of Li 2 Fe (SO 4 ) 2 compound and 25 mg of Super P® carbon were mixed by mechanical grinding in an SPEX 8000 mill for 20 minutes. A quantity of mixture corresponding to 8 mg of Li 2 Fe (SO 4 ) 2 per cm 2 was applied to a stainless steel current collector.
• the electrochemical cell was cycled between 2.8 and 4.5V vs. Li + / Li ° at a rate of C / 20.
• FIG. 6 represents the variation of the potential V (in Volts vs. Li + / Li °) as a function of the lithium insertion rate x in Li x Fe (SO 4 ) 2 , during the cycling of the cell at a steady state. of C / 20.
• the synthesis was carried out using a dehydrated sodium sulfate Na 2 SO 4 and a commercial iron sulphate FeSO 4 .7H 2 O.
• Figure 7 shows that the compound Na 2 Fe (SO 4 ) 2 is formed at 120 ° C in an allotropic form a.
• This phase a is perfectly stable up to 180 ° C., at which temperature we begin to observe the appearance of a new group of peaks that will grow at the expense of the diffraction peaks of the ⁇ -Na 2 Fe phase (SO 4 ) 2 up to the temperature of 350 ° C.
• This second group of diffraction peaks is characteristic of the P-Na 2 Fe (SO 4 ) 2 phase.
• This second phase P-Na 2 Fe (SO 4 ) 2 is stable up to at least 350 ° C.
• the recorded XRD diagram shows the presence of Na 2 SO 4 and Fe 2 O 3 , suggesting the decomposition of Na 2 Fe (SO 4 ) 2 between 350 and 500 ° C.
• An Na 2 Fe (SO 4 ) 2 compound was prepared according to the procedure of Example 8, carrying out the heat treatment at 170 ° C for 2 hours.
• FIG. 8 represents the diagram obtained. It shows the characteristic peaks of the a-Na 2 Fe (SO 4 ) 2 phase.
• the Na 2 Fe (SO 4 ) 2 compound of Example 9 above was tested as a positive electrode material in a Swagelok cell in which the electrode is an alkali metal film A (lithium or sodium) the two electrodes being separated by a fiberglass separator impregnated with a 1M solution of AC10 4 in propylene carbonate carbonate (PC).
• the electrode is an alkali metal film A (lithium or sodium) the two electrodes being separated by a fiberglass separator impregnated with a 1M solution of AC10 4 in propylene carbonate carbonate (PC).
• 100 mg of Na 2 Fe (SO 4 ) 2 compound and 40 mg of carbon were mixed by mechanical grinding in an SPEX 8000® mill for 15 minutes. A quantity of mixture corresponding to 8 mg of sulfate per cm 2 was applied to a stainless steel current collector.
• Figure 9 attached shows the variation of the potential V (V vs. Na + / Na °) depending on the sodium disinsertion T levels in the compound Na T Fe (SO 4) 2, during the cycling of the cell in which the anode is Na and the electrolyte contains NaClO 4 .
• FIG. 10 relates to a cell in which the anode is lithium and the salt of the electrolyte is LiClO 4 .
• Na + ions are extracted from the sulfate Na 2 Fe (SO 4) 2, in conjunction with the oxidation of Fe to Fe + II + III.
• the crude formula of the sulphate observed during this first charge is then Na 2- a'Fe (SO 4 ) 2 , with 0 ⁇ a ' ⁇ 1.
• Li ions are inserted in the host compound Na 2-a Fe (SO 4) 2, replacing the previously extracted Na + ions, and sulfate becomes Na 2-a> b Li > Fe (SO 4 ) 2 , with 0 ⁇ a ' ⁇ l, 0 ⁇ b' ⁇ 1 and l ⁇ 2-a '+ b' ⁇ 2.
• the first discharge / charge cycle therefore causes a partial replacement of Na by Li. Subsequent cycles then cause a disinsertion / insertion of lithium and / or sodium into the sulfate forming the active material of the cathode.

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