Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/04—Processes of manufacture in general
  • H01M4/0402—Methods of deposition of the material
  • H01M4/0416—Methods of deposition of the material involving impregnation with a solution, dispersion, paste or dry powder
• • 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
  • H01M4/134—Electrodes based on metals, Si or alloys
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/139—Processes of manufacture
  • H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
• • 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
  • H01M4/621—Binders
• • 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
  • H01M4/625—Carbon or graphite
• • 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
• • 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 relates to a composition for producing a negative composite electrode of a lithium-ion battery, a process for producing the composition and an electrode, and a battery comprising said electrode.
• a lithium ion battery comprises at least one negative or anode electrode and at least one positive electrode or cathode between which is placed a separator impregnated with an electrolyte.
• the electrolyte consists of a lithium salt dissolved in a solvent chosen to optimize the transport and dissociation of the ions.
• each of the electrodes generally comprises a current collector on which is deposited a composite material which comprises a material active towards lithium, a polymer which acts as a binder (for example a fluoride copolymer of vinylidene (PVdF), and an electronic conduction conferring agent (eg carbon black)
• PVdF fluoride copolymer of vinylidene
• an electronic conduction conferring agent eg carbon black
• Li-ion batteries are used in many devices that include portable devices such as mobile phones, computers and light equipment, or heavier devices such as two-wheeled vehicles (bicycles, mopeds). or four-wheeled (electric or hybrid motor vehicles). For all these applications, it is imperative to have batteries that have the highest specific energy density (Wh / kg) and density (Wh / L).
• Li-ion batteries used in mobile phones, computers and light equipment
• the active ingredient of the negative electrode is usually graphite and the active ingredient of the positive electrode is cobalt oxide.
• the specific energy density of Li-ion batteries based on this torque is 200 Wh / kg.
• Such Batteries are not safe enough to be used for transport applications.
• Li-ion batteries marketed for transport applications have the negative electrode graphite as the active material and the positive electrode as the iron phosphate, and their specific energy density is 110 Wh / kg.
• the theoretical capacity of graphite is 372 mAh / g of graphite, while those of Si and Sn are respectively 3580 mAh / g of Si and 1400 mAh / g of Sn.
• Si or Sn in place of graphite would therefore make it possible to obtain the same capacity with a smaller volume, or a larger capacity with the same volume of material.
• replacing silicon with graphite in Li-ion batteries could achieve an energy density of 320 Wh / kg for portable applications and 180 Wh / kg for transportation applications.
• thick negative electrodes which have a surface capacity of 3.0 mAh.cm -2 , are obtained by mixing Si particles with an electronically conductive agent (eg carbon black) and a polymeric binder. (eg PVdF)
• an electronically conductive agent eg carbon black
• a polymeric binder eg PVdF
• the poor cyclability of these electrodes is due to the collapse of the network formed by the carbon black and the loss of the Si / carbon contacts due to the expansion and then the contraction of the Si particles as well as from their fracture into very small particles during the formation of alloys with lithium [JH Ryu, JW Kim, YE Sung, SM Oh, Electrochem Solid State Lett., 2004, 7, A306; R. Liu, Z.-Z. Guo, W.-S. Young, D.-T. Shieh, H.-C. Wu, M.-H. Yang, NL Wu, J., Power Sources, 2005, 140, 139].
• nanoscale particles of silicon [U. Kasavajjula, C. Wang, AJ. Appleby, J. Power Sources, 2007, 163, 1003; ZP Guo, Wang JZ, Liu HK, Dou SX, Power Sources, 2005, 146, 448], or composite particles of Si and of various conductive materials (prepared for example by decomposition of organic precursors, by chemical deposition in vapor phase ("Chemical Vapor Deposition”: CVD), by mechanical chemical milling, by simple physical mixing, or by the reaction of gels) [U. Kasavajjula, C. Wang, AJ. Appleby, J. Power Sources, 2007 which is a review on silicon]. It has also been proposed nanostructured active materials [M.
• a composite electrode is prepared from a composition consisting of a mixture of submicron particles of an active material M (Si, Sn or Ge), carbon particles and a polymer, under certain pH conditions and relative proportions of the various constituents of the mixture, was obtained a battery having improved properties in terms of conservation of the capacity to charge and discharge during successive cycles, when said composition is produced in an acid medium.
• M active material
• the inventors believe that these improved properties result in particular from improved mechanical strength.
• the object of the present invention is to provide a composition for the development of a negative electrode for use in a lithium-ion battery, a method of producing said composition and the electrode, and a battery comprising such a negative electrode.
• a composition according to the invention is prepared by a method comprising a step of suspending in an aqueous medium an electrode active material, a binder and an agent generating an electronic conductivity.
• the method is characterized in that: the electrode active material is in the form of particles containing an element M selected from Si, Sn, Ge; said particles having an average size of less than 1 ⁇ m; the binder is a polymer which carries reactive groups capable of reacting with hydroxyl groups in acidic medium; the aqueous medium is an acid medium at pH 1 unbuffered, or an acid medium at a buffered pH of less than or equal to 4, obtained by addition of a strong base and an organic acid; the total amount of the constituents "active substance, binder, electronic conduction agent" introduced into the acidic aqueous medium is from 10 to 80% by weight of the total amount of the composition, and the proportions of said constituents in the aqueous medium are as follows:
• the amount of organic acid is such that it corresponds to a content greater than 0.5 ⁇ 10 -4 mol per gram of element M, and the ratio of organic acid mass + strong base of organic acid + strong base + M + binder + electronic conduction agent remains less than or equal to 20%, that is to say (d + e) / (a + b + c + d + e) ⁇ 0, 1, the letters a, b, c, d and e respectively denoting the amounts of active ingredient, binder, electronic conduction agent, acid and base.
• the particles of active material preferably have an average size of less than 200 nm. Silicon is particularly preferred as the active ingredient.
• the particles of active material may be constituted by a single element M, an alloy of M with Li, or a composite material comprising the element M or the alloy M-Li and a conducting material Q.
• the active ingredient when the active ingredient is in the form of composite particles, it can be obtained by various processes, in particular by decomposition of organic precursors in the presence of M, by CVD deposition, by chemical mechanical grinding, by simple physical mixing, by reaction of gels. , or by nanostructuration.
• the conducting material Q may be carbon in various forms, for example in the form of amorphous carbon, graphite, carbon nanotubes or carbon nanofibers.
• the conductive material Q may also be a metal that does not react with lithium, for example Ni or Cu.
• the polymer used as binder is advantageously chosen from polymers which are electrochemically stable in the window of potential 0-5 V with respect to Li ° / Li + , insoluble in liquid media which can be used as liquid electrolyte solvent, and which carry functions capable of reacting with OH groups in acidic medium, especially carboxyl, amine, alkoxysilane, phosphonate, and sulfonate groups.
• polymers that may be mentioned in particular are copolymers of acrylic acid, copolymers of acrylamide, copolymers of styrene sulfonic acid, copolymers of maleic acid, copolymers of itaconic acid, copolymers of the acid lignosulfonic acid, allylamine copolymers, ethylacrylic acid copolymers, polysiloxanes, epoxy-amine polymers, polyurethanes and carboxymethylcelluloses (CMC). CMCs are particularly preferred.
• the agent generating an electronic conductivity may be selected from carbon black, SP carbon, acetylene black, carbon nanofibers, and carbon nanotubes.
• the amount of organic acid is such that it corresponds to a content greater than 5.10 -4 mol per gram of element M and the organic acid mass ratio + strong organic acid base + strong base + M + binder + electronic conduction agent remains less than or equal to 10%.
• the total amount of the active ingredient, binder and electron-conducting agent components introduced into the acidic aqueous medium is preferably from 20 to 60% by weight of the total amount of the composition.
• the particles When the element M is in the form of particles, the particles have an oxide layer on at least a part of their surface.
• the pH of the composition containing them must be sufficiently acidic so that the oxide on the surface of the M particles is substantially in the form of MOH groups and the reactive functions of the polymer acting as a binder are substantially in the form of of groups COOH, NH 2 , PO 3 H 2 , Si- (OH) 3 , and SO 3 H.
• the aqueous acidic medium can be obtained by adding to the water either a strong acid in an amount sufficient to obtain an initial pH of 1, or using an aqueous solution buffered at a pH of less than or equal to 4.
• the buffered aqueous solution is obtained adding to the water a mixture of organic acid and a strong base in sufficient quantity.
• organic acid / strong base it is particularly advantageous to use an "organic acid / strong base" mixture, which makes it possible to maintain the pH constant during the conversion of the oxide of M into MOH so as to keep the reactive groups of the binder polymer in acid form.
• the simple addition of a strong acid would involve the use of larger initial amounts of acid, which would have the disadvantage of causing irreversible degradation of the various constituents of the electrode and the current collector when the material is used as a material.
• the strong base is advantageously an alkali metal hydroxide.
• the organic acid is chosen from weak acids, in particular glycine, aspartic acid, bromoethanoic acid, bromobenzoic acid, chloroethanoic acid, dichloroethanoic acid, trichloroethanoic acid and lactic acid. , maleic acid, malonic acid, phthalic acid, isophthalic acid, terephthalic acid, picric acid, salicylic acid, formic acid, acetic acid, oxalic acid , malic acid, fumaric acid and citric acid. Citric acid is particularly preferred.
• a negative electrode according to the present invention consists of a composite material on a conductive substrate. It is developed by applying to said conductive substrate, a composition according to the present invention as defined above, and then drying the deposited composition.
• the conductive substrate intended to form the current collector of the electrode, is preferably a sheet of a conductive material, for example a sheet of copper, nickel or stainless steel. Copper is particularly preferred.
• the drying can be carried out by a process comprising a step of drying in air at room temperature, then a drying step under vacuum with heating at a temperature between 70 and 150 ° C. A temperature of about 100 ° C. is preferred.
• the resulting electrode comprises a layer of composite material on a conductive substrate serving as a collector.
• the conductive substrate is as defined above.
• the proportions of the constituents of the composite material are such that: 30 to 90% by weight of particles of active material; 5 to 40% by weight of binder;
• the element M of the initial composition is Si, so that the active material of the composite electrode is Si.
• the element M is in the form of nanoparticles.
• Particularly preferred are compositions in which the element M is Si in the form of nanoparticles.
• compositions are:
• the electrode composite material according to the invention has improved properties, in particular as regards the mechanical strength, the resistance to degradation by an electrolyte, and the thickness of the passivation layer on the active material.
• a lithium-ion battery comprising an electrode according to the present invention is another object of the present invention.
• a lithium-ion battery according to the present invention comprises at least one negative electrode and at least one positive electrode between which is placed a solid electrolyte (polymer or vitreous) or a separator impregnated with a liquid electrolyte. It is characterized in that the negative electrode is an electrode according to the invention.
• the positive electrode is constituted by a current collector carrying a material capable of reversibly inserting lithium ions at a potential greater than that of the material of the negative electrode.
• This material is generally used in the form of a composite material further comprising a binder and an agent generating an electronic conductivity.
• the binder and the electronic conductivity agent may be selected from those mentioned for the negative electrode.
• the material capable of reversibly inserting the lithium ions at the positive electrode is preferably a material which has an electrochemical potential greater than 2 V relative to the lithium pair, and is advantageously chosen from: transition metal oxides having a spinel type of structure LiM 2 O 4, and transition metal oxides with layered structure type LiMO 2 wherein M represents at least one metal selected from the group consisting of Mn, Fe, Co, Ni Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B and Mo; - the oxides polyanionic structural LiM type y (XO z) n wherein M represents at least one metal selected from the group consisting of Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba , Ti, Al, Si, B and Mo and X represents an element selected from the group consisting of P, Si, Ge, S and As.
• Vanadium oxides Vanadium oxides.
• the oxides with a spinel structure of LiM 2 O 4 type those in which M represents at least one metal chosen from Mn and Ni are preferred.
• the oxides with lamellar structure of LiMO 2 type those in which M represents at least one metal chosen from Mn, Co and Ni are preferred.
• the polyanionic framework oxides of LiM type y (XO z ) n particularly preferred are the olivine structure-containing phosphates, the composition of which corresponds to the formula LiMPO 4 in which M represents at least one element selected from Mn, Fe, Co and Ni). LiFePO 4 is preferred.
• the electrolyte consists of a lithium salt dissolved in a solvent chosen to optimize the transport and dissociation of the ions.
• the lithium salt may be selected from LiPF 6, LiAsF 6, LiClO 4, LiBF 4, LiC 4 BO 8, Li (C 2 F 5 SO 2) 2 N, Li [(C 2 F 5) 3 PF 3] LiCF 3 SO 3 , LiCH 3 SO 3 , LiN (SO 2 CF 3 ) 2 , and LiN (SO 2 F) 2 ,
• the solvent may be a liquid solvent comprising one or more aprotic polar compounds selected from linear or cyclic carbonates, linear or cyclic ethers, linear or cyclic esters, linear or cyclic sulfones, sulfonamides and nitriles.
• the solvent is preferably at least two carbonates selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and methyl and ethyl carbonate.
• the solvent of the electrolyte may further be a solvating polymer.
• solvating polymers mention may be made of polyethers of linear structure, comb or block, forming or not a network, based on poly (ethylene oxide); copolymers containing the ethylene oxide or propylene oxide or allylglycidyl ether unit; polyphosphazenes; crosslinked networks based on polyethylene glycol crosslinked with isocyanates; copolymers of oxyethylene and of epichlorohydrin as described in FR-9712952; and the networks obtained by polycondensation and bearing 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 further contain a mixture of a polar aprotic liquid compound selected from the aprotic polar compounds mentioned above and a solvating polymer. It may comprise from 2 to 98% by volume of liquid solvent, depending on whether a plasticized electrolyte with a low content of polar aprotic compound or a gelled electrolyte with a high content of polar aprotic compound is desired.
• the lithium salt is optional.
• the solvent of the electrolyte may also contain a non-solvating polar polymer comprising units containing at least one heteroatom selected from sulfur, oxygen, nitrogen and fluorine.
• a non-solvating polymer may be chosen from homopolymers and copolymers of acrylonitrile, homopolymers and copolymers of fluorovinylidene, and homopolymers and copolymers of N-vinylpyrrolidone.
• the nonsolvating polymer may also be a polymer bearing ionic substituents, and in particular a polyperfluoroether sulfonate salt (such as a Nafion® mentioned above for example) or a polystyrene sulphonate salt.
• the electrolyte contains a nonsolvating polymer, it is necessary that it also contains at least one polar aprotic compound as defined above or at least one solvating polymer as defined above.
• nanoscale silicon in the form of particles having an average size of 100 nm and a purity of 99.999%, supplied by Alfa Aesar were used; micrometric silicon in the form of particles having an average size of 5 ⁇ m and a purity of 99.999%, supplied by Alfa Aesar; a CMC carboxymethylcellulose having a degree of substitution of protons by CH 2 CO 2 groups Na (DS) of 0.7 and a weight average molecular weight M w of 90,000, supplied by Aldrich.
• Example 1 Preparing a battery
• Buffered acid solution at pH 3 was prepared by dissolving in 100 mL of water, 3.842 g of citric acid and 0.402 g of KOH. T is the buffer concentration of this solution. 0.5 ml of this solution was dispersed 160 mg of nanoscale silicon, 16 mg of CMC and 24 mg of acetylene black. The dispersion was carried out using a ball mill (Pulverisette
• Fritsch which has a 12.5 mL grinding bowl containing 3 beads of 10 mm diameter, for 1 hr at 500 rpm.
• the initial composition thus obtained consists of 72.4% by weight of silicon particles 7.2% by weight of CMC binder, 10.8% by weight of acetylene black, 8.7% by weight of citric acid and 0.9% by weight of KOH.
• the entire initial composition was applied to a copper current collector having a thickness of 25 ⁇ m and an area of 10 cm 2 . It was then dried at ambient temperature for 12 hours and then at 100 ° C. under vacuum for 2 hours.
• the layer of composite material deposited on the current collector has a thickness of 10-20 ⁇ m, which corresponds to a quantity of silicon of 1-2 mg / cm 2 .
• the composite material obtained after drying has the following composition:
• the electrode thus obtained was mounted in a battery (designated by battery D) having as positive electrode a lithium metal sheet laminated on a nickel current collector, a fiberglass separator, a liquid electrolyte consisting of a solution 1M LiPF 6 dissolved in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC), EC / DMC 1/1.
• battery D a battery having as positive electrode a lithium metal sheet laminated on a nickel current collector, a fiberglass separator, a liquid electrolyte consisting of a solution 1M LiPF 6 dissolved in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC), EC / DMC 1/1.
• the cycling performance of the 4 batteries assembled according to the procedure of Example 1 were evaluated in cycling.
• the cycling was carried out with a constant specific capacity limited to 1200 mAh / g Si in the 0-1 V potential range.
• Li + / Li It was driven in static galvano current mode at a current I of 900 mA / g which corresponds to a regime of C, according to which each charge and discharge takes place in 1 hour.
• FIG. 1 shows the evolution of the capacitance and the faradic efficiency during the charge / discharge cycles, during a cycling of the battery (D) according to the invention.
• the specific capacitance CS in mAh / g and the coulombic efficiency in% are given as a function of the number of cycles N.
• the respective curves are as follows: m CS during a discharge, D CS during a charge, 0 output Faraday.
• FIG. 2 compares the evolution of the specific discharge capacity (CSD in mA / h) as a function of the number N, during cycling of the batteries (A), (B), (C) and (D). It shows the substantial improvement provided by a pH buffered to 3 compared to a pH of 7, for both micrometric particles and nanoscale particles.
• the correspondence between the curves and the batteries is as follows: o D battery m battery C 0 battery B • battery A
• the cycling performance of the 4 batteries assembled according to the procedure of Example 1 were evaluated in cycling without capacity limitation, in the range of 0-1 V vs. potential. Li + / Li.
• the cycling was controlled in galvanostatic current mode at a current I of 120 mA / g which corresponds to a regime of C / 7.5, according to which each charge and discharge takes place in 7.5 hours.
• FIG. 3 compares the evolution of the specific discharge capacity (CSD in mA / h) as a function of the number N, during cycling of the batteries (A), (B), (C) and
• the batteries were prepared at acidic pH, using a strong H 2 SO 4 acid and not a buffer.
• the batteries thus prepared have been studied in cycling, with limitation of capacity, according to the detailed protocol below.
• An unbuffered acid solution at pH 1 was prepared by dissolving in
• the entire initial composition was applied to a copper current collector having a thickness of 25 ⁇ m and an area of 10 cm 2 . It was then dried at ambient temperature for 12 hours and then at 100 ° C. under vacuum for 2 hours.
• the layer of composite material deposited on the current collector has a thickness of 10-20 .mu.m, which corresponds to a quantity of silicon of 1-2 mg / cm 2 .
• the electrode thus obtained (denoted by battery E) was mounted in batteries having, as positive electrode, a lithium metal sheet laminated on a nickel current collector, a fiberglass separator, a liquid electrolyte constituted by a solution 1M LiPF 6 dissolved in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC), EC / DMC 1/1.
• batteries having, as positive electrode, a lithium metal sheet laminated on a nickel current collector, a fiberglass separator, a liquid electrolyte constituted by a solution 1M LiPF 6 dissolved in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC), EC / DMC 1/1.
• the cycling performance of the 3 assembled batteries was evaluated in cycling.
• the cycling was carried out with a constant specific capacity limited to 1200 mAh / g Si in the 0-1 V potential range. Li + / Li. It was driven in static galvano current mode at a current I of 900 mA / g which corresponds to a regime of C, according to which each charge and discharge takes place in 1 hour.
• FIG. 4 compares the evolution of the specific discharge capacity (CSD in mA / h) as a function of the number N, during cycling of the batteries (E), (F), (G) and (A).
• the acidification leads to an improvement in performance, in the following order pH 1> pH 2> pH 3> pH 7.
• the correspondence between the curves and the batteries is as follows:
• FIG. 4 shows that the best performances are nevertheless obtained by using a mixture of citric acid and a strong base which makes it possible to buffer at pH 3 (battery D of example 1).
• the batteries were prepared at acidic pH, using a citric acid and KOH buffer.
• the buffer concentration was varied to take the following values: T710, T / 4, T / 2, 3T / 4, 3T / 2, 2T .
• Buffered acid solution at pH 3 was prepared by dissolving in 100 mL of water, 0.3842 g of citric acid and 0.0402 g of KOH.
• the buffer concentration of this solution is T710, because it is equal to 1/10 of the buffer concentration of the solution prepared in Example 1, the concentration of which has been noted T.
• TY10 160 mg of nanoscale silicon 16 mg of CMC and 24 mg of acetylene black were dispersed.
• the dispersion was carried out using a ball mill (Fritsch Spray) which has a 12.5 mL milling bowl containing 3 beads of 10 mm diameter for 1 hour at 500 rpm.
• the initial composition thus obtained consists of 79.83% by weight of silicon particles 7.98% by weight of CMC binder, 11.97% by mass of acetylene black, 0.19% by weight of citric acid and 0.02% by weight of KOH.
• the entire initial composition was applied to a copper current collector having a thickness of 25 ⁇ m and an area of 10 cm. It was then dried at ambient temperature for 12 hours and then at 100 ° C. under vacuum for 2 hours.
• the layer of composite material deposited on the current collector has a thickness of 10-20 ⁇ m, which corresponds to a quantity of silicon of 1-2 mg / cm 2 .
• the composite material obtained after drying has the following composition:
• the electrode thus obtained was mounted in a battery (designated battery H) having as a positive electrode a lithium metal sheet laminated on a copper current collector, a fiberglass separator, a liquid electrolyte consisting of a solution 1M LiPF 6 dissolved in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC), EC / DMC 1/1.
• a battery designated battery H having as a positive electrode a lithium metal sheet laminated on a copper current collector, a fiberglass separator, a liquid electrolyte consisting of a solution 1M LiPF 6 dissolved in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC), EC / DMC 1/1.
• the performance of the battery H has been evaluated in cycling.
• the cycling was carried out with a constant specific capacity limited to 1200 mAh / g Si in the 0-1 V potential range.
• Li + / Li It was driven in galvanostatic current mode at a current I of 900 mA / g which corresponds to a regime of C, according to which each charge and discharge takes place in 1 hour.
• the table below gives, for each of the tested batteries, the actual mAh / g electrode capacity, the number of cycles with constant specific capacity held by each battery and the average faradic efficiency during the charge / discharge cycles, during Cycling of the battery (H) and batteries (I), (J), (K), (D, Example 1), (L) and (M) according to the invention and A (neutral pH, unmodified). ).
• the amount of organic acid must be such that it corresponds to a content greater than 0.510 -4 mol per gram of element M, preferably a content of greater than 5.10 -4 mol per gram of element M because below this value the performance improvement is less interesting, and it is preferable that the mass ratio organic acid + strong base organic acid + strong base + M + binder + electronic conduction agent remains less than or equal to 10% because beyond this value there is no significant improvement in performance.
• the batteries were prepared at acidic pH, using an organic acid buffer and KOH.
• the organic acid being: aspartic acid (buffer pH 2), aspartic acid (buffer pH 3.9).
• Another battery was prepared with phosphoric mineral acid (buffer pH 3).
• Buffered acid solutions were prepared by dissolving in 10O mL water, some organic acid or mineral acid and some KOH. 0.5 ml of this solution was dispersed 160 mg of nanoscale silicon, 16 mg of CMC and 24 mg of acetylene black. The dispersion was carried out using a ball mill (Fritsch Spray) which has a 12.5 mL milling bowl containing 3 beads of 10 mm diameter for 1 hour at 500 rpm.
• the acid is either the organic aspartic acid (pH 2 buffer or pH 4 buffer) or the phosphoric mineral acid (pH 3 buffer).
• the entire initial composition was applied to a copper current collector having a thickness of 25 ⁇ m and an area of 10 cm 2 . It was then dried at ambient temperature for 12 hours and then at 100 ° C. under vacuum for 2 hours.
• the layer of composite material deposited on the current collector has a thickness of 10-20 ⁇ m, which corresponds to a quantity of silicon of 1-2 mg / cm 2 .
• the electrodes thus obtained were mounted in a battery having, as positive electrode, a metal lithium sheet laminated on a copper current collector, a fiberglass separator, a liquid electrolyte consisting of a 1M LiPF 6 solution dissolved in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC), EC / DMC 1/1.
• EC ethylene carbonate
• DMC dimethyl carbonate
• FIG. 5 compares the evolution of the specific discharge capacity (CSD in mA / h) as a function of the number N, during cycling of the batteries (D), (N), (O) and (P).
• Example 2 a battery was prepared according to Example 1 with the difference that the drying temperature is not 100 ° C., but 150 ° C.
• the entire initial composition was applied to a copper current collector having a thickness of 25 ⁇ m and an area of 10 cm. It was then dried at ambient temperature for 12 hours and then at 100 ° C. under vacuum for 2 hours.
• the layer of composite material deposited on the current collector has a thickness of 10-20 microns, which corresponds to a silicon amount of 1-2 mg / cm.
• the composite material obtained after drying has the following composition:
• the electrode thus obtained was mounted in a battery (designated Q battery) having as positive electrode a lithium metal sheet laminated on a nickel current collector, a fiberglass separator, a liquid electrolyte consisting of a solution 1M LiPF 6 dissolved in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC), EC / DMC 1/1.
• a battery designated Q battery having as positive electrode a lithium metal sheet laminated on a nickel current collector, a fiberglass separator, a liquid electrolyte consisting of a solution 1M LiPF 6 dissolved in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC), EC / DMC 1/1.
• the cycling performance of the battery was evaluated during cycling.
• the cycling was carried out with a constant specific capacity limited to 1200 mAh / g Si in the 0-1 V potential range. Li + / Li. It was driven in galvanostatic current mode at a current I of 900 mA / g which corresponds to a regime of C, according to which each charge and discharge takes place in 1 hour.
• FIG. 6 shows the evolution of the capacitance and the faradic efficiency during the charge / discharge cycles, during a cycling of the battery (D) according to the invention.
• the specific capacitance CS in mAh / g is given as a function of the number of cycles N. The respective curves are as follows:

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• 2009
  • 2009-01-30 FR FR0900410A patent/FR2941817B1/fr not_active Expired - Fee Related
• 2010
  • 2010-01-28 CA CA2750743A patent/CA2750743A1/fr not_active Abandoned
  • 2010-01-28 CN CN2010800099290A patent/CN102341938A/zh active Pending
  • 2010-01-28 WO PCT/FR2010/050135 patent/WO2010086558A1/fr active Application Filing
  • 2010-01-28 JP JP2011546923A patent/JP2012516531A/ja active Pending
  • 2010-01-28 EP EP10707608A patent/EP2392043A1/de not_active Withdrawn
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