Coated metal oxide particles with low dissolution rate, methods for preparing same and use thereof in electrochemical systems

Abstract

Particles comprising a core and a coat covering at least part of the core surface. The core has more than 50% of an acidic metal oxide and the core coating is based on a polymer, preferably based on a soiled polymer with high electrochemical stability. The particle has a solubility rate (ts), in fixed time, of the metal oxide migrating towards the electrolyte, per cycle, which is less than 5 per 10000. The particles are obtained by mixing the polymer and a metal oxide, via dry process with addition of solvent. The electrodes constituting an electrode substrate at least partly coated with a mixture consisting of at least 40 of those particles have remarkable electrochemical properties, in particular regarding the lifetime of batteries in which they are incorporated.

1 . A particle comprising a core and a coating that covers at least part, preferably at least 80%, even more preferentially at least 90% and most advantageously 100% of the surface of said core, wherein:
 said core is preferably composed to at least 90% and even more preferentially to at least 94% by weight of an acidic metal oxide, with a pH preferably of less than 6.5, and even more preferentially with a pH of between 3 and 6;   the coating of the core being based on a polymer, preferably based on a salified polymer, whose electrochemical stability is greater than or equal to 3.7 volts;   the mean thickness of the coating is preferentially between 500 nanometers and 2 micrometers and the coated core has a mean size d 50  preferably of between 500 nanometers and 40 micrometers, and even more preferentially this size is between 2 and 20 micrometers; and   the degree of solubility (ds), for a given time, of the metal oxide migrating toward the electrolyte, per cycle, is less than 5 per 10 000, and this degree is preferably between 2 and 4.5 per 10 000.   
     
     
         2 . The particle as claimed in  claim 1 , wherein the polymer used to prepare the coating is chemically stable. 
     
     
         3 . The particle as claimed in  claim 2 , wherein the polymer used to prepare the coating is chemically very stable. 
     
     
         4 . The particle as claimed in  claim 3 , wherein the polymer used to prepare the coating is chemically extremely stable. 
     
     
         5 . The particle as claimed in  claim 4 , wherein the electrochemical stability of the polymer used for the coating is between 3.75 and 5 volts. 
     
     
         6 . The particle as claimed in  claim 1 , in which the metal oxide is chosen from the group constituted by LiMn 2 O 4 , V 2 O 5 , LiMn (2-x) V x O 4  with x ranging from 0 to 1 limits inclusive, V 6 O 13  and LiV 3 O 8  and the metal oxide is more preferentially LiV 3 O 8 . 
     
     
         7 . The particle as claimed in  claim 1 , in which the core of the particle comprises from 1% to 12% and preferably from 6% to 10% by weight of a carbon preferably chosen from the group constituted by ethylene black, natural graphite, artificial graphite, Shawinigan carbon, Ketjen carbon, and mixtures of at least two thereof. 
     
     
         8 . The particle as claimed in  claim 1 , in which the core coating is based on:
 one or more salified polymers, preferably based on at least one polymer salified with at least one salt chosen from the group constituted by salts of the type LiFSI, LiTFSI, LiBETI, LiDCTA, LiBF 4  and LiPF 6 ; and   10% maximum of fillers preferably chosen from the group constituted by SiO 2 , ZrO 2  and Al 2 O 3 , and mixtures of at least two thereof.   
     
     
         9 . The particle as claimed in  claim 1 , in which the polymer constituting the coating is electrically conductive, and is preferably based on a polymer chosen from the group constituted by polyanilines, preferably from the group of polyanilines with an average molecular weight of greater than 1000 and preferably between 2500 and 50 000. 
     
     
         10 . The particle as claimed in  claim 1 , in which the polymer constituting the coating is electrically nonconductive and is preferably chosen from the group constituted by nonconductive polymers of multibranch type. 
     
     
         11 . The particle as claimed in  claim 10 , in which the electrically nonconductive polymer contains at least 3 branches, and is even more preferentially of 4-branch type, such as those described in international patent application WO 03/063 287 (and more particularly on pages 5, 8 and 9), filed in the name of Hydro-Quebec, and also in columns 1 and 2 of American patent U.S. Pat. No. 6,190,804 and which have acrylate (preferably methacrylate) and alkoxy (preferably alkoxy containing from 1 to 8 carbon atoms, even more preferentially methoxy or ethoxy), or vinyl hybrid end groups. 
     
     
         12 . The particle as claimed in  claim 1 , in which the metal oxide is a (50:50) mixture of LiV 3 O 8  and V 2 O 5 . 
     
     
         13 . The particle as claimed in  claim 1 , comprising an LiV 3 08 metal oxide core 5 microns in size, covered over 80% of its surface with a coating constituted by the polymer of 4-branch type and with a mean thickness of between 10 nanometers and 5 micrometers and preferably between 15 nanometers and 2 micrometers, comprising a ds of less than 5%. 
     
     
         14 . The particle as claimed in  claim 1 , comprising a V 2 O 5  metal oxide core 5 micrometers in size, covered over 80% of its surface with a coating constituted by the polymer 4B and with a mean thickness of between 10 nanometers and 5 micrometers and preferably between 15 nanometers and 2 micrometers, comprising a ds of less than 4%. 
     
     
         15 . A process for preparing a homogeneous mixture of particles as claimed in  claim 1 , by preparation of a mixture of the polymer and of a metal oxide, via the dry route without any addition of solvent, preferably in weight proportions of from 10% to 90% and preferably from 40% to 80% for each of the constituents of the mixture, the amount of metal oxide present in the mixture preferably being greater than that of the polymer. 
     
     
         16 . A process for preparing a homogeneous mixture of particles as claimed in  claim 1 , in which the mixing is performed:
 by preparing a mixture of the polymer and of a metal oxide, preferably in weight proportions of from 10% to 90% and preferably from 40% to 80% for each of the constituents of the mixture; preferably, the amount of metal oxide present in the mixture is greater than that of the polymer; and   with addition to the solvent of at least one solvent chosen from the group constituted by acetone, acetonitrile, toluene, MEK, NMP or mixtures of at least two thereof; preferably, the solvent used represents by volume from 10% to 80% and more preferentially from 20% to 70% of the total volume of the solvent and of the mixture   
     
     
         17 . The process as claimed in  claim 15 , in which the mixing is performed by ball milling, sand milling, HEBM, mechanofusion, in an Agglomaster or Nobita® mixer, or by using at least two of these techniques and preferably at a temperature of between 10 and 40° C., preferably in the presence of an inert gas chosen from the group constituted by nitrogen, argon or dry air. 
     
     
         18 . An electrode constituted by an electrode support, said support preferably being made of a metallic material or of a conductive plastic material, and at least partially covered, preferably homogeneously, with a mixture constituted by at least 40% and preferably from 50% to 80% by weight of particles comprising a core and a coating that covers at least part, preferably at least 80%, even more preferentially at least 90% and most advantageously 100% of the surface of said core, wherein:
 said core is preferably composed to at least 90% and even more preferentially to at least 94% by weight of an acidic metal oxide, with a pH preferably of less than 6.5, and even more Preferentially with a pH of between 3 and 6;   the coating of the core being based on a polymer, preferably based on a salified polymer, whose electrochemical stability is greater than or equal to 3.7 volts;   the mean thickness of the coating is preferentially between 500 nanometers and 2 micrometers and the coated core has a mean size d 50  preferably of between 500 nanometers and 40 micrometers, and even more preferentially this size is between 2 and 20 micrometers; and   
       the degree of solubility (ds), for a given time, of the metal oxide migrating toward the electrolyte, per cycle, is less than 5 per 10 000, and this degree is preferably between 2 and 4.5 per 10 000 or obtained by process defined in  claim 15 . 
     
     
         19 . The electrode as claimed in  claim 18 , in which at least one polymer is a binder for said electrode by creating bridges between the electrode support, the metal oxide-based particles and the polymer-based coating 
     
     
         20 . The electrode as claimed in  claim 19 , in which the binding polymer is a mixture of a coating polymer of high stability and of binding nature and of a polymer that ensures binding between the particles of the cathode and that is other than the polymer present in the coating. 
     
     
         21 . The electrode as claimed in  claim 19 , in which the binding polymer consists solely of the coating polymer of high electrochemical stability. 
     
     
         22 . The electrode as claimed in  claim 18 , comprising at least one polymer containing at least one lithium salt and at least one carbon with a specific surface area of greater than or equal to 1 m 2 /g, preferably at least one carbon with a specific surface area of greater than 50 m 2 /g. 
     
     
         23 . The electrode as claimed in  claim 22 , in which the (polymer-oxide-salt-carbon) mixture has been prepared without addition of solvent, preferably by using the doctor blade method and/or by extrusion. 
     
     
         24 . The electrode as claimed in  claim 22 , in which the (polymer-oxide-salt-carbon) mixture has been prepared with addition of a solvent preferably chosen from the group constituted by acetone, acetonitrile, toluene, MEK, VC, DEC, DMC, EMC, DME or mixtures of at least two thereof, preferably by using the doctor blade method and/or by extrusion. 
     
     
         25 . The electrode as claimed in  claim 23 , in which the composition of the polymer represents from 1% to 70% by weight relative to the total weight of the (polymer+salt+oxide+carbon) mixture. 
     
     
         26 . The electrode as claimed in  claim 25 , in which the composition of the carbon represents from 1% to 10% by weight relative to the total weight of the (polymer+salt+oxide+carbon) mixture. 
     
     
         27 . The electrode as claimed in  claim 18 , in which the concentration of the salt, present in the (polymer-oxide-salt-carbon) mixture, and expressed relative to the polymer, is between 0.1 M and 3 M and preferably between 0.7 M and 2 M. 
     
     
         28 . The electrode as claimed in  claim 18 , in which the carbon, present in the (polymer-oxide-salt-carbon) mixture, is a mixture of a first carbon of graphite nature with a specific surface area of less than 50 m 2 /g and of a second carbon of non-graphite type with a large surface area, the specific surface area of which is greater than 50 m 2 /g, the specific surface area being measured according to the BET method. 
     
     
         29 . The electrode as claimed in  claim 18 , in which the carbon is of VGCF carbon fiber, Ex mesophase or PAN (polyacrylonitrile) type. 
     
     
         30 . The electrode as claimed in  claim 29 , in which the salt is dissolved in the polymer and it is chosen from the group constituted by LiFSI, LiTFSI, LiBETI and LiPF 6  and mixtures of at least two thereof. 
     
     
         31 . A process for preparing an electrode as claimed in  claim 18 , in which an oxide-polymer-salt-carbon liquid mixture is spread onto a current collector of metal type by extrusion or with a doctor blade, slot die or coma. 
     
     
         32 . The process for preparing an electrode as claimed in  claim 31 , in which the polymer is of the four-branch type preferably with at least two branches capable of giving rise to crosslinking, and it is converted into a polymer matrix, optionally in the presence of an organic solvent, by crosslinking after spreading the mixture onto the electrode support. 
     
     
         33 . The process for preparing an electrode as claimed in  claim 32 , in which the crosslinking is performed without addition of a crosslinking agent other than the metal oxide. 
     
     
         34 . A process for preparing an electrochemical generator comprising at least one anode, at least one cathode and an electrolyte, in which at least one of the electrodes is as defined in  claim 18 . 
     
     
         35 . The process for preparing an electrochemical generator as claimed in  claim 34 , in which the electrochemical generator is of the lithium generator type and the spread cathode is introduced into said lithium generator with a dry polymer as electrolyte, the battery not containing any liquid solvent. 
     
     
         36 . The process for preparing an electrochemical generator as claimed in  claim 35 , in which the electrolyte is constituted of the same material as the binder and as the coating. 
     
     
         37 . The process for preparing an electrochemical generator as claimed in  claim 35 , in which the electrolyte is constituted of a material other than that which constitutes the binder and/or the coating. 
     
     
         38 . The process for preparing an electrochemical generator as claimed in  claim 34 , in which the electrolyte also acts as separator and is constituted by a dry polymer with an electrochemical stability of greater than 3.7 volts. 
     
     
         39 . The process for preparing an electrochemical generator as claimed in  claim 34 , in which the electrolyte also acts as separator and is constituted by a dry polymer with an electrochemical stability of less than 3.7 volts. 
     
     
         40 . The process for preparing an electrochemical generator as claimed in  claim 34 , in which the anode is of lithium or lithium alloy or carbon, graphite, carbon fiber, Li 4 Ti 5 O 12  or WO 2  type, preferably lithium metal or slightly alloyed lithium. 
     
     
         41 . The process for preparing an electrochemical generator as claimed in  claim 40 , in which the lithium is alloyed with Al, Sn, carbon, Si or Mg and the content of alloyed metals is greater than 50 ppm and preferably greater than 500 ppm. 
     
     
         42 . An electrochemical generator obtained by performing one of the processes as claimed in  claim 31 . 
     
     
         43 . An electrochemical generator containing at least one constituent element comprising particles comprising a core and a coating that covers at least part, preferably at least 80%, even more preferentially at least 90% and most advantageously 100% of the surface of said core, wherein:
 said core is preferably composed to at least 90% and even more preferentially to at least 94% by weight of an acidic metal oxide, with a pH preferably of less than 6.5, and even more preferentially with a pH of between 3 and 6;   the coating of the core being based on a polymer, preferably based on a salified polymer, whose electrochemical stability is greater than or equal to 3.7 volts;   the mean thickness of the coating is preferentially between 500 nanometers and 2 micrometers and the coated core has a mean size d 50  preferably of between 500 nanometers and 40 micrometers, and even more preferentially this size is between 2 and 20 micrometers; and   
       the degree of solubility (ds), for a given time, of the metal oxide migrating toward the electrolyte, per cycle, is less than 5 per 10 000, and this degree is preferably between 2 and 4.5 per 10 000 or as obtained by performing a process as claimed in  claim 15 . 
     
     
         44 . A generator obtained by performing one of the processes defined in  claim 36 . 
     
     
         45 . The use of a generator as claimed in  claim 44  in an electrical vehicle, in a hybrid vehicle, in telecommunications, in UPSs and in electrochromic devices. 
     
     
         46 . The process for preparing an electrode as claimed in  claim 31 , in which the polymer is of EG type, preferably with at least two branches capable of giving rise to crosslinking, and said polymer is converted into a polymer matrix, optionally in the presence of an organic solvent, by crosslinking after spreading the mixture onto the electrode support. 
     
     
         47 . A process for reducing the solubility of metal oxides in electrochemical systems, which consists in increasing the pH of the oxide, preferentially by selecting the nature and the amount of the carbon mixed with the oxide particles, more particularly by coating the oxide particles with a polymer, based on PEO, polyacrylonitrile, PMMA and/or PVC dissolved in a solvent (acetonitrile, water, acetone, methanol, etc) and then by drying the composition and carbonizing it at a temperature of about 600-700° C., under an inert atmosphere for 8-12 hours; the amount and type of the polymer used being linked to the residual content of carbon present at the surface of the oxide particles, and the mixing of the oxide and the polymer solution possibly being advantageously performed with a jar mill, a bar mill or a paint mixer. 
     
     
         48 . A process for preparing an electrochemical generator comprising at least one anode, at least one cathode and an electrolyte, as obtained by one of the processes defined in  claim 31 . 
     
     
         49 . A generator obtained by performing one of the processes as defined in  claim 42 .