The present invention relates to the field of lithium batteries, and more particularly lithium-polymer batteries and “All Solid” batteries. These batteries can involve in the electrolyte alkaline cations such as Na or Li, alkaline earth cations such as Ca or Mg or finally aluminum.

More particularly, the invention relates to a solid polymer electrolyte in the form of an organic-organic composite material, intended for use in such a battery. The invention also relates to a method of manufacturing such an electrolyte. This electrolyte is intended in particular for the production of a lithium-polymer battery, of a so-called “All Solid” battery, in particular as regards the ionic conductive separator. The invention therefore further relates to a battery separator comprising such a polymer electrolyte, to its manufacturing processes and to the battery incorporating this electrolyte.

TECHNICAL BACKGROUND

Conventional lithium-ion batteries include flammable liquid electrolytes based on solvents and lithium salts. Faced with the increasing use of this type of batteries in the field of electronic consumer products such as computers, tablets or mobile phones (smartphones), but also in the field of transport with in particular electric vehicles, the improvement safety and reducing the cost of manufacturing these lithium batteries have become major issues.

To solve this problem, lithium-polymer batteries, comprising solid polymer electrolytes, also denoted SPEs (acronym for “Solid Polymer Electrolytes”), replacing flammable liquid electrolytes, have been studied for several years. The solid polymer electrolytes SPEs, without liquid solvent, thus avoid the use of flammable liquid components as in conventional Li-ion batteries and allow the realization of thinner and more flexible batteries.

Despite their low intrinsic ionic conductivity, SPEs have shown great potential both for small-scale applications, such as three-dimensional micro batteries for example, and for large-scale energy storage applications, such as for electric vehicles. .

Currently, the most well-known polymers used as solid electrolyte polymers are polyethers, such as, for example, poly (ethylene oxide), also noted POE. However, these polymers have the drawback of easily crystallizing, especially at temperatures close to room temperature, which has the effect of very significantly reducing the ionic conductivity of the polymer. This is why these polymers only allow the battery in which they are inserted to be used at a minimum temperature of 60 ° C. However, it would be appropriate to be able to use such a battery at ambient temperature and even at negative temperature. In addition, these POEs are very hydrophilic and have a tendency to plasticize, especially in the presence of lithium salts, which reduces their mechanical stability.

Aliphatic polycarbonates have also been studied as a host polymer matrix for SPEs. To this end, cyclic carbonates can be ring-opened polymerized to create solid state linear macromolecular carbonates. Such ethylene carbonate polymers have been prepared and successfully used as conductive electrolytes for lithium Li + ions , although the stability of 5-atom cyclic carbonates, such as ethylene carbonate, make them suitable candidates. less ideal for controlled polymerization. The polymerization of ethylene carbonate is in fact accompanied by decarboxylation, resulting in a copolymer of carbonate and of ethylene oxide. [G. Rokicki et al., Prog. Polym. Sci. 25 (2000) 259-342]

The article by D. Brandell, Solid State Ionics 262 (2014) 738-742, describes the preparation of poly (trimethylene carbonate), also noted PTMC, by mass polymerization, by ring opening of the trimethylene carbonate (TMC) monomer. , initiated with tin di-octanoate. The polymer obtained has a molecular mass of 368,000 g / mol, a polydispersity of 1.36 and contains less than 7% of residual monomer. Such a polymer is amorphous and exhibits a relatively low glass transition temperature of -15 ° C. Likewise, in the article published in Journal of Power sources 298 (2015) 166-170, D. Brandell et al further describe that the copolymerization of caprolactone with trimethylene carbonate makes it possible to obtain an amorphous ionic conductive polymer, with a low glass transition temperature of -63.7 ° C. However, the polymers described in these documents remain dangerous for use as a solid polymer electrolyte for a battery. Indeed, the large amount of residual monomer presents a risk of flammability. Finally, the polymers described in these two documents have molecular masses in number much greater than 100,000 g / mol to avoid problems of mechanical stability, in particular at the level of the electrodes, so that they do not become detached from the metallic current collector. . However, the higher the polymer is of high molecular mass, the more it is to the detriment of the mobility of its chains and of its ionic conductivity. Finally, the polymers described in these two documents have molecular masses in number much greater than 100,000 g / mol to avoid problems of mechanical stability, in particular at the level of the electrodes, so that they do not become detached from the metallic current collector. . However, the higher the polymer is of high molecular mass, the more it is to the detriment of the mobility of its chains and of its ionic conductivity. Finally, the polymers described in these two documents have molecular masses in number much greater than 100,000 g / mol to avoid problems of mechanical stability, in particular at the level of the electrodes, so that they do not become detached from the metallic current collector. . However, the higher the polymer is of high molecular mass, the more it is to the detriment of the mobility of its chains and of its ionic conductivity.

Selective polymerization methods of a controlled and living nature making it possible, by organocatalysis, to obtain polyesters and polycarbonates which may or may not be copolymerized, have moreover been developed. In this case, the organo-catalyst is organic, such as AMS (methane sulfonic acid) or HOTf (trifluoromethane sulfonic acid), that is to say that the polymerization takes place without the introduction of derivatives metallic, such as tin salts.

Methane sulfonic acid (AMS) has been shown to be very effective in the polymerization of e-caprolactone (e-CL) or trimethylene carbonate (TMC), and trifluoromethane sulfonic acid (HOTf) is an organic catalyst of choice to achieve the controlled polymerization of b-butyrolactone.

Documents WO2008104723 and WO200810472 as well as the article entitled “Organo-catalyzed ROP of e-caprolactone: methanesulfonic acid competes with trifluoromethanesulfonic acid” Macromolecules 2008, Vol. 41, p. 3782-3784, in particular demonstrated the effectiveness of methanesulfonic acid as a catalyst for the polymerization of β-caprolactone. These documents also describe that in association with a protic initiator, of alcohol type, AMS is capable of promoting the controlled polymerization of the cyclic monomer of -caprolactone. In particular, the protic initiator allows fine control of the average molar masses as well as of the chain ends.

Oligomers possessing high ionic conductivity are known but they have no mechanical strength. Low glass transition temperatures (Tg) are sought to improve conductivity, but this comes at the expense of mechanical properties. Conversely, when these are better, it is either because the molar mass has been increased, or because the polymer has crystallinity.

The Applicant has therefore sought a solution for producing a solid polymer electrolyte exhibiting satisfactory ionic conductivity even at low temperature, that is to say at ambient temperature and even at negative temperature, typically at a temperature of between + 60 ° C. and -20 ° C, and to do this, it has chosen to separate the mechanical functions and the conduction functions.

The aim of the invention is therefore to remedy at least one of the drawbacks of the prior art. The invention aims in particular to provide a solid polymer electrolyte exhibiting satisfactory ionic conductivity even at low temperature, below 60 ° C and which can range down to -20 ° C.

For this, the conductive part of the electrolyte must have the lowest possible crystallinity and a glass transition temperature lower than the operating temperature of the battery for which it is intended. The polymer electrolyte material must also make it possible to produce electrodes which make it possible to have good cohesion of the particles, as well as good adhesion to the current collector.

The polymer electrolyte material must also make it possible to produce a separator having satisfactory electrochemical stability (potential depending on the cathode material used), and satisfactory ionic conductivity over the temperature range of use envisaged.

The invention further aims to provide a method of synthesizing such a material which is simple and quick to implement and inexpensive.

SUMMARY OF THE INVENTION

According to a first aspect, the invention relates to a solid polymer electrolyte intended for use in a battery operating at a temperature below 60 ° C, said electrolyte comprising:

- a thermoplastic polymer in the form of a porous film, said polymer having a molecular mass greater than 50,000 g / mol,

an oligomer impregnating said film of thermoplastic polymer, this oligomer being an ionic conductor, and

- one or more lithium salt (s).

According to one embodiment, the thermoplastic polymer is a compound of general formula: - [(CRiR 2 -CR 3 R 4 ) -] n where Ri, R 2 , R 3 and R 4 are independently H, F, CH 3 , Cl, Br, CF 3 , it being understood that at least one of these radicals is F or CF 3 .

According to one embodiment, the thermoplastic polymers are characterized by piezoelectric, ferroelectric, pyroelectric or ferroelectric relaxer properties.

The thermoplastic polymer entering into the solid polymer electrolyte composition is prepared in the form of a porous film.

The process for preparing said porous film comprising the following steps:

- providing an ink comprising the thermoplastic polymer and a vehicle comprising a solvent for said polymer and a non-solvent for said polymer, said solvent and said non-solvent being miscible with one another;

- the deposition of ink on a substrate;

- evaporation of the vehicle comprising the solvent and the non-solvent.

The solid polymer electrolyte according to the invention comprises an oligomer which impregnates the film of thermoplastic polymer. According to one embodiment, this ionically conductive oligomer carries at least one group having a physical or chemical affinity with the thermoplastic polymer.

The invention further relates to a separator for a lithium-polymer battery, said separator being characterized in that it comprises the solid polymer electrolyte described above.

Another subject of the invention is a lithium-polymer battery comprising a separator based on the solid polymer electrolyte described above, arranged between an anode made of lithium metal and a cathode.

According to another aspect, the invention relates to a lithium battery comprising a stack of layers, said stack comprising an anode preferably consisting of lithium metal, a cathode and a separator, said battery being characterized in that said separator comprises a polymer electrolyte solid as described above.

The present invention overcomes the drawbacks of the state of the art. It more particularly provides solid polymer electrolytes exhibiting satisfactory ionic conductivity even at low temperature.

This is achieved by using an organic-organic composite polymer material, consisting of a porous film of semi-crystalline thermoplastic polymer, which is impregnated with an ionically conductive oligomer having at least one function having an affinity for the thermoplastic polymer.

This type of polymer electrolyte is manufactured in a very simple, fast and inexpensive process. It is satisfied with operations of dissolution, drying and impregnation which can be done at very moderate temperatures.

The ionic conductivity of a polymer electrolyte is all the higher when the measurement is carried out at a temperature which is distant from and above the glass transition temperature of the thermoplastic polymer. Given the fact that the thermoplastic polymer backbone makes it possible to maintain the mechanical strength, the conduction and mechanical strength functions (mechanical modulus) are dissociated.

The solid polymer electrolyte of the invention ensures mechanical stability during the charge / discharge cycles of the battery, making it possible to maintain the cohesion of the electrode during the volume variations linked to the insertion / removal of the lithium, without compromising ionic conductivity with too long chains. Until now, to solve this problem of dimensional stability, in particular with POEs, it was necessary to produce polymers having very long chains and to ensure the mechanical stability of the electrode. However, this increase in the molecular mass of the polymer is done to the detriment of the mobility of its chains, and of its ionic conductivity.

Taking into account the dissociation of the mechanical and conduction functions, there are no longer any limitations due to these considerations.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention is described in detail below.

The invention relates to a solid polymer electrolyte for use in a battery operating at a temperature below 60 ° C, said electrolyte comprising:

• a thermoplastic polymer in the form of a porous film, said polymer having a molecular mass greater than 50,000 g / mol,

• an oligomer impregnating said thermoplastic polymer film, this oligomer being an ionic conductor, and

• one or more lithium salt (s).

Thermoplastic polymer film

The term “polymer” means a macromolecule consisting of a chain of one or more monomers, joined to each other by covalent bonds; this term here covers homopolymers, copolymers consisting of two different constituent units and copolymers consisting of three or more different constituent units. The term "thermoplastic polymer" as used refers to a polymer which transforms into a flowable, liquid or pasty fluid when heated and which can take on new forms by the application of heat and pressure. The thermoplastic polymer of the invention can be amorphous or semi-crystalline.

Advantageously, the thermoplastic polymer has good mechanical properties and can be crosslinked. The term “good mechanical properties” is understood to mean a Young's modulus at the maximum operating temperature of at least 1 MPa, preferably at least 10 MPa.

The thermoplastic polymer has a number average molecular weight greater than 50,000 g / mol. According to one embodiment, the thermoplastic polymer has a number-average molecular weight greater than 100,000 g / mol and preferably greater than 200,000 g / mol. The molecular weight can also be evaluated by measuring the melt index (10 minutes) at 230 ° C under a load of 10 kg according to ASTM D1238 (ISO 1133). The MFI measured under these conditions can be between 0.2 and 20 g / 10 minutes and preferably between 0.5 and 10 g / 10 minutes.

According to one embodiment, the thermoplastic polymer is a compound of general formula: [- (CR1R2-CR3R4H 11 where Ri, R2, R3 and R4 are independently H, F, CFL, Cl, Br, CF3, it being understood that the at least one of these radicals is F or CF3.

According to one embodiment, said thermoplastic polymer is a homopolymer of said monomer - (CR1R2-CR3R4) -. According to one embodiment, said thermoplastic polymer is the following homopolymer: [- (CH2-CF2H 11 ,

According to one embodiment, said thermoplastic polymer is a copolymer with two different constituent units or a terpolymer with three different constituent units or a copolymer with four or more different constituent units comprising units derived from said monomer and units derived from at least one. other comonomer. These copolymers with at least two different constituent units are random or block copolymers. In what follows, the term copolymer will be used to denote any copolymer consisting of at least two different constituent units.

According to one embodiment, the fluoropolymer is a polymer comprising units derived from vinylidene fluoride (VDF) as well as units derived from at least one other monomer of formula CXiX2 = CX3X4, in which each group Xi, X2, X3

and X4 is independently selected from H, Cl, F, Br, I and alkyl groups comprising from 1 to 3 carbon atoms, which are optionally partially or fully halogenated; and preferably the fluoropolymer comprises units derived from vinylidene fluoride and at least one monomer chosen from trifluoroethylene (TrFE), tetrafluoroethylene, chlorotrifluoroethylene (CTFE), 1,1-chlorofluoroethylene, hexafluoropropene, 3,3,3-trifluoropropene, 1, 3,3,3-tetrafluoropropene, 2,3,3,3-tetrafluoropropene, 1-chloro-3,3,3-trifluoropropene and 2-chloro-3, 3,3-trifluoropropene; and more preferably the fluoropolymer is chosen from poly (vinylidene-co-hexafluoropropene fluoride), poly (vinylidene-r -trifluoroethylene fluoride),

Preferably, the thermoplastic polymers and copolymers are semi-crystalline with degrees of crystallinity between 10 and 90% and preferably between 20 and 70%.

According to one embodiment, these thermoplastic polymers are characterized in that they have piezoelectric, ferroelectric, pyroelectric or ferroelectric relaxer properties.

According to one embodiment, such polymers are copolymers P (VDF-TrFE), the VDF / TrFE molar ratio of the structural units being between 9 and 0.1 and preferably being between 4 and 1.

A preferred example of copolymers are those of formula P (VDF-TrFE) and of 80/20 molar composition, which have a relative dielectric permittivity of the order of 9-12 measured at a frequency of 1 kHz and at room temperature.

According to another embodiment, such polymers are P terpolymers (VDF-TrFE-CTFE) in which the molar content of VDF varies from 40 to 95%, the molar content of TrFE varies from 5 to 60%, and the content molar of CTFE ranges from 0.5 to 20%.

A preferred example of terpolymers are those having a molar composition of 65/31/4 with a melting point (Mp) of 130 ° C and a relative dielectric permittivity equal to 60 to 50 ° C and 1 kHz.

Fe thermoplastic polymer forming part of the solid polymer electrolyte composition is prepared in the form of a porous film. For this, several techniques are possible but the Applicant has favored the solvent / non-solvent route.

The manufacture of the porous film of the invention comprises the following steps:

- providing an ink comprising the thermoplastic polymer and a vehicle comprising a solvent for said polymer and a non-solvent for said polymer, said solvent and said non-solvent being miscible with one another;

- the deposition of ink on a substrate;

- evaporation of the vehicle comprising the solvent and the non-solvent.

These last two steps are carried out at room temperature or close to room temperature and until the formation of a solid film. The deposition or “coating” processes are preferably coatings: by centrifugation (“spin-coating”), by spraying or atomization (“spray coating”), by coating in particular with a bar or a film puller ("Bar coating"), by coating with a slot-die coating, by immersion ("dip coating"), by roller printing ("roU-to-roU printing"), by printing in screen-printing, by flexographic printing, by lithography printing or by ink-jet printing.

The non-solvent is selected from the group consisting of benzyl alcohol, benzaldehyde, or a mixture thereof.

The solvent is selected from the group consisting of ketones, esters, especially cyclic esters, dimethylsulfoxide, phosphoric esters such as triethyl phosphate, carbonates, ethers such as tetrahydrofuran, and a mixture thereof, of preferably the solvent being chosen from the group consisting of ethyl acetate, methyl ethyl ketone, gamma-butyrolactone, triethyl phosphate, cyclopentanone, propylene glycol monomethyl ether acetate and a mixture of these.

According to one embodiment, the solvent is gamma-butyrolactone and the non-solvent is benzyl alcohol, or the solvent is ethyl acetate and the non-solvent is benzyl alcohol, or the solvent is methyl ethyl ketone and the non-solvent is benzyl alcohol.

The porous film thus obtained has pores having an average diameter of 0.1 to 10 µm, preferably 0.2 to 5 mm, more preferably 0.3 to 4 mm. The average pore diameter can be measured by scanning electron microscopy.

In terms of the actual preparation operations of the porous membranes, the above approach only counts the preparation of the ink, its deposition and its

drying, after which the porous membrane is formed. This method has the advantage of not requiring precipitation in water, which is a compound that can degrade the performance of membranes for electronic applications.

Ionic conductor oligomer

The solid polymer electrolyte according to the invention comprises an oligomer which impregnates the film of thermoplastic polymer.

An oligomer, or oligomer molecule, is an intermediate compound between a monomer and a polymer, the structure of which essentially comprises a small plurality of monomer units. An oligomer generally has a number of monomer units ranging from 5 to 100 and / or a number average molecular weight less than or equal to 5000 g / mole. The number of monomer units is most often less than 50, or even 30. The number-average molecular mass may in particular be less than 4000 g / mol, or 3000 g / mol, or else 2000 g / mol.

This oligomer is an ionic conductor, namely it advantageously exhibits an ionic conductivity of at least 0.1 mS / cm at 25 ° C. in the presence of Li salt. It is necessarily in the pure liquid state or must be dissolved in a liquid. solvent. According to one embodiment, the ionically conductive oligomer has a function having an affinity for the thermoplastic polymer. According to one embodiment, G oligomer advantageously comprises the group -CR2-O, where R is: H, alkyl, aryl or alkenyl, the preferred group being H.

According to one embodiment, the oligomer has at least one group of polyethylene glycol (PEG) type. Among these oligomers, the methoxy polyethylene glycol methacrylates are interesting. One of these products, the Sartomer SR 550, is shown below:

[Chem 1]

Solid polymer electrolyte

The solid polymer electrolyte exhibits a satisfactory ionic conductivity of at least 0.1 mS / cm, at 25 ° C.

In addition to the thermoplastic polymer film and the oligomer, it contains one or more lithium salt (s).

The electrolyte salts, which are dissolved in the oligomer, are chosen from at least one of the following salts, when the technology is a lithium-based technology: Lithium hexafluorophosphate (LiPL ô ); Lithium perchlorate (LiCICL); Lithium hexafluoroarsenate (LiAsL ô ); Lithium tetrafluoroborate (L1BL4); Lithium 4,5-dicyano-2- (trifluoromethyl) imidazol-1-ide (LiTDI); Lithium bis (fluorosulfonyl) imide (LiLSI); Lithium bis-trifluoromethanesulfonimide (LiTLSI); Lithium N-fluorosulfonyl-trifluoromethansulfonylamide (Li-LTLSI); Lithium tris (fluorosulfonyl) methide (Li-LSM); Lithium bis (perfluoroethylsulfonyl) imide (LiBETI); Lithium bis- (oxalato) borate (LiBOB); Lithium difluoro (oxalate) borate (LiDLOB); Lithium 3-polysulfide sulfolane (LiDMDO) or mixtures thereof.

In the solid polymer electrolyte according to the invention, the thermoplastic polymer is present in an amount ranging from 10% to 90%, preferably from 20% to 80%, and the oligomer is present in an amount ranging from 90% to 10%, preferably 80% to 20% based on the total weight of the solid polymer electrolyte.

The invention also relates to a process for manufacturing the polymer electrolyte, characterized in that it consists in dissolving the lithium salt (s) in the conductive oligomer and then in impregnating the polymer film with this solution. thermoplastic.

The thermoplastic polymer may or may not be crosslinked. In the case of crosslinking, this is carried out thermally using crosslinking agents such as free radical generators, among which there may be mentioned azo compounds such as azobisisobutyronitrile (AIBN) or peroxides such as Luperox ® 26.

The invention further relates to a separator for a lithium-polymer battery, said separator being characterized in that it comprises the solid polymer electrolyte described above.

According to one embodiment, in the separator, the solid polymer electrolyte is deposited on a porous support of cellulose, polyolefins or polyacrylonitrile type. Its thickness is between 4 and 50 microns, preferably between 7 and 35 microns, and even more preferably between 10 and 20 microns.

According to one embodiment, the separator can also include inorganic particles up to 50% by mass.

According to one embodiment, these particles are chosen from conductive ceramics, such as sulfur-containing ceramics LUS - P2S5 (molar ratio between LUS and P2S5 between 1 and 3) and their derivatives, Perovskites (Normal types A n B IV 0 3 ) incomplete type LU x La 2/3-x Ti0 3 can be doped with Al, Ga, Ge or Ba, garnets type LÎ 7 La 3 Zr 2 0i 2 can be doped Ta, W, Al, Ti, NASICON types LiGe 2 (P0 4 ) 3 , LiTÎ 2 (P0 4 ) 3may be doped Ti, Ge, Al, P, Ga, Si., Anti-perovskite type LhOCl, Na 3 0Cl being doped OH or Ba.

According to one embodiment, these particles are chosen from fillers which are intrinsically non-conductive or which have very low intrinsic conductivity at room temperature, such as silicas, aluminas, titanium oxides, zirconium oxides, and mixtures thereof.

According to one embodiment, these particles are chosen from fillers exhibiting relative permittivities greater than 2000, such as barium, strontium and lead titanates, lead zirconates, zirconium and lead titanates, and mixtures thereof. .

The separator may contain other additives, such as agents facilitating the mobility of the conductive chains, in particular succinonitrile.

Another subject of the invention is a lithium-polymer battery comprising a separator based on the solid polymer electrolyte described above, arranged between an anode made of lithium metal and a cathode.

According to another aspect, the invention relates to a lithium battery comprising a stack of layers, said stack comprising an anode preferably consisting of lithium metal, a cathode and a separator.

The cathode is made up of:

An electrochemically active material: between 35 and 98% by mass. More particularly, the electrochemically active material is chosen, without limitation, from at least one of the following materials: lithiated iron phosphate (LFP); Lithium oxide of nickel, manganese and cobalt (NMC); Lithium oxide of nickel, cobalt and aluminum (NCA); lithiated manganese oxide (LMO); lithiated oxide of nickel and manganese (NM); lithiated cobalt oxide (LCO), sulfur; or a mixture thereof. Low conductive materials such as iron or manganese phosphates

can be covered with a carbon layer to improve electronic conduction:

Conductive additives: between 0.15 and 25% by mass, chosen from at least one of the following carbon fillers: carbon black, single or multi-walled carbon nanotubes, carbon nanofibers, graphites, graphenes, fullerenes, or a mixture of these;

A polymer electrolyte between 20 and 60% by mass;

Optionally, a polymer to bind the particles together and improve the mechanical strength and adhesion to the collector between 0 and 5% by mass, chosen from at least one of the following binders: poly (vinylidene fluoride) (PVDF) and its derivatives and copolymers; carboxymethylcellulose (CMC); styrene-butadiene rubber (SBR); poly (ethylene oxide) (POE); poly (propylene oxide) (POP); polyglycols; or a mixture of these.

The current collector of such a cathode is made of aluminum, carbon coated aluminum or carbon.

The anode is composed of:

Electrochemically active material which may be treated lithium metal, graphite, lithiated titanium oxide (LTO), silicon, silicon-carbon composites, graphene. The active material can be coated with carbon to improve electronic conduction;

Conductive additives present at between 0.15 and 25% by mass, chosen from at least one of the following carbon fillers: carbon black, single or multi-walled carbon nanotubes, carbon nanofibers, graphites, graphenes, fullerenes or a mixture of these;

A polymer electrolyte between 15 and 60% by mass.

The current collector of such anode is made of copper, carbon or nickel, but for Li-metal technology, it is envisioned that the Li foil is its own collector.

The conductive additives entering into the constitution of the anode and / or of the cathode can be chosen from carbonaceous fillers. The term “carbonaceous fillers” according to the invention is understood to mean a filler comprising an element of the group formed by carbon nanotubes, carbon nanofibers, graphene, fullerenes and carbon black, or a mixture of these altogether. proportion. The term “graphene” according to the invention means a flat, isolated and individualized sheet of graphite, but also, by extension, an assembly comprising between one and a few tens of sheets and having a planar or more or less corrugated structure. This definition therefore includes FLGs (Few Layer Graphene or weakly stacked graphene), NGP (Nanosized Graphene Plates or graphene plates of nanometric dimension), CNS (Carbon NanoSheets or graphene nano-sheets), GNR (Graphene NanoRibbons or graphene nano-ribbons). On the other hand, it excludes carbon nanotubes and nanofibers, which respectively consist of the winding of one or more graphene sheets coaxially and of the turbostratic stacking of these sheets and the graphite which consists of an assembly comprising more than a few dozen sheets.

Preferably, the carbonaceous fillers are carbon nanotubes, alone or as a mixture with graphene.

The carbon nanotubes (CNTs) can be of the single wall type (SWCNT for “Single Wall Carbon NanoTube”), double wall or multiple walls (MWCNT for “Multi Wall Carbon NanoTube”). The double-walled nanotubes can in particular be prepared as described by Llahaut, E. et al, “Gram-scale CCVD synthesis of double-walled carbon nanotubes. »(2003) Chemical Communications (n ​​° 12) pp. 1442-1443. Nanotubes with multiple walls can for their part be prepared as described in document WO 03/02456. The nanotubes usually have an average diameter ranging from 0.1 to 100 nm, preferably from 0.4 to 50 nm and, better, from 1 to 30 nm, or even from 10 to 15 nm, and advantageously a length of 0.1 at 10 pm. Their length / diameter ratio is preferably greater than 10 and most often greater than 100.2 / g, advantageously between 200 and 300 m 2 / g, and their apparent density can in particular be between 0.05 and 0.5 g / cm3 and more preferably between 0.1 and 0.2 g / cm3. The multi-walled nanotubes can for example comprise from 5 to 20 sheets (or walls) and more preferably from 7 to 10 sheets.

An example of crude carbon nanotubes is especially commercially available from Arkema under the trade name Graphistrength® ® C100. Alternatively, these nanotubes can be purified and / or treated (for example oxidized) and / or ground and / or functionalized, before their use in the process according to the invention. The purification of the crude or ground nanotubes can be carried out by washing with a sulfuric acid solution, so as to rid them of any residual mineral and metallic impurities. Purification can be

carried out by heat treatment at high temperature (above 2200 ° C) under an inert atmosphere. The oxidation of the nanotubes is advantageously carried out by bringing them into contact with a solution of sodium hypochlorite or by exposure to oxygen in the air at a temperature of 600-700 ° C. The functionalization of the nanotubes can be carried out by grafting reactive units such as vinyl monomers on the surface of the nanotubes.

The graphene used can be obtained by chemical vapor deposition or CVD, preferably according to a process using a pulverulent catalyst based on a mixed oxide. It is typically present in the form of particles with a thickness of less than 50 nm, preferably less than 15 nm, more preferably less than 5 nm and lateral dimensions less than one micron, from 10 to 1000 nm. , preferably from 50 to 600 nm, and more preferably from 100 to 400 nm. Each of these particles generally contains from 1 to 50 sheets, preferably from 1 to 20 sheets and more preferably from 1 to 10 sheets. Various processes for preparing graphene have been proposed in the literature, including the so-called mechanical exfoliation and chemical exfoliation processes, consisting in tearing off layers of graphite by successive layers, respectively by means of an adhesive tape (Geim AK, Science, 306: 666, 2004) or by means of reagents, such as sulfuric acid combined with nitric acid, interposing between the layers of graphite and oxidizing them, so as to form graphite oxide which can be easily exfoliated in water in the presence of ultrasound. Another exfoliation technique consists in subjecting the graphite in dispersion to ultrasound, in the presence of a surfactant (US Pat. No. 7,824,651). Graphene particles can also be obtained by cutting carbon nanotubes along the longitudinal axis (“Micro-Wave Synthesis of Large Few-Layer Graphene Sheets in Aqueous Solution of Ammonia”, Janowska, I. et al, NanoResearch, 2009 or “Narrow Graphene nanoribbons from Carbon Nanotubes”, Jiao L. et al, Nature, 458: 877-880, 2009). Yet another method of preparing graphene consists in decomposing silicon carbide at high temperature, under vacuum. Finally, several authors have described a process for the synthesis of graphene by chemical vapor deposition (or CVD), possibly associated with a radio frequency generator (RF-CVD) (DERVISHI et al., J. Mater. ScL, 47: 1910-1919, 2012).

Fullerenes are molecules composed exclusively or almost exclusively of carbons that can take a geometric shape reminiscent of a sphere, an ellipsoid, a tube (called a nanotube) or a ring. Fullerenes can by

example be selected from: fullerene C60 which is a compound formed of 60 carbon atoms of spherical shape, C70, PCBM of formula [6,6] -phenyl-C61-methyl butyrate which is a derivative of fullerene whose chemical structure has been modified to make it soluble, and the PC 71 BM of the formula [6,6] -phenyl-C71-methyl butyrate.

Carbon nanofibers are, like carbon nanotubes, nanofilaments produced by chemical vapor deposition (or CVD) from a carbon source which is decomposed on a catalyst comprising a transition metal (Fe, Ni, Co, Cu), in the presence of hydrogen, at temperatures of 500 to 1200 ° C. Carbon nanofibers are composed of more or less organized graphitic zones (or turbostratic stacks) whose planes are inclined at varying angles with respect to the axis of the fiber. These stacks can take the form of platelets, fishbones or cups stacked to form structures having a diameter generally ranging from 100 nm to 500 nm or even more. Carbon nanofibers having a diameter of 100 to 200 nm, for example about 150 nm (VGCF ® of SHOWA DENKO), and advantageously a length of 100 to 200 μm are preferred in the process according to the invention.

Furthermore, carbon black can be used as carbonaceous fillers, which is a colloidal carbonaceous material manufactured industrially by incomplete combustion of heavy petroleum products, which is in the form of carbon spheres and aggregates of these spheres and whose dimensions are generally between 10 and 1000 nm.

Very advantageously, these conductive additives are added to the composition of each electrode with a content of between 0.25 and 25% by mass.

EXAMPLES

The following examples illustrate the invention without limiting it.

Example 1:

A film of p copolymer (VDF-TrFE) is prepared by dissolving 10 g of FC 20 copolymer from Piezotech in a mixture of solvents consisting of 75 g of g butyrolactone and 15 g of benzyl alcohol, then deposited on a slide of glass and 4 cm × 2 cm of the film obtained is allowed to dry, ie 0.0664 g; this film is then impregnated with 0.097 g of SR 550 in which 23.1 mg of LiTFSI have been dissolved beforehand in a glove box. This quantity corresponds to OE / Li = 13.

In less than 30 seconds, the SR 550 is absorbed into the porosity. The film is then left overnight in an oven at 50 ° C.

Example 2:

The operation of Example 1 is repeated for an EO / Li ratio = 17.

Example 3:

The operation of Example 1 is repeated for an EO / Li ratio = 25.

Example 4:

The ionic conductivity is determined by electrochemical impedance spectroscopy. The materials are placed between two stainless steel electrodes (measured thickness of the order of 100 μm), inside a sealed cell. The preparation of the films and the assembly of the cell are carried out in a glove box under an argon atmosphere. The cell is brought to 80 ° C for 1 hour to ensure good contact between the sample and the stainless steel electrodes. The actual measurement is performed using a Bio-Logic VMP3 potentiostat / galvanostat / EIS between 1 Hz and 1 MHz at an amplitude of 500 mV.

The values ​​found in the three examples are reported in Table 1 below. It can be seen that the values ​​do not depend very much on the EO / Li ratio, which constitutes an advantage for industrial extrapolation.

[Table 1]

Example 5:

Electrochemical stability represents the ability of an electrolyte to resist electrochemical decompositions. Electrochemical stability measurements were

produced in button cells (2 electrodes) CR2032 format at 60 ° C, using SUS 316L stainless steel as a working surface on a surface of 2.01 cm 2 on a sample of copolymer film prepared according to Example 2.

The electrochemical method used is slow cyclovoltametry implemented with a scanning speed of 1 mV / s. This method illustrates the oxidation current as a function of voltage: whenever the current approaches zero, the operating voltage of the polymer electrolyte is stable. The electrochemical stability is equal to 4.5 V. The curve I = f (Y) is perfectly flat down to 0 V.

CLAIMS

1. Solid polymer electrolyte for a battery operating at a temperature below 60 ° C, said electrolyte comprising:

• a thermoplastic polymer in the form of a porous film, said polymer having a molecular mass greater than 50,000 g / mol,

• an oligomer impregnating said thermoplastic polymer film, this oligomer being an ionic conductor, and

• one or more lithium salt (s).

2. Solid polymer electrolyte according to claim 1, wherein the thermoplastic polymer is a compound of the general formula: [- (CR1R2-CR3R4H 11 where R1, R2, R3 and R4 are independently H, F, CH3, Cl, Br, CF3 , at least one of these radicals being F or CF3.

3. Solid polymer electrolyte according to one of claims 1 or 2, wherein the thermoplastic polymer is a fluoropolymer chosen from poly (vinylidene-r -hexafluoropropene fluoride), poly (vinylidene-co-trifluoroethylene fluoride), poly (vinylidene fluoride- / er-trifluoroethylene- / er-chloiOtrifluoroethylene) and poly (vinylidene fluoride- / er-trifluoroethylene- / er- 1, 1 -chlorofluoroethylene).

4. Solid polymer electrolyte according to one of claims 1 to 3, wherein the thermoplastic polymer is a P copolymer (VDF-TrFE) in which the VDF / TrFE molar ratio of the structural units varies from 9 to 0, 1 and so preferred from 4 to 1.

5. Solid polymer electrolyte according to one of claims 1 to 3, wherein the thermoplastic polymer is a P terpolymer (VDF-TrFE-CTFE) in which the molar rate of VDF varies from 40 to 95%, the molar rate of TrFE varies from 5 to 60%, and the molar ratio of CTFE varies from 0.5 to 20%.

6. Solid polymer electrolyte according to one of claims 1 to 5, wherein G oligomer comprises the group -CR2-O, where R is: H, alkyl, aryl or alkenyl.

7. Solid polymer electrolyte according to claim 6, in which the oligomer has at least one group of polyethylene glycol type.

8. Solid polymer electrolyte according to one of claims 1 to 7 comprising one or more lithium salt (s) chosen from Lithium hexafluorophosphate (LiPF ô ); Lithium perchlorate (ILCl10 4 ); Lithium hexafluoroarsenate (LiAsF ô ); Lithium tetrafluoroborate (LÎBF4); Lithium 4,5-dicyano-2- (trifluoromethyl) imidazol-1-ide (LiTDI); Lithium bis (fluorosulfonyl) imide (LiFSI); Lithium bis-trifluoromethanesulfonimide (LiTFSI); LithiumN-fluorosulfonyltrifluoro-methansulfonylamide (Li-FTFSI); Lithium tris (fluorosulfonyl) methide (Li-FSM); Lithium bis (perfluoroethylsulfonyl) imide (LiBETI); Lithium bis- (oxalato) borate (LiBOB); Lithium difluoro (oxalate) borate (LiDFOB); Lithium 3-polysulfide sulfolane (LiDMDO) or mixtures thereof.

9. Solid polymer electrolyte according to one of claims 1 to 7 wherein the thermoplastic polymer is present in an amount ranging from 10 to 90%, preferably from 20 to 80%, and G oligomer is present in an amount ranging from 90 at 10%, preferably 80-20% based on the total weight of the solid polymer electrolyte.

10. Solid polymer electrolyte according to one of claims 1 to 9, wherein the porous film of thermoplastic polymer is manufactured according to a process comprising the following steps:

• providing an ink comprising the thermoplastic polymer and a vehicle comprising a solvent for said polymer and a non-solvent for said polymer, said solvent and said non-solvent being miscible with one another;

• depositing ink on a substrate;

evaporation of the vehicle comprising the solvent and the non-solvent.

11. Solid polymer electrolyte according to one of claims 1 to 10 having an ionic conductivity of at least 0.1 mS / cm at 25 ° C.

12. Solid polymer electrolyte according to one of claims 1 to 11 wherein the pores of the thermoplastic polymer film have an average diameter of 0.1 to 10 µm, preferably 0.2 to 5 mm, more preferably 0. , 3 to 4 mm, measured by scanning electron microscopy.

13. Solid polymer electrolyte according to any one of claims 1 to 12, wherein said oligomer has a number-average molecular mass less than or equal to 5000 g / mol, and preferably less than or equal to 2000 g / mol.

14. A method of manufacturing the solid polymer electrolyte according to one of claims 1 to 13 characterized in that it consists in dissolving the lithium salt (s) in G conductive oligomer and then impregnating the film with this solution. of thermoplastic polymer.

15. Separator for lithium-polymer battery, characterized in that it comprises the solid polymer electrolyte according to one of claims 1 to 13.

16. Separator according to claim 15 further comprising inorganic particles up to 50% by mass, said particles being chosen from conductive ceramics, non-conductive or very little conductive fillers intrinsic at room temperature and fillers having relative permittivities greater than. 2000.

17. Lithium-polymer battery comprising an anode consisting of lithium metal, a cathode and a separator arranged between the two electrodes, characterized in that the separator comprises the solid polymer electrolyte according to one of claims 1 to 13.