electrodes for quasi-solid-state lithium-ion batteries

Abstract

The present invention relates to a cathode composition comprising an intrinsically entrapped catholyte. The present invention also relates to a quasi-solid-state Li-ion battery comprising said cathode, an anode and a separator, and a method for producing said Li-ion battery.

Description

[Technical Field]

[0001] The present invention generally relates to the field of electrical energy storage in rechargeable secondary batteries of the Li-ion type. More specifically, the present invention relates to a cathode composition comprising essentially incorporated cathode liquid. The present invention also relates to a quasi-solid Li-ion battery comprising the cathode, anode and separator, and to a method for manufacturing the Li-ion battery. [Background technology]

[0002] A lithium-ion battery comprises at least one cathode or anode connected to a copper current collector, a positive electrode or cathode connected to an aluminum current collector, a separator, and an electrolyte. The electrolyte consists of a lithium salt, generally lithium hexafluorophosphate, mixed with a solvent which is a mixture of organic carbonates. These are selected to optimize ion transport and dissociation. A high dielectric constant promotes ion dissociation, thereby increasing the number of ions available in a given volume, while low viscosity is beneficial for ion diffusion, which plays a significant role among other parameters in the charging and discharging rates of the electrochemical system.

[0003] Rechargeable, or secondary, batteries have advantages over primary batteries (which are not rechargeable) because the associated chemical reactions at the positive and negative electrodes of the battery are reversible. The electrodes of a secondary cell can be regenerated multiple times by applying an electric charge. Many advanced electrode systems have been developed to store electric charge. In parallel, much effort has been made to develop electrolytes that can improve the capacity of electrochemical cells.

[0004] Lithium-ion batteries conventionally use a liquid electrolyte composed of a solvent, lithium salt, and additives. While these electrolytes have good ionic conductivity, they can leak or catch fire if the battery is damaged. These drawbacks can be overcome by using a solid or semi-solid electrolyte.

[0005] A further advantage of solid or semi-solid electrolytes is that they allow the use of lithium metal in the negative electrode, preventing the formation of dendrites, which can cause short circuits during cycling. Using lithium metal provides an energy density gain compared to insertion-type or alloy-type negative electrodes.

[0006] Nevertheless, solid or semi-solid electrolytes generally have lower conductivity than liquid electrolytes, especially at the cathode and anode. A solid or semi-solid electrolyte incorporated into the cathode is called the cathodelime. A common challenge in all-solid-state or semi-solid-state batteries is obtaining a cathodelime that is chemically and electrochemically compatible with the cathode while possessing sufficient conductivity and low resistivity at the interface with the cathode. Improving the cathode-cathodelime interface often requires applying high pressure or directly coating the cathode with the cathodelime, which adds an extra step to the manufacturing process.

[0007] Reference FR3049114 describes an all-solid-state battery comprising a solid polymer electrolyte, a negative electrode containing lithium metal or a lithium metal alloy, and a positive electrode containing an ion-conducting polymer. The drawback of this battery is that the ionic conductivity of the solid electrolyte incorporated in the cathode is low at ambient temperature, and the lithium-ion cell must be heated to 80°C to exhibit good electrochemical performance.

[0008] Poly(vinylidene fluoride) (PVDF) and its derivatives are favored as primary constituent materials for binders used in electrodes due to their electrochemical stability and their high dielectric constant, which promotes ion dissociation and thereby conductivity. The crystallinity of P(VDF-co-HFP) copolymers (copolymers of vinylidene fluoride (VDF) and hexafluoropropylene (HFP)) is lower than that of PVDF. The advantage of these P(VDF-co-HFP) copolymers is that they undergo greater swelling in electrolyte solvents, and therefore promote ionic conductivity in quasi-solid Li-ion battery cathodes.

[0009] Reference US9,997,803, with reference to Figure 2, describes a secondary battery cell 20 comprising a cathode 21, an anode 22, a separator 23, and an electrolyte 24. The electrolyte comprises a high molecular weight compound and an electrolyte solution prepared by dissolving an electrolyte salt in a solvent, the electrolyte solution being held within the high molecular weight compound to gel the electrolyte solution. The high molecular weight compound includes a first compound having a weight-average molecular weight of 550,000 or more, and a second compound having a weight-average molecular weight of 1,000 or more but not exceeding 300,000. The role of the first high molecular weight compound is to improve adhesion between the electrolyte 24, cathode 21, and anode 22. The intended role of the second high molecular weight compound is to improve the permeability of the electrolyte 24 in the cathode 21 and anode 22. A third high molecular weight compound may be incorporated into the electrolyte. Each of these compounds is selected from PVDF and P(VDF-co-HFP) copolymers. This copolymer is a block copolymer, and the amount of HFP by mass in the copolymer ranges from 3% to 7.5%.

[0010] In this document, a cathode mixture is prepared by mixing an active cathode material and a binder (VDF-HFP copolymer) and optionally an electrical conductor. The cathode mixture is then dispersed in a solvent such as 2-methylpyrrolidone to form a cathode mixture slurry. The cathode mixture slurry is applied to one or both sides of the current collector of cathode 21A, and after drying, a layer of active material of cathode 21B is formed by compression molding to form cathode 21. The materials applied to this cathode are, on the one hand, a solution formed from the high molecular weight compound dissolved in a solvent such as dimethyl carbonate, and on the other hand, an electrolyte solution obtained by mixing a solvent containing ethylene carbonate, propylene carbonate, and LiPF6. The active material layer 21B of the cathode is left at ambient temperature for 8 hours to allow the dimethyl carbonate to volatilize and generate electrolyte 24.

[0011] However, this preparation method is time-consuming and, as with the additional steps of coating the electrolyte solution and evaporating the dimethyl carbonate, it extends the time required to produce the electrolyte and incurs extra manufacturing costs.

[0012] There is still a need to develop new cathode compositions containing cathode liquid. These compositions are characterized by a good exchange between the ionic conductivity within the cathode at ambient temperature and low resistivity at the interface with the solid or semi-solid electrolyte, and are suitable for simplified implementation without prior conversion steps. Furthermore, the amount of cathode liquid in the cathode must be minimized to maximize the energy density of the Li-ion cell. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] French Patent No. 3049114 [Patent Document 2] U.S. Patent No. 9,997,803 [Overview of the Initiative] [Problems that the invention aims to solve]

[0014] Therefore, an object of the present invention is to address at least one of the drawbacks of the prior art, specifically to propose a cathode for a quasi-solid lithium-ion battery that includes a cathode liquid permeated into the electrode material and allows for sufficient swelling of a polymer binder incorporated into the material without any loss of cohesiveness in the cathode or loss of adhesion to the current collector. Sufficient swelling means that the ionic conductivity of the cathode containing the cathode liquid at ambient temperature is such that the capacity delivered in a C / 10 discharge is 80% or more of the theoretical reversible capacity.

[0015] Furthermore, the present invention relates to a rechargeable secondary Li-ion battery comprising a cathode containing a cathode liquid, an anode, and a separator.

[0016] Finally, the present invention relates to a method for manufacturing a Li-ion battery comprising the cathode containing the catholyte. This is compatible with ordinary industrial processes.

Means for Solving the Problems

[0017] The technical solution proposed by the present invention is a cathode containing a catholyte essentially mixed with an electrode material.

[0018] In a first aspect, the present invention relates to a cathode for a lithium-ion battery comprising an active electrode material, a conductive additive, an inorganic oxide, a polymer binder, and a catholyte.

[0019] Characteristically, the binder consists of a mixture of two fluoropolymers, namely, a fluoropolymer A containing at least one copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) having an HFP content of 3 wt% or more, and a fluoropolymer B containing a VDF homopolymer and / or at least one VDF-HFP copolymer, and the fluoropolymer B has an HFP mass content at least 3 wt% less than the HFP mass content of the polymer A.

[0020] The catholyte contains at least one solvent and at least one lithium salt.

[0021] In another aspect, the present invention provides a rechargeable secondary Li-ion battery comprising a cathode, an anode, and a separator, wherein the cathode is as described above.

[0022] Finally, the present invention relates to a method for manufacturing a Li-ion battery comprising the cathode.

[0023] By the present invention, it becomes possible to overcome the drawbacks of the prior art. The present invention is characterized in that the conductivity at the ambient temperature of the catholyte in the cathode is good. The cohesiveness and adhesiveness of the cathode, as well as its flexibility, are maintained in the catholyte.

[0024] The battery manufacturing method described in this invention requires no additional steps compared to conventional manufacturing methods used for the production of Li-ion cells. Specifically, there is no cathode liquid coating step, no intense heat treatment step of sintering at temperatures exceeding 500°C, which is required, for example, in the case of oxide-based solid electrolytes, no step of compression molding at very high pressure, and no need to monitor humidity or atmosphere compared to current methods.

[0025] The advantage of this technology is that, compared to liquid electrolytes, it provides a better assurance of safety due to the absence of electrolyte leakage and reduced flammability caused by the gelation of the cathode solution. [Brief explanation of the drawing]

[0026] [Figure 1] This diagram shows the cathode impedance spectrum of a symmetrical battery. [Figure 2] This figure shows the capacitance performance of the cathode according to the present invention and the cathode according to a comparative example at a discharge current of 1C. [Modes for carrying out the invention]

[0027] The present invention will be described in more detail and in a non-limiting manner in the following description.

[0028] In a first embodiment, the present invention relates to a cathode for a lithium-ion battery comprising an active electrode material, a conductive additive, an inorganic oxide, a polymer binder, and a cathode liquid. - The binder is a mixture of two fluoropolymers, namely fluoropolymer A, which contains at least one copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) having an HFP content of 3% by weight or more, and fluoropolymer B, which contains a VDF homopolymer and / or at least one VDF-HFP copolymer, wherein fluoropolymer B has an HFP mass content that is at least 3% by weight less than the HFP mass content of polymer A. - The cathode solution comprises at least one solvent and at least one lithium salt.

[0029] According to various embodiments, the cathode, when combined as appropriate, includes the following characteristics. The stated percentages are expressed by weight unless otherwise specified.

[0030] The active electrode material is selected from compounds of type xLi2MnO3·(1-x)LiMO2 (0≦x≦1), LiMPO4 type, Li2MPO3F type, Li2MSiO4 type (where M is Co, Ni, Mn, Fe or a combination thereof), LiMn2O4 type, or S8 type.

[0031] The conductive additive is selected from carbon black, graphite, natural or synthetic carbon fibers, carbon nanotubes, metal fibers and powders, or mixtures thereof.

[0032] The inorganic oxide is selected from silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, zeolite, or a mixture thereof.

[0033] <Polymer Binder> Fluoropolymer A comprises at least one VDF-HFP copolymer having an HFP content of 3% by weight or more, preferably 8% or more, and advantageously 13% or more. The VDF-HFP copolymer has an HFP content of 55% or less, preferably 50% or less.

[0034] This very low-crystalline copolymer swells readily in electrolyte solvents such as carbonates, nitriles, and glycers, thus providing good ionic conductivity to the binder. Swelling can be quantified by the increase in the binder's mass due to the electrolyte. It is advantageous that the increase in the copolymer's mass is at least 5% by weight.

[0035] According to one embodiment, fluoropolymer A consists of a single VDF-HFP copolymer having an HFP content of 3% or more. According to one embodiment, the HFP content of this VDF-HFP copolymer is 13% to 55% (including endpoints), preferably 15% to 50% (including endpoints).

[0036] According to one embodiment, fluoropolymer A consists of a mixture of two or more VDF-HFP copolymers, with each copolymer having an HFP content of 3% or more. According to one embodiment, each copolymer has an HFP content of 13% to 55% (including endpoints), preferably 15% to 50% (including endpoints).

[0037] Fluoropolymer B contains at least one VDF-HFP copolymer having an HFP mass content at least 3% less than the HFP mass content of polymer A. This allows the cathode to be given sufficient mechanical strength after swelling. Sufficient mechanical strength means that the adhesion of the cathode to the current collector is maintained after swelling, as well as the cohesiveness of the active material particles.

[0038] According to one embodiment, fluoropolymer B consists of a single VDF-HFP copolymer. According to one embodiment, the HFP content of this VDF-HFP copolymer is 1% to 5% (including endpoints). According to one embodiment, the HFP content of this VDF-HFP copolymer is 1% to 10% (including endpoints).

[0039] According to one embodiment, fluoropolymer B is a mixture of PVDF homopolymer and VDF-HFP copolymer, or a mixture of two or more VDF-HFP copolymers.

[0040] According to one embodiment, the HFP content of the mixture of polymers A and B exceeds 7% by weight.

[0041] According to one embodiment, a mixture of fluoropolymers A and B has a melting temperature of over 150°C.

[0042] The molar composition of units in fluoropolymers can be determined by various methods such as infrared spectroscopy or Raman spectroscopy. Conventional methods of elemental analysis of carbon, fluorine, and chlorine or bromine or iodine, such as X-ray fluorescence spectroscopy, allow for the precise calculation of the mass composition of the polymer from which the molar composition is estimated.

[0043] By analyzing solutions of polymers in a suitable deuterated solvent, multinuclear NMR techniques, particularly proton (1H) and fluorine (19F) NMR techniques, can also be used. NMR spectra are recorded using an FT-NMR spectrometer equipped with multinuclear probes. Then, specific signals given by various monomers in the spectrum, generated by one or more nuclei, are identified.

[0044] According to one embodiment, at least one of fluoropolymers A and B includes a unit having at least one of the following functional groups: carboxylic acid, carboxylic acid anhydride, carboxylic acid ester, epoxy group (such as glycidyl), amide, alcohol, carbonyl, mercapto, sulfide, oxazoline, and phenol.

[0045] The functional groups are introduced onto the fluoropolymer by a chemical reaction that allows for grafting using techniques known to those skilled in the art, or by copolymerization of the fluoropolymer with a compound having at least one of the functional groups.

[0046] According to one embodiment, the functional group is a terminal group located at the end of a fluoropolymer chain.

[0047] According to one embodiment, the monomer having the functional group is inserted into a fluoropolymer chain.

[0048] According to one embodiment, the carboxylic acid functional group is a (meth)acrylic acid type hydrophilic group selected from acrylic acid, methacrylic acid, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxyethylhexyl (meth)acrylate.

[0049] When fluoropolymer A or B is functionalized, the mass content of the functional group is at least 0.01% and no more than 5% based on the weight of the fluoropolymer.

[0050] According to one embodiment, the mass ratio of polymer A to polymer B is greater than 1.

[0051] <Cathode Liquid> The cathode solution comprises at least one solvent and at least one lithium salt.

[0052] According to one embodiment, the solvent is selected from cyclic and acyclic alkyl carbonates, ethers, grimes, formates, esters, nitriles, and lactones.

[0053] Examples of ethers include linear or cyclic ethers, such as dimethoxyethane (DME), methyl ethers of oligoethylene glycols with 2 to 100 oxyethylene units, dioxolane, dioxane, dibutyl ether, tetrahydrofuran, and mixtures thereof.

[0054] Examples of esters include phosphate esters and sulfite esters. For example, methyl formate, methyl acetate, methyl propionate, ethyl acetate, butyl acetate, or mixtures thereof.

[0055] The GRIM used has the general formula R1-O-R2-O-R3, where R1 and R3 are linear alkyl groups of 1 to 5 carbon atoms, and R2 is a linear or branched alkyl chain of 3 to 10 carbon atoms.

[0056] Among lactones, gamma-butyrolactone is a particularly noteworthy example.

[0057] Examples of nitriles include acetonitrile, pyronitrile, propionitrile, methoxypropionitrile, dimethylaminopropionitrile, butyronitrile, succinonitrile, isobutyronitrile, valeronitrile, pivalonitrile, isovaleronitrile, glutaronitrile, methoxyglutalonitrile, 2-methylglutalonitrile, 3-methylglutalonitrile, adiponitrile, malononitrile, and mixtures thereof.

[0058] Among carbonates, for example, cyclic carbonates, such as propylene carbonate (PC) (CAS: 108-32-7), butylene carbonate (BC) (CAS: 4437-85-8), dimethyl carbonate (DMC) (CAS: 616-38-6), diethyl carbonate (DEC) (CAS: 105-58-8), ethyl methyl carbonate (EMC) (CAS: 623-53-0), diphenyl carbonate (CAS: 102-09-0), and methylphenyl carbonate (CAS Examples include 13509-27-8), dipropyl carbonate (DPC) (CAS: 623-96-1), methylpropyl carbonate (MPC) (CAS: 1333-41-1), ethylpropyl carbonate (EPC), vinylene carbonate (VC) (CAS: 872-36-6), fluoroethylene carbonate (FEC) (CAS: 114435-02-8), trifluoropropylene carbonate (CAS: 167951-80-6), or mixtures thereof.

[0059] According to one embodiment, the lithium salt is selected from LiPF6 (lithium hexafluorophosphate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethane)sulfonimide), LiTDI (lithium 2-trifluoromethyl-4,5-dicyanoimidazolate), LiPO2F2, LiB(C2O4)2, LiF2B(C2O4)2, LiBF4, LiNO3, LiClO4, and mixtures thereof.

[0060] According to one embodiment, the cathode liquid further comprises a salt having a melting point of less than 100°C, such as an ionic liquid. This forms a liquid consisting only of cations and anions.

[0061] Examples of organic cations include, in particular, the following cations: ammonium, sulfonium, pyridinium, pyrrolidinium, imidazolium, imidazolinium, phosphonium, lithium, guanidinium, piperidinium, thiazolium, triazolium, oxazolium, pyrazolium, and mixtures thereof.

[0062] Examples of anions include imides, particularly bis(trifluoromethanesulfonyl)imides (abbreviated as NTF2-) and bis(fluorosulfonyl)imides; borates, particularly tetrafluoroborates (abbreviated as BF4-); phosphates, particularly hexafluorophosphates (abbreviated as PF6-); phosphinates and phosphonates, particularly alkylphosphonates; amides, particularly dicyanamides (abbreviated as DCA-); aluminates, particularly tetrachloroaluminates (AlCl4-); halides (bromide anions, chloride anions, iodide anions); cyanates; acetates (CH3COO-), particularly trifluoroacetates; sulfonates, particularly methanesulfonates (CH3SO3-), trifluoromethanesulfonates; and sulfates, particularly bisulfates.

[0063] According to one embodiment, the cathode liquid consists of a mixture of a solvent and a lithium salt and does not contain a polymer binder.

[0064] According to one embodiment, the cathode liquid is a lithium superionic conductor (LISICON) and derivatives, thio-LISICON, a Li4SiO4-Li3PO4 type structure, a sodium superionic conductor (NASICON) and derivatives, Li 1.3 Al 0.3 Ti 1.7 (PO4)3(LATP) type structure, garnet structure Li7La3Zr2O 12(LLZO) and derivatives, lithiated perovskite structures Li 3x La 2 / 3-2x□1 / 3-2x TiO3 (0 < x < 0.16) (LLTO), amorphous, crystalline or semi-crystalline sulfides such as LSS, LTS, LXPS, LXPSO or LATS sulfides where X is an element Si, Ge, Sn, As, Al or a combination of these elements, S is an element S or Si or a combination of these elements, and T is an element Sn, or solid electrolytes such as LiPSX, LiBSX, LiSnSX or LiSiSX sulfides where X is an element F, Cl, Br or I. According to one embodiment, the solid electrolyte in the cathode liquid may be a combination of the above solid electrolytes.

[0065] According to one embodiment, the cathode liquid further comprises a conductive organic polymer such as a polymer based on PEO, PAN, PMMA, PVA.

[0066] According to one embodiment, the cathode liquid has a salt concentration of 0.05 mol / L to 5 mol / L in a solvent.

[0067] According to one embodiment, the cathode has the following composition by mass. - 52% to 95.5%, preferably 65% to 92% of active material, - 1% to 11%, preferably 1.5% to 7.5% of conductive additive, - 1% to 11%, preferably 1.5% to 7.5% of polymer binder, - 0% to 2%, preferably 0% to 1% of inorganic oxide, - 2.5% to 28%, preferably 5% to 20% of cathode liquid, The sum of these ratios is 100%.

[0068] According to one embodiment, the mass ratio of the cathode liquid to the polymer binder in the cathode is 0.05 to 20, preferably 0.1 to 10.

[0069] According to one embodiment, the cathode has a mass ratio of conductive additive to polymer binder greater than 0.7. In fact, it was found that when the content of the conductive additive decreases relative to the content of the polymer binder, the contact resistance of the cathode increases.

[0070] The cathode described above is manufactured by a method that includes the following steps.

[0071] - A step of obtaining ink by mixing an active electrode material, a conductive additive, an inorganic oxide, and a polymer binder in a solvent. The mixture can be prepared using a planetary mixer or a dispersion disk. A solution of the polymer binder in the solvent is prepared to have a solid content of 2-20%.

[0072] Next, an inorganic oxide is dispersed in this solution. Then, a conductive additive is dispersed in this solution. Subsequently, the active material is dispersed in this solution, and the solid content of the ink is adjusted by adding solvent to reach a value of 30% to 80%.

[0073] - A step of coating the current collector support with the ink. The current collector may be an aluminum foil coated with an electronically conductive layer and / or a polymer layer of any thickness of 5 μm to 30 μm. The ink may be applied to one or both sides of the current collector.

[0074] - A step of drying the ink to form a film. Drying can be carried out on a hot plate or in an oven at a temperature varying between 20 and 150°C, with or without airflow.

[0075] - A step of calendering the assembly formed by the coating and current collector to obtain a temperature of 50 to 130°C.

[0076] - A step of impregnating the film with an electrolyte comprising at least one solvent and at least one lithium salt. The cathode is favorably impregnated into the Li-ion cell during filling and before the cell is sealed.

[0077] <Lithium-ion battery> In another embodiment, the present invention provides a rechargeable secondary lithium-ion battery comprising a cathode, an anode, and a separator, wherein the cathode is as described above.

[0078] According to one embodiment, the anode is a foil of lithium metal.

[0079] According to one embodiment, the anode includes lithium insertion materials such as graphite, metal oxides, non-graphitized carbon, pyrolysis carbon, coke, carbon fiber, activated carbon, alloy materials such as those based on Si, Sn, Mg, B, As, Ga, In, Ge, Pb, Sb, Bi, Cd, Ag, Zn, Zr, or a mixture of the anode materials.

[0080] According to one embodiment, the separator is a “conventional” separator comprising one or more porous polypropylene and / or polyethylene layers, and optionally having a coating on one or both sides of the separator. The coating comprises a polymer binder and inorganic particles.

[0081] According to one embodiment, the separator is a gelling polymer membrane comprising a fluoropolymer film and an electrolyte comprising at least one solvent and at least one lithium salt, wherein the fluorofilm comprises at least one layer, the layer comprising a mixture of two fluoropolymers, namely fluoropolymer A comprising at least one copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) having an HFP content of 3% by weight or more, and fluoropolymer B comprising a VDF homopolymer and / or at least one VDF-HFP copolymer, wherein fluoropolymer B has an HFP mass content at least 3% by weight less than the HFP mass content of polymer A.

[0082] According to one embodiment, the film consists of a single layer.

[0083] According to one embodiment, the mixture comprises the following: i. A mass percentage of polymer A of 10% to 99%, preferably 50% to 95%, and more preferably 25% to 95%, and ii. A mass percentage of polymer B of 1% or more and 90% or less, preferably less than 50% and more than 5%.

[0084] According to one embodiment, the monolayer fluoropolymer film has a thickness of 1 to 1000 μm, preferably 1 μm to 500 μm, and more preferably 5 μm to 100 μm.

[0085] According to one embodiment, if the film is a monolayer film, the fluoropolymer film can be produced by a solvent-mediated process. Polymers A and B are dissolved in a solvent known to polyvinylidene fluoride or its copolymer. Non-exclusive examples of solvents include N-methyl-2-methylpyrrolidone, dimethyl sulfoxide, dimethylformamide, methyl ethyl ketone, and acetone. The solution is applied to a flat substrate, and after the solvent is evaporated, a film is obtained.

[0086] According to one embodiment, the fluoropolymer film is a monolayer film in which at least one of the layers is composed of a mixture of polymers A and B according to the present invention. The overall thickness of the multilayer film is 2 μm to 1000 μm, and the thickness of the fluoropolymer layer according to the present invention is 1 μm to 999 μm.

[0087] The additional layer is selected from the following polymer compositions.

[0088] - A composition comprising a fluoropolymer selected from vinylidene fluoride homopolymer and, preferably, a VDF-HFP copolymer containing at least 90% by mass of VDF,

[0089] - A composition comprising a mixture of a fluoropolymer selected from vinylidene fluoride homopolymer and VDF-HFP copolymer containing at least 85% by mass of VDF, and a copolymer containing methyl methacrylate (MMA) homopolymer and at least 50% by mass of MMA and at least one other monomer copolymerizable with MMA. Examples of comonomers copolymerizable with MMA include alkyl (meth)acrylates, acrylonitrile, butadiene, styrene, isoprene, etc. The MMA polymer (homopolymer or copolymer) is advantageous to contain 0 to 20% by mass, preferably 5 to 15% by mass of C1 to C8 alkyl (meth)acrylate. Preferably, methyl acrylate and / or ethyl acrylate. The MMA polymer (homopolymer or copolymer) may be functionalized, meaning that the polymer contains, for example, acid, acyl chloride, alcohol and / or anhydride functional groups. These functional groups are introduced by grafting or copolymerization. The functional groups are advantageous to be acid functional groups, particularly those provided by acrylic acid comonomers. Alternatively, monomers having two adjacent acrylic acid functional groups that can undergo a dehydration reaction to produce an anhydride can be used. The proportion of functional groups can be 0 to 15% by mass of the MMA polymer, for example, 0 to 10% by mass.

[0090] According to one embodiment, the fluoropolymer film is produced by a transformation process of a molten polymer, such as flat film extrusion, blown film extrusion, calendering, or compression molding.

[0091] According to one embodiment, the film forming the separator further comprises an inorganic filler such as silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, zeolite, or a mixture thereof.

[0092] According to one embodiment, the film is a lithium superionic conductor (LISICON) and its derivatives, thio-LISICON, a Li4SiO4-Li3PO4 type structure, a sodium superionic conductor (NASICON) and its derivatives, Li1.3 Al 0.3 Ti 1.7 (PO4)3-type structures, garnet structure Li7La3Zr2O 12 (LLZO) and derivatives, lithiophilite structure Li 3x La 2 / 3-2x□1 / 3-2x TiO3(0 < x < 0.16)(LLTO), amorphous, crystalline or semi-crystalline sulfides, for example, where X is the element Si, Ge, Sn, As, Al or a combination of these elements, S is the element S or Si or a combination of these elements, and T is the element Sn, LSS, LTS, LXPS, LXPSO or LATS sulfides, and further includes solid electrolytes such as LiPSX, LiBSX, LiSnSX or LiSiSX sulfides where X is the element F, Cl, Br or I. According to one embodiment, the solid electrolyte in the film may be a combination of the above solid electrolytes.

[0093] According to one embodiment, the solvent is selected from cyclic and acyclic alkyl carbonates, ethers, glymes, formates, esters, nitriles and lactones.

[0094] Among the ethers, linear or cyclic ethers such as dimethoxyethane (DME), methyl ethers of oligoethylene glycol with 2 to 100 oxyethylene units, dioxolane, dioxane, dibutyl ether, tetrahydrofuran, and mixtures thereof can be mentioned.

[0095] Among the esters, phosphate esters and sulfite esters can be mentioned. For example, methyl formate, methyl acetate, methyl propionate, ethyl acetate, butyl acetate or mixtures thereof can be mentioned.

[0096] The glyme used has the general formula R1-O-R2-O-R3, where R1 and R3 are linear alkyls with 1 to 5 carbons, and R2 is a linear or branched alkyl chain with 3 to 10 carbons.

[0097] Among the lactones, particularly gamma-butyrolactone can be mentioned.

[0098] Examples of nitriles include acetonitrile, pyronitrile, propionitrile, methoxypropionitrile, dimethylaminopropionitrile, butyronitrile, succinonitrile, isobutyronitrile, valeronitrile, pivalonitrile, isovaleronitrile, glutaronitrile, methoxyglutalonitrile, 2-methylglutalonitrile, 3-methylglutalonitrile, adiponitrile, malononitrile, and mixtures thereof.

[0099] Among carbonates, for example, cyclic carbonates, such as ethylene carbonate (EC) (CAS: 96-49-1), propylene carbonate (PC) (CAS: 108-32-7), butylene carbonate (BC) (CAS: 4437-85-8), dimethyl carbonate (DMC) (CAS: 616-38-6), diethyl carbonate (DEC) (CAS: 105-58-8), ethyl methyl carbonate (EMC) (CAS: 623-53-0), diphenyl carbonate (CAS: 102-09-0), and methyl carbonate. Examples include phenyl carbonate (CAS: 13509-27-8), dipropyl carbonate (DPC) (CAS: 623-96-1), methylpropyl carbonate (MPC) (CAS: 1333-41-1), ethylpropyl carbonate (EPC), vinylene carbonate (VC) (CAS: 872-36-6), fluoroethylene carbonate (FEC) (CAS: 114435-02-8), trifluoropropylene carbonate (CAS: 167951-80-6), or mixtures thereof.

[0100] According to one embodiment, the lithium salt present in the separator is selected from LiPF6 (lithium hexafluorophosphate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethane)sulfonimide), LiTDI (lithium 2-trifluoromethyl-4,5-dicyanoimidazolate), LiPO2F2, LiB(C2O4)2, LiF2B(C2O4)2, LiBF4, LiNO3, LiClO4, and mixtures thereof.

[0101] According to one embodiment, the electrolyte present in the separator includes at least one additive as well as a solvent and a lithium salt. The additive can be selected from the group consisting of fluoroethylene carbonate (FEC), vinylene carbonate, 4-vinyl-1,3-dioxolan-2-one, pyridazine, vinylpyridazine, quinoline, vinylquinoline, butadiene, sebaconitrile, alkyl disulfide, fluorotoluene, 1,4-dimethoxytetrafluorotoluene, t-butylphenol, di-t-butylphenol, tris(pentafluorophenyl)borane, oxime, aliphatic epoxide, halogenated biphenyl, methacrylic acid, allyl ethyl carbonate, vinyl acetate, divinyl adipate, propanesultone, acrylonitrile, 2-vinylpyridine, maleic anhydride, methyl cinnamate, phosphonate, vinyl-containing silane compounds, and 2-cyanofuran.

[0102] The additive can also be selected from salts with a melting point below 100°C, such as ionic liquids. These form liquids consisting only of cations and anions.

[0103] Examples of organic cations include, in particular, the following cations: ammonium, sulfonium, pyridinium, pyrrolidinium, imidazolium, imidazolinium, phosphonium, lithium, guanidinium, piperidinium, thiazolium, triazolium, oxazolium, pyrazolium, and mixtures thereof.

[0104] Examples of anions include imides in particular, especially bis(trifluoromethanesulfonyl)imides and bis(fluorosulfonyl)imides, borates in particular, especially tetrafluoroborates (abbreviated as BF4). - ), phosphates, especially hexafluorophosphate (abbreviated as PF6 - ), phosphinates and phosphonates, especially alkyl phosphonates, amides, especially dicyanamide (abbreviated as DCA - ), aluminates, especially tetrachloroaluminate (AlCl4- ), halides (bromide anions, chloride anions, iodide anions), cyanates, acetates (CH3COO - ), especially trifluoroacetates, sulfonates, especially methanesulfonates (CH3SO3 - Examples include trifluoromethanesulfonates and sulfates, particularly hydrogen sulfates.

[0105] According to one embodiment, the electrolyte in the separator has a salt concentration of 0.05 mol / L to 5 mol / L in the solvent.

[0106] According to one embodiment, the ratio of electrolyte to fluoropolymer in the separator is 0.05 to 20, preferably 0.1 to 10.

[0107] According to one embodiment, the film in the separator has a mass increase of at least 5% by weight, preferably 10% to 1000%.

[0108] The gelled polymer membrane form of the separator is advantageously non-porous, which is why gas permeability tests (with a separator surface area of ​​10 cm²) are conducted. 2 In this case, the gas permeability of the separator is 0 ml / min, as detected when the pressure difference between the gases on both sides is 1 atmosphere and the time is 10 minutes.

[0109] According to one embodiment, the separator comprises a single gelling polymer membrane. According to another embodiment, the separator comprises a multilayer film in which each layer has the composition of the above-described film. In the separator, it is advantageous that the membrane is not supported by a support.

[0110] Finally, the present invention relates to a method for manufacturing a Li-ion battery including the cathode.

[0111] Li-ion cells are manufactured by assembling an anode, separator, and cathode.

[0112] According to one embodiment, a liquid electrolyte comprising at least one solvent and at least one lithium salt is introduced into the cell before the cell is sealed, and the swelling of the binder in the cathode forms the cathode liquid.

[0113] The cell can be heated at 30°C to 90°C, preferably 40°C to 70°C, for 5 minutes to 24 hours, preferably 30 minutes to 12 hours, to promote the swelling of the binder in the cathode impregnated with cathodelime and the polymer gel (if appropriate) in the separator. Furthermore, the Li-ion cell can be subjected to an increased pressure of 0.01 MPa to 3 MPa to promote the impregnation of the cathodelime.

[0114] According to one embodiment, the cathode containing the cathode liquid is assembled with a separator and an anode, and the separator may be a solid or semi-solid electrolyte such as a polymer gel electrolyte. [Examples]

[0115] The following examples illustrate the scope of the present invention in a non-limiting manner.

[0116] <Cathode Manufacturing>

[0117] <Product> - Active material (AS): NMC622 - Carbon Black (CB): Super C65

[0118] - Contains PVDF 1:25 wt% HFP, 100s -1 and a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) characterized by a melt viscosity of 1000 Pa·s at 230°C.

[0119] - PVDF 2:100s -1 and a vinylidene fluoride homopolymer characterized by a melt viscosity of 1000 Pa·s at 230°C.

[0120] - PVDF 3: Acid-functionalized with a functional group content of approximately 1% by mass, and in an NMP solution with a solid content of 10%, for 5 seconds. -1 and a vinylidene fluoride homopolymer characterized by a viscosity of 547 cP at 25°C.

[0121] Cathodelibrium: 0.75M lithium bis(fluorosulfonyl)imide (LiFSI) sold by Arkema in DME

[0122] Many quasi-solid cathodes are fabricated by mixing an active material, a carbon black electron conductor, and a binder. This can be a mixture of PVDF in an N-methylpyrrolidone solvent. An aluminum current collector is coated with this ink, and then dried to evaporate the solvent. The electrode is then calendered to reduce its porosity.

[0123] Table 1 summarizes the compositions based on the mass of various cathodes.

[0124] [Table 1]

[0125] <Measurement of cathode contact resistance using impedance spectroscopy> Impedance measurements are performed on a button cell containing two similar cathodes separated by a triple-layer PP / PE / PP separator. Figure 1 shows the impedance spectra obtained for the cathodes in Table 1. The diameter of the semicircle is proportional to the contact resistance at the interface between the cathode and the aluminum current collector. Despite their high binder content, the cathodes of Examples 1 and 2 have relatively low contact resistance, similar to that of Comparative Example 1. As shown in the CB / PVDF values ​​in Table 1, contact resistance increases as the carbon black content decreases relative to the binder.

[0126] <Evaluation of cathode performance at 1C> The cathode from Example 2 is assembled as a button cell with respect to a lithium metal anode. The separator is a membrane consisting of PVDF 1 and PVDF 2. 20 μl of liquid electrolyte containing 0.75 M LiFSI in dimethoxyethane solvent is injected into the button cell before sealing the cell. The cell is then heated at 45°C for 2 hours to allow the electrolyte to swell the polymer and form a gel in the separator and cathode solution.

[0127] The cathode of Comparative Example 1 is assembled as a button cell with respect to a lithium metal anode. The separator is a triple PP / PE / PP layer, and the electrolyte contains 1M LiPF6 in EC / EMC (3:7, vol).

[0128] Figure 2, attached, shows the capacitance supplied by cathodes E2 and CE1 at a discharge current of 1C.

[0129] The quasi-solid cathode of Example 2, assembled with a polymer gel electrolyte, exhibits similar performance at 1C to the cathode of Comparative Example 1, which operates with a liquid electrolyte.

Claims

1. A cathode for a lithium-ion battery comprising an active electrode material, a conductive additive, optionally an inorganic oxide, a polymer binder, and a cathode liquid, - The binder is a mixture of two fluoropolymers, namely, fluoropolymer A, which contains at least one copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) having an HFP content of 3% by weight or more, and fluoropolymer B, which contains a VDF homopolymer and / or at least one VDF-HFP copolymer, wherein fluoropolymer B has an HFP mass content that is at least 3% by weight less than the HFP mass content of polymer A. - The cathode liquid comprises at least one solvent and at least one lithium salt, The ratio of the mass content of the conductive additive to the polymer binder is greater than 0.

7. Cathode for lithium-ion batteries.

2. The cathode according to claim 1, wherein the HFP content of the at least one VDF-HFP copolymer that forms part of the composition of the fluoropolymer A is 8% or more and 55% or less.

3. The cathode according to claim 1 or 2, wherein the HFP content of the mixture of polymers A and B exceeds 7% by weight.

4. The cathode according to one of claims 1 to 3, wherein the mass ratio of polymer A to polymer B is greater than 1.

5. The active material is of type xLi ２ MnO ３ ·(1 - x)LiMO ２ (0 ≤ x ≤ 1), LiMPO ４ type, Li ２ MPO ３ F type, Li ２ MSiO ４ type (where M is Co, Ni, Mn, Fe or a combination thereof), LiMn ２ O ４ type, or S ８ The cathode according to any one of claims 1 to 4, selected from compounds of type S

6. The cathode according to one of claims 1 to 5, wherein the conductive additive is selected from carbon black, graphite, natural or synthetic carbon fibers, carbon nanotubes, metal fibers and powders, conductive metal oxides, or mixtures thereof.

7. The cathode according to one of claims 1 to 6, wherein the solvent present in the cathode liquid is selected from cyclic and acyclic alkyl carbonates, ethers, glycans, formates, esters, nitriles, and lactones.

8. The lithium salt present in the cathode solution is LiPF ６ , LiFSI, LiTFSI, LiTDI, LiPO ２ F ２ LiB(C) ２ O ４ ) ２ LiF ２ B (C ２ O ４ ) ２ LiBF ４ LiNO ３ and LiClO ４ A cathode according to any one of claims 1 to 7, selected from a mixture thereof.

9. The cathode according to one of claims 1 to 8, wherein the cathode liquid has a lithium salt concentration of 0.05 to 5 mol / L in the solvent.

10. The cathode according to one of claims 1 to 9, wherein the ratio of the cathode liquid to the polymer binder is 0.05 to 20, preferably 0.1 to 10.

11. The following compositions by mass, namely, - 52% to 95.5%, preferably 65% ​​to 92% of the active material, - 1% to 11%, preferably 1.5% to 7.5% of conductive additives, - 1% to 11%, preferably 1.5% to 7.5% of a polymer binder, - 0% to 2%, preferably 0% to 1% inorganic oxides, - 2.5% to 28%, preferably 5% to 20% of the cathode solution, A cathode according to one of claims 1 to 10, having a total of 100% of these proportions.

12. A secondary Li-ion battery comprising an anode, a cathode, and a separator, wherein the cathode has the composition described in one of claims 1 to 11.

13. The battery according to claim 12, wherein the separator comprises one or more porous layers of polypropylene and / or polyethylene, and optionally comprises a coating on one or both sides of the separator, the coating comprising a polymer binder and inorganic particles.

14. The battery according to claim 12, wherein the separator is a gelling polymer membrane comprising a fluoropolymer film and an electrolyte comprising at least one solvent and at least one lithium salt, the fluorofilm comprising at least one layer, the layer comprising a mixture of two fluoropolymers, namely, fluoropolymer A comprising at least one copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) having an HFP content of 3% by weight or more, and fluoropolymer B comprising a VDF homopolymer and / or at least one VDF-HFP copolymer, the fluoropolymer B having an HFP mass content at least 3% by weight less than the HFP mass content of polymer A.

15. The battery according to claim 14, wherein the solvent is selected from cyclic and acyclic alkyl carbonates, ethers, glycans, formates, esters, nitriles, and lactones.

16. The lithium salt is LiPF ６ , LiFSI, LiTFSI, LiTDI, LiPO ２ F ２ LiB(C) ２ O ４ ) ２ LiF ２ B (C ２ O ４ ) ２ LiBF ４ LiNO ３ and LiClO ４ A battery according to claim 14 or 15, selected from the above.

17. A method for manufacturing a Li-ion battery according to one of claims 12 to 16, comprising assembling the anode, the separator, and the cathode within a cell.

18. The method according to claim 17, comprising the step of introducing an electrolyte comprising at least one solvent and at least one lithium salt before sealing the cell.

19. A method for manufacturing a Li-ion battery according to claim 18, further comprising the step of heating the cell at 30 to 90°C for 5 minutes to 24 hours.

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