Particle coating process based on a cathode material

Abstract

A process for coating particles based on a cathode material. A process for preparing coated particles, comprising at least the steps of: a) having at least one basic particle comprising, for at least 95% of its mass, a cathode material; b) contacting, at least partially, the basic particle with a liquid component comprising at least one coating agent of formula (II) AOa[OSi(CmH2m+1)3]bHc, in which: 0 ≤ a ≤ 1, 1 ≤ m ≤ 4, 1 ≤ b ≤ 4, 0 ≤ c ≤ 3, and A being selected from P, Si, B and mixtures thereof, etc.; drying the liquid component to form a coating adhering to the surface of the basic particle. Figure for abstract: None

Description

Title of the invention: Method for coating particles based on a cathode material Technical field

[0001] The present invention relates to the field of cathode materials for lithium-ion batteries, more commonly called LIB cathode materials (in the English terminology "lithium-ion battery"), in particular intended to be used in the cathodes of lithium-ion batteries. More specifically, it relates to the field of cathode materials based on mixed oxides. Prior art

[0002] Mixed oxides known as active materials for a positive electrode, more simply called mixed oxide type LIB cathode materials, are generally oxides of lithium and one or more transition metals optionally containing one or more dopants. They comprise oxygen (O), lithium (Li), one or more elements from the d block of the periodic table of elements, such as nickel (Ni), manganese (Mn), cobalt (Co), and optionally one or more dopants such as aluminum (Al), zinc (Zn), niobium (Nb), iron (Fe), titanium (Ti), zirconium (Zr) and vanadium (V). Examples include mixed oxides of formula LiNixMnyCozO2 with x+y+z=l (called NMC), mixed oxides of formula LiNixCozAlwO2 with x+z+w=l (called NCA), LiCoO2 (called LCO), LiMn2O4 (called LMO), LiNiO2 (called LNO) and LiNio.5Mn1.5O4 (called LNMO).

[0003] Mixed oxide LIB cathode materials have been the subject of numerous studies because they have a high specific electrical capacity and can achieve a high voltage. NMC type materials are further advantageous with regard to their energy density, electrochemical stability and high temperature stability.

[0004] The specific electrical capacity and the energy storable by mixed oxide type LIB cathode materials, in particular NMC type, can be improved if the voltage range is widened to high voltages, for example from 4.2V to 4.8V, or even up to 5V. However, at such potentials, the usual electrolytes are unstable, which leads to their decomposition on the surface of the mixed oxide type materials and / or the electrodes, and therefore to the formation of a passivation layer which is detrimental to the performance of the electrode.

[0005] In order to overcome these drawbacks, it has been proposed to coat the surface of mixed oxide type materials with an ionically conductive film stable at voltages high, as in WO 2022 / 136425, US 2020 / 0373560 Al, WO 2020 / 251710 A2 and Kurinjimala et al., Surface & Coatings Technology, 2023, Morino et al., ACS Appl. Mater. Interfaces, 2023 and Xin et al., ACS Appl. Mater. Interfaces, 2019.

[0006] There is a continuing need for a new, inexpensive process that can be easily implemented on an industrial scale for preparing a mixed oxide cathode material that limits or even overcomes instability problems when used in a lithium-ion battery under high voltage conditions. Statement of the invention

[0007] The invention relates to a method for preparing coated particles, comprising at least the steps of: a) having at least one basic particle comprising, for at least 95% of its mass, a cathode material of formula (I) LiuNixMnyCozMwOt in which: 0 <u< 1, 0<x< 1, 0 < y < 2, 0<z< 1, 0 < w < 0,5, t = 2 ou t = 4, (x + y + z + w) / t = 0.5, and M being chosen from Al, Fe, Ti, Zr, V, Zn, Nb and their mixtures, b) bringing into contact, at least partially, the base particle with a liquid component comprising at least one coating agent of formula (II) AOa[OSi(CmH2m+i)3] bHc, in which: 0 <a< 1, 1 < m < 4, 1 < b < 4, 0 < c < 3, et A being chosen from P, Si, B and their mixtures, and (c) drying the liquid component to form a coating adhering to the surface of the base particle.

[0008] It has already been proposed to use tris(trimethylsilyl)phosphite (TMSPi) in lithium batteries (JP 2004-14351 A, EP 1 926 172 Al, US 2022 / 0029164 Al, US 2013 / 0164604, Song et al., J. Mater. Chem. A, 2014, Peebles et al., Journal of The Electrochemical Society, 2017, Han et al., ACS Appl. Mater. Interfaces, 2015 and Qi et al., RCS Adv., 2016), as an additive in liquid electrolytes.

[0009] To the inventors' knowledge, however, it had never been envisaged to coat a base particle comprising a cathode material of formula (I) with a coating agent of formula (II), in particular in order to form a cathode.

[0010] As is apparent from the examples below, the method according to the invention makes it possible to reduce the resistivity and improve the high current performance of the base particles. More particularly, the cathodes based on the coated particles obtained by the method exhibit a slower decrease in the specific electrical capacity and a better Coulomb efficiency during their operation in a lithium-ion battery cell.

[0011] Without being bound by any theory, the inventors attribute these performances to a reaction between the coating agent, in particular tris(trimethylsilyl)phosphite, and the surface of the base particles to form a protective and ionically conductive film, which is chemically stable in contact with a usual lithium-ion battery electrolyte and electrochemically stable up to potentials of at least 4.3V. In addition, advantageously, the method does not affect the structure of the base particles and therefore their high specific electrical capacity.

[0012] The invention also relates to a coated particle, preferably obtained by the method according to the invention, comprising: - a basic particle comprising, for at least 95% of its mass, a cathode material of formula (I) LiuNixMnyCozMwOt in which: 0 <u< 1, 0<x< 1, 0 < y < 2, 0<z< 1, 0 < w < 0,5 t = 2 ou t = 4, (x + y + z + w) / t = 0,5, et M étant choisi parmi Al, Fe, Ti, Zr, V, Zn, Nb et leurs mélanges, - un enrobage adhérant à la surface de la particule de base et enrobant au moins partiellement la particule de base, ledit enrobage comprenant plus de 40% de groupes choisis parmi les groupes phosphate, les groupes organophosphate, les groupes silicate, les groupes borate et leurs mélanges, et moins de 60% de groupes organiques, exprimés en pourcentages en nombre de moles sur la base de la somme du nombre de moles de groupes phosphate, de groupes organophosphate, de groupes silicate, de groupes borate et de groupes organiques dans l’enrobage.

[0013] The invention also relates to a powder comprising, or even consisting of, a plurality of particles coated according to the invention and / or obtained by the process according to the invention.

[0014] The invention also relates to a method of manufacturing an electrode, comprising at least the steps of: i) having a mixture comprising a plurality of particles coated according to the invention and / or obtained by the process according to the invention, one or more binders and optionally one or more electronically conductive additives, and ii) shape the mixture to obtain the electrode.

[0015] Thus, the invention also relates to an electrode, in particular a cathode, comprising, as active material, particles coated according to the invention and / or obtained by the method according to the invention, said electrode being in particular obtained by the method according to the invention.

[0016] It also relates to an electrochemical system comprising an electrode according to the invention, in particular a lithium-ion battery. Brief description of the drawings

[0017] [Fig. 1] shows the evolution of the specific electrical capacity (in mAh / g) at 25°C as a function of the number of charge / discharge cycles, at increasing rates (5 cycles at C / 10, C / 5, C, 2C, 5C, 10C, then return to C / 10), for the half-cells prepared in example 2, respectively implementing a conventional electrode comprising uncoated base particles and an electrode comprising the coated particles in accordance with the invention.

[0018] [Fig.2] shows the evolution of the specific electrical capacity (in mAh / g) at 25°C as a function of the number of charge / discharge cycles at a rate of C / 10 for the first two cycles then C / 5, for the half-cells prepared in example 2, respectively using a conventional electrode comprising uncoated base particles and an electrode comprising the coated particles in accordance with the invention.

[0019] [Fig.3] shows the evolution of the coulombic efficiency (in %) at 25°C as a function of the number of charge / discharge cycles at a rate of C / 10 for the first two cycles then C / 5, for the half-cells prepared in example 2, respectively using a conventional electrode comprising uncoated base particles and an electrode comprising the coated particles in accordance with the invention. Detailed description

[0020] The cathode material may be chosen from compounds of formula LiNixMn yCozO2 with x+y+z=l (also called NMC), LiNixCozAlwO2 with x+z+w=l (also called NCA), LiCoO2 (lithium cobalt oxide also called LCO), LiMn2O4 (lithium manganese oxide also called LMO), LiNiO2 (lithium nickel oxide also called LNO), LiNio,5Mni>504 (called LNMO) and mixtures thereof. In particular, the material cathode can be chosen from NMC, LCO, LNO and LNMO, more particularly from NMC and LNMO.

[0021] The coefficient u can be equal to 1.

[0022] The coefficient x can be strictly positive, in particular greater than or equal to 0.2, more particularly greater than or equal to 0.5, in particular greater than or equal to 0.6, or even greater than or equal to 0.8. The coefficient x may be strictly less than 1, more particularly less than or equal to 0.8.

[0023] The coefficient y may be less than or equal to 1, in particular less than or equal to 0.5, more particularly less than or equal to 0.3, in particular less than or equal to 0.2, or even less than or equal to 0.1. The coefficient y may be strictly positive, in particular greater than or equal to 0.05, more particularly greater than or equal to 0.1. Alternatively, the coefficient y may be strictly greater than 1, in particular greater than or equal to 1.5.

[0024] The coefficient z may be less than or equal to 0.5, more particularly less than or equal to 0.3, in particular less than or equal to 0.2, or even less than or equal to 0.1. In particular, the coefficient y may be strictly positive, in particular greater than or equal to 0.05, more particularly greater than or equal to 0.1.

[0025] The coefficient w may be less than or equal to 0.3, in particular less than or equal to 0.1.

[0026] M can be chosen from aluminum (Al), iron (Fe), titanium (Ti), zirconium (Zr), vanadium (V) and mixtures thereof, preferably M is Al.

[0027] In particular, the cathode material may be of formula (La) LiNixMnyCozMwOt in which: 0 <x< 1, 0 < y < 2, 0<z< < w < 0,5, t="4," ou (x + y z w) 1="0,5" et m étant choisi parmi al, fe, ti, zr, v, zn, nb leurs mélanges.

[0028] The cathode material may be of formula (La) with: 0 < x < 1, in particular 0 < x < 1, 0 < y < 0.5, 0 < z < 1, in particular 0 < z < 0.5, 0 < w < 0.5, t = 2, and M being chosen from Al, Fe, Ti, Zr, V, Zn, Nb and their mixtures, in particular from Al, Fe, Ti, Zr, V and their mixtures, or even being Al.

[0029] In particular, the cathode material may be of formula (La) with: 0 < x < 1, more particularly 0.2 < x < 1, in particular 0.5 < x < 1, 0 < y < 0.5, more particularly 0 < y < 0.4, in particular 0 < y < 0.3, 0 < z < 0.5, more particularly 0 < z < 0.4, in particular 0 < z < 0.3, w = 0, and t = 2.

[0030] Alternatively, the cathode material may be of formula (Ia) with:

[0031] 0 < x < 1, in particular 0 < x < 0.5 0 < y < 2, in particular 1 < y < 2 z = 0, w = 0, and t = 4.

[0032] Preferably, the cathode material is chosen from compounds of formula LiNixMnyCozO2 with x+y+z=l (called NMC), in particular from compounds of formulas LiNio^Mno^Coo 33O2 (called NMCm), LiNi0.5Mn0.3Co0,2O2 (called NMC532), LiNi0.6Mn0.2Coo .2O2 (called NMC622) and LiNi0.8Mn0.iCoo .iO2 (called NMC8h). Preferably, the cathode material is NMC8n.

[0033] In particular, the basic particle(s) have a size of between 0.2 and 30 μm, in particular between 0.2 and 20 μm. Usually, the “size” of a basic particle corresponds to the minimum mesh of a standard sieve through which said particle passes.

[0034] Preferably, the base particle(s) are in the form of a powder comprising a plurality of base particles.

[0035] The base particle(s) may have a ball shape. A ball has a sphericity, in other words the ratio between the smallest diameter and the largest diameter of the ball, greater than or equal to 0.6, in particular greater than or equal to 0.7, or even greater than or equal to 0.8, or even greater than or equal to 0.9.

[0036] Preferably, the base particle is prepared under an inert atmosphere. By "inert atmosphere" is meant an atmosphere that does not react with the cathode material. The inert atmosphere is preferably free of H2O and CO2, for example is an atmosphere of nitrogen, argon or oxygen.

[0037] Preferably, after their preparation and before step b), the base particle(s) are stored under an inert atmosphere.

[0038] The preparation of basic particles of formula (I), in particular of formula (La), is well known to those skilled in the art, and described for example in Malik et al., Materials Today Energy, 28 (2022).

[0039] The basic particle(s) may comprise, for at least 97%, in particular for at least 99%, of their mass relative to their total mass, said material cathode material of formula (I), in particular of formula (Ia). In particular, the base particle(s) may consist of said cathode material of formula (I), in particular of formula (Ia).

[0040] The coating agent is of formula (II) AOa[OSi(CmH2m+i)3]bHc.

[0041] Preferably, a, m, b and / or c are integers.

[0042] The coefficient a can be equal to 0 or 1. Preferably, a is equal to 0.

[0043] The coefficient b can be an integer such that 1 < b < 4, in particular 1 < b < 3, more particularly b is equal to 2 or 3, preferably b is equal to 3.

[0044] The coefficient c may be an integer such that 0 < c < 3, in particular 0 < c < 2, more particularly c is equal to 0 or 1, preferably c is equal to 0.

[0045] In particular, the sum of b and c can be equal to 3.

[0046] The coefficient m can be an integer such that 1 < m < 4, in particular m is less than or equal to 3, more particularly less than or equal to 2, preferably equal to 1.

[0047] A is chosen from phosphorus (P), silicon (Si), boron (B) and mixtures thereof. In particular, A is P or Si or B. Preferably A is phosphorus P.

[0048] The coating agent may be of formula (II) with: a = 0, 1 < m < 4, 1 < b < 3, 0 < c < 2, and A being chosen from P, Si, B and their mixtures, in particular being P. In particular, the coating agent may be of formula P[OSi(CmH2m+i)3]3 with 1 < m < 4. Preferably, the coating agent is tris(trimethylsilyl)phosphite of formula P[OSi(CH3)3]3.

[0049] Preferably, the liquid component comprises only the coating agent of formula (II) as coating agent.

[0050] The liquid component may be a solution of the coating agent in a solvent. In particular, the solution consists of a solvent and said coating agent. In particular, the solvent may be chosen from acetonitrile, methanol, ethanol, propanol, butanol, hexane, acetone and mixtures thereof. Preferably, the solvent is acetonitrile. In particular, the solution may comprise from 0.01 to 99.95%, in particular at least 0.1%, especially at least 1% of the coating agent, the percentages being expressed by mass relative to the mass of the solution.

[0051] Alternatively, the liquid component may consist of the coating agent in a liquid form.

[0052] In step b), the base particle is preferably brought entirely into contact with the liquid component. In other words, the entire surface of the base particle(s) can be brought into contact with the liquid component.

[0053] In particular, a suspension comprising a plurality of base particles immersed in the liquid component can be formed. The base particles can be used in an amount of 0.1% to 90% by mass, in particular 5% to 50% by mass, relative to the sum of the mass of the liquid component and the base particles. In particular, the coating agent and the base particles can be brought together in a coating agent / base particle mass ratio of between 0.1 and 10, in particular between 0.5 and 2.

[0054] The contacting in step b) can be carried out at a temperature between 5°C and 150°C, in particular between 15°C and 100°C, more particularly between 20°C and 40°C. The contacting conditions make it possible to ensure uniform deposition and optimal adhesion of the coating to the surface of the base particle during step c).

[0055] In particular, the contacting step may be carried out by mixing one or more base particles with the liquid component, in particular a solution containing the coating agent. The contacting may be maintained for at least 5 minutes, in particular at least 12 hours, more particularly at least 1 day, in particular at least 3 days.

[0056] Preferably, at least step b) of contacting is carried out under an inert atmosphere, for example under argon or under vacuum, in particular under argon.

[0057] After bringing the base particle into contact with the liquid component, the coating agent may be adsorbed onto the surface of the base particle and / or form bonds, in particular covalent bonds, with the surface of the base particle to form a coating layer. In particular, at the end of step b), the base particle is covered, at least in part, or even entirely, by a layer comprising the coating agent optionally modified by reaction with the surface of the base particle.

[0058] Preferably, the method further comprises, successively to step b) and before step c), a step of washing the particles obtained at the end of step b) with a washing liquid, in particular a solvent, more particularly an anhydrous solvent, in particular acetonitrile. Preferably, the washing step is carried out under an inert atmosphere. The washing step advantageously makes it possible to remove the coating agent molecules not attached to the surface and the other soluble residual molecules. By “residual” molecules is meant all the organic molecules resulting from any reactions between the coating agent and the particle, or the other molecules present in the liquid component.

[0059] The washing step may further comprise the separation of the particles obtained at the end of step b) and the washing liquid, in particular by centrifugation, for example at a speed of 14000 to 14500 rpm for 20 minutes.

[0060] The method may comprise one or more washing steps, in particular 3 washing steps.

[0061] The drying in step c) can be carried out at a temperature between 20°C and 700°C, in particular between 60°C and 100°C. The drying in step c) can be carried out under an inert atmosphere, in particular under argon or under vacuum, in particular under vacuum.

[0062] Drying is preferably carried out until complete evaporation of the solvent and possibly of the other residual molecules which are not adhered to the surface of the base particle.

[0063] At the end of step c), a coated particle can be recovered.

[0064] The coating adhering to the surface of the base particle preferably comprises more than 50%, in particular more than 60% of groups selected from phosphate groups, organophosphate groups, silicate groups, borate groups and mixtures thereof, expressed as a mole percentage based on the sum of the number of moles of phosphate groups, organophosphate groups, silicate groups, borate groups and organic groups in the coating. An "organic group" comprises, or even consists of, carbon and hydrogen atoms and optionally oxygen and / or nitrogen atoms. In particular, an organic group may comprise hydrocarbon groups such as methyl (CH3) groups.

[0065] The coating adhering to the surface of the base particle may comprise less than 50%, in particular less than 40% of organic groups, expressed as percentages by number of moles based on the sum of the number of moles of phosphate groups, organophosphate groups, silicate groups, borate groups and organic groups in the coating.

[0066] The content of phosphate groups, organophosphate groups, silicate groups, borate groups and organic groups can be measured by energy dispersive X-ray spectroscopy (EDX) in a scanning electron microscope.

[0067] In particular, phosphate groups, organophosphate groups, silicate groups, borate groups and organic groups represent more than 90% of the mass of the coating.

[0068] In particular, the coating comprises, or even consists of, groups grafted to the surface of the base particle, in particular derived from the coating agent molecules, for example trialkylsilyl groups and / or phosphate groups.

[0069] In particular, the coating comprises, or even consists of, grafted groups derived from the coating agent described in the present text on the surface of the base particle.

[0070] The coating may completely cover the surface of the base particle.

[0071] The thickness of the coating may be less than or equal to 5 μm, in particular between between 1 and 200 nm. The coating thickness can be measured by transmission electron microscopy (TEM).

[0072] Preferably, the coating covers the entire surface of the base particle.

[0073] In particular, the coated particle may consist of the base particle and the coating.

[0074] The coated particle can advantageously be used as an active electrode material, in particular a cathode.

[0075] An electrode may be prepared from the coated particles. The manufacture of the electrode may be carried out by any technique known to those skilled in the art.

[0076] In particular, the method according to the invention may comprise: - the preparation of a dispersion, more commonly called "ink", comprising, in one or more aqueous and / or organic solvents, said coated particles, the binder(s) and, where appropriate, the electronically conductive additive(s) to form said mixture, and - depositing the dispersion on the surface of a current collector, and evaporating said solvent(s) from the dispersion in step (ii).

[0077] The ink solvent may comprise water and / or one or more organic solvents, for example N-methyl-2-pyrrolidone.

[0078] Electronically conductive additives improve the electronic conductivity of the electrode. They can be chosen, for example, from carbon fibers, carbon black, carbon nanotubes and mixtures thereof.

[0079] Where appropriate, the content of said electronically conductive additive(s) may be between 1 and 10% by mass, in particular between 2 and 8% by mass, relative to the total mass of the electrode. It is understood that the total mass of the electrode does not include the mass of the current collector.

[0080] The binders ensure the mechanical strength of the electrode on the current collector, the cohesion of the different components of the electrode or even its flexibility properties. They can be chosen from polymer binders, in particular chosen from fluorinated polymers, for example from polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polymers derived from carboxymethylcellulose (CMC), polysaccharides and latexes, in particular of the styrene-butadiene rubber (BR) type or in English "stryrene-butadiene rubber" (SBR)).

[0081] A particularly preferred binder is poly(vinylidene fluoride) (PVDF).

[0082] Said binder(s) may be present in an amount less than or equal to 20% by mass, relative to the total mass of the electrode, in particular less than or equal to 10% by mass, in particular between 1 and 10% by mass, relative to the total mass of the electrode.

[0083] The coated particles may be present in a content of at least 70% by mass, in particular at least 80% by mass, more particularly ranging from 90% by mass to 95% by mass, relative to the total mass of the electrode.

[0084] The ink can be homogenized before spreading.

[0085] The deposition of the ink on the surface of the current collector can be carried out by any technique known to those skilled in the art, for example by coating, by a printing technique, by extrusion or by co-lamination.

[0086] The current collector may be solid, for example in the form of a strip or in the form of a grid.

[0087] The current collector may be made of a metallic material chosen from copper, aluminum, nickel or stainless steel potentially coated with carbon.

[0088] The evaporation of the solvent(s) from the ink may be carried out by drying, for example in an oven, at a temperature of between 20 and 150°C, in particular between 50 and 80°C, in particular for a period of between 1 and 15 hours.

[0089] Preferably, the step of evaporation of the solvent(s) is followed by a calendering step.

[0090] The grammage of the electrode, in other words the mass of the coated particles, per unit area, can be adjusted by controlling the rate of coated particles and the thickness of deposition, in particular coating, of the ink on the current collector. Preferably, the grammage of the electrode is between 0.1 mg / cm2 and 50 mg / cm2, in particular between 1 mg / cm2 and 30 mg / cm2, and more particularly between 3 mg / cm2 and 10 mg / cm2.

[0091] According to a particular embodiment, the manufacturing method may comprise the steps consisting of: - having a plurality of basic particles comprising, for at least 95% of their mass, a cathode material of formula (I) LiuNixMnyCozMwOt in which: 0 <u< 1, 0<x< 0 < y < 2, 0<z< < w < 0,5 t = 2 or t = 4, (x + y + z + w) / t = 0.5, and M being chosen from Al, Fe, Ti, Zr, V, Zn, Nb and their mixtures, - bringing the base particles into contact, at least partially, with a liquid component comprising at least one coating agent of formula (II) AOa[OSi(CmH2m+i)3] bHc, in which: 0 <a< 1, 1 < m < 4, < b 0 < c < 3, A being chosen from P, Si, B and their mixtures, and - drying the liquid component to form a coating adhering to the surface of the base particles, - preparing a mixture comprising said particles obtained after drying, one or more binders and optionally one or more electronically conductive additives, and - shape the mixture to obtain the electrode.

[0092] The electrode according to the invention may be a positive electrode of the electrochemical system.

[0093] The electrochemical system may comprise a liquid electrolyte comprising at least one alkali or alkaline earth metal salt in one or more organic solvents chosen from carbonate solvents, linear or cyclic ether solvents, nitrile solvents, lactone solvents, amide solvents, ester solvents and mixtures thereof.The alkali or alkaline earth metal salt is preferably selected from lithium salts, in particular selected from LiPF6, LiC104, LiBF4, LiAsF6, LiCF3SO3, LiN(C2F5SO2)2, lithium bistrifluoromethylsulfonylimide LiN[SO2CF3]2 (known by the abbreviation LiTFSI), lithium bis(fluorosulfonyl)amide (known by the abbreviation LiFSI) LiN[SO2F]2, lithium 4,5-dicyano-2-(trifluoromethyl)imidazole (known by the abbreviation LiTDI), lithium bispentafluoroethylsulfonylimide (known by the abbreviation LiBETI), lithium bis(oxalato)borate (known by the abbreviation LiBOB) and lithium difluoro(oxalato)borate (known by the abbreviation LiFOB) and mixtures of these.

[0094] Preferably, the electrolyte comprises at least one LiPF6 salt in one or more solvents chosen from ethylene carbonate, diethyl carbonate and their mixture. Examples

[0095] All tests were carried out with NMC8n particles marketed by BASF, having a size of 5 to 30 |am.

[0096] Example 1: preparation of coated particles according to the invention

[0097] The following synthesis steps were carried out under an argon atmosphere.

[0098] 1 g of NMC8n particles were placed in a sealed container. A A solution of 1 g of tris(trimethylsilyl)phosphite in 10 mL of acetonitrile was added to the container. The resulting suspension was mixed under a magnetic stirrer at 700 rpm (rotation per minute) for 1 day at 22°C, with all NMC8n particles immersed in the solution.

[0099] Then, all the particles obtained were placed in another container and washed 3 times with 100 mL of acetonitrile. After each wash, the contaminated acetonitrile was removed by centrifugation for 20 minutes at 14500 rpm. Between each washing cycle, the container was filled with acetonitrile.

[0100] The particles recovered after washing were then dried at 70°C under vacuum for 3 days until a solvent-free powder formed of NMC8n particles coated with tris(trimethylsilyl)phosphite was obtained.

[0101] Example 2: Electrodes comprising particles according to the invention and outside the invention

[0102] A cathode comprising 92% by mass of the particles prepared in Example 1, 4% by mass of Super C-65 (carbon black) and 4% by mass of PVDF, relative to its total mass, is formed by coating, on an aluminum-based current collector, an ink comprising these three compounds dispersed and / or solubilized in N-methyl-2-pyrrolidone.

[0103] The cathode is implemented in a half-cell of the "coin cell" type of lithium battery with a negative lithium electrode, a polypropylene-based separator, and an electrolyte consisting of a 1 mol / L solution of LiPF6 in a mixture of 50% ethylene carbonate and 50% diethyl carbonate.

[0104] A lithium battery half-cell is prepared as described above, but using a cathode comprising uncoated NMC8n particles, as commercially supplied.

[0105] Electrochemical tests are carried out by galvanostatic cycling at 22°C.

[0106] [Fig.l] represents the curve of the evolution of the specific electrical capacity for the two half-cells comprising particles according to the invention and outside the invention, as a function of the number of cycles at different speeds in a voltage interval of 2.8V-4.3V for the first two formation cycles then 3.0V-4.3V for the following cycles. A higher specific electrical capacity is observed for the electrode according to the invention at high speeds as well as a slower decrease in the specific electrical capacity during the cycles.

[0107] [Fig. 2] represents the curve of the evolution of the specific electrical capacity for the two half-cells comprising particles according to the invention and outside the invention, as a function of the number of cycles at a regime of C / 10 in a voltage interval of 2.8V-4.3V for the first two formation cycles then at a regime of C / 5 in a voltage interval of 3.0V-4.3V for the following cycles. A slower decrease in the specific electrical capacity is observed during the cycles for the electrode according to the invention.

[0108] [Fig.3] represents the coulombic efficiency during the cycles during the same test. It is observed that the coulombic efficiency of the electrode according to the invention is higher than that of the electrode outside the invention.

[0109] It is clear from these figures that the half-cell implementing the electrode comprising coated particles according to the invention has a slower drop in specific electrical capacity and better coulombic efficiency than the electrodes comprising uncoated particles. It is also observed that the electrode comprising coated particles is less resistive and has better performance at high current.

Claims

Claims

1. Process for the preparation of coated particles, comprising at least the steps of: a) providing at least one base particle comprising, for at least 95% of its mass, a cathode material of formula (I) LiuNi xMnyCozMwOt in which: 0 <u< 1, 0 < x < 1, 0 < y < 2, 0<z< 1, 0 < w < 0,5, t = 2 ou t = 4, (x + y + z + w) / t = 0,5, et M étant choisi parmi Al, Fe, Ti, Zr, V, Zn, Nb et leurs mélanges, b) mettre en contact, au moins partiellement, la particule de base avec un composant liquide comprenant au moins un agent d’enrobage de formule (II) AOa[OSi(CmH2m+i)3]bHc, dans laquelle : 0< a< 1, 1 < m < 4, 1 < b < 4, 0 < c < 3, et A étant choisi parmi P, Si, B et leurs mélanges, et c) sécher le composant liquide pour former un enrobage adhérant à la surface de la particule de base.

2. A method according to the preceding claim, wherein the base particle(s) are in the form of a powder comprising a plurality of base particles.

3. A method according to claim 1 or 2, wherein the cathode material is of formula (Ia) LiNixMnyCozMwOt in which: 0 <x< 1, 0 < y < 2, 0<z< 1, 0 < w < 0,5, t = 2 ou t = 4, (x + y + z + w) / 1 = 0,5 et M étant choisi parmi Al, Fe, Ti, Zr, V, Zn, Nb et leurs mélanges.

4. Method according to the preceding claim, in which the cathode material is of formula (Ia) with: 0 <x< 1, 0 < y < 0,5, 0 < z < 0,5, 0 < w < 0,5, t = 2, et M étant choisi parmi Al, Fe, Ti, Zr, V, Zn, Nb et leurs mélanges, notamment parmi Al, Fe, Ti, Zr, V et leurs mélanges, voire étant Al, en particulier 0 < x < 1, 0 < y < 0,5, 0 < z < 0,5, w = 0, et t = 2.

5. A method according to any one of claims 1 to 3, wherein the cathode material is selected from compounds of formula LiNi xMnyCozO2 with x+y+z=l (also called NMC), LiNixCozAlwO2 with x+z+w=l (also called NCA), LiCoO2 (also called LCO), LiMn2O4 (also called LMO), LiNiO2 (also called LNO), LiNi0>5 Mni>504 (also called LNMO) and mixtures thereof, preferably from compounds of formula LiNixMnyCozO2 with x+y+z=l such as LiNi0j8MnojiCo0ji02.

6. A method according to any one of the preceding claims, wherein the base particle(s) has a size of between 0.2 and 30 pm, in particular between 0.2 and 20 pm.

7. A method according to any one of the preceding claims, wherein the coating agent is of formula (II) with: a = 0, 1 < m < 4, 1 < b < 3, 0 < c < 2, and A being chosen from P, Si, B and mixtures thereof, in particular being P, in particular the coating agent is of formula P[OSi(CmII2m+i)3]3 with 1 < m < 4, preferably is tris(trimethylsilyl)phosphite of formula P[OSi(CH3)3]3.

8. A method according to any preceding claim, wherein the liquid component is a solution of the agent coating in a solvent, the solvent being in particular chosen from acetonitrile, methanol, ethanol, propanol, butanol, hexane, acetone and mixtures thereof, preferably acetonitrile.

9. A method according to any one of the preceding claims, wherein the contacting in step b) is carried out at a temperature between 15°C and 100°C, in particular between 20°C and 40°C.

10. A method according to any preceding claim, wherein the entire surface of the base particle(s) is contacted with the liquid component.

11. Process according to any one of the preceding claims, in which the drying in step c) is carried out at a temperature between 20°C and 700°C, in particular between 60°C and 100°C, in particular under vacuum.

12. A method according to any one of the preceding claims, wherein steps b) and c) are carried out under an inert atmosphere, in particular under argon or under vacuum.

13. Method according to any one of the preceding claims, further comprising, successively to step b) and before step c), a step of washing the particles obtained at the end of step b) with an anhydrous solvent, in particular acetonitrile, the washing step being in particular carried out under an inert atmosphere.

14. Coated particle, preferably obtained by the method defined in any one of the preceding claims, comprising: - a base particle comprising, for at least 95% of its mass, a cathode material of formula (I) LiuNixMnyCozMwOt in which: 0 <u< 1, 0 < x < 1, < y < 2, 0<z< < w < 0,5 t="0,5," ou (x + y z w) et m étant choisi parmi al, fe, ti, zr, v, zn, nb leurs mélanges, - un enrobage adhérant à la surface de particule base enrobant au moins partiellement base, ledit comprenant plus 40% groupes choisis les phosphate, organophosphate, silicate, lesborate groups and mixtures thereof, and less than 60% organic groups, expressed as mole percentages based on the sum of the moles of phosphate groups, organophosphate groups, silicate groups, borate groups and organic groups in the coating.

15. A coated particle according to the preceding claim, wherein the coating completely covers the surface of the base particle.

16. A coated particle according to claim 14 or 15, wherein the coating comprises, or even consists of, grafted groups derived from the coating agent defined in claim 1 or 7 on the surface of the base particle.

17. A method of manufacturing an electrode, comprising at least the steps of: i) providing a mixture comprising a plurality of coated particles according to any one of claims 14 to 16 and / or obtained by the method according to any one of claims 1 to 13, one or more binders and optionally one or more electronically conductive additives, and ii) shaping the mixture to obtain the electrode, the method comprising in particular: - preparing a dispersion comprising, in one or more aqueous and / or organic solvents, said coated particles, the binder(s) and, where appropriate, the electronically conductive additive(s) to form said mixture, and - depositing the dispersion on the surface of a current collector, and evaporating said solvent(s) from the dispersion in step (ii).

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