Method for preparing a coated cathode active material precursor, said precursor and uses thereof

Abstract

The present invention relates to a method for preparing a precursor material of a coated cathode active material comprising: (a) a step of preparing a solution containing a hydroxide, a nitrate, an acetate or an alkoxide of a metal M with M being other than lithium, (b) a step of bringing the particles of a precursor material of a cathode active material in oxide, hydroxide or carbonate form into contact with the solution prepared in step (a), (c) optionally a step of recovering the particles obtained at the end of step (b), (d) a step of drying the suspension obtained at the end of step (b) or optionally the particles recovered in step (c), whereby a precursor material of a cathode active material coated with a layer based on a metal M is obtained. The present invention also relates to the use of said method for preparing a coated cathode active material.

Description

[0001] METHOD FOR PREPARING A COATED CATHODE ACTIVE MATERIAL PRECURSOR, SAID PRECURSOR AND ITS USES

[0002] TECHNICAL FIELD

[0003] The present invention relates to the general field of Li-ion type batteries and more particularly to the cathode active materials (CAM for "Cathode Active Material") of such batteries.

[0004] Indeed, the present invention proposes a method for preparing a coated precursor of a cathode active material (PCAM), in which the coating step is carried out in solution with coating layer precursors such as hydroxides, nitrates, acetates, or metal alkoxides. The present invention also relates to the coated PCAM, with a core-shell structure, thus prepared, and its uses, particularly for preparing a coated cathode active material. Finally, the present invention relates to said coated cathode active material, with a core-shell structure, thus prepared, and its uses.

[0005] PREVIOUS STATE OF THE ART

[0006] Currently, lithium batteries are used and recommended in numerous applications such as electric and hybrid vehicles, and portable devices like computers, mobile phones, camcorders, cameras, and GPS units. The Li-ion battery market is experiencing strong growth due to new applications primarily related to the emergence and development of hybrid and all-electric vehicles.

[0007] Lithium-ion batteries consist of a negative electrode, a positive electrode, a separator, an electrolyte, and a casing which can be a polymer pouch or a metallic coating.

[0008] By convention, a positive electrode is the electrode that acts as the cathode when the battery is delivering current (i.e., in the process of discharging) and acts as the anode when the battery is in the process of charging, while a negative electrode acts as the anode when the battery is delivering current and acts as the cathode when the battery is in the process of charging.

[0009] In a lithium-ion battery, the negative electrode is typically made of graphite mixed with a carboxymethylcellulose (CMC) binder deposited on a copper foil. The positive electrode comprises a metallic lithium interstitial material (e.g., LiCoO2, LiMnCh, LiNiC2, LiNiMnCoZCh with x+y+z = 1 (or NMC), LiFePC) mixed with an organic binder, such as a polymeric binder like polyvinylidene fluoride, and an electrical conductor, more specifically a carbon-based agent, deposited on an aluminum foil. The electrolyte consists of a mixture of non-aqueous solvents and lithium salt(s), and possibly additives to slow down side reactions.Battery electrolytes can be composed of binary or ternary mixtures based on cyclic carbonates such as ethylene carbonate, propylene carbonate and butylene carbonate, linear carbonates or branched carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and dimethoxyethane in various proportions, in which a lithium salt such as, for example, LiPFe, LiCF3SO3, LiBF4 and LiClO4 is dissolved.

[0010] The process is as follows: during charging, lithium deintercalates from the metal oxide and intercalates within the graphite, where it is thermodynamically unstable. During discharging, the process is reversed, and lithium ions intercalate within the lithium metal oxide.

[0011] Polycrystalline NMC cathode materials are generally degraded during battery cycling. This degradation leads to damage to the CAM spheres and a reduction in battery lifespan. The insertion and removal of lithium in a lamellar oxide causes a change in the lattice parameter along the c-axis. This volume expansion can, over time, lead to fracturing of the spheres composed of crystals oriented in different directions.

[0012] Cathode material coating is a well-known technique in the literature that preserves the sphericity of CAM particles by applying a protective layer to their surface. The quality of the coating and its positive effect during battery cycling depend on several criteria, such as the coating method used (mechanical or solution coating, or atomic layer deposition, or ALD), the choice of coating phase, its mass percentage, and the type of coating applied to PCAM or CAM.

[0013] US patent 10,501,335 Bl [1] describes a coating process applied to CAMs such as NMC811 or NCA93-04-03. The coating phases studied are aluminum and / or cobalt-based. This process allows the diffusion of the coating phases inside the CAM spheres to strengthen the bonds between primary particles (coated primary particles). Such coating has improved the power and lifespan of the battery.

[0014] The coating applied to PCAMs in solution is a method that has received little attention in the literature due to its complexity. Firstly, it can lead to a non-homogeneous coating phase. Furthermore, the presence of the coating phase can disrupt the conversion of PCAMs, which are generally hydroxides or oxides of nickel and cobalt, manganese, iron, and / or titanium, into CAMs, i.e., lithium-ion battery positive electrode materials containing lithium. Moreover, in nickel-rich CAMs, Ni ions 3+ are not very stable at high temperatures. A small portion of these Ni ions 3+ can be reduced to Ni 2+ which tend to replace Li sites +During lithiation, this blocks lithium diffusion pathways and significantly reduces electrochemical performance. The presence of a foreign element, such as a coating metal, can exacerbate this phenomenon if the coating conditions are not properly optimized. Indeed, the coating metal no longer remains solely on the surface but can diffuse into the CAM structure, leading to Ni reduction. 3+ in Ni 2+ , Ni ions 2+ then exchanging with Li ions + .

[0015] Several patent applications describe coating processes for positive electrode materials for lithium-ion batteries in which the lithiation of the material precursor is carried out at the same time as the coating layer forms on the material.

[0016] In patent application EP 3959762 A1 [2], an aqueous suspension comprising hydrated nickel(II) carbonate, cobalt(II) carbonate, manganese(II) carbonate, and lithium carbonate is added dropwise to a mixture of oxalic acid dihydrate before 18 h of stirring. Hydrated niobium(V) oxalate is then added to the oxalate-based mixture, which is mixed for 2 h and then spray-dried. The resulting powder undergoes heat treatment under oxygen. After grinding, the powder is an NMC material coated with a layer of niobium oxide.

[0017] Furthermore, a process for coating PCAM using boron oxide is described in patent application EP 4048639 Al [3]. This patent application describes a coating process in which, in a first variant, non-lithianed nickel hydroxide particles are dry-mixed with micronized boron oxide or, in a second variant, metal salts, including nickel salts, are co-precipitated in solution with boron oxide. Regardless of the variant, the resulting precursor mixture is then calcined and mixed with a lithium source and calcined a second time to obtain a lithia-coated oxide with a boron coating layer.

[0018] Similarly, patent application CN 116845223 A [4] proposes a high-level nickel-doped ternary cathode material, obtained by mixing a cathode material precursor with niobium oxide and a lithium source such as lithium hydroxide and then subjecting the whole to calcination.

[0019] The operating procedure described in patent application EP 4048639 Al [3] and in patent application CN 116845223 A [4] is often used in the literature to carry out structural doping rather than coating since the final material must be calcined, washed with water to remove the remaining lithia-coated oxides on the surface and then calcined again.

[0020] In the process described in patent application EP 4048639 A1 [3], the boron oxide particles on the surface of the PCAMs can, after lithiation, transform into lithia-coated boron particles, which are then present in a heterogeneous and non-uniform manner on the surface of the CAMs. The size of the lithia-coated boron particles depends largely on the size of the initial oxide particles. Thus, since the oxide particles used are on the order of a few microns, the lithia-coated boron must also be on the order of a few microns and therefore greater than 1 µm. Similarly, the coating in patent application CN 116845223 A [4] is not distributed uniformly and homogeneously on the surface of the CAM spheres, as LiNbxOy agglomerates are formed.

[0021] However, for a coating to be beneficial during battery cycling, it must be stable, homogeneous, uniform, with a low thickness of the coating phase not exceeding 15 nm.

[0022] The inventors therefore set themselves the goal of proposing a process which makes it possible to prepare coated cathode active material precursors from which cathode active materials can be prepared having a coating with such characteristics as a stable, homogeneous, uniform coating and a low thickness.

[0023] Furthermore, this preparation process must be simple and easy to implement compared to processes with post-processing of the prior art.

[0024] DESCRIPTION OF THE INVENTION

[0025] The goals set by the inventors and others are achieved by the invention which proposes a method for preparing a precursor of active cathode material which has a surface coating.

[0026] Indeed, the inventors' work has led to the development of a process for preparing solution-coated PCAMs that can be used on oxidation-sensitive materials. Subsequently, it is possible to create a protective layer on the surface of cathode material particles from the PCAM thus prepared. This coating prevents the degradation of the CAM spheres during battery cycling.

[0027] The coating phase studied by the inventors is a metal oxide, such as niobium and lithium. A lithia-based coating phase is chosen to improve the ionic conductivity on the surface of the CAMs. The treatment applied directly to the PCAM—i.e., a metal-based coating phase such as niobium—allows for the application of a lithia-based metal oxide coating, such as lithia-coated niobium oxide, directly during the PCAM lithiation step without any additional post-treatment. The aim is to obtain a protective coating with better ionic conductivity than metal oxide-based coatings, particularly non-lithia-coated niobium oxide, described in the literature, without any additional steps.

[0028] More particularly, the present invention relates to a process for preparing a precursor material of a coated cathode active material comprising: a) a step of preparing a solution comprising a hydroxide, a nitrate, an acetate or an alkoxide of a metal M with M other than lithium, b) a step of contacting the particles of a precursor material of a cathode active material in the form of oxide, hydroxide or carbonate with the solution prepared in step a), c) optionally a step of recovering the particles obtained at the end of step b), d) a step of drying the suspension obtained at the end of step b) or optionally the particles recovered during step c) by means of which a precursor material of a cathode active material coated by a layer based on metal M is obtained.

[0029] More particularly, the present invention relates to a process for preparing a precursor material of a coated cathode active material comprising: a) a step of preparing a solution containing a hydroxide, a nitrate, an acetate or an alkoxide of a metal M with M other than lithium and the solvent of which is an alcohol, b) a step of contacting, with the solution prepared in step a), particles of a precursor material of a cathode active material, said precursor material being a non-lithia material in the form of a mixed metal oxide, hydroxide or carbonate, c) optionally a step of recovering the particles obtained at the end of step b), d) a step of drying the suspension obtained at the end of step b) or optionally the particles recovered during step c) by means of which a precursor material of a cathode active material coated by a layer based on metal M is obtained.The term "precursor material of a cathode active material" refers to any material capable of yielding, after a lithiation step, a cathode active material, i.e., a lithium cation insertion material, which is generally a composite. Such a lithiation step comprises contacting the precursor material with at least one compound containing lithium and possibly other dopants, followed by a calcination-type heat treatment.

[0030] The expression "precursor material of an active cathode material" is equivalent to the abbreviation PCAM and this expression and this abbreviation may be used interchangeably in the present.

[0031] Similarly, the expression "cathode active material" is equivalent to the abbreviation CAM and this expression and abbreviation may be used interchangeably in the present.

[0032] Finally, the expressions "coating layer", "coating phase" and "coating layer" are equivalent and can be used interchangeably in this document.

[0033] Typically, within the scope of the present invention, the precursor material of a cathode active material is a non-lithia material generally in the form of a mixed metal oxide, hydroxide, or carbonate.

[0034] Advantageously, a precursor material of a cathode active material can conform to one of the following formulas:

[0035] - NiwMnxCoyMzOa (case of a mixed metal oxide),

[0036] - NiwMnxCoyMz(OH)2 (case of a mixed metal hydroxide), or

[0037] - NiwMnxCoyMzCOî (case of a mixed metal carbonate), in which M is chosen from the group consisting of Al, Mg, Ti and Zr, the sum (w + x + y + z) is equal to 1, at least one among w, x, y and z can be equal to 0 and a is an integer from 1 to 4 (i.e. a = 1, 2, 3 or 4).

[0038] The term "precursor material of an coated cathode active material" refers to a PCAM, as previously defined, that has a coating layer (or encapsulating layer) on its surface and on the surface of the pores of the PCAM particles opening onto the PCAM surface. This can be described as a core-shell type material, with the coating layer (or encapsulating layer) forming the shell of this material.

[0039] Step a) of the process according to the invention consists of dissolving, in a suitable solution, a precursor compound of the coating phase i.e. a compound based on the metal M other than lithium, present, at the end of the process, at the level of the coating layer of the coated PCAM obtained.

[0040] It should be noted that PCAMs, and in particular PCAM particles, are very sensitive to degradation by oxidation and attrition. They are largely affected by the nature of the solvent, the nature of the precursors in the coating phase, and the duration of impregnation.

[0041] In a first implementation, the precursor compound of the coating phase is a hydroxide of a metal M, where M is different from lithium. Such a compound typically has the formula M(OH)n, where n represents the valence of the metal M.

[0042] In a second embodiment, the precursor compound of the coating phase is a nitrate of a metal M, where M is different from lithium. Such a compound typically has the formula MfNChJn, where n represents the valence of the metal M.

[0043] In a third embodiment, the precursor compound of the coating phase is an acetate of a metal M, where M is different from lithium. Such a compound typically has the formula MfCzHgOzJn, where n represents the valence of the metal M.

[0044] In a fourth embodiment, the precursor compound of the coating layer is an alkoxide of a metal M other than lithium. Such an alkoxide may have the formula M(OR)n, where R represents an alkyl group and n represents the valence of the metal M.

[0045] The term "alkyl group" refers to a linear, branched, or cyclic alkyl group comprising from 1 to 10 carbon atoms, and in particular 1, 2, 3, 4, or 5 carbon atoms. Typically, the alkyl group of the alkoxide used in the process of the invention does not include any heteroatoms.

[0046] Depending on the precursor compounds used, these may include:

[0047] - nitrogen, which is the case for nitrates of a metal M;

[0048] - carbon, which is the case for acetates and alkoxides of a metal M, nitrogen and carbon being eliminated during heat treatment under oxygen

[0049] (O2) during CAM preparation;

[0050] - neither nitrogen nor carbon, which is the case for hydroxides of a metal M.

[0051] In some embodiments, it will be preferable to choose precursor compounds for the coating layer that do not contain nitrogen to avoid potential degradation of the PCAM produced at the end of the process according to the invention.

[0052] In the process according to the invention, the metal M, other than lithium, can be any metal capable of forming with lithium a layer exhibiting good ionic conductivity on the surface of the coated CAM obtained from the coated PCAM prepared by the process according to the invention. In other words, the metal M is capable of forming a stable, ionically conductive layer after lithiation.

[0053] Typically, the metal M other than lithium is chosen from the group consisting of transition metals, post-transition metals and metalloids.

[0054] According to the IUPAC definition, transition metals are chemical elements whose atoms have an incomplete d electron subshell, or which can form cations with an incomplete d electron subshell. By this definition, transition metals correspond to the elements in groups 3 to 11 of the periodic table, including most of the lanthanides and actinides.

[0055] Post-transition metals, sometimes called post-transition metals, are metallic chemical elements located in the periodic table between the transition metals to their left and the metalloids to their right. The post-transition metals generally include gallium, indium, tin, thallium, lead, bismuth, aluminum, polonium, and some or all of the elements in group 12, namely zinc, cadmium, mercury, and copernicium.

[0056] Finally, the six elements generally recognized as metalloids are boron, silicon, germanium, arsenic, antimony, and tellurium.

[0057] In particular, the metal M other than lithium is chosen from the group consisting of titanium, vanadium, zinc, tungsten, molybdenum, zirconium, yttrium, aluminum, tin, boron, antimony, cobalt, and niobium. More specifically, the metal M other than lithium is chosen from the group consisting of zirconium, tungsten, molybdenum, and niobium.

[0058] More specifically, the metal M, other than lithium, is niobium. In this particular embodiment, the precursor compound for the coating layer is chosen from the group consisting of niobium hydroxide, niobium nitrate, niobium acetate, and a niobium alkoxide. Niobium ethoxide is advantageously used as a niobium alkoxide.

[0059] Based on the experimental part below, a person skilled in the art will be able to determine, without inventive effort, the quantity of hydroxide, nitrate, acetate or alkoxide of metal M to be used in step a) of the process, as a function of the mass % of the coating phase based on lithium oxides and metal M desired in the coated CAM.

[0060] Furthermore, the solvent used in step a) of the process according to the invention must not degrade the PCAMs, and in particular nickel-rich PCAM particles such as the precursors of NMC 811, which are highly sensitive to oxidation. At the same time, the solvent used in step a) of the process according to the invention must be capable of dissolving the precursor of the coating layer.

[0061] Typically, the solvent of the solution implemented in step a) of the process according to the invention is water.

[0062] Alternatively, the solvent of the solution implemented in step a) of the process according to the invention is an alcohol.

[0063] In particular, the solvent of the solution implemented in step a) of the process according to the invention is chosen from the group consisting of methanol, ethanol, isopropanol and n-butanol.

[0064] More particularly, the solvent of the solution implemented in step a) of the process according to the invention is an alcohol in particular such as previously defined absolute i.e. a dehydrated alcohol.

[0065] More specifically, the solvent of the solution used in step a) of the process according to the invention is absolute ethanol. Typically, the solution used in step a) of the process according to the invention does not include potassium hydroxide, citric acid, or ethylene glycol.

[0066] Advantageously, step a) is carried out at room temperature (i.e. 22°C ± 5°C).

[0067] During step b) of the process according to the invention, the PCAMs to be coated are added to the solution in which a hydroxide, nitrate, acetate or alkoxide of metal M other than lithium is dissolved, prepared in step a).

[0068] These substances are in powder form, i.e., as particles, particularly porous particles. Those skilled in the art are familiar with various precipitation or co-precipitation techniques for preparing such PCAM particles.

[0069] Advantageously, the average diameter of the PCAM particles used in step b) of the process according to the invention is between 3 pm and 15 pm and in particular between 8 pm and 12 pm.

[0070] In step b) of the process according to the invention, the PCAM particles used are in the form of oxide, hydroxide, or carbonate. To achieve this, the PCAM particles may have undergone calcination prior to step b).

[0071] The calcination, if carried out prior to step b) of the process, is in particular performed at a temperature greater than or equal to 100°C and less than or equal to 300°C. This calcination is in particular carried out at a temperature of around 250°C (i.e. 250°C ± 5°C).

[0072] Moreover, this calcination is carried out in particular for a period of between 1 h and 10 h and, in particular, on the order of 5 h (i.e. 5 h ± 1 h).

[0073] In step b) of the process according to the invention, a suspension is obtained from the PCAM particles and the solution prepared in step a). This solution is advantageously kept under agitation for a sufficient time to impregnate the PCAM particles and homogenize the dispersion of the hydroxides, nitrates, acetates or metal alkoxides M ie precursors of the coating phase, on the surface of the PCAM particles.

[0074] Advantageously, the suspension obtained in step b) is kept under stirring for a period greater than or equal to 5 h, in particular greater than or equal to 10 h and, in particular, on the order of 15 h (i.e., 15 h ± 2 h). Advantageously, step b) of the process is carried out at ambient temperature.

[0075] Step d) of the process of the invention consists of drying the suspension obtained at the end of step b) or the particles obtained at the end of step c).

[0076] When the drying in step d) is carried out on the particles obtained at the end of step b), the process according to the invention includes a step c) aimed at separating these particles from the solution containing them and recovering these particles. This separation is typically carried out by filtration.

[0077] In a preferred embodiment, step d) of the process of the invention consists of drying the suspension obtained at the end of step b).

[0078] Any drying technique known to a person skilled in the art can be used during step d) of the process according to the invention.

[0079] This drying is typically carried out at a temperature less than or equal to 200°C, in particular less than or equal to 170°C and, in particular, in the order of 140°C (i.e. 140°C ± 20°C).

[0080] In a particular embodiment promoting homogeneity and uniformity of the coating precursor layer on the surface of the PCAM particles, the drying used in step d) is spray drying, in particular, at a temperature as previously defined.

[0081] Furthermore, in order to avoid oxygenation and therefore deterioration of the PCAM, the drying during step d) of the process of the invention is advantageously carried out under inert gas and, in particular, under nitrogen.

[0082] Following this drying step (d), PCAM particles coated or coated with a metal-based layer (M) are obtained. This coating layer may include metal oxides. In the PCAM thus prepared, i.e., the PCAM in particle form coated with a metal-based layer (M), the mass percentage of the coating layer is between 2% and 5% by mass relative to the total mass of the material.

[0083] The present invention also relates to a precursor material for a metal-based M-coated cathode active material prepared by the preparation process as previously defined. The present invention also relates to the use of such a precursor material for a metal-based M-coated cathode active material to prepare a coated cathode active material.In other words, the present invention relates to a process for preparing a coated cathode active material comprising: i) a step of preparing a precursor material of a coated cathode active material according to the preparation process as previously defined, ii) a step of bringing the precursor material of a coated cathode active material prepared in step i) into contact with a lithium precursor and then mixing the whole, iii) a step of heat treating the mixture obtained in step ii) by means of which a cathode active material coated by a layer of metal oxide M and lithium is obtained.

[0084] The coated PCAM implemented during step i) is, due to its preparation process, in the form of particles as previously defined.

[0085] Steps ii) and iii) of the process according to the invention are classic steps and well known to those skilled in the art in the field of CAM preparation from PCAM.

[0086] Typically, the lithium precursor used in step ii) of the process according to the invention is lithium hydroxide (LiOH), optionally hydrated, or lithium carbonate (U2CO3), optionally hydrated. Advantageously, the lithium precursor used in step ii) is lithium hydroxide (LiOH), optionally hydrated.

[0087] In particular, the lithium precursor used in step ii) of the process according to the invention is in solid form, whereby the mixing carried out in step ii) is a dry mixing.

[0088] Furthermore, the contacting and mixing during step ii) of the process according to the invention are carried out under air and at ambient temperature (i.e. 22°C ± 5°C).

[0089] Step iii) in the process according to the invention is necessary because it leads to the conversion of coated PCAM into coated CAM. A person skilled in the art will be able to determine, without inventive effort, the parameters of this heat treatment, such as temperature, duration, and atmosphere, particularly as a function of the chemical composition of the PCAM to be converted.

[0090] In particular, it is necessary to completely eliminate the nitrogen and / or carbon resulting from the decomposition of the precursor compounds of the coating phase and to preserve the structure of the active cathode material. For example, the presence of carbon could lead to the formation of lithium carbonate as the coating phase, which would result in a decrease in electrochemical performance due to its low ionic conductivity. Thus, advantageously, step iii) of the process according to the invention is carried out under pure oxygen.

[0091] Furthermore, during step iii), the heat treatment consists of bringing the coated PCAM from the ambient temperature at which step ii) is carried out to the temperature at which the heat treatment is performed (temperature T t t).

[0092] Advantageously, the temperature Ttt is between 800°C and 950°C, especially between 830°C and 900°C and, in particular, around 883°C (i.e. 883°C ± 5°C).

[0093] The transition from ambient temperature to temperature T t t can be done in an increasing manner, either linearly or with at least one plateau. By "plateau," we mean a temperature T between the ambient temperature and the temperature T tt which is maintained constant for a time typically between 30 minutes and 2 hours, and in particular on the order of 1 hour (i.e., 1 hour ± 15 minutes). The temperature increase between ambient temperature and temperature T tt can have from 1 to 10 steps, and in particular from 2 to 5 steps. These steps are between the ambient temperature and the first step, between two consecutive steps, and between the last step and temperature T. tt , the temperature is increased linearly with a ramp of 0.5°C to 10°C per min, in particular a ramp of 1°C to 5°C per min and, in particular, on the order of 2°C per min (i.e. 2°C ± 0.5°C).

[0094] In the experimental section below, those skilled in the art will find an example of a protocol applicable to step iii) of the process according to the invention, with three temperature steps. This protocol is particularly suitable for nickel-rich PCAMs, i.e., PCAMs in which nickel oxide represents at least 60% by mass of the oxides forming these PCAMs. At the end of step iii), an active cathode material coated with a layer of metal oxide M and lithium is obtained. Note that after this high-temperature heat treatment step, the final material obtained is typically in solid form. It may therefore be necessary to grind it to a fine powder.

[0095] The present invention relates to the coated cathode active material obtained at the end of step iii) of the process according to the invention i.e. relates to the coated cathode active material prepared by the preparation process as previously defined.

[0096] This material is in the form of particles and in particular porous particles with a core-shell structure in which the coating layer (or cladding layer) of metal oxide M and lithium forms the shell.

[0097] This coating layer (or cladding layer) is in contact with the surface of the CAM and with the surface of the pores of the CAM particles opening onto the surface of the CAM.

[0098] The layer of metal oxide M and lithium coating the active cathode material according to the invention or obtained at the end of step iii) of the process according to the invention has an average thickness less than or equal to 15 nm and in particular less than or equal to 10 nm.

[0099] The layer of metal oxide M and lithium coating the active cathode material according to the invention or obtained at the end of step iii) of the process according to the invention represents 1% to 3% by mass relative to the mass of said material i.e. said active cathode material.

[0100] Advantageously, the average diameter of the particles of the active cathode material according to the invention or obtained at the end of step iii) of the process according to the invention is between 5 pm and 17 pm and in particular between 10 pm and 14 pm.

[0101] The core of the cathode active material particles according to the invention, or obtained at the end of step iii) of the process according to the invention, is, depending on the PCAM used, a lithium cation insertion material, generally a composite, such as lithium cobalt oxide LiCoO2, lithium manganese oxide, possibly substituted, LiM₂C, or a transition metal oxide, such as lamellar materials, for example, a LiNi-based materialx Mn y Co z O2 with x+y+z = 1, such as LiNio.33Mno.33Coo.33O2 more commonly known as "NMC111", LiNio.6Mno.2Coo.2O2 more commonly known as "NMC622" or LiNio.8Mno.1Coo.1O2 more commonly known as "NMC811" or a LiNixCo-based material y Al z O2 with x+y+z = 1, such as LiNio.8Coo.15Alo.05O2 more commonly called “NCA”.

[0102] The present invention also relates to a positive electrode for a lithium-ion battery comprising such an active cathode material. Typically, this material is mixed with a polyvinylidene fluoride binder and a carbon source deposited on an aluminum foil.

[0103] The present invention relates, finally, to a lithium-ion battery comprising such a positive electrode. This lithium-ion battery is composed, in addition to the positive electrode according to the invention, of a negative electrode, a separator, an electrolyte, and a casing which may be a polymer pouch or a metallic coating. The anode is generally made of graphite mixed with a carboxymethylcellulose (CMC) binder deposited on a copper foil. The electrolyte consists of a mixture of non-aqueous solvents and lithium salts, as well as additives to slow down side reactions.Battery electrolytes can be composed of binary or ternary mixtures based on cyclic carbonates such as ethylene carbonate, propylene carbonate and butylene carbonate, linear carbonates or branched carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and dimethoxyethane in various proportions, in which a lithium salt such as, for example, LiPFe, UCF3SO3, LiBF4 and UCIIO4 is dissolved.

[0104] Other features and advantages of the present invention will become apparent to the person skilled in the art upon reading the examples below, given by way of illustration and not limitation, with reference to the attached figures.

[0105] BRIEF DESCRIPTION OF THE DRAWINGS

[0106] Figure 1 shows the protocol according to the invention for synthesizing PCAM into an embedded CAM, via an embedded PCAM. Figure 2 shows the diffractograms of pristine NMC (comparative example) and LiNbxOy-NMC (present invention).

[0107] Figure 3A shows a scanning electron microscopy image of LiNbxOy-NMC (present invention).

[0108] Figure 3B shows a scanning electron microscopy image of pristine NMC (comparative example).

[0109] Figure 4 shows the evolution of the capacity C (in mAh / g) of pristine NMC (comparative example) and LiNbxOy-NMC (present invention), at different discharge regimes, as a function of the number of cycles N.

[0110] Figure 5 shows the evolution of the capacity C (in mAh / g) of pristine NMC (comparative example) and LiNbxOy-NMC (present invention), as a function of the number of cycles N at a discharge regime of C / 5.

[0111] DETAILED DESCRIPTION OF SPECIFIC METHODS OF IMPLEMENTATION

[0112] I. Preparation of LiNbxOy-NMC811 according to the present invention

[0113] Step 1: Impregnation

[0114] 0.2 g of niobium ethoxide (NbfOCHzCHgJs, powder 99.95%, Sigma Aldrich) is dissolved under magnetic stirring in 50 ml of absolute ethanol at room temperature.

[0115] 3 g of PCAM811 powder, in oxide form when partially calcined at 250°C or in hydroxide form when dried at 120°C, are then added to the solution. The mixture is kept under magnetic stirring at room temperature for 15 h.

[0116] Step 2: Drying the particles

[0117] The suspension, comprising the precursor and the powder, is spray dried under nitrogen at 140°C by Spray drying (Buchi mini spray dryer 290).

[0118] Step 3: Lithiation

[0119] 3 g of coated PCAM811 powder are manually mixed dry with 1.75 g of lithium hydroxide (LiOH. H2O). The mixture is made under air and at room temperature.

[0120] Step 4: Heat Treatment The coated and lithia-coated PCAM powder is transferred to a tubular furnace and heated by applying a temperature increase of 2°C / min under a flow of ch until reaching 650°C, 750°C and 800°C. The temperature is maintained for 1 hour before increasing to the next temperature.

[0121] The tubular furnace is then heated by applying a 2°C increase up to 883°C. The holding time is set at 6 hours.

[0122] After cooling, the LiNb powder x O y -NMC811 is manually ground and stored under argon. The mass percentage of the coating phase relative to the target PCAM mass is 3%. The synthesis protocol is described in Figure 1.

[0123] Method for calculating the percentage of the coating phase:

[0124] For 3 g of PCAM, the target coating percentage (x) is 3%, therefore [x / (x + 3)] = 0.03, so x = 0.092 g. The coating mass must be equal to 0.092 g.

[0125] The molar mass of LiNbO3 is 147.85 g / mol. Knowing that the molar mass of Nb is 92.906 g / mol, % Nb in LiNbO3 = 92.906 / 147.85 * 100 = 63%.

[0126] Since the molar mass of niobium ethoxide is 318.21 g / mol, the % Nb in niobium ethoxide = 92.906 / 318.21 * 100 = 29%.

[0127] The mass of Nb in the coating is 0.092*0.63 = 0.058 g. To obtain such a mass, a molar mass of niobium ethoxide of 0.58 / 0.29, or 0.2 g, must be used.

[0128] II. Preparation of NMC-pristine (comparative example)

[0129] 3 g of PCAM powder are manually mixed dry with 1.7 g of lithium hydroxide (LiOH.FbO). The mixture is made under air and at room temperature.

[0130] The final powder is then transferred to a tubular furnace and heated by applying a temperature increase of 2°C / min under a flow of ch until reaching 650°C, 750°C and 800°C. The temperature is maintained for 1 hour before increasing to the next temperature.

[0131] The tubular furnace is then heated by applying a 2°C increase up to 883°C. The holding time is set at 6 hours. After cooling, the powder is manually ground, stored under argon, and named NMC-pristine. III. Characterization of the coated LiNbxOy-NMC811 CAM and comparison with the

[0132] CAM NMC uncoated

[0133] 111.1. X-ray Diffraction

[0134] NMC-pristine diffractograms (uncoated) and LiNb x O y-NMC811 are shown in Figure 2. The structure and lattice parameters of the two materials are very similar, indicating the preservation of the crystallographic structure of the NMC particles after coating.

[0135] The c / a value was not changed after coating, allowing us to conclude that the lamellar aspect of nickel-rich CAMs was not disturbed by the coating.

[0136] On the other hand, the coating phase is not perceptible on DRX despite a theoretical content of 3% by mass relative to the mass of PCAM.

[0137] 111.2. Scanning Electron Microscopy

[0138] The positive effect of the coating on the morphology of the NMC particles is visible in the SEM images in Figure 3A and Figure 3B.

[0139] Without coating (Figure 3B), some NMC811 particles are cracked and / or damaged after lithiation.

[0140] In contrast, the sphericity of LiNb particles x O y -NMC811 (Figure 3A) appears to be well preserved with the coating.

[0141] 111.3. Galvanostatic cycling

[0142] A. Ink Formulation

[0143] The same ink formulation protocol is adopted for both materials developed.

[0144] The prepared materials were characterized using a button cell. The powder was mixed with a carbon source (Super P®) and 10% PVDF8130 in N-methyl-2-pyrrolidone (NMP). 1.1 g of NMP was then added, and the mixture was stirred magnetically at 300 rpm for 10 min. The mass composition was in the following ratio: 92 / 4 / 4 (active material / PVDF / carbon).

[0145] The ink produced is coated onto an aluminum sheet and then left to dry for 24 hours at 55°C. From this coated sheet, 14 mm electrodes are cut and then dried under vacuum at 80°C for 48 hours. The electrodes are then placed in a glove box and a button cell is assembled using lithium metal as the anode, Celgard 2500® as the separator and LiPFe EC / PC / DMC (1 / 1 / 3 vol) as the electrolyte, EC, PC, DMC corresponding respectively to ethyl carbonate, propylene carbonate and dimethyl carbonate.

[0146] B. Experimental Results

[0147] Stability curves using galvanostatic cycling were performed.

[0148] Measurements are performed at a controlled temperature of 25°C between 2, 7-4, and 3 V vs Li. A power signature of the material is first obtained over the first 9 cycles at different charge / discharge regimes of C / 20, C / 10, C / 5, C / 3, C / 2, IC, 2C, 5C, and 10C. From the io éme cycle, the battery is charged to C / 10 and discharged to C / 5. This power signature, shown in Figure 4, demonstrates the material's performance as a function of the applied charge / discharge regime.

[0149] The electrochemical performance of NMC811 cathode materials is significantly improved after coating (LiNb x O y -NMC) and approach the theoretical curve. The power, reversibility of the coated material, and its capacity retention during cycles are higher compared to the uncoated material (NMC-pristine). It has a reversibility of 93% and a capacity retention of approximately 93% after 100 cycles (Figure 5).

[0150] Bibliographical references

[0151] [1] US Patent 10,501,335 B1 in the name of CAMX Power LLC published on December 10, 2019.

[0152] [2] Patent application EP 3959762 Al in the name of Nano One Materials Corp, published on March 2, 2022.

[0153] [3] Patent application EP 4048639 Al in the name of CAMX Power LLC published on August 31, 2022.

[0154] [4] Patent application CN 116845223 A in the name of Hefei Guoxuan Kehong New Energy Tech Co. Ltd published on October 3, 2023.

Claims

DEMANDS 1. A process for preparing a precursor material of a coated cathode active material comprising: a) a step of preparing a solution containing a hydroxide, nitrate, acetate or alkoxide of a metal M with M other than lithium and having an alcohol as its solvent, b) a step of contacting particles of a precursor material of a cathode active material with the solution prepared in step a), said precursor material being a non-lithiumized material in the form of a mixed metal oxide, hydroxide or carbonate, c) optionally a step of recovering the particles obtained at the end of step b), d) a step of drying the suspension obtained at the end of step b) or optionally the particles recovered during step c) thereby obtaining a precursor material of a coated cathode active material with a layer based on metal M.

2. Preparation process according to claim 1, characterized in that said metal M other than lithium is selected from the group consisting of zirconium, tungsten, molybdenum and niobium.

3. Preparation process according to claim 1 or 2, characterized in that the solvent of the solution used in said step a) is absolute ethanol.

4. A preparation method according to any one of claims 1 to 3, characterized in that said particles of a precursor material of an active cathode material have undergone, prior to step b), calcination carried out at a temperature greater than or equal to 100°C and less than or equal to 300°C.

5. Preparation method according to any one of claims 1 to 4, characterized in that said suspension obtained in step b) is kept under agitation and in particular for a period greater than or equal to 5 h, in particular greater than or equal to 10 h and, in particular, of the order of 15 h (i.e. 15 h ± 2 h).

6. Preparation process according to any one of claims 1 to 5, characterized in that the drying during said step d) is spray drying under inert gas, in particular, at a temperature less than or equal to 200°C, in particular less than or equal to 170°C and, in particular, in the order of 140°C (i.e. 140°C ± 20°C).

7. A process for preparing a coated cathode active material comprising i) a step of preparing a precursor material of a coated cathode active material according to the preparation process as defined in any one of claims 1 to 6, ii) a step of bringing the precursor material of a coated cathode active material prepared in step i) into contact with a lithium precursor and then mixing the whole, iii) a step of heat treating the mixture obtained in step ii) thereby obtaining a cathode active material coated with a layer of metal oxide M and lithium.

8. Preparation process according to claim 7, characterized in that said lithium precursor is lithium hydroxide (LiOH) optionally hydrated or lithium carbonate (Li2CO3) optionally hydrated.

9. Preparation process according to claim 7 or 8, characterized in that said step iii) is carried out under pure oxygen.

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