Lithium manganese phosphate-based active materials and lithium ion electrochemical element electrode comprising such active materials

Abstract

The invention relates to an electrode comprising one or more active materials, wherein one of the active materials is a lithium manganese iron phosphate of formula LixMn1-y-zFeyM2PO4 (LMFP) where 0.8≤x≤1.2; 0.5≤1-y-z<1; 0<y≤0.5; 0≤z≤0.2; M being one or more elements chosen from the group consisting of Al, B, Mg, Si, Ca, Ti, V, Cr, Co, Cu, Ni, Zn, Y, Zr, Nb, W and Mo, the electrode being characterised in that the lithium manganese iron phosphate is in the form of almost spherical particles and the internal porosity of the lithium manganese iron phosphate particles is less than or equal to 5%.

Description

Description Title: Active materials based on lithium manganese and iron phosphate and lithium-ion electrochemical element electrode comprising said active materials Technical field of the invention

[0001] The technical field of the present invention is that of active materials based on lithium manganese and iron phosphate (LMFP) intended to be used in the cathode, that is to say the positive electrode, of an electrochemical element of the lithium-ion type, also called a lithium-ion element. Background to the invention

[0002] Lithium manganese and iron phosphates, abbreviated LMFP in the following, are known as active material in the positive electrode of lithium-ion electrochemical cells. These phosphates have satisfactory thermal stability but insufficient volume capacity. This is partly due to the difficulty in obtaining a low-porosity electrode. The available LMFP particles have a flaky or granular shape with irregular contours. However, this particular shape makes it difficult to obtain a positive electrode with low porosity, and therefore with a high volume capacity. Typically, a positive electrode based on LMFP has a porosity ranging from 40 to 50%. Approximately half of the electrode volume is therefore empty. Therefore, an attempt has been made to increase the volume capacity of an electrode comprising an active material based on LMFP.

[0003] CN 113072049 (A) describes, for example, a process for preparing spherical LMFP nanoparticles. The internal porosity value of the produced particles is not mentioned. No density value of the produced particles is indicated.

[0004] CN 1821065 (A) describes a process for preparing spherical lithium iron phosphate LiFePCU (LFP) particles. The density values ​​obtained range from 2.0 to 2.3 g / cm 3 . However, the theoretical density of LiFePO4 is 3.6 g / cm 3 As a result, the porosity of the LiFePO4 powder produced under the process conditions described in this document is approximately 40%, which remains high.

[0005] Document CN 1632970 (A) describes a process for preparing spherical LFP or LMFP particles. Examples 4 to 7 of this document describe the preparation of a powder of LMFP particles of size ranging from 8 to 10 pm and having a density of 2.08-2.20 g / cm 3 . However, the average theoretical density of LMFP is 3.3 g / cm 3 As a result, the porosity of the LMFP powder produced under the conditions of this process is approximately 36%, which remains high.

[0006] The aim is to achieve a powder porosity of less than or equal to 30%, which guarantees that an electrode porosity of 30% can be achieved by applying reasonable pressure forces. Summary of the invention

[0007] The subject of the present invention is an electrode comprising one or more active materials, one of which is a lithium manganese and iron phosphate of formula Li x Mni-y-zFe yMzPO4 (LMFP) where 0.8 <x<1 ,2 ; 0,5<1-y-z<1 ; 0<y<0,5 ; 0<z<0,2 ; M étant un ou plusieurs éléments choisis dans le groupe consistant en Al, B, Mg, Si, Ca, Ti, V, Cr, Co, Cu, Ni, Zn, Y, Zr, Nb, W et Mo, l’électrode étant caractérisée en ce que : - the lithium manganese and iron phosphate is in the form of particles, at least 90% by number of the particles have a sphericity factor greater than or equal to 0.90 and less than 1, the sphericity factor of a particle being defined as the ratio between the surface area of ​​a sphere having the same volume as the particle and the surface area of ​​this particle, and in that - the internal porosity of the lithium manganese and iron phosphate particles is less than or equal to 5%, the internal porosity being defined by the ratio V v ide / V L MFP where Vvoid represents the void volume inside the lithium manganese iron phosphate particles, VLMFP represents the geometric volume of lithium manganese iron phosphate particles.

[0008] The invention is based on the discovery that the use of LMFP particles having on the one hand a quasi-spherical shape and on the other hand an internal porosity of less than or equal to 5% makes it possible to reduce the porosity of the electrode. Low electrode porosity values ​​in the range of 20 to 30% are achievable.

[0009] According to one embodiment, the sphericity factor is greater than or equal to 0.95.

[0010] According to one embodiment, the sphericity factor is greater than or equal to 0.98.

[0011] According to one embodiment, the internal porosity of the lithium manganese and iron phosphate particles ranges from 2 to 3%.

[0012] According to one embodiment, at least 95% by number of the particles of lithium manganese and iron phosphate have a sphericity factor greater than or equal to 0.9 and less than 1.

[0013] According to one embodiment, the particles of lithium manganese and iron phosphate are in the form of primary particles having a median diameter in volume D V 5O ranging from 500 nm to 20 pm or from 5 to 15 pm or from 1.5 to 4 pm.

[0014] According to one embodiment, the particles of lithium manganese and iron phosphate are in the form of secondary particles having a median diameter in volume D V 5O ranging from 1 pm to 50 pm, a secondary particle consisting of the agglomeration of primary particles having a volume median diameter Dv5o in the range from 50 nm to 20 pm.

[0015] According to one embodiment, the lithium manganese and iron phosphate particles have a bimodal distribution, the first population being characterized by a first median diameter Dvso 1 , the second population being characterized by a second median diameter Dvso 2 , the ratio between Dvso 1 and Dvso 2 ranging from 3 to 10.

[0016] According to one embodiment, in lithium manganese and iron phosphate, 0.70<1-yz<1.

[0017] According to one embodiment, the electrode further comprises one or more active materials chosen from: - a lithium iron phosphate of formula iii) Li x Fei-yM y PO4 (LFP) where 0.8 <x<1 ,2 ; 0<y<0,6 et M est choisi dans le groupe consistant en B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Cu, Zn, Y, Zr, Nb et Mo ; - a lithium vanadium fluorophosphate of formula iv) Lii+xVPOtF (LVPF) where 0 <x<0,15, ou à un de ses dérivés de formule v) Lh+xVi-yMyPCUFz (LVMPF) où 0<x<0,15, 0<y<0,5, 0,8<z<1 ,2 et M est choisi dans le groupe consistant en Ti, Al, Y, Cr, Cu, Mg, Mn, Fe, Co, Ni, et Zr ; - a lithium oxide of nickel, manganese and cobalt of formula a) Li w (Neither x Mn y Co z Mt)O2 (NMC) where 0.9 <w<1 ,1 ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci, - a lithium oxide of nickel, cobalt and aluminum of formula b) Liw(Ni x COyAl z Mt)O2 (NCA) where 0.9 <w<1 ,1 ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de B, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, Sr, Ce, Ga, Ta, Nd, Pr, La et des mélanges de ceux-ci, - a lithium oxide of nickel and manganese of formula c) Li w (Neither x Mn y Co z Mt)O2 (NMX) where 0.9 <w<1 ,1 ; 0,60<x<0,80 ; 0<y ; 0<z<0,02 ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci, - a lithium oxide of nickel and manganese of formula d) Li w (Neither x Mn y Co z Mt)O2 where 1,1 <w<1 ,6 ; 0<x ; 0,50<y<0,80 ; 0<z<0,02 ; 0<t ; M étant choisi in the group consisting of Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La and mixtures thereof.

[0018] According to one embodiment, said one or more active materials is a lithium nickel oxide chosen from: - a lithium oxide of nickel, manganese and cobalt of formula a) Liw(Ni x Mn yCOzMt)O2 (NMC) where 0.9 <w<1 ,1 ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci, - a lithium oxide of nickel, cobalt and aluminum of formula b) Li w (Neither x Co y Al z Mt)O2 (NCA) where 0.9 <w<1 ,1 ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de B, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, Sr, Ce, Ga, Ta, Nd, Pr, La et des mélanges de ceux-ci, et - a lithium oxide of nickel and manganese of formula c) Liw(Ni x Mn y COzMt)O2 (NMX) where 0.9 <w<1 ,1 ; 0,60<x<0,80 ; 0<y ; 0<z<0,02 ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci, - a lithium oxide of nickel and manganese of formula d) Liw(Nix Mn y Co z Mt)O2 where 1,1 <w<1 ,6 ; 0<x ; 0,50<y<0,80 ; 0<z<0,02 ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci.

[0019] According to one embodiment, the lithium manganese and iron phosphate represents from 40 to 99% by mass of the total mass of lithium manganese and iron phosphate and lithium nickel oxide(s) and said one or more lithium nickel oxides represents from 1 to 60% by mass of the total mass of lithium manganese and iron phosphate and lithium nickel oxide(s).

[0020] According to one embodiment, the lithium manganese and iron phosphate represents from 70 to 99% by mass of the total mass of lithium manganese and iron phosphate and lithium nickel oxide(s) and said one or more lithium nickel oxides represents from 1 to 30% by mass of the total mass of lithium manganese and iron phosphate and lithium nickel oxide(s).

[0021] The invention also relates to a lithium-ion electrochemical element comprising at least one positive electrode which is the electrode as described above and at least one negative electrode.

[0022] Finally, the invention also relates to a process for preparing iron and manganese phosphate particles having a sphericity factor greater than or equal to 0.90 and less than 1 and an internal porosity less than or equal to 5%, the sphericity factor of a particle being defined as the ratio between the surface area of a sphere having the same volume as the particle and the surface area of ​​this particle, the internal porosity being defined by the ratio Vvide / VuviFP where Vvoid represents the void volume inside the lithium manganese and iron phosphate particles, VLMFP represents the geometric volume of lithium manganese and iron phosphate particles, said method comprising the steps of: a) degassing a volume of water, b) dispersing in the degassed volume of water a mixture comprising: i) an iron precursor, such as the compounds of formula FeSO4 xH2O, FeCI2xH2O, FeC2C>4 xH2O and a mixture thereof, ii) a manganese precursor, such as compounds of formula MnSC>4 xH2O, MnCI2xH2O, MnC2C>4 xH2O and a mixture thereof, iii) a precursor of ammonium ions such as ammonia, diammonium phosphate, ammonium phosphate and a mixture thereof, iv) a precursor of phosphate ions such as phosphoric acid, diammonium phosphate and ammonium phosphate, c) hydrothermal synthesis to obtain a compound of formula NH4(Fe,Mn)PC>4, freed from sulfate, chloride or oxalate ions, for example by washing, d) decomposition of NH4(Fe,Mn)PC>4 to (Fe,Mn)HPC>4 by exposure of NH4(Fe,Mn)PC>4 at a temperature between 250°C and 400°C. Brief description of the figures

[0023] Embodiments of the invention are described below in more detail with reference to the figures below.

[0024] [Fig.1] is a scanning electron microscopy photograph of a powder of the active ingredient of Example A. This powder consists of non-porous, non-spherical primary LMFP nanoparticles with a dimension of around 100 nm. The contours of a primary nanoparticle were drawn in order to individualize it and highlight its size.

[0025] [Fig.2] is a scanning electron microscopy photo of a powder of the active ingredient of Example B. This powder consists of porous spherical agglomerates resulting from the agglomeration of the primary nanoparticles of Example A. We have drew the outline of an agglomerate in order to individualize it and highlight its diameter.

[0026] [Fig. 3] represents the variation of the porosity of powders of particles of the active materials A to D of the examples as a function of the pressure applied to these powders. The porosity on the ordinate is the sum of the porosity between the particles and the internal porosity of the particles. Description of embodiments of the invention Active material(s) of the positive electrode

[0027] A positive electrode according to the invention comprises one or more active materials, one of which is made up of LMFP particles characterized on the one hand by a quasi-spherical shape and on the other hand by an internal porosity less than or equal to 5%. By quasi-spherical is meant a sphericity factor greater than or equal to 0.9, preferably greater than or equal to 0.95, more preferably greater than or equal to 0.97.

[0028] Preferably, at least 90% or at least 95% of the LMFP particles meet the sphericity criterion.

[0029] The degree of sphericity of LMFP particles can be assessed by scanning electron microscopy (SEM). On a SEM image of particles, the smallest and largest dimensions of each particle are measured, and a statistical average of the ratio of the two is taken.

[0030] The fact that LMFP particles only have a shape close to the sphere does not allow to obtain low values ​​of electrode porosity. It is necessary that the LMFP particles also have an internal porosity less than or equal to 5%.

[0031] LMFP particles having a nearly spherical shape and an internal porosity of less than or equal to 5% can be obtained by preparing a non-lithiated spherical Fe and Mn phosphate precursor by sol-gel or hydrothermal method, preferably using an acid complexing agent rather than a basic complexing agent or no complexing agent. The iron and manganese precursors can be, but are not limited to, hydrated or unhydrated iron and / or manganese sulfates, hydrated or unhydrated iron and / or manganese chlorides, or hydrated or unhydrated iron and / or manganese oxalates. The phosphate ion precursors can be, but are not limited to, phosphoric acid, diammonium phosphate, or ammonium phosphate. An ammonium ion precursor is also used. It can be selected from ammonia, diammonium phosphate, or ammonium phosphate. In the case of a hydrothermal route, the water used is first degassed from the gases, which canresult in oxidation of the iron precursors. The degassing step is also important for obtaining an internal porosity of less than or equal to 5%. During this step, the precursors of iron, manganese, phosphate ions and ammonium ions are added to the degassed water as well as the possible complexing agent. The pH of the liquid part of the reaction medium is less than or equal to 7.0. The aerial part of the reaction medium is purged with nitrogen or argon before the medium is sealed and brought to a temperature of at least 150°C and less than 300°C for a period not exceeding 12 hours. After hydrothermal synthesis, a compound containing iron and / or manganese, an ammonium ion and a phosphate ion (NH4(Fe,Mn)PO4) is obtained. This compound may or may not contain water.This compound is then thermally decomposed at a temperature between 250°C and 400°C, and preferably between 325°C and 350°C in order to obtain a product containing only hydrogen, iron and / or manganese and phosphorus in the form of phosphate ion. One or more sintering operations are then carried out, preferably at a temperature greater than or equal to 600°C, applied after lithiation of the precursor and during the production of the possible carbon coating by pyrolysis of a carbon precursor.

[0032] Characterization of the porosity of LMFP particles: Mercury powder porosimetry allows visualization of the progressive absorption of mercury in the sample in two stages: - a first stage at low pressure (<150 bar) due to the absorption of mercury in the inter-particle spaces, - a second stage at high pressure (>150 bar) corresponding to the absorption of mercury in the open intra-particle porosity. The volume of mercury absorbed in this stage represents the internal open porosity of the LFMP. The closed internal porosity of the particles is inaccessible to mercury and is assessed by helium pycnometry. The difference in density between the theoretical density and the density measured by helium pycnometry is due to the closed internal porosity of the particles. The term internal porosity of LFMP particles here refers to the sum of the closed internal porosity and the open internal porosity of the LFMP particles.

[0033] Lithium manganese and iron phosphate has the formula Li x Mni-y-zFe yMzPO4 (LMFP) where 0.8 <x<1 ,2 ; 0,5<1-y-z<1 ; 0<y<0,5 ; 0<z<0,2 ; M étant un ou plusieurs éléments choisis dans le groupe consistant en Al, B, Mg, Si, Ca, Ti, V, Cr, Co, Cu, Ni, Zn, Y, Zr, Nb, W et Mo.

[0034] The stoichiometric index 1-yz of manganese may be at least 0.6 or at least 0.7 or at least 0.8. It may range from 0.7 to 0.9 or from 0.75 to 0.80. Preferably, 0.70<1-yz<1.

[0035] The stoichiometric index y of iron can be at most 0.4 or at most 0.3 or at most 0.2.

[0036] Examples of LMFP are LiMno.sFeo^PCU, LiMnojsFeo^PCU, LiMnojFeo.sPCU, LiMn2 / 3Fei / 3PO4 and LiMno.5Feo.5PO4.

[0037] LMFP can be coated with a carbon layer. It can be coated in particular with graphite or amorphous carbon or carbon nanotubes.

[0038] Several LMFP type compounds of different formulas can be used in mixture.

[0039] The invention can be implemented using: - either disjointed LMFP particles, also called primary particles, having a median diameter Dvso ranging from 500 nm to 20 pm or from 1 to 20 pm or from 5 to 15 pm or from 1.5 to 4 pm; - or agglomerates of primary LMFP particles, also called secondary particles, these agglomerates resulting from the agglomeration of primary particles characterized by a median diameter Dvso ranging from 50 nm to 20 pm or from 5 pm to 15 pm or 1.5 pm to 4 pm. The median diameter Dvso of the secondary particles can range from 1 to 50 pm.

[0040] The expression "median diameter in volume D v so" means that, in a given population of particles, 50% of the volume of particles consists of particles having an equivalent diameter less than the value D v so and 50% of the particle volume consists of particles having an equivalent diameter equal to or greater than the value Dv so. The expression "equivalent diameter" of a particle designates the diameter of a sphere having the same volume as this particle. D v so can be measured by laser granulometry.

[0041] The particle size distribution of LMFP can be monomodal or bimodal. A monomodal distribution allows powder porosity values ​​ranging from 25 to 30% to be achieved. Preferably, the distribution is bimodal. The first population is characterized by a first median diameter Dvso 1 , the second population is characterized by a second median diameter Dvso 2 , the ratio between Dvso 1 and Dvso 2preferably ranges from 3 to 10. Such a particle size distribution makes it possible to reduce the void volume between the LMFP particles and therefore to reduce the porosity of the electrode. A bimodal distribution makes it possible to achieve powder porosity values ​​ranging from 20 to 30%. According to one embodiment, the mass percentage of particles characterized by a second median diameter D v so 2 less than the first median diameter D v so 1 ranges from 10 to 20% relative to the mass of all LMFP particles.

[0042] LMFP can be mixed with one or more lithium phosphates containing cobalt or nickel or iron of respective formulas: i) LixCoi.yMyPO4(LCP) and 0.8 <x<1 ,2 ; 0<y<0,6 où M est choisi dans le groupe consistant en B, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Ni, Cu, Zn, Y, Zr, Nb et Mo ; ii) LixNii- y M yPO4 (LNP) and 0.8 <x<1 ,2 ; 0<y<0,6 où M est choisi dans le groupe consistant en B, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Y, Zr, Nb et Mo ; iii) Li x Fei- y M y PO4 (LFP) and 0.8 <x<1 ,2 ; 0<y<0,6 où M est choisi dans le groupe consistant en B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Cu, Zn, Y, Zr, Nb et Mo. Preferably, it is LFP.

[0043] LMFP can be mixed with a lithium vanadium fluorophosphate of formula iv) Lii+xVPCUF (LVPF) where 0 <x<0,15, ou à un de ses dérivés de formule v) Lii +x Vi. y M y PO4F z (LVMPF) where 0 <x<0,15, 0<y<0,5, 0,8<z<1 ,2 et M est choisi dans le groupe consistant en Ti, Al, Y, Cr, Cu, Mg, Mn, Fe, Co, Ni et Zr.

[0044] LMFP may be mixed with one or more lamellar lithiated oxides of transition metals chosen from: a) Liw(Ni x Mn y Co zMt)O2 (NMC) where 0.9 <w<1 ,1 ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci, b) Liw(Ni x Co y Al z Mt)O2 (NCA) where 0.9 <w<1 ,1 ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de B, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, Sr, Ce, Ga, Ta, Nd, Pr, La et des mélanges de ceux-ci, et c) Li w (Neither x Mn y Co z Mt)O2 (NMX) where 0.9 <w<1 ,1 ; 0,60<x<0,80 ; 0<y ; 0<z<0,02 ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci. NMX peut être monocristallin ou polycristallin. d) Li w (Neither x Mn y Co zMt)O2 where 1,1 <w<1 ,6 ; 0<x ; 0,50<y<0,80; 0<z<0,02 ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci.

[0045] Preferably, LMFP is mixed with one or more NMC type compounds.

[0046] Preferably, the mass percentage of LMFP represents at least 50% or at least 70% or at least 90% of the mass of all the active materials of the positive electrode. In this embodiment in which LMFP is the majority, the preferred lamellar lithium oxide is of the NMC type. Positive electrode

[0047] The positive electrode of the element comprises a current collector, at least one of the faces of which is coated with a layer of a composition of positive active materials. By "composition of active materials" is meant a composition comprising: - one or more active ingredients as described above, one of which is consisting of LMFP particles of almost spherical shape and internal porosity less than or equal to 5%, and - possibly one or more binders and one or more electronically conductive materials.

[0048] The overall porosity of the electrode is the sum of the open internal porosity, the closed internal porosity of the active material particles (including the LMFP particles) and the porosity between the active material particles, the binder particles and the particles of any incorporated electronically conductive additive. The technique for measuring the open internal porosity and the closed internal porosity of the LMFP particles is described above.

[0049] The positive current collector is a solid or perforated metal strip which may be made of aluminum or an aluminum alloy or steel or stainless steel. Its thickness may be in the range of 6 to 30 μm or 5 to 20 μm or 10 to 15 μm, preferably 10 to 15 μm.

[0050] Before the current collector is coated with the active material composition layer, it may be coated on one or both sides with a coating intended to improve the electronic conductivity between the active material composition layer and the foil and / or to improve the adhesion of the active material composition layer to the foil. The coating material may be selected from the group consisting of amorphous carbon, graphite, carbon fibers, carbon nanotubes, and mixtures thereof. It is preferably made of amorphous carbon. The coating material may be obtained by coating the foil with a dispersion of the material and then evaporating the solvent from the dispersion, or it may be obtained by sputtering. Only certain portions of the foil may be coated with the coating material.The coated portions may be separated from each other by predetermined or periodic intervals ("intermittent coating"). The intermittent coating is preferably present on both sides of the foil. It facilitates the processing of the electrodes. Alternatively, one or both sides of the foil may have undergone a surface treatment intended to increase the adhesion of the active material composition layer to the foil. This may be a surface treatment creating asperities or micro-roughness, such as chemical etching or laser treatment.

[0051] The binder generally used in the active material composition strengthens the cohesion between the active material particles and improves the adhesion of the active material composition layer to the current collector. The binder may contain one or more of the following compounds: polyvinylidene fluoride (PVDF) and its copolymers, polytetrafluoroethylene (PTFE) and its copolymers, polyacrylonitrile (PAN), poly(methyl or butyl methacrylate), poly(vinyl chloride) (PVC), poly(vinyl formal), polyester, block polyetheramides, polymers of acrylic acid, methacrylic acid, acrylamide, itaconic acid, sulfonic acid, elastomers, and cellulose compounds such as carboxymethylcellulose (CMC). The elastomers that can be used as binders can be chosen from styrene-butadiene (SBR), butadiene-acrylonitrile (NBR), hydrogenated butadiene-acrylonitrile (HNBR). The binder can represent from 1% to 10% or from 1 to 5% or from 2 to 5% of the mass of the dry composition of active ingredients.

[0052] The electronically conductive material is generally selected from graphite, carbon black, acetylene black, soot, graphene, carbon fibers, single-walled carbon nanotubes, multi-walled carbon nanotubes, and mixtures thereof. It may represent from 0.1 to 10% or from 0.1 to 5% of the mass of the dry composition of active materials. Preparation of the positive electrode:

[0053] An ink is prepared by dispersing the active ingredient(s) in a solvent or a mixture of several solvents. Optionally, a binder and an electronically conductive material are added to the dispersion. By varying the amount of solvent incorporated in the mixture, the viscosity of the ink can be varied before it is deposited on one side of the current collector. The ink-coated current collector is dried and then rolled to adjust its thickness. After evaporation of the solvent(s), a layer of an active ingredient composition is obtained, the proportions of the various constituents of which are typically: - from 80 to 98% or from 90 to 95% by mass of positive active ingredients, - from 1 to 10% or from 2 to 5% by mass of binder(s), - from 0.1 to 10% or from 2 to 5% by mass of electronically conductive material. Negative electrode:

[0054] At least one negative electrode comprises a current collector, at least one of two faces of which is coated with a layer of a negative active material composition. The negative active material composition comprises at least one negative active material and optionally a binder and an electronically conductive material. The negative current collector is a solid or perforated metal strip which may be made of copper or a copper-based alloy. Its thickness may range from 3 to 10 μm, preferably from 5 to 8 μm.

[0055] Before the current collector is coated with the ma- composition layer active materials, it may be coated, on one of its faces or on both faces, with a coating intended to improve the electronic conductivity between the active material composition layer and the foil and / or to improve the adhesion of the active material composition layer to the foil. The coating material and the coating deposition method may be the same as those described for the current collector of the positive electrode.

[0056] The negative active material may be selected from carbon, graphite, coke, carbon black, glassy carbon, silicon, silicon oxide, a silicon-carbon composite, a silicon carbide, a titanium oxide, a lithiated titanium oxide, a titanium niobium oxide and a mixture thereof. The titanium oxide may be selected from FLTieOis, FLTi^Chs and TiCh. The lithiated titanium oxide may be selected from Li4TisOi2, Li2TiC>3, Li2Ti3O?, Lil^CU and Li2Na2TieOi4. The titanium niobium oxide may be selected from TiNb2O?, Ti2Nb2O9 and Ti2Nb O29. Preparation process of the negative electrode:

[0057] The negative electrode is prepared in a conventional manner. An ink is prepared by dispersing in a solvent or a mixture of solvents one or more negative active materials, optionally with a binder. The binder may be such as those described in connection with the positive electrode.

[0058] The ink-coated current collector is dried and then rolled to adjust its thickness, resulting in a negative electrode. Typical proportions of the components of the negative active ingredient composition layer, after evaporation of the solvent contained in the ink, are: - from 85 to 98% or from 90 to 98% by mass of negative active ingredients, - from 1 to 10% or from 1 to 5% by mass of binder(s), - from 0 to 5% by mass or from 1 to 5% of an electronically conductive material. Electrolyte:

[0059] The electrolyte can be liquid or solid. The liquid electrolyte is obtained by dissolving one or more lithium salts in one or more organic solvents. The solvent can be chosen from saturated cyclic carbonates, unsaturated cyclic carbonates, non-cyclic carbonates, alkyl esters, ethers, nitrile solvents and tetrahydrothiophene dioxide (sulfolane).

[0060] Saturated cyclic carbonates include ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), butylene carbonate (BC), and mixtures thereof.

[0061] Unsaturated cyclic carbonates include vinylene carbonate (VC).

[0062] Non-cyclic carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dipropyl carbonate (DPC), and mixtures thereof.

[0063] Alkyl esters include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and mixtures thereof.

[0064] Ethers include dimethyl ether (DME), diethyl ether (DEE), and mixtures thereof.

[0065] The lithium salt may be selected from lithium perchlorate LiCICU, lithium hexafluorophosphate LiPF6, lithium tetrafluoroborate LiBF4, lithium hexafluoroarsenate LiAsFe, lithium hexafluorantimonate LiSbFe, lithium trifluoromethanesulfonate UCF3SO3, lithium bis(fluorosulfonyl)imide Li(FSC>2)2N (LiFSI), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SC>2)2 (LiTFSI), lithium tris(fluoromethanesulfonyl)methylide LiC(CF3SC>2)3 (LiTFSM), lithium bis(pentafluoroethylsulfonyl)imide LiN(C2F(SC>2)2 (LiBeTI), lithium-4,5-dicyano-2-(trifluoromethyl)imidazolide (LiTDI), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LIDFOB), lithium tris(pentafluoroethyl)trifluorophosphate LiPF3(CF2CF3)3 (LiFAP), lithium difluorophosphate UPO2F2, and mixtures thereof.

[0066] The concentration of said at least one lithium salt may be in the range from 0.75 to 1.5 mol / L. It is preferably in the range from 1 to 1.5 mol / L. It is even better in the range from 1 to 1.2 mol / L. Separator:

[0067] A separator is interposed between a positive electrode and a negative electrode. The material of the separator may be selected from the following materials: a polyolefin, for example polypropylene PP, polyethylene PE, a polyester, polymer-bonded glass fibers, polyimide, polyamide, polyaramid, polyamide-imide, and cellulose. The polyester may be selected from polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). Advantageously, the polyester or polypropylene or polyethylene contains or is coated with a ceramic material selected from the group consisting of metal oxides, oxyhydroxides, carbides, nitrides, borides, silicides, and sulfides. This ceramic material may be SiC>2 or AI2O3. The separator may be a layer of polyolefin coated with ceramic, preferably a layer of polyethylene coated with ceramic on both sides. Preparation of the electrochemical beam:

[0068] An electrochemical beam is formed by inserting a separator between at least one positive electrode and at least one negative electrode. The electrochemical bundle is inserted into the cell container. The cell container can be parallelepipedal or cylindrical. In the latter case, the electrochemical bundle is spiraled to form a cylindrical assembly of electrodes.

[0069] The electrochemical element can also be in pouch format. Filling and closing the container:

[0070] In the case of a parallelepiped or cylindrical container, a lid is assembled onto the cell container, for example by laser welding. The cell container is filled with electrolyte. For this purpose, the lid may include a filling hole through which the electrolyte is introduced. Once the electrolyte has been introduced, this filling hole is closed by a stainless steel ball via electrical welding of the ball to the hole. EXAMPLES

[0071] The porosities of powders of different active ingredients were compared. Table 1 below shows the active ingredients used. [Table 1] Electrode outside the invention

[0072] Figures 1 and 2 are SEM photographs of the powders of active ingredients A and B. A primary particle is highlighted in Figure 1. An agglomerate is highlighted in Figure 2.

[0073] The powders of active ingredients A and B were subjected to an increasing compression force. Figure 3 represents the variation in the porosity of a powder of active ingredient A and that of a powder of active ingredient B, as a function of the applied pressure. It can be seen that even for a high pressure of 1000 bar, the porosity of a powder of active ingredient A or B outside the invention remains greater than 40%. Concerning the active material powder A, its high porosity is due to the non-spherical nature of the particles. Concerning active material powder B, its high porosity is due to the porous nature of the particles. The theoretical porosity of an active material powder C according to the invention comprising particles with a monomodal size distribution is 26%. That of an active material powder D according to the invention comprising particles with a bimodal size distribution is 20%. The lower porosity value of active material powder D than that of active material powder C is explained by the bimodal distribution of the particles. Active materials C and D therefore make it possible to increase the volume capacity of the positive electrode by approximately 40 to 50% compared to active materials A and B.

Claims

Claims

1. An electrode comprising one or more active materials, one of the active materials being a lithium manganese and iron phosphate of formula LixMni-y-zFe y MzPO4 (LMFP) where 0.8 <x<1 ,2 ; 0,5<1-y-z<1 ; 0<y<0,5 ; 0<z<0,2 ; M étant un ou plusieurs éléments choisis dans le groupe consistant en Al, B, Mg, Si, Ca, Ti, V, Cr, Co, Cu, Ni, Zn, Y, Zr, Nb, W et Mo, l’électrode étant caractérisée en ce que : - the lithium manganese and iron phosphate is in the form of particles, at least 90% by number of the particles have a sphericity factor greater than or equal to 0.90 and less than 1, the sphericity factor of a particle being defined as the ratio between the surface area of ​​a sphere having the same volume as the particle and the surface area of ​​this particle, and in that - the internal porosity of the lithium manganese and iron phosphate particles is less than or equal to 5%, the internal porosity being defined by the ratio Vvide / VuviFP where Vvoid represents the void volume inside the lithium manganese and iron phosphate particles, VLMFP represents the geometric volume of lithium manganese iron phosphate particles.

2. An electrode according to claim 1, wherein the sphericity factor is greater than or equal to 0.

95.

3. The electrode of claim 2, wherein the sphericity factor is greater than or equal to 0.

98.

4. Electrode according to one of claims 1 to 3, in which the internal porosity of the particles of lithium manganese and iron phosphate ranges from 2 to 3%.

5. Electrode according to one of the preceding claims, in which at least 95% by number of the particles of lithium manganese and iron phosphate have a sphericity factor greater than or equal to 0.9 and less than 1.

6. Electrode according to one of the preceding claims, in which the particles of lithium manganese and iron phosphate are in the form of primary particles having a median diameter in volume D v so ranging from 500 nm to 20 pm or from 5 to 15 pm or from 1.5 to 4 pm.

7. Electrode according to one of claims 1 to 5, in which the particles of lithium manganese and iron phosphate are in the form of secondary particles having a median diameter in volume D vso ranging from 1 pm to 50 pm, a secondary particle consisting of the agglomeration of primary particles having a volume median diameter Dvso located in the range from 50 nm to 20 pm.

8. Electrode according to one of the preceding claims, in which the particles of lithium manganese and iron phosphate have a bimodal distribution, the first population being characterized by a first median diameter Dvso 1 , the second population being characterized by a second median diameter Dvso 2 , the ratio between Dvso 1 and Dvso 2 ranging from 3 to 10.

9. Electrode according to one of the preceding claims, in which in the lithium manganese and iron phosphate, 0.70<1-yz<1.

10. Electrode according to one of the preceding claims, further comprising one or more active materials chosen from: - a lithium iron phosphate of formula iii) Li x Fei.yM y PO4 (LFP) where 0.8 <x<1 ,2 ; 0<y<0,6 et M est choisi dans le groupe consistant en B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Cu, Zn, Y, Zr, Nb et Mo ; - a lithium vanadium fluorophosphate of formula iv) Lh+xVPCUF (LVPF) where 0 <x<0,15, ou à un de ses dérivés de formule v) Lii+xVi.yMyPCUFz (LVMPF) où 0<x<0,15, 0<y<0,5, 0,8<z<1 ,2 et M est choisi dans le groupe consistant en Ti, Al, Y, Cr, Cu, Mg, Mn, Fe, Co, Ni, et Zr ; - a lithium oxide of nickel, manganese and cobalt of formula a) Liw(Ni x Mn y COzMt)O2 (NMC) where 0.9 <w<1 ,1 ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci, - a lithium oxide of nickel, cobalt and aluminum of formula b) Li w (NixCOyAl zMt)O2 (NCA) where 0.9 <w<1 ,1 ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de B, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, Sr, Ce, Ga, Ta, Nd, Pr, La et des mélanges de ceux-ci, - a lithium oxide of nickel and manganese of formula c) Liw(Ni x Mn y COzMt)O2 (NMX) where 0.9 <w<1 ,1 ; 0,60<x<0,80 ; 0<y ; 0<z<0,02 ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci, - a lithium oxide of nickel and manganese of formula d) Liw(NixMn y COzMt)O2 where 1,1 <w<1 ,6 ; 0<x ; 0,50<y<0,80 ; 0<z<0,02 ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux- ci.

11. An electrode according to claim 10, wherein said one or more active materials is one or more lithium nickel oxides selected from: - a lithium oxide of nickel, manganese and cobalt of formula a) Liw(Ni x Mn y COzMt)O2 (NMC) where 0.9 <w<1 ,1 ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci, - a lithium oxide of nickel, cobalt and aluminum of formula b) Liw(Ni x Co y Al z Mt)O2 (NCA) where 0.9 <w<1 ,1 ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de B, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, Sr, Ce, Ga, Ta, Nd, Pr, La et des mélanges de ceux-ci, et - a lithium oxide of nickel and manganese of formula c) Liw(Ni x Mn y Co zMt)O2 (NMX) where 0.9 <w<1 ,1 ; 0,60<x<0,80 ; 0<y ; 0<z<0,02 ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci, et - a lithium oxide of nickel and manganese of formula d) Li w (Neither x Mn y Co z Mt)O2 where 1,1 <w<1 ,6 ; 0<x ; 0,50<y<0,80 ; 0<z<0,02 ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux- ci.

12. An electrode according to claim 11, wherein: - lithium manganese and iron phosphate represents from 40 to 99% by mass of the total mass of lithium manganese and iron phosphate and lithium nickel oxide(s); - said one or more lithium nickel oxides represent from 1 to 60% by mass of the total mass of lithium manganese and iron phosphate and lithium nickel oxide(s).

13. An electrode according to claim 12, wherein: - lithium manganese and iron phosphate represents from 70 to 99% by mass of the total mass of lithium manganese and iron phosphate and lithium nickel oxide(s); - said one or more lithium nickel oxides represent from 1 to 30% by mass of the total mass of lithium manganese and iron phosphate and lithium nickel oxide(s).

14. Lithium-ion electrochemical element comprising: - at least one positive electrode which is the electrode according to one of claims 1 to 13, - at least one negative electrode.

15. A process for preparing iron and manganese phosphate particles having a sphericity factor greater than or equal to 0.90 and less than 1 and an internal porosity less than or equal to 5%, the sphericity factor of a particle being defined as the ratio between the surface area of ​​a sphere having the same volume as the particle and the surface area of ​​this particle, the internal porosity being defined by the ratio Vvoid / Vi.MFP where Vvoid represents the void volume inside the lithium manganese and iron phosphate particles, VLMFP represents the geometric volume of the lithium manganese and iron phosphate particles, said process comprising the steps of: a) degassing a volume of water, b) dispersing in the degassed volume of water a mixture comprising: i) an iron precursor, such as the compounds of formula FeSCU xHhO, FeCh xF , FeC2C>4 xH2O and a mixture thereof, ii) a manganese precursor such as compounds of formula MnSCU xbkO,MnCh xFW, MnC2C>4 xH2O and a mixture thereof, iii) a precursor of ammonium ions such as ammonia, diammonium phosphate, ammonium phosphate and a mixture thereof, iv) a precursor of phosphate ions such as phosphoric acid, diammonium phosphate and ammonium phosphate, c) hydrothermal synthesis to obtain a compound of formula NH4(Fe,Mn)PO4, freed from sulfate, chloride or oxalate ions, for example by washing, d) decomposition of NH4(Fe,Mn)PO4 to (Fe,Mn)HPC>4 by exposing NH4(Fe,Mn)PO4 to a temperature between 250°C and 400°C.,

16. A method according to claim 15, wherein the decomposition of NH4(Fe,Mn)PC>4 into (Fe,Mn)HPC>4 in step d) occurs by exposing NH4(Fe,Mn)PC>4 to a temperature between 325°C and 350°C.

17. Method according to claim 15 or 16, further comprising a step e) of lithiation of (Fe,Mn)HPC>4 to obtain particles of a lithiated compound of formula Li(Fe,Mn)PC>4.

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