Multilayer electrode

Abstract

An electrode comprising: - a foil (C) made of aluminum or aluminum alloy, the foil either being covered at least partially on one or both faces by a coating intended to improve the electron conductivity between a coated layer and the foil and / or to improve the adhesion of a coated layer to the foil, or having been subjected to a surface treatment aimed at increasing the adhesion and / or the contact area of the coated layer with respect to the foil, - at least two superposed layers (L1, L2), each layer comprising a first active material (MA1) which is a lithiated phosphate of one or more transition metals and at least a second active material (MA2), characterized in that, in a layer in question, the weight proportion of the lithiated phosphate relative to all the active material weights of this layer is greater than the weight proportion of lithiated phosphate in the adjacent layer further away from the foil than the layer in question.

Description

Description Title: Multilayer electrode Technical field of the invention

[0001] The technical field of the invention is that of electrodes usable as positive electrodes (cathodes) in lithium-ion type electrochemical elements. Background to the invention

[0002] High specific capacity and high specific power are two objectives that are difficult to reconcile when designing an electrode for an electrochemical element. Generally, obtaining an electrode with a high specific capacity is achieved at the expense of specific power. Indeed, obtaining a high specific capacity involves depositing a significant amount of active material on the current collector of the electrode, and therefore creating a thick layer containing the active material. However, in a thick layer, the active material located near the current collector, due to its distance from the electrolyte, is less quickly accessible by the electrolyte than the active material located directly in contact with the electrolyte. A thick layer therefore constitutes an obstacle to good impregnation of the active material by the electrolyte and to the transport of lithium ions from the electrolyte to the active material.This drawback results in limited performance of the element during high current discharges or charges. Therefore, a way is sought to deposit thick layers of active material without sacrificing the available power.

[0003] In order to improve the impregnation of the active material by the electrolyte in the case of a thick layer of active material, it is known to superimpose several layers of active material on the current collector, all of the layers being characterized by a porosity gradient.

[0004] Documents US 2012 / 0328942 and US 2011 / 0168550 describe for example an arrangement of layers in which the layer of active material furthest from the collector comprises a first type of active material particles. The layer of active material in contact with the current collector comprises a second type of active material particles, the layer furthest from the current collector having a porosity greater than that of the layer in contact with the current collector.

[0005] WO 2019227016 describes an electrode comprising two superimposed layers of active material in which there is a porosity gradient from one layer to the other. The outer layer has a porosity greater than that of the layer in contact with the current collector. The outer layer comprises a mixture of an active material and of a conductive material, the mixture being dispersed / diluted in a liquid electrolyte. This outer layer is called "semi-solid". It can take the form of a suspension, an emulsion, a gel or micelles. Using a semi-solid outer layer has certain disadvantages. On the one hand, the choice of liquid electrolyte used in the manufacture of the outer layer dictates the choice of electrolyte that will be used later to impregnate the electrochemical bundle of the element. On the other hand, the use of a liquid electrolyte in the outer layer does not allow the humidity level of the electrode to be controlled below the maximum permissible limit. The semi-solid electrode cannot be prepared under the controlled atmosphere of a glove box.

[0006] New ways are being sought to facilitate the impregnation of a thick layer of active material by the electrolyte. In particular, a means is being sought to facilitate the impregnation by the electrolyte of a thick layer based on lithium phosphate of one or more transition metals. This electrode is intended to be used as the positive electrode of a lithium-ion electrochemical cell. Summary of the invention

[0007] To this end, the invention proposes an electrode comprising: - a strip of aluminum or aluminum alloy, the strip being either covered at least partially on one or both of its faces by a coating intended to improve the electronic conductivity between a coated layer and the strip and / or to improve the adhesion of a coated layer to the strip, or having undergone a surface treatment intended to increase the adhesion and / or the contact surface of the coated layer to the strip; - at least two superimposed layers, each layer comprising a first active material which is a lithium phosphate of one or more transition metals and at least one second active material, characterized in that, in a layer considered, the mass proportion of the lithium phosphate of one or more transition metals relative to all the masses of active materials of this layer is greater than the mass proportion of lithium phosphate of one or more transition metals in the adjacent layer further from the strip than the layer considered.

[0008] It has been discovered that a multilayer electrode in which the proportion of lithium phosphate increases from one layer to the next in the direction of the current collector makes it possible to increase the rate of impregnation of the electrode by the electrolyte. To enable the manufacture of an electrode richer in lithium phosphate near the current collector, particularly for lithium iron and manganese phosphates, and to maintain both a high electrode density (i.e. low porosity) and good electronic and mechanical contact with the current collector, it is necessary to use a current collector which is an aluminum or aluminum alloy strip covered with at least partially on one or both sides by a coating intended to improve the electronic conductivity between the layer coated with active material and the strip and / or to improve the adhesion of the layer coated with active material to the strip. Alternatively to the coating, the strip may have undergone a surface treatment aimed at increasing the adhesion and / or the contact surface of the coated layer to the strip. It is then possible to obtain a positive electrode having both a high grammage, good mechanical strength and good performance in discharge or charge under high currents.

[0009] According to one embodiment, the mass proportion of the first active material increases continuously from the layer furthest from the strip to the layer in contact with the strip.

[0010] According to one embodiment, the lithium phosphate of one or more transition metals is selected from the group consisting of: i) LixFePC>4 (LFR) with 0.8 <x<1 ,2 ; ii) LixMni-y-zFe y MzPO4 (LMFP) with 0.8 <x<1 ,2 ; 0,5<1-y-z<1 ; 0<y<0,5 ; 0<z<0,2 et M est choisi dans le groupe constitué de B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb et Mo, pris seuls ou en mélange ; iii) LixVPOtF (LVPF) avec 0,8<x<1 ,2, ou l’un de ses dérivés de formule Li x Vi-yMyPO4F z where 0.8 <x<1 ,2 ; 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, et iv) un mélange de deux ou trois des composés i) à iii).

[0011] According to one embodiment, the second active material is a lithium oxide of formula LixMi.yz-wM'yM”zM'” wO2(LMO2) where M, M', M” and M'” are selected from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, W and Mo with the proviso that at least M or M' or M” or M'” is selected from Mn, Co, Ni, or Fe; M, M', M” and M'” being different from each other; and 0.8 <x<1 ,4 ; 0<y<0,5 ; 0<z<0,5 ; 0<w<0,2 et x+y+z+w<2,1.

[0012] According to one embodiment, the lithium oxide is chosen from: 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, Sr, Ce, Ta, Ga, Nd, Pr, La et leurs mélanges, et 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 leurs mélanges.

[0013] According to one embodiment, in each layer, - the mass proportion of the first active ingredient is in the range from 50 to 99% relative to the mass of all the active ingredients in the layer considered; - the mass proportion of the second active ingredient is in the range from 1 to 50% relative to the mass of all the active ingredients in the layer considered.

[0014] According to one embodiment, the electrode comprises: - a first layer in contact with the strip, in which the mass proportion of the first active material is in the range from 95 to 85% relative to the mass of all the active materials of the first layer and the mass proportion of the second active material is in the range from 5 to 15% relative to the mass of all the active materials of the first layer; - a second layer in contact with the first layer, in which the mass proportion of the first active material is in the range from 40 to 60% relative to the mass of all the active materials of the second layer and the mass proportion of the second active material is in the range from 60 to 40% relative to the mass of all the active materials of the second layer.

[0015] According to one embodiment, - the first active ingredient is a compound of formula LixMni-y-zFe y MzPO4 (LMFP) with 0.8 <x<1 ,2 ; 0,5<1-y-z<1 ; 0<y<0,5 ; 0<z<0,2 et M est choisi dans le groupe constitué de B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb et Mo, pris seuls ou en mélange et - the second active ingredient is a compound of formula Li w (Neither 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, Sr, Ce, Ta, Ga, Nd, Pr, La et leurs mélanges.

[0016] According to one embodiment, the lithium phosphate of one or more transition metals has the formula Li x Mni- y -zFe y M z PO4 (LMFP) and 0.7<1-yz<0.9.

[0017] According to one embodiment, the second active material is a lithium oxide of formula Li x Mid- y -z-wM' y M” z M'”wO2 (LMO2) where M, M', M” and M'” are selected from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, W and Mo with the proviso that at least M or M' or M” or M'” is the element Ni and the stoichiometric index of nickel is greater than or equal to 0.6, preferably greater than or equal to 0.8.

[0018] According to one embodiment, the coating intended to improve the electronic conductivity between a coated layer and the foil and / or to improve the adhesion of a coated layer to the foil comprises or consists of carbon or graphite or carbon nanotubes, alone or as a mixture.

[0019] According to one embodiment, the first active material is in the form of particles having a first median diameter in volume Dvso 1 and the second active ingredient is in the form of particles having a second median diameter in volume Dvso 2 and the Dv5o ratio 2 / Dvso 1 is at least greater than or equal to 2.

[0020] According to one embodiment, the first active material is in the form of particles having a first median diameter in volume Dvso 1 ranging from 0.05 to 11 pm and the second active ingredient is in the form of particles with a second median diameter in volume Dvso 2 ranging from 2 to 15 pm, the first and second median diameters being determined by laser diffraction.

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

[0022] Embodiments of the invention are described below in more detail with reference to the accompanying figures.

[0023] [Fig.1] schematically represents a sectional view of an electrode according to the invention comprising a current collector and two superimposed layers of active material compositions.

[0024] [Fig.2] compares the internal resistances at the electrolyte / electrode interface of the electrodes of examples A, B, C and D.

[0025] [Fig.3] represents the percentage of the nominal capacity charged of the electrodes of examples A, B, C and D for different charging regimes. Description of embodiments of the invention Positive electrode: Positive electrode current collector:

[0026] The current collector used is a strip of aluminum or aluminum-based alloy. It can be solid or perforated. It is necessarily covered at least partially on one or both sides with a coating intended to improve the electronic conductivity between the layer of coated active material composition and the strip and / or to improve the adhesion of the layer of coated active material composition to the strip.

[0027] The coating may consist of a layer of carbon or graphite or carbon fibers or carbon nanotubes, alone or in a mixture. Preferably, it is a layer of carbon. The carbon coating may be obtained by coating the strip with a carbon dispersion followed by evaporation of the solvent or by cathode sputtering. Alternatively, instead of a coating, one or both surfaces of the strip may have undergone a surface treatment aimed at improving adhesion and increasing the contact surface of the layer of active material composition to the strip. This may be a surface treatment creating asperities or micro-roughness, for example by physical, chemical stripping or laser treatment.

[0028] The thickness of the strip can range from 3 to 30 μm. In a preferred embodiment, the strip is particularly thin and has a thickness ranging from 5 to 20 μm or from 10 to 16 μm.

[0029] The coating or surface treatment compensates for the increase in internal resistance induced by the presence of a significant proportion (> 50%) of lithium phosphate in the layer in contact with the current collector. The coating or surface treatment improves, on the one hand, the electronic conductivity between the collector and the different layers of active material composition and, on the other hand, the adhesion of the layer of active material composition adjacent to the current collector. Positive active ingredient composition layers:

[0030] Active material composition means a composition comprising a first active material, a second active material and optionally one or more binders and one or more electronically conductive materials. At least one of the two faces of the current collector is coated with at least two superimposed layers of active material compositions. The two faces of the current collector may each be coated with at least two superimposed layers of active material compositions.

[0031] The first positive active material is a lithium phosphate of one or more transition metals, preferably selected from the group consisting of: i) LixFePCL (LFP) with 0.8 <x<1 ,2 ; ii) LixMni-y-zFe yMzPO4 (LMFP) with 0.8 <x<1 ,2 ; 0,5<1-y-z<1 ; 0<y<0,5 ; 0<z<0,2 et M est choisi dans le groupe constitué de B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb et Mo, pris seuls ou en mélange ; iii) LixVPCLF (LVPF) avec 0,8<x<1 ,2, ou l’un de ses dérivés de formule LixVi-yMyPCLFz où 0,8<x<1 ,2 ; 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 ; et iv) un mélange de deux ou trois des composés i) à iii).

[0032] The lithium phosphate is preferably coated with a layer of carbon or carbon nanotubes or graphite or a mixture thereof.

[0033] Alternatively, the lithium phosphate is an LMFP-type compound optionally coated with carbon nanotubes or amorphous carbon. Alternatively, in the formula of LMFP, 0.7<1-yz<0.9 or 0.75<1-yz<0.80.

[0034] Examples of LMFP type lithiated phosphate are LiMno.sFeo^PCL, LiMnojFeo.sPCL, LiMn2 / 3Fei / 3PO4 and LiMno.5Feo.sPO4.

[0035] The second positive active ingredient is not particularly limited. Preferably, it is a lithium oxide of formula LixMi-yz-wM'yM” z M'”wO2 (LMO2) where M, M', M” and M'” are selected from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, W and Mo with the proviso that at least M or M' or M” or M'” is selected from Mn, Co, Ni, or Fe; M, M', M” and M'” being different from each other; and 0.8 <x<1 ,4 ; 0<y<0,5 ; 0<z<0,5 ; 0<w<0,2 et x+y+z+w<2,1 .

[0036] More preferably, the lithium oxide is chosen from: Liw(NixMriyC0zMt)02 (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, Sr, Ce, Ta, Ga, Nd, Pr, La et leurs mélanges, et Li w (NixCOyAlz 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 leurs mélanges.

[0037] Preferably, in the NMC compound, 0.6 <x ou 0,7<x ou 0,8<x.

[0038] Preferably, in the NCA compound, 0.8 <x. Examples of NMC type compounds are LiNii / 3Mni / 3Coi / 3O2, LiNio,eMno,2Coo,202, LiNio,84Mno,osCoo,o802, LiNio,87Mno,o6Coo,o?02 and LiNio,89Mno,o6Coo,os02. Examples of NCA type compounds are LiNio,84Coo,o8Alo,os02, LiNio,85Coo,ioAlo,os02, LiNio,87COo,06Alo,0?02 ©t LiNio,89COo,06Alo,Os02.

[0039] Preferred mixtures of first and second active ingredients are: - an LFP type compound with an NCA type compound; - an LFP type compound with an NMC type compound; - an LFP type compound with an NCA type compound and an NMC type compound; - a LMFP type compound with an NCA type compound; - a LMFP type compound with an NMC type compound; - a LMFP type compound with an NCA type compound and an NMC type compound.

[0040] An active material composition layer may contain other active materials than the first and second active materials. Preferably, each layer does not comprise any other active material than the first and second active materials. Preferably, the active material composition layer does not comprise a compound of formula Li x Mn2-yM y O4 where 1 <x<1 ,4 ; 0<y<1 et M représente un ou plusieurs éléments choisis dans le groupe consistant en B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb et Mo. Par exemple, elle ne comprend pas le composé de formule LiMn2Û4.

[0041] In each layer except the outer layer, the mass proportion of lithium phosphate of one or more transition metals, relative to the total mass of active materials in this layer, is greater than the mass proportion of lithium phosphate of one or more transition metals in the adjacent layer further from the foil than the layer in question. This results in faster penetration of the electrolyte into the electrode layers, higher ionic conductivity and better performance of the element in high current discharge.

[0042] The number of superimposed layers is not limited. Each layer may have a thickness after calendering ranging from 10 to 200 μm or from 20 to 150 μm or from 30 to 100 μm or from 50 to 80 μm. The superimposed layers may be of equal or different thicknesses. In a preferred embodiment, the electrode comprises two superimposed layers each with a thickness ranging from 40 to 70 μm.

[0043] With an equal quantity of active material deposited on the current collector, a multilayer electrode according to the invention is impregnated with electrolyte more quickly than an electrode comprising only a single layer. The increase in the proportion of lithium phosphate as one approaches the current collector allows for faster impregnation of the electrolyte. For example, an electrode comprising a first layer in contact with the current collector comprising a mixture of LMFP and NMC in the proportions of 90% / 10% and a second layer comprising a mixture of LMFP and NMC in the proportions of 50% / 50% has a higher electrolyte absorption rate than an electrode comprising only a single layer comprising a mixture of LMFP and NMC in the proportions of 70% / 30%, while the total quantities of LFMP and NMC are identical in the two electrodes.

[0044] Figure 1 schematically represents a sectional view of an electrode comprising a current collector (C), a first layer (L1) adjacent to the current collector and a second layer (L2) deposited on the first layer. The first layer and the second layer each comprise a mixture of a first active material (MA1) and a second active material (MA2). The proportion of the first active material in the first layer is greater than the proportion of the first active material in the second layer.

[0045] The mixture of the first and second active ingredients can be made up of: - from 50 to 99% or from 60 to 95% or from 70 to 90% or from 75 to 85% of lithium phosphate, - from 1 to 50% or from 5 to 40% or from 10 to 30% or from 15 to 25% of one or more lithiated oxides.

[0046] The mixture of the first and second active ingredients may consist of: - 60 to 40% lithium phosphate, - 40 to 60% of one or more lithium oxides.

[0047] In a preferred embodiment, one of the faces of the current collector comprises only two layers. In the layer closest to the current collector, the mixture of the first and second active materials consists of: - 85 to 95% lithium phosphate, - 5 to 15% of one or more lithium oxides. In the layer furthest from the current collector, the mixture of the first and second active materials consists of: - 40 to 60% or 45 to 55% lithium phosphate, - 60 to 40% or 55 to 45% of one or more lithium oxides. In these examples, the lithium phosphate is preferably a LMFP type compound and the lithium oxide is preferably a NMC type compound. In the layer closest to the current collector, the mixture of the first and second active materials can consist of: - 90% lithium phosphate, - 10% of one or more lithium oxides. In the layer furthest from the current collector, the mixture of the first and second active materials can consist of: - 50% lithium phosphate, - 50% of one or more lithium oxides.

[0048] According to one embodiment, the mass proportion of lithium phosphate in the first layer is greater than 70% or greater than or equal to 80% or greater than or equal to 90%.

[0049] According to one embodiment, the mass proportion of lithium phosphate in the second layer is greater than 30% or greater than or equal to 50% or greater than or equal to 70%.

[0050] According to one embodiment, the electrode comprises three superimposed layers and the mass proportion of lithium phosphate in the third layer is less than 20% or less than or equal to 10% or less than or equal to 5%.

[0051] Lithium phosphate can be present in the form of either disjointed particles, called primary particles, or agglomerated particles, called secondary particles. The median diameter in volume Dvso 1 of primary or secondary particles is in the range from 0.05 pm to 11 pm. Primary particles may have a volume median diameter Dvso 1 ranging from 0.05 to 1.5 pm. Secondary particles may have a volume median diameter Dvso 1 ranging from 2.9 to 6 pm or from 2.9 to 11 pm. The volume median diameter can be measured by laser diffraction.

[0052] The lithium oxide can have a volume median particle diameter Dvso 2ranging from 2 to 3 pm.

[0053] Preferably, the sizes of the particles of active materials are chosen such that the DV5O ratio 2 / DV5O 1 either at least greater than or equal to 2 or at least greater than or equal to 5 or at least greater than or equal to 7.

[0054] Typically, an electrode weight ranging from 15 to 80 mg / cm 2 or 30 to 60 mg / cm 2 per face can be obtained, the grammage corresponds to the mass of dry material composition deposited per unit of surface and per face of the strip.

[0055] The binder generally used in the active material composition serves to strengthen the cohesion between the active material particles and to improve the adhesion of the active material composition 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, polyvinyl chloride (PVC), poly(vinyl formalin), polyester, block polyetheramides, polymers of acrylic acid, methacrylic acid, acrylamide, itaconic acid, sulfonic acid, elastomers and cellulose compounds. such as carboxymethylcellulose (CMC). The elastomer(s) that can be used as a binder can be chosen from styrene-butadiene (SBR), butadiene-acrylonitrile (NBR), hydrogenated butadiene-acrylonitrile (HNBR).

[0056] The electronically conductive material generally used in the active material composition is generally selected from graphite, carbon black, acetylene black, soot, graphene, carbon fibers, carbon nanotubes, or a mixture thereof. It may also be in the form of a carbon coating around the active material particles. It generally represents 5% or less or 0.1 to 3% or less than 1% of the mass of the dry material composition. Preparation of the positive electrode:

[0057] An ink is prepared by dispersing the first and second active materials in a solvent or a mixture of several solvents, optionally with one or more binders and optionally one or more electronically conductive materials. By varying the amount of solvent incorporated in the mixture, the viscosity of the ink can be varied before depositing it on one of the faces of the current collector. The ink-coated current collector is dried and then laminated in order to adjust its thickness and porosity. A person skilled in the art will be able to adjust the pressure applied to obtain the desired thickness and porosity. After evaporation of the solvent(s), a layer of active material composition is obtained, the proportions of the various constituents of which are typically: - from 75 to 98% by mass of positive active material or from 90 to 95%; - from 1 to 10% by mass of binder(s), or from 2 to 5%; - from 1 to 10% by mass of electronically conductive material, or from 2 to 5%.

[0058] A second layer of active ingredient composition may be prepared using the same procedure as the first layer and deposited on top of the first layer. The second layer may have a thickness equal to or different from that of the first layer. The coating, drying, and lamination operations are repeated as many times as the desired number of layers.

[0059] The opposite face of the current collector not yet covered can in turn be covered with one or more layers of active material composition. Negative electrode:

[0060] Negative electrode foil: The current collector of the negative electrode is generally a copper foil or an alloy comprising mainly copper. The negative electrode foil has a thickness generally between 3 and 30 μm. In a preferred embodiment, the foil is particularly thin and has a thickness ranging from 5 to 20 μm or from 10 to 15 μm. he Negative active ingredient:

[0061] The negative active material is not particularly limited. It may be selected from: a) metallic lithium and lithium alloys; b) compounds capable of inserting lithium into their structure, such as: i) carbon, graphite, coke, carbon black and glassy carbon; ii) tin, silicon, carbon and silicon-based compounds, carbon and tin-based compounds and carbon, tin and silicon-based compounds; iii) lithiated titanium oxides (LTO) of formula Lix-aMa Tiy-bM'bO4-c-dXc in which 0 <x<3 ; 1 <y<2,5 ; 0<a<1 ; 0<b<1 ; 0<c<2 et -2,5<d<2,5 ; où M représente au moins un élément choisi dans le groupe constitué de Na, K, Mg, Ca, B, Mn, Fe, Co, Cr, Ni, Al, Cu, Ag, Pr, Y et La ; M’ représente au moins un élément choisi dans le groupe constitué de B, Mo, Mn, Ce, Sn, Zr, Si, W, V, Ta, Sb, Nb, Ru, Ag, Fe, Co, Ni, Zn, Al, Cr, La, Pr, Bi, Sc, Eu, Sm, Gd, Ce, Y et Eu ; X est au moins un élément choisi dans le groupe consistant en S, F, Cl et Br. Examples of lithium titanium oxide (LTO) are Ü4TisOi2 (Li4 / 3Tis / 3O4), U2TC3, Li2TiaO7, LiTi2Û4, Li x Ti2O4 with 0 <x<2 et Li2Na2TieOi4 . iv) les oxydes de titane et de niobium (TNO) de formule Tii.yMyNb2-zM’zO7-c-dXc où 0<y<1 ; 0<z<2 ; 0<c<2 et 0<d<2 ; 0<1-y ; 0<2-z. Un exemple de ce type de composé est TiNb2O7. How to prepare a negative electrode:

[0062] The negative electrode is prepared in a conventional manner. An ink is prepared by dispersing in a solvent or a mixture of several solvents one or more negative active materials, optionally with one or more binders and optionally one or more electronically conductive materials. The binder and the electronically conductive material may be as described in relation to the positive electrode.

[0063] The ink-coated current collector is dried and then rolled to adjust its thickness. A negative electrode is thus obtained.

[0064] Typical proportions of the components of the negative active material composition layer, after evaporation of the solvent contained in the ink, are: - from 75 to 98% by mass of negative active material, or from 90 to 98%; - from 1 to 10% by mass of binder(s), or from 1 to 5%; - from 0 to 5% by mass of electronically conductive compound, or from 1 to 5%. There is usually no electronically conductive compound, except for LTO. Electrolyte:

[0065] The electrolyte may be liquid. It is obtained by dissolving one or more lithium salts in one or more organic solvents. The solvent may be chosen from saturated cyclic carbonates, unsaturated cyclic carbonates, non-cyclic carbonates, alkyl esters, ethers, nitrile solvents, and tetrahydrothiofene dioxide (sulfolane).

[0066] Examples of saturated cyclic carbonates include ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), butylene carbonate (BC), and mixtures thereof.

[0067] Among the unsaturated cyclic carbonates, we can cite vinylene carbonate (VC).

[0068] Non-cyclic carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dipropyl carbonate (DPC), and mixtures thereof.

[0069] Examples of alkyl esters include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and mixtures thereof.

[0070] Examples of ethers include dimethyl ether (DME) or diethyl ether (DEE) and mixtures thereof.

[0071] The lithium salt may be selected from lithium perchlorate LiCIC>4, lithium hexafluorophosphate LiPFe, lithium tetrafluoroborate UBF4, lithium hexafluoroarsenate LiAsFe, lithium hexafluoroantimonate 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 CFsSChh (LiTFSM), lithium bis(pentafluoroethylsulfonyl)imide LiN(C2FsSO2)2 (LiBETI), lithium 4,5-dicyano-2-(trifluoromethyl) imidazolide (LiTDI), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LID-FOB), lithium tris(pentafluoroethyl)trifluorophosphate LiPF3(CF2CF3)3 (LiFAP), lithium difluorophosphate UPO2F2 and mixtures thereof.

[0072] The concentration of said at least one lithium salt can range from 0.75 to 1.5 mol.L-1 . Preferably, it ranges from 1 to 1.5 mol.L -1 . Preferably, it is approximately equal to 1 mol.L -1 .

[0073] Some salts are used as additives, for example UPO2F2, but also sometimes LiBOB and LIDFOB. In these cases, their quantity is expressed as a mass percentage added to 100% electrolyte. Typically, from plus 1 to plus 5% and at most plus 10%. Separator:

[0074] A separator is inserted between a positive electrode and a negative electrode. The separator material can be chosen from the following materials: a polyolefin or a mixture of polyolefins, for example polypropylene PP, polyethylene PE, a polyester, glass fibers bonded together by a polymer, polyimide, polyamide, polyaramide, polyamideimide and cellulose. The polyester may be chosen from polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). Advantageously, the polyester or polypropylene or polyethylene contains or is coated with a material chosen from the group consisting of a metal oxide, a carbide, a nitride, a boride, a silicide and a sulfide. This material may be SiC>2 or AI2O3, or boehmite. The separator may be coated with an organic coating, for example comprising an acrylate or PVdF or P(VdF-HFP). Manufacture of the electrochemical element:

[0075] An electrochemical bundle is formed by superimposing at least one positive electrode, at least one separator, and at least one negative electrode, each positive electrode being separated from the negative electrode by a separator. The element format can be of any type, for example prismatic, cylindrical, button, or pocket.

[0076] For a prismatic cell, the positive and negative electrodes and the separator are planar. The electrochemical bundle is parallelepipedal and is introduced into the container. The electrochemical bundle is impregnated with electrolyte and the container opening is sealed with a lid.

[0077] For a cylindrical cell, the electrochemical bundle is wound into a spiral and then introduced into the container. It is impregnated with electrolyte and the container opening is sealed with a lid.

[0078] For a button-shaped cell, a positive electrode, a separator, and a negative electrode are placed on the bottom of the container. The negative electrode, the positive electrode, and the separator are impregnated with electrolyte. A lid is placed on the top electrode. The edges of the container are crimped against the lid to seal the electrochemical cell.

[0079] For a pouch-type cell, a stack of a positive electrode, a separator, and a negative electrode is made. This assembly is inserted into a flexible pouch. The pouch is formed by welding the edges of two multilayer films, each multilayer film comprising a metal layer, usually aluminum, sandwiched between two layers of plastic. The pouch thus formed is filled with an electrolyte and then sealed.

[0080] The manufactured element is secondary. It can be used in applications involving high currents. Examples

[0081] Four positive electrodes were fabricated. Their structure is summarized in Table 1 below. [Table 1] outside of invention

[0082] 1. The electrodes were immersed in an electrolyte and the internal resistance of the interface between the electrode and the electrolyte was measured. The electrolyte used consisted of a mixture of four solvents: dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) / ethylene carbonate (EC) / propylene carbonate (PC) in the respective volume proportions of 45% / 25% / 10% / 20% in which lithium hexafluorophosphate LiPFe was dissolved. The electrolyte obtained was supplemented with 3% vinylene carbonate (VC) and 1% ethylene monofluorocarbonate (FEC). The separator used was a three-layer separator consisting of PP / PE / PP layers.

[0083] For comparison purposes, the internal resistance values ​​have been shown in Figure 2. Comparing the results obtained for electrode B with those obtained for electrode A shows that the multilayer structure alone does not reduce the internal resistance. Indeed, the interface resistance of the multilayer electrode A is 290 Ω, therefore higher than that of the single-layer electrode B, which is 105 Ω. Comparing the interface resistance of electrode D with that of electrode A, we note the significant benefit provided by the carbon coating. The interface resistance drops from 290 Ω to 14 Ω, a decrease in the internal resistance of the interface by a factor of 20. We conclude that the transition from the single-layer structure to the multilayer structure only brings a benefit if the current collector is coated with carbon. The improvement in the adhesion of the layer coated with active material to the current collector current between electrode A and electrode D can be estimated at a factor of 3. Comparing the result obtained for electrode C with that of electrode D shows that the transition from a single-layer structure to a multi-layer structure allows a reduction of approximately 30% in internal resistance. In fact, the internal resistance goes from approximately 18 Q for electrode C to 14 Q for electrode D. This is explained by an improvement in ionic conductivity. Furthermore, the time taken for the electrode to be impregnated by the electrolyte is divided by a factor of 2 for electrode D compared to electrode C.

[0084] 2. Button-type electrochemical cells comprising a positive electrode which is one of electrodes A, B, C or D and a negative graphite electrode were fabricated. The cells were charged at different charging rates. The charged capacity at the C / 20 rate is the reference capacity. The charged capacities at the C / 5, C / 3, C / 2, 2C and 3C rates were expressed relative to the reference capacity. The results are shown in Figure 3. The results are consistent with those shown in Figure 2, i.e., the change from the single-layer structure to the multi-layer structure only provides a benefit if the current collector is coated with carbon. The change from a single-layer structure (Example C) to a multi-layer structure (Example D) increases the charged capacity by about 10% for a charge at the 3C rate.

Claims

Claims

1. Electrode comprising: - a strip (C) made of aluminum or aluminum alloy, - at least two superimposed layers (L1, L2), deposited on one of the faces of the strip, each layer comprising a first active material (MA1) which is a lithium phosphate of one or more transition metals and at least one second active material (MA2), characterized in that, in a layer considered, the mass proportion of the lithium phosphate of one or more transition metals (MA1) relative to all the masses of active materials of this layer (MA1, MA2) is greater than the mass proportion of lithium phosphate of one or more transition metals in the adjacent layer further from the strip than the layer considered, the strip being covered at least partially on one or both of its faces by a coating intended to improve the electronic conductivity between the strip and the layer with which the strip is in contact and / or to improve the adhesion of said layer to the strip.

2. Electrode according to claim 1, in which, in each layer with the exception of the external layer, the mass proportion of the lithium phosphate of one or more transition metals (MA1) relative to all the masses of active materials of this layer (MA1, MA2) is greater than the mass proportion of lithium phosphate of one or more transition metals in the adjacent layer further from the strip than the layer in question.

3. Electrode according to one of the preceding claims, in which the lithium phosphate of one or more transition metals is chosen from the group consisting of: i) Li x FePO4 (LFR) with 0.8 <x<1 ,2 ; ii) LixMni-y-zFe yMzPO4 (LMFP) with 0.8 <x<1 ,2 ; 0,5<1-y-z<1 ; 0<y<0,5 ; 0<z<0,2 et M est choisi dans le groupe constitué de B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb et Mo, pris seuls ou en mélange ; iii) LixVPOtF (LVPF) avec 0,8<x<1 ,2, ou l’un de ses dérivés de formule Li x Vi.yMyPO4Fz where 0.8 <x<1 ,2 ; 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, et iv) un mélange de deux ou trois des composés i) à iii).

4. Electrode according to one of the preceding claims, in which the second active material (MA2) is a lithium oxide of formula Li xMi-yz-wM'yM”zM”'wO2 (LMO2) where M, M', M” and M'” are selected from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, W and Mo with the proviso that at least M or M' or M” or M'” is selected from Mn, Co, Ni, or Fe; M, M', M” and M'” being different from each other; and 0.8 <x<1 ,4 ; 0<y<0,5 ; 0<z<0,5 ; 0<w<0,2 et x+y+z+w<2, 1 .

5. Electrode according to claim 4, in which the lithium oxide is chosen from: 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, Sr, Ce, Ta, Ga, Nd, Pr, La et leurs mélanges, et Li w (NixCOyAl 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 leurs mélanges.

6. Electrode according to one of the preceding claims, in which in each layer, - the mass proportion of the first active material (MA1) is in the range from 50 to 99% relative to the mass of all the active materials (MA1, MA2) of the layer considered; - the mass proportion of the second active material (MA2) is in the range from 1 to 50% relative to the mass of all the active materials (MA1, MA2) of the layer considered.

7. Electrode according to one of claims 1 to 5, comprising: - a first layer (L1) in contact with the strip (C), in which the mass proportion of the first active material (MA1) is in the range from 95 to 85% relative to the mass of all (MA1, MA2) of the active materials of the first layer and the mass proportion of the second active material (MA2) is in the range from 5 to 15% relative to the mass of all (MA1, MA2) of the active materials of the first layer; - a second layer (L2) in contact with the first layer (L1), in which the mass proportion of the first active material (MA1) is in the range from 40 to 60% relative to the mass of the set (MA1, MA2) of the active materials of the second layer and the mass proportion of the second active material (MA2) is in the range from 60 to 40% relative to the mass of the set (MA1, MA2) of the active materials of the second layer.

8. Electrode according to one of the preceding claims, in which; - the first active ingredient (MA1) is a compound of formula Li x Mni-y-zFe y MzP04 (LMFP) with 0.8 <x<1 ,2 ; 0,5<1-y-z<1 ; 0<y<0,5 ; 0<z<0,2 et M est choisi dans le groupe constitué de B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb et Mo, pris seuls ou en mélange et - the second active ingredient (MA2) is a compound of formula 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, Sr, Ce, Ta, Ga, Nd, Pr, La et leurs mélanges.

9. Electrode according to one of claims 3 to 8, in which the lithium phosphate of one or more transition metals has the formula Li x Mni- y -zFe y M z PO4 (LMFP) and 0.7<1-yz<0.

9.

10. Electrode according to one of claims 4 to 9, in which the second active material (MA2) is a lithium oxide of formula LixMi- y -z-wM' y M” z M'”wO2 (LMO2) where M, M', M” and M'” are selected from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, W and Mo with the proviso that at least M or M' or M” or M'” is the element Ni and the stoichiometric index of nickel is greater than or equal to 0.6, preferably greater than or equal to 0.

8.

11. An electrode according to any preceding claim, wherein the coating for improving the electronic conductivity between a coated layer and the foil and / or for improving the adhesion of a coated layer to the foil comprises or consists of carbon or graphite or carbon nanotubes, alone or as a mixture.

12. Electrode according to one of the preceding claims, in which the first active material is in the form of particles having a first median diameter in volume Dvso 1 and the second active ingredient is in the form of particles having a second median diameter in volume Dvso 2 and the Dv5o ratio 2 / Dvso 1 is at least greater than or equal to 2.

13. Electrode according to one of the preceding claims, in which the first active material is in the form of particles having a first median diameter in volume Dvso 1 ranging from 0.05 to 11 pm and the second active ingredient is in the form of particles having a second median diameter in volume Dvso 2 ranging from 2 to 15 pm, the first and second median diameters being determined by laser diffraction.

14. Lithium-ion electrochemical element comprising at least one positive electrode which is the electrode according to one of the preceding claims.

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