Composition of electrode active materials based on lithium phosphate

Abstract

The present invention relates to an aqueous formulation of electrode active materials, the coated strip-based electrodes comprising the composition of active materials and the electrochemical elements that comprise same. The invention also relates to a method for preparing an electrode comprising the composition of active materials, the method for preparing the ink not using, as a solvent, substances identified as substances of very high concern appearing in the candidate list provided in Article 59 of Regulation (EC) No. 1907 / 2006 (REACH), or substances subject to restrictions appearing in the list provided in Annex XVII of Regulation (EC) No. 1907 / 2006.

Description

[0001] DESCRIPTION

[0002] TITLE: COMPOSITION OF ACTIVE ELECTRODE MATERIALS BASED ON LITHIUM PHOSPHATE

[0003] The present invention relates to the field of energy storage and lithium batteries in particular. More specifically, the present application relates to active material compositions intended for positive electrodes, and to ink formulations containing them which are coated on current collectors to manufacture these cathodes.

[0004] The invention is particularly useful in the field of rechargeable electrochemical elements of the lithium-ion (Li-ion) type.

[0005] The electrodes, particularly the positive ones, consist of a metal current collector on which is coated a composition of active material and additives such as binder(s), dispersant(s), conductive element(s), etc.

[0006] The electrodes are prepared from an ink comprising the composition, generally formulated in an organic solvent medium, coated on a current collector, from which the solvent is evaporated, before calendering so as to adjust the thickness of the ink layer on the collector.

[0007] Lithium phosphates of manganese and iron of formula Li x Mni.y.zFe y MzPO4 (LMFP) with 0.8 <x<1 ,2 ; 1 -y-z> 0.5; 0.05 <y<0,5 et 0<z<0,2 sont connus pour leur utilisation comme matière active cathodique d’éléments lithium-ion. Ces phosphates contiennent du manganèse, du fer et un ou plusieurs éléments substituants symbolisés par le symbole M. Ces composés sont connus pour offrir une sécurité d’utilisation supérieure en raison du fait que les phosphates lithiés de métaux de transition sont stables à température élevée.

[0008] The mixture of a lithium phosphate with a lithium nickel oxide has been proposed.

[0009] The nickel in the lithium oxide can be combined with manganese, cobalt, and possibly one or more chemical elements (NMC type oxide), or can be combined with cobalt, aluminum, and possibly one or more chemical elements (NCA type oxide). The mixture of a lithium phosphate and a lithium nickel oxide allows for better charge control and energy savings without significantly compromising safety.

[0010] Thus, positive electrodes based on active material consisting of a mixture of lithium manganese and iron phosphate (LMFP) and lithium nickel oxide type NMC and / or NCA have been described. FR 3 115 633 describes such ink compositions, however having low contents of lamellar oxide. In addition, the nature of the binders is not specified. The electrodes described comprise a current collector whose surface has been stripped.

[0011] FR 3 122 286 describes an ink formulation. However, this is made up of an organic solvent. In fact, the composition actually described cannot contain an exclusively aqueous binder.

[0012] Thus, inks are typically formulated in an organic solvent such as N-methyl-2-pyrrolidone (NMP), with one or more binders suitable for organic solvent media, such as polyvinylidene fluoride (PVDF) in powder form that dissolves in an organic solvent.

[0013] However, for safety and health reasons, the use of organic solvents is avoided. As such, regulations such as the European Union's Regulation on the Registration, Evaluation, and Authorization of Chemicals (REACH) may restrict the use of certain substances (such as the solvent N-methyl-2-pyrrolidone, for example). Cost control also encourages the replacement of these solvents.

[0014] Aqueous ink formulations have therefore been proposed.

[0015] WO 2015 / 036882 concerns inks formulated in an aqueous medium for positive electrodes and addresses the problem of cathode corrosion by water. Coating of active material particles with a polymer is proposed.

[0016] However, this particle coating technology can induce a decrease in the electronic and ionic conductivities of the electrode, thus penalizing the cell's performance. In addition, this document does not address the corrosion-related problem that appears for mixtures of active materials with lithium oxides with a high nickel content. In any case, it does not describe a mixture of active materials including a lithium phosphate of iron or manganese and iron in an aqueous formulation.

[0017] It therefore remains to provide alternative aqueous ink formulations free from these drawbacks.

[0018] One aim of the invention is then to propose an active material composition compatible with an aqueous ink formulation, according to a process without organic solvent. Another aim is also to prevent corrosion of the collector in the case of an aqueous formulation of a cathodic active material composition comprising a lithium nickel oxide with a high nickel content.

[0019] More particularly, the invention provides a positive electrode for a lithium-ion type electrochemical generator which has both increased safety during use and a high mass capacity, by using a cathodic active material with a formulation not involving the use of organic solvent for its preparation, in particular not involving the use of N-methyl-2-pyrrolidone (NMP).

[0020] To this end, the invention relates to an electrode comprising:

[0021] - a metal strip covered on at least one of its faces with an anti-corrosion coating; and

[0022] - a composition of active materials comprising: as electrochemically active materials, a mixture of:

[0023] • at least one lithium manganese and iron phosphate (LMFP) compound corresponding to the formula Li x Mni. y.z Fe y MzPO4 in which

[0024] M is selected from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo,

[0025] 0.8< x <1.2;

[0026] 0.5<1-yz<1 ;

[0027] 0.05< y <0.5;

[0028] 0 < z <0.2 ; and

[0029] • at least one lithium nickel oxide compound chosen from: i) lithium nickel, manganese and cobalt (NMC) oxides of formula Li w (NixMn yC0zMt)O2 where 0.9 <w<1 ,1 ; 0,4<x ; 0<y ; 0<z ; 0<t ; M étant au moins un élément 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 et La ; et ii) les oxydes lithiés de nickel, de cobalt et d’aluminium (NCA) de formule Li w (NixCo y Al z M t )02 where 0.9 <w<1 ,1 ; 0,6<x ; 0<y ; 0<z ; 0<t ; M étant au moins un élément 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 et La ; et iii) les mélanges des composés i) et ii) ; et à titre de liant : un ou plusieurs liants choisis parmi les liants polymériques solubles dans l’eau ou les liants dispersables dans l’eau; ladite composition étant enduite sur ledit revêtement anti-corrosion.

[0030] According to the invention, the preparation of the composition of active ingredients does not involve the use of organic solvents, in particular of the NMP type (N-methyl-2-pyrrolidone or 1-methyl-2-pyrrolidone) conventionally used for the preparation of inks. N-methyl-2-pyrrolidone or 1-methyl-2-pyrrolidone is a compound that is part, on the one hand, of the list of substances subject to restriction and on the other hand, of the list of substances of very high concern in the European Union regulation relating to the registration, evaluation and authorization of chemical substances (REACH). On the other hand, for the compound N-methyl-2-pyrrolidone, occupational exposure limit values ​​have been established for France and the European Union requiring companies that use this compound in their processes to continuously monitor the exposure levels of their employees.Advantageously, the composition according to the invention can be prepared aqueously, without using such solvents, in particular without using N-methyl-2-pyrrolidone.

[0031] According to one embodiment, the electrode does not contain NMP.

[0032] The electrode according to the invention makes it possible to address the problem of corrosion of the current collector, mainly linked to the increase in pH due to the level of nickel contained in the lithiated nickel oxide materials.

[0033] It also makes it possible to improve electrochemical performance by reducing the interfacial contact resistance between the lithium manganese iron phosphate (LMFP) materials and the current collector, thus leading to a reduction in internal resistance and an increase in the C rate. Thus, surprisingly, the applicant found that the aqueous formulation of an electrode comprising a lithium nickel oxide as cathodic active material made it possible to reduce the internal resistance of the cell. The reduction in internal resistance results, on the one hand, in an increase in the electrical performance of the element when it is used for charging or discharging at a high current (or rate), and, on the other hand, in less significant heating during cycling.

[0034] The electrode according to the invention further promotes good adhesion of the active material composition to the aluminum current collector. The metal strip acts as a current collector. Said metal strip may be made of aluminum or an alloy comprising predominantly aluminum. Advantageously, the metal strip is made of aluminum.

[0035] According to the invention, said strip is covered on at least one of its faces with an anti-corrosion coating.

[0036] Anti-corrosion coating means a layer of material that limits or reduces the attack on the strip by an excessively acidic or basic pH that could affect the surface condition, integrity or performance of the strip, such as pitting corrosion.

[0037] The said anti-corrosion coating can also improve the electronic conductivity and adhesion between the coated active material layer and the foil.

[0038] Typically, said coating may consist of carbon, graphite, carbon black or titanium for example. Preferably, said coating is little or not porous.

[0039] According to one embodiment, said strip is an aluminum strip coated with carbon. Advantageously, the carbon coating can be applied to the collector in an N-methyl-2-pyrrolidone / polyvinylidene fluoride (NMP / PVDF) solvent medium.

[0040] Said strip may be covered with said coating on one or both of its faces.

[0041] Typically, the active ingredient composition is coated onto said coating.

[0042] The coated current collector can therefore be covered on one or each of its faces with said composition of active materials.

[0043] The term "active material composition" means the composition comprising all the compounds, including the electrochemically active materials which cover the current collector on at least one of its faces. Generally, this composition comprises, in addition to the electrochemically active materials, electronically conductive materials, and possible additives, such as binders, etc.

[0044] Said composition of active materials comprises, as electrochemically active materials:

[0045] • at least one lithium manganese and iron phosphate (LMFP) compound and

[0046] • at least one lithium nickel oxide type compound.

[0047] LMFP type compounds have the formula

[0048] LixMni-y.zFeyMzPCU in which: M is selected from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo and mixtures thereof,

[0049] 0.8< x <1.2;

[0050] 0.5<1-yz<1 ;

[0051] 0.05< y <0.5;

[0052] 0< z <0.2.

[0053] According to one embodiment, 0.7<1-yz<0.9.

[0054] According to another embodiment, 0.7<1-yz<0.85.

[0055] Examples of LMFP-type active ingredients include compounds of formula LiMno.sFeo^PCU, LiMnojFeo.sPCU, LiMn^Fei / sPC t and LiMno.sFeo.sPCU.

[0056] The lithium nickel oxide type compounds are preferably chosen from nickel-rich lithium nickel oxides, preferably comprising more than 60% (based on the atomic ratio) of nickel.

[0057] Thus, they are chosen from i) lithium oxides of nickel, manganese and cobalt (NMC); ii) lithium oxides of nickel, cobalt and aluminum (NCA); and ll) mixtures of NMC and NCA.

[0058] Nickel-rich NMC compounds have the formula:

[0059] Li w (NixMn y C0zMt)O2

[0060] In which

[0061] 0.9 <w<1 ,1 ;

[0062] 0.60 <x ;

[0063] 0 <y ;

[0064] 0 <z ;

[0065] 0 <t ;

[0066] M being at least one element selected from the group consisting of Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, Sr, Ce, Ta, Ga, Nd, Pr and La and mixtures thereof.

[0067] M may be chosen in particular from the group consisting of Al, B, Mg and their mixtures. Preferably, M is Al and t<0.05. The majority transition element is preferably nickel, preferably x>0.6. A high amount of nickel in the lithium nickel oxide is preferable because it provides high energy to the lithium nickel oxide. As a nickel-rich lithium nickel, manganese and cobalt (NMC) oxide type compound, the following compounds may be mentioned in particular:

[0068] LiNi0.6Mn0.2Co0.2O2 (NMC 622),

[0069] LiNi0.8Mn0.1Co0.1O2 (NMC 81 1).

[0070] Nickel-rich lithium nickel cobalt aluminum (NCA) oxide compounds have the formula:

[0071] Li w (NixCo y AlzMt)02

[0072] In which

[0073] 0.9 <w<1 ,1 ;

[0074] 0.8 <x ;

[0075] 0 <y ;

[0076] 0 <z ;

[0077] 0 <t ;

[0078] M being at least one element selected from the group consisting of B, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, Sr, Ce, Ga, Ta, Nd, Pr and La and mixtures thereof.

[0079] Preferably M may be chosen from the group consisting of B, Mg and their mixtures. Examples include: LiNiO,8CoO,i5AlO,05O2.

[0080] According to one embodiment, the mixture of electrochemically active materials typically comprises:

[0081] - from 30 to 90%, preferably from 60 to 80% of lithium manganese and iron phosphate (LMFP) compound(s);

[0082] - from 10 to 70%, preferably from 20 to 40% of lithium nickel, manganese and cobalt (NMC) oxide type compound, and / or said lithium nickel, cobalt and aluminium (NCA) oxide type compound(s); the percentages being by weight, relative to the total weight of electrochemically active materials in said composition of active materials.

[0083] According to a more particular embodiment, the mixture of electrochemically active materials may comprise:

[0084] - from 60 to 80% of said lithium manganese and iron phosphate (LMFP) compound(s); and

[0085] - from 20 to 40% of said compound(s) of the lithium oxide type of nickel, manganese and cobalt (NMC), and / or of said compound(s) of the lithium oxide type of nickel, cobalt and aluminium (NCA), the percentages being expressed by weight and relative to the total weight of electrochemically active materials in said composition of active materials.

[0086] Said active ingredient composition also comprises one or more water-soluble or water-dispersible polymeric binders.

[0087] A "binder" is a compound that strengthens the cohesion between the particles of active materials and improves the viscosity and / or adhesion of the composition of active materials to the current collector.

[0088] Solubility is considered here under normal temperature and pressure conditions. It can typically be defined in terms of mass / volume of water considered.

[0089] As used herein, the term "water soluble" defines the ability of a binder to be soluble in water at a concentration greater than or equal to 1 g / L at 20°C.

[0090] According to the invention, the binder is a water-soluble, i.e. water-soluble, or water-dispersible polymeric binder, such as latex-type dispersions. Typically, the water-soluble or water-dispersible polymeric binder can be used in an aqueous medium for the preparation of the active ingredient composition.

[0091] Said binder can therefore be chosen from water-soluble or water-insoluble binders in the form of aqueous dispersion (latex).

[0092] The binder may be one or more of the following compounds and their copolymers: water-soluble polymers such as cellulose and its derivatives such as carboxymethylcellulose (CMC), hydroxypropylcellulose (HPC), hydroxymethylcellulose (HMC), hydroxyethylcellulose (HEC), hydroxypropylmethylcellulose (HPMC), diacetylcellulose, acrylic acid polymers and their alkali salts, sodium or lithium alginate, guar or xanthan gums, polyethers such as polyethylene glycol or polyethyleneoxide, polyurethanes;water-dispersible polymers, i.e. polymers capable of forming an aqueous dispersion such as latex-type dispersions, such as styrene-butadiene rubber (SBR), butadiene-acrylonitrile rubber (NBR), hydrogenated butadiene-acrylonitrile rubber (HNBR), styrene-acrylonitrile rubber (SAN), polypyrrole, polyaniline, epoxy resin, polydimethylsiloxane (PDMS), polyacrylonitrile (PAN), P(AN-MA): (Poly acrylonitrile-co-methyl-acrylate), polytetrafluoroethylene (PTFE), polymethylmethacrylate (PMMA), polyvinylidene fluoride (PVDF).;

[0093] Water-dispersible polymers are generally insoluble in water but can be stably dispersed in water. Thus, water-dispersible PVDF typically comes in the form of nanosized PVDF particles, which can form stable aqueous dispersions.

[0094] According to one embodiment, said water-soluble or water-dispersible polymeric binder(s) may be chosen from elastomers and cellulose compounds, such as carboxymethylcellulose (CMC), styrene-butadiene (SBR), butadiene-acrylonitrile rubber (NBR), hydrogenated butadiene-acrylonitrile rubber (HNBR) and mixtures thereof. Mention may thus be made more particularly of the CMC / SBR binder composition.

[0095] Said composition may further comprise one or more ingredients selected from electronically conductive materials, dispersants, and / or pH buffers.

[0096] The electronically conductive material may generally be selected from graphite, carbon black, acetylene black, soot, graphene, carbon nanotubes or a mixture thereof.

[0097] The composition may also comprise one or more dispersants. Polyvinylpyrrolidone (PVP) may thus be mentioned as a dispersant suitable for the invention.

[0098] One or more pH buffer compounds may also be present in the active ingredient composition. Typically, the ink giving rise to the composition has a very basic pH, in particular greater than 11. It may therefore be desirable to neutralize the pH by adding a pH buffer solution, such as an aqueous solution of Na2SiOs, to the ink. Thus, buffer, such as residual Na2SiOs, typically at a level of less than 2% by mass, may be present in the active ingredient composition.

[0099] According to one embodiment, said composition of active materials may comprise:

[0100] - 80 to 98% electrochemically active materials;

[0101] - from 0.5 to 10% of one or more electronically conductive materials;

[0102] - from 0.5 to 10% of one or more water-soluble or water-dispersible binders;

[0103] - from 0 to 1% of one or more dispersants; and

[0104] - from 0 to 2% of a pH buffer; the percentages being by weight, relative to the total weight of the active ingredient composition.

[0105] According to a particular embodiment, said composition of active materials may comprise:

[0106] - from 90 to 98% of electrochemically active materials:

[0107] - 1 to 5% carbon black;

[0108] - 1 to 5% of one or more water-soluble or water-dispersible binders;

[0109] - from 0 to 0.5% of dispersants; the percentages being expressed by weight and related to the total weight of the composition.

[0110] According to a particular embodiment, said composition of active materials may comprise:

[0111] - from 90 to 98% of electrochemically active materials comprising: from 60 to 80% of said lithium manganese and iron phosphate (LMFP) compound(s); and from 20 to 40% of said lithium nickel, manganese and cobalt oxide (NMC) compound(s), such as LiNii / 3Mni / 3Coi / 302 (NMC 1 11 ), LiNi0.6Mn0.2Co0.2O2 (NMC 622), LiNi0.8Mn0.1Co0.1O2 (NMC 811 ), and / or said lithium nickel, cobalt and aluminum oxide (NCA) compound(s), the percentages being expressed by weight and relative to the total weight of electrochemically active materials;

[0112] - 1 to 5% carbon black;

[0113] - 1 to 5% of one or more binders chosen from carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR) and their mixtures;

[0114] - from 0 to 0.5% of polyvinylpyrrolidone (PVP); the percentages being expressed by weight and related to the total weight of the composition.

[0115] According to another object, the present invention also relates to a method for preparing an electrode comprising:

[0116] - the preparation of an ink comprising the addition of the ingredients of the composition according to the invention and the mixing of the dispersion obtained in a solvent;

[0117] - the deposition of said ink on the coating of said metal strip;

[0118] - drying; and

[0119] - calendering. According to one embodiment, said preparation step is characterized by the use as solvent of no substance identified as substances of very high concern (substances classified as CMR (Carcinogenic, Mutagenic or toxic for Reproduction), PBT (Persistent in the environment or organisms, Bioaccumulative and Toxic), vPvB (very Persistent and very Bioaccumulative) or presenting a level of concern equivalent to the preceding substances) and appearing on the Candidate List provided for in Article 59 of Regulation (EC) No. 1907 / 2006, nor of any substance subject to restriction and appearing on the list provided for in Annex XVII of Regulation (EC) No. 1907 / 2006.

[0120] More particularly, the method for preparing an electrode according to the invention is characterized in that said step of preparing an ink is carried out aqueously and does not use N-methyl-2-pyrrolidone (NMP).

[0121] Generally, an electrode can be manufactured by preparing an ink comprising one or more active materials mixed with one or more binders, one or more electronically conductive materials, and water.

[0122] Typically the ink is in the form of an aqueous dispersion and typically comprises from 40 to 90%, preferably from 50 to 60% of said composition of active materials, the percentages being expressed by weight of dry matter and relative to the volume of said ink.

[0123] This ink can then be coated on at least one of the faces of a current collector coated with an anti-corrosion coating.

[0124] The ink may be dried in an oven, an oven, and / or by infrared to evaporate the water. In one embodiment, the drying comprises infrared drying.

[0125] Typically, the active ingredient composition comprising less than 300 ppm of residual water, in particular less than 150 ppm, or even less than 100 ppm of residual water.

[0126] The thickness of the composition thus coated can then be adjusted in a calendering step, by passing the electrode between two rollers exerting pressure on the surface of the electrode.

[0127] Another subject of the invention is an electrochemical element comprising at least one electrode as defined above. According to one embodiment, said electrode is a positive electrode (cathode) within said element.

[0128] According to one embodiment, the electrochemical element is of the lithium-ion type.

[0129] The lithium-ion cell can be manufactured in a conventional manner. At least one cathode, at least one separator and at least one anode are superimposed. The assembly can be rolled up to form a cylindrical electrochemical bundle. The invention is not limited to the manufacture of cylindrical-format cells. The cell format can also be prismatic or pouch-type. The electrodes can also be stacked to form a planar electrochemical bundle. A connection piece is fixed to an edge of the cathode not covered with active material. It is connected to a current output terminal.

[0130] The anode can be electrically connected to the cell container. Conversely, the cathode can be connected to the cell container and the anode to a current output terminal. After being inserted into the cell container, the electrochemical bundle is impregnated with electrolyte. The cell is then sealed. The cell can also be conventionally equipped with a safety valve that causes the cell container to open if the cell's internal pressure exceeds a predetermined value.

[0131] The electrolyte may be liquid and include a lithium salt dissolved in an organic solvent. This lithium salt may be chosen from lithium perchlorate LiCICU, 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 trifluoromethanesulfonimide LiN(CFsSO2)2 (LiTFSI), lithium trifluoromethanesulfonemethide LiC(CF3SC>2)3 (LiTFSM), lithium bisperfluoroethylsulfonimide LiN(C2FsSO2)2 (LiBETI), lithium 4,5-dicyano-2-(trifluoromethyl) imidazolide (LiTDI), lithium bis(oxalatoborate) (LiBOB), lithium difluoro(oxalato)borate (LIDFOB), lithium tris(pentafluoroethyl)trifluorophosphate LiPF3(CF2CF3)3 (LiFAP), lithium difluorophosphate UPO2F2 and mixtures thereof.

[0132] The solvent of the electrolyte may be selected from saturated cyclic carbonates, unsaturated cyclic carbonates, linear carbonates, alkyl esters, ethers, cyclic esters, such as lactones. Alternatively, the electrolyte may be solid. It may be a lithium ion-conducting compound, selected for example from lithium ion-conducting oxides and lithium ion-conducting sulfides. The electrolyte may also be a lithium ion-conducting polymer, such as polyethylene oxide (PEO), polyphenylene sulfide (PPS), and polycarbonate.

[0133] The electrolyte can also be in the form of a gel obtained by impregnating a polymer with a liquid mixture comprising at least one lithium salt and an organic solvent.

[0134] The separator may consist of a layer of polypropylene (PP), polyethylene (PE), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyester such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), cellulose, polyimide, glass fibers or a mixture of layers of different natures. The polymers mentioned may be coated with a ceramic layer and / or polyvinylidene difluoride (PVdF) or polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) or acrylates.

[0135] Figures

[0136] [Fig. 1] Figure 1 schematically represents the structure of an electrode according to the invention, comprising a current collector (1), such as an aluminum foil, covered on one of its faces by an anti-corrosion coating (2), such as a carbon coating, constituting a coated collector (3).

[0137] On this coated face of the current collector is present a layer (10) of the composition of active materials comprising in particular particles of lamellar oxide (8) such as a lithium oxide of nickel, manganese and cobalt (NMC type) and particles of a lithium phosphate of manganese and iron (LMFP) (7), constituting the mixture of electrochemically active materials (9). The layer (10) further comprises binders (4) and (5) which may in particular be carboxymethylcellulose and styrene-butadiene rubber, respectively, as well as a conductive element (6), such as carbon black.

[0138] [Fig. 2] Figure 2 shows the reversible capacity evolution curves at different discharge regimes comparing the performance of an aqueous formulation and a solvent-based formulation (NMP) for electrochemical cells with positive electrodes comprising a lithium oxide of nickel, manganese and cobalt. [Fig. 3] Figure 3 shows scanning electron microscopy (SEM) images of an uncoated aluminum current collector (A), with a carbon coating (B) or a graphite coating (C), after removal of the aqueous active material composition layer.

[0139] EXAMPLES

[0140] The following composition of active ingredients is prepared:

[0141] 94.4% electrochemically active materials consisting of:

[0142] 70% of LMFP, and

[0143] 30% of NMC811

[0144] 3% carbon black,

[0145] 0.1% PVP,

[0146] 1.25% CMC

[0147] 1.25% SBR, percentages being reported by weight.

[0148] A typical preparation procedure is as follows:

[0149] At 50% dry extract, the CMC is dispersed in all the water (typically 1 h, 45°C, 600rpm, deflocculating) then PVP, an optional buffer, carbon black, NMC, and LMFP are added (for about 30 min, at room temperature and 600rpm). Then the SBR is added (5 min, room temperature, 300rpm).

[0150] An optional pH buffer can be added (by adjusting the percentage of active ingredients).

[0151] This composition is prepared in an aqueous medium by mixing the ingredients with water. The ink thus formed is applied to a carbon-coated aluminum collector, then dried and calendered.

[0152] A representation of the electrode thus formed is illustrated in Figure 1.

[0153] In order to test the proper functioning and performance of a cell comprising a positive electrode comprising a lithium nickel oxide with a high nickel content formulated in an aqueous process, coin cell cells were produced with positive electrodes formulated in an aqueous process and comprising a lithium nickel, manganese and cobalt (NMC) oxide and lithium metal as a negative electrode. Comparative cells were produced, in the same format, with the same cathodic active material but formulated in an organic process (NMP). The internal resistance of each cell was measured. To carry out this measurement, a reference cycle was carried out consisting of a charge then a discharge at the C / 5 rate, where C is the nominal capacity of the cell. During the discharge, for a cell state of charge close to 50%, a discharge pulse lasting 10 seconds at a rate of 2C was carried out.This impulse allowed the internal resistance Ri to be calculated by applying the formula: Ri = (Uc / 5 — LLc) / (hc -Ic / s) where Uc / s and l. c / 5 respectively designate the voltage and current of the cell in discharge at the C / 5 rate before the application of the discharge pulse; LLc designates the voltage of the cell at the end of 10 seconds of application of the discharge pulse at the discharge rate l 2C The internal resistance is then multiplied by the cathode area coated on the foil to obtain a resistance expressed in ohms per cm2 (Q x cm2).

[0154] For the tested elements, the internal resistance resulting from this measurement is 19 Q.cm2 for the elements whose cathode active material composition was formulated in an aqueous way and 52 Q.cm2 for the elements whose cathode active material composition was formulated in an organic way. This lower internal resistance for the elements with the cathode active material formulated in an aqueous way leads to a better cyclability of these elements and less heating during cycling. On the other hand, it is clear from the evolution curves in Figure 2 that the capacity retention at high discharge rate (C as well as 1.3C) is better for the elements whose cathode active material comprises a lithium nickel oxide formulated in an aqueous way compared to the elements with the same cathode active material formulated in an organic way.

[0155] The SEM images demonstrate that the collector (A) has undergone corrosion and that the collectors (B) and (C) have not undergone corrosion.

[0156] The properties of the aqueous LMFP / NMC (70 / 30) type formulations according to the invention can be compared with the solvent-based formulations (NMP), as follows: [Table 1]

[0157] Thus, the electrodes according to the invention have electrochemical performances at least equivalent or even superior to electrodes of the same composition formulated with organic solvent. In addition, due to their aqueous formulation, the electrodes according to the invention make it possible to limit health risks during their manufacture while reducing the associated costs and do not use in the preparation process, as solvent, a substance included in the list of substances subject to restriction or included in the list of substances of very high concern according to the European Union regulation on the registration, evaluation, authorization and restriction of chemical substances REACH.

Claims

CLAIMS 1. Electrode comprising: - a metal strip covered on at least one of its faces with an anti-corrosion coating; and - a composition of active materials comprising: as electrochemically active materials, a mixture of: at least one lithium manganese and iron phosphate (LMFP) compound corresponding to the formula Li x Mni. y.z Fe y MzPO4 in which M is selected from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo, 0.8< x <1.2; 0.5<1-yz<1 ; 0.05< y <0.5; 0 < z < 0.2 ; at least one lithium nickel oxide compound chosen from: i) lithium nickel, manganese and cobalt (NMC) oxides of formula Li w (Neither x Mn y Co z M t)02 where 0.9 <w<1 ,1 ; 0,40<x ; 0<y ; 0<z ; 0<t ; M étant au moins un élément 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 et La ; ii) les oxydes lithiés de nickel, de cobalt et d’aluminium (NCA) de formule Li w (Neither x Co y Al z M t )02 where 0.9 <w<1 ,1 ; 0,6<x 0<y 0<z 0<t m étant au moins un élément 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 et la ill) les mélanges nmc nca à titre liant : ou plusieurs liants choisis parmi polymériques solubles l’eau dispersables l’eau; ladite composition enduite sur ledit revêtement anti-corrosion.

2. Electrode according to claim 1 such that the strip is an aluminum strip coated with carbon.

3. Electrode according to claim 1 or 2 such that the water-soluble or water-dispersible polymeric binders are chosen from elastomers and cellulose compounds, such as carboxymethylcellulose (CMC), styrene-butadiene (SBR), butadiene-acrylonitrile rubber (NBR), hydrogenated butadiene-acrylonitrile rubber (HNBR).

4. Electrode according to any one of the preceding claims such that said composition further comprises one or more ingredients chosen from electronically conductive materials, dispersants, and / or pH buffers.

5. Electrode according to any one of the preceding claims such that said composition comprises: - 80 to 98% electrochemically active materials; - from 0.5 to 10% of one or more electronically conductive materials; - from 0.5 to 10% of one or more water-soluble or water-dispersible binders; - from 0 to 1% of one or more dispersants; and - from 0 to 2% of a pH buffer; the percentages being by weight.

6. Electrode according to any one of the preceding claims, such that the mixture of electrochemically active materials comprises: - from 30 to 90%, preferably from 60 to 80% of lithium manganese and iron phosphate (LMFP) type compound(s); - from 10 to 70%, preferably from 20 to 40% of lithium nickel oxide type compound; the percentages being by weight, relative to the total weight of electrochemically active materials.

7. Electrode according to any one of the preceding claims such that said composition comprises: - from 90 to 98% of electrochemically active materials comprising: from 60 to 80% of said lithium manganese and iron phosphate (LMFP) compound(s); and from 20 to 40% of said lithium nickel, manganese and cobalt oxide (NMC) compound(s), such as LiNi0.6Mn0.2Co0.2O2 (NMC 622), LiNio.8Mno.iCoo.i02 (NMC 811), and / or said lithium nickel, cobalt and aluminium oxide (NCA) compound(s), the percentages being expressed by weight and relative to the total weight of electrochemically active materials; - 1 to 5% carbon black; - 1 to 5% of one or more water-soluble or water-dispersible binders chosen from carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR) and mixtures thereof; - 0 to 0.5% polyvinylpyrrolidone (PVP); the percentages being expressed by weight and related to the total weight of the composition.

8. Method for preparing an electrode according to any one of claims 1 to 7 comprising: - The preparation of an ink comprising the addition of the ingredients of the composition according to any one of claims 1 to 7 and the mixing of the dispersion obtained in a solvent; - the deposition of said ink on the coating of said metal strip; - drying; and - calendering; said preparation step being characterized by the use as a solvent of no substance identified as a substance of very high concern and appearing on the Candidate List provided for in Article 59 of Regulation (EC) No 1907 / 2006, nor of any substance subject to restriction and appearing on the list provided for in Annex XVII to Regulation (EC) No 1907 / 2006.

9. Method for preparing an electrode according to claim 8, characterized in that said step of preparing an ink is carried out aqueously and does not use the solvent N-methyl-2-pyrrolidone (NMP).

10. Electrochemical element comprising at least one positive electrode according to any one of claims 1 to 7.

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