Lithium phosphate-based positive electrode and components comprising same

Abstract

The present invention relates to a positive electrode comprising a metal strip covered on at least one of its faces with an active material composition comprising: a) as electrochemically active materials, at least one lithium manganese iron phosphate compound of formula LixMn1-y-zFeyMzPO4 with 0.8 ≤ x ≤ 1.2; 0.5 ≤ 1-y-z < 1; 0 < y ≤ 0.5; 0 ≤ z ≤ 0.2 and M is chosen from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb, S, W, K, Pb, V, Mo, W and mixtures thereof; and b) as binder, a mixture comprising: - at least a first binder chosen from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) and its copolymers, polyacrylonitrile (PAN), poly(methyl) or poly(butyl) methacrylate, polyvinyl chloride (PVC), poly(vinyl formal), polyesters, block polyetheramides, acrylic acid polymers, methacrylic acid, acrylamide, itaconic acid, sulfonic acid, elastomers, cellulose compounds and any mixture thereof, and - at least a second binder chosen from non-functionalized vinylidene fluoride (VDF) and hexafluoropropylene (HFP) copolymers.

Description

[0001] TITLE: POSITIVE ELECTRODE BASED ON LITHIUM PHOSPHATE AND LA ELEMENTS

[0002] INCLUDING

[0003] The present invention relates to the field of energy storage, in particular lithium batteries. More specifically, the present application relates to an electrode, in particular a positive electrode, comprising an active material of the lithium manganese and iron phosphate type.

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

[0005] Rechargeable electrochemical cells of the lithium-ion type are known from the state of the art. Due to their high mass and volume energy density, they constitute a promising source of electrical energy. They comprise at least one positive electrode and at least one negative electrode, and an electrolyte.

[0006] The electrodes 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.

[0007] 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.

[0008] Lithium phosphates of manganese and iron of formula Li x Mni.y.zFe yMzPO4 (LMFP) with 0.8 <x<1 ,2 ; 0<1-y-z<1 ; 0<y<1 ; 0< z< 0,6 sont connus pour leur utilisation comme matière active cathodique d’éléments lithium-ion. Ces phosphates lithiés 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.

[0009] The mixture of a lithium phosphate with a lithium nickel oxide has been proposed. 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. Thus, positive electrodes based on active material consisting of lithium manganese and iron phosphate (LMFP) compounds, alone or mixed with lithium nickel oxides of the NMC and / or NCA type, have been described.

[0010] Electrodes based on lithium manganese and iron phosphates are, however, difficult to handle due to their high rigidity after calendering. This rigidity is mainly due to the small size of the active material particles but also to the presence of a carbon layer on the surface of the active material particles. Thus, the integration of these electrodes into an electrochemical element sometimes proves difficult, if not impossible.

[0011] This handling problem is all the more important in the context of applications requiring high energy, such as for example for an electrical power storage system on board a vehicle such as an aircraft, in particular for 100% electric aviation, a rail transport vehicle, a road transport vehicle or a maritime or river transport vehicle.

[0012] Indeed, energy gain generally involves the use of increasingly thick electrodes. However, the thicker the electrode, the more difficult it is to integrate into an element.

[0013] There therefore remains to be provided electrodes, in particular positive electrodes, based on a positive active material of the lithium manganese and iron phosphate type, having improved handling, in particular greater flexibility and / or suppleness. In particular, there remains a need for electrodes, in particular positive electrodes, based on a positive active material of the lithium manganese and iron phosphate type having a high energy density, typically greater than or equal to 250 Wh / Kg, and easily integrated into an electrochemical element. More particularly, there remains a need for electrodes, in particular positive electrodes, based on a positive active material of the lithium manganese and iron phosphate type having both a high energy density, typically greater than or equal to 250 Wh / Kg, and a high power, typically greater than or equal to 1800 W / Kg, and easily integrated into an electrochemical element.

[0014] DE 10 2014 218 144 A1 teaches electrodes whose binder is composed of a mixture of polyvinylidene fluoride (PVDF) and a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP). It explains that the use of this binder makes it possible to increase the service life of the electrodes by improving their mechanical stability. The grafting rate of the copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) is not specified. WO 2022 / 234227 A1 teaches binder compositions in the form of a mixture of polytetrafluoroethylene (PTFE) and a vinylidene fluoride polymer (VDF), in order to improve the cohesion of the active composition.

[0015] US 2023 / 0084563 A1 teaches a solvent-free electrode comprising a binder consisting of a mixture of a vinylidene fluoride (VDF) and hexafluoropropylene (HFP) copolymer and a vinylidene fluoride (VDF) polymer, the two polymers having different crystallinity.

[0016] However, none of these documents specifically address electrodes based on a positive active material of the lithium manganese and iron phosphate type. In particular, none of these documents address the problems of handling and integration of this type of electrode.

[0017] An aim of the invention is then to propose a positive electrode based on a positive active material of the lithium manganese and iron phosphate type, having improved handling.

[0018] In particular, one aim of the invention is to propose positive electrodes based on a positive active material of the lithium manganese and iron phosphate type having a high energy density, typically greater than or equal to 250 Wh / Kg, and easily integrated into an electrochemical element.

[0019] More particularly, an aim of the invention is to propose positive electrodes based on a positive active material of the lithium manganese and iron phosphate type having both a high energy density, typically greater than or equal to 250 Wh / Kg, and a high power, typically greater than or equal to 1800 W / Kg, and easily integrated into an electrochemical element.

[0020] Summary of the invention

[0021] The invention firstly relates to a positive electrode comprising a metal strip covered on at least one of its faces with an active material composition comprising: a) as electrochemically active materials, at least one lithium phosphate compound of manganese and iron of formula Li x Mni.y.zFe yMzPO4 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, S, W, K, Pb, V, Mo, W et leurs mélanges ; et b) à titre de liant, un mélange comprenant :

[0022] - at least one first binder chosen from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) and its copolymers, polyacrylonitrile (PAN), poly(methyl)- or (butyl)methacrylate, polyvinyl chloride (PVC), poly(vinyl formal), polyesters, block polyetheramides, acrylic acid polymers, methacrylic acid, acrylamide, itaconic acid, sulfonic acid, elastomers, cellulose compounds and any of their mixtures, and

[0023] - at least one second binder chosen from non-functionalized vinylidene fluoride (VDF) and hexafluoropropylene (HFP) copolymers.

[0024] Preferably, the first binder is selected from vinylidene fluoride homopolymers, functionalized or non-functionalized, polytetrafluoroethylene (PTFE) and its copolymers, polyacrylonitrile (PAN), poly(methyl)- or (butyl)methacrylate, polyvinyl chloride (PVC), poly(vinyl formal), polyesters, block polyetheramides, acrylic acid polymers, methacrylic acid, acrylamide, itaconic acid, sulfonic acid, elastomers, cellulose compounds and any of their mixtures.

[0025] Preferably, the first binder is chosen from vinylidene fluoride homopolymers, functionalized or non-functionalized.

[0026] Preferably, the first binder has a mass average molecular weight greater than 650,000 g.mol-1.

[0027] Advantageously, the second binder is chosen from non-functionalized polyvinylidene fluoride (PVDF) and hexafluoropropylene (HFP) copolymers having a grafting rate greater than or equal to 5% by mass, relative to the total mass of the copolymer.

[0028] According to one embodiment, the positive electrode of the invention further comprises, as electrochemically active materials, one or more additional lithium compounds chosen from: i) lithium nickel, manganese and cobalt (NMC) oxide type compounds of formula Li w (Neither x Mn y Co z Mt)02 with 0.9 <w<1 ,1 ; 0<x ; 0<y ; 0<z ; 0<t ; et M 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 leurs mélanges, ii) les composés de type oxyde lithié de nickel, cobalt et aluminium (NCA) de formule Li w (NixCo y Al zMt)02 with 0.9 <w<1 ,1 ; 0<x ; 0<y ; 0<z ; 0<t ; et M 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, iii) les composés de formule Lii +x Mid- x O2- y F y of cubic structure where M represents at least one element selected from the group consisting of Na, K, Mg, Ca, B, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Y, Zr, Nb, Mo, Ru, Ag, Sn, Sb, Ta, W, Bi, La, Pr, Eu, Nd, Sm and mixtures thereof; where 0 < x < 0.5 and 0 < y < 1; iv) lithium nickel manganese oxide (NMX) compounds of formula Li a (Nii-xy-zMn x C0yMz)O2 with 0.9 <a<1 ,1 ; 0,60<1-x-y-z<0,80 ; 0<x ; 0<y<0,02 ; 0<z ; et M choisi dans le groupe consistant en Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ga, Ta, Nd, Pr, La et leurs mélanges ; et v) les composés de type oxyde lithié de nickel et de manganèse de formule Li w (NixMnyCoz Mt)02 with 1.1 <w<1 ,60 ; 0<x ; 0,50<y<0,80 ; 0<z<0,02 ; 0<t et M choisi dans le groupe consistant en 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 leurs mélanges ; vi) les mélanges de ceux-ci.

[0029] Preferably, i) lithium nickel, manganese and cobalt (NMC) oxide type compounds of formula Li w (NixMnyCo z Mt)02 with 0.9 <w<1 ,1 ; 0<x<1 ,1 ; 0<y<1 ,1 ; 0<z<1 ,1 ; 0<t<1,1 .

[0030] Preferably, ii) lithium nickel, cobalt and aluminum (NCA) oxide type compounds of formula Li w (Neither x COyAl z Mt)02 with 0.9 <w<1 ,1 ; 0<x<1 , 1 ; 0<y<1 ,1 ; 0<z<1 ,1 ; 0<t<1 ,1.

[0031] Preferably, iv) lithium nickel manganese oxide (NMX) compounds of formula Li a (Nii.xy-zMn x COyMz)02 with 0.9 <a<1 , 1 ; 0,60<1-x-y-z<0,80 ; 0<x<1 ,1 ; 0<y<0,02 ; 0<z<1 ,1 ;

[0032] Preferably, v) lithium oxide compounds of nickel and manganese of formula Li w (Neither x MnyCo z Mt)02 with 1.1 <w<1 ,60 ; 0<x<1 , 1 ; 0,50<y<0,80 ; 0<z<0,02, 0<t<1 ,1 . Avantageusement, la composition de matière active comprend en outre au moins un conducteur électronique, de préférence choisi parmi : le graphite, le noir de carbone, le noir d'acétylène, la suie, le graphène, les nanotubes de carbone, le silicium et l’un quelconque de leurs mélanges.

[0033] Preferably, the active material composition has, after calendering, a thickness of 50 pm to 500 pm, preferably 100 pm to 250 pm, more preferably 150 pm to 200 pm.

[0034] Advantageously, the active material composition has a grammage greater than 20 mg / cm 2 per electrode face, preferably greater than 22 mg / cm 2 per side, more preferably ranging from 20 to 30 mg / cm 2per side, even more preferably from 22 to 28 mg / cm 2 per side.

[0035] In particular, the active ingredient composition has a grammage greater than 20 mg / cm 2 per face of the electrode, preferably ranging from 20 to 30 mg / cm 2 per side, more preferably 22 to 28 mg / cm 2 per side.

[0036] Preferably, the second binder represents from 10% to 40% by mass, relative to the total mass of binder, preferably from 20% to 35% by mass, more preferably from 25% to 35% by mass. The invention also relates to an electrochemical element comprising a positive electrode according to the invention, a negative electrode, a separator and at least one electrolyte.

[0037] Preferably, the negative electrode comprises, as negative active material, graphite or a mixture of graphite and silicon, or lithium metal.

[0038] According to one embodiment, the electrochemical element is such that said separator, and optionally said negative electrode, comprise second binder diffused from the positive electrode.

[0039] Preferably, according to this embodiment, the positive electrode has a porosity of less than 50%, more preferably less than or equal to 45%, even more preferably ranging from 32% to 40%.

[0040] The invention also relates to a method for manufacturing an electrochemical element according to the invention, said method comprising the following successive steps: a) the superposition of a positive electrode according to the invention, a separator, and a negative electrode, and b) the impregnation of the superposition obtained in a) with an electrolyte.

[0041] According to one embodiment, the method comprises an additional step of thermal impregnation of said electrochemical element by heating the electrochemical element to a temperature greater than or equal to 40°C, for a duration greater than or equal to 3600 seconds.

[0042] The use, as binder, of a mixture comprising at least one first binder and at least one second binder chosen from non-functionalized vinylidene fluoride (VDF) and hexafluoropropylene (HFP) copolymers makes it possible to obtain an electrode having improved handling.

[0043] More specifically, the first binder guarantees the mechanical integrity of the electrode while the addition of the second binder improves its workability.

[0044] Once the electrode is integrated into an electrochemical element, a thermal impregnation step makes it possible to at least partially fluidize the second binder, thus causing at least partial migration of the second binder from the positive electrode into the separator, and possibly into the negative electrode. The migration of at least part of the second binder is accompanied by the creation in the positive electrode of a porosity resulting on the scale of the electrochemical element in a power gain.

[0045] Detailed description of the invention

[0046] The invention firstly relates to a positive electrode comprising a metal strip covered on at least its faces with a composition of active materials comprising: - at least one electrochemically active material, and

[0047] - at least one binder.

[0048] Electrodes typically consist of a metal current collector on which is coated a composition of active material(s) and additive(s) such as binder(s), dispersant(s), conductive element(s), etc.

[0049] The active material composition is coated on the current collector.

[0050] The current collector can therefore be covered on one or each of its faces by said composition of active materials.

[0051] 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.

[0052] POSITIVE ELECTRODE

[0053] The current collector (positive electrode)

[0054] The current collector of the electrode of the invention is generally in the form of a solid or perforated metal strip. The strip can be made from different materials. Examples include copper or copper alloys, aluminum or aluminum alloys, nickel or nickel alloys, steel, and stainless steel.

[0055] The current collector of the positive electrode of the invention is generally a strip of aluminum or an alloy comprising predominantly aluminum. The strip of the positive electrode typically has a thickness of 6 μm to 30 μm.

[0056] According to one embodiment, the aluminum collector of the positive electrode is covered with a conductive coating, such as carbon black, graphite and mixtures thereof.

[0057] Positive active ingredient

[0058] The positive electrode comprises, as positive active material, at least one lithium manganese and iron phosphate compound of formula Li x Mni. y.z Fe y MzPO4 with 0.8 <x<1 ,2 ; 0,5<1-y-z<1 ; 0<y<0,5 ; 0<z<0,2 ; et M choisi dans le groupe constitué de : B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb, S, W, K, Pb, V, Mo, W et leurs mélanges.

[0059] Preferably, said at least one lithium phosphate compound is chosen from lithium manganese and iron phosphate (LMFP) compounds 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, S, W, K, Pb, V, Mo, W and mixtures thereof,

[0060] 0.8< x <1.2;

[0061] 0.5<1-yz<1 ;

[0062] 0.05< y <0.5;

[0063] 0< z <0.2.

[0064] Advantageously, 0.6<1-yz<0.9.

[0065] Even more advantageously, 0.6<1-yz<0.85.

[0066] Examples of LMFP-type active ingredients include compounds of formula LiMno.sFeo^PC , LiMnojFeo.sPC , LiM^ / sFei / sPC and LiMno.sFeo.sPC .

[0067] Advantageously, the lithium manganese and iron phosphate (LMFP) compound(s) are coated with a layer of carbon and / or carbon nanotubes, in particular in order to increase their conductivity and / or their ionic diffusivity.

[0068] According to one embodiment, the entire positive active material consists of lithium manganese and iron phosphate (LMFP) type compounds.

[0069] According to an alternative embodiment, the positive electrode comprises, in addition to the lithium manganese and iron phosphate (LMFP) compound(s), at least one additional lithium compound chosen from the following groups: a) lithium nickel oxide compounds, b) compounds of formula Lii +x Mid- x O2- y F y of cubic structure where M represents at least one element selected from the group consisting of Na, K, Mg, Ca, B, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Y, Zr, Nb, Mo, Ru, Ag, Sn, Sb, Ta, W, Bi, La, Pr, Eu, Nd, Sm and mixtures thereof; where 0 < x < 0.5 and 0 < y < 1; c) mixtures of compounds a) and b).

[0070] 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.

[0071] Thus, they are preferably chosen from: i) lithium oxide type compounds of nickel, manganese and cobalt (NMC) of formula Li w (Neither x Mn y Co z Mt)02 with 0.9 <w<1 ,1 ; 0<x ; 0<y ; 0<z ; 0<t ; et M 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 leurs mélanges, ii) les composés de type oxyde lithié de nickel, cobalt et aluminium (NCA) de formule Li w (NixCo y Al z M t )02 with 0.9 <w<1 ,1 ; 0<x ; 0<y ; 0<z ; 0<t ; et M 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, iii) les composés de type oxyde lithié de nickel et de manganèse (NMX) de formule Li a (Nii . x -y-zMn xCOyMz)02 with 0.9 <a<1 ,1 ; 0,60<1-x-y-z<0,80 ; 0<x ; 0<y<0,02 ; 0<z ; et M choisi dans le groupe consistant en Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ga, Ta, Nd, Pr, La et leurs mélanges ; iv) les composés de type oxyde lithié de nickel et de manganèse de formule Li w (NixMnyCo z Mt)02 with 1.1 <w<1 ,60 ; 0<x ; 0,50<y<0,80 ; 0<z<0,02 ; 0<t et M choisi dans le groupe consistant en 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 leurs mélanges ; v) les mélanges de ceux-ci.

[0072] Preferably, i) lithium nickel, manganese and cobalt (NMC) oxide type compounds of formula Li w (NixMnyCo z Mt)02 with 0.9 <w<1 ,1 ; 0<x<1 ,1 ; 0<y<1 ,1 ; 0<z<1 ,1 ; 0<t<1,1 .

[0073] Preferably, ii) lithium nickel, cobalt and aluminum (NCA) oxide type compounds of formula Li w (Neither x COyAl zMt)02 with 0.9 <w<1 ,1 ; 0<x<1 , 1 ; 0<y<1 ,1 ; 0<z<1 ,1 ; 0<t<1 ,1.

[0074] Preferably, iii) lithium nickel manganese oxide (NMX) compounds of formula Li a (Nii.xy-zMn x COyMz)02 with 0.9 <a<1 , 1 ; 0,60<1-x-y-z<0,80 ; 0<x<1 ,1 ; 0<y<0,02 ; 0<z<1 ,1 ;

[0075] Preferably, iv) lithium oxide compounds of nickel and manganese of formula Li w (Neither x MnyCo z Mt)02 with 1.1 <w<1 ,60 ; 0<x<1 , 1 ; 0,50<y<0,80 ; 0<z<0,02, 0<t<1 ,1 .

[0076] Nickel-rich NMC compounds have the formula:

[0077] Li w (NixMnyCo z Mt)02

[0078] In which

[0079] 0.9 <w<1 ,1 ;

[0080] 0.60 <x ;

[0081] 0 <y ;

[0082] 0 <z ;

[0083] 0 <t ;

[0084] 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, La and mixtures thereof.

[0085] M may be selected in particular from the group consisting of Al, B, Mg and mixtures thereof. 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.

[0086] Preferably, nickel-rich NMC-type compounds have the formula: Li w (NixMn y C0zMt)O2

[0087] In which

[0088] 0.9 <w<1 ,1 ;

[0089] 0.60 <x<1 ,1 ;

[0090] 0 <y<1 ,1 ;

[0091] 0 <z<1 ,1 ;

[0092] 0 <t<1 ,1 ;

[0093] As a lithium oxide type compound of nickel, manganese and cobalt (NMC), rich in nickel, we can notably cite the following compounds:

[0094] LiNi0.6Mn0.2Co0.2O2 (NMC 622),

[0095] LiNi0.8Mn0.1Co0.1O2 (NMC 81 1).

[0096] Nickel-rich lithium nickel cobalt aluminum (NCA) oxide compounds have the formula:

[0097] Li w (NixCo y AlzMt)02 in which

[0098] 0.9 <w<1 ,1 ;

[0099] 0.8 <x ;

[0100] 0 <y ;

[0101] 0 <z ;

[0102] 0 <t ;

[0103] 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, La and mixtures thereof.

[0104] Nickel-rich lithium nickel cobalt aluminum (NCA) oxide compounds have the formula:

[0105] Li w (NixCOyAl z Mt)02 in which

[0106] 0.9 <w<1 ,1 ;

[0107] 0.8 <x<1 ,1 ;

[0108] 0 <y<1 ,1 ;

[0109] 0 <z<1 ,1 ;

[0110] 0 <t<1 ,1 ;

[0111] Preferably M may be chosen from the group consisting of B, Mg and mixtures thereof. Examples include: LiNiO, 8CoO, 15AlO, 05O2. Preferably, the lithium manganese and iron phosphate (LMFP) compound(s) represent(s) at least 30% by mass of the positive active material of the electrode, more preferably at least 50% by mass, even more preferably at least 70% by mass, advantageously at least 80% by mass, relative to the total mass of the positive active material.

[0112] More preferably, the positive active material comprises, preferably consists of:

[0113] - from 30% to 100% by mass of lithium manganese and iron phosphate (LMFP) compound(s), and

[0114] - from 0% to 70% by mass of additional active compound, preferably chosen from NMC compounds, NCA compounds, NMX compounds and their mixtures, more preferably chosen from NMC compounds.

[0115] Advantageously, the positive active material comprises, preferably consists of:

[0116] - from 70% to 100% by mass of lithium manganese and iron phosphate (LMFP) compound(s), and

[0117] - from 0% to 30% by mass of additional active compound, preferably chosen from NMC compounds, NCA compounds, NMX compounds and their mixtures, more preferably chosen from NMC compounds.

[0118] Positive electrode binder

[0119] The positive active material of the positive electrode is mixed with one or more binders, the function of which is to bind the particles of active material together as well as to bind them to the current collector on which it is deposited.

[0120] More particularly, the electrode of the invention comprises, as binder, a mixture comprising: at least one first binder, and at least one second binder.

[0121] The first binder is typically selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) and its copolymers, polyacrylonitrile (PAN), poly(methyl)- or (butyl)methacrylate, polyvinyl chloride (PVC), poly(vinyl formal), polyesters, block polyetheramides, acrylic acid polymers, methacrylic acid, acrylamide, itaconic acid, sulfonic acid, elastomers, cellulose compounds and any mixtures thereof.

[0122] Preferably, the first binder is selected from polyvinylidene fluoride (PVDF), also called vinylidene fluoride (VDF) homopolymers. The polyvinylidene fluoride (PVDF) may be functionalized or non-functionalized. Preferably, it is non-functionalized.

[0123] The second binder is typically selected from non-functionalized vinylidene fluoride (VDF) and hexafluoropropylene (HFP) copolymers.

[0124] Preferably, the copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) has a content of hexafluoropropylene monomer units ranging from 2% to 23% by mass, relative to the total mass of the copolymer, more preferably from 4% to 15% by mass.

[0125] According to one embodiment, the non-functionalized vinylidene fluoride (VDF) and hexafluoropropylene (HFP) copolymer(s) are chosen from graft copolymer(s).

[0126] Preferably, according to this embodiment, the non-functionalized vinylidene fluoride (VDF) and hexafluoropropylene (HFP) copolymer(s) are chosen from vinylidene fluoride (PVDF) polymers onto which polyhexafluoropropylene (HFP) chains are grafted.

[0127] More preferably, the copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) has a grafting rate greater than or equal to 5% by mass, even more preferably greater than or equal to 10% by mass, typically ranging from 10% to 20% by mass, relative to the total mass of the copolymer.

[0128] For the purposes of the invention, the term "grafting rate" means the mass percentage represented by the grafted functional groups in relation to the total mass of the copolymer. In particular, the grafting rate is calculated by taking the ratio between the mass of the grafted chains and the total mass of the grafted copolymer, expressed as a percentage.

[0129] Preferably, the first binder and the second binder are present in a mass ratio ranging from 5:1 to 1:5, more preferably from 1:5 to 1:1, even more preferably from 3:1 to 1:1.

[0130] Advantageously, the second binder represents from 10% to 40% by mass, relative to the total mass of binder, preferably from 20% to 35% by mass, more preferably from 25% to 35% by mass.

[0131] Optional additive(s)

[0132] The active ingredient composition may further comprise one or more ingredients selected from electronically conductive materials, dispersants, and / or pH buffers.

[0133] The electronically conductive material may generally be chosen from graphite, carbon black, acetylene black, soot, graphene, carbon nanotubes or a mixture thereof. The active material composition may also comprise one or more dispersants. Polyvinylpyrrolidone (PVP) may thus be mentioned as a dispersant suitable for the invention.

[0134] Manufacturing of the positive electrode

[0135] Generally, an electrode can be manufactured by preparing an ink comprising one or more active materials mixed with the binder, one or more electronically conductive materials, and a solvent, typically N-methyl-2-pyrrolidone (NMP).

[0136] Typically, the ink is in the form of a dispersion and typically comprises from 40 to 90%, preferably from 60 to 70% of said composition of active ingredients, the percentages being expressed by weight of dry matter and relative to the volume of said ink.

[0137] This ink can then be coated on at least one side of a current collector.

[0138] The ink may be dried in an oven, an oven, and / or by infrared to evaporate the solvent. In one embodiment, the drying comprises infrared drying.

[0139] 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.

[0140] The positive electrode (before thermal impregnation)

[0141] As explained in detail below, the implementation of a thermal impregnation step of an electrochemical element integrating a positive electrode according to the invention leads to modifications of the composition and certain physical properties of the electrode as such. The following characteristics relate to the positive electrode of the invention, before the implementation of a thermal impregnation step, typically before its integration into an electrochemical element.

[0142] ELECTROCHEMICAL ELEMENT

[0143] The invention also relates to an electrochemical element comprising:

[0144] - at least one positive electrode as defined above,

[0145] - at least one negative electrode,

[0146] - at least one separator, and

[0147] - at least one electrolyte.

[0148] Negative electrode

[0149] The negative electrode typically consists of a metal current collector coated with a composition of negative active material(s) and additive(s) such as binder(s), dispersant(s), conductive element(s), etc. The current collector of the negative electrode is generally in the form of a solid or perforated metal strip. The strip can be made from different materials. The current collector of the negative electrode is generally a copper strip or an alloy comprising mainly copper.

[0150] Negative active ingredient

[0151] In the context of the present invention, the negative electrode may be of any known type. The anode typically consists of a conductive support used as a current collector on which the anode active material and a carbon electronic material are deposited. A binder may also be incorporated into the mixture.

[0152] The anodic active material is not particularly limited. It can be selected from the following groups and their mixtures:

[0153] - Metallic lithium or a metallic lithium alloy

[0154] - Graphite

[0155] - Silicon

[0156] - a titanium and niobium oxide TNO having the formula:

[0157] LixTia-yMyNbb-zM zO((x+4a+5b) / 2)-c-dXc where:

[0158] 0 < x < 5; 0 < y < 1; 0 < z < 2; 1 < a < 5; 1 < b < 25; 0.25 < a / b < 2; 0 < c < 2 and 0 < d < 2; ay > 0; bz > 0;

[0159] M and M' each represent at least one element selected from the group consisting of Li, Na, K, Mg, Ca, B, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Y, Zr, Nb, Mo, Ru, Ag, Sn, Sb, Ta, W, Bi, La, Pr, Eu, Nd and Sm;

[0160] X represents at least one element selected from the group consisting of S, F, Cl and Br.

[0161] The d index represents an oxygen vacancy. The d index can be less than or equal to 0.5.

[0162] Said at least one titanium and niobium oxide may be chosen from TiNb2O?, Ti2Nb2O?, Ti2Nb2O9 and Ti2Nb O29.

[0163] - a lithiated titanium oxide or a titanium oxide capable of being lithiated. The lithiated titanium oxide is chosen from the following oxides: i) Lix-aMaTiy.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 ; 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 ;

[0164] M' represents at least one element selected from the group consisting of 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, Ti, Ce, Y and Eu;

[0165] X represents at least one element selected from the group consisting of S, F, Cl and Br; The subscript d represents an oxygen vacancy. The subscript d may be less than or equal to 0.5. ii) HxTiyCU in which 0 <x<1 ; 0<y<2, et iii) un mélange des composés i) à ii).

[0166] Examples of lithiated titanium oxides belonging to group i) are spinel Li4Ti50i2, Li2TiOs, ramsdellite Li2Ti3O7, LiTi2C>4, Li x Ti2C>4, with 0 <x<2 et Li2Na2Ti60i4.

[0167] A preferred LTO compound has the formula Li^aMaTis-bM'bCU, for example Li4Ti50i2 which is also written as Li^sTis / sC -

[0168] According to a preferred embodiment, the negative active material is graphite or a mixture of graphite and silicon.

[0169] Negative electrode binder

[0170] The negative active material of the electrochemical element is generally mixed with one or more binders, the function of which is to bind the particles of active material together as well as to bind them to the current collector on which they are deposited.

[0171] The binder of the negative electrode may be selected from carboxymethylcellulose (CMC), styrene butadiene copolymer (SBR), polytetrafluoroethylene (PTFE), polyamideimide (PAI), polyacrylic acid (PAA), polyimide (PI), styrene butradiene rubber (SBR), polyvinyl alcohol, polyvinylidene fluoride (PVDF) and a mixture thereof. These binders may typically be used in the cathode and / or in the anode.

[0172] Optional additive(s)

[0173] By analogy with the positive active material, the composition of negative active materials may further comprise one or more ingredients chosen from electronically conductive materials, dispersants, and / or pH buffers.

[0174] Electrode manufacturing

[0175] The negative electrode is typically prepared by a process similar to that described above in the context of the positive electrode.

[0176] Separator

[0177] 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.

[0178] Electrolyte The electrolyte in liquid form is obtained by dissolving one or more lithium salts in one or more organic solvents.

[0179] The solvent may be selected from saturated cyclic carbonates, unsaturated cyclic carbonates, non-cyclic carbonates, alkyl esters, ethers, nitrile type solvents and tetrahydrothiophene dioxide (sulfolane), ethylene sulfate (ESA).

[0180] Saturated cyclic carbonates include ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), butylene carbonate (BC), and mixtures thereof.

[0181] Unsaturated cyclic carbonates include vinylene carbonate (VC). Noncyclic carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dipropyl carbonate (DPC), and mixtures thereof.

[0182] Alkyl esters include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, butyl propionate, methyl butyrate, ethyl bu-tyrate, propyl butyrate, and mixtures thereof.

[0183] Ethers include dimethyl ether (DME), diethyl ether (DEE), and mixtures thereof.

[0184] The lithium salt may be selected from lithium perchlorate UCIO4, lithium hexafluorophosphate LiPFe, lithium tetrafluoroborate UBF4, lithium hexafluoroarsenate LiAsFe, lithium hexafluorantimonate LiSbFe, lithium trifluoromethanesulfonate ÜCF3SO3, lithium bis(fluorosulfonyl)imide Li(FSC>2)2N (LiFSI), lithium bis(trifluoromethanesulfonyl)imide LiN(CFsSO2)2 (LiT-FSI), lithium tris(fluoromethanesulfonyl)methylide LiC(CFsSO2)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.

[0185] The concentration of said at least one lithium salt may be in the range from 0.75 mol / L to 1.5 mol / L. It is preferably in the range from 1 mol / L to 1.5 mol / L. It is even better in the range from 1 to 1.2 mol / L.

[0186] According to one embodiment, the electrolyte (before impregnation) is free of binder, in particular free of copolymers of vinylidene fluoride (VDF) and hexafluoropropolylene (HFP).

[0187] According to one embodiment, the electrochemical element is of the lithium-ion type. METHOD FOR MANUFACTURING AN ELECTROCHEMICAL ELEMENT

[0188] The invention also relates to a method of manufacturing an electrochemical element as defined above. The lithium-ion element can be manufactured in a conventional manner.

[0189] The method according to the invention typically comprises the following successive steps: a) the superposition of a positive electrode, a separator, and a negative electrode as defined above, and b) the impregnation of the superposition obtained in a) with an electrolyte composition.

[0190] More particularly, 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, then inserted into a container. The invention is not limited to the manufacture of elements of cylindrical format. The format of the element can also be prismatic or pouch type. The electrodes can also be stacked to form a planar electrochemical bundle. A connection piece is fixed on an edge of the cathode not covered with active material. It is connected to a current output terminal.

[0191] 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.

[0192] According to one embodiment, the manufacturing method according to the invention further comprises an additional step of thermal impregnation of said electrochemical element. This additional step is typically carried out after step b) defined above, in particular after closing the element.

[0193] For the purposes of the invention, the term "thermal impregnation" means a step during which the electrochemical element undergoes a heat treatment, in particular by heating to one or more temperatures and for specific periods of time. The purpose of this impregnation step is to wet the electrode, in particular to impregnate the electrode with the electrolyte. Preferably, the thermal impregnation step is carried out by heating the electrochemical element to a temperature greater than or equal to 40°C and less than or equal to 80°C, for a period greater than or equal to 1 hour and less than or equal to 48 hours.

[0194] The implementation of a thermal impregnation step as described above leads to the migration of at least a portion of the second binder present in the positive electrode to the other constituents of the electrochemical element, in particular to the separator and possibly to the negative electrode. In particular, the heating of the electrochemical element has the effect of at least partially fluidizing the second binder present in the positive electrode, thus allowing its migration (at least partial) to the separator, and possibly to the negative electrode.

[0195] ELECTROCHEMICAL ELEMENT (AFTER THERMAL IMPREGNATION)

[0196] The invention therefore relates to an electrochemical element obtained by implementing a manufacturing method as described above, without implementing a thermal impregnation step as defined.

[0197] In this case, the electrochemical element includes:

[0198] - at least one positive electrode as defined above,

[0199] - at least one negative electrode,

[0200] - at least one separator, and

[0201] - at least one electrolyte.

[0202] The invention also relates to an electrochemical element according to the invention obtained by implementing a manufacturing method as described above comprising the implementation of a thermal impregnation step as described above.

[0203] In particular, the invention relates to an electrochemical element in which a part of the second binder initially present in the positive electrode has diffused into the other parts of the electrochemical element, in particular into the separator and possibly into the negative electrode.

[0204] More particularly, the invention relates to an electrochemical element comprising:

[0205] - at least one positive electrode as defined above,

[0206] - at least one negative electrode,

[0207] - at least one separator, and

[0208] - at least one electrolyte, in which the separator, and optionally the negative electrode, comprise a second binder having diffused from the positive electrode.

[0209] For the purposes of the invention, the term "binder having diffused from the positive electrode" means the binder initially present in the positive electrode and having migrated and / or diffused, in particular under the effect of heat, towards other parts of the electrochemical element, in particular towards the separator and possibly towards the negative electrode.

[0210] The implementation of an impregnation step typically leads to a reduction in the second binder content in the positive electrode.

[0211] This reduction in the concentration of second binder in the positive electrode is accompanied by the introduction into the separator, and possibly into the negative electrode, of a second binder, in particular non-functionalized vinylidene (VDF) and hexafluoropropylene (HFP) copolymer(s).

[0212] Advantageously, the content of second binder, in particular non-functionalized vinylidene (VDF) and hexafluoropropylene (HFP) copolymer(s), in the separator and / or in the negative electrode, after impregnation, is lower than the concentration of second binder, in particular non-functionalized vinylidene (VDF) and hexafluoropropylene (HFP) copolymer(s), in the positive electrode after impregnation.

[0213] Thus, the active material composition of the positive electrode typically has, after calendering, a thickness of 50 pm to 500 pm, preferably 100 pm to 250 pm, more preferably 150 pm to 200 pm.

[0214] The active material composition of the positive electrode typically has, before thermal impregnation, a grammage greater than 20 mg / cm 2 per electrode face, preferably greater than 22 mg / cm 2 per side, more preferably ranging from 20 to 30 mg / cm 2 per side, even more preferably from 22 to 28 mg / cm 2 per side.

[0215] Preferably, the positive electrode of the invention has a porosity of less than 50%, more preferably less than or equal to 45%, even more preferably ranging from 32% to 40%.

[0216] The thermal impregnation step can also have an effect on at least some of the following properties of the positive electrode: its thickness, its weight.

[0217] MEASUREMENT METHODS:

[0218] THICKNESS AND WEIGHT:

[0219] Thickness and weight are determined by measurement or weighing and calculation.

[0220] The grammage corresponds to the mass of dry material composition deposited per unit of surface and per face of the strip.

[0221] POROSITY: The porosity of the electrode is defined as the percentage of the pore volume to the geometric volume of the electrode. The pore volume includes the volume of the void present between the particles of the compounds in the layer deposited on the current collector and the volume of the pores inside the particles of the compounds in the layer deposited on the current collector. The pores inside the particles include the accessible pores and the inaccessible pores. The porosity of the electrode can be obtained by the following method: the theoretical density d is calculated from the density of each compound in the layer deposited on the current collector. The apparent bulk density d is calculated by knowing the mass and the volume of the layer deposited on the current collector. The relationship that connects the porosity with the actual density and with the apparent density is:

[0222] [MATH 1]

[0223] Porosity = 1" (apparent / real).

[0224] APPLICATIONS

[0225] The invention also relates to an electrochemical module comprising the stack of at least two electrochemical elements according to the invention, before or after thermal impregnation, each element being electrically connected with one or more other element(s), in particular via their current collectors.

[0226] The invention also relates to a battery comprising one or more modules according to the invention.

[0227] For the purposes of the invention, the term “battery” means the assembly of several modules.

[0228] Said assemblies can be in series and / or parallel.

[0229] The element according to the invention finds applications in the marine field, the field of portable devices, electric and hybrid vehicles, the space field, the aeronautical field, telecommunications and emergency lighting equipment.

[0230] The battery according to the invention is in particular intended to be used within an electrical power storage system on board a vehicle such as an aircraft, a rail transport vehicle, a road transport vehicle or a maritime or river transport vehicle.

[0231] Alternatively, the element may be intended for the static storage of electrical energy, for example in the form of at least one electrical storage bay in which several battery modules are stacked.

[0232] The invention may also relate to an aircraft, in particular a fully electric aircraft, for example vertical take-off and landing (VTOL), conventional take-off and landing (CTOL), and short take-off and landing (STOL), comprising a battery according to the invention.

[0233] FIGURES

[0234] [Fig. 1] Figure 1 is a schematic representation of an electrochemical element according to the invention before (part A) and after (part B) thermal impregnation.

[0235] [Fig. 2] Figure 2 shows the cold load profile of the E elements a summer b .

[0236] [Fig. 3] Figure 3 shows the discharge profile at C of the E elements a summer b .

[0237] [Fig. 4] Figure 4 shows the pulse charge / discharge profile followed by continuous discharge (charge at C / 10 at room temperature, 3 pulses at 2C at room temperature and continuous discharge at C / 5 at -20°C) of E cells a summer b .

[0238] Figure 1 represents an electrochemical element 10 according to the invention. The electrochemical element 10 comprises a positive electrode 12 and a negative electrode 16, each represented by oblique hatching separated by a separator 15, the whole immersed in an electrolyte 14. The positive electrode 12 according to the invention consists of a metal strip (not shown) covered on one of its faces with an active material composition (not shown) comprising at least one lithium phosphate compound of manganese and iron and, as binder, a mixture of a first binder and a second binder as defined above.

[0239] Before thermal impregnation (configuration A), the entirety of the second binder is located in the positive electrode 12. In particular, the negative electrode 16 and the electrolyte 14 are, in this configuration A, free of second binder.

[0240] During the thermal impregnation step, a portion of the second binder migrates from the positive electrode 12 into the electrolyte and possibly into the negative electrode 16.

[0241] Thus, after thermal impregnation (configuration B), the amount of second binder present in the positive electrode has significantly reduced. In addition, a significant amount of second binder (corresponding to the amount of second binder missing in the positive electrode 12) is present in the electrolyte 14, and possibly in the negative electrode 16.

[0242] The invention is illustrated by the following examples given without limitation.

[0243] Examples Different electrochemical elements were manufactured. They differ in the composition of their cathode, more particularly in the presence or absence of a second binder according to the invention. In the data below, and unless explicitly indicated otherwise, the contents are expressed by mass.

[0244] 1. Preparation of electrochemical elements

[0245] Electrochemical elements E a summer b in button format have been manufactured. They all comprise a negative electrode whose active material is lithium metal and a positive electrode whose active material layer composition is specified in Table 1 below. The electrolyte comprises a mixture of cyclic carbonates and linear carbonates to which LiPFe has been added at a concentration of 1 mol.L -1 The separator inserted between the positive electrode and the negative electrode is of the polyolefin type.

[0246] In both cases, the active material of the positive electrode is composed of a mixture of an LMFP compound and LiNi8 / ioMni / ioCoi / io02 (NMC).

[0247] The first binder is high molecular weight, unfunctionalized polyvinylidene fluoride (PVDF), typically greater than 650,000 g. mol -1 .

[0248] The second binder is a vinylidene fluoride (VDF) copolymer onto which polyhexafluoropropylene (HFP) chains are grafted. The grafting rate is greater than or equal to 5% by mass, relative to the total mass of the copolymer.

[0249] [Table 1]

[0250] The electrochemical element E a is comparative in that it does not comprise a second binder. The electrochemical element Eb is according to the invention.

[0251] The adhesion and resistivity measurements carried out below were performed before thermal impregnation of the positive electrodes. The swelling measurements and electrochemical tests carried out below were carried out after thermal impregnation of the positive electrodes, in particular after heating the electrochemical elements E a summer b

[0252] 2. Evaluation of electrochemical elements a) Measurement protocols

[0253] The performance of electrochemical elements E a summer b were evaluated according to the following protocols:

[0254] Adhesion: A tensile bench was used to perform the so-called tear-off method. This method consists of using double-sided adhesive tape to stick the sample to the fixed support of the tensile bench. The second mobile support also has adhesive tape, which will apply a certain pressure to the sample so that all the samples are stuck in the same way; the goal being to have reproducibility between the samples. After this step, the device will perform a tensile test and measure the maximum force to have a rupture of the composite. The measurement of the adhesion force is measured in newtons (N).

[0255] Transverse resistivity (R trans): a square of electrode is cut and positioned between two copper supports. The lower copper support is placed on a fixed pad while a piston exerts a force on the upper copper support. An ohmmeter connected to the two copper supports is used to measure the resistance of the electrode. During the experiment, the force exerted by the piston varies from 0 to 15-20 bars, the pressure exerted within a functioning accumulator. The resistance as a function of the pressure exerted is recorded. The resistivity is then calculated using the following formula:

[0256] [MATH 2] with :

[0257] - p: transversal resistivity (Q.cm 2 / pm);

[0258] - R: measured resistance (Q);

[0259] - S: surface on which the resistance is measured (surface of the copper supports);

[0260] - e: thickness of active material of the electrode (pm).

[0261] Weight:

[0262] The weight (G, mg / cm 2 ) corresponds to the mass of dry matter composition (m, mg) deposited per unit area (S, cm 2 ) and per side of the strip, calculated according to the following formula:

[0263] [MATH 3]

[0264] Swelling :

[0265] The procedure for determining the swelling rate is as follows: a sample of each electrode with a thickness Ei (pm) is introduced into an excess electrolyte for at least 7 days at a temperature of 60°C in order to reach their swelling equilibrium. The swollen samples are cleaned and then dried at the same temperature for at least 1 day. Their thickness E f (pm) is measured again.

[0266] The swelling (Q, pm) is then estimated using the following formula:

[0267] Q = E f - E i

[0268] Cold test: charge at C / 10 up to 4.3V with floating C / 100 at room temperature then put at -20°C of the button, discharge at 2C for 30s three times in a row then discharge C / 5 up to 2.5V no floating at the end of discharge

[0269] Discharge at C: a charge is carried out at C / 10 up to 4.3V with “floating” C / 100 at room temperature then discharge at C up to 2.5V no “floating” at the end of discharge b) Results

[0270] Part of the results is given in Table 2 below.

[0271] [T able 2]

[0272] It is observed that the element Eb according to the invention has improved adhesion compared to the element E a Comparison: the electrode according to the invention is less fragile and easier to implement, particularly to integrate into an element. This property is very important for applications that require high thicknesses.

[0273] Furthermore, the element Eb according to the invention has a significantly reduced transverse resistivity compared to the element E a comparative, which results in greater power.

[0274] The weight of the elements is equivalent.

[0275] Finally, the swelling associated with element Eb according to the invention is significantly reduced compared to that associated with element E a comparative. This reduction in swelling results in a gain in power for the element according to the invention and therefore in improved performance.

[0276] The electrochemical performances of the elements were then evaluated by subjecting them to different charge and discharge cycles. The results obtained are reported in Figures 2 to 4. In all the figures, the continuous line curve A relates to element E acomparative while curve B in broken line relates to element Eb according to the invention.

[0277] In Figure 2, it can be seen, for equal capacity, that the voltage difference between the charge line and the discharge line is lower in the case of the electrochemical element Eb according to the invention, compared to the electrochemical element E a . There is therefore less polarization in the context of the electrochemical element Eb according to the invention, compared to the electrochemical element E a .

[0278] In Figure 3, we observe that the discharge capacity of the electrochemical element Eb is significantly increased, compared to that of the electrochemical element Ea: at low speed the two electrodes show similar properties while by increasing the speed, Eb shows an increased discharge capacity.

[0279] In Figure 4, it is observed that the electrochemical element Eb according to the invention is capable of delivering high power with a high energy density, even at low temperature. In particular, it is observed that at equivalent voltage the element Eb is capable of providing a higher discharge energy density compared to the element E a according to the invention.

Claims

CLAIMS 1. Positive electrode comprising a metal foil covered on at least one of its faces with an active material composition comprising: a) as electrochemically active materials, at least one lithium phosphate compound of manganese and iron of formula Li x Mni. y.z Fe y MzPO4 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, S, W, K, Pb, V, Mo, W et leurs mélanges ; et b) à titre de liant, un mélange comprenant : - at least one first binder chosen from vinylidene fluoride homopolymers, functionalized or non-functionalized, polytetrafluoroethylene (PTFE) and its copolymers, polyacrylonitrile (PAN), poly(methyl)- or (butyl)methacrylate, polyvinyl chloride (PVC), poly(vinyl formal), polyesters, block polyetheramides, acrylic acid polymers, methacrylic acid, acrylamide, itaconic acid, sulfonic acid, elastomers, cellulose compounds and any of their mixtures, and - at least one second binder chosen from non-functionalized vinylidene fluoride (VDF) and hexafluoropropylene (HFP) copolymers.

2. Positive electrode according to claim 1, in which the first binder is chosen from vinylidene fluoride homopolymers, functionalized or non-functionalized.

3. A positive electrode according to claim 1 or claim 2, wherein the first binder has a mass average molecular weight greater than 650,000 g. mol -1 .

4. Electrode according to any one of claims 1 to 3, in which the second binder is chosen from non-functionalized polyvinylidene fluoride (PVDF) and hexafluoropropylene (HFP) copolymers having a grafting rate greater than or equal to 5% by mass, relative to the total mass of the copolymer.

5. Positive electrode according to any one of the preceding claims, further comprising, as electrochemically active materials, one or more additional lithium compounds chosen from: i) lithium nickel, manganese and cobalt (NMC) oxide type compounds of formula Li w (Neither x Mn y Co z M t )02 with 0.9 <w<1 ,1 ; 0<x ; 0<y ; 0<z ; 0<t ; et M choisi dans le 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, ii) lithium nickel, cobalt and aluminium (NCA) oxide type compounds of formula Li w (NixCo y Al z Mt)02 with 0.9 <w<1 ,1 ; 0<x ; 0<y ; 0<z ; 0<t ; et M 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, iii) les composés de type oxyde lithié de nickel et de manganèse (NMX) de formule Li a (Nii-xy-zMn x C0yMz)O2 with 0.9 <a<1 ,1 ; 0,60<1-x-y-z<0,80 ; 0<x ; 0<y<0,02 ; 0<z ; et M choisi dans le groupe consistant en Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ga, Ta, Nd, Pr, La et leurs mélanges ; et iv) les composés de type oxyde lithié de nickel et de manganèse de formule Li w (NixMnyCo zMt)02 with 1.1 <w<1 ,60 ; 0<x ; 0,50<y<0,80 ; 0<z<0,02 ; 0<t et M choisi dans le groupe consistant en 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 leurs mélanges ; v) les mélanges de ceux-ci.

6. Positive electrode according to any one of the preceding claims, in which the active material composition further comprises at least one electronic conductor, preferably chosen from: graphite, carbon black, acetylene black, soot, graphene, carbon nanotubes, silicon and any of their mixtures.

7. Positive electrode according to any one of the preceding claims, wherein said active material composition has, after calendering, a thickness of 50 pm to 500 pm, preferably of 100 pm to 250 pm, more preferably of 150 pm to 200 pm.

8. Positive electrode according to any one of the preceding claims, in which said active material composition has a grammage greater than 20 mg / cm 2 per face of the electrode, preferably ranging from 20 to 30 mg / cm 2 per side, more preferably 22 to 28 mg / cm 2 per side.

9. Positive electrode according to any one of the preceding claims, in which the second binder represents from 10% to 40% by mass, relative to the total mass of binder, preferably from 20% to 35% by mass, more preferably from 25% to 35% by mass.

10. Electrochemical element comprising a positive electrode according to any of claims 1 to 9, a negative electrode, a separator and at least one electrolyte.

11. An electrochemical element according to claim 10, wherein said separator, and optionally said negative electrode, comprise second binder diffused from the positive electrode.

12. Electrochemical element according to claim 10 or 11, in which the negative electrode comprises, as negative active material, graphite or a mixture of graphite and silicon, or lithium metal.

13. Electrochemical element according to any one of claims 1 1 and 12, in which the positive electrode has a porosity of less than 50%, more preferably less than or equal to 45%, even more preferably ranging from 32% to 40%.

14. Method for manufacturing an electrochemical element according to any one of claims 10 to 13, said method comprising the following successive steps: a) the superposition of a positive electrode according to any one of claims 1 to 8, of a separator, and of a negative electrode, and b) the impregnation of the superposition obtained in a) with an electrolyte.

15. Method according to claim 14, further comprising an additional step of thermal impregnation of said electrochemical element by heating the electrochemical element to a temperature greater than or equal to 40°C, for a duration greater than or equal to 3600 seconds.

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