Electrochemical element Li-ion exhibiting high power stability and energy density

Abstract

Li-ion electrochemical element exhibiting high power stability and energy density. The present invention relates to an electrochemical element comprising: - a negative electrode comprising at least particles including silicon; and - a positive electrode comprising, as active material: i) at least one compound LixMn1-y-zFeyMzPO4(I), in which M is selected from (B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb, S, K, Pb, V, Mo, W, Hf, Bi, Se and mixtures thereof); with 0.8 ≤ x ≤ 1.2; 0.5 ≤ 1 - yz < 1; 0

Description

Title of the invention: Electrochemical element Li-ion exhibiting high power stability and energy density

[0001] The present invention relates to the field of energy storage, and in particular to lithium batteries. More specifically, the present application relates to an electrochemical element comprising a specific combination of negative and positive active materials in specific proportions, making it possible to obtain improved electrochemical performance while maintaining a high level of safety.

[0002] The invention is particularly useful in the field of rechargeable lithium-ion (Li-ion) type electrochemical elements.

[0003] The operation of lithium-ion batteries is based on reversible exchange of lithium ion between a positive electrode and a negative electrode, separated by an electrolyte, the lithium being stored at the negative electrode during charging operation.

[0004] Rechargeable lithium-ion batteries offer excellent energy and volume densities compared to other electrochemical energy storage technologies and now occupy a dominant position, particularly in the electric propulsion market, which includes but is not limited to electric and hybrid vehicles as well as electric aeronautics.

[0005] Electrochemical elements comprising positive electrodes based on lithium manganese and iron phosphates of formula LixMniyzFe yMzP04 (LMFP) are known in particular, with 0.8 < x < 1.2; 1-yz > 0.5; 0.05 < y < 0.5 and 0 < z < 0.2. These phosphates contain manganese, iron and one or more substituent elements symbolized by the symbol M. These compounds are known to offer high safety in use due to the fact that the lithium transition metal phosphates are stable at high temperature.

[0006] The main limitation of using the lithium phosphate compound of manganese and iron is its very low lithium diffusion coefficient, which greatly limits its chargeability and dischargeability performance. Two approaches are then used to overcome this limitation:

[0007] - Using nanometric materials to minimize distances from diffusion of lithium within materials. This then poses significant problems in terms of electrode manufacturing processes, but also in terms of lifespan and safety given the significant increase in the electrode / electrolyte contact surface and therefore the reactivity of the material;

[0008] - Increase the amount of iron in the LMFP material in order to significantly increase The diffusion coefficient of lithium in the material. This second option, however, presents the problem of limiting the energy of the electrochemical elements containing LMFP material. Adding particles containing silicon to the negative electrode compensates for this limitation.

[0009] One of the objectives of the invention is therefore to propose an electrochemical element having a positive electrode based on lithium phosphate compounds of manganese and iron exhibiting improved performance, in particular in terms of power, stability of internal resistance, safety, and whose energy density is high.

[0010] To this end, the invention relates in particular to an electrochemical element comprising:

[0011] - a negative electrode comprising a negative active layer comprising, as of active material, at least particles comprising silicon; and

[0012] - a positive electrode comprising a positive active layer comprising, as a active ingredient:

[0013] i) at least one lithium phosphate compound of manganese and iron of formula (I): Lix Mni y zFeyMzPO4 (I), wherein:

[0014] M is chosen from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb, S, K, Pb, V, Mo, W, Hf, Bi, Se and any of their mixtures,

[0015] 0.8 < x < 1.2;

[0016] 0.5 < 1-yz < 1;

[0017] 0 < y < 0.5;

[0018] 0 < z < 0.2;

[0019] ii) at least one lamellar oxide-type compound of formula (II) Liw(NixMnyCozM't )O2 (II) wherein:

[0020] M' is chosen from the group consisting of Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La and any mixture thereof;

[0021] 0.9 <w <1,1;

[0022] 0 < x ;

[0023] 0 < y ;

[0024] 0 < z ;

[0025] 0 < t;

[0026] in which:

[0027] a) The ratio (%Si / A) between the mass content of silicon (%Si) in the active material of the negative active layer and the product (A) is such that: 0.7 < (%Si / A) < 4.0, where A is the product of the mass content of compound of formula (I) (%(I)) in the active material of the positive active layer expressed as a percentage of the total mass in compound of formula (I) and in compound of formula (II), and the molar content of iron (%Fe) in compound of formula (I) expressed as a percentage of the total molar content of iron and manganese in compound (I), and (%Si) being the mass content of silicon in the active material of the negative active layer, expressed as a percentage of the total mass of the active material of the negative active layer; and

[0028] b) the ratio (N / P) between the first charge capacitance of the negative electrode (N) and the first charge capacitance of the positive electrode (P) is such that: 1.1 < (N / P) < 1.7.

[0029] Indeed, the inventors observed that the presence of particles comprising silicon at the negative electrode and at least one lithium phosphate compound of manganese and iron at the positive electrode could surprisingly lead to a rapid increase in the internal resistance of the cycling element.

[0030] The inventors have discovered that all or part of the technical problem described above can be solved by adapting the compositions of the negative and positive active layers such that a combination of related characteristics: - At the ratio (%Si / A) - At the ratio (N / P), and preferably also: - To the product (A) between the mass content of compound of formula (I) (%(I)) in the active material of the positive active layer and the iron content (%Fe) in the compound of formula (I), - The silicon mass content (%Si) in the active material of the negative active layer,

[0031] responds to specific values.

[0032] Preferably, in the electrochemical element of the invention:

[0033] a) 0.7 < (%Si / A) < 3.0, preferably 0.7 < (%Si / A) < 2.5, preferably 0.7 < (%If / A) < 2.0; and / or

[0034] b) 1.1 < (N / P) < 1.6, preferably 1.1 < (N / P) < 1.5.

[0035] Preferably, the electrochemical element is also characterized by (c) the product (A) between the mass content of compound of formula (I) (%(1)) in the active material of the positive active layer expressed as a percentage of the total mass of compound of formula (I) and compound of formula (II), and the molar content of iron (%Fe) in compound of formula (I) expressed as a percentage of the total molar content of iron and manganese in compound (I). The product (A) is therefore calculated according to the following relationship:

[0036] A = %(1) x %Fe

[0037] The product (A) is such that: 0.1 < (A) < 0.5, preferably 0.1 < (A) < 0.4, preferably 0.1 < (A) < 0.3, preferably 0.15 < (A) < 0.25.

[0038] Preferably, the electrochemical element is also characterized by d) the silicon mass content (%Si) in the active material of the negative active layer, expressed as a percentage of the total mass of the active material of the active layer negative (%Si) is such that: 0.05 < (%Si) < 0.6, preferably 0.07 < (%Si) < 0.6, preferably 0.1 < (%Si) < 0.5, preferably 0.1 < (%Si) < 0.4, preferably 0.1 < (%Si) < 0.3. Negative electrode

[0039] The negative electrode generally comprises a current collector covered by a negative active layer.

[0040] The term "current collector" means an element such as a pad, plate, sheet, or other, with a 2D or 3D structure, made of a conductive material, and ensuring the conduction of the flow of electrons between the electrodes and the terminals of the battery. The current collector is generally in the form of a solid or perforated metal strip. The strip can be made from various materials. Examples include copper or copper alloys, aluminum or aluminum alloys, nickel or nickel alloys, steel, and stainless steel. The current collector may also consist of a layer of plastic material covered with a metallic layer as defined in the preceding sentence.

[0041] The current collector of the negative electrode is generally a copper strip or an alloy consisting mainly of copper. The negative electrode strip typically has a thickness of 4 µm to 30 µm.

[0042] According to one embodiment, the copper or copper-coated polymer collector of the negative electrode can be coated with a conductive coating, such as carbon black, graphite, carbon nanotubes, and mixtures thereof. Thus, the strips can optionally be coated on one or two of their faces with a layer of carbon not exceeding a few micrometers in thickness.

[0043] The term "active negative layer" refers to all the materials that coat the current collector of the negative electrode on at least one of its faces. Generally, this layer includes, in addition to electrochemically active materials (active materials), electronically conductive materials, binders, and any additives.

[0044] The expression "electrochemically active material" or "active material" refers to materials which are the site of the electrochemical reaction.

[0045] The negative electrode of the electrochemical element according to the invention comprises a negative active layer comprising particles comprising silicon.

[0046] Preferably, the particles comprising silicon are chosen from silicon-carbon composite particles and silicon oxide particles SiOx where 0 < x < 2.

[0047] Preferably, the particles comprising silicon are silicon-carbon composite (Si-C) particles.

[0048] The silicon-carbon composite particles preferably have a Si content of between 30% and 70% by mass, preferably between 40% and 65% by mass, preferably between 40% and 60% by mass, relative to the mass of the silicon-carbon composite particles.

[0049] Preferably, the content of silicon-carbon composite particles in the active material of the negative active layer is between 10% and 98% by mass expressed in relation to the mass of the active material of the negative active layer, preferably between 10% and 80%, preferably between 20% and 60%, preferably between 30% and 50%, preferably between 40% and 50%.

[0050] Preferably, the negative active layer of the negative electrode has a porosity ranging from 30% to 60%, preferably ranging from 30% to 50%, preferably ranging from 35% to 45%.

[0051] The porosity of the negative active layer is defined as the percentage of the pore volume relative to the geometric volume of the electrode, excluding the current collector. The pore volume includes the volume of the void space between the compound particles in the negative active layer deposited on the current collector and the volume of the pores within the compound particles in the negative active layer deposited on the current collector. The pores within the particles include both accessible and inaccessible pores. The porosity of the negative active layer can be obtained by the following method:

[0052] The theoretical density dreue is calculated from the density of each compound in the negative active layer deposited on the current collector. The apparent density dapsente is calculated by knowing the mass and volume of the negative active layer deposited on the current collector. The relationship that links the porosity with the actual density and with the apparent density is:

[0053] Porosity = l-(apparentd / actuald).

[0054] Such porosity makes it possible to improve both the lifespan of the electrochemical element and its power.

[0055] According to one embodiment, the active material of the negative active layer may also include graphite particles. Preferably, according to this embodiment, the content of silicon-carbon composite particles is between 10% and 100% by mass expressed relative to the total mass of silicon-carbon composite particles and graphite particles, preferably between 10% and 80%, preferably between 20% and 60%, preferably between 30% and 50%.

[0056] According to one embodiment, the active material of the negative active layer consists of graphite particles and Si-C composite particles.

[0057] Typically, the active material of the negative active layer comprises:

[0058] - from 20% to 90%, preferably from 20% to 80%, particularly from 40% to 60% of silicon-carbon composite particles; and

[0059] - from 10% to 80%, preferably from 20% to 80%, particularly from 40% to 60% of graphite;

[0060] the percentages being understood in terms of mass, expressed in relation to the total mass of the active material of the negative active layer, or in relation to the total mass of silicon-carbon composite particles and graphite particles.

[0061] The term “binder” means a compound that strengthens the cohesion between the particles of active materials and improves the viscosity and / or adhesion of the negative active layer with the current collector.

[0062] The binder can be selected from butadiene-styrene copolymer (SBR), polyethylene oxide (PEO), polyamideimide (PAI), polyimide (PI), polyvinyl alcohol, functionalized or non-functionalized polyvinylidene fluoride (PVDF), vinylidene fluoride copolymers such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene (PTFE) and its copolymers, polyacrylonitrile (PAN), poly(methyl)- or (butyl) methacrylate, polyvinyl chloride (PVC), poly(vinyl formaldehyde), polyesters, sequenced polyetheramides, acrylic acid polymers, methacrylic acid, acrylamide, itaconic acid, sulfonic acid, elastomers such as poly(styrene / butadiene) (SBR) and hydrogenated butadiene-acetonitrile copolymers (HNBR), cellulosic compounds such as carboxymethylcellulose (CMC) and any of their mixtures.

[0063] Preferably, the binder can be chosen from carboxymethylcellulose (CMC), styrene-butadiene (SBR), lithium polyacrylic acid (LiPAA) and non-lithiumized polyacrylic acid (PAA, PAAH or PAAN).

[0064] These binders can typically be used for the positive electrode and / or the negative electrode.

[0065] The term “conductive material” typically refers to an electronic conductor, such as a carbonaceous material, for example graphite, carbon black, acetylene black, soot, graphene, carbon nanotubes (CNTs), or a mixture thereof. In one embodiment, the conductive material is selected from carbon black and carbon nanotubes.

[0066] These electronically conductive materials can typically be used for the positive electrode and / or the negative electrode.

[0067] Possible additives may include dispersants and / or pH buffers. Polyvinylpyrrolidone (PVP) is one example of a dispersant.

[0068] These additives can typically be used for the positive electrode and / or the negative electrode.

[0069] The negative electrode is typically obtained by applying a composition comprising the compounds of the negative active layer to the current collector. This application can be carried out by any technique known to those skilled in the art. Positive electrode

[0070] The positive electrode generally comprises a current collector covered by a positive active layer.

[0071] The current collector of the positive electrode is generally in the form of a solid or perforated metal strip. The strip can be made from various materials. Examples include copper or copper alloys, aluminum or aluminum alloys, nickel or nickel alloys, steel, and stainless steel. The current collector can also consist of a layer of plastic material covered with a metallic layer as defined in the preceding sentence.

[0072] The current collector of the positive electrode is generally an aluminum strip or an alloy consisting mainly of aluminum. The positive electrode strip typically has a thickness of 6 µm to 30 µm.

[0073] According to one embodiment, the aluminum collector of the positive electrode can be coated with a conductive coating, such as carbon black, graphite, carbon nanotubes, and mixtures thereof. Thus, the strips can optionally be coated on one or two of their faces with a layer of carbon not exceeding a few micrometers in thickness.

[0074] The thickness of the positive electrode strip may be different from that of the negative electrode strip.

[0075] The term "active positive layer" refers to all the materials that coat the current collector of the positive electrode on at least one of its faces. Generally, this layer includes, in addition to electrochemically active materials, electronically conductive materials, binders, and any additives.

[0076] As an active material, the positive electrode comprises at least one compound of formula (I) and at least one compound of formula (II).

[0077] The positive electrode comprises at least one lithium phosphate compound of manganese and iron of formula (I): LixMni y zFeyMzPO4 (I), wherein:

[0078] 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, Hf, Bi, Se and any mixture thereof,

[0079] 0.8 < x < 1.2;

[0080] 0.5 < 1-yz < 1;

[0081] 0 <y<0,5;

[0082] 0 < z < 0.2.

[0083] Preferably, in the compound of formula (I):

[0084] - 0.05 < y < 0.5, and / or

[0085] - 0.5 < 1-yz < 0.95, and / or

[0086] -x=l, and / or

[0087] - z = 0.

[0088] Preferably, the compound of formula (I) is such that the molar content of iron (%Fe) in the compound of formula (I), expressed as a percentage of the total molar content of iron and manganese in the compound (I), is 0.2 to 0.5.

[0089] Typically, the compound of formula (I) can be chosen from LiMnoj8Feoj2P04, LiMnojFeo sPCU LiMno^Feo^PCU and LiMno.5Fco.5PO4.

[0090] Advantageously, the lithium manganese iron phosphate (LMFP) type compound(s) of formula (I) are coated with a layer of carbon and / or carbon nanotubes, in particular to increase their electronic conductivity.

[0091] The positive electrode further comprises at least one lamellar oxide-type compound corresponding to formula (II): Liw(NixMnyCozM't)O2 (II) in which:

[0092] M' is chosen from the group consisting of Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La and any mixture thereof;

[0093] 0.9 <w <1,1;

[0094] 0 < x ;

[0095] 0 < y ;

[0096] 0 < z ;

[0097] 0 < t.

[0098] Preferably, the compound of formula (II) is such that:

[0099] 0.5 < x < 1.1; and / or

[0100] 0 < y < 1.1 ; and / or

[0101] 0 < z < 1.1 ; and / or

[0102] 0 <t<l,l.

[0103] Preferably, in the compound of formula (II), 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. M can in particular be chosen from the group consisting of Al, B, Mg and their mixtures. Preferably, M is Al. Preferably, t < 0.05.

[0104] Preferably, the compound of formula (II) is chosen from:

[0105] i) a lithium nickel manganese cobalt oxide (NMC) of formula (lia) Liw (NixMnyCozMt)O2 where 0.9 < w < 1.1; 0 < x < 1.1; 0 < y < 1.1; 0 < z < 1.1; 0 < t < 1.1; M being at least one element chosen 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 more particularly 0.5 < x;

[0106] ii) a lithium nickel, cobalt, and aluminium (NCA) oxide of formula (Ilb) Liw(Ni xCoyAlzMt)O2 where 0.9 < w < 1.1; 0 < x < 1.1; 0 < y < 1.1; 0 < z < 1.1; 0 < t < 1.1; 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; more particularly 0.80 < x; and

[0107] iii) a lithium oxide of nickel, manganese, cobalt and aluminium (NMCA) of formula (Ile) Liw(NixCoyAlzMntMs)O2 where 0.9 < w < 1.1 ; 0 < x < 1.1 ; 0 < y < 1.1 ;0 < z < 1.1; 0 < t < 1.1, 0 < s < 1.1, M being at least one element chosen 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, more particularly 0.83 < x.

[0108] iv) nickel and manganese lithium oxide (NMX) type compounds of formula

[0109] Lia(Nii_x_y_zMnxCoyMz)O2 with 0.9 < a ​​< 1.1; 0.60 < 1-xyz < 0.80; 0 < x < 1.1; 0 < y < 0.02 ; 0 < z < 1.1 ; and M chosen from the group consisting of Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ga, Ta, Nd, Pr, La and their mixtures;

[0110] v) mixtures of these.

[0111] As examples of lamellar oxide compounds of formula (II), the following compounds may be cited in particular:

[0112] LiNio.8oCoo.i5Alo.o502,

[0113] LiNi0.6Mno.2Co0.202 (NMC 622),

[0114] LiNio.8Mn0.iCoo.i02 (NMC 811).

[0115] Preferably, the content of compound of formula (I) is between 10% and 99% by mass expressed in relation to the total mass of the active material of the positive active layer, or in relation to the total mass of compound of formula (I) and of compound of formula (II), preferably between 20% and 85%, preferably between 30% and 80%, preferably between 40% and 70%.

[0116] According to one embodiment, the active material of the positive active layer consists of one or more compounds of formula (I) and one or more compounds of formula (II).

[0117] According to one embodiment, the active material of the positive active layer of the positive electrode comprises (or consists of):

[0118] - between 10% and 99% by mass, preferably between 20% and 85% by mass, of preference between 30% and 80% of a compound of formula (I); and

[0119] - between 1% and 90% by weight, preferably between 15% and 80% by mass, preferably between 20% and 70% by mass of a compound of formula (II);

[0120] the percentages being expressed in relation to the total mass of the active material of the positive active layer, or in relation to the total mass of compound of formula (I) and of compound of formula (II).

[0121] Preferably, 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 45%.

[0122] The binders, electronically conductive materials and possible additives can be chosen from the same lists as for the negative electrode.

[0123] The positive electrode is typically obtained by applying a composition comprising the compounds of the positive active layer to the current collector. This application can be carried out by any technique known to those skilled in the art.

[0124] Preferably, the electrochemical element according to the invention further comprises a separator and an electrolyte.

[0125] Separator

[0126] The electrochemical element may include a separator, typically between the positive and negative electrodes. The separator is designed to prevent short circuits while remaining permeable to lithium ions. It may, in particular, be made of a nonwoven fabric or a polymer film. The separator may consist of a layer of polypropylene (PP), polyethylene (PE), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyester such as polyethylene terephthalate (PET), poly(butylene) terephthalate (PBT), cellulose, polyimide, glass fibers, or a mixture of layers of different materials. The aforementioned polymers may be coated with a ceramic layer and / or polyvinylidene difluoride (PVdF) or poly(vinylidene-hexafluoropropylene fluoride (PVdF-HFP) or acrylates.

[0127] Electrolyte

[0128] The electrolyte may be liquid and comprise a lithium salt dissolved in an organic solvent. This lithium salt can be chosen from lithium perchlorate LiC104, lithium hexafluorophosphate LiPF6, lithium tetrafluoroborate LiBF4, lithium hexafluoroarsenate LiAsF6, lithium hexafluoroantimonate LiSbF6, lithium trifluoromethanesulfonate LiCF3SO3, lithium bis(fluorosulfonyl)imide Li(FSO2)2N (LiFSI), lithium trifluoromethanesulfonimide LiN(CF3SO2)2 (LiTFSI), lithium trifluoromethanesulfonemethide LiC(CF3SO2)3 (LiTFSM), lithium bisperfluoroethylsulfonimide LiN(C2F5SO2)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) and mixtures thereof.

[0129] The solvent may be selected from saturated cyclic carbonates, unsaturated cyclic carbonates, non-cyclic carbonates, alkyl esters, ethers, nitrile-type solvents, tetrahydrothiophene dioxide (sulfolane), and ethylene sulfate (ESA). Saturated cyclic carbonates include ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), butylene carbonate (BC), and mixtures thereof. Unsaturated cyclic carbonates include vinylene carbonate (VC). Non-cyclic carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dipropyl carbonate (DPC), and mixtures thereof. Alkyl esters include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and mixtures thereof.Ethers include dimethyl ether (DME), diethyl ether (DEE) and mixtures thereof.

[0130] The concentration of said at least one lithium salt may be in the range of 0.75 mol / L to 1.5 mol / L. It is preferably in the range of 1 mol / L to 1.5 mol / L. It is even better in the range of 1 to 1.2 mol / L.

[0131] 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. Electrochemical element

[0132] According to one embodiment, the electrochemical element is of the lithium-ion type.

[0133] A lithium-ion electrochemical element can be manufactured conventionally. At least one positive electrode, at least one separator, and at least one negative electrode are superimposed, and then the resulting superposition is impregnated with an electrolyte composition.

[0134] More specifically, at least one positive electrode, at least one separator, and at least one negative electrode are stacked. The assembly can be wound to form a cylindrical electrochemical bundle and then inserted into a container. The invention is not limited to the manufacture of cylindrical electrochemical elements. The electrochemical element can also be prismatic or pouch-type. The electrodes can also be stacked to form a planar electrochemical bundle. A connecting piece is attached to an edge of the positive electrode not covered with active material. It is connected to a current output terminal.

[0135] The negative electrode can be electrically connected to the electrochemical element container. Conversely, the positive electrode can be connected to the electrochemical element container and the negative electrode to a current output terminal. After being inserted into the electrochemical element container, the electrochemical bundle is impregnated with electrolyte. The electrochemical element is then hermetically sealed. The electrochemical element can also be conventionally equipped with a safety valve that opens the electrochemical element container if the internal pressure of the electrochemical element exceeds a predetermined value.

[0136] According to another object, the present invention also relates to an electrochemical module comprising the stacking of at least two electrochemical elements according to the invention, each electrochemical element being electrically connected with one or more other electrochemical element(s).

[0137] The term “module” therefore refers here to the assembly of several electrochemical elements, said assemblies being able to be in series and / or parallel.

[0138] Another object of the invention is yet another battery comprising one or more modules according to the invention.

[0139] The term “battery” or accumulator means the assembly of several modules according to the invention. Uses

[0140] The electrochemical element according to the invention is in particular intended to be used within an electrical energy storage system, such as a battery.

[0141] The invention therefore relates in particular to the use of an electrochemical element according to the invention, to limit the growth of its internal resistance and thus improve the power stability of a battery comprising such an electrochemical element.

[0142] The invention will become clearer upon reading the following examples, given solely by way of non-limiting example.

[0143] EXAMPLES

[0144] Preparation of the electrochemical elements described in Table 3

[0145] Electrochemical elements 1 to 6 can be manufactured according to the following method: They all comprise a positive electrode whose composition of the active material layer is specified in Table 1 and a negative electrode whose composition of the active material layer is specified in Table 2 below.

[0146] The electrolyte comprises a mixture of cyclic carbonates and linear carbonates with lithium salts and additives. The separator interposed between the positive and negative electrodes is of the polyolefin type.

[0147] The positive electrode can be prepared according to the mixtures described in Table 1 and coated onto an aluminum collector using any technique known to those skilled in the art. It is then calendered before being mounted with the separator and the negative electrode.

[0148] [Tables] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Active material NMC NMC811 Active material LMFP LiMno.7oFe0.3oP04 LiMn0.60Fe0.40P o4 LiMno.7oFeo.3oP o4 %mass LMFP / % mass NM C versus total mass of active material 60 / 40 50 / 50 60 / 40 Binder(s) & percolating carbon(s) <5% total mass of the electrode layer

[0149] The negative electrode can be prepared according to the mixtures described in Table 2 and coated onto a copper collector by any technique known to those skilled in the art; it is then calendered before assembly with the separator and the positive electrode.

[0150] [Tables2] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Active material Si-C (1) / Graphite Binder(s) & percolating carbon(s) <5% mass of the total electrode layer.

[0151] (1): with a Si content of 30 to 70% by mass expressed relative to the mass silicon-carbon composite particles, and with 20 to 60% mass of Si-C relative to the total mass of active material chosen to obtain the %Si in the active material of the negative layer as described in the examples in Table 3

[0152] The electrochemical elements were then assembled in pouch format and tested under cycling conditions at room temperature (symmetrical cycles at C / 2 regime between 2.7 and 4.2V).

[0153] Internal resistance measurements were carried out for a fixed state of charge at 50% and during a discharge test lasting 30s at the 3C regime at the beginning of the element's life (after 1 cycle) and after 1000 cycles.

[0154] The results obtained are presented in the following table:

[0155] [Tables3] No. Fe / Mn Ratio LMF Ratio P / NMC A (%Si) (%Si / A) (N / P) Increase in internal resistance after 1000 cycles (%) 1 (according to the invention) 30 / 70 60 / 40 0.18 0.13 0.72 1.1 26 2 (according to the invention) 30 / 70 50 / 50 0.15 0.13 0.87 1.1 19 3 (according to the invention) 30 / 70 60 / 40 0.18 0.25 1.39 1.1 22 4 (according to the invention) 30 / 70 60 / 40 0.18 0.13 0.72 1.4 17 5 (comparative) 40 / 60 60 / 40 0.24 0.13 0.54 1.1 156 6 (comparative) 30 / 70 60 / 40 0.18 0.07 0.39 1.1 121

[0156] - (A) is the product between the mass content of compound of formula (I) (%(i)) in the active material of the positive active layer expressed relative to the total mass of compound of formula (I) and of compound of formula (II), and the molar content of iron (%Fe) in the compound of formula (I) expressed relative to the total molar content of iron and manganese; (A) expresses the iron content in the active material of the positive active layer;

[0157] - (%Si) is the mass content of silicon in the active material of the active layer negative, expressed in relation to the total mass of the active material of the negative active layer;

[0158] - (%Si / A) is the ratio between the mass content of silicon (%Si) in the material active of the negative active layer and product (A); and

[0159] - (N / P) is the ratio between the first charge capacity of the negative electrode (N) and the first charge capacity of the positive electrode (P).

[0160] The inventors of the present invention have discovered that the technical problem described in the above introduction can be solved by adapting the compositions of negative and positive active layers.

[0161] Thus, for 1.1 < (N / P) < 1.7, it is possible to vary A and (%Si) such that (%Si / A) remains greater than or equal to 0.7, a value for which, at minimum (N / P), the increase in internal resistance remains less than 30% after 1000 cycles. Tests 2 and 3 show cases where (%Si / A) is strictly greater than 0.7, resulting in an increase in internal resistance of less than 19% and 22%, respectively. Test 4 shows that by increasing (N / P), the increase in internal resistance remains less than 30%. Conversely, comparative examples 5 and 6 show values ​​of (%Si / A) < 0.7, which translates into a very significant increase in internal resistance, greater than 100%, and is therefore unsuitable for solving the technical problem of the present invention.

Claims

1. Demands Electrochemical element comprising: - a negative electrode comprising a negative active layer comprising, as active material, at least particles comprising silicon; and - a positive electrode comprising a positive active layer comprising, as active material: (i) at least one lithium phosphate compound of manganese and iron of formula (I): LixMni y zFeyMzPO4 (I), wherein: M is chosen from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb, S, K, Pb, V, Mo, W, Hf, Bi, Se and any of their mixtures, 0.8 < x < 1.2; 0.5 < 1 - yz < 1; 0 < y < 0.5; 0 < z < 0.2; ii) at least one lamellar oxide-type compound of formula (II): Liw(NixMnyCozM't)O2 (II) wherein: M' is chosen from the group consisting of Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La and any of their mixtures; 0.9 <w <1,1 ; 0 <x; 0 <y ; 0 < z; 0 <t; in which: a) The ratio (%Si / A) between the mass content of silicon (%Si) in the active material of the negative active layer and the product (A) is such that: 0.7 < (%Si / A) < 4.0, where A is the product of the mass content of compound of formula (I) (%(I)) in the active material of the positive active layer expressed as a percentage of the total mass of compound of formula (I) and compound of formula (II), and the molar content of iron (%Fe) in compound of formula (I) expressed as a percentage of the total molar content of iron and manganese in compound (I), and (%Si) is the mass content of silicon in the active material of the negative active layer, expressed as a percentage of the total mass of active material of the negative active layer; and b) the ratio (N / P) between the first charge capacity of the negative electrode (N) and the first charge capacity of the positive electrode (P) is such that: 1.1 < (N / P) < 1.

7.

2. Electrochemical element according to claim 1, wherein: a) 0.7 < (%Si / A) < 3.0, preferably 0.7 < (%Si / A) < 2.5, preferably 0.7 < (%Si / A) < 2.0; and / or b) 1.1 < (N / P) < 1.6, preferably 1.1 < (N / P) < 1.

5.

3. Electrochemical element according to claim 1 or 2, wherein c) the product (A) enters the mass content of compound of formula (I) (% <!)) dans la matière active de la couche active positive exprimée par rapport à la masse totale en composé de formule (I) et en composé de formule (II), et la teneur molaire en fer (%Fe) dans le composé de formule (I) exprimée par rapport à la teneur molaire totale en fer et en manganèse dans le composé (I), est tel que : 0,1 < (A) < 0,5, de préférence 0,1 < (A) < 0,4, de préférence 0,1 < (A) < 0,3, de préférence 0,15 < (A) < 0,2.

4. Electrochemical element according to any one of the preceding claims, wherein d) the silicon mass content (%Si) in the active material of the negative active layer, expressed as a percentage of the total mass of the active material of the negative active layer, is such that: 0.05 < (%Si) < 0.6, preferably 0.07 < (%Si) < 0.6, preferably 0.1 < (%Si) < 0.5, preferably 0.1 < (%Si) < 0.4, preferably 0.1 < (%Si) < 0.

3.

5. Electrochemical element according to any one of the preceding claims, wherein the particles comprising silicon are selected from silicon-carbon composite particles and silicon oxide particles SiOx where 0 < x < 2.

6. Electrochemical element according to any one of the preceding claims, wherein the particles comprising silicon are silicon-carbon composite particles, preferably having a Si content of between 30% and 70% by mass, preferably between 40% and 60% by mass, relative to the mass of the silicon-carbon composite particles.

7. Electrochemical element according to claim 6, wherein the content of silicon-carbon composite particles in the active material of the negative active layer is between 10% and 98% in niasse expressed in relation to the mass of the active material of the negative active layer, preferably between 10% and 80%, preferably between 20% and 60%, preferably between 30% and 50%, preferably between 40% and 50%.

8. Electrochemical element according to any one of the preceding claims, wherein the active material of the negative active layer further comprises graphite particles.

9. Electrochemical element according to any one of the preceding claims, wherein the active material of the negative active layer comprises: - from 20% to 90%, preferably from 20% to 80%, particularly from 40% to 60% of silicon-carbon composite particles; and - from 10% to 80%, preferably from 20% to 80%, particularly from 40% to 60% of graphite, the percentages being understood as by mass, expressed in relation to the total mass of silicon-carbon composite particles and graphite particles.

10. Electrochemical element according to any one of the preceding claims, wherein the compound of formula (I) is such that the molar content of iron (%Fe) in the compound of formula (I), expressed as a percentage of the total molar content of iron and manganese in the compound (I), is 0.2 to 0.

5.

11. Electrochemical element according to any one of the preceding claims, wherein the content of compound of formula (I) is between 10% and 99% by mass expressed relative to the total mass of compound of formula (I) and compound of formula (II), preferably between 20% and 85%, preferably between 30% and 80%, preferably between 40% and 70%.

12. Electrochemical element according to any one of the preceding claims, wherein the compound of formula (II) is such that: 0.5 < x < 1.1; and / or 0 < y < 1.1; and / or 0 < z < 1.1; and / or 0 <t< 1,1.

13. Use of an electrochemical element according to any one of claims 1 to 12, to limit the growth of its internal resistance and improve the power stability of a battery comprising such an electrochemical element.