Lithium-ion electrochemical element with high power and chargeability

Abstract

The present invention relates to an electrochemical element comprising: - a negative electrode comprising a negative active layer that comprises, as active material, at least one silicon-carbon composite, the negative active layer having a porosity ranging from 35% to 50%; - a positive electrode comprising a positive active layer that comprises, as active material: a) at least one lithium manganese iron phosphate compound of formula (I): LixMn1-y-.zFeyMzPO4 (I), wherein: 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, Hf, Bi, Se and any mixture thereof, 0.8 ≤ x ≤ 1.2; 0.5 ≤ 1-y-z < 1; 0 < y ≤ 0.5; 0 ≤ z ≤ 0.2; b) at least one lamellar oxide compound of formula (II): Liw(NixMnyCozM't)O2 (II), wherein: M' is selected 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; 0.9 ≤ w ≤ 1.4; 0 < x; 0 ≤ y; 0 ≤ z; 0 ≤ t.

Description

[0001] TITLE: High Power and Chargeability Lithium-ion Electrochemical Element

[0002] The present invention relates to the field of energy storage, and lithium batteries in particular. More specifically, this application relates to an electrochemical element comprising a specific combination of negative and positive active materials, enabling improved electrochemical performance while maintaining a high level of safety.

[0003] The invention is particularly useful in the field of rechargeable lithium-ion (Li-ion) type electrochemical elements, especially those used in electric or hybrid vehicles.

[0004] The operation of lithium-ion batteries is based on the reversible exchange of lithium ions between a positive electrode and a negative electrode, separated by an electrolyte, with lithium being stored at the negative electrode during charging operation.

[0005] Lithium-ion rechargeable 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.

[0006] Although based on the same technology, these two applications do not have exactly the same specifications. In the field of electric vehicles, one of the major challenges is chargeability, in order to ensure users can fully recharge as quickly as possible, whereas the aeronautics industry primarily requires high power. The electric vehicle sector also tends to favor a high energy density by volume, while the aeronautics industry seeks to optimize energy density by mass. However, these two consumer applications share the common goal of a high level of safety.

[0007] However, it is desirable to develop Li-ion-type electrochemical cells to create Li-ion batteries suitable for both types of applications; that is, electrochemical cells exhibiting both high volumetric and mass energy density, high power, and high chargeability, while also ensuring a high level of safety. These objectives are inherently incompatible, since high energy density implies a loss of power, and increased power implies a degradation of safety.

[0008] The aim of the invention is therefore to provide a Li-ion type electrochemical element exhibiting high volumetric and / or mass energy density, and / or high power and / or chargeability, while ensuring a high level of safety during charge and discharge cycles. The aim of the invention is, in particular, to provide a Li-ion type electrochemical element exhibiting high volumetric and mass energy density, and high power and chargeability, while ensuring a high level of safety and a long lifespan.

[0009] A particular objective of the invention is to provide a Li-ion electrochemical cell with a volumetric energy density of at least 500 Wh / L and / or a mass energy density of at least 250 Wh / kg. This same electrochemical cell must be capable of operating in continuous discharge at a rate of at least 5D and / or in continuous charge at a rate of at least 2C, while ensuring a high level of safety and a long lifespan. The rate, denoted nD for discharge or nC for charge, corresponds to the current required to discharge or charge the cell's nominal capacity in 1 / n hours. The reference nominal capacity is measured between the fully charged and discharged states over a period of 5 hours.

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

[0011] - a negative electrode comprising a negative active layer comprising, as active material, at least one silicon-carbon composite, the negative active layer having a porosity ranging from 35% to 50%,

[0012] - a positive electrode comprising a positive active layer comprising, as active material: a) at least one lithium phosphate compound of manganese and iron of formula (I): Li x Mn 1.y.z FeyM z PO4(I), in which:

[0013] 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, Hf, Bi, Se and any of their mixtures, 0.8 < x < 1.2;

[0014] 0.5 < 1 - yz < 1;

[0015] 0 < y < 0.5;

[0016] 0 < z < 0.2; b) at least one lamellar oxide-type compound of formula (II): Li w (Neither x Mn y Co z M' t)O2(II), in which: 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;

[0017] 0.9 < w < 1.4;

[0018] 0 < x;

[0019] 0 < y;

[0020] 0 < z;

[0021] 0 < t

[0022] The inventors discovered that the combination of the active materials of formulas (I) and (II) of the positive active layer, and the active materials of the negative active layer, combined with a specific porosity of the negative active layer, makes it possible to obtain an electrochemical element exhibiting:

[0023] - a high volumetric energy density (typically at least 500 Wh / L),

[0024] - a high specific energy density (typically at least 250 Wh / kg),

[0025] - continuous discharge operation at a minimum 5D regime,

[0026] - high chargeability (typically at a rate of at least 2C (continuous)),

[0027] - combined with a high level of security.

[0028] In particular, the presence of compound (I) in the positive active layer helps maintain the high safety of the electrochemical element despite the increased energy supplied by the Si-C composite to the negative electrode. The porosity of the negative active layer also plays a role in improving the power of the electrochemical element and its lifespan.

[0029] Negative electrode

[0030] A "silicon-carbon composite" is defined as a heterogeneous mixture of silicon and carbon particles. These particles exhibit strong interpenetration and adhesion. Therefore, it is not silicon carbide (SiC), which is a homogeneous solid in which each silicon atom is covalently bonded to a carbon atom. Nor is it an alloy, which is a metallic mixture of several elements.

[0031] Two types of composite can typically be used.

[0032] One type consists of silicon nanoparticles embedded (i.e., embedded) in a carbon matrix. "Nanoparticles" are defined as particles with a largest dimension of 500 nm or less. In some cases, the largest dimension may be 100 nm or less. The largest dimension can be determined by laser granulometry coupled with scanning electron microscopy.

[0033] A second type of composite consists of silicon particles embedded in pores within a carbon matrix. The pores can be located on the surface of the carbon matrix or within it. The silicon particles can partially or completely cover the surface of the carbon matrix pores. The carbon pores can have a diameter ranging from 1 nm to 100 nm. The diameter of the carbon pores can be determined by laser granulometry coupled with scanning electron microscopy.

[0034] In both types of composite, the silicon and carbon used can be either amorphous or crystalline, independently of each other. The mass proportion of silicon in the composite typically ranges from 5% to 80%, or from 25% to 70%, or from 30% to 70%, or from 40% to 65%, or from 40% to 60%, or from 40% to 55%. The mass proportion of carbon in the composite typically ranges from 20% to 95%, or from 30% to 75%, or from 30% to 70%, or from 35% to 60%, or from 40% to 60%.

[0035] The negative electrode typically includes a current collector covered by a negative active layer.

[0036] The term "current collector" refers to a 2D or 3D element, such as a pad, plate, sheet, or other component, made of a conductive material, that ensures the conduction of electron flow between the electrodes and the battery terminals. The current collector is generally in the form of a solid or perforated metal strip. This strip can be made from various materials, including 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.

[0037] The negative electrode current collector is typically a copper strip or a strip of a copper-rich alloy. The negative electrode strip is typically 4 µm to 18 µm thick, preferably 4 µm to 10 µm.

[0038] In one embodiment, the copper collector of the negative electrode is coated with a conductive material, such as carbon black, graphite, carbon nanotubes, and mixtures thereof. Thus, the strips may optionally be coated on one or two of their faces with a layer of carbon no more than a few micrometers thick. 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, electronic conductors, binders, and any other additives.

[0039] The expression "electrochemically active material" or "active material" refers to materials that are the site of the electrochemical reaction.

[0040] The negative electrode of the electrochemical element according to the invention comprises a negative active layer comprising at least one silicon-carbon composite, also called Si-C.

[0041] Preferably, the silicon-carbon composite content is between 10% and 98% by mass expressed relative to the total 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%.

[0042] Silicon-carbon composite particles preferably have a silicon 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 silicon-carbon composite particles.

[0043] The negative active layer of the negative electrode has a porosity ranging from 35% to 50%.

[0044] Preferably, the porosity of the negative active layer ranges from 35% to 45%.

[0045] 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 encompasses both the void volume between the compound particles in the negative active layer deposited on the current collector and the pore volume 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 using the following method: the theoretical density d rée | teis calculated from the density of each compound in the negative active layer deposited on the current collector. The apparent density of a pp arente 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:

[0046] Porosity — 1-(d a pp aren t e / d r e e ii e ). Such porosity makes it possible to improve both the lifespan of the electrochemical element and its power.

[0047] 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 graphite particles in the active material of the negative active layer is between 2% and 90% by mass expressed relative to the mass of the active material of the negative active layer, preferably between 20% and 90%, preferably between 40% and 80%, preferably between 50% and 70%, preferably between 50% and 60%.

[0048] According to one embodiment, the active material of the negative active layer consists of graphite particles and the Si-C composite.

[0049] Typically, the active material of the negative active layer includes (or even consists of):

[0050] - from 10% to 98%, preferably from 10% to 80%, particularly from 20% to 60%, and more particularly from 30% to 50% of Si-C composite; and

[0051] - from 2% to 90%, preferably from 20% to 90%, particularly from 40% to 80%, more particularly from 50% to 70% of graphite; the percentages are understood to be by mass, expressed in relation to the total mass of silicon-carbon composite and graphite particles (or in relation to the total mass of the active material of the negative active layer).

[0052] As a specific example, the active material of the negative active layer comprises, or even consists of, 45% by mass of Si-C composite and 55% by mass of graphite, expressed relative to the mass of the active material of the negative active layer.

[0053] The term “binder” refers to 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.

[0054] The binder can be chosen from a 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.

[0055] 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).

[0056] These binders can typically be used for the positive electrode and / or the negative electrode.

[0057] 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.

[0058] These electronically conductive materials can typically be used for the positive electrode and / or the negative electrode.

[0059] Possible additives may include dispersants and / or pH buffers. Polyvinylpyrrolidone (PVP) is one example of a dispersant.

[0060] These additives can typically be used for the positive electrode and / or the negative electrode.

[0061] 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.

[0062] Positive electrode

[0063] The positive electrode generally includes a current collector covered by a positive active layer.

[0064] The current collector for the positive electrode is usually in the form of a solid or perforated metal strip. The strip can be made from various materials, including 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 described in the preceding sentence.

[0065] The current collector of the positive electrode is typically an aluminum strip or an alloy consisting mainly of aluminum. The positive electrode strip typically has a thickness of 6 µm to 30 µm.

[0066] In one embodiment, the aluminum collector of the positive electrode is coated with a conductive material, 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 no more than a few micrometers thick.

[0067] The thickness of the positive electrode strip may be different from that of the negative electrode strip.

[0068] 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 possible additives.

[0069] As an active material, the positive electrode comprises at least one compound of formula (I) and at least one compound of formula (II).

[0070] Thus, according to the invention, the positive active layer comprises: a) at least one lithium manganese iron phosphate compound (LMFP) of formula

[0071] (I): Li x Mn 1.y.z FeyM z PO4(I), in which:

[0072] 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, Hf, Bi, Se and any mixture thereof,

[0073] 0.8 < x < 1.2;

[0074] 0.5 < 1 - yz < 1;

[0075] 0 < y < 0.5; and

[0076] 0 < z < 0.2; b) at least one lamellar oxide-type compound of formula (II): Li w (Neither x Mn y Co z M' t )O2

[0077] (II), in which:

[0078] 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;

[0079] 0.9 < w < 1.4;

[0080] 0 < x;

[0081] 0 < y;

[0082] 0 < z; and

[0083] 0 < t.

[0084] Preferably, in the compound of formula (I):

[0085] - 0.05 < y < 0.5, preferably 0.1 < y < 0.5, and / or

[0086] - 0.5 < 1-yz < 0.95, advantageously, 0.5 < 1-yz < 0.9, and / or

[0087] - x = 1, and / or

[0088] - z = 0.

[0089] Preferably, the compound of formula (I) has a Mn / Fe molar ratio ranging from 50 / 50 to Typically, the compound of formula (I) can be chosen from LiMn 0.8 Feo.2P04,

[0090] LiMnO2.7FeO3PO4, LiMn2 / 3Fe 1 / 3 PO4 and LiMno.5Feo.5PO4.

[0091] 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 conductivity and / or ionic diffusivity.

[0092] Preferably, 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.

[0093] Preferably, the compound of formula (II) is such that 0 < y < 1.1 and / or 0 < z < 1.1 and / or 0 < t < 1.1, in particular 0 < y < 1.1 and / or 0 < z < 1.1.

[0094] Preferably, the compound of formula (II) may be chosen from the list below: i) a lithium nickel manganese cobalt oxide (NMC) of formula (lia)Li w (Neither x Mn y Co z M t)O2où 0,9 < w < 1,1 ; 0 <x<1 ,1 ; 0<y<1 ,1 ; 0<z<1 ,1 ; 0<t<1 ,1 ; M étant au moins un élément choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, Sr, Ce, Ta, Ga, Nd, Pr et La, et plus particulièrement 0,5 < x ; ii) un oxyde lithié de nickel, de cobalt et d’aluminium (NCA) de formule (llb) Li w (Ni x Co y Al z M t )O2où 0,9 < w < 1,1 ; 0 <x<1 ,1 ; 0<y<1 ,1 ; 0<z<1 ,1 ; 0<t<1 ,1 ; M étant au moins un élément choisi dans le groupe constitué de B, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, Sr, Ce, Ga, Ta, Nd, Pr et La ; plus particulièrement 0,80 < x ; iii) un oxyde lithié de nickel, de manganèse, de cobalt et d’aluminium (NMCA) de formule (Ile) Li w (Ni x Co y Al z Mr t M s)O2où 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 étant au moins un élément choisi dans le groupe constitué de B, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, Sr, Ce, Ga, Ta, Nd, Pr et La, plus particulièrement 0,83 < x ; iv) un composé de type oxyde lithié de nickel et de manganèse (NMX) de formule Li a (Ni 1.x.y.z Mr x Co y M z )O2avec 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 ; 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 mélanges de ceux-ci.

[0095] Preferably, in the compound of formula (Ila), x > 0.6. A high amount of nickel in the nickel lithium oxide is preferable because it provides high energy to the nickel lithium oxide. Examples of nickel manganese cobalt lithium oxide compounds of formula (Ila) (NMC) include the following:

[0096] Li N i0.6M ri0.2Co0.2O2 (NMC 622),

[0097] LiNi0.8Mn0.1Co0.1O2 (NMC 811).

[0098] Examples of lithium nickel, cobalt, and aluminium oxide compounds with formula (II b) (NCA) include the following compound:

[0099] Li N io 80CO0.15AI0.05^2 ■

[0100] 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, preferably between 20% and 85%, preferably between 30% and 80%, preferably between 40% and 70%.

[0101] Preferably, the content of compound of formula (I) is between 10% and 99% by mass expressed 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%.

[0102] 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).

[0103] According to one embodiment, the active material of the positive active layer of the positive electrode comprises, or even consists of:

[0104] - between 10% and 99% by mass, preferably between 20% and 85% by mass, preferably between 30% and 80% of compound(s) of formula (I); and

[0105] - between 1% and 90% by mass, preferably between 15% and 80% by mass, preferably between 20% and 70% by mass of compound(s) of formula (II); the percentages being expressed in relation to the total mass of compound(s) of formula (I) and compound(s) of formula (II) (or in relation to the total mass of the active material of the positive active layer).

[0106] 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%.

[0107] The binders, electronically conductive materials and any additives can be chosen from the same lists as for the negative electrode.

[0108] 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. Preferably, the electrochemical element according to the invention further comprises a separator and an electrolyte.

[0109] Separator

[0110] The electrochemical element may include a separator, typically located between the positive and negative electrodes. The separator's purpose is to prevent short circuits while remaining permeable to lithium ions. It may be made of a non-woven fabric or a polymer film. The separator can consist of a layer of polypropylene (PP), polyethylene (PE), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyester such as polyethylene terephthalate (PET) or poly(butylene) terephthalate (PBT), cellulose, polyimide, glass fibers, or a mixture of different materials. The aforementioned polymers may be coated with a ceramic layer and / or polyvinylidene difluoride (PVdF), poly(vinylidene-hexafluoropropylene fluoride (PVdF-HFP), or acrylates.

[0111] Electrolyte

[0112] The electrolyte can be liquid and consist of a lithium salt dissolved in an organic solvent. This lithium salt can be chosen from lithium perchlorate LiClO4, 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.

[0113] The solvent can be chosen 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), methylethyl 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.

[0114] 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.

[0115] 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.

[0116] Electrochemical element

[0117] According to one embodiment, the electrochemical element is of the lithium-ion type.

[0118] A lithium-ion element can be manufactured in a conventional manner. 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.

[0119] 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 elements. The 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 that is not covered with active material. It is connected to a current output terminal.

[0120] 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 element exceeds a predetermined value. According to another aspect, the present invention also relates to an electrochemical module comprising a stack of at least two electrochemical elements according to the invention, each electrochemical element being electrically connected to one or more other elements.

[0121] The term "module" here therefore refers to the assembly of several electrochemical elements, said assemblies being able to be in series and / or parallel.

[0122] Another object of the invention is a battery comprising one or more modules according to the invention.

[0123] The term “battery” or accumulator refers to the assembly of several modules according to the invention.

[0124] Uses

[0125] The electrochemical element according to the invention is particularly 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, in particular in an electric or hybrid aircraft or road transport vehicle.

[0126] The invention therefore relates in particular to the use of an electrochemical element according to the invention, to improve the chargeability of a battery comprising such an electrochemical element at a charging regime up to at least 2C.

[0127] The invention also relates to the use of an electrochemical element according to the invention, to improve the chargeability of an electric or hybrid vehicle battery comprising such an electrochemical element at a charging regime up to at least 2C.

[0128] The invention also relates to the use of an electrochemical element according to the invention, to improve the power of a battery comprising such an electrochemical element by allowing continuous discharge operation under a regime of at least 5D.

[0129] The invention also relates to the use of an electrochemical element according to the invention, to improve the power of an electric or hybrid aircraft battery comprising such an electrochemical element by allowing continuous discharge operation under a regime of at least 5D.

[0130] The invention also relates to the use of an electrochemical element according to the invention to improve the electric propulsion of a means of transport, for example, an electric or hybrid road vehicle or an electric aircraft. The invention will become clearer upon reading the following examples, given solely by way of non-limiting illustration, and made with reference to the drawings in which:

[0131] Figure 1 is a graph representing the evolution of the voltage as a function of the capacitance in the complete cell of the electrochemical elements of example 1.

[0132] Figure 2 is a graph representing the evolution of the percentage of charge as a function of the charging regime for the electrochemical elements of example 1.

[0133] Figure 3 is a graph representing the evolution of the percentage of discharge as a function of the discharge regime for the electrochemical elements of example 1.

[0134] Figure 4 is a graph comparing the evolution of the discharged capacitance during a C / 3 / D / 3 cycle between 2.5V and 4.2V of electrochemical elements analogous to electrochemical element A of example 1 but whose negative electrode porosity is 32% or 45% (example 2).

[0135] EXAMPLES

[0136] Example 1: Effect of the presence of Si-C composite in the negative active layer

[0137] Two electrochemical elements A (according to the invention) and B (comparative) were prepared as follows:

[0138] Electrochemical elements A and B can be manufactured according to the following method: They all comprise a positive electrode whose active material layer composition is composed of a mixture of 60% NMC and 40% LMFP in both cases and a negative electrode whose active material layer composition is for electrochemical element A a mixture of 45% Si-C and 55% graphite and for electrochemical element B only graphite, in both cases the active materials are accompanied by a mixture of binder and percolating carbons.

[0139] The electrolyte comprises a mixture of cyclic and linear carbonates with lithium salts and additives. The separator interposed between the positive and negative electrodes is of the polyolefin type.

[0140] The positive electrode can be prepared and coated on 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. The negative electrode can be prepared according to the mixtures described and coated on a copper collector using any technique known to those skilled in the art; it is then calendered before being mounted with the separator and the positive electrode.

[0141] The electrodes assembled with the separator are then mounted in a pouch format and then filled with the electrolyte.

[0142] These two electrochemical elements A and B are then evaluated according to criteria of chargeability, dischargeability, capacity, volumetric and mass energy and safety, the results are presented in Table 1.

[0143] The cell capacity is measured after a charge at C / 5 up to 4.2V with a holding potential ('floating') until the measured residual current value is less than C / 100, during a discharge at D / 5 down to 2.5V. The voltage profile is shown in Figure 1.

[0144] Chargeability is tested by charging the electrochemical elements at increasing rates from C / 10 to 2C without holding the potential ('floating') at the end of the charge up to 4.2V and with discharges to C / 10 between each charge. The charged capacitance is compared to that obtained for a C / 5 rate. The results are shown in Figure 2.

[0145] Dischargeability is tested by charging the electrochemical elements at increasing rates from D / 10 to 5D up to 2.5V and with C / 10 charges up to 4.2V, maintaining the potential until the measured residual current is less than C / 100 between each discharge. The discharged capacitance is compared to that obtained at a D / 5 rate. The results are shown in Figure 3.

[0146] Figure 1 illustrates the gain in capacity obtained by going from the electrochemical element B to the object of the invention (electrochemical element A).

[0147] Figure 2 illustrates the improvement in chargeability for continuous 2C charging with a 14% gain in charged capacity.

[0148] Figure 3 illustrates the improvement in dischargeability for continuous discharge at D / 5 with a 40% gain in discharged capacity.

[0149] The results obtained during these different tests are used to calculate the volumetric and mass energy by taking the capacity restored during a discharge at D / 5 multiplied by the average voltage of the electrochemical element and divided by either the volume of the electrochemical element or its mass to arrive at the values ​​mentioned in Table 1.

[0150] The overload and overheating results shown in this table were obtained by subjecting electrochemical elements A and B to overheating tests (cell charged to 100% state of charge (4.2V) heated at a rate of 5°C / min until an event occurred) and overload tests (one electrochemical element was charged from a discharged state at a rate of 2C without voltage limit until an event occurred). The temperatures mentioned are the average over two electrochemical elements and refer to the temperature at which thermal runaway began.

[0151] [Table 1]

[0152] These results show that, for a similar weight and format, the addition of Si-C composite in the negative active layer improves the power of the electrochemical element and the energy density, without degrading the safety that usually accompanies an increase in power.

[0153] Example 2: Influence of the porosity of the negative active layer

[0154] Two electrochemical elements C (according to the invention) and D (comparative) exhibiting different negative porosities were prepared according to the protocol described in Example 1. They share the composition of electrochemical element A of Example 1 and the only differentiating factor is the porosity of the negative electrode, equal to 45% (electrochemical element C) or 32% (electrochemical element D).

[0155] The porosity is modulated during the calendering stage in which the negative electrode is compressed by rollers of significant mass and defined distance.

[0156] The lifetime of these electrochemical elements C and D was evaluated according to the following protocol: following an initial cycle at C / 10-D / 10 and a second at C / 5-D / 5, the electrochemical elements C and D were cycled at a C / 3-D / 3 regime for 250 cycles. The capacitance is normalized with respect to the second cycle at C / 5-D / 5 in the graph in Figure 4 and shows a higher value after 250 cycles for electrochemical element C, whose negative electrode has a porosity of 45%. The results obtained are shown in Figure 4.

Claims

DEMANDS 1. Electrochemical element comprising: - a negative electrode comprising a negative active layer comprising, as active material, at least one silicon-carbon composite, the negative active layer having a porosity ranging from 35% to 50%, - a positive electrode comprising a positive active layer comprising, as active material: a) at least one lithium phosphate compound of manganese and iron of formula (I): Li x Mn 1.y.z FeyM z PO4(I), in which: 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, 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; b) at least one lamellar oxide-type compound of formula (II): Li w (Neither x Mn y Co z M't)O2(II), in which: 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 < 1.4; 0 < x; 0 < y; 0 < z; 0 < t 2. Electrochemical element according to claim 1, wherein the silicon-carbon composite content in the active material of the negative active layer is between 10% and 98% by mass expressed relative 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%.

3. Electrochemical element according to claim 1 or 2, wherein the porosity of the negative active layer ranges from 35% to 45% 4. Electrochemical element according to any one of the preceding claims, wherein the active material of the negative active layer further comprises graphite particles.

5. Electrochemical element according to claim 4, wherein the graphite particle content in the active material of the negative active layer is between 2% and 90% by mass expressed relative to the mass of the active material of the negative active layer, preferably between 20% and 90%, preferably between 40% and 80%, preferably between 50% and 70%, preferably between 50% and 60%.

6. Electrochemical element according to any one of the preceding claims, wherein the active material of the negative active layer comprises 45% by mass of Si-C composite and 55% by mass of graphite, expressed relative to the mass of the active material of the negative active layer.

7. Electrochemical element according to any one of the preceding claims, wherein the compound of formula (I) has a Mn / Fe molar ratio ranging from 50 / 50 to 80 / 20.

8. 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.

9. Electrochemical element according to any one of the preceding claims, wherein the compound of formula (II) is such that 0 < y < 1.1 and / or 0 < z < 1.1 and / or 0 < t < 1.1, in particular 0 < y < 1.1 and / or 0 < z < 1.

1.

10. Electrochemical element according to any one of the preceding claims, wherein 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), and consists of: - between 10% and 99% by mass, preferably between 20% and 85% by mass, preferably between 30% and 80% of compound(s) of formula (I); and - between 1% and 90% by mass, preferably between 15% and 80% by mass, preferably between 20% and 70% by mass of compound(s) of formula (II); the percentages being expressed in relation to the total mass of compound(s) of formula (I) and compound(s) of formula (II).

11. Use of an electrochemical element according to any one of claims 1 to 10, to improve the chargeability of a battery comprising such an electrochemical element at a charging regime up to at least 2C.

12. Use of an electrochemical element according to any one of claims 1 to 10, to improve the chargeability of an electric or hybrid vehicle battery comprising such an electrochemical element at a charging regime up to at least 2C.

13. Use of an electrochemical element according to any one of claims 1 to 10, to improve the power of a battery comprising such an electrochemical element by enabling continuous discharge operation under a regime of at least 5D.

14. Use of an electrochemical element according to any one of claims 1 to 10, to improve the power of an electric or hybrid aircraft battery comprising such an electrochemical element by enabling continuous discharge operation under a regime of at least 5D.

15. Use of an electrochemical element according to any one of claims 1 to 10, to improve the electric propulsion of a means of transport, for example an electric or hybrid road vehicle or an electric aircraft.

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