Lithium-ion electrochemical element having high power stability and high energy density

Abstract

The present invention relates to an electrochemical element comprising: a negative electrode comprising at least particles comprising silicon; and a positive electrode comprising, as active material: i) at least one compound LixMn1.y.zFeyMzPO4 (I), wherein M is selected from among (B, Mg, AI, 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-y-z < 1; 0 < y ≤ 0.5; 0 ≤ z ≤ 0.2; ii) at least one compound Liw(NixMnyCozM't)O; (II), wherein M' is selected from among (AI, 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); with 0.9 ≤ w ≤ 1.1; 0 < x; 0 ≤ y; 0 ≤ z; 0 ≤ t; wherein: a) the ratio (% Si / A) is such that: 0.7 ≤ (% Si / A) ≤ 4.0, (A) being the product of the content by weight of compound (I) in the positive active layer, expressed relative to the total weight of compounds (I) and (II), and the molar content of iron (%Fe) in compound (I), expressed relative to the molar content of iron and manganese in compound (I); and (%Si) being the content by weight of silicon in the active material of the negative active layer, expressed relative to the total weight of the active material of the negative active layer; and ≤ b) the ratio (N / P) between the first-charge capacity of the negative electrode and the first-charge capacity of the positive electrode is such that: 1.1 ≤ (N / P) ≤ 1.7.

Description

[0001] TITLE: Electrochemical element Li-ion exhibiting high power stability and energy density

[0002] 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, 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.

[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] We know in particular the electrochemical elements comprising positive electrodes based on lithiated manganese and iron phosphates of formula LixMn^y. z Fe y M zPO4(LMFP) 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 transition metal lithium phosphates are stable at high temperature.

[0007] The main limitation of using lithium manganese and iron phosphate compounds is their very low lithium diffusion coefficient, which greatly limits their chargeability and dischargeability. Two approaches are used to overcome this limitation:

[0008] - Using nanometric materials to minimize lithium diffusion distances 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 electrode / electrolyte contact area and therefore the reactivity of the material;

[0009] - Increasing the amount of iron in the LMFP material significantly increases the lithium diffusion coefficient within the material. However, this second option presents the problem of limiting the energy of the electrochemical elements within the LMFP material. Adding silicon-containing particles to the negative electrode compensates for this limitation.

[0010] One of the objectives of the invention is therefore to propose an electrochemical element having a positive electrode based on lithia phosphate compounds of manganese and iron exhibiting improved performance, in particular in terms of power, stability of internal resistance, safety, and which has a high energy density.

[0011] To this end, the invention relates in particular to an electrochemical element comprising:

[0012] - a negative electrode comprising a negative active layer comprising, as active material, at least particles comprising silicon; and

[0013] - 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): Li x Mn 1.y.z Fe y M z PO4 (I), in which:

[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, 0.8 < x < 1.2;

[0015] 0.5 < 1 - yz < 1;

[0016] 0 < y < 0.5;

[0017] 0 < z < 0.2; ii) at least one lamellar oxide-type compound of formula (II)Li w (Neither x Mn y Co z M' t )O2(II) in which:

[0018] 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;

[0019] 0.9 < w < 1.1;

[0020] 0 < x;

[0021] 0 < y;

[0022] 0 < z ; 0 < t; in which: a) the ratio (%Sj / 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, A being the product between the mass content of compound of formula (I) (%(l)) 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 the compound of formula (I) expressed as a percentage of the total molar content of iron and manganese in the 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 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.

[0023] Indeed, the inventors observed that the presence of particles including 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.

[0024] The inventors 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 in such a way that a combination of related characteristics:

[0025] - At the ratio (%Si / A)

[0026] - At the ratio (N / P), and preferably also:

[0027] - To the product (A) between the mass content of compound of formula (I) (%(l)) in the active material of the positive active layer and the iron content (%Fe) in the compound of formula (I),

[0028] - The silicon mass content (%Si) in the active material of the negative active layer corresponds to specific values.

[0029] Preferably, in the electrochemical element of the invention: 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. Preferably, the electrochemical element is also characterized by c) the product (A) of the mass content of the 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 of compound of formula (II), and 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 compound (I). Product (A) is therefore calculated according to the following relationship:

[0030] A = %(|) * %Fe

[0031] 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.

[0032] 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 negative active layer (%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.

[0033] Negative electrode

[0034] The negative electrode typically includes a current collector covered by a negative active layer.

[0035] 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.

[0036] The negative electrode current collector is typically a copper strip or a copper-rich alloy. The negative electrode strip is typically 4 µm to 30 µm thick.

[0037] In one embodiment, the copper or copper-clad polymer collector of the negative electrode can be 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. 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.

[0038] The expression "electrochemically active material" or "active material" refers to materials that are the site of the electrochemical reaction.

[0039] The negative electrode of the electrochemical element according to the invention comprises a negative active layer comprising particles including silicon.

[0040] Preferably, the particles containing silicon are chosen from silicon-carbon composite particles and silicon dioxide (SiO₂) particles. x where 0 < x < 2.

[0041] Preferably, the particles containing silicon are silicon-carbon composite (Si-C) particles.

[0042] 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 silicon-carbon composite particles.

[0043] 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 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%.

[0044] 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%.

[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 | te is calculated from the density of each compound in the negative active layer deposited on the current collector. The apparent density of a pp aren t eis 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 n e ) .

[0047] Such porosity makes it possible to improve both the lifespan of the electrochemical element and its power.

[0048] 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%.

[0049] According to one embodiment, the active material of the negative active layer consists of graphite particles and Si-C composite particles.

[0050] Typically, the active material in the negative active layer includes:

[0051] - from 20% to 90%, preferably from 20% to 80%, particularly from 40% to 60% of silicon-carbon composite particles; and

[0052] - from 10% to 80%, preferably from 20% to 80%, particularly from 40% to 60% of graphite; the percentages being understood as mass, expressed in relation to the total mass of the active material of the negative active layer, or even in relation to the total mass of silicon-carbon composite particles and graphite particles.

[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 generally an aluminum strip or a strip made primarily of aluminum alloy. The positive electrode strip typically has a thickness of 6 µm to 30 µm. In one embodiment, the aluminum collector of the positive electrode can be 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.

[0066] The thickness of the positive electrode strip may be different from that of the negative electrode strip.

[0067] 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.

[0068] As an active material, the positive electrode comprises at least one compound of formula (I) and at least one compound of formula (II).

[0069] The positive electrode comprises 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:

[0070] 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,

[0071] 0.8 < x < 1.2;

[0072] 0.5 < 1 - yz < 1;

[0073] 0 < y < 0.5;

[0074] 0 < z < 0.2.

[0075] Preferably, in the compound of formula (I):

[0076] - 0.05 < y < 0.5, and / or

[0077] - 0.5 < 1 - yz < 0.95, and / or

[0078] - x = 1, and / or

[0079] - z = 0.

[0080] Preferably, the compound of formula (I) is such that the molar content of iron (% Fe ) in the compound of formula (I), expressed in relation to the total molar content of iron and manganese in the compound (I), is 0.2 to 0.5.

[0081] Typically, the compound of formula (I) can be chosen from LiMn 0i8 Feo i2 P04,

[0082] LiMn0,7Fe0,3PO4, LiMn0,6Fe0,4PO4 and LiMn0,5Feo,5PO4. Advantageously, the lithium manganese iron phosphate (LMFP) compound(s) of formula (I) are coated with a layer of carbon and / or carbon nanotubes, in particular to increase their electronic conductivity.

[0083] The positive electrode further comprises at least one lamellar oxide-type compound corresponding to formula (II): Li w (Neither x Mn y Co z M' t )O2(II) in which:

[0084] 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; 0.9 <w<1,1 ;

[0085] 0 < x;

[0086] 0 < y;

[0087] 0 <z;

[0088] 0 <t

[0089] Preferably, the compound of formula (II) is such that:

[0090] 0.5 < x < 1.1; and / or

[0091] 0 < y < 1, 1; and / or

[0092] 0 < z < 1, 1; and / or

[0093] 0 <t< 1,1.

[0094] 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 be chosen, in particular, from the group consisting of Al, B, Mg, and mixtures thereof. Preferably, M is Al. Preferably, t < 0.05.

[0095] Preferably, the compound of formula (II) is chosen from: i) a lithium nickel manganese cobalt oxide (NMC) of formula (lia)Li w (Neither x Mn y Co z M t )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; ii) a lithium oxide of nickel, cobalt and aluminum (NCA) of formula (llb)Li w (Neither x Co y Al z M t)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 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 iii) a lithium oxide of nickel, manganese, cobalt, and aluminum (NMCA) of formula (Ile)Li w (Neither x Co y Al z Mn t M s )O2where 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) les composés de type oxyde lithié de nickel et de manganèse (NMX) de formule Li a (Neither 1.x .y. z Mn x Co y M z)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; v) mixtures of these.

[0096] Examples of lamellar oxide compounds with formula (II) include the following:

[0097] LiNio 80CO0.15Al0.05O2,

[0098] LiNig .6Mn0.2Co0.2O2 (NMC 622),

[0099] LiNio.8Mn0.1Co0.1O2 (NMC 811).

[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, 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%.

[0101] 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).

[0102] According to one embodiment, the active material of the positive active layer of the positive electrode comprises (or consists of):

[0103] - between 10% and 99% by mass, preferably between 20% and 85% by mass, preferably between 30% and 80% of a compound of formula (I); and

[0104] - between 1% and 90% by mass, preferably between 15% and 80% by mass, preferably between 20% and 70% by mass of a compound of formula (II); the percentages being expressed in relation to the total mass of the active material of the positive active layer, or even in relation to the total mass of compound of formula (I) and compound of formula (II).

[0105] 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%.

[0106] The binders, electronically conductive materials, and any additives can be chosen from the same lists as for the negative electrode. 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 using any technique known to those skilled in the art.

[0107] Preferably, the electrochemical element according to the invention further comprises a separator and an electrolyte.

[0108] Separator

[0109] 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.

[0110] Electrolyte

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] Electrochemical element

[0116] According to one embodiment, the electrochemical element is of the lithium-ion type.

[0117] 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.

[0118] 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 that is not covered with active material. It is connected to a current output terminal.

[0119] 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 container if the internal pressure of the electrochemical element exceeds a predetermined value.

[0120] 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).

[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 energy storage system, such as a battery.

[0126] 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.

[0127] The invention will become clearer upon reading the examples that follow, given only as a non-limiting example.

[0128] EXAMPLES

[0129] Preparation of the electrochemical elements described in Table 3

[0130] Electrochemical elements 1 to 6 can be manufactured according to the following method: They all comprise a positive electrode whose active material layer composition is specified in Table 1 and a negative electrode whose active material layer composition is specified in Table 2 below.

[0131] 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. 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 [Table 1].

[0132] The negative electrode can be prepared according to the mixtures described in Table 2 and coated onto 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.

[0133] [Table 2] (1): with a Si content of 30 to 70% by mass relative to the mass of the silicon-carbon composite particles, and with 20 to 60% Si-C by mass 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. 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). Internal resistance measurements were performed for a fixed state of charge of 50% and during a 30s discharge test at 3C regime at the beginning of the element's life (after 1 cycle) and after 1000 cycles.

[0134] The results obtained are presented in the following table:

[0135] [Table 3]

[0136] - (A) is the product between 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 of compound of formula (II), and the molar content of iron (% Fe ) in the compound of formula (I) expressed in relation to the total molar content of iron and manganese; (A) expresses the iron content in the active material of the positive active layer;

[0137] - (%Si) is the mass content of silicon in the active material of the negative active layer, expressed relative to the total mass of the active material of the negative active layer;

[0138] - (%Si / A) is the ratio between the mass content of silicon (%Si) in the active material of the negative active layer and the product (A); and

[0139] - (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).

[0140] 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.

[0141] Thus, for 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

DEMANDS 1. 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): 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, K, Pb, V, Mo, W, Hf, Bi, Se and any mixture thereof, 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): 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 < 1.1; 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, A being the product between the mass content of compound of formula (I) (%(l)) 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) 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 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.

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) (% ( i)) in the active material of the positive active layer expressed as a percentage of 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 with respect to the total molar content of iron and manganese in the compound (I), 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.

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. An electrochemical element according to any one of the preceding claims, wherein the particles comprising silicon are selected from silicon-carbon composite particles and silicon dioxide (SiO₂) particles. x 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% 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%.

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 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 in relation to 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 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%.

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.

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