LITHIUM-ION ELEMENT WITH ENERGY RESERVE

Abstract

LITHIUM-ION ELEMENT WITH ENERGY RESERVE The present invention relates to a lithium-ion electrochemical element based on lithium manganese iron phosphate (LMFP) and lithium metal oxide (LNMO) at the positive electrode and a silicon-carbon composite at the negative electrode, providing an energy reserve without compromising safety. Figure for abstract: None

Description

Title of the invention: LITHIUM ELEMENT- ION WITH ENERGY RESERVE

[0001] The present invention relates to the field of energy storage and lithium batteries in particular. More specifically, the present application relates to an electrochemical energy storage element, as well as the device comprising this element and an associated charger.

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

[0003] In Li-ion type elements, different mixtures of active materials have been proposed, both for the positive electrode and for the negative electrode.

[0004] Thus, the lithium manganese and iron phosphates of formula LixMni y zFeyMzPO4 (LMFP) with 0.8 <x<l,2 ; l-y-z> 0.5; 0.05 <y<0,5 et 0<z<0,2 sont connus pour leur utilisation comme matière active cathodique d’éléments lithium-ion. ces phosphates contiennent du manganèse, fer un ou plusieurs éléments substituants symbolisés par le symbole m. composés offrir une sécurité d’utilisation supérieure en raison fait que les lithiés de métaux transition stables à température élevée l’état chargé.

[0005] The mixture of a lithium phosphate with a lithium nickel oxide has been proposed.

[0006] Mixtures of a lithium phosphate and a lithium nickel oxide allow for better charge control and energy gain, but these may reduce the advantage of a lithium phosphate in terms of safety.

[0007] We are therefore constantly looking for compositions of active materials at the positive electrode which can improve energy gain, without affecting safety.

[0008] At the negative electrode, graphite is typically used as the active material.

[0009] A silicon-carbon composite, referred to as Si-C, has also been proposed. This composite exhibits a capacity approximately six times greater than that of graphite, but its capacity retention during cycling is lower.

[0010] Furthermore, for certain applications, it is desirable to provide batteries with an energy reserve that can be called upon, and only engaged on demand.

[0011] One object of the invention is therefore to provide an electrochemical element capable of triggering an additional energy reserve under load. To this end, consideration is given to increasing the operating voltage while maintaining a satisfactory cycle life and safety level.

[0012] To this end, the invention relates to an electrochemical element comprising: - A positive electrode comprising a composition of active materials comprising a mixture of:

[0013] at least one lithium manganese iron phosphate (LMFP) type compound corresponding to the formula (I): LixMni y zFeyMzPO4 (I)

[0014] in which

[0015] M is chosen from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo,

[0016] 0.8 <x<l,2;

[0017] 0,5 <l-y-z<l;

[0018] 0.05 < y < 0.5;

[0019] 0 < z < 0.2; and

[0020] at least one compound of the type of lithium metal oxide and of so-called spinel structure of formula (II):

[0021] Li. Mm. Ni. M\O; i; (LNMO) (II)

[0022] in which

[0023] M' represents one or more elements, identical or different, chosen from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Co, Cu, Zn, Y, Zr, Nb, Ru, W and Mo; and

[0024] 1 <x’<1,4 ; 0<y’<0,6 0<z’<0,2 0<d’<l 0<c’<l - A negative electrode comprising an active material composition including at least one silicon-carbon composite, known as Si-C; and - An electrolyte.

[0025] The element according to the invention includes an additional energy reserve that can be switched according to the applied charging voltage, without affecting the safety of the element.

[0026] As will appear below, the element according to the invention involves a synergy between the active materials of formula (I) and (II) of the active material composition of the positive electrode, and the active materials of the active material composition of the negative electrode.

[0027] This is made possible in particular by the addition of lithium metal oxide compounds with a so-called spinel structure of the LNMO type (II) to the active material composition of the positive electrode. These compounds (II) exhibit a high operating voltage (4.7 V relative to lithium) which compensates for their average capacitance and offers high safety. Thus, when the LMFP (I) and LNMO (II) type compounds are used in a mixture, their respective voltage plateaus (3.55 and 4.05 V relative to Li for LMFP, 4.7 V relative to Li for LNMO) allow the charge to be adjusted and used in two modes: one focused on the lifetime, where the LMFP is the only material to undergo (de)charge, and the other focused on energy, where the LMNO also participates in (de)charge.

[0028] Furthermore, LMFP (I) and LNMO (II) type compounds are both safer than lithium nickel oxides.

[0029] At the negative electrode, a mixture of Si-C and graphite typically exhibits a reversible capacitance of 1000 mAh / g against 350 mAh / g for graphite alone and ensures that the energy lost by relying solely on the LMFP is compensated by the higher energy density of the mixture of negative materials (compared to LMFP / pure graphite).

[0030] The present invention is therefore based on the synergy between the materials of the positive and negative electrodes to manufacture an element capable of providing additional energy by adjusting the maximum charging voltage, without compromising safety.

[0031] Thus, the elements according to the invention allow: - To ensure a satisfactory level of safety, by avoiding the use of lithium nickel oxides; - To increase the lifespan by performing a charge involving only compounds of formula (I) of type LMFP; - To provide additional energy, on demand, by triggering a charge involving compounds of formula (II) of type LNMO.

[0032] The term "energy reserve" refers to the energy stored by means of the capacitance of the compounds of formula (II). The energy thus stored in this reserve is defined as the charge (or capacitance) multiplied by the voltage under which this charge is discharged.

[0033] The energy reserve is therefore directly correlated to the capacity provided by the compounds of formula (II).

[0034] The electrodes

[0035] Each of the positive and negative electrodes is typically made up of a current collector covered by a composition of active materials.

[0036] The current collector for the positive and / or negative electrodes 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.

[0037] The current collector of the positive electrode is generally an aluminum strip or an alloy consisting mainly of aluminum. The current collector of the negative electrode is generally a copper strip or an alloy consisting mainly of copper. The thickness of the positive electrode strip may differ from that of the negative electrode strip.

[0038] According to one embodiment, the aluminum collector of the positive electrode is coated with a conductive coating, such as carbon black, graphite, 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.

[0039] Advantageously, the carbon coating can be applied to the collector in a solvent medium, for example in N-methyl-2-pyrrolidone / polyvinylidene fluoride (NMP / PVDF) medium.

[0040] The current collector of the negative electrode is generally a copper strip.

[0041] The term "active material composition" refers to all the electrochemically active materials that coat the current collector on at least one of its faces. Generally, this active material composition of the positive and / or negative electrode includes, in addition to the electrochemically active materials, electronically conductive materials, binders, and any additives, etc.

[0042] The expression "electrochemically active material" or "active material" typically refers to materials ensuring the reversible insertion of lithium.

[0043] The positive and / or negative active materials of the electrochemical element are generally mixed with one or more binder(s).

[0044] 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 composition of active materials to the current collector.

[0045] The binder can be selected from a butadiene-styrene copolymer (SBR), polyamideimide (PAI), polyimide (PI), polyvinyl alcohol, functionalized or non-functionalized polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) and its copolymers, polyacrylonitrile (PAN), poly(methyl)- or (butyl)methacrylate, polyvinyl chloride (PVC), poly(vinyl formyl), polyesters, sequenced polyetheramides, acrylic acid polymers, methacrylic acid, acrylamide, itaconic acid, sulfonic acid, elastomers, cellulosic compounds such as carboxymethylcellulose (CMC) and any mixture thereof.

[0046] These binders can typically be used for the positive electrode and / or the negative electrode.

[0047] The electronically conductive material provides electrical conduction and the percolation network. It can generally be chosen from graphite, carbon black, acetylene black, soot, graphene, carbon nanotubes or a mixture thereof.

[0048] Said composition may further include one or more additives, such as dispersants.

[0049] As a dispersant, polyvinylpyrrolidone (PVP) can be cited as a suitable dispersant for the invention.

[0050] The composition of active materials of the positive electrode

[0051] According to the invention, said composition of active materials for the positive electrode comprises a mixture of:

[0052] at least one lithium manganese iron phosphate (LMFP) type compound corresponding to the formula (I): LixMni y zFeyMzPO4 (I)

[0053] in which

[0054] M is chosen from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo,

[0055] 0.8 <x<l,2;

[0056] 0,5 <l-y-z<l;

[0057] 0.05 < y < 0.5;

[0058] 0 < z < 0.2; and

[0059] at least one compound of the type of lithium metal oxide and of so-called spinel structure of formula (II):

[0060] Li. Mm. Ni. M\O; i; (LNMO) (II)

[0061] in which

[0062] M' represents one or more elements, identical or different, chosen from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Co, Cu, Zn, Y, Zr, Nb, Ru, W and Mo; and

[0063] 1 <x’<1,4 ; 0<y’<0,6 0<z’<0,2 0<d’<l 0<c’<l.

[0064] The mixture of LMFP compounds of formula (I) and LNMO-type compounds of formula (II) allows access to complementary energy profiles, depending on the applied charging potential. This is made possible by the distinct operating voltages of each of these compounds, LMFP on the one hand and LNMO on the other, which have little or no overlap.

[0065] Thus, in operation at "low potential", only the LMFP type compound is involved, thereby ensuring operation that promotes cycle life.

[0066] Alternatively, in "high potential" operation, the LNMO-type compound is also involved. This therefore constitutes an energy reserve that can be triggered by the application of a higher potential, on demand, depending on the desired application, for example.

[0067] The term "low potential" means an applied load up to an applied voltage less than or equal to 4.2V.

[0068] The term "high potential" means a load applied up to an applied voltage strictly greater than 4.2 V, preferably between more than 4.2 V and 6 V, in particular approximately equal to 4.9 V.

[0069] According to one embodiment, the active ingredient composition comprises at least one compound of Formula (I) and at least one compound of Formula (II) mentioned above, as the sole active ingredients. In other words, according to this embodiment, said composition does not comprise lamellar lithia nickel oxide, of type NMC, type NCA, or type NMCA.

[0070] The term NMC-type compound refers to the lithia-cobalt oxides of nickel, manganese, and cobalt with the formula Liw(NixMnyCozMt)O2 with 0.9 <w<l,l ; 0<x<l,l 0<y< 1,1 0<z<l,l 0<t< et m choisi dans le groupe constitué de al, b, mg, si, ca, ti, v, cr, fe, cu, zn, y, zr, nb, w, mo, s, sr, ce, ta, ga, nd, pr, la leurs mélanges.

[0071] The term NCA-type compound refers to the lithia-coated oxides of nickel, cobalt and aluminum of formula Liw(NixCoyAlzMt)O2 with 0.9 <w<l,l ; 0<x<l,l 0<y< 1,1 0<z<l,l 0<t< et m choisi dans le groupe constitué de b, mg, si, ca, ti, v, cr, mn, fe, cu, zn, y, zr, nb, w, mo, sr, ce, ga, ta, nd, pr, la leurs mélanges.

[0072] NMCA is defined as a lithium oxide of nickel, manganese, cobalt and aluminum (NMCA) with the formula Liw(NixCoyAlzMnt)O2 where 0.9 <w<l,l ; 0<x<l,l 0<y< 1,1 0<z<l,l 0<t< 1,1, plus particulièrement 0,83< x.

[0073] According to this embodiment, the active materials consist of a mixture of one or more compound(s) of Formula (I) and one or more compound(s) of Formula (II) mentioned above.

[0074] According to one embodiment, the active material composition of the positive electrode comprises:

[0075] From 75 to 95% of a compound of formula (I); and

[0076] From 5 to 25%, preferably from 5 to 15% of a compound of formula (II);

[0077] The percentages are understood to be by weight, relative to the total weight of the mixture of active materials of the active material composition of the positive electrode.

[0078] According to one embodiment, the compound of formula (I) is chosen from compounds having an average operating voltage relative to the lithium torque less than or equal to 4.1V.

[0079] The average operating voltage with respect to the lithium torque is understood to be the quotient obtained by dividing the integrated area of ​​the voltage curve as a function of the capacity by the maximum capacity reached during discharge.

[0080] Typically, the compound of formula (I) can be chosen from LiMnoj8Feoj2P04, LiMnoj7Feoj3P04, LiMn2 / 3Fei / 3PO4 and LiMn03Fc()3PO4.

[0081] According to one embodiment, the spinel-type compound of formula (II) is chosen from compounds having an average operating voltage relative to the lithium torque strictly greater than 4.1V.

[0082] It can in particular be chosen from compounds of formula (II-A):

[0083] LiNi1 / 2Mn3 / 2M'z.O4(II-A)

[0084] where M' represents Fe and / or Co, et0 <z’<0,2, notamment le composé linii 2mn3 2o4.

[0085] Thus, according to one embodiment, the positive electrode comprises a composition of active materials comprising a mixture of:

[0086] A compound selected from LiMnOj8FeOj2PO4, LiMnOj7FeOj3PO4, LiMn2 / 3FeI / 3PO4 and LiMnO5FeOj5PO4, and

[0087] A compound of formula (II-A) LiNii / 2Mn3 / 2M'z O4(II-A) where M' represents Fe and / or Co, et0 <z’<0,2.

[0088] The composition of active materials of the negative electrode

[0089] According to the invention, the active material composition of the anode comprises at least one silicon-carbon composite called Si-C.

[0090] The silicon-carbon composite can be produced from carbon materials comprising a pore volume including micropores, mesopores, and / or macropores. These carbon mixtures can serve as scaffolds for the creation of silicon-carbon composite materials, for example, by impregnating porous carbon materials with silicon, according to methods known per se.

[0091] According to one embodiment, the active material composition of the negative electrode further comprises graphite.

[0092] Thus, according to one embodiment, the negative electrode comprises a composition of active materials comprising graphite and the Si-C composite;

[0093] Typically, the active material composition of the negative electrode comprises:

[0094] From 20% to 100%, preferably from 20% to 80%, particularly from 40% to 60% of Si-C composite; and

[0095] From 0 to 80%, preferably from 20 to 80%, particularly from 40 to 60% of graphite;

[0096] The percentages are understood to be by weight, relative to the total weight of the mixture of active materials of the active material composition of the negative electrode.

[0097] According to one embodiment, the electrochemical element comprises: - A positive electrode comprising an active material composition including a mixture of:

[0098] A compound selected from LiMnOj8FeOj2PO4, LiMnOj7FeOj3PO4, LiMn2 / 3FeI / 3PO4 and LiMnO5FeOj5PO4, and

[0099] A compound of formula (ILA) LiNii / 2Mn3 / 2M'z O4(II-A) where M' represents Fe and / or Co, et0 <z’<0,2; - A negative electrode comprising an active material composition including graphite and the Si-C composite; and - An electrolyte.

[0100] The electrolyte

[0101] The electrolyte may be liquid and comprise a lithium salt dissolved in an organic solvent.

[0102] The lithium salt may be selected 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), lithium difluorophosphate LiPO2F2 and mixtures thereof.

[0103] The electrolyte in liquid form is obtained by dissolving one or more lithium salts in one or more organic solvents.

[0104] The solvent can be chosen from saturated cyclic carbonates, unsaturated cyclic carbonates, non-cyclic carbonates, alkyl esters, ethers, nitrile-type solvents and tetrahydrothiophene dioxide (sulfolane), ethylene sulfate (ESA).

[0105] Saturated cyclic carbonates include ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), butylene carbonate (BC), and mixtures thereof.

[0106] 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.

[0107] Alkyl esters include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and mixtures thereof.

[0108] Ethers include dimethyl ether (DME), diethyl ether (DEE) and mixtures thereof.

[0109] As an alternative, the electrolyte may be a solid. It may be a lithium-ion-conducting compound, chosen for example from lithium-ion-conducting oxides and lithium ion-conducting sulfides. The electrolyte can also be a lithium ion-conducting polymer, such as polyethylene oxide (PEO), polyphenylene sulfide (PPS) and polycarbonate.

[0110] 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.

[0111] Electrode manufacturing

[0112] Generally, an electrode can be manufactured by preparing an ink comprising one or more active materials mixed with a solvent or a mixture of several solvents, with one or more binders, and optionally with one or more electronically conductive materials and possible additives.

[0113] This ink can then be coated on at least one of the faces of a current collector.

[0114] The ink can then be dried.

[0115] The thickness of the ink thus coated can then be adjusted in a calendering step, by passing the electrode between two rollers exerting pressure on the surface of the electrode.

[0116] After evaporation of the solvent(s) by drying, a composition is obtained comprising the electrochemically active materials, electronically conductive materials, binders, and possible additives.

[0117] The separator

[0118] The electrochemical element comprises a separator between the positive and negative electrodes. 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.

[0119] Manufacturing of an element

[0120] According to one embodiment, the electrochemical element is of the lithium-ion type.

[0121] A lithium-ion element can be manufactured conventionally. 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. 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 bundle. electrochemical plane. A connecting piece is fixed to an edge of the cathode not covered with active material. It is connected to a current output terminal.

[0122] The anode can be electrically connected to the element container. Conversely, the cathode can be connected to the element container and the anode to a current output terminal. After being inserted into the element container, the electrochemical bundle is impregnated with electrolyte. The element is then hermetically sealed. The element can also be conventionally equipped with a safety valve that opens the element container if the internal pressure of the element exceeds a predetermined value.

[0123] Use of the electrochemical element

[0124] Due to the discharge profiles of the compounds of Formula (I) and (II) (absence of overlap of the voltage plateaus), the elements according to the invention allow to operate in two different modes (bimodal operation), switchable from one to the other, by modification of the maximum voltage applied during charging.

[0125] According to another object, the present invention therefore also relates to the use of an electrochemical element according to the invention to extend its life, comprising one or more charge and discharge cycles, the charge being carried out up to a voltage applied to the element less than or equal to 4.2 V.

[0126] In this operation (the so-called "low potential" operating mode), only the compound of formula (I) as the active material of the positive electrode is involved. Due to the stability of the compounds of formula (I) at high temperatures, this use allows for a high level of operational safety, and consequently, a long cycle life of the element is expected.

[0127] According to another object, the present invention further relates to the use of an electrochemical element according to the invention to extend its autonomy, comprising one or more charge and discharge cycles, the charge being carried out up to a voltage applied to the element of between more than 4.2 V and 6 V, in particular between more than 4.2 V and 5 V.

[0128] In this operation (the so-called "high potential" operating mode), the compound of formula (II) is also involved as the active material of the positive electrode. The combination of compounds of formulas (I) and (II) allows for a long battery life.

[0129] Device

[0130] According to another object, the present invention further relates to a device comprising:

[0131] at least one electrochemical element according to the invention; and

[0132] a charger powering said at least one electrochemical element, said charger allowing switching between the two charging modes M1 and M2, such that mode M1 is implemented up to a voltage applied to the element less than or equal to 4.2 V, and the second mode M2 ​​is carried out up to a voltage between 4.2 V and 6 V, preferably 4.9 V.

[0133] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0134] [Fig-1] [Fig.1] represents the discharge profiles (D / 10) for the LMFP compound of formula LiMno.8Feo.2PO4 and the compound LNMO of formula (II) LiNii / 2Mn3 / 2O4.

[0135] [Fig.2] Fig.2 represents the discharge profiles (D / 10) for graphite, the Si-C composite and Si-C:graphite mixture (40:60), for a negative electrode comprising a copper current collector.

[0136] [Fig.3] Fig.3 represents the evolution of the specific energy (in Wh / litre) for a stacking of elements comprising the following active materials, respectively at the following cathode and anode: i. LMFP / / graphite ii. 95% LMFP-5% LNMO / / Si-C: graphite (40:60%) iii. 90% LFMP-10% LNMO / / Si-C: graphite (40:60%) iv. 75% LFMP-25% LNMO / / Si-C: graphite (40:60%) v. 50% LFMP-50% LNMO / / Si-C: graphite (40:60%)

[0137] Histograms ii-v illustrate the possible involvement of compounds of formula (II) in bimodal functioning:

[0138] The darkest fraction of the histograms represents the energy in operation at low potential, involving compounds of formula (I) without activation of compounds of formula (II), while the lightest fraction of the histograms represents the energy in operation up to higher potential, with the involvement of compounds of formula (II). Examples

[0139] One embodiment thus consists of preparing a positive electrode containing a mixture of active materials consisting of 90% LMFP and 10% LNMO (by mass), representing more than 90% by mass of the materials coated on the positive current collector, to which a conductive carbon additive and a PVDF-type binder are also added, the sum of which is less than 10% by mass of the coated materials. On the other hand, a negative electrode is prepared consisting of 40% Si-C and 60% graphite, representing more than 90% by mass of the materials coated on the negative current collector, to which a conductive carbon additive and a mixture of CMC and SBR-type binders are also added, the sum of which is less than 10% of the coated materials. An element is then prepared by assembling these two electrodes and a separator and inserting them into a metal cup at the terminals of which The electrodes will be connected. This element is then cycled over a potential range between 2.5 and 4.2 V in use to maximize lifespan and then over an extended potential range between 2.5 and 4.9 V in order to maximize energy.

[0140] Properties of the active materials for the positive electrode

[0141] [Tables 1] Material Reversible Capacity (D / 5) Average E (y s. Li) Density Safety Cycle Life LiMn0.8Fe0.2PO4 140 mAh / g 3.85 V 3.29 g / cm³ Excellent Excellent LiNi i^Mn^Cl 137 mAh / g 4.7 V 4.42 g / cm³ Very Good Average

[0142] Table 1. Characteristics of representative LMFP and LNMO positive electrode materials

[0143] Fig. 1 demonstrates the existence of two distinct plateaus, without significant overlap of the compounds of formula (I) (4.1V) and the compounds of formula (II) (4.7V), respectively.

[0144] This result allows bi-modal operation, the (II) compounds constituting an energy reserve, activated in operation at high potential (greater than 4.7V).

[0145] Properties of the active materials for the negative electrode

[0146] [Tables2 Material Reversible Capacity (D / 5) Average E (y s. Li) Density Safety Other characteristics Graphite 350 mAh / g 0.1 V 2.2 g / cm3 Average High cycle life Si-C compound 2000 mAh / g 0.4 V 2.2 g / cm3 Same as graphite (DSC method) Average cycle life Tendency to swell Si-C:graphite mixture (40:60) Proportional Proportional 2.2 g / cm3 Average

[0147] Table 2. Characteristics of graphite, Si-C and Si-C mixture. Graphite as representative active materials for the negative electrode.

[0148] Fig. 2 illustrates the gain provided by the Si-C composite in the graphite: Si-C mixture.

[0149] Synergy of the active materials of the positive and negative electrodes

[0150] Figure 3 shows the evolution of several combinations of active materials at the positive and negative electrodes compared to an element based on LMFP / graphite: i. LMFP / / graphite ii. 95% LMFP-5% LNMO / / Si-C: graphite (40: 60%) iii. 90% LFMP-10% LNMO / / Si-C: graphite (40: 60%) iv. 75% LFMP-25% LNMO / / Si-C: graphite (40: 60%) v. 50% LFMP-50% LNMO / / Si-C: graphite (40: 60%)

[0151] As demonstrated in [Fig.3], the addition of 5% to 25% (by weight) of compound of formula (II) LNMO in the active material composition of the positive electrode and of Si-C+graphite (1000 mAh / g) in the active material composition of the negative electrode makes it possible to obtain a satisfactory energy level at low potential (+2% to -21% Wh / 1) compared to the reference element (LMFP / / graphite), making it possible to optimize the lifetime of the element.

[0152] Furthermore, such an element provides an additional available energy reserve by activating the compound of formula (II) LNMO, thus leading to an increase in total energy (+14.8% to +22.3% Wh / L) compared to the reference element (LMFP / graphite). This high-potential activatable mode increases the element's autonomy. < / x<l,2;> < / x<l,2;>

Claims

Demands

1. Electrochemical element comprising: - A positive electrode comprising an active material composition comprising a mixture of: at least one lithium manganese iron phosphate (LMFP) compound corresponding to the formula (I): LixMni y zFeyMzPO4 (I) in which M is selected from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo, 0.8 <x<l,2; 0,5<l-y-z<l; 0,05< y <0,5; 0< z <0,2 ; et au moins un composé de type oxyde de métal lithié et de structure dite spinelle de formule (II) : Ei. Mm. z NUM^O; , I-, (LNMO) (II) dans laquelle M’ représente un ou plusieurs éléments, identiques ou différents, choisis dans le groupe consistant en B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Co, Cu, Zn, Y, Zr, Nb, Ru, W et Mo; et 1<x’<1,4 ; 0<y’<0,6 ; 0<z’<0,2 ; 0<d’<l ; 0<c’<l ; - Une électrode négative comprenant une composition de matières actives comprenant au moins un composite silicium-carbone dit Si-C ; et - Un électrolyte.

2. Electrochemical element according to claim 1 such that the spinel-type compound is selected from compounds having an average operating voltage relative to the lithium torque strictly greater than 4.1V.

3. Electrochemical element according to claim 1 or 2 such that the compound of formula (II) is selected from the compounds of formula (II-A): LiNi1 / 2Mn3 / 2M'z.O4(II-A) where M' represents Fe and / or Co, et0 <z’<0,2, notamment le composé LiNii / 2Mn3 / 2O4.

4. Electrochemical element according to any one of the preceding claims such that the active material composition of the positive electrode comprises: From 75 to 95% of a compound of formula (I); and From 5 to 25%, preferably from 5 to 15% of a compound of formula (II); The percentages being understood as weights, relative to the total weight of the active material mixture of the active material composition of the positive electrode.

5. Electrochemical element according to any one of the preceding claims, such that the compound of formula (I) is selected from LiMnO2Fe2PO4, LiMnO2Fe2PO4, LiMnO2 / 3Fe2PO4, LiMnO2 / 3Fe2PO4 and LiMnO2 / 3Fe2PO4 and LiMnO2 / 3Fe2PO4

6. Electrochemical element according to any one of the preceding claims such that the active material composition of the negative electrode further comprises graphite.

7. Electrochemical element according to any one of the preceding claims such that the active material composition of the negative electrode comprises: From 20% to 100%, preferably from 20% to 80%, particularly from 40% to 60% of Si-C composite; and From 0% to 80%, preferably from 20% to 80%, particularly from 40% to 60% of graphite; The percentages being understood as weights, relative to the total weight of the active material mixture of the active material composition of the negative electrode. [Claim 8FeO2PO4, LiMnO2 / 7FeO2 / 3PO4, LiMn2 / 3FeO2 / 3PO4 and LiMnO2 / 3FeO2 / 3PO4 and LiMnO2 / 3FeO2 / 3PO4 and a compound of formula (ILA) LiN2 / 2Mn3 / 2MnO4(II-A) where M' represents Fe and / or Co, and <z’<0,2; - Une électrode négative comprenant une composition de matières actives comprenant du graphite et le composite Si-C ; et - An electrolyte.

9. Use of an electrochemical element as defined according to any one of the preceding claims to extend its service life, comprising one or more charge and discharge cycles, the charge being carried out up to a voltage applied to the element less than or equal to 4.2 V.

10. Use of an element as defined according to any one of claims 1 to 8 to extend its autonomy, comprising one or more charge and discharge cycles, the charge being carried out up to a voltage applied to the element of between plus 4.2 V and 6 V, in particular less than 5 V.

11. Device comprising: at least one electrochemical element according to any one of claims 1 to 8; and a charger supplying said at least one electrochemical element enabling switching between the two charging modes M1 and M2, such that mode M1 is realized up to a voltage less than or equal to 4.2 V, and the second mode M2 ​​is realized up to a voltage applied to the element of between 4.2 V and 6 V, preferably 4.9 V.

Images