Electrochemical element with a very long calendar lifetime

Abstract

Electrochemical element with a very long calendar lifetime. The present invention relates to a positive electrode composition comprising a) as electrochemically active materials: i) a lithium phosphate compound of manganese and iron of formula LixMn1-y-zFeyMzPO4 (LMFP) with 0.8≤x≤1.2; 0.5≤1-yz<1; 0

Description

Title of the invention: Electrochemical element with a very long calendar lifetime

[0001] The present invention relates to the field of energy storage and lithium batteries in particular. More specifically, the present application relates to a composition for a positive electrode, a positive electrode, an electrochemical element, and a battery comprising said composition.

[0002] The invention is particularly useful for rechargeable electrochemical elements and / or electricity storage of the lithium-ion (Li-ion) type, more particularly for such elements associated with phosphate technology and applied to renewable energies.

[0003] Rechargeable lithium-ion electrochemical cells using phosphate technology are known in the prior art. Due to their safety performance and cycle life, they represent a promising source of electrical energy, particularly in the field of renewable energies, which are currently experiencing rapid development due to environmental concerns. They comprise at least one positive electrode and at least one negative electrode, and an electrolyte.

[0004] However, the specifications for batteries using such elements are becoming increasingly stringent, particularly in terms of calendar life, an issue just as critical for the environment as the energy source itself. The challenge, therefore, is to achieve very long calendar lives for such types of batteries while maintaining all the other required characteristics of power, energy, and rapid cycling.

[0005] The calendar life corresponds to the period from the date of production until the end of a battery's life. Indeed, a battery undergoes calendar aging, impacted in particular, for example, by its state of charge and / or by thermal variations or extreme temperatures that it may experience during or even before its use. Furthermore, during use, it is known that the calendar life of Li-ion cells decreases when the specific surface area of ​​the carbon electronic conductor in the positive electrode is increased due to the surface reactivity of the electronic conductor with the electrolyte.

[0006] Unexpectedly, the present inventors discovered that the addition of single-walled carbon nanotubes (SWCNTs) to a positive electrode containing electrochemically active materials of the LMFP and NMC type, as described below, improves the calendar lifetime of Li-ion elements, even if the total specific surface area of ​​the carbon conductors in the electrode is not decreased or is even increased. Contrary to expectations, this improvement in calendar lifetime is not obtained with other carbon nanotubes, particularly with conventional carbon nanotubes such as multi-walled carbon nanotubes (MWCNTs).

[0007] The invention therefore relates to a positive electrode composition comprising: a) as electrochemically active substances: - a lithium phosphate compound of manganese and iron of formula LixMnby_ zFeyMzPO 4 (LMFP) with 0.8 <x<l,2 ; 0,5<l-y-z<l ; 0<y<0,5 ; 0<z<0,2 et M est choisi dans le groupe constitué de B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb, S, W, K, Pb, V, Mo, Hf, Bi, Se et leurs mélanges ; et - a lithium nickel, manganese and cobalt oxide (NMC) compound of the formula Liw(NixMnyCozMt)O2 with 0.9 <w<l,l ; 0<x<l,l ; 0<y<l, 1 ; 0<z<l,l ; 0 <t< 1,1 ; et M choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et leurs mélanges ; et b) à titre de conducteur électronique : - more than 0.01% by weight of single-walled carbon nanotubes (SWCNTs) relative to the total weight of the composition, preferably more than 0.05% and even more preferably more than 0.1% by weight relative to the total weight of the composition.

[0008] According to other advantageous aspects of the invention, the composition according to the invention comprises one or more of the following characteristics, taken individually or in all technically possible combinations.

[0009] The term "composition" or "positive electrode composition" means a composition which covers the current collector of an electrode on at least one of its faces.

[0010] It is obtained from an ink prepared with said ingredients, generally in a solvent medium such as N-Methyl-2-pyrrolidone (NMP) for example, intended to be coated on the collector, then subjected to drying and calendering in order to produce said composition.

[0011] Generally, this composition of the positive electrode includes, in addition to electrochemically active materials, electronically conductive materials, binders and possible additives.

[0012] According to one embodiment, the composition according to the invention is suitable for a positive electrode, in particular for electrochemical elements of the Li-ion type in which the electrochemically active material of the positive electrode is of the phosphate type. Electrochemically active materials#

[0013] The composition according to the invention comprises, as electrochemically active materials, preferably consisting of: - a lithium phosphate compound of manganese and iron with the formula LixMniy_ zFeyMzPO 4 (LMFP) with 0.8 <x<l,2 ; 0,5<l-y-z<l ; 0<y<0,5 ; 0<z<0,2 et M est choisi dans le groupe constitué de B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb, S, W, K, Pb, V, Mo, Hf, Bi, Se et leurs mélanges ; et - a lithium nickel, manganese and cobalt oxide (NMC) compound of the formula Liw(NixMnyCozMt)O2 with 0.9 <w<l,l ; 0<x<l,l ; 0<y<l, 1 ; 0<z<l,l ; 0<t< 1,1 ; et M choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et leurs mélanges

[0014] The expression "electrochemically active material" typically refers to materials that are the site of the electrochemical reaction.

[0015] Lithium phosphate compound of manganese and iron of formula Li x Mn Fe v M z PO 4 (LMFP)

[0016] The composition according to the invention comprises at least one lithium manganese iron phosphate compound (LMFP) of formula:

[0017] LixMnby_ zFeyMzPO4

[0018] with

[0019] 0.8 <x<l,2 ;

[0020] 0.5 <l-y-z<l ;

[0021] 0 <y<0,5 ;

[0022] 0 <z<0,2 et

[0023] 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 mixtures thereof

[0024] According to one embodiment, the LMFP compound has a Fe / Mn molar ratio of 20 / 80 to 50 / 50, preferably of 30 / 70.

[0025] According to one embodiment, 0.7 <l-y-z<0,9.

[0026] According to another embodiment, 0.7 <l-y-z<0,85.

[0027] As examples of LMFP type active material, we can cite for example the compounds of formula LiMno8Feo>2P04, LiMno 7Feo 3P04, LiMn2 / 3Fei / 3PO4, LiMno 6Feo4P04 and LiMn0>5 Fe0j5PO4.

[0028] Nickel, manganese and cobalt (NMC) oxide type compound of formula Li w, (Ni x Mn v Co ZM t )O 2

[0029] The composition according to the invention comprises at least one nickel manganese cobalt lithium oxide (NMC) compound of formula

[0030] Liw(NixMnyCozMt)O2

[0031] with

[0032] 0.9 <w<l,l ;

[0033] 0 <x<l,l ;

[0034] 0 <y<l,l ;

[0035] 0 <z<l,l ;

[0036] 0 <t<l,l;et

[0037] M 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 their mixtures.

[0038] M can in particular be chosen from the group consisting of Al, B, Mg and mixtures thereof. Preferably, M is Al and t<0.05. The major transition element is preferably nickel, preferably x>0.6. A high amount of nickel in the lithium nickel oxide is preferable because it provides high energy to the lithium nickel oxide.

[0039] According to one embodiment, the NMC compound has a nickel content of 60% to 88%.

[0040] As examples of nickel-rich lithium oxide compounds of nickel, manganese and cobalt (NMC), the following compounds may be cited in particular:

[0041] Li1(Ni0.6Mno.2Coo.2)02 (NMC 622),

[0042] Li1(Ni0.6Mn0.3Co0.i)O2 (NMC 631),

[0043] Li^Nio.8 3Mn0. osCoo.! 2)O2 (NMC 811).

[0044] According to one embodiment, the LMFP / NMC mass ratio is from 30 / 70 to 90 / 10, preferably from 40 / 60 to 80 / 20, more preferably from 60 / 40 to 80 / 20.

[0045] According to one embodiment, the composition of the positive electrode is substantially free of nickel, cobalt, and aluminum (NCA) lithium oxide compounds of the 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, fe, cu, zn, y, zr, nb, w, mo, sr, ce, ga, ta, nd, pr, la leurs mélanges.

[0046] Here, "substantially free" means a composition comprising less than 10% by weight of NCA compound relative to the total weight of the composition, preferably less than 5% by weight, more preferably less than 1% by weight of NCA compound relative to the total weight of the composition.

[0047] According to one embodiment, the electrochemically active materials of the composition according to the invention consist of a mixture of an LMFP compound as described above and an NMC compound as described above. Electronic driver(s)

[0048] Single-walled carbon nanotubes (SWCNTs)

[0049] The composition according to the invention comprises, as an electronic conductor, more than 0.01% by weight of single-walled carbon nanotubes (SWCNTs) relative to the total weight of the composition, preferably more than 0.05% and even more preferably more than 0.1% by weight relative to the total weight of the composition.

[0050] In general, carbon nanotubes (CNTs) are an allotropic form of carbon belonging to the fullerene family. They are composed of sheets of carbon atoms rolled up on themselves forming a tube.

[0051] The term "carbon nanotubes", designated by the acronym CNT, generally refers to multi-walled carbon nanotubes ("multi-walled carbon nanotubes" in English, whose acronym is "MWCNT"). Such multi-walled nanotubes typically have an outer diameter of the order of 10 to 25 nm.

[0052] The composition according to the invention comprises, for its part, more than 0.01% by weight of single-walled carbon nanotubes (SWCNTs). These are therefore composed of a single sheet of carbon atoms rolled up on itself and forming a tube. They have a smaller outer diameter than MWCNTs.

[0053] Unexpectedly, the present inventors discovered that only the addition of specific carbon nanotubes, namely single-walled carbon nanotubes (SWCNTs), improves the calendar lifetime of Li-ion cells in a positive electrode containing electrochemically active materials of the LMFP and NMC type. This improvement was demonstrated even if the total specific surface area of ​​the carbon conductors in the electrode is not decreased, or is even increased.

[0054] According to one embodiment, the single-walled carbon nanotubes have an outside diameter of 1 to 4 nm, preferably of 1.5 to 2 nm.

[0055] The outside diameter is evaluated by transmission electron microscopy imaging.

[0056] According to one embodiment, the single-walled carbon nanotubes have a length of more than 5 pm, this length being preferably measured by atomic force microscopy (AFM).

[0057] According to one embodiment, the single-walled carbon nanotubes have a ratio between the G and D peaks, measured by Raman spectroscopy, greater than 70.

[0058] The SWCNTs referred to herein act as percolating electronic conducting agents in the composition according to the invention.

[0059] According to one embodiment, the single-walled carbon nanotubes have a specific surface area SSA greater than 300 m2 / g, preferably from 300 to 600 m2 / g, more preferably from 300 to 450 m2 / g.

[0060] The specific surface area can be measured by the BET method (Brunauer, Emmett, and Teller Theory), based on the assumption that the adsorbed gas molecules are located in monomolecular layers on the surface of the material (gas physisorption). The amount of gas adsorbed at a given pressure is measured (adsorption isotherm curve) and used to calculate the specific surface area using the BET equation.

[0061] The procedure for measuring specific surface area by the BET method is indicated in ASTM D6556-21.

[0062] Additional conductor

[0063] The composition according to the invention may include at least one additional electronic conductor. Preferably, it may be chosen from: graphite, carbon black, acetylene black, soot, graphene and any mixture thereof, preferably carbon black.

[0064] The carbon black(s) referred to herein act as percolating electronic conducting agent(s) in the composition of the positive electrode.

[0065] Carbon black is a partially crystalline carbonaceous product resulting from the partial decomposition of hydrocarbons which has a structure in the form of primary particles, connected in aggregates and possibly agglomerated.

[0066] Thus, carbon black can be obtained from: - acetylene black, for example by thermal decomposition at 1200°C; - furnace black, for example by gaseous phase recovery with a water curtain in a furnace, - soot, - lamp black, - black thermal with natural gas, or - black in the tunnel from the walls of the furnace.

[0067] In particular, graphite, graphene, fullerene, carbon fibers, carbon nanotubes and activated carbon do not fall within the definition of the term "carbon black".

[0068] Carbon black typically has a divided appearance. It can be characterized by the specific surface area (SSA) of the primary particle aggregates.

[0069] The primary particle size of carbon black can typically be between 20 nm and 100 nm.

[0070] According to one embodiment, the electronic conductor(s) of the present invention have a total surface area greater than 150 m2 per 100 g of dry matter of the composition, preferably from 250 to 2500 m2 per 100 g of dry matter of the composition. Link(s)

[0071] The term "binder" means a compound that strengthens the cohesion between the particles of the composition, the adhesion of the composition to the current collector, and improves the viscosity of the ink.

[0072] According to one embodiment, the composition of the positive electrode further comprises at least one binder selected from functionalized or non-functionalized vinylidene fluoride homopolymers, non-functionalized vinylidene fluoride (PVDF) and / or hexafluoropropylene (HFP) copolymers, 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, cellulosic compounds and any mixture thereof, preferably vinylidene fluoride (PVDF) homopolymers, in particular homopolymers of functionalized polyvinylidene fluoride (PVDF) exhibiting a grafting rate greater than or equal to 5% by mass, relative to the total mass of the homopolymer.

[0073] According to a preferred embodiment, the composition comprises at least one vinylidene fluoride (PVDF) homopolymer as a binder.

[0074] Preferably, the binder is present at a concentration of 0.05 to 5% by weight, preferably 2 to 3% by weight relative to the total weight of the composition. Additive(s)

[0075] Said composition may further include one or more additives such as dispersants.

[0076] Polyvinylpyrrolidone (PVP) can thus be cited as a suitable dispersant for the invention.

[0077] According to one embodiment, the composition comprises, as a percentage by weight relative to the total weight of the composition:

[0078] - from 80 to 98%, preferably from 85% to 95% of electrochemically active;

[0079] - from 0.5 to 10%, preferably 2 to 5%, of one or more conductive materials electronics;

[0080] - from 0.5 to 10%, preferably 1 to 5% of one or more binders;

[0081] - from 0 to 1%, preferably from 0.01 to 1% of one or more dispersants. Positive electrode

[0082] The electrode typically consists of a current collector covered on at least one of its faces by the composition according to the invention.

[0083] Typically, the electrode acts as a positive electrode.

[0084] A metal strip can act as a current collector.

[0085] Said metal strip may be made of aluminium or an alloy comprising mainly aluminium, possibly covered with a conductive material, such as carbon.

[0086] Advantageously, the metal strip is made of carbon-coated aluminum.

[0087] Electrode repair

[0088] Generally, an electrode can be manufactured by preparing an ink comprising the components of the composition mixed with a solvent, which is then coated onto the current collector. The ink can be dried in an oven, a furnace, and / or by infrared to evaporate the solvent. After evaporation of the solvent(s), a composition is obtained that constitutes the material of the electrode. The ink thus ultimately gives rise to the composition of the positive electrode.

[0089] The ink coated on the collector and then dried can then be subjected to a calendering step, by passing the electrode between two rollers exerting pressure on the surface of the electrode.

[0090] In addition to at least one positive electrode, the electrochemical elements also comprise at least one negative electrode and an electrolyte and, optionally, a separator. Negative electrode

[0091] The negative electrode comprises a current collector, at least one face of which is coated with a layer of a negative active material composition. The current collector is prepared in a conventional manner. The negative electrode active material is not particularly limited. It can be selected from the following groups and mixtures thereof:

[0092] - Metallic lithium or a metallic lithium alloy

[0093] - Graphite

[0094] - Silicon

[0095] - Anode-free type

[0096] - a titanium niobium oxide of the TNO type

[0097] - a lithia-bound titanium oxide or a titanium oxide capable of being lithia-bound, of the LTO type.

[0098] Examples of lithiased titanium oxides are spinel LqTisOn, Li2TiO3, ramsdellite Li2Ti3O7, LiTi2O4, LixTi2O4, with 0 <x<2 et li2na2ti60i4.

[0099] A preferred LTO compound has the formula Lq aMaTi5 bM'bO4, for example Li4Ti50i2 which can also be written Li4 / 3Ti5 / 3O4.

[0100] The term "negative electrode" refers to the electrode operating as the anode when the battery is discharging, and the electrode operating as the cathode when the battery is charging. Electrolyte

[0101] The electrolyte may be liquid and comprise a lithium salt dissolved in a mixture of organic solvents.

[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).

[0107] Non-cyclic carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dipropyl carbonate (DPC), and mixtures thereof.

[0108] Alkyl esters include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and mixtures thereof.

[0109] Ethers include dimethyl ether (DME), diethyl ether (DEE) and mixtures thereof.

[0110] 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 may also be a lithium-ion-conducting polymer, such as polyethylene oxide (PEO), polyphenylene sulfide (PPS), and polycarbonate.

[0111] 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. Separator

[0112] The electrochemical element may include 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. Use of an electrochemical element

[0113] The invention also relates to the use of an electrochemical element comprising a positive electrode comprising a composition such as described above to improve the calorific vacuum duration of said electrochemical element.

[0114] By way of example, a protocol for evaluating the calendar lifetime of an electrochemical element may be such as that described in the example in this application.

[0115] The invention also relates to a positive electrode comprising the composition as described above.

[0116] The invention finally relates to an electrochemical element comprising a positive electrode as described above and a battery comprising one or more of these electrochemical elements.

[0117] The electrochemical elements or batteries according to the present invention have an improved calendar life as demonstrated below.

[0118] The invention will become clearer upon reading the following examples given solely by way of illustration, not limitation of the invention. Examples

[0119] In the examples below, the positive electrode comprises a current-collecting support which is a carbon-coated aluminum strip. A homogeneously mixed layer of a paste composition, consisting of a paste after solvent evaporation, is deposited onto this support by coating: • as electrochemically active substances and electronic conductors, the compounds described in Table 1 below; • as a binder, a polymeric binder of the polyvinylidene fluoride PVDF type (K1300 supplied by the company Kureha) at a rate of 2.5% by weight relative to the total dry weight of the composition; • as a dispersant, a polyvinylpyrrolidone PVP type dispersant (K30 supplied by Sima Aldrich) at a rate of 0.05% by weight relative to the total dry weight of the composition.

[0120] Composition of table 1:

[0121] The percentages of each of the compounds are given as a percentage by weight (w%) relative to the dry weight of the composition detailed above. Electrochemically active substances

[0122] _ LMFP: lithium phosphate compound of manganese and iron of formula LiiMno.7Feo.3 PO4.

[0123] Unless otherwise stated in Table 1 (compositions 1-9 and 12-16), the LMFP compound has a stoichiometric Mn / Fe ratio of 70 / 30. This ratio is 60 / 40 for compositions 10 and 11.

[0124] _ NMC1: nickel, manganese and cobalt (NMC) oxide type compound of formula Lii(Nio.83Mno.o5Co0.i2)02 (NMC811)

[0125] _ NMC2: nickel, manganese and cobalt (NMC) oxide type compound of formula Lii(Nio.6Mno.2Coo.2)02 (NMC622)

[0126] _ NCA: nickel, cobalt and aluminium lithium oxide compound (NCA) of formula Li1(Ni0.8oCoo.i5Alo.o5)02 Electronic conductors

[0127] _ SWCNT: single-walled carbon nanotubes (outer diameter = 1.7 nm; SSA = 350 m2 / g; length: more than 5 pm measured by AFM; ratio between peaks G and D, measured by Raman spectroscopy, greater than 70)

[0128] _ MWCNT: multi-walled carbon nanotubes (outer diameter = 12 nm; SSA = 250 m2 / g; length: approximately 1 pm measured by AFM; ratio between peaks G and D, measured by Raman spectroscopy, less than 1)

[0129] _ NCI: SSA carbon black = 100 m2 / g

[0130] _ NC2: SSA carbon black = 790 m2 / g

[0131] Carbon surface percolating electronic conductors:

[0132] The surface area of ​​percolating carbon reported in Table 1 is calculated as follows: considering 100g of the dry extract of the ink from the composition of the positive electrode, the surface area (in m2) is calculated as the sum of the products of each of the specific surfaces of the percolating carbons (m2 / g) multiplied by their mass in 100g of dry extract (g).

[0133] For example, for example 1, there is 2.65% of NCI at 100 m2 / g and 0.1% of SWCNT at 350 m2 / g, so for 100g of dry matter, there is an area equal to (2.65* 100)+(0.1*350) or 300 m2. Batteries

[0134] The positive electrode as described above is assembled in a battery further comprising a negative electrode whose electrochemically active material is graphite and an electrolyte.

[0135] The calendar life of the batteries thus obtained was evaluated according to the protocol below.

[0136] Calendar life assessment protocol

[0137] After assembling the components to form a battery, the following electrochemical tests were carried out:

[0138] - An electrochemical formation. It consists of a charge and discharge cycle at 60°C at C / 3 regime between 2.7V and 4.2V

[0139] - An initial capacity check cycle. The check cycle consists of a charge and discharge cycle at 25°C under C / 3 regime between 2.7V and 4.2V

[0140] - A calendar lifetime test according to the following steps:

[0141] Charge elements at C / 3, 25°C up to 4.2V and disconnect them

[0142] Store the elements thus charged in a study at 45 °C

[0143] After 1 month, 2 months and 200 days, remove the elements from the oven and wait until they are at 25 °C

[0144] Discharge the elements at C / 3, 25°C down to 2.7V

[0145] Perform a control cycle similar to the initial control cycle and report the discharged capacity

[0146] - The loss of capacity after 200 days is calculated as the difference between the The capacity discharged during the control cycle after 200 cycles is compared to the capacity discharged during the initial control cycle. This loss is expressed as a percentage of the capacity discharged during the initial control cycle. The capacity loss after 200 days, expressed as a percentage of the capacity discharged during the initial control cycle, is shown in Table 1.

[0147] [Tables] Electrochemically active materials Electronic conductor(s) Percolating carbon surface area (m2) Capacitance loss (%) Material 1 w% Material 2 w% Conductor 1 w% Conductor 2 w% Composition 1 (Invention) LMFP 66.29 NMC1 28.41 NCI 2.65 SWCNT 0.1 300 5.9 Composition 2 (Comparative) LMFP 66,11 NMC1 28, 34 NCI 3 - 300 11,2 Composition 3 (Invention) LMFP 66,33 NMC1 28, 42 NCI 2,65 SWCNT 0,05 283 7,1 Composition 4 (Comparative) LMFP 66,35 NMC1 28, 44 NCI 2,65 SWCNT 0,01 269 10,9 Composition 5 (Invention) LMFP 66,47 NMC1 28, 48 NCI 2,3 SWCNT 0,2 300 4,3 Composition 6 (Invention) LMFP 66,29 NMC1 28, 41 NC2 2,65 SWCNT 0,1 2129 9,4 Composition 7 (Comparative) LMFP 66,32 NMC1 28, 43 NC2 2,7 - 2133 12,5 Composition 8 (Invention) LMFP 67,91 NMC1 29, 11 NC2 0,33 SWCNT 0,1 296 6,3 Composition 9 (Comparative) LMFP 67,94 NMC1 29, 12 NC2 0,39 - 308 11,7 Composition 1 0 (Invention) LMFP (60 / 40) 66,29% NMC1 28, 41 NCI 2,65 SWCNT 0,1 300 5,8 Composition 1 1 (Comparativ e) LMFP (60 / 40) 66,11 NMC1 28, 34 NCI 3 300 10,7 Composition 1 2 (Invention) LMFP 37,88 NMC1 56, 82 NCI 2,65 SWCNT 0,1 300 7,8 Composition 1 3 (Comparativ e) LMFP 37,78 NMC1 56, 67 NCI 3 - 300 11,9 Composition 1 4 (Invention) LMFP 66,29 NMC228,4 1 NCI 2,65 SWCNT 0,1 300 5,1 Composition 1 5 (Comparativ e) LMFP 66.11 NMC2 28.34 NCI 3 - 300 10.4 Composition 1 6 (Comparativ e) LMFP 66.22 NMC1 28.38 NCI 2.75 MWCNT 0.1 300 11.4 , Composition 1 7 (Comparativ e) LMFP 66.29 NCA 28.41 NCI 2.65 SWCNT 0.1 300 12.6 Composition 1 8 (Comparativ e) LMFP 66.11 NCA 28.34 NCI 3 - 300 12.4

[0148] For all compositions 1-11 and 14-18, the mass ratio LMFP / NMC1, LMFP / NMC2 or LMFP / NCA is 70 / 30. For compositions 12 and 13, the mass ratio LMFP / NMC1 is 40 / 60.

[0149] Unexpectedly, the addition of more than 0.01% by weight of SWCNT single-walled carbon nanotubes in the composition of the positive electrode comprising electrochemically active materials LMFP and NMC improves the calendar lifetime of the Li-ion elements, even if the total surface area of ​​the carbon conductors in the electrode is not decreased (compositions 1 to 5) or is even increased (compositions 6 and 7).

[0150] This improvement is observed regardless of the LMFP / NMC mass ratio in the electrode (compositions 1, 12, and 13), the composition of the carbon black (compositions 6, 7, 8, and 9), the composition of the NMC material (compositions 1, 14, and 15), the Fe / Mn ratio of the LMFP (compositions 1, 10, and 11), and the nature of the carbon black (compositions 1, 14, and 15). This beneficial effect is not obtained if the single-walled carbon nanotubes are replaced by multi-walled carbon nanotubes (compositions 1 and 16).

[0151] Unexpectedly, the addition of more than 0.01% by weight of SWCNT single-walled carbon nanotubes in a positive electrode composition comprising electrochemically active materials other than LMFP and NMC, in particular such as LMFP and NCA (compositions 17 and 18) does not improve the calendar lifetime of the Li-ion elements.

Claims

Demands

1. Positive electrode composition comprising: a) as electrochemically active materials: - a lithium manganese and iron phosphate compound of formula Lix Mnby_ zFeyMzPO4 (LMFP) with 0.8 <x<l,2 ; 0,5<l-y-z<l ; 0<y<0,5 ; 0<z<0,2 et M est choisi dans le groupe constitué de B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb, S, W, K, Pb, V, Mo, Hf, Bi, Se et leurs mélanges ; et - un composé de type oxyde lithié de nickel, de manganèse et de cobalt (NMC) de formule Liw(NixMnyCozMt)O2avec 0,9<w<l,l ; 0<x<l,l ; 0<y< 1,1 ; 0<z<l,l ; 0<t< 1,1 ; et M choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et leurs mélanges ;and b) as an electronic conductor: - more than 0.01% by weight of single-walled carbon nanotubes (SWCNTs) relative to the total weight of the composition, preferably more than 0.05% and even more preferably more than 0.1% by weight relative to the total weight of the composition.

2. Composition according to claim 1, characterized in that the mass ratio LMFP / NMC is from 30 / 70 to 90 / 10, preferably from 40 / 60 to 80 / 20, more preferably from 60 / 40 to 80 / 20.

3. Composition according to claim 1 or 2, characterized in that it further comprises at least one additional electronic conductor, preferably selected from: graphite, carbon black, acetylene black, soot, graphene and any mixture thereof, preferably carbon black.

4. Composition according to any one of the preceding claims, characterized in that the single-walled carbon nanotubes have an outside diameter of 1 to 4 nm, preferably 1.5 to 2 nm.

5. Composition according to any one of the preceding claims, characterized in that the single-walled carbon nanotubes have a specific surface area SSA greater than 300 m2 / g, preferably from 300 to 600 m2 / g, more preferably from 300 to 450 m2 / g.

6. Composition according to any one of the preceding claims, characterized in that the total surface area of ​​the electronic conductors is greater than 150 m2 per 100 g of dry matter of the composition, preferably from 250 to 2500 m2 per 100 g of dry matter of the composition.

7. Composition according to any one of the preceding claims, such that the composition is substantially free from nickel, cobalt, and aluminium (NCA) lithium oxide compounds of the formula Liw(NixCoyAlzMt)O2 with 0.9 <w<l,l ; 0<x<l,l ; 0<y< 1,1 ; 0<z<l,l ; 0<t< 1,1 ; et M choisi dans le groupe constitué de B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, Sr, Ce, Ga, Ta, Nd, Pr, La et leurs mélanges.

8. Composition according to any one of the preceding claims, wherein the composition further comprises at least one binder, preferably at least one vinylidene fluoride (PVDF) homopolymer.

9. Positive electrode comprising the composition according to any one of the preceding claims.

10. Electrochemical element comprising a positive electrode according to claim 9.

11. Use of an electrochemical element comprising a positive electrode comprising a composition according to claims 1 to 8 to improve the calendar vacuum duration of said electrochemical element.

12. Battery comprising one or more electrochemical elements according to claim 10.