Electrochemical element with very long calendar life

Abstract

The present invention relates to a cathode composition, comprising a) as an electrochemically active material: i) a lithiated manganese iron phosphate (LMFP) compound of the formula Li x Mn 1‑y‑z Fe y M z PO4, wherein 0.8≤x≤1.2; 0.5≤1‑y‑z<1; 0<y≤0.5; 0≤z≤0.2, and M is selected from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb, S, W, K, Pb, V, Mo, Hf, Bi, Se and mixtures thereof; and ii) a compound of lithiated nickel manganese cobalt (NMC) oxide type of the formula Li w (Ni x Mn y Co z M t )O2, wherein 0.9≤w≤1.1; 0

Description

Technical Field

[0001] This invention relates to energy storage, particularly to the field of lithium batteries. More specifically, this application relates to cathode compositions, cathodes comprising said compositions, electrochemical cells, and battery packs.

[0002] This invention is particularly applicable to lithium-ion (Li-ion) type rechargeable electrochemical batteries and / or power storage electrochemical batteries, and more specifically to such batteries associated with phosphate technology and applied to renewable energy sources. Background Technology

[0003] Lithium-ion rechargeable electrochemical batteries associated with phosphate technology are known in the prior art. Due to their performance in terms of safety and their lifespan during cycling, they constitute a promising source of electrical energy, particularly in the field of renewable energy, which is currently underdeveloped due to environmental concerns. They comprise at least one positive electrode and at least one negative electrode, as well as an electrolyte.

[0004] However, the specifications for battery packs using this type of battery are becoming increasingly critical, particularly in terms of calendar life, an environmental issue as important as the source of energy supply. Therefore, achieving a very high calendar life for this type of battery while maintaining all other desired characteristics such as power, energy, and rapid cycling is a challenge.

[0005] Calendar life corresponds to the period from the manufacturing date until the end of the battery's life. In reality, batteries undergo calendar aging, particularly affected by factors such as their state of charge and / or thermal changes or extreme temperatures that they are prone to experience during or even before their use. Furthermore, it is known that the calendar life of lithium-ion batteries decreases during their use when the specific surface area of ​​the carbon electronic conductor in the positive electrode increases due to the surface reactivity of the electronic conductor with the electrolyte. Summary of the Invention

[0006] Surprisingly, the inventors have discovered that adding single-walled carbon nanotubes (SWCNTs) to the cathode containing electrochemically active materials of the LMFP and NMC types described below improves the lifespan of lithium-ion batteries, even if the total specific surface area of ​​the carbon conductors in the electrode does not decrease or even increases. For all expectations, this improvement in calendar life cannot be achieved using other carbon nanotubes, particularly conventional carbon nanotubes using multi-walled carbon nanotubes (MWCNTs).

[0007] Therefore, the present invention relates to a positive electrode composition comprising:

[0008] a) As an electrochemically active material:

[0009] - Formula Li x Mn 1-y-z Fey M z lithiated manganese iron phosphate (LMFP) compound of formula PO₄, wherein 0.8≤x≤1.2; 0.5≤1-y-z<1; 0<y≤0.5; 0≤z≤0.2, and M is selected from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb, S, W, K, Pb, V, Mo, Hf, Bi, Se and mixtures thereof; and

[0010] - Li w (Ni x Mn y Co z M t )O₂ lithium nickel manganese cobalt oxide (NMC) type compound, wherein 0.9≤w≤1.1; 0<x≤1.1; 0<y≤1.1; 0<z≤1.1; 0≤t≤1.1; and M is selected from the group consisting of Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La and mixtures thereof; and

[0011] b) as an electron conductive agent:

[0012] - based on the total weight of the composition, the content of single-walled carbon nanotubes (SWCNT) is greater than 0.01% by weight, preferably greater than 0.05% by weight, and more preferably greater than 0.1% by weight, based on the total weight of the composition.

[0013] According to other advantageous aspects of the present invention, the composition according to the present invention comprises one or more of the following features, taken alone or in any technically possible combination.

[0014] The term "composition" or "positive electrode composition" is understood to mean a composition that covers the current collector of an electrode on at least one surface thereof.

[0015] It is obtained from an ink prepared with said components, usually in a solvent medium such as N-methyl-2-pyrrolidone (NMP), which is intended to be coated on a current collector, then dried and calendered subsequently to obtain said composition.

[0016] Generally, in addition to the electrochemically active material, this positive electrode composition further comprises an electronically conductive material, a binder and optionally additives.

[0017] According to one embodiment, the composition according to the present invention is suitable for a positive electrode, particularly for a lithium-ion type electrochemical cell, wherein the electrochemically active material of the positive electrode is of the phosphate type.

[0018] Electrochemical active materials

[0019] The composition according to the present invention comprises: as an electrochemically active material, preferably said electrochemically active material consists of:

[0020] - a lithiated manganese iron phosphate (LMFP) compound of formula Li x Mn 1-y-z Fe y M z PO4, wherein 0.8≤x≤1.2; 0.5≤1-y-z<1; 0<y≤0.5; 0≤z≤0.2, and M is selected from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb, S, W, K, Pb, V, Mo, Hf, Bi, Se and mixtures thereof; and

[0021] - a lithiated nickel manganese cobalt oxide (NMC) type compound of formula Li w (Ni x Mn y Co z M t )O2, wherein 0.9≤w≤1.1; 0<x≤1.1; 0<y≤1.1; 0<z≤1.1; 0≤t≤1.1; and M is selected from the group consisting of Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La and mixtures thereof.

[0022] The expression "electrochemically active material" generally refers to a material that acts as a substrate for electrochemical reactions.

[0023] Lithiated manganese iron phosphate compound (LMFP) of formula Li x Mn 1-y-z Fe y M z PO4 (LMFP)

[0024] The composition according to the present invention comprises at least one lithiated manganese iron phosphate compound (LMFP) of the following formula:

[0025] Li x Mn 1-y-z Fe y M z PO4

[0026] wherein

[0027] 0.8≤x≤1.2;

[0028] 0.5≤1-y-z<1;

[0029] 0 <y≤0.5;

[0030] 0≤z≤0.2 and

[0031] M is selected from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb, S, W, K, Pb, V, Mo, Hf, Bi, Se, and mixtures thereof.

[0032] According to one embodiment, the Fe / Mn molar ratio of the LMFP compound is from 20 / 80 to 50 / 50, preferably 30 / 70.

[0033] According to one implementation, 0.7 ≤ 1-yz ≤ 0.9.

[0034] According to another embodiment, 0.7 ≤ 1-yz ≤ 0.85.

[0035] As an LMFP-type active material, LiMn can be mentioned as an example. 0.8 Fe 0.2 PO4, LiMn 0.7 Fe 0.3 PO4, LiMn 2 / 3Fe 1 / 3 PO4, LiMn 0.6 Fe 0.4 PO4 and LiMn 0.5 Fe 0.5 Compounds of PO4.

[0036] Formula Li w (Ni x Mn y Co z M t Lithium-ionized nickel manganese cobalt oxide (NMC) type compounds of O2

[0037] The compositions according to the present invention comprise at least one lithium-ion nickel manganese cobalt oxide (NMC) type compound of the following formula:

[0038] Li w (Ni x Mn y Co z M t O2

[0039] in

[0040] 0.9≤w≤1.1;

[0041] 0 <x≤1.1;

[0042] 0 <y≤1.1;

[0043] 0 <z≤1.1;

[0044] 0 ≤ t ≤ 1.1; and

[0045] M is selected from the group consisting of Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La, and mixtures thereof.

[0046] M can be specifically selected from the group consisting of Al, B, Mg, and mixtures thereof. Preferably, M is Al and t ≤ 0.05. The main transition element is preferably nickel, and more preferably x ≥ 0.6. A high nickel content in nickel lithiation oxide is preferred because it provides high energy to nickel lithiation oxide.

[0047] According to one embodiment, the NMC compound has a nickel content of 60% to 88%.

[0048] As nickel-rich lithium-ion nickel manganese cobalt oxide (NMC) type compounds, those composed of the following compounds can be specifically mentioned:

[0049] Li1(Ni 0.6 Mn 0.2 Co 0.2 O2(NMC 622),

[0050] Li1(Ni 0.6 Mn 0.3 Co 0.1 O2 (NMC 631),

[0051] Li1(Ni 0.83 Mn 0.05 Co 0.12 O2(NMC 811).

[0052] According to one embodiment, the LMFP / NMC mass ratio is 30 / 70 to 90 / 10, preferably 40 / 60 to 80 / 20, and more preferably 60 / 40 to 80 / 20.

[0053] According to one implementation, the positive electrode is substantially free of the formula Li. w (Ni x Co y Al z M t) A lithiated nickel manganese cobalt oxide (NCA) type compound of O2, wherein 0.9≤w≤1.1; 0<x≤1.1; 0<y≤1.1; 0<z≤1.1; 0≤t≤1.1; and M is selected from the group consisting of B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, Sr, Ce, Ga, Ta, Nd, Pr, La and mixtures thereof.

[0054] As used herein, the expression "substantially free" is understood to mean that the composition comprises less than 10% by weight of the NCA compound relative to the total weight of the composition, preferably the composition comprises less than 5% by weight, more preferably less than 1% by weight of the NCA compound relative to the total weight of the composition.

[0055] According to one embodiment, the electrochemically active material of the composition according to the present invention consists of a mixture of the LMFP compound as described above and the NMC compound as described above.

[0056] Electron conductive agent

[0057] Single-walled carbon nanotubes (SWCNT)

[0058] The composition according to the present invention comprises single-walled carbon nanotubes (SWCNT) as an electron conductive agent, in an amount greater than 0.01% by weight relative to the total weight of the composition, preferably greater than 0.05% by weight, and even more preferably greater than 0.1% by weight relative to the total weight of the composition.

[0059] Generally, carbon nanotubes ("CNT") are an allotrophic form of carbon belonging to the fullerene family. They consist of sheets of carbon atoms rolled up on themselves to form a tube.

[0060] The term "carbon nanotube" represented by the abbreviation CNT is generally understood to mean multi-walled carbon nanotubes ("MWCNT"). Such multi-walled nanotubes generally have an outer diameter on the order of 10 to 25 nm.

[0061] For its part, the composition according to the present invention comprises more than 0.01% by weight of single-walled carbon nanotubes (SWCNT). Accordingly, they consist of a single layer of carbon atoms rolled up on themselves to form a tube. Their outer diameter is smaller than that of MWCNT.

[0062] Surprisingly, the inventors have found that the addition of only specific carbon nanotubes, i.e., single-walled carbon nanotubes ("SWCNT"), improves the calendar life of lithium-ion batteries in positive electrodes comprising an electrochemically active material of the LMFP and NMC type. This improvement was confirmed even when the total specific surface area of the carbon conductive agent in the electrode was not reduced or was even increased.

[0063] According to one embodiment, the outer diameter of the single-walled carbon nanotube is 1 to 4 nm, preferably 1.5 to 2 nm.

[0064] The outer diameter was assessed using transmission electron microscopy imaging.

[0065] According to one embodiment, the single-walled carbon nanotubes have a length greater than 5 μm, which is preferably measured by atomic force microscopy (AFM).

[0066] According to one embodiment, the single-walled carbon nanotube has a ratio between the G peak and the D peak as measured by Raman spectroscopy greater than 70.

[0067] The SWCNT described herein is used as a permeable electron conductive agent in the compositions according to the present invention.

[0068] According to one embodiment, single-walled carbon nanotubes have a diameter greater than 300 μm. 2 / g, preferably 300-600m 2 / g, more preferably 300-450m 2 Specific surface area SSA / g.

[0069] Specific surface area can be measured using the BET method (Brunauer, Emmett, and Teller theory), based on the assumption that adsorbed gas molecules exist in a monolayer on the material surface (physical adsorption of the gas). The amount of gas adsorbed at a given pressure (adsorption isotherm curve) is measured and used to calculate the specific surface area using the BET equation.

[0070] The procedure for measuring specific surface area by the BET method is shown in standard ASTM D6556-21.

[0071] Additional conductive agent

[0072] The compositions according to the invention may contain at least one additional electronically conductive agent. Preferably, the additional electronically conductive agent may be selected from: graphite, carbon black, acetylene black, soot, graphene, and any mixture thereof, with carbon black being preferred.

[0073] The carbon black described in this paper serves as an electron-permeating conductive agent in the positive electrode composition.

[0074] Carbon black is a partially crystalline carbonaceous product resulting from the partial decomposition of hydrocarbons. It has a primary particulate structure that is linked by aggregates and optionally agglomerates.

[0075] Therefore, carbon black can be obtained from the following:

[0076] - Acetylene black, for example, through thermal decomposition at 1200°C;

[0077] - Furnace black, for example, recovered in the gas phase by using a water curtain in the furnace.

[0078] - Smoke black,

[0079] - The lights are off.

[0080] - Using the thermal blackening of natural gas, or

[0081] - Black tunnels through the wall of the furnace.

[0082] In particular, graphite, graphene, fullerene, carbon fiber, carbon nanotubes, and activated carbon are not within the scope of the definition of the term "carbon black".

[0083] Carbon black typically has a dispersed appearance. It can be characterized by the specific surface area (SSA) of aggregates of primary particles.

[0084] The primary particle size of carbon black can typically range from 20 nm to 100 nm.

[0085] According to one embodiment, the total surface area of ​​one or more electronically conductive agents of the present invention is greater than 150m². 2 / 100g of the dry matter of the composition, preferably 250-2500mg / g 2 / 100g of the dry matter of the composition.

[0086] adhesives

[0087] The term "adhesive" is understood to refer to compounds that allow for enhanced cohesion between particles in a composition, adhesion between the composition and the current collector, and improved viscosity of inks.

[0088] According to one embodiment, the positive electrode composition further comprises at least one binder selected from functionalized or unfunctionalized vinylidene fluoride homopolymers, unfunctionalized 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), polyester, serialized polyether amide, acrylic polymers, methacrylic acid, acrylamide, itaconic acid, sulfonic acid, elastomers, cellulose compounds, and any mixtures thereof, preferably vinylidene fluoride homopolymers (PVDF), particularly functionalized vinylidene fluoride (PVDF) homopolymers with a grafting rate greater than or equal to 5% by mass (compared to the total mass of the homopolymer).

[0089] According to a preferred embodiment, the composition contains at least one vinylidene fluoride homopolymer (PVDF) as a binder.

[0090] Preferably, the adhesive is present in a proportion of 0.05 to 5% by weight, more preferably 2 to 3% by weight, relative to the total weight of the composition.

[0091] additive

[0092] The composition may further contain one or more additives, such as dispersants.

[0093] Therefore, polyvinylpyrrolidone (PVP) can be referred to as a dispersant suitable for use in this invention.

[0094] According to one embodiment, the composition comprises (by weight percentage) the following relative to its total weight:

[0095] - 80% to 98%, preferably 85% to 95% of electrochemically active materials;

[0096] - 0.5% to 10%, preferably 2% to 5%, of one or more electronically conductive materials;

[0097] - 0.5% to 10%, preferably 1% to 5%, of one or more adhesives;

[0098] - 0% to 1%, preferably 0.01% to 1% of one or more dispersants.

[0099] positive electrode

[0100] The electrode is typically composed of a current collector that is covered on at least one side by the composition according to the invention.

[0101] Typically, the electrode acts as the positive electrode.

[0102] Metal foil can be used as a current collector.

[0103] The metal foil may be made of aluminum or an alloy that mainly contains aluminum, and may optionally be coated with a conductive material, such as carbon.

[0104] Advantageously, the metal foil is made of carbon-coated aluminum.

[0105] Electrode preparation

[0106] Typically, electrodes are manufactured by preparing an ink containing a compound mixed with a solvent, and then coating it onto a current collector. The ink can be dried in an oven, furnace, and / or by infrared radiation to evaporate the solvent. After one or more solvents have evaporated, a composition constituting the electrode material is obtained. Thus, the ink ultimately constitutes the composition of the positive electrode.

[0107] Then, the ink coated on the current collector and then dried can be subjected to a calendering step by passing the electrode between two rollers to apply pressure to the electrode surface.

[0108] In addition to at least one positive electrode, the electrochemical element further comprises at least one negative electrode, an electrolyte, and an optional separator.

[0109] negative electrode

[0110] The negative electrode comprises a current collector, at least one surface of which is coated with a layer of a negative electrode active material composition. The current collector is prepared in a conventional manner. The negative electrode active material is not particularly limited, and may be selected from the following group and mixtures thereof:

[0111] - Metallic lithium or alloys of metallic lithium

[0112] - Graphite

[0113] - Silicon

[0114] - Anode-free type

[0115] - Titanium and niobium oxides of TNO type

[0116] - Lithiated titanium oxides of LTO type or titanium oxides capable of being lithiated.

[0117] Examples of lithiated titanium oxides are spinel Li4Ti5O 12 , Li2TiO3, ramsdellite Li2Ti3O7, LiTi2O4, LixTi2O4 (0<x≤2) and Li2Na2Ti6O 14 .

[0118] Preferred LTO compounds have the formula Li 4-a M a Ti 5-b M' b O4, for example Li4Ti5O 12 , which is also written as Li 4 / 3 Ti 5 / 3 O4.

[0119] The term "negative electrode" refers to an electrode that operates as an anode when a battery is discharged, and operates as a cathode when the battery is charged.

[0120] electrolytes

[0121] The electrolyte may be liquid and comprises a lithium salt dissolved in a mixture of organic solvents.

[0122] The lithium salt can be selected from lithium perchlorate LiCIO4, lithium hexafluorophosphate LiPF6, lithium tetrafluoroborate LiBF4, lithium hexafluoroarsenate LiAsF6, lithium hexafluoroantimonyate LiSbF6, lithium trifluoromethanesulfonate LiCF3SO3, lithium bis(fluorosulfonyl)imide Li(FSO2)2N (LiFSI), lithium trifluoromethanesulfonylimide LiN(CF3SO2)2 (LiTFSI), lithium trifluoromethanesulfonylmethyl LiC(CF3SO2)3 (LiTFSM), lithium bisperfluoroethylsulfonylimide LiN(C2F5SO2)2 (LiBETI), lithium 4,5-dicyano-2-(trifluoromethyl)imidazolium (LiTDI), lithium bis(oxalateborate) (LiBOB), lithium difluoro(oxalateborate) (LIDFOB), lithium tri(pentafluoroethyl)trifluorophosphate LiPF3(CF2)PF3 (LiFAP), lithium difluorophosphate LiPO2, and mixtures thereof.

[0123] Electrolytes in liquid form are obtained by dissolving one or more lithium salts in one or more organic solvents.

[0124] The solvent can be selected from saturated cyclic carbonates, unsaturated cyclic carbonates, acyclic carbonates, alkyl esters, ethers, nitrile solvents, tetrahydrothiophene dioxide (sulfolane), and vinyl sulfate (ESA).

[0125] Saturated cyclic carbonates include ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), butene carbonate (BC), and mixtures thereof.

[0126] Unsaturated cyclic carbonates include vinylene carbonate (VC).

[0127] Acyclic carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dipropyl carbonate (DPC), and mixtures thereof.

[0128] Alkyl esters include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and mixtures thereof.

[0129] Ethers include dimethyl ether (DME), diethyl ether (DEE), and mixtures thereof.

[0130] Alternatively, the electrolyte can be a solid. It can be a lithium-ion conducting compound, selected from, for example, 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.

[0131] Electrolytes can also be obtained in the form of a gel by impregnating a polymer with a liquid mixture containing at least one lithium salt and an organic solvent.

[0132] diaphragm

[0133] Electrochemical components may include a separator between the positive and negative electrodes. The separator may be composed of layers of polypropylene (PP), polyethylene (PE), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyesters (such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT)), cellulose, polyimide, glass fiber, or a mixture of layers with different properties. The polymer may be coated with a ceramic layer and / or polyvinylidene fluoride (PVdF) or poly(vinylidene fluoride-hexafluoropropylene (PVdF-HFP)) or acrylate.

[0134] Applications of electrochemical components

[0135] The present invention also has the purpose of using an electrochemical element comprising a positive electrode for improving the calendar life of the electrochemical element, the positive electrode comprising the composition as described above.

[0136] For example, a scheme for evaluating the calendar lifetime of an electrochemical element may be as described in the embodiments of this application.

[0137] Another objective of this invention is to include a positive electrode comprising the aforementioned composition.

[0138] The ultimate objective of this invention is to include an electrochemical element with a positive electrode as described above, and a battery pack comprising one or more of these electrochemical elements.

[0139] The electrochemical elements or battery packs according to the present invention exhibit improved calendar life, as shown below. Detailed Implementation

[0140] The invention will become clearer by reading the following embodiments, which are for illustrative purposes only and are not intended to limit the invention.

[0141] Example

[0142] In the embodiments described below, the positive electrode includes a current collector support, which is a carbon-coated aluminum foil. A uniformly mixed layer of the composition is formed by coating a slurry containing the evaporated solvent.

[0143] • The compounds are described in Table 1 below as electrochemically active materials and electronically conductive agents;

[0144] • As an adhesive, the polyvinylidene fluoride (PVDF) polymer adhesive (K1300 supplied by Kureha Corporation) is 2.5% by weight (compared to the total dry weight of the composition);

[0145] • As a dispersant, polyvinylpyrrolidone (PVP) dispersant (K30 supplied by Sima Aldrich) is used at 0.05% by weight (compared to the total dry weight of the composition).

[0146] The composition of Table 1:

[0147] The percentage of each compound is given as a weight percentage (w%) relative to the dry weight of the above composition.

[0148] Electrochemical active materials

[0149] _LMFP: Formula Li1Mn 0.7 Fe 0.3 Lithiumized manganese phosphate compound of PO4.

[0150] Unless otherwise stated in Table 1 (Compositions 1-9 and 12-16), the Mn / Fe stoichiometric ratio of the LMFP compounds is 70 / 30. For compositions 10 and 11, this ratio is 60 / 40.

[0151] _NMC1: Formula Li1(Ni 0.83 Mn 0.05 Co 0.12 Lithiumized nickel manganese cobalt oxide (NMC) type compound of O2 (NMC811)

[0152] _NMC2: Formula Li1(Ni 0.6 Mn 0.2 Co 0.2 Lithiumized nickel manganese cobalt oxide (NMC) type compounds of O2 (NMC622)

[0153] _NCA: Formula Li1(Ni 0.80 Co 0.15 Al 0.05 Lithium-ionized nickel-cobalt-aluminum oxide (NCA) compounds of O2

[0154] Electron conductive agent

[0155] SWCNT: Single-walled carbon nanotubes (outer diameter = 1.7 nm; SSA = 350 nm) 2 / g; Length: greater than 5μm as measured by AFM; Ratio between G and D peaks as measured by Raman spectroscopy greater than 70)

[0156] MWCNT: Multi-walled carbon nanotubes (outer diameter = 12 nm; SSA = 250 m) 2 / g; Length: approximately 1 μm as measured by AFM; The ratio between the G peak and the D peak as measured by Raman spectroscopy is less than 1).

[0157] _ NC1: SSA=100m 2 / g of carbon black

[0158] _ NC2: SSA=790m 2 / g of carbon black

[0159] Increase the surface area of ​​carbon through which the electron-conducting agent permeates:

[0160] The surface area of ​​the percolating carbon reported in Table 1 was calculated as follows: Considering the dry extract of the ink from 100g of the cathode composition, the surface area (in m²) is calculated. 2 The specific surface area (m²) of the percolating carbon is calculated as follows: 2 The sum of the products of (g) multiplied by their mass (g) in 100g of dry extract.

[0161] For example, in Example 1, 100m 2 The NC1 content is 2.65% per g, and 350m 2 The SWCNT content is 0.1% per gram, therefore, for 100g of dry matter, the surface area is equal to (2.65*100) + (0.1*350), which is 300m². 2 .

[0162] Battery

[0163] As described above, the positive electrode is assembled into a battery pack, which also includes a negative electrode made of graphite and an electrolyte.

[0164] The resulting battery pack calendar life is evaluated using the following method.

[0165] Scheme for assessing calendar life

[0166] After assembling the components to form a battery pack, the following electrochemical tests were performed:

[0167] - Electrochemical shaping. It includes charge and discharge cycling at 60°C with a C / 3 ratio between 2.7 V and 4.2 V.

[0168] - Cycles used to check initial capacity. The check cycles consist of charge and discharge cycles at 25°C between 2.7 V and 4.2 V at a C / 3 rate.

[0169] - Perform a calendar lifetime test according to the following steps:

[0170] Charge the batteries at 25°C (C / 3) until they reach 4.2V, then disconnect them.

[0171] The battery was stored at 45°C during the study.

[0172] Remove the batteries from the case after 1 month, 2 months, and 200 days, and wait until they reach 25°C.

[0173] Discharge the battery to 2.7 V at 25°C using a C / 3 discharge rate.

[0174] Perform a check cycle similar to the initial check cycle and report the discharge capacity.

[0175] - Capacity loss after 200 days is calculated as the difference between the capacity discharged in the inspection cycle after 200 cycles and the capacity discharged in the initial inspection cycle. This loss is simplified to a percentage of the capacity discharged in the initial inspection cycle. Table 1 reports the capacity loss after 200 days, expressed as a percentage of the capacity discharged in the initial inspection cycle.

[0176] [Table 1]

[0177]

[0178] For all compositions 1-11 and 14-18, the mass ratio of LMFP / NMC1, LMFP / NMC2, or LMFP / NCA is 70 / 30. For compositions 12 and 13, the mass ratio of LMFP / NMC1 is 40 / 60.

[0179] Surprisingly, the addition of more than 0.01% by weight of single-walled carbon nanotubes (SWCNTs) to compositions containing electrochemically active materials LMFP and NMC improved the calendar life of lithium-ion batteries, even though the total surface area of ​​the carbon conductive agents in the electrode did not decrease (compositions 1 to 5) or even increased (compositions 6 and 7).

[0180] This improvement was verified 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 properties of the carbon black (compositions 1, 14, and 15). This beneficial effect was not achieved if single-walled carbon nanotubes were replaced with multi-walled carbon nanotubes (compositions 1 and 16).

[0181] Surprisingly, adding more than 0.01% by weight of single-walled carbon nanotubes (SWCNTs) to cathode compositions containing electrochemically active materials other than LMFP and NMC (especially LMFP and NCA (compositions 17 and 18)) did not improve the calendar life of lithium-ion batteries.

Claims

1. A positive electrode composition, comprising: a) as an electrochemically active material: - Formula Li x Mn 1-y-z Fe y M z The lithium-ionized manganese iron phosphate (LMFP) compound of PO4, wherein, 0.8≤x≤1.2; 0.5≤1-y-z<1; 0<y≤0.5; 0≤z≤0.2, and M is selected from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb, S, W, K, Pb, V, Mo, Hf, Bi, Se and mixtures thereof; and - Formula Li w (Ni x Mn y Co z M t )O2 lithiated nickel manganese cobalt oxide (NMC) compound, wherein 0.9≤w≤1.1; 0<x≤1.1; 0<y≤1.1; 0<z≤1.1; 0≤t≤1.1; and M is selected from the group consisting of Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La and mixtures thereof; and b) as an electronic conductive agent: - based on the total weight of the composition, the content of single-walled carbon nanotubes (SWCNT) is greater than 0.01 wt%, preferably greater than 0.05 wt%, and more preferably greater than 0.1 wt%, based on the total weight of the composition.

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

3. The composition according to claim 1 or 2, characterized in that, The composition further comprises at least one additional electronic conductive agent, and the additional electronic conductive agent is preferably selected from the group consisting of graphite, carbon black, acetylene black, carbon soot, graphene and any mixture thereof, and is preferably carbon black.

4. The composition according to any one of the preceding claims, characterized in that, The outer diameter of the single-walled carbon nanotubes is 1 nm to 4 nm, preferably 1.5 nm to 2 nm.

5. The composition according to any one of the preceding claims, characterized in that, The single-walled carbon nanotubes have a diameter greater than 300 μm. 2 / g, preferably 300 to 600m 2 / g, more preferably 300 to 450m 2 Specific surface area SSA / g.

6. The composition according to any one of the preceding claims, characterized in that, The total surface area of ​​the electronically conductive agent is greater than 150m². 2 / 100g of the dry matter of the composition, preferably 250 to 2500 mg / 100g 2 / 100g of the dry matter of the composition.

7. The composition according to any one of the preceding claims, wherein the composition is substantially free of formula Li w (Ni x Co y Al z M t Lithium-ionized nickel-cobalt-aluminum oxide (NCA) compounds of O2, wherein, 0.9≤w≤1.1; 0<x≤1.1; 0<y≤1.1; 0<z≤1.1; 0≤t≤1.1; and M is selected from the group consisting of B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, Sr, Ce, Ga, Ta, Nd, Pr, La and mixtures thereof.

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

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

10. An electrochemical cell comprising the positive electrode according to claim 9.

11. Use of an electrochemical cell comprising a positive electrode for improving the calendar life of the electrochemical cell, wherein the positive electrode comprises the composition according to claims 1 to 8.

12. A battery pack comprising one or more electrochemical cells according to claim 10.

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