Rechargeable lithium electrochemical cell for aviation applications

Abstract

An electrochemical pocket element (1) comprising at least one positive electrode and at least one negative electrode, wherein the positive electrode comprises a layer of a composition of positive active materials, said composition comprising a mixture of: a) 30 to 50 wt% of a lithium manganese and iron phosphate of formula LixMn1-y-zFeyMzPO4 where 0.8 ≤ x ≤ 1.2; 0.5 ≤ (1-yz) < 1; 0 < y ≤ 0.5; 0 ≤ z ≤ 0.2; a) M being chosen from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, and their mixtures, b) 70 to 50 wt% of at least one lithium and nickel oxide chosen from Liw(NixCoyAlzMt)O2 where 0.9 ≤ w ≤ 1.1 ; 0 < x ; 0 < y ; 0 < z ; 0 ≤ t ; M being chosen from the group consisting of B, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, W, Mo and their mixtures, and Liw(NixMnyCozMt)O2 where 0.9 ≤ w ≤ 1.1 ; 0 < x ; 0 < y ; 0 < z ; 0 ≤ t ;M being chosen from the group consisting of Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo and their mixtures, and in which the porosity of the positive electrode is less than or equal to 40%, and the porosity of the negative electrode is less than or equal to 30%. Figure for the abbreviation: Figure 1;

Description

Title of the invention: Rechargeable lithium electrochemical element for aviation applications Field of invention

[0001] The invention relates to the technical field of rechargeable (secondary) lithium electrochemical elements usable in flying machines, specifically electrically powered flying machines and hybrid electrically powered flying machines. Background of the invention

[0002] Battery electric vehicles (BEVs) and hybrid electric vehicles (HEVs) can reduce aircraft emissions. They are entering the consumer aviation markets. These vehicles require batteries with high specific power, high specific energy, and high operational safety. It would be desirable to have an electrochemical element that meets the following three requirements: 1) a high specific energy, of at least 250 Wh / kg, 2) a high specific power, at least 1000 W / kg, even at a low state of charge, for example 20% (for comparison, the specific power requirement for an electrochemical element intended for use in the automotive field is only 500 W / kg). 3) high operational safety when the cell is exposed to a temperature above the nominal limits. The European Automotive Research Council (EUCAR) has established a scale from 0 to 7 to quantify the level of danger associated with the use of batteries, with level 0 corresponding to the lowest risk and level 7 corresponding to the highest risk. An electrochemical cell intended for use in an aeronautical application must meet EUCAR safety test 4 or lower.

[0003] An electrochemical cell meeting only one of the above three requirements can be easily designed, but a cell meeting all three requirements together cannot be easily designed. For example, a cell having a specific energy greater than 250 Wh / kg can be produced, but it will not pass the safety test. A cell having a specific power greater than 1000 W / kg can also be produced, but it will not meet the high specific energy requirement or the safety requirement.

[0004] A cathode whose active material consists solely of a lithium nickel manganese cobalt (NMC) oxide or a lithium nickel cobalt aluminum oxide (NCA) does not meet the requirement for high operational safety. Indeed, it is known that nickel-rich lithium oxides are not stable at high temperatures, typically above 100 °C. To overcome the lack of stability of these oxides, it has been proposed to mix them with a material with greater thermal stability, such as a lithium manganese-iron phosphate of general formula Lix MnlyzFeyMzPO4 (LMFP) where 0.8 < x < 1.2; 0.5 < 1-yz < 1; 0 < y < 0.5; 0 < z < 0.2 and M is a doping chemical element. The LMFP compound improves the thermal stability of the electrode. However, it has insufficient specific capacity. Thus, to the applicant's knowledge, existing elements with a positive electrode containing a mixture of LMFP and a lithium and nickel oxide have a specific energy of less than 250 Wh / kg.Furthermore, to the applicant's knowledge, existing electrochemical cells with a specific energy density of 250 Wh / kg or more are rated 6 or 7 on the EUCAR scale.

[0005] In conclusion, an electrochemical element is sought having a positive electrode containing a mixture of LMFP and a lithium and nickel oxide having a specific energy of at least 250 Wh / kg, a specific power of at least 1000 W / kg and which passes the EUCAR 4 safety test or lower.

[0006] Document WO-A-2021 / 259991 describes an active material composition comprising a mixture consisting of 50 to 90% by mass of LMFP and 10 to 50% by mass of a lithium and nickel oxide for an electrode of an element intended to be used in the automotive field.

[0007] Document WO-A-2016 / 184896 describes an active material composition comprising a majority of an LMFP compound characterized by a volume median particle diameter Dv502 greater than or equal to 500 nm and a minority of an NMC compound having a volume median particle diameter DV501 greater than or equal to 500 nm, and in which the ratio DvsqVDvso1 is greater than or equal to 1.5. Summary of the invention

[0008] The invention provides a rechargeable electrochemical element satisfying the above three requirements. The pouch electrochemical element comprises at least one positive electrode and at least one negative electrode, the positive electrode comprising a layer of a composition of positive active materials, said composition comprising a mixture of: a) 30 to 50% by weight of a lithium manganese and iron phosphate of formula LixMn iy zFeyMzPO4 where 0.8 < x < 1.2; 0.5 < (1-yz) <1;0 <y<0,5;0<z< 0,2 ; M being chosen from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, and mixtures thereof, b) 70 to 50% by weight of at least one lithium and nickel oxide chosen from Liw(NixCoyAlzMt)O2 where 0.9 < w < 1.1 ;0 <x;0<y;0<z;0<t;M étant choisi dans le groupe constitué par B, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, W, Mo et leurs mélanges, et Liw(NixMnyCozMt)O2 where 0.9 < w < 1.1 ;0 <x;0<y;0<z;0<t;M étant choisi dans le groupe constitué par Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo et leurs mélanges, et dans lequel la porosité de l'électrode positive est inférieure ou égale à 40 %, et la porosité de l'électrode négative est inférieure ou égale à 30 %.

[0009] The invention is based on the discovery that by decreasing the porosity of a positive electrode containing a mixture of LMFP and a lithium nickel oxide to a value of 40% or less, and by decreasing the porosity of the associated negative electrode to a value of 30% or less, and by choosing the pouch format, it is possible to obtain an element having a high specific energy of 250 Wh / kg or more, a high specific power of more than 1000 W / kg, even at low states of charge of about 20%, and which meets the requirements of the EUCAR 4 test or lower, in particular the nail test and the overheating test.

[0010] In one embodiment, the lithium nickel oxide is Liw(NixMnyCozMt)O2 with 0.7 < x, preferably 0.8 < x.

[0011] In one embodiment, the secondary particles of lithium nickel oxide have a first volume median diameter Dvso1 and the secondary particles of lithium manganese iron phosphate have a second volume median diameter Dv502, the ratio DV50VDV502 being from 2 to 9, preferably from 3 to 7.

[0012] In one embodiment, the positive electrode comprises a current collector that is an aluminum foil or an aluminum alloy foil at least partially coated on one side or both sides. The coating may be made of a material selected from the group consisting of carbon, graphite, carbon nanotubes, and mixtures thereof.

[0013] In one embodiment, the current collector has a thickness in the range of 5 to 20 μm, preferably 10 to 16 μm.

[0014] In one embodiment, the negative electrode comprises a current collector having a thickness in the range of 3 to 10 μm, preferably 5 to 8 μm.

[0015] In one embodiment, the layer of the positive active material composition contains one or more binders and / or one or more electronically conductive materials and the mass of said one or more binders represents 1% or less of the mass of the layer; the mass of said one or more electronically conductive materials represents 1% or less of the mass of the layer.

[0016] In one embodiment, the layer of the positive active material composition contains carbon nanotubes.

[0017] In one embodiment, said at least one negative electrode comprises a layer of a negative active material composition, said composition comprising a mixture of at least one anisotropically grown carbon with at least one isotropically grown carbon.

[0018] In one embodiment, the mass of the isotropically grown carbon represents from 10 to 60% or from 20 to 50% of the mass of the mixture.

[0019] In one embodiment, the negative active material composition further comprises a silicon-based compound.

[0020] Another object of the invention is a battery comprising a plurality of pouch electrochemical elements as described above.

[0021] Another object of the invention is a battery-powered flying machine.

[0022] In one embodiment, the flying machine is an electric flying machine or a hybrid electric flying machine.

[0023] In one embodiment, the electric flying machine or the hybrid flying machine is chosen from the group consisting of: - an electric vertical takeoff and landing (e-VTOL) vehicle, - an electric conventional takeoff and landing (e-CTO) vehicle, and - an electric short takeoff and landing (e-STOL) vehicle.

[0024] In one embodiment, the flying machine is an aircraft. Brief description of the drawings

[0025] [Fig-1] [Fig.l] schematically represents an external view of an element pocket.

[0026] [Fig.2] [Fig.2] represents the percentage of the reference discharged capacity as a function of the discharge rate. The capacity discharged at a rate of C / 10 is taken as the reference discharged capacity. Detailed description of the invention Structure of the electrochemical element pouch

[0027] A first requirement to achieve the above objectives is to manufacture a pouch-shaped element. To manufacture a pouch element, a stack of at least one positive electrode, a separator and at least one negative electrode is assembled. This assembly is inserted inside a flexible pouch. The pouch has been previously formed by welding the edges of two multilayer films, each multilayer film comprising a metal layer, generally aluminum, sandwiched between two layers of plastic material. A portion of the positive current collector of the positive electrode located in the vicinity of an edge of the positive electrode is not coated with positive active materials. Said current collector portion not coated with positive active materials is used for connection to a terminal of positive current output. Similarly, a portion of the negative current collector of the negative electrode located in the vicinity of one edge of the negative electrode is not coated with negative active materials. Said current collector portion not coated with negative active materials serves for connection to a negative current output terminal. The positive current output terminal and the negative current output terminal extend outside the volume of the pouch, and generally project from the same edge of the pouch. They may also project from two opposite edges of the pouch. The pouch is filled with an electrolyte and then hermetically sealed. [Fig.l] schematically shows an external view of a pouch element (1). A plate block (2) consisting of a positive electrode, a negative electrode and a separator is housed in a rectangular pouch (3).The positive (4) and negative (5) current output terminals protrude from one edge of the pouch. A heat seal line (6) extends along all four edges of the pouch to hermetically seal the pouch. Positive electrode:

[0028] The at least one positive electrode comprises a positive current collector of which at least one of its two sides is coated with a layer of a composition of positive active materials. By "composition of active materials" is meant a composition comprising one or more active materials and optionally one or more binders and one or more electronically conductive materials.

[0029] The positive current collector is a solid or perforated metal foil which can be made of aluminum or an aluminum alloy or of steel or stainless steel. Its thickness can be in the range of 6 to 30 μm or 5 to 20 μm or 10 to 15 μm, preferably 10 to 15 μm. A small thickness makes it possible to increase the mass of the layer of the positive active material composition and to obtain the desired specific energy and specific power.

[0030] Before the current collector is coated with the layer of the active material composition, the current collector may be coated, on one or both sides, with a coating intended to improve the electronic conductivity between the layer of the active material composition and the foil and / or to improve the adhesion of the layer of the active material composition to the foil. The coating material may be selected from the group consisting of carbon, graphite, carbon fibers, carbon nanotubes, and mixtures thereof. It is preferably made of carbon. The coating material may completely or partially cover one or both sides of the foil. The coating material may be obtained by coating the foil with a dispersion of the material and then evaporating the solvent from the dispersion, or it may be obtained by sputtering. Portions of the The current collector may be coated with the coating material. The coated portions may be separated from each other by predetermined or periodic intervals ("intermittent coating"). The intermittent coating is preferably present on both sides of the current collector. It facilitates the processing of the electrodes. Alternatively, one or both of the surfaces of the foil may have undergone a surface treatment intended to increase the adhesion of the active material composition layer to the foil. This may be a surface treatment that creates asperities or microroughness, such as chemical etching or laser treatment.

[0031] The composition of positive active materials comprises a mixture consisting of: a) 30 to 50% by weight of a lithium manganese and iron phosphate of formula LixMn ly.zFeyMzPO4 (LMFP) where 0.8 < x < 1.2; 0.5 < (1-yz) < 1; 0 < y < 0.5; 0 < z < 0.2; M being chosen from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, and mixtures thereof, b) 70 to 50% by weight of at least one lithium and nickel oxide chosen from Liw(NixCoyAlzMt)O2 (NCA) where 0.9 < w < 1.1;0 <x;0<y;0<z;0<t;M étant choisi dans le groupe constitué par B, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, W, Mo et leurs mélanges, et Liw(NixMnyCozMt)O2 (NMC) where 0.9 < w < 1.1;0 <x;0<y;0<z;0<t;M étant choisi dans le groupe constitué par Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo et leurs mélanges.

[0032] Lithium nickel oxide can be in the form of a single crystal or a polycrystal.

[0033] It may be a mixture of LMFP, NCA and / or NMC. Preferably, the composition of active materials does not contain active materials other than LMFP, NCA and / or NMC. Preferably, the mixture of active materials consists of LMFP and NMC.

[0034] The mixture may consist of: - 30 to 45% or 30 to 40% or 30 to 35% of LMFP, - 70 to 55% or 70 to 60% or 70 to 65% of at least one lithium and nickel oxide.

[0035] The mixture may consist of: - 35 to 50% or 35 to 45% or 35 to 40% of LMFP, - 65 to 50% or 65 to 55% or 65 to 60% of at least one lithium and nickel oxide.

[0036] The mixture may consist of: - 40 to 50% or 40 to 45% of LMFP, - 60 to 50% or 60 to 55% of at least one lithium and nickel oxide.

[0037] The LMFP can be coated with carbon or carbon nanotubes.

[0038] According to one embodiment, in the LMFP, 0.5 < 1-yz < 1 or 0.7 < 1-yz < 0.9 or 0.75 < 1-yz < 0.80.

[0039] Examples of LMFP type compounds are LiMnosFeo^PCL, LiMn()7XFc022PO4, LiMnojFeosPCL, LiMn2 / 3Fei / 3PO4 and LiMno.5Fco.5PO4.

[0040] As for the NMC compound, preferably 0.6 < x or 0.7 < x or 0.8 < x. Preferred examples of NMC compounds are LiNiO,7MnO,2Coo,iO2 (NMC 721) and LiNiO,gMnO,jCooaOz (NMC 811).

[0041] As for the NCA compound, preferably 0.6 < x or 0.7 < x or 0.8 < x. Examples of NCA compounds are LiNi0.84Co0_08Al0.08O2, LiNio,85Coo.ioAlo,o502, LiNi0.87Co0.06AI0.07O2, and LiNi0.89Co0.0eAl0.05O2.

[0042] For both NMC and NCA, a high stoichiometric index of nickel makes it possible to obtain a positive electrode having a high specific energy.

[0043] The following mixtures are particularly preferred: 1) 50% LMFP / 50% NMC where x in NMC is equal to or greater than 0.8, 2) 40% LMFP / 60% NMC where x in NMC is equal to or greater than 0.8, 3) 50% LMFP / 50% NCA where x in NCA is equal to or greater than 0.8, 4) 40% LMFP / 60% NCA where x in NCA is equal to or greater than 0.8. Mixtures 2 and 4 achieve good discharge performance under high current.

[0044] Both lithium manganese iron phosphate and lithium nickel oxide can be either in the form of disjointed particles, also called primary particles, or in the form of agglomerated particles, also called secondary particles. A population of particles is characterized by its size distribution. One parameter characterizing a size distribution is the volume median diameter Dv50. The term "volume median diameter Dv50" means that, in a given population of particles, 50% of the volume of the particles consists of particles having an equivalent diameter less than the Dv50 value and 50% of the volume of the particles consists of particles having an equivalent diameter equal to or greater than the Dv50 value. The term "equivalent diameter" of a particle means the diameter of a sphere having the same volume as that particle. The volume median diameter can be measured by laser diffraction.

[0045] The lithium nickel oxide may be a polycrystal and may be in the form of secondary particles having a volume median diameter DV501 in the range of 8 to 15 pm or 8 to 13 pm. In one embodiment, the lithium nickel oxide is a polycrystalline NMC in which x in the NMC is 0.8 or greater and which forms secondary particles having a Dvio1 value in the range of 4 to 7 pm, a DV501 value in the range of 8 to 10 pm and a Dvço1 value in the range of 15 to 20 pm. Dvio1 refers to a population of particles in which 10% of the particle volume consists of particles having an equivalent diameter less than the value Dvio1 and 90% of the particle volume consists of particles having an equivalent diameter greater than or equal to the value Dvio1. Dvço1 refers to a population in which 90% of the particle volume consists of particles having an equivalent diameter less than the value Dvço1 and 10% of the particle volume consists of particles having an equivalent diameter equal to or greater than the value Dvço1.

[0046] The LMFP may be in the form of secondary particles having a volume median diameter Dv502 in the range of 1 pm to 5 pm or 1.5 to 4 pm.

[0047] Preferably, the particle sizes of the active materials are chosen so that the Dvso' / Dvso2 ratio is in the range from 2 to 9 or from 3 to 7 or from 3 to 5.

[0048] The binder generally used in the active material composition strengthens the cohesion between the active material particles and improves the adhesion of the active material composition layer to the current collector. The binder may contain one or more of the following compounds: polyvinylidene fluoride (PVDF) and its copolymers, polytetrafluoroethylene (PTFE) and its copolymers, polyacrylonitrile (PAN), polymethyl or butyl methacrylate, polyvinyl chloride (PVC), polyvinyl formal, polyester, block polyetheramides, polymers of acrylic acid, methacrylic acid, acrylamide, itaconic acid, sulfonic acid, elastomers, and cellulose compounds such as carboxymethylcellulose (CMC). The elastomers that can be used as binders can be chosen from styrene-butadiene (SBR), butadiene-acrylonitrile (NBR), hydrogenated butadiene-acrylonitrile (HNBR).The binder may represent from less than 1% to 10% or from 1 to 5% or from 2 to 5% of the mass of the dry composition of active materials.

[0049] The electronically conductive material is generally chosen from graphite, carbon black, acetylene black, soot, graphene, carbon fibers, single-walled carbon nanotubes, multi-walled carbon nanotubes, and mixtures thereof. It may represent less than 1 to 10% or 1 to 5% or 2 to 5% of the mass of the dry composition of active materials. Preparation of the positive electrode:

[0050] An ink is prepared by dispersing LMFP and at least one of NCA and NMC in a solvent or a mixture of several solvents. Optionally, a binder and an electronically conductive material are added to the dispersion. By varying the amount of solvent incorporated in the mixture, the viscosity of the ink can be varied before it is deposited on one side of the current collector. The ink-coated current collector is dried and then rolled to adjust its thickness. After evaporation of the solvent(s), a layer of an active material composition is obtained, the proportions of the various constituents of which are ty- pricking: - from 75 to 98% or from 90 to 95% by mass of positive active materials, - from 1 to 10% or from 2 to 5% by mass of binder(s), - from 1 to 10% or from 2 to 5% by mass of electronically conductive material.

[0051] Typically, the mass of the deposited positive active material composition may be in the range of 20 to 30 mg / m2 per side or 25 to 30 mg / cm2 per side.

[0052] The positive electrode is characterized by a porosity less than or equal to 40%, or less than or equal to 35%, or less than or equal to 30%, or less than or equal to 25%.

[0053] Mixing the LMFP with at least one lithium nickel oxide, preferably an NMC, in the prescribed proportions of 30 to 50% LMFP / 70 to 50% lithium nickel oxide allows a porosity of less than or equal to 40% to be obtained, which in turn improves the energy density of the element. Other process conditions that are useful for further reducing the porosity are as follows: - coating the current collector, preferably on both sides, with an intermittent coating as described above prior to ink deposition; - the selection of a Dvso' / Dvso2 ratio greater than or equal to 3, preferably greater than or equal to 5; - reducing the carbon black content or even replacing it with a less porous electronically conductive material such as graphite, carbon nanotubes or graphene.

[0054] Electrode porosity for both positive and negative electrodes is defined as the percentage of pore volume to the geometric volume of the electrode. Pore volume includes the volume of void space present between the particles of the compounds in the layer deposited on the current collector and the volume of pores within the particles of the compounds in the layer deposited on the current collector. Pores within the particles include accessible pores and inaccessible pores. Electrode porosity can be achieved through the following two methods: - In a first method, the mercury technique is used to determine the pore volume. The geometric volume of the electrode is obtained by multiplying the thickness of the layer deposited on the current collector by the surface area coated by the layer. The porosity is obtained by calculating the ratio between the pore volume and the geometric volume of the electrode. - In a second method, the theoretical density d^æ is calculated from the density of each compound in the layer deposited in the current collector. The apparent density dbuik is calculated knowing the mass and volume of the layer deposited on the current collector. The relationship that links porosity to true density and apparent density is: Porosity = 1 - (dbuik / dtrue). Negative electrode:

[0055] The at least one negative electrode comprises a negative current collector, at least one of its two sides of which is coated with a layer of a negative active material composition. The negative active material composition comprises at least one negative active material and optionally a binder and an electronically conductive material. The negative current collector is a solid or perforated metal foil which may be made of copper or a copper-based alloy. Its thickness may be in the range of 3 to 10 μm, preferably 5 to 8 μm. A small current collector thickness makes it possible to increase the mass of the layer of the negative active material composition and to obtain the desired specific energy and specific power.

[0056] The at least one negative active material is preferably chosen from carbon, graphite, coke, carbon black, and vitreous carbon.

[0057] Preferably, the negative active material is a mixture of at least one anisotropically grown carbon, also called "soft" carbon, with at least one isotropically grown carbon, also called "hard" carbon.

[0058] The anisotropically grown carbon may be in the form of elongated platelets. It may be in a crystallized form. The anisotropically grown carbon may be a modified artificial graphite. The anisotropically grown carbon may be a mixture of a modified artificial graphite and a surface-coated modified artificial graphite.

[0059] The isotropically grown carbon may be highly pyrolytic graphite (HPG). The mass of the isotropically grown carbon may be 10 to 60% or 20 to 50% or about 40% of the mass of the mixture.

[0060] The mass of the anisotropically grown carbon may represent from 90 to 40% or from 80 to 50% or about 60% of the mass of the mixture.

[0061] The mass of the modified artificial graphite can represent from 20 to 40% of the mass of the mixture.

[0062] The mass of the surface-coated modified artificial graphite can represent from 20 to 40% of the mass of the mixture.

[0063] A preferred example of a negative active material is a mixture consisting of: - 30% of a modified artificial graphite, - 30% of a surface-coated modified artificial graphite, - 40% of a highly pyrolytic graphite.

[0064] Both anisotropically grown carbon and isotropically grown carbon may exhibit a particle size distribution characterized by a Dv50 value located in the range of 5 to 30 pm or 10 to 25 pm or 15 to 25 pm.

[0065] Blending the at least one anisotropically grown carbon with the at least one isotropically grown carbon allows one to take advantage of the good calenderability of the anisotropically grown carbon to reduce porosity, while preventing shrinkage of the negative electrode structure using the isotropically grown carbon as pillars. As a result, the electrode has both low porosity, for example, less than or equal to 30%, and low tortuosity. This blend also allows one to reduce the electrode ionic resistivity by a factor of 2 compared to a negative active material consisting solely of an isotropically grown carbon. In addition, lithium plating at the electrode surface is reduced or prevented. The composition of the negative active materials may further comprise a silicon-based compound. Preparation process of the negative electrode:

[0066] The negative electrode is prepared in a conventional manner. An ink is prepared by dispersing in a solvent or in a mixture of solvents one or more negative active materials, optionally with a binder. The binder may be such as those described in relation to the positive electrode.

[0067] The ink-coated current collector is dried and then rolled to adjust its thickness. This results in a negative electrode. Typical proportions of the components of the negative active material composition layer, after evaporation of the solvent contained in the ink, are: - from 75 to 98% or from 90 to 98% by mass of negative active materials, - from 1 to 10% or from 1 to 5% by mass of binder(s), - from 0 to 5% by mass or from 1 to 5% of an electronically conductive material.

[0068] The negative electrode is characterized by a porosity less than or equal to 30%. Electrolyte:

[0069] The electrolyte may be liquid. It is obtained by dissolving one or more lithium salts in one or more organic solvents. The solvent may be chosen from saturated cyclic carbonates, unsaturated cyclic carbonates, non-cyclic carbonates, alkyl esters, ethers, nitrile type solvents and tetrahydrothiophene dioxide (sulfolane).

[0070] Saturated cyclic carbonates include ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), butylene carbonate (BC), and mixtures thereof.

[0071] Unsaturated cyclic carbonates include vinylene carbonate (VC).

[0072] Non-cyclic carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (EMC), carbonate dipropyl (DPC), and mixtures thereof.

[0073] Alkyl esters include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and mixtures thereof.

[0074] Ethers include dimethyl ether (DME), diethyl ether (DEE), and mixtures thereof.

[0075] The lithium salt may be chosen from lithium perchlorate LiC104, lithium hexafluorophosphate LiPF6, lithium tetrafluoroborate LiBF4, lithium hexafluoroarsenate LiAsF6, lithium hexafluorantimonate LiSbF6, lithium trifluoromethanesulfonate LiCF3SO3, lithium bis(fluorosulfonyl)imide Li(FSO2)2N (LiFSI), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium tris(fluoromethanesulfonyl)methylide LiC(CF3SO2)3 (LiTFSM), lithium bis(pentafluoroethylsulfonyl)imide LiN(C2F(SO2)2 (LiBeTI), lithium-4,5-dicyano-2-(trifluoromethyl)imidazolide (LiTDI), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LIDFOB), lithium tris(pentafluoroethyl)trifluorophosphate LiPF3(CF2CF3)3 (LiFAP), lithium difluorophosphate LiPO2F2, and mixtures thereof.

[0076] The concentration of said at least one lithium salt may be in the range from 0.75 to 1.5 mol / l. It is preferably in the range from 1 to 1.5 mol / l. It is even better in the range from 1 to 1.2 mol / l. Separator:

[0077] A separator is interposed between a positive electrode and a negative electrode. The material of the separator may be selected from the following materials: a polyolefin, for example polypropylene PP, polyethylene PE, a polyester, polymer-bonded glass fibers, polyimide, polyamide, polyaramid, polyamide-imide, and cellulose. The polyester may be selected from polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). Advantageously, the polyester or polypropylene or polyethylene contains or is coated with a ceramic material selected from the group consisting of metal oxides, carbides, nitrides, borides, silicides, and sulfides. This ceramic material may be SiO2 or Al2O3. The separator may be a layer of polyolefin coated with ceramic, preferably a layer of polyethylene coated with ceramic on both sides. Manufacturing process of the pouch element

[0078] A method of manufacturing the pocket element according to the invention will now be described.

[0079] In a first step, at least one positive electrode and at least one negative electrode are obtained. The layers of positive and negative active material compositions negatives were previously deposited on their respective current collectors, care having been taken to reserve, on one edge of the current collectors, a strip which does not carry a layer of active material composition. This strip not covered with active materials will be used to make the weld with the current output terminal.

[0080] In a second step, the at least one positive electrode or the at least one negative electrode is wrapped by a separator. Preferably, it is the electrode having the largest surface area that is wrapped. This ensures that there is no portion at the periphery of an electrode that is not electrically insulated from the electrode having an opposite polarity.

[0081] In a third step, the at least one positive electrode and the at least one negative electrode separated by a separator are stacked to obtain a block of plates. The at least one positive electrode and the at least one negative electrode are preferably oriented so that the strip not covered with a layer of active material composition of the positive electrode and the strip not covered with a layer of active material composition of the negative electrode are arranged on the same edge of the block of plates. A template can be used to center the at least one positive electrode and the at least one negative electrode.

[0082] In a fourth step, the connection of the positive current output terminal to the strip not covered with a layer of active material composition of said at least one positive electrode and the connection of the negative current output terminal to the strip not covered with a layer of active material composition of said at least one negative electrode are carried out. This connection can be carried out by laser welding or by resistance welding or by ultrasonic welding.

[0083] In a fifth step, a pouch is manufactured by welding several edges of two electrically insulating multilayer films, for example by heat sealing three of the four edges of the two multilayer films. The block of plates is inserted inside the pouch.

[0084] The pouch is filled with an electrolyte. A vacuum may be created inside the pouch. Then the pouch is sealed, for example by heat sealing.

[0085] The fifth step may be preceded by a step of preforming the two electrically insulating multilayer films. This preforming step consists of stamping the two electrically insulating multilayer films in order to create an impression of a positive electrode or a negative electrode on the surface of these two films. The electrode having the largest surface area is chosen. The stamping may be carried out at room temperature using a hydraulic press. This step makes it possible to avoid the formation of folds on the surface of the two multilayer films. Applications

[0086] The pouch element according to the invention can be used to power one of the following flying machines: an electric flying machine, a hybrid electric flying machine, or an aircraft using a 28 V direct current bus system supported by on-board batteries.

[0087] The categories of aircraft covered by the invention are airplanes, rotorcraft, powered elevators, gliders, powered parachutes, ultralight pendulums, and lighter-than-air aircraft.

[0088] The classes of aircraft covered by the invention are single-engine land aircraft, single-engine marine aircraft, multi-engine land aircraft, multi-engine marine aircraft, helicopters, gyroplanes, powered-lift land aircraft, and powered-lift marine aircraft, airships, balloons, powered-parachute land aircraft, powered-parachute marine aircraft, ultralight pendulum land aircraft, and ultralight pendulum marine aircraft. Examples

[0089] Three pouch cells A, B and C were manufactured, all in accordance with the invention. The composition of the positive and negative electrodes used in these cells is summarized in Table 1. The electrolyte composition in all cells was obtained by dissolving LiPF6 at a concentration of 1 mol / l in a mixture of ethylene carbonate / propylene carbonate / ethyl methyl carbonate / dimethyl carbonate (EC / PC / EMC / DMC) mixed in the respective volume proportions of 10 / 20 / 25 / 45. Vinylene carbonate (VC) and fluoroethylene carbonate (FEC) were then added as additives in proportions of 3% and 1% by mass, respectively. The separator in all cells was a 9 µm polyethylene film coated on both sides with a 3 µm ceramic coating.

[0090] [Table 1] Table 1 Cell Cell capacity (Ah) Positive electrode active material Positive electrode porosity (%) Negative electrode active material Negative electrode porosity (%) A 21 50% / 50% LiMnO78FeO22PO4 / LiNio,8MnO2CoojiO2 34 30% modified artificial graphite + 30% surface-coated modified artificial graphite + 40% highly pyrolytic graphite 27 B 21 40% / 60% LiMnO78FeO22PO4 / LiNio>8MnO2CoojiO2 38.5 28.5 C 42 40% / 60% LiMnO78FeO22PO4 / LiNio>8MnO2CoojiO2 38.5 28.5

[0091] [Table 2] Table 2 Element Specific energy (Wh / kg) at C / 5 regime Percentage of reference discharged capacity* (%) B 250 C / 5: 99 C: 93 2C: 86 C 260 C / 5: 99 C: 94 2C: 90 * The reference discharged capacity is measured at a discharge current of C / 10.

[0092] Battery C could be discharged at 25 °C under a high specific power of 1000 W / kg for 30-second pulses at different states of charge ranging from 100% down to a low state of charge of 20%. Low porosity in both the positive and negative electrodes makes it possible to achieve both a high specific energy of at least 250 Wh / kg and a high specific power of at least 1000 W / kg.

[0093] The ability of the cells to provide a high capacity even under a high discharge current was determined. For this purpose, five B-type cells (B 1 to B5) and one C-type cell were discharged at 25°C under various discharge currents of C / 10, C / 5, IC and 2C, C being the nominal capacity of the cell. Each discharge was preceded by a charging step consisting of charging the cell at a rate of C / 5 until a voltage of 4.2 V was reached and then continuing the charging until the charging current fell below C / 50. The discharged capacity at a rate of C / 10 was considered to be the reference discharged capacity. The discharged capacity measured at the rates of C / 5, IC and 2C was compared with the reference discharged capacity, and it was expressed as the percentage of the reference discharged capacity. [Fig.2] represents the percentage of the reference discharged capacity as a function of the discharge rate. Table 2 shows the percentage of the reference discharged capacity as a function of the discharge rate. It should be noted that this percentage remains above 85% for B and C cells even under a high discharge current of 2C.

[0094] Cells A and B were placed in an oven and gradually heated at a rate of +5°C / min. The temperature of the batteries was monitored and any deformation of the cell pouch or the appearance of an opening was detected.

[0095] The test results indicate that the maximum temperatures reached by cells A and B were 170°C and 210°C, these values ​​being within acceptable limits. Openings were observed in both cells when their temperature reached 121°C. However, no thermal runaway or fire was observed. This situation corresponds to level 4 of the EUCAR classification. It was observed that the addition of LMFP to lithium nickel oxide allowed a reduction in the amount of gas released during thermal runaway and a reduction in the rate at which the gas is released compared to a cell whose positive electrode would contain only NMC 622 or NMC 811 as active material.

Claims

Claims

1. A pouch electrochemical element (1) comprising at least one positive electrode and at least one negative electrode, wherein the positive electrode comprises a layer of a composition of positive active materials, said composition comprising a mixture of: a) 30 to 50% by weight of a lithium manganese and iron phosphate of formula LixMni y zFeyMzPO4 where 0.8 < x < 1.2; 0.5 < (1-yz) < 1; 0 < y < 0.5; 0 < z < 0.2; M being chosen from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, and mixtures thereof, b) 70 to 50% by weight of at least one lithium and nickel oxide chosen from Liw(NixCoyAlzMt)O2 where 0.9 < w < 1.1;0 <x;0<y;0<z;0<t;M étant choisi dans le groupe constitué par B, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, W, Mo et leurs mélanges, et Liw(NixMnyCozMt)O2 où 0,9 < w < 1,1 ; 0 < x ; 0 < y ; 0 < z ; 0 <t ;M being selected from the group consisting of Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo and mixtures thereof, and wherein the porosity of the positive electrode is less than or equal to 40%, and the porosity of the negative electrode is less than or equal to 30%, wherein said at least one negative electrode comprises a layer of a negative active material composition comprising a mixture of at least one anisotropically grown carbon with at least one isotropically grown carbon.;

2. The electrochemical pouch element of claim 1, wherein the lithium nickel oxide is Liw(NixMnyCozMt)O2 with 0.7 < x, preferably 0.8 < x.

3. Electrochemical pouch element according to any one of claims 1 and 2, wherein the secondary particles of lithium nickel oxide have a first volume median diameter DV501 and wherein the secondary particles of lithium manganese iron phosphate have a second volume median diameter Dv502, the ratio DV50VDV502 being from 2 to 9, preferably from 3 to 7.

4. A pouch electrochemical cell according to any preceding claim, wherein the positive electrode comprises a current collector which is an aluminum foil or a foil of aluminum alloy at least partially coated on one or both sides.

5. The electrochemical pouch element of claim 4, wherein the coating is made of a material selected from the group consisting of carbon, graphite, carbon nanotubes and mixtures thereof.

6. An electrochemical pouch element according to any one of claims 4 and 5, wherein the current collector has a thickness in the range of 5 to 20 µm, preferably 10 to 16 µm.

7. The electrochemical pouch element of any one of claims 1 to 6, wherein the negative electrode comprises a current collector having a thickness in the range of 3 to 10 µm, preferably 5 to 8 µm.

8. An electrochemical pouch element according to any preceding claim, wherein the layer of positive active material composition contains one or more binders and / or one or more electronically conductive materials, and wherein the mass of said one or more binders represents 1% or less of the mass of the layer; the mass of said one or more electronically conductive materials represents 1% or less of the mass of the layer.

9. An electrochemical pouch element according to any preceding claim, wherein the layer of positive active material composition contains carbon nanotubes.

10. Electrochemical pouch element according to one of the preceding claims, in which the mass of the isotropically grown carbon represents from 10 to 60% or from 20 to 50% of the mass of the mixture.

11. The electrochemical pouch element of any preceding claim, wherein the negative active material composition further comprises a silicon-based compound.

12. A battery comprising a plurality of pouch electrochemical cells according to any one of the preceding claims.

13.

14. A battery-powered flying machine according to claim 12. A flying machine according to claim 13, which is an electric flying machine or a hybrid electric flying machine.

15. An electric flying machine or hybrid electric flying machine according to claim 14, selected from the group consisting of: - an electric vertical takeoff and landing (e-VTOL) machine, - an electric conventional takeoff and landing (e-CTO) machine, and - an electric short take-off and landing (e-STOL) vehicle.

16. A flying machine according to claim 13, which is an aircraft.

Images