Electrochemical element sodium-ion

Abstract

An electrochemical element consisting of a sodium ion comprising an electrolyte including vinylene carbonate, hexane-1,3,6-tricarbonitrile, one or more sodium salts, and one or more solvents. Abbreviated figure: Figure 1

Description

Title of the invention: Electrochemical element sodium-ion technical field

[0001] The technical field of the invention is that of rechargeable electrochemical elements (or accumulators) of the sodium-ion type. Background

[0002] A sodium-ion electrochemical element is known in the prior art. It generally comprises a positive electrode containing an active material capable of inserting sodium into its structure, a negative electrode containing an active material such as carbon, and an electrolyte. The electrolyte comprises one or more organic solvents in which one or more sodium salts are dissolved. The electrolyte fills the internal volume of the element and allows sodium ions to move between the positive and negative electrodes. The operation of the electrochemical element is based on the principle of the reversible insertion of sodium into the host structure of an electrochemically active material. During the charging of the element, the positive active material is oxidized and disinserts sodium from its structure, while the negative active material is reduced and sodium is inserted into its structure.Conversely, during the discharge of the element, the positive active matter is reduced and inserts sodium into its structure, while the negative active matter is oxidized and sodium is removed from its structure.

[0003] A sodium-ion element is an attractive alternative to a lithium-ion element due to the greater abundance of sodium compared to lithium and its lower cost. However, one of the current disadvantages of a sodium-ion element is its shorter cycle life compared to that of a lithium-ion element.

[0004] Document CN107171020 describes an electrochemical element sodium-ion comprising a non-aqueous electrolyte. This electrolyte contains an additive that contributes to the formation of a stable protective film on the surface of the element's positive electrode. This film helps maintain the element's performance during cycling. The additive molecule contains at least two nitrile groups. The additive can be selected from succinonitrile (or butanedinitrile), glutaronitrile (or pentanedinitrile), and hexanetrinitrile. The negative active material is soft carbon. The positive active material is Na[Cu-Fe-Mn]O2 of type O3.

[0005] Document CN 114824474 describes a sodium-ion electrochemical element comprising a non-aqueous electrolyte. The electrolyte contains a first additive, which is a nitrile compound selectable from succinonitrile, glutaronitrile, and hexanetrinitrile, and a second additive, which is ethyl 4,4,4-trifluorobutenoate. The The electrolyte solvent can be a cyclic or linear carbonate. The negatively charged active material can be hard carbon.

[0006] Document CN114400377 describes a sodium-ion electrochemical element comprising a non-aqueous electrolyte. The electrolyte contains a first additive, which is a nitrile compound selectable from succinonitrile, glutaronitrile, and rhexanetritrile, and a second additive, which is a thiosulfate. The solvent of the electrolyte may be a cyclic or linear carbonate. The negatively active material may be hard carbon.

[0007] Document WO2023 / 109708 describes a sodium-ion electrochemical element comprising a non-aqueous electrolyte. The electrolyte comprises a first additive in the form of a sodium salt such as NaNO3, NaBOB (sodium bis(oxalato)borate), or NaDFOB (sodium difluro(oxalato)borate), and a second additive in the form of a co-solvent, such as fluorobenzene and succinonitrile. Hexanenitrile may be used as a co-solvent, and therefore in a high proportion in the electrolyte. The total concentration of sodium salts ranges from 3 to 15 mol / L*. It is stated that the active ingredient is a graphite-based material.

[0008] We are looking for new sodium-ion electrochemical elements exhibiting a high cycling lifetime. Summary

[0009] To this end, the invention proposes a sodium-ion electrochemical element comprising an electrolyte comprising vinylene carbonate (VC), rhexane-1,3,6-tricarbonitrile (HTCN), one or more sodium salts and one or more solvents.

[0010] It has been discovered that the association of vinylene carbonate with rhexane-1,3,6-tricarbonitrile makes it possible to extend the lifetime of the element in cycling.

[0011] According to one embodiment, the sodium-ion electrochemical element comprises a positive electrode comprising a positive active material selected from: a) an oxide of formula Naw(NixFeyMnzMt)O2 where 0.9 <w<l,l ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci ; b) a polyanion; c) Prussian blue and its analogues; and d) mixtures of these.

[0012] According to one embodiment, the positive active material is an oxide of formula Naw (NixFeyMnzMt)O2 where 0.9 <w<l,l ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci.

[0013] According to one embodiment, the sodium-ion electrochemical element comprises a negative electrode comprising a negative active material which is a hard carbon or a soft carbon or a mixture of a soft carbon and a hard carbon.

[0014] According to one embodiment, the sodium salt is NaPF6.

[0015] According to one embodiment, the sodium salts are NaPF6 mixed with sodium bis(fluorosulfonyl)imide Na(FSO2)2N (NaFSI).

[0016] According to one embodiment, the solvents are propylene carbonate and ethyl methyl carbonate.

[0017] According to one embodiment, the sodium salt is NaPF6, the solvents are propylene carbonate and ethyl methyl carbonate, the positive active ingredient is an oxide of formula Naw(NixFeyMnzMt)O2 where 0.9 <w<l,l ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci, et la matière active négative est un carbone dur.

[0018] According to one embodiment, x<0.5; y <0.5; z<0.5; x+y+z=l and t=0.

[0019] According to one embodiment, x=y=z=l / 3.

[0020] According to one embodiment, the mass proportion of vinylene carbonate ranges from 0.5 to 5% expressed in relation to the total mass of said one or more sodium salts and said one or more solvents.

[0021] According to one embodiment, the mass proportion of vinylene carbonate ranges from 1 to 3% expressed in relation to the total mass of said one or more sodium salts and said one or more solvents.

[0022] According to one embodiment, the mass proportion of hexane-1,3,6-tricarbonitrile ranges from 0.5 to 3% expressed in relation to the total mass of said one or more sodium salts and said one or more solvents.

[0023] According to one embodiment, the mass proportion of hexane-1,3,6-tricarbonitrile ranges from 1 to 2% expressed in relation to the total mass of said one or more sodium salts and said one or more solvents.

[0024] According to one embodiment, propylene carbonate represents 10 to 30% of the total volume of solvents, ethyl methyl carbonate represents 90 to 70% of the total volume of solvents. Brief description of the figure

[0025] [Fig. 1] represents the variation of the ratio between the capacity discharged by elements A, B and C and their initial capacity as a function of the cycle number. Detailed description of the implementation methods

[0026] Electrolyte:

[0027] The electrolyte of the sodium-ion element comprises one or more solvents, one or several sodium salts, vinylene carbonate and hexane-1,3,6-tricarbonitrile. The electrolyte can be liquid or gelled.

[0028] The solvent can be chosen from saturated cyclic carbonates, unsaturated cyclic carbonates, linear carbonates, alkyl esters, cyclic esters (lactones), linear ethers, cyclic ethers and mixtures thereof.

[0029] Among the saturated cyclic carbonates, ethylene carbonate (EC), ethylene monofluorocarbonate (FEC), propylene carbonate (PC), butylene carbonate (BC) and mixtures thereof may be cited.

[0030] Among the linear carbonates, we can mention dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dipropyl carbonate (DPC) and mixtures thereof.

[0031] The electrolyte may be free of ethylene monofluorocarbonate (FEC).

[0032] Preferably, the cyclic carbonate(s) represent 50% or less of the total solvent volume, and the linear carbonate(s) represent 50% or more of the total solvent volume. The cyclic carbonate(s) may represent 10 to 40% or 20 to 30% of the total solvent volume, and the linear carbonate(s) may represent 60 to 90% or 70 to 80% of the total solvent volume. In one embodiment, the electrolyte comprises a mixture of propylene carbonate (PC) and ethyl methyl carbonate (EMC).

[0033] Examples of alkyl esters include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate and mixtures thereof.

[0034] Among the ethers, we can mention tetrahydrofuran (THF), 1,3-dioxolane, dimethyl ether (DME) or diethyl ether (DEE) and mixtures thereof.

[0035] According to one embodiment, the electrolyte is free of ether or ester.

[0036] The mass proportion of vinylene carbonate is generally less than 10% relative to the total mass of said sodium salt(s) and said solvent(s). It may range from 0.5 to 5% or from 1 to 3%. The mass proportion of hexane-1,3,6-tricarbonitrile is generally less than 10% relative to the total mass of said sodium salt(s) and said solvent(s). It may range from 0.5 to 3% or from 1 to 2%.

[0037] According to one embodiment, the electrolyte contains no other additive than vinylene carbonate and hexane-1,3,6-tricarbonitrile.

[0038] The sodium salt may be hexafluorinated or tetrafluorinated. It may be selected from the group consisting of NaPF6, NaBF4, NaCl4, NaAsF6, NaSbF6. Preferably, it is NaPF6.

[0039] The sodium salt can also be chosen from sodium bis(fluorosulfonyl)imidide Na(FSO2)2N (NaFSI), sodium bis(trifluoromethanesulfonyl)imidide NaN(CF3SO2)2 )2 (NaTFSI), sodium tris(fluoromethanesulfonyl)methylide NaC(CF3SO2)3 (NaTFSM), sodium bis(pentafluoroethylsulfonyl)imidide NaN(C2F5SO2)2 (NaBETI), sodium 4,5-dicyano-2-(trifluoromethyl)imidazolide (NaTDI), sodium bis(oxalato)borate (NaBOB), sodium difluoro(oxalato)borate (NaDFOB), sodium tris(pentafluoroethyl)trifluorophosphate NaPF3(CF2CF3)3 (NaFAP), sodium difluorophosphate NaPO2F2 and mixtures thereof.

[0040] The total concentration of sodium salts generally ranges from 0.7 to 2 mol.L 1 or from 1 to 1.5 mol.L1.

[0041] Preferably, the electrolyte contains a mixture of propylene carbonate (PC) and ethyl methyl carbonate (EMC) as solvents, NaPF6 as the sodium salt, and vinylene carbonate and rhexane-1,3,6-tricarbonitrile as the only additives. Positive electrode:

[0042] The positive electrode includes a current collector, at least one of whose faces is coated with a layer of a composition of positive active materials, which includes one or more active materials and optionally one or more binders and one or more electronically conductive materials.

[0043] The positive current collector is a solid or perforated metal strip which may be made of aluminum or an aluminum alloy or steel or stainless steel. Its thickness may be in the range of 6 to 30 µm or 5 to 20 µm or 10 to 15 µm, preferably 10 to 15 µm.

[0044] The positive active ingredient can be chosen from: a) a lamellar oxide of formula NaMO2 where M denotes at least one transition metal; b) a polyanion; (c) a compound of Prussian blue or its analogues whose formula is AxP[R(CN)6]y .zH2O, where A is an alkali cation, and P and R are divalent or trivalent transition metal cations, 0 <x<2 ; y<l ; 0<z ; et d) mixtures of these.

[0045] Among the compounds of type a), the preferred ones have the formula Naw(NixFeyMnzMt)O2 where 0.9 <w<l,l ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci. Cette matière active est avantageuse en ce qu’elle est dépourvue de cobalt lequel présente une certaine toxicité.

[0046] Among type b compounds, the preferred ones are phosphates, such as Na3V2(PO4)3 and Na3V2(PO4)2F3.

[0047] Among the type c compounds), Na2Mn[Fe(CN)6] is preferred.

[0048] An ink is prepared by dispersing one or more positive active substances in a solvent or in a mixture of several organic or aqueous solvents. Even Typically, a binder and an electronically conductive material are added to the dispersion. By varying the amount of solvent incorporated into the mixture, the viscosity of the ink can be varied before it is deposited onto a face of the current collector. The ink-coated current collector is dried and then laminated to adjust its thickness. After evaporation of the solvent(s), a layer is obtained composed of one or more active materials, the proportions of whose various constituents are typically: - 80 to 98% or 90 to 95% by mass of one or more active ingredients, - 1 to 10% or 2 to 5% by mass of one or more binders, - from 0.1 to 10% or from 2 to 5% by mass of one or more electronically conductive materials.

[0049] The binder can be selected from poly(vinylidene fluoride) (PVDF) and its copolymers, polytetrafluoroethylene (PTFE) and its copolymers, polyacrylonitrile (PAN), poly(methyl or butyl methacrylate), poly(vinyl chloride) (PVC), poly(vinyl formalin), polyester, sequenced polyetheramides, polymers of acrylic acid, methacrylic acid, acrylamide, itaconic acid, sulfonic acid, elastomers, and cellulosic compounds such as carboxymethylcellulose (CMC). Elastomers usable as binders can be selected from styrene-butadiene (SBR), butadiene-acrylonitrile (NBR), and hydrogenated butadiene-acrylonitrile (HNBR). Said at least one binder may be dispersible in aqueous media, such as polytetrafluoroethylene (PTFE), carboxymethylcellulose (CMC), styrene-butadiene (SBR), butadiene-acrylonitrile (NBR), hydrogenated butadiene-acrylonitrile (HNBR) and polyvinyl alcohol (PVA).

[0050] The electronically conductive material is generally chosen from graphite, carbon black, acetylene black, soot, graphene, carbon fibers, carbon nanotubes or a mixture thereof. Negative electrode:

[0051] The negative electrode includes a current collector, at least one of whose faces is coated with a layer of a composition of negative active materials, which includes one or more negative active materials and optionally one or more binders and one or more electronically conductive materials.

[0052] The active material may be hard carbon or soft carbon, or a mixture thereof. Preferably, it is hard carbon because it exhibits higher cycling capacity and stability than soft carbon. Even more preferably, the negative electrode contains no active material other than hard carbon.

[0053] Hard carbon is defined as carbon that cannot be transformed into graphite (non-graphitizable), even when heated to a temperature exceeding 2500 °C. It generally has a disordered, non-crystalline structure. It is obtained by Pyrolysis of a precursor under an inert atmosphere at a temperature of approximately 1000°C. The precursor can be a synthetic polymer such as a phenolic resin, polyaniline (PANI), or polyacrylonitrile (PAN). It can also be a biopolymer such as sucrose, glucose, cellulose, cotton, or chitosan. Finally, it can be derived from raw biomass such as leaves, algae, wheat straw, or pine.

[0054] Soft carbon is defined as carbon that can be transformed into graphite (graphitizable) by pyrolysis of a precursor at a temperature of approximately 3000°C. This precursor can be polyvinyl chloride (PVC) or petroleum coke.

[0055] The current collector is preferably a two-dimensional conductive support such as a solid or perforated strip, preferably made of aluminum or an aluminum alloy. The current collector may be coated on one or both sides with a layer of carbon. Its thickness may range from 3 to 25 µm, preferably from 10 to 15 µm.

[0056] To obtain the negative active material composition, an ink is prepared by dispersing one or more negative active materials, and optionally one or more binders and one or more electronically conductive compounds, in a solvent or a mixture of solvents, preferably aqueous. The binder(s) may be chosen from the same list as that described in relation to the positive electrode, without necessarily being the same as those of the positive electrode. Similarly, the electronically conductive material(s) may be chosen from the same list as that described in relation to the positive electrode, without necessarily being the same as those of the positive electrode.

[0057] The ink-coated current collector is dried and then laminated to adjust its thickness. After evaporation of the solvent(s), a layer is obtained composed of one or more active materials, the proportions of whose various constituents are typically: - 85 to 98% or 90 to 98% by mass of one or more negatively charged active substances, - 1 to 10% or 1 to 5% by mass of one or more binders, - 0 to 5% by mass or 1 to 5% of one or more electronically conductive materials. Separator:

[0058] A separator is generally interposed between a negative electrode and a positive electrode to prevent possible short circuits. It prevents electrical contact between a negative electrode and a positive electrode but nevertheless allows the transport of ions between these two electrodes. The separator material can be chosen from the following materials: a polyolefin, for example polypropylene and polyethylene, a polyester, or glass fibers bonded together by a The polymer, polyimide, polyamide, polyaramid, polyamideimide, and cellulose are preferred materials. The polyester may be selected from polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). Advantageously, the polyester, polypropylene, or polyethylene may contain or be coated with a material selected from the group consisting of a metal oxide, carbide, nitride, boride, silicide, and sulfide. This material may be SiO2 or Al2O3. The separator may be coated with an organic coating, for example, comprising an acrylate, PVDF, or P(VdF-HFP). A preferred separator is made of polyethylene or consists of a combination of three layers: polypropylene (PP), polyethylene (PE), and polypropylene (PP).

[0059] A preferred electrochemical element sodium-ion comprises: - a negative electrode comprising an active material which is hard carbon, - a positive electrode comprising an active substance of the formula Naw(NixFeyMnzMt)O2 where 0.9 <w<l,l ; 0<x<0,5 ; 0<y<0,5 ; 0<z<0,5 avec x+y+z=l ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci ; - an electrolyte comprising a mixture of propylene carbonate (PC) and methyl ethyl carbonate (EMC) as solvents, NaPF6 as sodium salt, vinylene carbonate and rhexane-1,3,6-tricarbonitrile as the only additives.

[0060] The electrochemical element is manufactured in a conventional manner. It can be in prismatic, cylindrical, pocket or button format. Examples

[0061] Three sodium-ion electrochemical elements A, B, and C were manufactured. In these three elements, the negative electrode contains hard carbon as the active material, and the positive electrode contains Na(Ni / 3Fei / 3Mni / 3)O2 as the active material. Elements A, B, and C differ in the composition of their electrolyte, which is shown in Table 1 below. Solvent percentages are expressed by volume. Additive percentages are expressed relative to the total mass of solvents and NaPF6. The elements were cycled at 25°C under C / 3 and D / 3 regimes. [Tables 1] Element Electrolyte Composition Cycle Number corresponding to a percentage of initial capacity of 90% A* EC / PC / EMC (20 / 20 / 60) NaPF61 moLL1 + 2% FEC 82 B* PC / EMC (20 / 80) NaPF61 moLL1 + 2% VC 195 C PC / EMC (20 / 80) NaPF61 moLL1 + 2% VC + 1% HTCN 240 * Element not included in the invention

[0062] The results of the cycling test of these elements are shown in [Fig. 1]. It can be seen that the element that retains its initial capacity the longest during cycling is element C. The electrolyte of element C contains a combination of vinylene carbonate (VC) and hexane-1,3,6-tricarbonitrile (HTCN). The comparison between element C and element B shows the beneficial effect of hexane-1,3,6-tricarbonitrile on the lifetime of the element during cycling.

Claims

Demands

1. Electrochemical sodium-ion element comprising an electrolyte comprising vinylene carbonate, rhexane-1,3,6-tricarbonitrile, one or more sodium salts and one or more solvents.

2. Electrochemical sodium-ion element according to claim 1, comprising a positive electrode comprising a positive active material selected from: a) an oxide of formula Naw(NixFeyMnzMt)O2 where 0.9 <w<l,l ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci ; b) un polyanion ; c) le bleu de Prusse et ses analogues ; et d) des mélanges de ceux-ci.

3. Electrochemical sodium-ion element according to claim 2, wherein the positive active material is an oxide of formula Naw(NixFeyMnz Mt)O2 where 0.9 <w<l,l ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci.

4. Electrochemical sodium-ion element according to any one of the preceding claims, comprising a negative electrode comprising a negative active material which is hard carbon or soft carbon or a mixture of soft carbon and hard carbon.

5. Electrochemical sodium-ion element according to any one of the preceding claims, wherein the sodium salt is NaPF6.

6. Electrochemical sodium-ion element according to any one of the preceding claims, wherein the sodium salts are NaPF6 mixed with sodium bis(fluorosulfonyl)imidide Na(FSO2)2N (NaFSI).

7. Electrochemical sodium-ion element according to any one of the preceding claims, wherein the solvents are propylene carbonate and ethyl methyl carbonate.

8. Electrochemical element sodium-ion according to claims 3, 4, 5 and 7, wherein: - the sodium salt is NaPF6, - the solvents are propylene carbonate and ethyl methyl carbonate, - the positive active substance is an oxide of formula Naw(NixFeyMnzMt)O 2 where 0.9 <w<l,l ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci, - la matière active négative est un carbone dur.

9. Electrochemical sodium-ion element according to claim 8, wherein x<0.5; y <0.5; z<0.5; x+y+z=l and t=0.

10. Electrochemical sodium-ion element according to claim 9, in which x=y=z=l / 3.

11. Electrochemical sodium-ion element according to any one of the preceding claims, wherein the mass proportion of vinylene carbonate is from 0.5 to 5% expressed in relation to the total mass of said one or more sodium salts and said one or more solvents.

12. Electrochemical sodium-ion element according to claim 11, wherein the mass proportion of vinylene carbonate is from 1 to 3% expressed in relation to the total mass of said one or more sodium salts and said one or more solvents.

13. Electrochemical sodium-ion element according to any one of the preceding claims, wherein the mass proportion of hexane-1,3,6-tricarbonitrile is from 0.5 to 3% expressed in relation to the total mass of said one or more sodium salts and said one or more solvents.

14. Electrochemical sodium-ion element according to claim 13, wherein the mass proportion of hexane-1,3,6-tricarbonitrile is from 1 to 2% expressed in relation to the total mass of said one or more sodium salts and said one or more solvents.

15. Electrochemical sodium-ion element according to any one of claims 8 to 14, wherein: - propylene carbonate represents 10 to 30% of the total volume of solvents, - ethyl methyl carbonate represents 90 to 70% of the total volume of solvents.

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