Electrolyte solution for secondary battery, secondary battery, battery module, battery pack, and electric device

Abstract

The invention provides an electrolyte for a secondary battery, the secondary battery, a battery module, a battery pack and an electric device. The electrolyte for the secondary battery comprises a fluoroether solvent and an additive, wherein the additive comprises one or more of an ionic liquid additive, an amide compound additive, a cation shielding additive and an alloy additive. One or more of the ionic liquid additive, the amide compound additive, the cation shielding additive and the alloy additive are added into the electrolyte containing the fluoroether solvent, so that the interface stability of the secondary battery is remarkably improved, and the cycle performance and the storage stability of the secondary battery are improved; and the overall safety of the secondary battery is improved.

Description

Electrolyte for secondary batteries, secondary batteries, battery modules, battery packs and power-consuming devices Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to an electrolyte for a secondary battery, a secondary battery, a battery module, and an electrical device. Background Art

[0002] In recent years, secondary batteries have been widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. With the widespread use of secondary batteries, higher requirements have been placed on their energy density and cycle performance.

[0003] Electrolytes are the medium that transports ions between the positive and negative electrodes. As an important component of secondary batteries, they play a vital role in the rate performance, cycle life, and safety of secondary batteries. Liquid electrolytes are usually called electrolytes. Electrolytes often have good ionic conductivity, which gives the battery excellent kinetic performance. However, electrolytes are highly reactive and are particularly prone to side reactions with metal negative electrodes, which makes it difficult to effectively improve the battery's cycle performance and storage performance. Therefore, it is necessary to further optimize the electrolyte composition to provide an electrolyte that has both stable electrochemical properties and can improve the overall electrochemical performance of secondary batteries.

[0004] Summary of the Invention

[0005] The present application is made in view of the above-mentioned problems, and its purpose is to provide an electrolyte for secondary batteries, by adding one or more of ionic liquid additives, amide compound additives, cationic shielding additives and alloy additives to a fluoroether solvent obtained by direct fluorine substitution of ether molecules, to provide an electrolyte with stable electrochemical properties. The secondary battery prepared using the electrolyte has improved interface stability, high temperature performance, cycle performance and storage stability.

[0006] In a first aspect, the present application provides an electrolyte for a secondary battery, comprising a fluoroether solvent and an additive, wherein the additive comprises one or more of an ionic liquid additive, an amide compound additive, a cationic shielding additive, and an alloy additive. In any embodiment, the fluoroether solvent is obtained by directly replacing hydrogen on a carbon atom of a corresponding ether molecule with fluorine.

[0007] In any embodiment, the cations of the ionic liquid additive include one or more of nitrogen-containing onium ions and phosphonium-containing onium ions, and the anions of the ionic liquid additive include one or more of halogen ions, phosphate ions, borate ions, sulfonimide compound anions, and sulfonamide compound anions.

[0008] By adding one or more additives selected from ionic liquid additives, amide compound additives, cationic shielding additives and alloy additives to an electrolyte containing a fluoroether solvent, the interfacial stability of the secondary battery can be significantly improved, the cycle performance and storage stability of the secondary battery can be improved, and the overall safety of the secondary battery can be enhanced.

[0009] In any embodiment, the cation of the ionic liquid additive comprises one or more of 1-butyl-3-methylimidazolium, 1-benzyl-3-methylimidazolium, 3-methyl-1-ethoxycarbonylmethylimidazolium, 1-alkyl-3-methylimidazolium, 1-[(trimethylsilyl)methyl]benzotriazolium, N-alkyl-N-methylpiperidinium, 5-azoniaspiro[4.4]nonane, trihexyl(tetradecyl)phosphine ion, tetrabutylphosphine ion, and n-butyl-N-methylpyrrolidinium, and may be 1-benzyl-3-methylimidazolium or 1-alkyl-3-methylimidazolium.

[0010] In any embodiment, the anion of the ionic liquid additive comprises one or more of chloride ion, bromide ion, iodide ion, hexafluorophosphate, tetrafluoroborate, dicyandiamide anion, bis(fluorosulfonyl)amide anion, bis(trifluoromethylsulfonyl)amide anion, bis(fluorosulfonyl)imide anion, and bis(trifluoromethylsulfonyl)imide anion, and can be selected from one or more of chloride ion, bis(fluorosulfonyl)amide anion, bis(trifluoromethylsulfonyl)amide anion, bis(fluorosulfonyl)imide anion, and bis(trifluoromethylsulfonyl)imide anion.

[0011] In any embodiment, the ionic liquid additive includes one or more selected from 1-butyl-3-methylimidazolium-bis(fluorosulfonyl)imide salt, 1-butyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)amide salt, 1-benzyl-3-methylimidazolium-bis(fluorosulfonyl)imide salt, 1-benzyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)amide salt, 1-alkyl-3-methylimidazolium-bis(fluorosulfonyl)imide salt, 1-alkyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)amide salt, 1-alkyl-3-methylimidazolium-chloride salt, and N-alkyl-N-methylpiperidinium-tetrafluoroborate salt.

[0012] In any embodiment, the amide compound additive comprises one or more compounds represented by Formula I, Formula II or Formula III,

[0013]

[0014] wherein R1 to R9 are each independently selected from hydrogen, a silyl group, a ketocarbonyl group, an unsubstituted or at least one fluorine-substituted C1-C3 alkyl group, and an unsubstituted or at least one fluorine-substituted aromatic group.

[0015] In any embodiment, the amide compound additive includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylacetoacetamide, 1,1,1-trifluorofluoro-N,N-dimethylmethanesulfonamide, N,O-bis(trimethylsilyl)trifluoroacetamide, 2,3,6-trifluorobenzenesulfonamide, N,N-dimethyl-4-fluorobenzenesulfonamide, and N-methyl-N-trimethylsilanetrifluoroacetamide.

[0016] In any embodiment, the cationic shielding additive comprises a salt whose cation is an alkali metal element or an alkaline earth metal element.

[0017] In any embodiment, the cationic shielding additive comprises one or more of lithium nitrate, lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, potassium hexafluorophosphate, potassium bisoxalatoborate, potassium difluorooxalatoborate, potassium bis(fluorosulfonyl)imide, potassium bis(trifluoromethylsulfonyl)imide, cesium nitrate, cesium hexafluorophosphate, cesium bis(fluorosulfonyl)imide, cesium chloride, cesium bromide, calcium nitrate, strontium nitrate, and barium nitrate.

[0018] In any embodiment, the alloying additive is a compound having a Group IVA or Group VA element.

[0019] In any embodiment, the alloying additive comprises one or more of antimony trifluoride, antimony pentafluoride, tin difluoride, tin tetrafluoride, bismuth trichloride, and fumed silica.

[0020] In any embodiment, the mass content of the additive is 1-10% based on the total mass of the electrolyte.

[0021] When the mass content of the additive is 1-10% based on the total mass of the electrolyte, a stable SEI film can be formed at the interface between the negative electrode and the electrolyte, and an effective barrier can be constructed at the interfacial double layer to prevent the shuttling and side reactions of some ions and free radicals in the electrolyte, thereby improving the interface stability, cycle performance and storage stability of the battery.

[0022] In any embodiment, the fluoroether solvent comprises a compound represented by Formula IV or a crown ether substituted with a fluorine atom,

[0023]

[0024] wherein R7, R8, and R9 are each independently selected from hydrogen, unsubstituted or fluorine- or hydroxy-substituted straight-chain or branched C1-C6 alkyl, and at least one of R7, R8, and R9 contains a fluorine atom, and R7 and R9 optionally form a 5- or 6-membered saturated heterocyclic ring together with the oxygen to which they are connected and the oxygen-connected R8, in which at least one hydrogen atom on the ring is substituted by fluorine or a fluoroalkyl group.

[0025] In any embodiment, the fluoroether solvent comprises 2,2,3,3-tetrafluoro-1,4-dimethoxybutane, 2-(2-ethoxyethoxy)-1,1,1-trifluoroethane, 1,2-bis(2,2-difluoroethoxy)ethane, 2-(2-(2,2-difluoroethoxy)ethoxy)-1,1,1-trifluoroethane, 1,2-bis(2,2,2-trifluoroethoxy)ethane , 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, 2,2,2-trifluoroethyl-1,1,2,3,3,3-hexafluoropropyl ether, 2,2-bis(trifluoromethyl)-1,3-dioxolane, 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane, 2-ethoxy-4-(trifluoromethyl)-1,3-dioxolane, octafluorotetrahydrofuran, at least one fluorine One or more of fluorine-substituted ethylene glycol dimethyl ether, at least one fluorine atom-substituted diethylene glycol dimethyl ether, at least one fluorine atom-substituted triethylene glycol dimethyl ether, at least one fluorine atom-substituted tetraethylene glycol dimethyl ether, at least one fluorine atom-substituted diethylene glycol diethyl ether, at least one fluorine atom-substituted diisopropyl ether, at least one fluorine atom-substituted dibutyl ether, at least one fluorine atom-substituted diethylene glycol dibutyl ether, at least one fluorine atom-substituted 1,4-diethoxybutane, at least one fluorine atom-substituted 15-crown-5, at least one fluorine atom-substituted 12-crown-4, at least one fluorine atom-substituted 18-crown-6; and optionally at least one of 2,2,3,3-tetrafluoro-1,4-dimethoxybutane and 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane.

[0026] In any embodiment, based on the total mass of the electrolyte, the mass content of the fluoroether solvent is 20%-90%.

[0027] In any embodiment, the electrolyte salt is a sodium salt, and the sodium salt includes one or more of sodium nitrate, sodium perchlorate, sodium hexafluorophosphate, sodium tetrafluoroborate, sodium tetrafluoroyttrium, sodium hexafluoroarsenate, sodium acetate, sodium trifluoroacetate, sodium bisoxalatoborate, sodium difluorooxalatoborate, sodium tetraphenylborate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, and sodium (perfluorobutylsulfonyl)imide.

[0028] In any embodiment, based on the total mass of the electrolyte, the mass content of the electrolyte salt is 2%-70%, optionally 20%-70%.

[0029] When the mass content of the electrolyte salt is 2%-70% based on the total mass of the electrolyte, a stable SEI film can be formed at the interface between the negative electrode and the electrolyte, and an effective barrier can be constructed at the interfacial double layer to prevent the shuttling of ions and free radicals and side reactions, thereby improving the interface stability of the battery.

[0030] A second aspect of the present application provides a secondary battery comprising the electrolyte of the first aspect.

[0031] In any embodiment, the secondary battery comprises one or more of a lithium metal battery and a sodium metal battery.

[0032] In any embodiment, the secondary battery is a negative electrode-less sodium metal battery.

[0033] In any embodiment, the secondary battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes one or more of a Prussian blue compound, a polyanionic compound, and a layered oxide.

[0034] In any embodiment, the surface of the positive electrode active material particles has a coating layer, and the coating layer includes one or more of carbon materials (amorphous, graphite, graphene), polyaniline, polypyrrole, poly (3,4-ethylenedioxythiophene), aluminum oxide, zinc oxide, titanium oxide, zirconium oxide, magnesium oxide, silicon oxide, lanthanum oxide, sodium fluoride, lithium fluoride and aluminum fluoride.

[0035] The coating layer on the surface of the positive electrode active material particles can prevent the surface of the positive electrode metal from directly contacting the electrolyte and causing side reactions, inhibit the dissolution of the positive electrode transition metal, and improve the electrode / electrolyte interface stability.

[0036] In any embodiment, the coating layer has a thickness of 2 nm to 1000 nm.

[0037] In any embodiment, the secondary battery includes a negative electrode plate, the negative electrode plate includes a negative electrode current collector and a primer layer provided on at least one surface of the negative electrode current collector, the primer layer includes one or more of carbon nanotubes, graphite, graphene, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.

[0038] In any embodiment, the negative electrode current collector comprises at least one of a metal foil, a metal foam current collector, a metal mesh current collector, a carbon felt current collector, a carbon cloth current collector, a carbon paper current collector, and a composite current collector.

[0039] In any embodiment, the surface density of the primer layer is 2 g / m 2 -50g / m 2 .

[0040] In any embodiment, the primer layer has a thickness of 1 μm to 100 μm.

[0041] A third aspect of the present application provides a battery module including the secondary battery of the second aspect.

[0042] A fourth aspect of the present application provides a battery pack comprising the secondary battery of the second aspect or the battery module of the third aspect.

[0043] A fifth aspect of the present application provides an electrical device comprising at least one of the secondary battery of the second aspect, the battery module of the third aspect, or the battery pack of the fourth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0045] FIG2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG1 ;

[0046] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0047] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0048] FIG5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG4 ;

[0049] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0050] Reference numerals:

[0051] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0052] Below, the embodiments of the binder, preparation method, electrode, battery, and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0053] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0054] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0055] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0056] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0057] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0058] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0059] Ether solvents are commonly used solvents for secondary battery electrolytes. However, they cannot match all positive electrode active materials, especially layered oxides with high energy density and high working potential. The applicant unexpectedly found that ether solvents after fluorination modification, that is, fluoroether solvents, can effectively increase the absolute value of the highest occupied molecular orbital (HOMO value) of ether compounds, thereby widening the electrochemical stability window of the electrolyte and being able to match positive electrode materials with high working potential to increase the operating voltage of the battery. However, the direct application of fluoroether solvents in secondary batteries, especially in batteries without negative electrodes, still has problems such as low battery cycle performance and poor storage performance.

[0060] [Electrolyte for secondary batteries]

[0061] Based on this, the present application provides an electrolyte for a secondary battery, which includes a fluoroether solvent and an additive, wherein the additive includes one or more of an ionic liquid additive, an amide compound additive, a cationic shielding additive, and an alloy additive.

[0062] In this article, "fluoroether solvent" refers to a solvent obtained by directly replacing ether solvent molecules with fluorine. Unlike common fluoroether inert diluents, the fluoroether solvent in this application is used as the main solvent in the electrolyte.

[0063] In this article, the term "additive" refers to a component present in a relatively small amount in the electrolyte, which can be a gas, liquid, or solid. Conceptually, the difference between additives, primary solvents, and electrolyte salts lies solely in their concentration in the electrolyte. Solvents or salts present in relatively small amounts can be collectively referred to as additives.

[0064] As used herein, the term "ionic liquid additive" refers to a salt added to the electrolyte in small amounts, consisting entirely of cations and anions, that is liquid at or near room temperature. Room temperature refers to 25°C ± 5°C.

[0065] In this article, the term "amide compound additive" refers to an additive added to the electrolyte in a small amount. Group compound.

[0066] In this article, the term "cationic shielding additive" refers to a salt added to the electrolyte in a small amount that can ionize cations. The cations can play a role in eliminating shuttle ions and free radicals that cause side reactions at the double-layer interface of the negative electrode.

[0067] As used herein, the term “alloying additive” refers to a compound added to the electrolyte in a relatively small amount and having an element that can form an alloy with the metal cations in the electrolyte salt in the SEI film.

[0068] In some embodiments, the additive comprises an ionic liquid additive. In some embodiments, the additive comprises an amide compound additive. In some embodiments, the additive comprises a cation shielding additive. In some embodiments, the additive comprises an alloy additive. In some embodiments, the additive is a mixture of an ionic liquid additive and an amide compound additive. In some embodiments, the additive is a mixture of an ionic liquid additive and a cation shielding additive. In some embodiments, the additive is a mixture of an ionic liquid additive and an alloy additive. In some embodiments, the additive is a mixture of an amide compound additive and an alloy additive. In the present application, by adding one or more of ionic liquid additives, amide compound additives, cation shielding additives and alloy additives to a fluoroether electrolyte, the occurrence of side reactions between the metal negative electrode and the electrolyte and the resulting unstable and fragile solid electrolyte interface (SEI) film can be suppressed, thereby significantly improving the interface stability of the secondary battery, improving the cycle performance and storage stability of the secondary battery, and enhancing the overall safety of the secondary battery.

[0069] In some embodiments, the cations of the ionic liquid additive include one or more of nitrogen-containing onium ions and phosphonium-containing onium ions, and the anions of the ionic liquid additive include one or more of halide ions, phosphate ions, borate ions, sulfonyl imide compound anions, and sulfonyl amide compound anions.

[0070] In some embodiments, the cation of the ionic liquid additive comprises one or more of 1-butyl-3-methylimidazolium, 1-benzyl-3-methylimidazolium, 3-methyl-1-ethoxycarbonylmethylimidazolium, 1-alkyl-3-methylimidazolium, 1-[(trimethylsilyl)methyl]benzotriazolium, N-alkyl-N-methylpiperidinium, 5-azoniaspiro[4.4]nonane, trihexyl(tetradecyl)phosphine ion, tetrabutylphosphine ion, and n-butyl-N-methylpyrrolidinium, and may be 1-benzyl-3-methylimidazolium or 1-alkyl-3-methylimidazolium.

[0071] In some embodiments, the anions of the ionic liquid additive include one or more of chloride, bromide, iodide, hexafluorophosphate, tetrafluoroborate, dicyandiamide, bis(fluorosulfonyl)amide, bis(trifluoromethylsulfonyl)amide, bis(fluorosulfonyl)imide, and bis(trifluoromethylsulfonyl)imide, and may be selected from one or more of chloride, bis(fluorosulfonyl)amide, bis(trifluoromethylsulfonyl)amide, bis(fluorosulfonyl)imide, and bis(trifluoromethylsulfonyl)imide.

[0072] In some embodiments, the ionic liquid additive includes one or more selected from 1-butyl-3-methylimidazolium-bis(fluorosulfonyl)imide salt, 1-butyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)amide salt, 1-benzyl-3-methylimidazolium-bis(fluorosulfonyl)imide salt, 1-benzyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)amide salt, 1-alkyl-3-methylimidazolium-bis(fluorosulfonyl)imide salt, 1-alkyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)amide salt, 1-alkyl-3-methylimidazolium-chloride salt, and N-alkyl-N-methylpiperidinium-tetrafluoroborate salt.

[0073] Adding ionic liquid additives to fluoroether solvents, especially ionic liquids containing bis(fluorosulfonyl)imide and bis(trifluoromethylsulfonyl)imide, can strengthen the SEI film formed at the negative electrode and reduce the direct reaction between the negative electrode and the fluoroether solvent molecules or free radicals. At the same time, the ionic liquid additive can also play a role in displacing solvent molecules at the double layer at the interface between the negative electrode and the electrolyte, thereby further reducing the direct reaction between the negative electrode and the fluoroether solvent molecules or free radicals, and synergistically improving the stability at the interface between the negative electrode and the electrolyte, thereby improving the cycle performance and storage performance of the battery at room temperature and high temperature. In some embodiments, the amide compound additive comprises one or more of the compounds shown in Formula I, Formula II or Formula III,

[0074]

[0075] wherein R1 to R9 are each independently selected from hydrogen, a silyl group, a ketocarbonyl group, an unsubstituted or at least one fluorine-substituted C1-C3 alkyl group, and an unsubstituted or at least one fluorine-substituted aromatic group.

[0076] As used herein, the term "silyl" refers to -Si(R 10 )(R 11 )(R 12 ) group, wherein R 10 、R 11 、R 12 are each independently selected from hydrogen, substituted or unsubstituted C 1-3Alkyl. As an example, silyl groups include, but are not limited to, -SiH3, -Si(CH3)3.

[0077] As used herein, the term "ketocarbonyl" refers to a -R-CO-R'- group, wherein R and R' are both hydrocarbon groups.

[0078] As used herein, the term "aryl" refers to an aromatic ring system in which at least one ring is aromatic, including but not limited to phenyl, biphenyl, indanyl, 1-naphthyl, 2-naphthyl, and tetrahydronaphthyl.

[0079] In this article, the term “C 1-3 "Alkyl" refers to a straight or branched hydrocarbon chain radical consisting solely of carbon and hydrogen atoms, with no unsaturation present in the radical, having from one to three carbon atoms, and attached to the rest of the molecule by a single bond.

[0080] As used herein, the term "substituted" refers to a compound or chemical moiety in which at least one hydrogen atom is replaced by another chemical moiety, wherein the substituents are each independently selected from the group consisting of hydroxyl, thiol, amino, cyano, nitro, aldehyde, halogen, alkenyl, alkynyl, aryl, heteroaryl, C 1-6 Alkyl, C 1-6 Alkoxy.

[0081] In some embodiments, the amide compound additive includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylacetoacetamide, 1,1,1-trifluorofluoro-N,N-dimethylmethanesulfonamide, N,O-bis(trimethylsilyl)trifluoroacetamide, 2,3,6-trifluorobenzenesulfonamide, N,N-dimethyl-4-fluorobenzenesulfonamide, and N-methyl-N-trimethylsilanetrifluoroacetamide.

[0082] When amide compound additives are added to a fluoroether solvent, the SEI film formed at the negative electrode will contain inorganic nitrides. The presence of inorganic nitrides improves the film formation stability, thereby greatly improving the electrochemical stability of the battery. At the same time, some amide compound additives have Lewis alkalinity and can coordinate with the Lewis acid in the fluoroether solvent, thereby preventing the Lewis acid components in the electrolyte from continuing to react with the negative electrode, further improving the negative electrode interface stability of the battery. Through the above effects, amide compound additives can significantly improve the cycle performance and storage performance of secondary batteries, especially metal batteries (including batteries without negative electrodes).

[0083] In some embodiments, the cationic shielding additive comprises a salt whose cation is an alkali metal element or an alkaline earth metal element.

[0084] In this context, alkali metal elements refer to metal elements in Group IA of the periodic table except hydrogen (H). In some embodiments, the cationic shielding additive comprises lithium, potassium, or cesium.

[0085] In this document, alkaline earth metal elements refer to elements in Group IIA of the periodic table. In some embodiments, the cationic shielding additive includes calcium, strontium, or barium.

[0086] In some embodiments, the cationic shielding additive comprises one or more of lithium nitrate, lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, potassium hexafluorophosphate, potassium bisoxalatoborate, potassium difluorooxalatoborate, potassium bis(fluorosulfonyl)imide, potassium bis(trifluoromethylsulfonyl)imide, cesium nitrate, cesium hexafluorophosphate, cesium bis(fluorosulfonyl)imide, cesium chloride, cesium bromide, calcium nitrate, strontium nitrate, and barium nitrate.

[0087] By adding cationic shielding additives to fluoroether solvents, cations different from the metal ions in the electrolyte salt can be introduced. The cations in the cationic shielding additives can not only exclude some shuttle ions and free radicals that cause side reactions through the double layer at the negative electrode interface, but also guide the uniform deposition and stripping of the metal ions of the electrolyte salt at the negative electrode. At the same time, some anions contained in the cationic shielding additives can also play a role in increasing the inorganic components in the SEI film and stabilizing the SEI, thereby further improving the negative electrode interface stability of the battery, improving the secondary battery, especially the cycle performance and storage performance of metal batteries (including non-negative electrode batteries). In some embodiments, the alloying additive is a compound having an element of group IVA or group VA.

[0088] In some embodiments, the alloying additive includes one or more of antimony trifluoride, antimony pentafluoride, tin difluoride, tin tetrafluoride, bismuth trichloride, and fumed silica.

[0089] In this article, the term "fumed silica" is also called fumed white carbon black, which is a type of amorphous nano-silica particles.

[0090] When the above alloy additives are added to the fluoroether electrolyte, a double-layer SEI film of the negative electrode can be formed. One layer of the SEI film is rich in alloy components formed by group IVA or group VA elements and sodium elements, while the other layer of the SEI film is rich in inorganic substances such as sodium fluoride. This not only improves the stability of the SEI film, but also inhibits the formation of dendrites at the negative electrode, thereby improving the cycle performance and storage stability of the secondary battery, and reducing gas production, which helps to improve the overall safety of the secondary battery.

[0091] In some embodiments, the mass content of the additive is 1-10% based on the total mass of the electrolyte.

[0092] In some embodiments, the mass content of the additive may be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% based on the total mass of the electrolyte.

[0093] When the mass content of the additive is 1-10% based on the total mass of the electrolyte, a stable SEI film can be formed at the interface between the negative electrode and the electrolyte, and the transmission of ions in the battery will not be affected by the excessive thickness of the SEI film, thereby improving the overall performance of the battery.

[0094] In some embodiments, the ether solvent is a fluoroether solvent, and the fluoroether solvent comprises a compound represented by Formula IV or a crown ether substituted with a fluorine atom or a fluoroalkyl group.

[0095]

[0096] wherein R7, R8, and R9 are each independently selected from hydrogen, unsubstituted or fluorine- or hydroxy-substituted straight-chain or branched C1-C6 alkyl, and at least one of R7, R8, and R9 contains a fluorine atom, and R7 and R9 optionally form a 5- or 6-membered saturated heterocyclic ring together with the oxygen to which they are connected and the oxygen-connected R8, in which at least one hydrogen atom on the ring is substituted by fluorine or a fluoroalkyl group.

[0097] In this article, the term “C 1-6 "Alkyl" can refer to the term "C 1-3 This is understood from the definition of "alkyl".

[0098] As used herein, the term "fluoroalkyl" refers to an alkyl group containing at least one fluorine atom.

[0099] In some embodiments, the fluoroether solvent comprises 2,2,3,3-tetrafluoro-1,4-dimethoxybutane (FDMB, ), 2-(2-ethoxyethoxy)-1,1,1-trifluoroethane (F3DEE, ), 1,2-bis(2,2-difluoroethoxy)ethane (F4DEE, ), 2-(2-(2,2-difluoroethoxy)ethoxy)-1,1,1-trifluoroethane (F5DEE, ), 1,2-bis(2,2,2-trifluoroethoxy)ethane (F6DEE, ), 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, 2,2,2-trifluoroethyl-1,1,2,3,3,3-hexafluoropropyl ether, 2,2-bis(trifluoromethyl)-1,3-dioxolane, 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane, 2-ethoxy-4-(trifluoromethyl)-1,3-dioxolane, octafluorotetrahydrofuran, ethylene glycol dimethyl ether substituted with at least one fluorine atom, diethylene glycol dimethyl ether substituted with at least one fluorine atom, triethylene glycol dimethyl ether substituted with at least one fluorine atom, tetraethylene glycol dimethyl ether substituted with at least one fluorine atom, to One or more of diethylene glycol diethyl ether substituted with at least one fluorine atom, diisopropyl ether substituted with at least one fluorine atom, dibutyl ether substituted with at least one fluorine atom, diethylene glycol dibutyl ether substituted with at least one fluorine atom, 1,4-diethoxybutane substituted with at least one fluorine atom, 15-crown-5 substituted with at least one fluorine atom, 12-crown-4 substituted with at least one fluorine atom, and 18-crown-6 substituted with at least one fluorine atom; and optionally at least one of 2,2,3,3-tetrafluoro-1,4-dimethoxybutane and 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane.

[0100] Direct fluorination of ether molecules can increase the absolute value of the highest occupied molecular orbital (HOMO) of ethers, thereby broadening the electrochemical stability window of the corresponding electrolyte after the electrolyte salt is dissolved, improving the electrochemical stability of the electrolyte, and enabling the electrolyte to be used with higher potential positive electrode active materials, thereby increasing the operating voltage of the secondary battery.

[0101] In some embodiments, the mass content of the fluoroether solvent is 20%-90% based on the total mass of the electrolyte.

[0102] In some embodiments, the mass content of the fluoroether solvent is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90% based on the total mass of the electrolyte.

[0103] Unlike using fluoroether solvents as inert diluents, fluoroether solvents have a higher mass content in the electrolyte. As the main solvent, they can effectively improve the electrochemical stability of the electrolyte, allowing the electrolyte to be used with higher potential positive electrode active materials, thereby increasing the operating voltage of the secondary battery.

[0104] In some embodiments, the electrolyte salt is a sodium salt, and the sodium salt includes one or more of sodium nitrate, sodium perchlorate, sodium hexafluorophosphate, sodium tetrafluoroborate, sodium tetrafluoroyttrium, sodium hexafluoroarsenate, sodium acetate, sodium trifluoroacetate, sodium bisoxalatoborate, sodium difluorooxalatoborate, sodium tetraphenylborate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, and sodium (perfluorobutylsulfonyl)imide.

[0105] In some embodiments, the mass content of the electrolyte salt is 2%-70%, optionally 20%-70%, based on the total mass of the electrolyte.

[0106] In some embodiments, the mass content of the electrolyte salt is 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70% based on the total mass of the electrolyte.

[0107] When the mass content of the electrolyte salt is 2%-70% based on the total mass of the electrolyte, the electrolyte provided in this application can effectively improve the chemical stability, cycle performance, and storage performance of the battery. When the mass content of the electrolyte salt is 20%-70% based on the total mass of the electrolyte, the high concentration of electrolyte salt can further reduce the free solvent molecules in the solvent, reduce the side reaction between the solvent and the negative electrode, and improve the cycle performance, storage performance, and high-temperature performance of the battery.

[0108] [Secondary battery]

[0109] In some embodiments, a secondary battery includes the above-described electrolyte.

[0110] In some embodiments, the secondary battery is a lithium metal battery or a sodium metal battery.

[0111] A lithium metal battery is a battery whose negative electrode is lithium metal and uses lithium ions to migrate back and forth between the positive and negative electrodes.

[0112] A sodium metal battery is a battery whose negative electrode is sodium metal and uses sodium ions to migrate back and forth between the positive and negative electrodes.

[0113] In some embodiments, the secondary battery is a cathode-free sodium metal battery. These batteries utilize no negative electrode active material and only a negative electrode current collector as the negative electrode. During the initial charge, sodium is plated on the negative electrode, and then returned to the positive electrode during discharge, completing the charge-discharge cycle. Because they lack negative electrode material and utilize only a negative electrode current collector, cathode-free batteries can effectively overcome the shortcomings of sodium metal batteries and achieve higher energy density than sodium metal anodes.

[0114] Although fluoroether solvents can effectively improve the electrochemical stability of batteries, the side reactions they cause are more significant in anode-free batteries. This application adds one or more of ionic liquid additives, amide compound additives, cationic shielding additives, and alloy additives to a fluoroether solvent to form a stable SEI film at the electrode / electrolyte interface. This also creates an effective barrier at the interfacial double layer to prevent the shuttle of some ions and free radicals and side reactions, significantly improving the cycling performance and storage stability of anode-free sodium batteries.

[0115] In some embodiments, a secondary battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes one or more of a Prussian blue compound, a polyanionic compound, and a layered oxide.

[0116] The transition metal in the layered transition metal oxide can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Optionally, the layered transition metal oxide is, for example, NaxMO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0<x≤1.

[0117] Polyanionic compounds can be metal ions, transition metal ions and tetrahedral (YO4) n- A class of compounds with anionic units. The metal ion can be selected from sodium ion, lithium ion, potassium ion, and zinc ion; the transition metal can be selected from at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be selected from at least one of P, S, and Si; n represents (YO4) n- valence.

[0118] Prussian blue compounds can be compounds containing sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Prussian blue compounds are, for example, Na a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0<a≤2, 0<b<1, 0<c<1.

[0119] In some embodiments, the positive electrode active material includes NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2、Na(Cu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn1 / 3 )O2、Na 2 / 3 Ni 1 / 6 Mn 2 / 3 Cu 1 / 9 Mg 1 / 18 O2, Na4Fe3(PO4)2P2O7, NaFePO4, Na3V2(PO4)3, Na 1.9 One or more of CoFe(CN)6, Na2NiFe(CN)6, and NaMnFe(CN)6.

[0120] Electrodeless sodium metal batteries exhibit excellent cycling performance in ether electrolytes, particularly when paired with polyanionic cathodes, including sodium vanadium phosphate (Na₃V₂(PO₄)₃) and sodium iron pyrophosphate (Na₄Fe₃(PO₄)₂P₂Oₐ). Layered oxides have higher energy density, and when combined with the electrolytes provided herein, they can effectively improve the low coulombic efficiency and poor cycling performance of these batteries in ether electrolytes.

[0121] In some embodiments, the surface of the positive electrode active material particles has a coating layer, which includes one or more of carbon materials (amorphous carbon, graphite, graphene, etc.), polyaniline, polypyrrole, poly (3,4-ethylenedioxythiophene), aluminum oxide, zinc oxide, titanium oxide, zirconium oxide, magnesium oxide, silicon oxide, lanthanum oxide, sodium fluoride, lithium fluoride and aluminum fluoride.

[0122] The coating of the coating layer can effectively improve the stability of the positive electrode active material, reduce the metal dissolution and particle breakage of the positive electrode active material during the cycle, and effectively improve the cycle performance and storage stability of the battery.

[0123] In some embodiments, the coating layer has a thickness of 2 nm to 1000 nm.

[0124] A coating layer of appropriate thickness can effectively improve the battery performance by preventing excessively high positive electrode diaphragm resistance and decreased battery performance caused by an excessively thick coating layer.

[0125] In some embodiments, a secondary battery includes a negative electrode plate, which includes a negative electrode collector and a primer layer disposed on at least one surface of the negative electrode collector, wherein the primer layer includes one or more of carbon nanotubes, graphite, graphene, silver-composite carbon nanoparticles, and tin-composite carbon nanoparticles.

[0126] In some embodiments, the basecoat layer has an areal density of 2 g / m 2 -50g / m 2 .

[0127] In some embodiments, the primer layer has a thickness of 1 μm to 100 μm.

[0128] A primer layer within the above range can effectively guide negative electrode deposition, reduce the formation of negative electrode sodium dendrites, and improve the uniformity of sodium metal deposition. Furthermore, a primer layer with an appropriate surface density and thickness can truly achieve the effect of eliminating the negative electrode, improving the battery's energy density and safety performance.

[0129] In some embodiments, the current collector of the negative electrode-free sodium metal battery includes at least one of a metal foil, a metal foam current collector, a metal mesh current collector, a carbon felt current collector, a carbon cloth current collector, a carbon paper current collector, and a composite current collector.

[0130] In some embodiments, the metal foil can be copper foil, aluminum foil, stainless steel foil, or titanium foil, and the metal foam current collector can be copper foam, aluminum foam, nickel foam, or the like. The metal mesh current collector can be copper mesh, aluminum mesh, or stainless steel mesh. Composite current collectors include those with a primer layer or those with a polymeric base film. The composite current collector can have a "sandwich" structure, with the polymeric base film in the middle and metal foil on either side. Alternatively, the composite current collector can have a metal foil on one side of the polymeric base film. The polymeric base film can be selected from polyamide, polyterephthalate, polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, acrylonitrile-butadiene-styrene copolymer, polybutylene terephthalate, poly(p-phenylene terephthalamide), polypropylene, polyoxymethylene, epoxy resin, phenolic resin, polytetrafluoroethylene, polyvinylidene fluoride, silicone rubber, and polycarbonate. In some embodiments, the secondary battery can include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte.

[0131] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0132] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 5 with a square structure as an example.

[0133] In some embodiments, referring to FIG2 , the outer package may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0134] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0135] Figure 3 shows an example battery module 4. Referring to Figure 3 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0136] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0137] In some embodiments, the battery modules described above may be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0138] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0139] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0140] As an electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0141] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0142] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0143] Example

[0144] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0145] Example 1

[0146] 1. Preparation method

[0147] 1. Preparation of positive electrode sheet

[0148] The positive electrode active material carbon-coated sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7 / C), binder polyvinylidene fluoride (PVDF), and conductive agent conductive carbon black (Super-P) were mixed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 96%:2%:2% to prepare a positive electrode slurry. The positive electrode slurry was coated on the surface of aluminum foil using an extrusion coater according to the positive electrode active material unit area mass requirement and dried. The coated electrode was then pressed by a cold press at a pressure of 2.5 g / cm 3 The designed compaction is cold pressed to prepare the final positive electrode sheet.

[0149] 2. Preparation of negative electrode sheet

[0150] Carbon nanotubes and sodium carboxymethyl cellulose were added to water in a mass ratio of 1:2 and stirred to form a uniform slurry. The slurry was coated on the negative electrode current collector, dried, and cut to obtain a negative electrode sheet without a negative electrode structure. The surface density of the base coating was 10 g / m 2 , wherein the thickness of the primer layer is 5 μm.

[0151] 3. Isolation film

[0152] Polyethylene film (PE film) is used as the separator.

[0153] 4. Preparation of electrolyte

[0154] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), 20wt.% sodium bis(fluorosulfonyl)imide was dissolved in 70wt.% of 2,2,3,3-tetrafluoro-1,4-dimethoxybutane organic solvent, and then 10wt.% of 1,1,1-trifluoro-N,N-dimethylmethanesulfonamide additive was added and dissolved in the organic solvent, and stirred evenly to obtain the electrolyte of Example 1.

[0155] 5. Preparation of batteries

[0156] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to serve as an isolation layer. The electrolyte is then added to form a button battery.

[0157] See Table 1 for specific parameters.

[0158] In Examples 2-39, the components of the electrolyte for secondary batteries were adjusted, and the specific parameters are shown in Table 1. In Examples 15-19, the mass ratio of the additive components was 1:1.

[0159] In Examples 40-43, the positive electrode active material is Na[Cu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 ]O2, the specific parameters of other components are shown in Table 1.

[0160] In Examples 44-47, the positive electrode active material is ZrO2-coated Na 2 / 3 Ni 1 / 6 Mn 2 / 3 Cu 1 / 9 Mg 1 / 18 O2, and the specific parameters of other components are shown in Table 1.

[0161] In Comparative Examples 1-23, the electrolyte components or the positive electrode active materials of the secondary batteries were adjusted. The specific parameters are shown in Table 1. The preparation method is basically the same as that of Example 1.

[0162] 2. Battery performance test

[0163] 1) Electrochemical stability window test

[0164] An electrochemical workstation was used to perform the window test of the electrolyte. The test temperature was 25°C, the voltage range was 1.0-5.0 V, and the scan rate was 0.1 m V / s. The usage window of the electrolyte was determined based on the starting position of the peak potential in the CV curve. The cyclic voltammetry (CV) tests in this experiment were all performed on a 1470 multi-channel electrochemical workstation from Solartron, UK.

[0165] 2) Normal temperature / high temperature cycle performance

[0166] At 25 / 60°C and atmospheric pressure (0.1 MPa), the battery was charged at a constant current of 0.1C to a voltage of 4V (layered oxide cathode) or 3.7V (sodium iron pyrophosphate cathode), then charged at a constant voltage of 4 / 3.7V to a current of 0.01C, and then discharged at a constant current of 0.1C to a voltage of 3.0V. This was the first charge-discharge cycle. The battery was then charged at a constant current of 1C to a voltage of 4 / 3.7V, then charged at a constant voltage of 4 / 3.7V to a current of 0.1C, and then discharged at a constant current of 1C to a voltage of 3.0V. The capacity at the first discharge was considered 100%, and the number of cycles required to reach 80% of the discharged capacity was recorded.

[0167] 3) Normal temperature / high temperature storage performance

[0168] At 25 / 60°C and normal pressure (0.1MPa), the battery was charged to 4V (layered oxide positive electrode) or 3.7V (sodium iron pyrophosphate positive electrode) at a constant current of 0.1C, then charged to a current of 0.01C at a constant voltage of 4 / 3.7V, and then discharged to 3V at a constant current of 0.1C to obtain the discharge capacity before storage (Cd1); the sodium battery was charged to 4 / 3.7V at a constant current of 0.1C at 25°C, and then charged to 100% SOC at a constant voltage of 4 / 3.7V. The battery was stored in a constant temperature environment of 25 / 60°C, and the storage days when the battery storage capacity retention rate was 80% were recorded.

[0169] The test method for the discharge capacity after storage (Cdn) is as follows: at 25 / 60°C, the battery is charged to 4 / 3.7V at a constant current of 0.1C, then charged at a constant voltage of 4 / 3.7V until the current drops to 0.01C, and then discharged to 3V at a constant current of 0.1C. The discharge capacity of the sodium battery after storage for n days is obtained and recorded as Cdn.

[0170] Storage capacity retention rate=discharge capacity after storage (Cdn) / discharge capacity before storage (Cd1)*100%.

[0171] The test results of the above embodiments and comparative examples are shown in Tables 1 and 2.

[0172] Table 1

[0173]

[0174]

[0175]

[0176]

[0177]

[0178] Table 2

[0179]

[0180]

[0181]

[0182]

[0183]

[0184] As can be seen from Tables 1 and 2, the electrolytes of the negative electrode-free sodium batteries of Examples 1 to 47 include fluoroether solvents and additives, wherein the fluoroether solvent is used as the main solvent of the electrolyte, and the additives are selected from one or more of ionic liquid additives, amide compound additives, cationic shielding additives, and alloy additives. Examples 1-5 use ionic liquid additives as additives, Examples 6-8 use amide compound additives as additives, Examples 9-11 use cationic shielding additives as electrolyte additives, Examples 12-14 use alloy additives as additives, and Examples 15-19 use a combination of one or more selected from ionic liquid additives, amide compound additives, cationic shielding additives, and alloy additives as additives. Compared to Comparative Example 18 using an ether solvent as the main solvent, the batteries of Examples 1 to 47 exhibit a wider electrochemical stability window, and the electrolyte has better electrochemical stability.

[0185] In addition, from the comparison of Examples 1 to 19 with Comparative Examples 1 to 2, the comparison of Examples 20 to 27 with Comparative Examples 3 to 6, the comparison of Examples 28 to 30 with Comparative Examples 7 to 9, the comparison of Examples 35 to 39 with Comparative Examples 10 to 14, the comparison of Examples 40 to 43 with Comparative Example 15, and the comparison of Examples 44 to 47 with Comparative Example 16, it can be seen that the addition of additives to the electrolyte can greatly improve the storage performance of the negative electrode-free battery at room temperature and high temperature.

[0186] As can be seen from Examples 1 to 14, amide compound additives are more effective in improving the cycle performance and storage performance of negative electrode-free batteries. As can be seen from Examples 1 to 5, compared with 1-alkyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, 1-alkyl-3-methylimidazolium bis(fluorosulfonyl)amide, 1-butyl-3-methylimidazolium bis(fluorosulfonyl)imide, and N-alkyl-N-methylpiperidinium tetrafluoroborate are more effective in improving the cycle performance and storage performance of negative electrode-free batteries. Among them, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide is the most significant in improving the cycle performance and storage performance of negative electrode-free batteries at room temperature and high temperature. As can be seen from Examples 9 to 11, potassium bis(oxalatoborate) in the cationic shielding additive has a better effect on improving the cycle performance and storage performance of negative electrode-free batteries. As can be seen from Examples 12 to 14, fumed silica in the alloy additive is more effective in improving the cycle performance and storage performance of the battery.

[0187] As can be seen from Examples 15 to 19, the addition of two different types of additives can also effectively improve the cycle performance and storage performance of the battery. In Example 17, the co-addition of the ionic liquid additive 1-butyl-3-methylimidazolium bis(fluorosulfonyl)imide salt and the amide compound additive 1,1,1-trifluorofluoro-N,N-dimethylmethanesulfonamide played a synergistic role, resulting in a three-fold increase in the number of cycles for the negative electrode-free battery to retain 80% of its capacity at room temperature, and a five-fold increase in the number of cycles compared to the negative electrode-free battery without additives in Comparative Example 1. The number of cycles at high temperature increased by 10 times, and the number of storage days increased by 18 times.

[0188] It can be seen from Examples 20 to 27 that the additives provided in this application are suitable for various fluoroether solvents. For electrolyte systems using various fluoroether solvents as main solvents, they can effectively improve the cycle performance and storage performance of the battery, and improve the electrochemical stability and cycle life of the battery.

[0189] It can be seen from Examples 28 to 30 that the electrolyte provided in this application is applicable to a variety of different sodium salts, and the batteries can exhibit excellent cycle performance and storage performance.

[0190] It can be seen from Examples 6 and 31 to 34 that when the mass content of the additive is 1-10% based on the total mass of the electrolyte, the battery can exhibit a wider electrochemical window and excellent cycle performance and storage performance at room temperature and high temperature.

[0191] As can be seen from Examples 6, 35 to 39, based on the total mass of the electrolyte, when the mass content of the fluoroether solvent is 20%-90%, the battery can show a wider electrochemical window, excellent cycle performance and storage performance at room temperature and high temperature. As can be seen from Examples 6, 31 to 39, based on the total mass of the electrolyte, when the mass content of the electrolyte salt is 2%-70%, the battery can show a wider electrochemical window, excellent cycle performance and storage performance at room temperature and high temperature. In addition, from the comparison of 6, 31 to 36 with Examples 37 to 39, it can be seen that when the mass content of the electrolyte salt is 20%-70%, the electrochemical window stability, cycle performance and storage performance of the battery are even better.

[0192] From the comparison of Examples 40 to 47 with Comparative Examples 18 to 23, it can be seen that the electrolyte provided in the present application is applicable to a variety of positive electrode materials, whether for polyanions or layered oxides, and can effectively improve the electrochemical stability window width of the battery and the cycle performance and storage stability of the battery.

[0193] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. An electrolyte for a secondary battery, characterized in that The invention comprises a fluoroether solvent and an additive, wherein the additive comprises one or more of an ionic liquid additive, an amide compound additive, a cationic shielding additive and an alloy additive.

2. The electrolyte according to claim 1, characterized in that The cations of the ionic liquid additive include one or more of nitrogen-containing onium ions and phosphonium-containing onium ions, and the anions of the ionic liquid additive include one or more of halogen ions, phosphate ions, borate ions, sulfonimide compound anions, and sulfonamide compound anions.

3. The electrolyte according to claim 1 or 2, characterized in that The cation of the ionic liquid additive includes one or more of 1-butyl-3-methylimidazolium, 1-benzyl-3-methylimidazolium, 3-methyl-1-ethoxycarbonylmethylimidazolium, 1-alkyl-3-methylimidazolium, 1-[(trimethylsilyl)methyl]benzotriazolium, N-alkyl-N-methylpiperidinium, 5-azoniaspiro[4.4]nonane, trihexyl(tetradecyl)phosphine ion, tetrabutylphosphine ion, and n-butyl-N-methylpyrrolidinium, and may be 1-benzyl-3-methylimidazolium or 1-alkyl-3-methylimidazolium.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The anions of the ionic liquid additive include one or more of chloride ion, bromide ion, iodide ion, hexafluorophosphate, tetrafluoroborate, dicyandiamide anion, bis(fluorosulfonyl)amide anion, bis(trifluoromethylsulfonyl)amide anion, bis(fluorosulfonyl)imide anion, and bis(trifluoromethylsulfonyl)imide anion, and can be selected from one or more of chloride ion, bis(fluorosulfonyl)amide anion, bis(trifluoromethylsulfonyl)amide anion, bis(fluorosulfonyl)imide anion, and bis(trifluoromethylsulfonyl)imide anion.

5. The electrolyte according to any one of claims 1 to 3, characterized in that The ionic liquid additive includes one or more selected from 1-butyl-3-methylimidazolium-bis(fluorosulfonyl)imide salt, 1-butyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)amide salt, 1-benzyl-3-methylimidazolium-bis(fluorosulfonyl)imide salt, 1-benzyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)amide salt, 1-alkyl-3-methylimidazolium-bis(fluorosulfonyl)imide salt, 1-alkyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)amide salt, 1-alkyl-3-methylimidazolium-chloride salt, and N-alkyl-N-methylpiperidinium-tetrafluoroborate salt.

6. The electrolyte according to any one of claims 1 to 5, characterized in that The amide compound additive comprises one or more compounds represented by formula I, formula II or formula III wherein R1 to R9 are each independently selected from hydrogen, a silyl group, a ketocarbonyl group, an unsubstituted or at least one fluorine-substituted C1-C3 alkyl group, and an unsubstituted or at least one fluorine-substituted aromatic group.

7. The electrolyte according to any one of claims 1 to 6, characterized in that The amide compound additive includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylacetoacetamide, 1,1,1-trifluorofluoro-N,N-dimethylmethanesulfonamide, N,O-bis(trimethylsilyl)trifluoroacetamide, 2,3,6-trifluorobenzenesulfonamide, N,N-dimethyl-4-fluorobenzenesulfonamide, and N-methyl-N-trimethylsilanetrifluoroacetamide.

8. The electrolyte according to any one of claims 1 to 7, characterized in that The cationic shielding additive comprises a salt whose cation is an alkali metal element or an alkaline earth metal element.

9. The electrolyte according to any one of claims 1 to 8, characterized in that The cationic shielding additives include one or more of lithium nitrate, lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, potassium hexafluorophosphate, potassium bisoxalatoborate, potassium difluorooxalatoborate, potassium bis(fluorosulfonyl)imide, potassium bis(trifluoromethylsulfonyl)imide, cesium nitrate, cesium hexafluorophosphate, cesium bis(fluorosulfonyl)imide, cesium chloride, cesium bromide, calcium nitrate, strontium nitrate, and barium nitrate.

10. The electrolyte according to any one of claims 1 to 9, characterized in that The alloying additive is a compound containing Group IVA or Group VA elements.

11. The electrolyte according to any one of claims 1 to 10, characterized in that The alloy additives include one or more of antimony trifluoride, antimony pentafluoride, tin difluoride, tin tetrafluoride, bismuth trichloride, and fumed silica.

12. The electrolyte according to any one of claims 1 to 11, characterized in that Based on the total mass of the electrolyte, the mass content of the additive is 1-10%.

13. The electrolyte according to any one of claims 1 to 12, characterized in that The ether solvent is a fluoroether solvent, and the fluoroether solvent comprises a compound represented by Formula IV or a crown ether substituted with a fluorine atom. wherein R7, R8, and R9 are each independently selected from hydrogen, unsubstituted or fluorine- or hydroxy-substituted straight-chain or branched C1-C6 alkyl, and at least one of R7, R8, and R9 contains a fluorine atom, and R7 and R9 optionally form a 5- or 6-membered saturated heterocyclic ring together with the oxygen to which they are connected and the oxygen-connected R8, in which at least one hydrogen atom on the ring is substituted by fluorine or a fluoroalkyl group.

14. The electrolyte according to any one of claims 1 to 13, characterized in that The fluoroether solvents include 2,2,3,3-tetrafluoro-1,4-dimethoxybutane, 2-(2-ethoxyethoxy)-1,1,1-trifluoroethane, 1,2-bis(2,2-difluoroethoxy)ethane, 2-(2-(2,2-difluoroethoxy)ethoxy)-1,1,1-trifluoroethane, 1,2-bis(2,2,2-trifluoroethoxy)ethane, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, 2,2,2-trifluoroethyl-1,1,2,3,3,3-hexafluoropropyl ether, 2,2-bis(trifluoromethyl)-1,3-dioxolane, 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane, 2-ethoxy-4-(trifluoromethyl)-1,3-dioxolane, octafluorotetrahydrofuran, at least one fluorine atom substituted One or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether substituted with at least one fluorine atom, triethylene glycol dimethyl ether substituted with at least one fluorine atom, tetraethylene glycol dimethyl ether substituted with at least one fluorine atom, diethylene glycol diethyl ether substituted with at least one fluorine atom, diisopropyl ether substituted with at least one fluorine atom, dibutyl ether substituted with at least one fluorine atom, diethylene glycol dibutyl ether substituted with at least one fluorine atom, 1,4-diethoxybutane substituted with at least one fluorine atom, 15-crown-5 substituted with at least one fluorine atom, 12-crown-4 substituted with at least one fluorine atom, and 18-crown-6 substituted with at least one fluorine atom; and optionally at least one of 2,2,3,3-tetrafluoro-1,4-dimethoxybutane and 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane.

15. The electrolyte according to any one of claims 1 to 14, characterized in that Based on the total mass of the electrolyte, the mass content of the fluoroether solvent is 20%-90%.

16. The electrolyte according to any one of claims 1 to 15, characterized in that The electrolyte salt is a sodium salt, and the sodium salt includes one or more of sodium nitrate, sodium perchlorate, sodium hexafluorophosphate, sodium tetrafluoroborate, sodium tetrafluoroyttrium, sodium hexafluoroarsenate, sodium acetate, sodium trifluoroacetate, sodium bisoxalatoborate, sodium difluorooxalatoborate, sodium tetraphenylborate, sodium trifluoromethylsulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, and sodium (perfluorobutylsulfonyl)imide.

17. The electrolyte according to any one of claims 1 to 16, characterized in that Based on the total mass of the electrolyte, the mass content of the electrolyte salt is 2%-70%, and optionally 20%-70%.

18. A secondary battery, characterized in that: Comprising the electrolyte according to any one of claims 1 to 17.

19. The secondary battery according to claim 18, wherein The secondary battery includes one or more of a lithium metal battery and a sodium metal battery.

20. The secondary battery according to claim 18 or 19, characterized in that: The secondary battery is a negative electrode-free sodium metal battery.

21. The secondary battery according to any one of claims 18 to 20, characterized in that The secondary battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes one or more of a Prussian blue compound, a polyanion compound, and a layered oxide.

22. The secondary battery according to any one of claims 18 to 21, characterized in that The surface of the positive electrode active material particles has a coating layer, which includes one or more of carbon material, polyaniline, polypyrrole, poly(3,4-ethylenedioxythiophene), aluminum oxide, zinc oxide, titanium oxide, zirconium oxide, magnesium oxide, silicon oxide, lanthanum oxide, sodium fluoride, lithium fluoride and aluminum fluoride.

23. The secondary battery according to any one of claims 18 to 22, characterized in that: The thickness of the coating layer is 2nm-1000nm.

24. The secondary battery according to any one of claims 18 to 23, characterized in that The secondary battery includes a negative electrode plate, which includes a negative electrode collector and a primer layer arranged on at least one surface of the negative electrode collector, wherein the primer layer includes one or more of carbon nanotubes, graphite, graphene, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.

25. The secondary battery according to any one of claims 18 to 24, characterized in that The negative electrode current collector comprises at least one of a metal foil, a metal foam current collector, a metal mesh current collector, a carbon felt current collector, a carbon cloth current collector, a carbon paper current collector and a composite current collector.

26. The secondary battery according to claim 24 or 25, characterized in that The surface density of the primer layer is 2 g / m 2 -50g / m 2 .

27. The secondary battery according to claim 24 or 25, characterized in that The thickness of the primer layer is 1 μm-100 μm.

28. A battery module, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 18 to 27.

29. A battery pack, characterized in that: The secondary battery according to any one of claims 18 to 27 or the battery module according to claim 27 is included.

30. An electrical device, characterized in that: The invention comprises at least one of the secondary battery according to any one of claims 18 to 27, the battery module according to claim 28, and the battery pack according to claim 29.

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