Secondary battery, battery module, battery pack, and electric device

Abstract

The invention provides a secondary battery, a battery module, a battery pack and an electric device. The secondary battery comprises a positive pole piece and an electrolyte, the electrolyte contains a film-forming additive, and the diaphragm resistance x omega of the positive pole piece and the mass content y% of the film-forming additive based on the total mass of the electrolyte meet the following relation: x * y is less than or equal to 25. The diaphragm resistance and the film-forming additive of the secondary battery provided by the invention meet the corresponding relation, and the coulombic efficiency, the high-temperature cycle performance and the high-temperature storage performance of the battery can be improved by regulating and controlling the diaphragm resistance and the film-forming additive of the secondary battery.

Description

Secondary batteries, battery modules, battery packs and electrical devices Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery, a battery module, a battery pack, 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] Secondary batteries typically consist of a positive electrode, a negative electrode, and an electrolyte. Metal ions migrate back and forth between the positive and negative electrodes to enable charging and discharging. Therefore, the performance of secondary batteries is not determined by a single factor, but rather by the effective coordination of the composition and parameters of the battery's various components.

[0004] Summary of the Invention

[0005] This application is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery that improves the electrochemical performance of the secondary battery, especially the performance of the battery at high temperatures, by coordinating the parameters between different components of the secondary battery.

[0006] A first aspect of the present application provides a secondary battery comprising a positive electrode plate and an electrolyte, wherein the electrolyte contains a film-forming additive, wherein the film resistance xΩ of the positive electrode plate and the mass content y% of the film-forming additive based on the total mass of the electrolyte satisfy the following relationship: x*y≤25.

[0007] The applicant unexpectedly discovered a synergistic effect between the sheet resistance of the battery's positive electrode and the content of the film-forming additive. The amount of film-forming additive added can be adjusted based on the sheet resistance of the secondary battery's positive electrode to ensure an overall improvement in the battery's comprehensive performance, including coulombic efficiency, cycling performance, and safety. Controlling the sheet resistance xΩ of the battery's positive electrode and the mass content y% of the film-forming additive based on the total mass of the electrolyte within the numerical range of x*y≤25 can reduce the battery's capacity loss during the initial charge and discharge, effectively improve the battery's coulombic efficiency, high-temperature cycling performance, and high-temperature storage performance, and inhibit the formation of dendrites in the battery, thereby comprehensively improving the battery's safety and electrochemical performance.

[0008] In any embodiment, based on the total mass of the electrolyte, the mass content of the film-forming additive in the electrolyte is 0.2%-5%, optionally 0.5%-2%.

[0009] Batteries within the above mass content range exhibit excellent coulombic efficiency, high-temperature performance, and the ability to suppress sodium dendrite formation.

[0010] In any embodiment, the sheet resistance of the positive electrode plate does not exceed 50Ω, and can optionally be no more than 10Ω.

[0011] Batteries with a positive electrode sheet resistance of no more than 50Ω exhibit excellent coulombic efficiency, high-temperature performance and the ability to inhibit sodium dendrite formation.

[0012] In any embodiment, the film-forming additive includes one or more selected from sulfate compounds, sulfonate compounds, and sulfite compounds.

[0013] Sulfate compounds, sulfite compounds, and sulfonate compounds are reduced preferentially over electrolyte salts and solvents, forming a dense, uniform, and thin solid electrolyte interface (SEI) film on the surface of the negative electrode to reduce direct contact between the negative electrode and the electrolyte. In addition, the salts generated by sulfate compounds, sulfite compounds, and sulfonate compounds in the SEI film have high-temperature resistance and can effectively improve the electrochemical performance of the battery at high temperatures. The addition of sulfate compounds, sulfite compounds, and sulfonate compound additives can improve the coulombic efficiency, high-temperature cycle performance, and high-temperature storage performance of the battery, and inhibit the formation of dendrites.

[0014] In any embodiment, the sulfate ester compound includes one or more compounds selected from the group consisting of:

[0015]

[0016] wherein n is any integer from 0 to 3, R1 and R2 are each independently selected from hydrogen, fluorine, cyano, olefin, substituted or unsubstituted C 1-6 alkyl,

[0017] In any embodiment, the sulfate compound includes one or more selected from ethylene sulfate, 4-methyl-ethylene sulfate, 4-fluoroethylene sulfate, 4-n-propylethylene sulfate, 4,4'-diethylene sulfate, 4-vinyl-ethylene sulfate, 4-ethylethylene sulfate, 4,5-difluoroethylene sulfate, and 4-cyanoethylene sulfate.

[0018] In any embodiment, the sulfonate compound comprises one or more selected from salts with sulfonate anions or compounds represented by formula II or formula III:

[0019]

[0020] wherein p is any integer from 0 to 5, R3 and R4 are each independently selected from substituted or unsubstituted C 1-6 alkyl,

[0021]

[0022] wherein R5 and R6 together with the sulfur and oxygen to which they are attached form a 4, 5 or 6-membered ring, the ring optionally having a double bond and optionally containing one or two sulfonate groups, the hydrogen on the ring optionally being replaced by halogen, C 1-3 Alkyl substitution.

[0023] In any embodiment, the sulfonate compound includes one or more selected from 1,3-propane sultone, 3-fluoro-1,3-propane sultone, 1-methyl-1,3-propane sultone, 1,4-butane sultone, 1,4-butene sultone, 1,3-propene sultone, methylene disulfonate, pyridinium propanesulfonate, and 1,4-butanediol dimethanesulfonate.

[0024] In any embodiment, the sulfite additive includes one or more compounds selected from the group consisting of compounds represented by Formula IV:

[0025]

[0026] wherein R7 and R8 are each independently selected from substituted or unsubstituted C 1-6 Alkyl or R7 and R8 together with the oxygen to which they are attached and the sulfur to which the oxygen is attached form a 5- or 6-membered ring, the ring optionally having a double bond, the hydrogen on the ring optionally being replaced by halogen, C 1-3 Alkyl substitution.

[0027] In any embodiment, the sulfite includes one or more selected from 1,3-propylene sulfite, ethylene sulfite, butylene sulfite, dimethyl sulfite, and diethyl sulfite.

[0028] In any embodiment, the electrolyte further comprises a sodium salt and an ether solvent, wherein the molar concentration of the sodium salt is 0.5 mol / L to 4 mol / L, and optionally 0.8 mol / L to 2 mol / L.

[0029] Controlling the molar concentration of sodium salt within an appropriate range can improve the coulombic efficiency, high-temperature cycle performance and high-temperature storage performance of the battery.

[0030] The molecules of ether solvents can build a stable electrode / electrolyte interface on the negative electrode surface, form a stable SEI film, reduce electrochemical polarization, and improve the coulombic efficiency, high-temperature cycle performance and high-temperature storage performance of the battery.

[0031] In any embodiment, the sodium salt includes one or more selected from sodium hexafluorophosphate, sodium difluorooxalatoborate, sodium tetrafluoroborate, sodium bisoxalatoborate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethylsulfonyl)imide.

[0032] In any embodiment, the ether solvent includes one or more selected from ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyltetrahydrofuran, diphenyl ether, crown ether, and fluoroether.

[0033] The molecules of ether solvents in ether electrolytes can construct a stable electrode / electrolyte interface on the surface of sodium metal negative electrode (including no negative electrode), carbon material negative electrode and other non-carbon material negative electrode, forming a stable solid electrolyte interface (SEI), reducing electrochemical polarization, and improving the coulombic efficiency, high-temperature cycle performance and high-temperature storage performance of the battery.

[0034] In any embodiment, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes one or more selected from layered transition metal oxides, polyanionic compounds, or Lushi Blue analogs.

[0035] In any embodiment, the secondary battery is a lithium ion battery or a sodium ion battery.

[0036] In any embodiment, the secondary battery is a negative electrode-less sodium metal battery.

[0037] A second aspect of the present application provides a battery module including the secondary battery of the first aspect.

[0038] A third aspect of the present application provides a battery pack including the secondary battery of the first aspect or the battery module of the second aspect.

[0039] A fourth aspect of the present application provides an electrical device comprising at least one of the secondary battery of the first aspect, the battery module of the second aspect, or the battery pack of the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0041] FIG2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG1 ;

[0042] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0043] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0044] FIG5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG4 ;

[0045] 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.

[0046] Reference numerals:

[0047] 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

[0048] Below, the embodiments of the secondary battery, battery module, battery pack and power 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 are 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 the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0049] " 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.

[0050] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0051] 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.

[0052] 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.

[0053] 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).

[0054] [Secondary battery]

[0055] The present application provides a secondary battery comprising a positive electrode sheet and an electrolyte, wherein the electrolyte contains a film-forming additive, wherein the film resistance xΩ of the positive electrode sheet and the mass content y% of the film-forming additive based on the total mass of the electrolyte satisfy the following relationship: x*y≤25.

[0056] In this article, the term "sheet resistance" refers to the resistance of the positive electrode sheet. The sheet resistance can be measured by any known method, including but not limited to the single-probe method, the four-probe method, and the DC two-probe method. The contact area between the probe and the positive electrode sheet is set to 49πmm. 2 As an example, the diaphragm resistance R of the positive electrode sheet is tested using a Hioki BT23562 internal resistance tester. The upper and lower sides of the positive electrode sheet are clamped between two conductive terminals of the tester and pressure is applied to secure it. The diameter of the conductive terminals is 14 mm, and the applied pressure is 15 MPa to 27 MPa. This is how the diaphragm resistance of the positive electrode sheet is measured.

[0057] In this article, the term "film-forming additive" refers to additives that form and improve the SEI or CEI film at the anode (or cathode). In anode-free sodium metal batteries, the anode active material is formed in situ by initial sodium removal and deposition at the cathode, without any supply of active material at the anode. Therefore, the addition of film-forming additives can significantly improve the coulombic efficiency of anode-free sodium metal batteries.

[0058] In this article, the term "additive" refers to a relatively minor component 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 concentrations in the electrolyte. Solvents or salts with relatively minor concentrations can be collectively referred to as additives.

[0059] The applicant unexpectedly discovered a synergistic effect between the sheet resistance of the battery's positive electrode and the content of the film-forming additive. The amount of film-forming additive added can be adjusted based on the sheet resistance of the secondary battery's positive electrode to ensure improvements in the battery's overall performance, including coulombic efficiency and cycle performance. Controlling the sheet resistance xΩ of the battery's positive electrode and the mass content y% of the film-forming additive based on the total mass of the electrolyte within the numerical range of x*y≤25 can reduce the battery's capacity loss during the initial charge and discharge, effectively improving the battery's coulombic efficiency, high-temperature cycle performance, and high-temperature storage performance, while also suppressing the formation of dendrites in the battery, thereby comprehensively improving the battery's safety and electrochemical performance.

[0060] In some embodiments, the mass content of the film-forming additive in the electrolyte is 0.2%-5% based on the total mass of the electrolyte. In some embodiments, the mass content of the film-forming additive in the electrolyte can be optionally 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5% based on the total mass of the electrolyte. The upper and lower limits of the mass content of the film-forming additive in the electrolyte can be selected from the above values.

[0061] Controlling the mass content of the film-forming additive in the electrolyte within an appropriate range can avoid the poor SEI film stability caused by too low a content of the film-forming additive, and can also avoid the increased electrolyte viscosity, reduced ionic conductivity, poor kinetic performance, excessive SEI film thickness, and increased battery internal resistance caused by too high a content of the film-forming additive. Batteries within this mass content range exhibit excellent coulombic efficiency, high-temperature performance, and the ability to suppress sodium dendrite formation.

[0062] In some embodiments, the mass content of the film-forming additive in the electrolyte is 0.5%-2% based on the total mass of the electrolyte. Within this range, the coulombic efficiency of the battery is further improved, the high-temperature cycle capacity retention rate and the high-temperature storage capacity retention rate are further improved, and the high-temperature cycle resistance is further reduced.

[0063] In some embodiments, the sheet resistance of the positive electrode sheet does not exceed 50Ω. In some embodiments, the sheet resistance of the positive electrode sheet can be selected from 1Ω, 2Ω, 3Ω, 5Ω, 10Ω, 15Ω, 20Ω, 25Ω, 30Ω, 35Ω, 40Ω, 45Ω, and 50Ω.

[0064] Batteries with a positive electrode sheet resistance of no more than 50Ω exhibit excellent coulombic efficiency, high-temperature performance and the ability to inhibit sodium dendrite formation.

[0065] In some embodiments, the sheet resistance of the positive electrode sheet does not exceed 10Ω. When the sheet resistance of the positive electrode sheet does not exceed 10Ω, the coulombic efficiency, high-temperature cycle capacity retention rate, and high-temperature storage capacity retention rate of the battery are further improved, and the high-temperature cycle internal resistance and high-temperature storage internal resistance are further reduced.

[0066] In some embodiments, the film-forming additive includes one or more selected from sulfate compounds, sulfonate compounds, and sulfite compounds.

[0067] In this article, the term "sulfate compound" refers to Group compound.

[0068] In this context, the term "sulfonate compound" refers to a compound comprising Group or of compounds.

[0069] In this article, the term "sulfite compound" refers to Group compound.

[0070] Sulfate compounds, sulfite compounds, and sulfonate compounds are reduced in preference to electrolyte salts and solvents, forming a dense, uniform, and thin SEI film on the surface of the negative electrode to reduce direct contact between the negative electrode and the electrolyte. In addition, the salts generated by sulfate compounds, sulfite compounds, and sulfonate compounds in the SEI film have high-temperature resistance and can effectively improve the electrochemical performance of the battery at high temperatures. The addition of sulfate compounds, sulfite compounds, and sulfonate compound additives can improve the coulombic efficiency, high-temperature cycle performance, and high-temperature storage performance of the battery, and inhibit the formation of dendrites. Especially for sodium metal batteries without negative electrodes, sulfate compounds, sulfite compounds, and sulfonate compound additives form an effective combination with the negative electrode current collector, which can greatly improve the loss of sodium elements in the battery by the solvent and improve the coulombic efficiency and high-temperature performance of the battery.

[0071] In some embodiments, the sulfate ester compound comprises one or more compounds selected from the group consisting of:

[0072]

[0073] wherein n is any integer from 0 to 3, R1 and R2 are each independently selected from hydrogen, fluorine, cyano, olefin, substituted or unsubstituted C 1-6 alkyl,

[0074] As used herein, the term "cyano" refers to -CN.

[0075] As used herein, the term "alkene" refers to an unsaturated hydrocarbon group having at least one carbon-carbon double bond.

[0076] As used herein, the term "C1-6 alkyl" refers to a straight or branched hydrocarbon chain radical consisting solely of carbon and hydrogen atoms, with no unsaturation present, having from one to six carbon atoms, and attached to the remainder of the molecule by a single bond.

[0077] 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.

[0078] In some embodiments, n is 0, and the carbon atom connected to R1 and the carbon atom connected to R2 are directly connected by a single bond.

[0079] In some embodiments, R1 and R2 are each independently selected from hydrogen, fluorine, cyano, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, vinyl, propenyl,

[0080] In some embodiments, the sulfate compound includes ethylene sulfate (DTD, ), 4-methyl-ethylene sulfate (MeDTD, ), 4-fluoroethylene sulfate (FDTD, ), 4-n-propyl ethylene sulfate (PEGLST, ), 4,4'-disulfate (BiDTD, ), 4-vinyl-ethylene sulfate (VDTD, ), 4-ethyl ethylene sulfate (EtDTD, ), 4,5-difluoroethylene sulfate (DFDTD, ), 4-cyanoethylene sulfate (CDTD, )

[0081] The above-mentioned sulfate ester compounds exhibit excellent film-forming properties in secondary batteries, can effectively improve the battery's coulombic efficiency, high-temperature cycle performance, and high-temperature storage performance, and inhibit the generation of dendrites in the battery, thereby comprehensively improving the battery's safety performance and electrochemical performance.

[0082] In some embodiments, the sulfate compound is selected from one or more of ethylene sulfate, 4-methyl-ethylene sulfate, 4-fluoroethylene sulfate, 4-cyanoethylene sulfate, and 4-vinyl-ethylene sulfate. In some embodiments, the sulfate compound is selected from one or more of ethylene sulfate, 4-methyl-ethylene sulfate, and 4-fluoroethylene sulfate.

[0083] The above-mentioned sulfate compounds are particularly suitable for negative electrode-free batteries and can significantly improve the coulombic efficiency, high-temperature cycle performance and high-temperature storage performance of negative electrode-free batteries.

[0084] In some embodiments, the sulfonate compound comprises one or more selected from salts with sulfonate anions or compounds of Formula II or Formula III:

[0085]

[0086] wherein p is any integer from 0 to 5, R3 and R4 are each independently selected from substituted or unsubstituted C 1-6 alkyl,

[0087]

[0088] wherein R5 and R6 together with the sulfur and oxygen to which they are attached form a 4, 5 or 6-membered ring, the ring optionally having a double bond and optionally containing one or two sulfonate groups, the hydrogen on the ring optionally being replaced by halogen, C 1-3 Alkyl substitution.

[0089] Herein, the term "C1-3 alkyl" can be understood with reference to the definition of the term "C1-6 alkyl".

[0090] In this document, the term "halogen" may refer to F, Cl, Br, or I.

[0091] In some embodiments, p is selected from 1, 2, or 3.

[0092] In some embodiments, R3 and R4 are each independently selected from hydrogen, fluorine, cyano, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, vinyl, and propenyl.

[0093] In some embodiments, the sulfonate compound includes 1,3-propane sultone (1,3-PS, ), 3-fluoro-1,3-propane sultone (FPS, )、1-methyl-1,3-propane sultone (2,4-BS, ), 1,4-butane sultone (BS, )、1,4-Butenesultone (BST, ), 1,3-propene sultone (PES, ), methylene methane disulfonate (MMDS, ), propane pyridinium sulfonate (PPS, )、1,4-Butanediol dimethanesulfonate (BDDMS, )

[0094] The above-mentioned sulfonate compounds exhibit excellent film-forming properties in secondary batteries, can effectively improve the battery's coulombic efficiency, high-temperature cycle performance, and high-temperature storage performance, and inhibit the generation of dendrites in the battery, thereby comprehensively improving the battery's safety performance and electrochemical performance.

[0095] In some embodiments, the sulfonate compound is selected from one or more of 3-fluoro-1,3-propane sultone, 1-methyl-1,3-propane sultone, 1,3-propene sultone, methylene disulfonate, pyridinium propanesulfonate, and 1,3-propane sultone. In some embodiments, the sulfonate compound is selected from one or more of 1,3-propane sultone, 3-fluoro-1,3-propane sultone, and 1,3-propene sultone.

[0096] The above-mentioned sulfonate compounds are particularly suitable for negative electrode-free batteries and can significantly improve the coulombic efficiency, high-temperature cycle performance and high-temperature storage performance of negative electrode-free batteries.

[0097] In some embodiments, the sulfite compound comprises one or more compounds selected from the group consisting of:

[0098]

[0099] wherein R7 and R8 are each independently selected from substituted or unsubstituted C 1-6 Alkyl or R7 and R8 together with the oxygen to which they are attached and the sulfur to which the oxygen is commonly attached form a 5- or 6-membered ring, the ring optionally having a double bond, the hydrogen on the ring optionally being replaced by halogen, C 1-3 Alkyl substitution.

[0100] In some embodiments, the sulfite comprises 1,3-propylene sulfite selected from Ethylene sulfite (ES, ), butylene sulfite (PS, ), dimethyl sulfite (DMS, ), diethyl sulfite (DES, )

[0101] The above-mentioned sulfite compounds exhibit excellent film-forming properties in secondary batteries, can effectively improve the battery's coulombic efficiency, high-temperature cycle performance, and high-temperature storage performance, and inhibit the generation of dendrites in the battery, thereby comprehensively improving the battery's safety performance and electrochemical performance.

[0102] In some embodiments, the electrolyte further comprises a sodium salt and an ether solvent, wherein the molar concentration of the sodium salt is 0.5 mol / L to 4 mol / L, and optionally 0.8 mol / L to 2 mol / L.

[0103] As used herein, the term "ether solvent" refers to an organic solvent containing an ether bond.

[0104] In some embodiments, the molar concentration of the sodium salt is 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, or 4 mol / L.

[0105] Controlling the molar concentration of sodium salt within an appropriate range can improve the coulombic efficiency, high-temperature cycle performance and high-temperature storage performance of the battery.

[0106] The molecules of ether solvents can construct a stable electrode / electrolyte interface on the negative electrode surface, forming a stable solid electrolyte interface (SEI), reducing electrochemical polarization, and improving the battery's coulombic efficiency, high-temperature cycle performance, and high-temperature storage performance.

[0107] Taking the negative electrode-free sodium metal battery as an example, ether solvents have good compatibility with sodium metal negative electrodes. They can effectively passivate sodium metal and form a thin, uniform and dense SEI film on the surface of sodium metal, further preventing the formation of sodium dendrites and preventing the SEI film from further thickening due to the growth and evolution of sodium dendrites, thereby affecting the conduction of ions.

[0108] In some embodiments, the sodium salt includes one or more of sodium hexafluorophosphate (NaPF6), sodium difluorooxalatoborate (NaDFOB), sodium tetrafluoroborate (NaBF4), sodium bisoxalatoborate (NaBOB), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium trifluoromethylsulfonate (NaOTf), and sodium bis(trifluoromethylsulfonyl)imide (NaTFSI).

[0109] In some embodiments, the ether solvent includes one or more of ethylene glycol dimethyl ether (DME), ethylene glycol diethyl ether (DEE), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TRGDME), tetraethylene glycol dimethyl ether (TEGDME), 1,3-dioxolane (DOL), tetrahydrofuran (THF), methyltetrahydrofuran (MeTHF), diphenyl ether, crown ether, and fluoroether.

[0110] Fluorinated ether refers to an ether solvent containing fluorine. In some embodiments, the fluorinated ether includes one or more of 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, methoxynonafluorobutane, and ethoxynonafluorobutane.

[0111] In some embodiments, the ether solvent is selected from one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, 1,3-dioxolane, and tetrahydrofuran.

[0112] In some embodiments, the electrolyte includes other solvents in addition to ether solvents. Non-limiting examples of other solvents include at least one selected from vinylene carbonate, ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0113] In some embodiments, the electrolyte may optionally include additional additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve thermal stability of the electrolyte, and the like.

[0114] In some embodiments, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes one or more selected from layered transition metal oxides, polyanionic compounds, or Lushi Blue analogs.

[0115] 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. x MO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0<x≤1.

[0116] 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.

[0117] 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.

[0118] In some embodiments, the secondary battery is a lithium ion battery or a sodium ion battery.

[0119] Lithium-ion batteries are batteries that use lithium ions to migrate back and forth between positive and negative electrodes.

[0120] Sodium-ion batteries are batteries that use sodium ions to migrate back and forth between positive and negative electrodes.

[0121] In some embodiments, the secondary battery is a negative electrode-free sodium metal battery. The negative electrode-free sodium metal battery does not use a negative electrode active material, but only uses a negative electrode current collector as the negative electrode. The sodium plating of the negative electrode is completed during the first charging process, and then returns to the positive electrode during discharge to achieve a charge and discharge cycle. Since there is no negative electrode material and only a negative electrode current collector is used, the negative electrode-free battery can effectively overcome the defects of the sodium metal battery and obtain a higher energy density than the metallic sodium negative electrode. However, since the negative electrode-free battery has no negative electrode, it often has problems such as low coulomb efficiency and severe sodium dendrites. The present application creatively solves this problem and greatly improves the high temperature performance of the negative electrode-free battery.

[0122] 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.

[0123] In some embodiments, the metal foil can be copper foil, aluminum foil, stainless steel foil, iron foil, zinc foil, titanium foil, and the metal foam current collector can be copper foam, aluminum foam, zinc foam, etc. The metal mesh current collector can be copper mesh or aluminum mesh. The composite current collector includes a current collector with a primer layer or a current collector with a polymer base film. The composite current collector can be a "sandwich" structure, with the polymer base film in the middle and metal foil on both sides. The composite current collector can also be a polymer base film with metal foil on one side. The polymer base film can be selected from one of 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.

[0124] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0125] 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.

[0126] The present application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 5 with a square structure as an example.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] In some embodiments, the battery modules described above may also 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.

[0132] 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 placed 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.

[0133] 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.

[0134] As an electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0135] 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.

[0136] 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.

[0137] Example

[0138] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not 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 field or in accordance with the product instructions are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially. In the following embodiments, only the case where the secondary battery is a sodium ion battery is shown, but the present application is not limited thereto.

[0139] 1. Preparation method

[0140] Example 1

[0141] (1) Preparation of positive electrode sheet

[0142] Taking the total weight of polyvinylidene fluoride binder, carbon black conductive agent, and positive electrode active material Na4Fe3(PO4)2P2O7 as 100 parts by weight, 10 parts by weight of polyvinylidene fluoride binder are fully dissolved in N-methylpyrrolidone. Then, 10 parts by weight of carbon black conductive agent and 80 parts by weight of positive electrode active material Na4Fe3(PO4)2P2O7 are added to form a uniformly dispersed slurry. The slurry is evenly coated on the surface of aluminum foil and then transferred to a vacuum drying oven for complete drying. The resulting electrode sheet is roll-pressed and then punched to obtain the positive electrode sheet.

[0143] (2) Preparation of negative electrode sheet

[0144] With the total weight of the negative electrode slurry as 100 parts by weight, 4 parts by weight of carbon nanotube material and 1.6 parts by weight of polymer binder sodium carboxymethyl cellulose are added to water and stirred into a uniform slurry. The slurry is coated on the surface of the copper foil and then transferred to a vacuum drying oven for complete drying, and then punched to obtain the negative electrode sheet.

[0145] (3) Preparation of electrolyte

[0146] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), sodium hexafluorophosphate NaPF6 and 1,3-propane sultone (1,3-PS) were dissolved in an organic solvent, ethylene glycol dimethyl ether (DME), and stirred evenly to obtain an electrolyte with a sodium salt concentration of 1 mol / L, i.e., the electrolyte of Example 1.

[0147] (4) Isolation membrane

[0148] Polypropylene film is used as the isolation film.

[0149] (5) Preparation of batteries

[0150] 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 play an isolating role, and the electrolyte is added to assemble a laminated battery.

[0151] Example 2-37

[0152] Except for the different electrolyte formulations, the other steps of Examples 2-37 are the same as those of Example 1. The sheet resistance of the positive electrode sheet is adjusted by adjusting the compaction density of the positive electrode sheet.

[0153] Comparative Examples 1-4

[0154] Except for the different electrolyte formulas, the other steps of Comparative Examples 1-4 are the same as those of Example 1. Specific parameters are shown in Table 1.

[0155] 2. Battery performance test

[0156] 1. Diaphragm resistance test

[0157] The upper and lower sides of the positive electrode sheet are clamped between the two conductive terminals of the Hioki BT23562 internal resistance tester and pressure is applied to fix them. The diameter of the conductive terminals is 14 mm and the applied pressure is 15 MPa to 27 MPa. The resistance R of the positive electrode sheet is measured.

[0158] 2. Coulomb efficiency

[0159] Taking Example 1 as an example, the prepared sodium secondary battery was charged to 3.7 V at a constant current of 1 / 3C at 25°C, and then charged at a constant voltage of 3.7V until the current dropped to 0.05C to obtain the initial charge capacity (Cc1); then discharged to 2.5 V at a constant current of 1 / 3C to obtain the initial discharge capacity (Cd1), and the coulombic efficiency of the sodium battery was calculated according to the following formula.

[0160] Sodium battery coulombic efficiency = first discharge capacity (Cd1) / first charge capacity (Cc1) * 100%

[0161] The testing procedures of the comparative example and other embodiments are the same as above.

[0162] 3. High temperature cycle capacity retention rate

[0163] Taking Example 1 as an example, the sodium battery is charged to 3.7V at a constant current of 1C at 45°C, then charged at a constant voltage of 3.7V until the current drops to 0.05C, and then discharged to 2.5V at a constant current of 1C to obtain the first cycle discharge capacity (Cd1); this charge and discharge is repeated until the nth cycle, and the discharge capacity of the sodium battery after n cycles is obtained, recorded as Cdn, and the sodium battery capacity retention rate is calculated according to the following formula:

[0164] Capacity retention rate = discharge capacity after n cycles (Cdn) / first cycle discharge capacity (Cd1) * 100%

[0165] The high-temperature cycle capacity retention rate in this application refers to the capacity retention rate of the battery after 100 cycles at high temperature.

[0166] The testing procedures of the comparative example and other embodiments are the same as above.

[0167] 4. High temperature cycle DCR

[0168] DC internal resistance (DCR) refers to the resistance to current flow within a battery cell. After discharging, the battery voltage will rebound due to polarization. DC impedance technology calculates the battery's internal resistance by measuring the difference between the voltage immediately before the end of intermittent discharge and the voltage after the discharge stabilizes.

[0169] Taking Example 1 as an example, the sodium ion battery was charged to 3.7V at a constant current of 1C at 25°C, then charged at a constant voltage of 3.7V until the current dropped to 0.05C, and then discharged to 2.5V at a constant current of 1C. After that, it was left for 5 minutes (stabilization time) and continued to the next cycle. The battery voltage before discharge termination and the battery voltage after battery voltage stabilization were recorded in each cycle. Then, the DC impedance R=ΔU / I was calculated using the following formula (where: ΔU is the voltage difference, R is the DC resistance, and I is the discharge current).

[0170] The high temperature cycle DCR tested in this application is the DC resistance of the battery after 100 cycles of high temperature cycling.

[0171] The testing procedures of the comparative example and other embodiments are the same as above.

[0172] 5. Sodium dendrites

[0173] The sodium battery after 100 cycles was disassembled in an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), and the surface morphology of the negative electrode was visually observed to determine whether sodium dendrites were generated.

[0174] The absence of white spots on the negative electrode is judged as “no” sodium dendrites;

[0175] The presence of sporadic white spots on the negative electrode is considered to be a "mild" condition of sodium dendrites;

[0176] The negative electrode is densely packed with white spots, indicating a "serious" sodium dendrite situation.

[0177] The testing procedures of the comparative example and other embodiments are the same as above.

[0178] 6. High temperature storage capacity retention rate

[0179] Taking Example 1 as an example, the sodium battery is charged to 3.7V at a constant current of 1C at 25°C, then charged at a constant voltage of 3.7V until the current drops to 0.05C, and then discharged to 2.5V at a constant current of 1C to obtain the discharge capacity before storage (Cda); the sodium battery is charged to 3.7V at a constant current of 1C at 25°C, and then charged at a constant voltage of 3.7V until the current drops to 0.05C. This step is to recharge to 100% SOC; the battery is placed in a constant temperature environment of 45°C and stored for 60 days; after 60 days of storage, the battery is taken out of the constant temperature environment of 45°C, cooled to room temperature, charged to 3.7V at a constant current of 1C at 25°C, then charged at a constant voltage of 3.7V until the current drops to 0.05C, and then discharged to 2.5V at a constant current of 1C to obtain the discharge capacity of the sodium battery after 60 days of storage, recorded as Cdb, and the capacity retention rate of the sodium battery is calculated according to the following formula:

[0180] Capacity retention rate = discharge capacity after 60 days of storage (Cdb) / discharge capacity before storage (Cda) * 100%.

[0181] The testing procedures of the comparative example and other embodiments are the same as above.

[0182] 7. High temperature storage DCR

[0183] Taking Example 1 as an example, the sodium battery stored at 45°C for 60 days was charged to 3.7V at a constant current of 1C at 25°C, then charged at a constant voltage of 3.7V until the current dropped to 0.05C, and then discharged to 2.5V at a constant current of 1C. After that, it was left for 5 minutes (stabilization time), and the battery voltage before discharge was terminated and the battery voltage after the battery voltage stabilized were recorded. Then, the DC impedance R=ΔU / I (where: ΔU is the voltage difference, R is the DC resistance, and I is the discharge current) was calculated using the following formula.

[0184] The testing procedures of the comparative example and other embodiments are the same as above.

[0185] 3. Test Results

[0186] The test results of the above embodiments and comparative examples are shown in Table 1.

[0187] Table 1

[0188]

[0189]

[0190] Table 1 shows that the positive electrode membrane resistance xΩ and the mass content y% of the film-forming additive based on the total mass of the electrolyte of Examples 1-37 satisfy the following relationship: x*y≤25. Compared with Comparative Examples 1-4, the sodium batteries of Examples 1-37 exhibit higher coulombic efficiency, high-temperature cycle capacity retention, and high-temperature storage capacity retention, lower high-temperature cycle direct current resistance (DCR) and high-temperature storage DCR, and no sodium dendrites appear in the electrode sheets.

[0191] As can be seen from Examples 1 to 5, when the mass content of the film-forming additive in the electrolyte is 0.2%-5% based on the total mass of the electrolyte, the battery exhibits excellent coulombic efficiency, high-temperature performance, and the ability to inhibit sodium dendrite formation. When the mass content of the film-forming additive in the electrolyte is 0.5%-2% based on the total mass of the electrolyte, the battery's coulombic efficiency is further improved, the high-temperature cycle capacity retention rate and high-temperature storage capacity retention rate are further improved, and the high-temperature cycle resistance is further reduced.

[0192] As shown in Examples 1 to 37, when the sheet resistance of the positive electrode sheet does not exceed 50Ω, the battery exhibits excellent coulombic efficiency, high-temperature performance, and the ability to inhibit sodium dendrite formation. A comparison of Examples 1, 6, and 7 with Example 8 shows that when the sheet resistance of the positive electrode sheet does not exceed 10Ω, the battery's coulombic efficiency, high-temperature cycle capacity retention, and high-temperature storage capacity retention are further improved, while the high-temperature cycle internal resistance and high-temperature storage internal resistance are further reduced.

[0193] It is worth noting that in Comparative Examples 1 and 2, although the film-forming additive content y% and the internal resistance xΩ of the positive electrode membrane of the negative electrode-free sodium battery are also within the above range, they do not satisfy the relationship of x*y≤25. As a result, although the performance is improved compared with Comparative Examples 3 and 4, the coulombic efficiency of the battery cannot be increased to more than 90% to meet the actual application requirements.

[0194] As can be seen from Examples 1-37, the film-forming additive includes one or more compounds selected from sulfate ester compounds, sulfonate ester compounds, and sulfite ester compounds. A comparison of Examples 1-37 with Comparative Examples 3-4 shows that the film-forming additive significantly improves coulombic efficiency, high-temperature performance, and the ability to inhibit sodium dendrite formation.

[0195] From the comparison of Examples 1, 13 to 22 with Example 23, it can be seen that sulfate compounds and sulfonate compounds are more effective in improving the coulombic efficiency and high-temperature performance of batteries than sulfite compounds. Among them, 3-fluoro-1,3-propane sultone (FPS), 4-methyl-ethylene sulfate (MeDTD) and 4-fluoroethylene sulfate (FDTD) can further increase the coulombic efficiency of the negative electrode-free battery to more than 93%, and increase the high-temperature cycle capacity retention rate to more than 91%. 1,3-Propene sultone (PES) and ethylene sulfate (DTD) can increase the coulombic efficiency of the negative electrode-free battery to more than 94%, and increase the high-temperature cycle capacity retention rate to more than 92%. 1,3-Propane sultone (1,3-PS) can even increase the coulombic efficiency of the negative electrode-free battery to more than 95%, and increase the high-temperature cycle capacity retention rate to more than 93%.

[0196] From the comparison of Examples 24-27 and Example 28, it can be seen that ether solvents are more suitable for anode-free sodium batteries than ester solvents, which helps to improve the coulombic efficiency and electrochemical performance of anode-free sodium batteries. Ethylene glycol dimethyl ether (DME) and diethylene glycol dimethyl ether (DEGDME) in the ether solvents show better adaptability to anode-free sodium batteries, which further significantly improves the coulombic efficiency and high-temperature cycle capacity retention rate of anode-free sodium batteries.

[0197] As can be seen from Examples 1, 29 to 32, when the molar concentration of the electrolyte sodium salt is 0.5 mol / L to 4 mol / L, it can effectively ensure that the negative electrode-free sodium battery has excellent coulombic efficiency, high temperature performance and the ability to inhibit sodium dendrite growth. From the comparison of Examples 1, 30, and 31 with Examples 29 and 32, it can be seen that when the molar concentration of the electrolyte sodium salt is 0.8 mol / L to 2 mol / L, the coulombic efficiency of the negative electrode-free sodium battery is increased to more than 91%, and the high temperature cycle capacity retention rate is increased to more than 90%, showing more excellent electrochemical performance.

[0198] It can be seen from Examples 33 to 37 that sodium salts such as sodium hexafluorophosphate (NaPF6), sodium difluorooxalatoborate (NaDFOB), sodium tetrafluoroborate (NaBF4), sodium bis(fluorosulfonyl)imide (NaFSI), sodium trifluoromethylsulfonate (NaOTf), and sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) are all suitable for the technical solution provided in this application, and the negative electrode-free batteries using them as electrolyte salts all exhibit excellent coulombic efficiency, high temperature cycle performance, and high temperature storage performance.

[0199] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present application, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present application. In addition, within the scope of the subject matter of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery, characterized in that: It includes a positive electrode sheet and an electrolyte, wherein the electrolyte contains a film-forming additive. The sheet resistance xΩ of the positive electrode sheet and the mass content y% of the film-forming additive based on the total mass of the electrolyte satisfy the following relationship: x*y≤25.

2. The secondary battery according to claim 1, wherein Based on the total mass of the electrolyte, the mass content of the film-forming additive in the electrolyte is 0.2%-5%, and can be optionally 0.5%-2%.

3. The secondary battery according to claim 1 or 2, characterized in that The membrane resistance of the positive electrode plate does not exceed 50Ω, and can be optionally not more than 10Ω.

4. The secondary battery according to any one of claims 1 to 3, characterized in that The film-forming additive includes one or more of sulfate compounds, sulfonate compounds, and sulfite compounds.

5. The secondary battery according to claim 4, wherein The sulfate ester compound includes one or more compounds represented by formula I: wherein n is any integer from 0 to 3, R1 and R2 are each independently selected from hydrogen, fluorine, cyano, olefin, substituted or unsubstituted C 1-6 alkyl, 6. The secondary battery according to claim 4 or 5, characterized in that: The sulfate ester compound includes one or more of ethylene sulfate, 4-methyl-ethylene sulfate, 4-fluoroethylene sulfate, 4-n-propylethylene sulfate, 4,4'-diethylene sulfate, 4-vinyl-ethylene sulfate, 4-ethylethylene sulfate, 4,5-difluoroethylene sulfate, and 4-cyanoethylene sulfate.

7. The secondary battery according to any one of claims 4 to 6, characterized in that The sulfonate compound includes one or more selected from salts with sulfonate anions or compounds represented by formula II or formula III: wherein p is any integer from 0 to 5, R3 and R4 are each independently selected from substituted or unsubstituted C 1-6 alkyl, wherein R5 and R6 together with the sulfur and oxygen to which they are attached form a 4, 5 or 6-membered ring, the ring optionally having a double bond and optionally containing one or two sulfonate groups, the hydrogen on the ring optionally being replaced by halogen, C 1-3 Alkyl substitution.

8. The secondary battery according to any one of claims 4 to 7, characterized in that The sulfonate compound includes one or more selected from 1,3-propane sultone, 3-fluoro-1,3-propane sultone, 1-methyl-1,3-propane sultone, 1,4-butane sultone, 1,4-butene sultone, 1,3-propene sultone, methylene disulfonate, pyridinium propanesulfonate, and 1,4-butanediol dimethanesulfonate.

9. The secondary battery according to any one of claims 4 to 8, characterized in that The sulfite compound includes one or more compounds selected from the group consisting of compounds represented by formula IV: wherein R7 and R8 are each independently selected from substituted or unsubstituted C 1-6 Alkyl or R7 and R8 together with the oxygen to which they are attached and the sulfur to which the oxygen is commonly attached form a 5- or 6-membered ring, the ring optionally having a double bond, the hydrogen on the ring optionally being replaced by halogen, C 1-3 Alkyl substitution.

10. The secondary battery according to any one of claims 4 to 9, characterized in that The sulfite includes one or more selected from 1,3-propylene sulfite, ethylene sulfite, butylene sulfite, dimethyl sulfite, and diethyl sulfite.

11. The secondary battery according to any one of claims 1 to 10, characterized in that: The electrolyte further includes a sodium salt and an ether solvent, wherein the molar concentration of the sodium salt is 0.5 mol / L to 4 mol / L, and can be optionally 0.8 mol / L to 2 mol / L.

12. The secondary battery according to claim 11, wherein The sodium salt includes one or more selected from sodium hexafluorophosphate, sodium difluorooxalatoborate, sodium tetrafluoroborate, sodium bisoxalatoborate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethylsulfonate, and sodium bis(trifluoromethylsulfonyl)imide.

13. The secondary battery according to claim 11 or 12, characterized in that: The ether solvent includes one or more selected from ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyltetrahydrofuran, diphenyl ether, crown ether, and fluoroether.

14. The secondary battery according to any one of claims 1 to 13, characterized in that The positive electrode plate includes a positive electrode active material, and the positive electrode active material includes one or more selected from layered transition metal oxides, polyanion compounds, or Lushi blue analogs.

15. The secondary battery according to any one of claims 1 to 14, characterized in that The secondary battery is a lithium ion battery or a sodium ion battery.

16. The secondary battery according to any one of claims 1 to 15, characterized in that The secondary battery is a negative electrode-free sodium metal battery.

17. A battery module, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 16.

18. A battery pack, characterized in that: A secondary battery according to any one of 1 to 16 or a battery module according to claim 17.

19. An electrical device, characterized in that: The battery comprises at least one selected from the group consisting of the secondary battery according to any one of claims 1 to 16, the battery module according to claim 17, and the battery pack according to claim 18.

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