Electrolyte for sodium secondary battery, sodium secondary battery and power consumption device

Abstract

The present application provides an electrolyte for a sodium secondary battery, a sodium secondary battery, and a power consuming device. The electrolyte for a sodium secondary battery includes a diluent, and the diluent is represented by the general formula C n H 2n+2 The diluent contains an alkane, and the value of n is 8 to 13. The diluent can improve the high-temperature cycle performance of the battery, reduce the high-temperature gas generation phenomenon of the battery, and improve the electrochemical performance and safety performance of the battery at high temperatures.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application incorporates by reference Chinese patent application No. 202310070404.7, filed on January 16, 2023, entitled "Electrolyte for Sodium Secondary Battery, Sodium Secondary Battery and Power Consumption Device," which is incorporated herein by reference in its entirety.

[0002] The present application relates to the technical field of sodium secondary batteries, and in particular to an electrolyte for sodium secondary batteries, a sodium secondary battery, and a power consuming device. [Background technology]

[0003] With the development of battery technology, lithium secondary batteries have dominated the portable electronics market and are gradually expanding into large-scale electrical energy storage applications. However, traditional lithium resources are no longer able to meet the urgent demand for large-scale, high-energy density energy storage systems. Therefore, sodium secondary batteries, which have abundant sodium reserves, low cost, and similar electrochemical properties to lithium secondary batteries, have emerged due to the situation. However, the sodium secondary batteries currently being widely studied have relatively poor high-temperature cycle performance and suffer from serious high-temperature gas generation, which severely limits the further application of sodium secondary batteries. Summary of the Invention

[0004] The present application has been made in view of the above-mentioned problems, and an object of the present application is to provide an electrolyte for a sodium secondary battery that improves the high-temperature cycle performance of the battery, reduces the high-temperature gas generation phenomenon of the battery, and improves the electrochemical performance and safety performance of the sodium secondary battery at high temperatures.

[0005] A first aspect of the present application provides an electrolyte for a sodium secondary battery, the electrolyte comprising a diluent, the diluent being represented by the general formula C n H 2n+2The value of n is 8 to 13, and the alkanes are represented by the general formula C n H 2n+2 By using an alkane as a diluent, a protective layer is formed around the solvated structure, which reduces direct contact between the solvent and the positive and negative electrodes, reduces side reactions between the positive and negative electrodes and the solvent, improves the high-temperature cycle performance of the battery, suppresses gas generation during high-temperature cycles of sodium secondary batteries, and improves the electrochemical performance and safety performance of the battery at high temperatures.

[0006] In any embodiment, the diluent comprises one or more of n-octane, n-nonane, n-decane, n-undecane, n-dodecane, n-tridecane, 2,3-dimethylheptane, 3-methylheptane, 4-methylheptane, 3-ethylhexane, and optionally one or two of n-nonane and n-decane.

[0007] In any embodiment, the electrolyte further comprises a co-solvent, the co-solvent comprising a compound represented by structural formula I: JPEG2025530929000002.jpg17165Here, R1 is C 3-9 alkyl group, and R2 is selected from halogen-substituted or unsubstituted C 1-3 The alkyl group is selected from the group consisting of:

[0008] The co-solvent can improve the miscibility of the solvent and diluent, and contribute to the diluent forming a protective layer around the solvated structure. The co-solvent also acts as a bridge connecting the solvated structure and the diluent, forming a protective layer structure around the solvated structure with the co-solvent as the inner layer and the diluent as the outer layer, reducing side reactions between the positive and negative electrodes and the solvent, and providing the battery with excellent room temperature cycle performance and high temperature cycle performance, and low high-temperature gas generation.

[0009] In any embodiment, R2 includes one or more of -CF3, -CH3, -CH2-CF3, -CH2-CH3, -CF2-CF3, and optionally one or two of -CF2-CF3, -CF3.

[0010] In any embodiment, the co-solvent comprises one or more of methyl propyl ether, methyl butyl ether, methyl heptyl ether, ethyl propyl ether, 2-ethoxybutane, ethyl heptyl ether, ethyl amyl ether, methyl octyl ether, propyl butyl ether, propyl nonyl ether, trifluoromethyl heptyl ether, 1,1,2,2,2-pentafluoroethyl propyl ether, 2,2,2-trifluoroethyl butyl ether, and optionally one or more of methyl butyl ether, methyl heptyl ether, ethyl propyl ether, ethyl heptyl ether, trifluoromethyl heptyl ether, and 1,1,2,2,2-pentafluoroethyl propyl ether.

[0011] In either embodiment, the molar ratio of diluent to co-solvent is from 1:7 to 7:1, and optionally from 1:5 to 5:1.

[0012] The molar ratio of the diluent to the co-solvent within an appropriate range contributes to the formation of a protective layer structure around the solvated structure, with the co-solvent as the inner layer and the diluent as the outer layer, and further reduces side reactions between the positive and negative electrodes and the solvent, providing the battery with excellent room temperature cycle performance and high temperature cycle performance and low gas generation.

[0013] In either embodiment, the electrolyte comprises an ethylene glycol ether based solvent.

[0014] The ethylene glycol ether solvent allows the battery to have excellent normal temperature cycle performance and high temperature cycle performance, and low high temperature gas generation.

[0015] In any embodiment, the molar ratio of the ethylene glycol ether solvent to the diluent is 1:5 to 3:1, and optionally 1:3 to 1:1.

[0016] When the molar ratio of the ethylene glycol ether solvent to the diluent is within an appropriate range, the diluent is advantageous in forming a protective layer around the solvated structure, and the battery has excellent room temperature cycle performance and high temperature cycle performance, and low high temperature gas generation.

[0017] In any embodiment, the ethylene glycol ether solvent includes one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, and ethylene glycol dibutyl ether.

[0018] In any embodiment, the electrolyte further comprises a sodium salt, the sodium salt comprising at least one of a first sodium salt and a second sodium salt, the first sodium salt comprising one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, and sodium trifluoroacetate, and the second sodium salt comprising one or more of sodium difluoro(oxalato)borate, sodium bis(oxalato)borate, sodium tetraphenylborate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide.

[0019] With the appropriate sodium salt, the battery has excellent normal temperature cycle performance and high temperature cycle performance, and low high temperature gas generation.

[0020] In any embodiment, the mass content of the first sodium salt is 3% to 40%, and optionally 5% to 30%, based on the total mass of the sodium salt, the ethylene glycol ether solvent, and the co-solvent.

[0021] When the first sodium salt has an appropriate mass content, the battery has excellent room temperature cycle performance and high temperature cycle performance, and a low amount of high temperature gas generation.

[0022] In any embodiment, the mass content of the second sodium salt is 0.1% or more, and optionally 1% or more, based on the total mass of the sodium salt, the ethylene glycol ether system, and the co-solvent.

[0023] When the second sodium salt has an appropriate mass content, it can improve the room temperature cycle performance and high temperature cycle performance of the battery and reduce the high temperature gas generation phenomenon of the battery.

[0024] A second aspect of the present application provides a sodium secondary battery, the sodium secondary battery including the electrolyte of any of the embodiments.

[0025] In any embodiment, the sodium secondary battery includes a negative electrode plate, and the negative electrode plate includes a negative electrode current collector and an undercoating formed on at least one side of the negative electrode current collector.

[0026] The undercoating can improve the room temperature cycle performance and high temperature cycle performance of the battery, reduce the high temperature gas generation phenomenon of the battery, and improve the electrochemical performance and safety performance of the battery.

[0027] In any embodiment, the areal density of the undercoating is between 5 and 50 g / m 2 is.

[0028] An appropriate range of undercoating area density can optimize the metal deposition effect, improve the high-temperature cycle performance and room-temperature cycle performance of the battery, and reduce the high-temperature gas generation phenomenon of the battery. At the same time, an appropriate range of undercoating area density can increase the energy density of the battery and meet the usage demands of the battery.

[0029] In either embodiment, the undercoating comprises one or more of a carbon coating, an alloy coating, and a metal oxide coating, and optionally is a carbon coating.

[0030] In either embodiment, the undercoating comprises one or more of superconducting carbon black, ketjen black, acetylene black, carbon nanotubes, and graphene.

[0031] In either embodiment, the sodium secondary battery is a non-anode sodium metal battery.

[0032] A sodium secondary battery is a negative electrode-free sodium metal battery that can improve the room temperature cycle performance and high temperature cycle performance of the battery, reduce the high temperature gas generation phenomenon of the battery, and improve the electrochemical performance and safety performance of the battery.

[0033] A third aspect of the present application provides a battery module, which includes the sodium secondary battery of the second aspect.

[0034] A fourth aspect of the present application provides a battery pack, which includes the sodium secondary battery of the second aspect or the battery module of the third aspect.

[0035] A fifth aspect of the present application provides a power consumption device, which includes at least one of the sodium secondary battery of the second aspect, the battery module of the third aspect, or the battery pack of the fourth aspect. [Brief explanation of the drawings]

[0036] [Figure 1] 1 is a schematic diagram of a sodium secondary battery according to an embodiment of the present application. [Figure 2] FIG. 2 is an exploded view of the sodium secondary battery according to the embodiment of the present application shown in FIG. 1. [Figure 3] 1 is a schematic diagram of a battery module according to an embodiment of the present application; [Figure 4] 1 is a schematic diagram of a battery pack according to an embodiment of the present application; [Figure 5] FIG. 5 is an exploded view of the battery pack according to the embodiment of the present application shown in FIG. 4. [Figure 6]1 is a schematic diagram of a power consumption device that uses a sodium secondary battery according to an embodiment of the present application as a power source. DETAILED DESCRIPTION OF THE INVENTION

[0037] Hereinafter, with appropriate reference to the drawings, embodiments specifically disclosing the sodium secondary battery, battery module, battery pack, and power consumption device of the present application will be described in detail. However, unnecessary detailed description may be omitted. For example, detailed description of well-known matters and redundant description of actually identical structures may be omitted. This is to avoid the following description becoming unnecessarily long and to facilitate understanding by those skilled in the art. Note that 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.

[0038] The "ranges" disclosed in this application are defined in the form of lower and upper limits, and a given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of the particular range. Such defined ranges may be inclusive or exclusive of the end values, and any combination is possible; i.e., any lower limit can be combined with any upper limit to form a single range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also possible. Furthermore, if 1 and 2 are listed as minimum range values ​​and 3, 4, and 5 are listed as maximum range values, the ranges 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5 are all possible. In this application, unless otherwise specified, a numerical range "a to b" is a shorthand notation for any combination of real numbers a to b, where a and b are both real numbers. For example, the numerical range "0-5" represents that the present specification has already listed all real numbers between "0-5," and "0-5" is merely a shorthand representation of combinations of these numbers. Also, expressing a parameter as an integer ≧2 is equivalent to disclosing that this parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0039] Unless otherwise stated, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0040] Unless otherwise stated, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0041] Unless otherwise specified, the terms "comprise" and "include" used in this application may be open-ended or closed-ended. For example, the terms "comprise" and "include" may further include or include other components not listed, or may include or include only the listed components.

[0042] Unless otherwise stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, "A or B" is satisfied when A is true (or exists) and B is false (or does not exist), when A is false (or does not exist) but B is true (or exists), or when both A and B are true (or exist).

[0043] When a sodium secondary battery is used or stored at high temperatures, the reaction activity between the positive and negative electrodes and the electrolyte is enhanced, which significantly increases side reactions during the battery cycle process, generating large amounts of gas and making the battery more likely to expand in volume. In serious cases, this may even cause a short circuit inside the battery, which may have serious impacts on the electrochemical performance and safety performance of the battery.

[0044] [Electrolyte for sodium secondary batteries] The present application provides an electrolyte for a sodium secondary battery, the electrolyte including a diluent, the diluent having the general formula C n H 2n+2 The alkanes include those with n values ​​between 8 and 13.

[0045] In this specification, the term "sodium secondary battery" refers to a secondary battery that uses sodium ions as a charge carrier, and the negative electrode active material of the sodium secondary battery includes a carbon-based material, a titanium-based material, an alloy material, a layered transition metal oxide, a layered transition metal selenide, an organic material, or metallic sodium, and a sodium secondary battery that uses metallic sodium as the negative electrode active material is referred to as a sodium metal battery.

[0046] In some embodiments, the negative electrode active material of the sodium secondary battery comprises one or more of a graphitic carbon material, an amorphous carbon material, and a nanocarbon material.

[0047] In some embodiments, the negative electrode active material of the sodium secondary battery is hard carbon.

[0048] In some embodiments, the negative electrode active material of the sodium secondary battery is metallic sodium.

[0049] As used herein, the term "anodeless sodium metal battery" refers to a sodium metal battery in which the assembly process uses a current collector as the anode, and during charging, sodium ions deposit on the current collector to form a sodium metal anode.

[0050] As used herein, the term "electrolyte" refers to a carrier that transports ions in a sodium secondary battery, and includes a liquid electrolyte, a solid electrolyte, or a quasi-solid electrolyte.

[0051] As used herein, the term "diluent" refers to an insoluble or sparingly soluble component of an electrolyte salt in which there is no significant coordination or association between the diluent molecules and the cations of the electrolyte salt, and the diluent does not disrupt the solvation structure.

[0052] A solvated structure occurs when the solvent molecules in an electrolyte have a much stronger binding force to cations than to anions, and after a sodium salt dissolves in the solvent, the solvent aggregates around the sodium ions. The aggregates formed by the sodium ions and the solvent are called solvated structures.

[0053] As used herein, the term "alkane" refers to a linear saturated hydrocarbon, a compound in which all carbon atoms in the molecule are joined by single bonds and all remaining valence bonds are bonded to hydrogen.

[0054] General formula C n H 2n+2The alkane has a relatively low solubility in sodium salts, and the alkane does not directly contribute to the solvation structure of sodium ions, so it does not affect the film formation performance on the surfaces of the positive and negative electrodes of sodium secondary batteries. The alkane also forms a protective layer around the solvation structure, reducing direct contact between the solvent and the positive and negative electrodes and reducing side reactions between the positive and negative electrodes and the solvent, improving the high-temperature cycle performance of the battery and suppressing gas generation during high-temperature cycles of sodium secondary batteries. Furthermore, the addition of an alkane diluent reduces the viscosity of the electrolyte, increases the ionic conductivity of the electrolyte, and improves the electrochemical performance of the battery without destroying the solvation structure.

[0055] Taking sodium metal batteries as an example, alkanes are highly stable against sodium metal and do not undergo chemical reactions with the sodium metal anode. The alkanes form a protective layer around the solvation structure, reducing direct contact between the solvent and the cathode and anode, while the surrounding alkanes do not react with the cathode and anode. This reduces side reactions between the cathode and anode and the solvent, improving the electrochemical and safety performance of the battery at high temperatures.

[0056] To summarize the above, general formula C n H 2n+2 The alkane diluent can improve the high-temperature cycle performance of the battery, reduce the high-temperature gas generation phenomenon of the battery, and improve the electrochemical performance and safety performance of the battery at high temperatures.

[0057] In some embodiments, the diluent has the general formula CH 18 , C9H 20 , C 10 H 22 , C 11 H 24 , C 12 H 26 , C 13 H 28 The alkanes may include one or more of the following alkanes:

[0058] In some embodiments, the diluent comprises one or more of n-octane and its isomers, n-nonane and its isomers, n-decane and its isomers, n-undecane and its isomers, n-dodecane and its isomers, and n-tridecane and its isomers.

[0059] As used herein, the term "isomer" refers to compounds that have the same molecular formula but different structures. By way of example, isomers of n-octane include, but are not limited to, 2-methylheptane, 3-methylheptane, 4-methylheptane, 3-ethylhexane, 2,2-dimethylhexane, 2-methyl-3-ethylpentane, 2,2,3-trimethylpentane, and 2,2,3,3-tetramethylbutane.

[0060] In some embodiments, the diluent comprises one or more of n-octane, n-nonane, n-decane, n-undecane, n-dodecane, n-tridecane, 2,3-dimethylheptane, 3-methylheptane, 4-methylheptane, and 3-ethylhexane.

[0061] In some embodiments, the diluent comprises one or two of n-nonane and n-decane.

[0062] The appropriate diluent makes the protective layer structure around the solvated structure more stable, and the electrolyte has appropriate viscosity and excellent ionic conductivity, which can further improve the room temperature cycle performance and high temperature cycle performance of the battery and reduce the high temperature gas generation phenomenon of the battery.

[0063] In some embodiments, the electrolyte further comprises a co-solvent, the co-solvent comprising a compound represented by Structural Formula I: JPEG2025530929000003.jpg17165Here, R1 is C 3-9 alkyl group, and R2 is selected from halogen-substituted or unsubstituted C 1-3 The alkyl group is selected from the group consisting of:

[0064] In this specification, the term "C 3-9An "alkyl group" is a straight or branched hydrocarbon chain radical consisting solely of carbon and hydrogen atoms, the radical being free of unsaturation, having from 3 to 9 carbon atoms, and attached to the remainder of the molecule through a single bond.

[0065] In this specification, the term "C 1-3 An "alkyl group" is a straight or branched hydrocarbon chain radical consisting solely of carbon and hydrogen atoms, the radical being free of unsaturation, having from 1 to 3 carbon atoms, and attached to the remainder of the molecule through a single bond.

[0066] As used herein, the term "halogen-substituted" means that at least one hydrogen atom of the compound or chemical moiety is replaced with a halogen atom or a halogenalkyl group.

[0067] As used herein, the term "halogenalkyl group" is an alkyl group that contains at least one halogen atom.

[0068] As used herein, the term "halogen" refers to fluorine, chlorine, bromine or iodine.

[0069] Taking ethylene glycol ether-based solvents as an example, R1 is a long-chain alkyl group that is mutually soluble with the alkane diluent, and R2 forms an alkoxy group together with an oxygen atom that is mutually soluble with the solvent. The co-solvent can improve the miscibility of the solvent and diluent, helping the diluent form a protective layer around the solvated structure. The co-solvent also acts as a bridge between the solvated structure and the diluent, forming a protective layer structure around the solvated structure with the co-solvent as the inner layer and the diluent as the outer layer, reducing side reactions between the positive and negative electrodes and the solvent, and providing the battery with excellent room temperature cycling performance and high temperature cycling performance and low high-temperature gas generation.

[0070] In some embodiments, R2 comprises one or more of -CF3, -CH3, -CH2-CF3, -CH2-CH3, -CF2-CF3.

[0071] In some embodiments, R2 includes one or two of -CF2-CF3, -CF3.

[0072] In some embodiments, R2 comprises -CF2-CF3.

[0073] In some embodiments, the co-solvent comprises one or more of methyl propyl ether, methyl butyl ether, methyl heptyl ether, ethyl propyl ether, 2-ethoxybutane, ethyl heptyl ether, ethyl amyl ether, methyl octyl ether, propyl butyl ether, propyl nonyl ether, trifluoromethyl heptyl ether, 1,1,2,2,2-pentafluoroethyl propyl ether, 2,2,2-trifluoroethyl butyl ether.

[0074] In some embodiments, the co-solvent comprises one or more of methyl butyl ether, methyl heptyl ether, ethyl propyl ether, ethyl heptyl ether, trifluoromethyl heptyl ether, 1,1,2,2,2-pentafluoroethyl propyl ether.

[0075] In some embodiments, the molar ratio of diluent to co-solvent is 1:7 to 7:1. In some embodiments, the molar ratio of diluent to co-solvent is optionally 1:7 to 1:6, 1:7 to 1:5, 1:7 to 1:4, 1:7 to 1:3, 1:7 to 1:2, 1:7 to 1:1, 1:7 to 2:1, 1:7 to 3:1, 1:7 to 4:1, 1:7 to 5:1, 1:7 to 6:1, 1:7 to 7:1, 1:6 to 1:5, 1:6 to 1:4, 1:6 to 1:3, 1:6 to 1:2, 1:6 to 1:1 , 1:6~2:1, 1:6~3:1, 1:6~4:1, 1:6~5:1, 1:6~6:1, 1:6~7:1, 1:5~1:4, 1:5~1:3, 1:5~1:2, 1:5~1:1, 1:5~2:1, 1:5~3:1, 1:5~4:1, 1:5~5:1, 1:5~6:1, 1:5~7:1, 1:4~1:3, 1:4~1:2, 1:4~1:1, 1:4~2:1, 1:4~3: 1, 1:4~4:1, 1:4~5:1, 1:4~6:1, 1:4~7:1, 1:3~1:2, 1:3~1:1, 1:3~2:1, 1:3~3:1, 1:3~4:1, 1:3~5:1, 1:3~6:1, 1:3~7:1, 1:2~1:1, 1:2~2:1, 1:2~3:1, 1:2~4:1, 1:2~5:1, 1:2~6:1, 1:2~7:1, 1:1~2:1, 1:1~3 :1, 1:1 to 4:1, 1:1 to 5:1, 1:1 to 6:1, 1:1 to 7:1, 2:1 to 3:1, 2:1 to 4:1, 2:1 to 5:1, 2:1 to 6:1, 2:1 to 7:1, 3:1 to 4:1, 3:1 to 5:1, 3:1 to 6:1, 3:1 to 7:1, 4:1 to 5:1, 4:1 to 6:1, 4:1 to 7:1, 5:1 to 6:1, 5:1 to 7:1, 6:1 to 7:1.

[0076] When the molar ratio of the diluent to the co-solvent is within an appropriate range, the diluent forms a protective structure on the outer layer of the solvated structure, which is advantageous in reducing side reactions between the positive and negative electrodes and the solvent, and provides the battery with excellent room temperature cycle performance and high temperature cycle performance and low gas generation.

[0077] In some embodiments, the molar ratio of diluent to co-solvent is 1:5 to 5:1. In some embodiments, the molar ratio of diluent to co-solvent is optionally 1:5 to 1:4, 1:5 to 1:3, 1:5 to 1:2, 1:5 to 1:1, 1:5 to 2:1, 1:5 to 3:1, 1:5 to 4:1, 1:5 to 5:1, 1:4 to 1:3, 1:4 to 1:2, 1:4 to 1:1, 1:4 to 2:1, 1:4 to 3:1, 1:4 to 4:1, 1:4 to 5:1, 1:3 to 1:2, 1:3 to 1: It is one of the following: 1, 1:3-2:1, 1:3-3:1, 1:3-4:1, 1:3-5:1, 1:2-1:1, 1:2-2:1, 1:2-3:1, 1:2-4:1, 1:2-5:1, 1:1-2:1, 1:1-3:1, 1:1-4:1, 1:1-5:1, 2:1-3:1, 2:1-4:1, 2:1-5:1, 3:1-4:1, 3:1-5:1, 4:1-5:1.

[0078] When the molar ratio of the diluent to the co-solvent is within an appropriate range, a protective structure is formed on the outer layer of the solvated structure, which is advantageous for reducing side reactions between the positive and negative electrodes and the solvent, thereby further improving the room temperature cycle performance and high temperature cycle performance of the battery and reducing the high temperature gas generation phenomenon of the battery.

[0079] In some embodiments, the electrolyte comprises an ethylene glycol ether based solvent.

[0080] In some embodiments, the ethylene glycol ether solvent comprises one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether.

[0081] As used herein, the term "ethylene glycol ether" refers to a compound having the structure shown in Formula II: JPEG2025530929000004.jpg13150 where m is a value between 1 and 4, and R3 is C 1-6 The alkyl group is selected from the group consisting of:

[0082] In this specification, the term "C 1-6 An "alkyl group" is a straight or branched hydrocarbon chain radical consisting solely of carbon and hydrogen atoms, the radical being free of unsaturation, having from 1 to 6 carbon atoms, and attached to the remainder of the molecule through a single bond.

[0083] The molecules of the ethylene glycol ether-based solvent build a stable electrode / electrolyte interface on the surface of the negative electrode, forming a stable SEI, reducing electrochemical polarization, and providing the battery with excellent room-temperature cycle performance and high-temperature cycle performance, as well as low high-temperature gas generation.

[0084] In some embodiments, the molar ratio of the ethylene glycol ether solvent to the diluent is 1:5 to 3: 1. In some embodiments, the molar ratio of the ethylene glycol ether solvent to the diluent is any one of 1:5 to 1:4, 1:5 to 1:3, 1:5 to 1:2, 1:5 to 1:1, 1:5 to 2:1, 1:5 to 3:1, 1:4 to 1:3, 1:4 to 1:2, 1:4 to 1:1, 1:4 to 2:1, 1:4 to 3:1, 1:3 to 1:2, 1:3 to 1:1, 1:3 to 2:1, 1:3 to 3:1, 1:2 to 1:1, 1:2 to 2:1, 1:2 to 3:1, 1:1 to 2:1, 1:1 to 3:1, and 2:1 to 3:1.

[0085] When the molar ratio of the ethylene glycol ether solvent to the diluent is within an appropriate range, the diluent is advantageous in forming a protective layer around the solvated structure, and the battery has excellent room temperature cycle performance and high temperature cycle performance, and low high temperature gas generation.

[0086] In some embodiments, the molar ratio of the ethylene glycol ether solvent to the diluent is 1:3 to 1:1. In some embodiments, the molar ratio of the ethylene glycol ether solvent to the diluent is any one of 1:3 to 1:2, 1:3 to 1:1, and 1:2 to 1:1.

[0087] When the molar ratio of the ethylene glycol ether solvent to the diluent is within an appropriate range, the diluent can form a protective layer around the solvated structure, which can further improve the room temperature cycle performance and high temperature cycle performance of the battery and reduce the high temperature gas generation phenomenon of the battery.

[0088] In some embodiments, the electrolyte further comprises a sodium salt, the sodium salt comprising at least one of a first sodium salt and a second sodium salt.

[0089] In some embodiments, the sodium salt comprises a first sodium salt and a second sodium salt.

[0090] In some embodiments, the first sodium salt comprises one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, and sodium trifluoroacetate.

[0091] The first sodium salt has a weak bonding force between the anions and sodium ions, which allows for rapid deposition and release of sodium metal, and is advantageous for improving the dynamic performance of the battery. Particularly in anode-less sodium metal batteries, the first sodium salt can effectively ensure the cycle performance of the battery. With the appropriate sodium salt, the electrolyte has appropriate viscosity and excellent ionic conductivity, and the battery has excellent room temperature cycle performance and high temperature cycle performance, and low high-temperature gas generation.

[0092] In some embodiments, the second sodium salt comprises one or more of sodium difluoro(oxalato)borate, sodium bis(oxalato)borate, sodium tetraphenylborate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide.

[0093] The second sodium salt includes a sulfur-containing organic sodium salt or a boron-containing organic sodium salt, which easily participates in the formation of a structurally stable and uniformly distributed SEI, and is used to improve the high-temperature cycling performance of the battery and reduce the high-temperature gas generation phenomenon of the battery. With the appropriate sodium salt, the electrolyte has appropriate viscosity and excellent ionic conductivity, and the battery has excellent room-temperature cycling performance and high-temperature cycling performance and a low amount of high-temperature gas generation.

[0094] In some embodiments, the mass content of the first sodium salt is 3% to 40%, based on the total mass of the sodium salt, ethylene glycol ether solvent, and co-solvent. In some embodiments, the mass content of the first sodium salt is optionally 3% to 5%, 3% to 10%, 3% to 15%, 3% to 20%, 3% to 25%, 3% to 30%, 3% to 35%, 3% to 40%, 5% to 10%, 5% to 15%, 5% to 20%, 5% to 25%, 5% to 30%, 5% to 35%, 5% to 40%, 10% to 50%, 10% to 50%, 15 ... It is one of the following: %~15%, 10%~20%, 10%~25%, 10%~30%, 10%~35%, 10%~40%, 15%~20%, 15%~25%, 15%~30%, 15%~35%, 15%~40%, 20%~25%, 20%~30%, 20%~35%, 20%~40%, 25%~30%, 25%~35%, 25%~40%, 30%~35%, 30%~40%, 35%~40%.

[0095] When the mass content of the first sodium salt is in an appropriate range, the electrolyte has appropriate viscosity and excellent ionic conductivity, and the battery has excellent room temperature cycle performance and high temperature cycle performance, has a low amount of high-temperature gas generation, and extends the operating temperature of the battery.

[0096] In some embodiments, the mass content of the first sodium salt is 5% to 30% based on the total mass of the sodium salt, ethylene glycol ether solvent, and co-solvent, or alternatively any one of 5% to 10%, 5% to 15%, 5% to 20%, 5% to 25%, 5% to 30%, 10% to 15%, 10% to 20%, 10% to 25%, 10% to 30%, 15% to 20%, 15% to 25%, 15% to 30%, 20% to 25%, 20% to 30%, and 25% to 30% based on the total mass of the sodium salt, ethylene glycol ether solvent, and co-solvent.

[0097] When the mass content of the first sodium salt is within an appropriate range, the electrolyte has appropriate viscosity and excellent ionic conductivity, and can improve the room temperature cycle performance and high temperature cycle performance of the battery, thereby improving the electrochemical performance of the battery.

[0098] In some embodiments, the weight content of the second sodium salt is 0.1% or more, based on the total weight of the sodium salt, the ethylene glycol ether system, and the co-solvent, or any one or more of 0.2%, 0.3%, 0.4%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, and 40% based on the total weight of the sodium salt, the ethylene glycol ether system, and the co-solvent.

[0099] When the mass content of the second sodium salt is within an appropriate range, the electrolyte has appropriate viscosity and excellent ionic conductivity, and can improve the room temperature cycle performance and high temperature cycle performance of the battery and reduce the high temperature gas generation phenomenon of the battery.

[0100] In some embodiments, the weight content of the second sodium salt is 1% or more, based on the total weight of the sodium salt, the ethylene glycol ether system, and the co-solvent, and in some embodiments, the weight content of the second sodium salt is any one or more of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, and 40%, based on the total weight of the sodium salt, the ethylene glycol ether system, and the co-solvent.

[0101] When the mass content of the second sodium salt is within an appropriate range, the electrolyte has appropriate viscosity and excellent ionic conductivity, which can further improve the room temperature cycle performance and high temperature cycle performance of the battery and reduce the high temperature gas generation phenomenon of the battery.

[0102] In some embodiments, the electrolyte optionally further comprises other additives that can improve certain performance aspects of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the thermal stability of the electrolyte, etc.

[0103] [Sodium secondary battery] The present application provides a sodium secondary battery, which includes the electrolyte in any of the embodiments.

[0104] In some embodiments, the sodium secondary battery includes a negative electrode plate, the negative electrode plate including a negative electrode current collector and an undercoating formed on at least one side of the negative electrode current collector.

[0105] As used herein, the term "undercoating on at least one side of a negative electrode current collector" refers to an undercoating on one or both sides of the current collector, and the undercoating may be in direct contact with the current collector, i.e., no other structure is included between the current collector and the undercoating, or the undercoating may not be in direct contact with the current collector, i.e., another structure is included between the current collector and the undercoating.

[0106] The undercoating has the characteristic of low metal nucleation potential, which can effectively improve metal deposition / dissolution performance, and can also reduce the large volume changes that the metal deposition / dissolution process brings to the battery core, stabilize the battery core structure, improve the room temperature cycle performance and high temperature cycle performance of the battery, reduce the high temperature gas generation phenomenon of the battery, and improve the electrochemical performance and safety performance of the battery.

[0107] In some embodiments, the areal density of the undercoating is between 5 and 50 g / m 2 is.

[0108] In some embodiments, the areal density of the undercoating is preferably between 5 and 10 g / m 2 , 5 to 20 g / m 2 , 5 to 30 g / m 2 , 5~40g / m 2 , 5~50g / m 2 , 10-20g / m 2 , 10-30g / m 2 , 10~40g / m 2 , 10~50g / m 2 , 20-30g / m 2 , 20~40g / m 2 , 20~50g / m 2 , 30-40g / m 2 , 30~50g / m 2 , 40-50g / m 2 It is one of the following.

[0109] An appropriate range of undercoating area density can optimize the metal deposition effect, improve the high-temperature cycle performance and room-temperature cycle performance of the battery, and reduce the high-temperature gas generation phenomenon of the battery. At the same time, an appropriate range of undercoating area density can increase the energy density of the battery and meet the usage demands of the battery.

[0110] In either embodiment, the undercoating comprises one or more of a carbon coating, an alloy coating, and a metal oxide coating, and optionally is a carbon coating.

[0111] In either embodiment, the undercoating comprises one or more of superconducting carbon black, ketjen black, acetylene black, carbon nanotubes, and graphene.

[0112] In some embodiments, the undercoating comprises an adhesive, the adhesive comprising any one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene butadiene rubber, sodium alginate, lithium / sodium polyacrylate, polytetrafluoroethylene, polyimide, and polyurethane.

[0113] In some embodiments, the undercoating is a metal coating, the metal has a body-centered cubic structure, and the metal comprises any one of α-Fe, V, Nb, Cr, Mo, Ta, and W.

[0114] In some embodiments, the undercoating is an alloy coating, and the alloy includes any one or more of the metals Au, Ag, Sn, and Sb.

[0115] In some embodiments, the undercoating is a metal oxide coating, and the oxide comprises at least one of copper oxide and aluminum oxide.

[0116] In some embodiments, the undercoating is a conductive polymer coating, and the conductive polymer comprises any one of polyaniline, polythiophene, polypyrrole, and polyphenylene vinylene.

[0117] In some embodiments, the undercoating is a conductive ceramic coating, and the conductive ceramic material comprises at least one of TiB2, TiC, and B4C3.

[0118] In some embodiments, the undercoating is a conductive carbon coating, and the conductive carbon comprises at least one of conductive carbon black, graphite, carbon fiber, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, and fullerenes.

[0119] In some embodiments, the sodium secondary battery is a non-anode sodium metal battery.

[0120] In some embodiments, the sodium secondary battery is a non-anode sodium metal battery. Non-anode sodium metal batteries do not use anode active materials, but instead use only anode current collectors as anodes. During the initial charging process, sodium plating is completed on the anode, which is then returned to the cathode during discharge, achieving charge-discharge cycling. Because they do not use anode materials and only use anode current collectors, non-anode sodium metal batteries effectively overcome the shortcomings of sodium metal batteries and can achieve higher energy densities than metallic sodium anodes.

[0121] A sodium secondary battery is a negative electrode-free sodium metal battery that can improve the room temperature cycle performance and high temperature cycle performance of the battery, reduce the high temperature gas generation phenomenon of the battery, and improve the electrochemical performance and safety performance of the battery at high temperatures.

[0122] In some embodiments, the CB value of the anode-less sodium metal battery is 0.1 or less.

[0123] The CB value is calculated by dividing the capacity per unit area of ​​the negative electrode plate in a sodium secondary battery by the capacity per unit area of ​​the positive electrode plate. Because no-anode sodium metal batteries contain any negative active material, the capacity per unit area of ​​the negative electrode plate is relatively small, and the CB value of the secondary battery is less than 0.1.

[0124] In some embodiments, the negative electrode current collector used in the negative electrode plate includes at least one of a metal foil current collector, a metal foam current collector, a metal mesh current collector, a carbon felt current collector, a carbon cloth current collector, and a carbon paper current collector. Because sodium ions do not form an alloy with aluminum, and considering cost and weight reduction, sodium secondary batteries preferentially employ aluminum-based current collectors, which are either aluminum foil, aluminum alloy foil, or aluminum-based composite current collectors. The aluminum-based composite current collector includes a polymer base film and aluminum foil and / or aluminum alloy foil formed on both sides of the polymer base film. Specifically, the aluminum-based composite current collector has a "sandwich" structure, with a polymer base film located in the center and aluminum foils on both sides, or aluminum foils on both sides. Alternatively, an aluminum alloy foil may be provided on one side of a polymer base film and an aluminum alloy foil on the other side, and the polymer base film may be made of any one of polyamide, polyterephthalate, polyimide, polyethylene, polypropylene, polystyrene, polychloroethylene, acrylonitrile-butadiene-styrene copolymer, polybutylene terephthalate, polyparaphenylene terephthalamide, polypropylethylene, polyformaldehyde, epoxy resin, phenol resin, polytetrafluoroethylene, polyvinylidene fluoride, silicone rubber, and polycarbonate.

[0125] [Positive electrode plate] In some embodiments, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer formed on at least a portion of the surface of the positive electrode current collector, the positive electrode active material layer including a positive electrode active material, which may include at least one of a layered transition metal oxide, a polyanion-type compound, and a Prussian blue-based compound.

[0126] The transition metal in the layered transition metal oxide may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Optionally, the layered transition metal oxide may be, for example, NaxMO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0 <x≦1である。

[0127] Polyanionic compounds include metal ions, transition metal ions, and tetrahedral (YO4) n- The compound may have an anionic unit, wherein the metal ion is optionally one of sodium ion, lithium ion, potassium ion, and zinc ion, the transition metal is optionally at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, Y is optionally at least one of P, S, and Si, and n is (YO4) n- represents the valence state of

[0128] Prussian blue compounds contain sodium ions, transition metal ions, and cyanide ions (CN - The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The Prussian blue compound may be, for example, Na a Me b Me' c (CN)6, where Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn; <a≦2、0<b<1、0<c<1である。

[0129] The positive electrode active material layer may further include a conductive agent to improve the conductive performance of the positive electrode, which may be one or more of Super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphite, graphene, and carbon nanofibers.

[0130] The positive electrode active material layer may further include an adhesive to firmly adhere the positive electrode active material and optional conductive agent to the positive electrode current collector, and the adhesive may be at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), polyvinyl alcohol (PVA), ethylene-vinyl acetate copolymer (EVA), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), sodium alginate (SA), polymethacrylic acid (PMA), and carboxymethyl chitosan (CMCS).

[0131] The positive electrode current collector may be a conductive carbon piece, a metal foil, a carbon-coated metal foil, a porous metal plate, or a composite current collector. The conductive carbon material of the conductive carbon piece may be one or more of Super P, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite, graphene, and carbon nanofibers. The metal materials of the metal foil, the carbon-coated metal foil, and the porous metal plate may each independently be at least one of copper, aluminum, nickel, and stainless steel. The composite current collector may be a composite current collector formed by combining a metal foil with a polymer base film.

[0132] In some embodiments, a positive electrode plate can be manufactured as follows: Components for manufacturing the positive electrode plate, such as a positive electrode active material, a conductive agent, an adhesive, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, which is then coated onto a positive electrode current collector, and the positive electrode plate is obtained after processes such as drying and cold pressing.

[0133] [Separator] In some embodiments, the sodium secondary battery further includes a separator. The present application does not particularly limit the type of separator, and any known porous separator with good chemical stability and mechanical stability may be selected.

[0134] In some embodiments, the separator may be made of at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers. The separator may be a single-layer film or a multi-layer composite film, without any particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without any particular limitation.

[0135] In some embodiments, the positive and negative electrodes and the separator can be fabricated into an electrode assembly by a winding or lamination process.

[0136] In some embodiments, the sodium secondary battery may include an outer casing, which may be used to package the electrode assembly and the electrolyte.

[0137] In some embodiments, the exterior of the sodium secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The exterior of the sodium secondary battery may be a pouch, such as a bag-shaped pouch. The pouch may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0138] The present application does not particularly limit the shape of the sodium secondary battery, which may be cylindrical, rectangular, or any other shape. For example, Fig. 1 shows an example of a sodium secondary battery 5 having a rectangular structure.

[0139] In some embodiments, referring to FIG. 2 , the exterior body may include a case 51 and a cover plate 53. Here, the case 51 may include a bottom plate and a side plate connected to the bottom plate, where the bottom plate and the side plate together form a surrounding accommodating cavity. The case 51 has an opening communicating with the accommodating cavity, and the cover plate 53 can cover the opening to seal the accommodating cavity. The positive electrode plate, the negative electrode plate, and the separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged within the accommodating cavity. An electrolyte is impregnated into the electrode assembly 52. ​​The sodium secondary battery 5 may include one or more electrode assemblies 52, and those skilled in the art can select the number of electrode assemblies 52 according to specific needs.

[0140] In some embodiments, the sodium secondary batteries may be assembled into a battery module, and the number of sodium secondary batteries included in the battery module may be one or more, and the specific number can be selected by those skilled in the art depending on the application and capacity of the battery module.

[0141] Fig. 3 shows an example of a battery module 4. Referring to Fig. 3, in the battery module 4, a plurality of sodium secondary batteries 5 may be arranged in order along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the plurality of sodium secondary batteries 5 may be fixed by fasteners.

[0142] Optionally, the battery module 4 may further include a housing having an accommodating space, and the plurality of sodium secondary batteries 5 are accommodated in this accommodating space.

[0143] In some embodiments, the battery modules may be further assembled into a battery pack, and the number of battery modules included in the battery pack may be one or more, the specific number of which can be selected by those skilled in the art depending on the application and capacity of the battery pack.

[0144] 4 and 5 show an example of a battery pack 1. Referring to FIGS. 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 installed in the battery box. The battery box includes an upper housing 2 and a lower housing 3, and the upper housing 2 covers the lower housing 3 and may form a sealed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0145] The present application also provides a power consuming device, the power consuming device including at least one of a sodium secondary battery, a battery module, or a battery pack according to the present application. The sodium secondary battery, the battery module, or the battery pack may be used as a power source for the power consuming device or as an energy storage unit for the power consuming device. The power consuming device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0146] The power consumption device can be selected as a sodium secondary battery, a battery module, or a battery pack depending on its usage needs.

[0147] 6 shows an example of a power consumption device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density needs of sodium secondary batteries, a battery pack or battery module can be employed.

[0148] Other examples of the device may be a mobile phone, a tablet computer, a laptop computer, etc. These devices are generally required to be thin, and can employ a sodium secondary battery as a power source.

[0149] Example Examples of the present application are described below. The examples described below are illustrative and are intended only to interpret the present application and should not be understood as limitations on the present application. While specific techniques or conditions are not specified in the examples, they are carried out according to techniques or conditions described in literature in the art or according to product specifications. Manufacturers of the reagents and instruments used are not indicated, and all are commercially available ordinary products. While the following examples only describe the case where the secondary battery is a sodium-ion battery, the present application is not limited thereto.

[0150] 1. Manufacturing method Example 1 1) Electrolyte production In an argon gas atmosphere glove box with a moisture content of <10 ppm, a first sodium salt, sodium hexafluorophosphate, and a second sodium salt, sodium bis(fluorosulfonyl)imide, were added to an ethylene glycol dimethyl ether solvent to obtain a mixed solution, and then a diluent, n-nonane, and a co-solvent, methyl butyl ether, were added to the mixed solution to obtain an electrolyte, in which the molar ratio of n-nonane to methyl butyl ether was 1:1, and the molar ratio of ethylene glycol dimethyl ether to n-nonane was 1:2. Based on the total mass of the first sodium salt, the second sodium salt, ethylene glycol dimethyl ether, and methyl butyl ether, the mass content of sodium hexafluorophosphate was 15% and the mass content of sodium bis(fluorosulfonyl)imide was 3%.

[0151] 2) Manufacturing of positive electrode plates The positive electrode active material Na3V2(PO4)3, the adhesive polyvinylidene fluoride (PVDF), and the conductive carbon black (Super-P) were uniformly mixed in a mass ratio of 96%:2%:2% in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. This was then applied to the surface of an aluminum foil using a squeeze coater according to the mass requirement per unit area of ​​the positive electrode active material, dried, and then pressed into a cold press to form a coated electrode plate at a density of 2.5 g / cm. 3The final positive electrode plate was obtained by cold pressing at the design pressure density.

[0152] 3) Manufacturing of negative electrode plates The carbon nanotubes and sodium alginate were added to deionized water and stirred into a uniform slurry. The slurry was coated onto a negative electrode current collector, dried, and cut to obtain a negative electrode plate with a no-anode structure, where the areal density of the undercoating was 20 g / m. 2 is.

[0153] 4) Separator A polyethylene film (PE separator) was used as the separator.

[0154] 5) Battery manufacturing The positive electrode plate, separator, and negative electrode plate were stacked in this order, and a separator was placed between the positive and negative electrodes to provide isolation. The electrolyte was added to the positive and negative electrodes to form a button battery.

[0155] Examples 2 to 38 Except for the different electrolyte formulations and / or manufacturing parameters of the negative electrode plates, the other steps of Examples 2 to 38 are the same as those of Example 1. Here, the manufacturing methods of the negative electrode plates of Examples 37 and 38 are as follows, and the specific parameters are as shown in Tables 1 and 2.

[0156] Example 37: Carbon nanotubes and sodium alginate were added to deionized water and stirred into a uniform slurry, which was then coated onto an aluminum foil negative electrode current collector, dried, and cut to obtain a negative electrode current collector with an undercoating, where the areal density of the undercoating was 20 g / m 2 The negative electrode active material hard carbon, the conductive agent acetylene black, the adhesive styrene-butadiene rubber (SBR), and the thickener hydroxymethyl cellulose (CMC) were mixed in a weight ratio of 90:5:4:1 in an appropriate amount of deionized water and thoroughly stirred to form a uniform negative electrode slurry. The negative electrode slurry was then coated onto a negative electrode current collector having an undercoat, dried at 100°C, and pressed to obtain a negative electrode plate.

[0157] Example 38: The negative electrode plate is aluminum foil.

[0158] Comparative Examples 1 to 6 Except for the electrolyte composition and / or negative electrode plate manufacturing parameters, Comparative Example 5 is the same as the negative electrode plate manufacturing method of Example 37, and Comparative Example 6 is the same as the negative electrode plate manufacturing method of Example 38, and the specific parameters are as shown in Tables 1 and 2.

[0159] 2. Battery performance test 1) Room temperature cycle performance At 25°C and atmospheric pressure (0.1 MPa), the battery was charged at a constant current of 0.5 C to a voltage of 3.5 V, and then discharged at a constant current of 1 C to a voltage of 3.2 V, which constituted one charge-discharge cycle. The initial discharge capacity was taken as 100%, and the charge-discharge cycle was repeated 500 times. After the test was stopped, the cycle capacity retention rate was recorded, and the room temperature capacity retention rate was used as an index to evaluate the room temperature cycle performance of the battery.

[0160] 2) High-temperature cycle performance At 60°C and atmospheric pressure (0.1 MPa), the battery was charged at a constant current of 0.5 C to a voltage of 3.5 V, and then discharged at a constant current of 1 C to a voltage of 3.2 V, which constituted one charge-discharge cycle. The initial discharge capacity was taken as 100%, and the charge-discharge cycle was repeated 500 times. After the test was stopped, the cycle capacity retention rate was recorded, and the high-temperature capacity retention rate was used as an index for evaluating the high-temperature cycle performance of the battery.

[0161] 3) High-temperature gas generation performance At room temperature (25°C), the battery was charged to 3.5V at a constant current of 0.5C. After the battery was fully charged, the initial volume of the battery was measured using the drainage method. The battery was stored in an oven at 60°C for 24 days, then removed and left at room temperature for 60 minutes. After cooling to room temperature, the battery volume was measured using the drainage method within 60 minutes. The volume expansion rate of the battery was calculated based on the volume of the battery before storage. The volume expansion rate (%) after storing the battery at 60°C for 24 days = (volume of battery measured after storage / volume of battery measured before storage) - 1.

[0162] The test procedures for the comparative example and other examples were the same as those described above.

[0163] 3. Test results The test results for the above examples and comparative examples are shown in Tables 1 and 2.

[0164] [Table 1-1] [Table 1-2] [Table 1-3]

[0165] [Table 2-1] [Table 2-2] [Table 2-3] [Table 2-4]

[0166] As can be seen from the above results, the sodium secondary battery electrolytes in Examples 1 to 38 all contained a diluent, and the diluent included n-nonane, n-decane, n-octane, n-tridecane, or 2,3-dimethylheptane. Comparisons of Examples 1 to 21, 23 to 26, and 28 to 36 with Comparative Examples 1 and 2, Example 22 with Comparative Example 3, Example 27 with Comparative Example 4, and Examples 37 to 38 with Comparative Examples 5 and 6 reveal that the diluent improved the high-temperature capacity retention of the battery, improved the high-temperature cycle performance of the battery, reduced the high-temperature expansion rate of the battery, reduced the high-temperature gas generation phenomenon of the battery, and improved the electrochemical performance and safety performance of the battery at high temperatures.

[0167] As can be seen from the comparison between Examples 1-2 and Examples 3-5, the diluent containing n-nonane or n-decane can further improve the room temperature cycle performance and high temperature cycle performance of the battery and reduce the high temperature gas generation phenomenon of the battery.

[0168] The sodium secondary battery electrolytes in Examples 1 to 38 all contained a co-solvent, which was methyl butyl ether, methyl heptyl ether, ethyl propyl ether, or ethyl heptyl ether, and the batteries had excellent room temperature cycle performance and high temperature cycle performance, and low high-temperature gas generation.

[0169] The molar ratio of diluent to co-solvent in Examples 1 to 38 was 1:7 to 7:1, and the batteries had excellent normal temperature cycle performance and high temperature cycle performance, and low high temperature gas generation.

[0170] As can be seen from the comparison between Examples 1, 10-11 and Examples 9 and 12, when the molar ratio of diluent to co-solvent was 1:5-5:1, the room temperature cycle performance and high temperature cycle performance of the battery were further improved and the high temperature gas generation phenomenon of the battery was reduced.

[0171] The electrolytes for sodium secondary batteries in Examples 1 to 38 were all contained in ethylene glycol ether-based solvents, and the diluents were ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, or diethylene glycol dimethyl ether. The batteries had excellent room temperature cycle performance and high temperature cycle performance, and low high-temperature gas generation.

[0172] In Examples 1 to 38, the molar ratio of the ethylene glycol ether solvent to the diluent was 1:5 to 3:1, and the batteries had excellent normal temperature cycle performance and high temperature cycle performance, and a low amount of high temperature gas generation.

[0173] As can be seen from the comparison between Examples 1, 14-15 and Examples 13 and 16, the molar ratio of the ethylene glycol ether solvent to the diluent was 1:3 to 1:1, which further improved the room temperature cycle performance and high temperature cycle performance of the battery and reduced the high temperature gas generation phenomenon of the battery.

[0174] The electrolytes in Examples 1 to 38 further contained a sodium salt, and the sodium salt included one or two of a first sodium salt and a second sodium salt, where the first sodium salt included sodium hexafluorophosphate (NaPF), sodium tetrafluoroborate (NaBF), or sodium trifluoroacetate (CFCOONa), and the second sodium salt included sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), or sodium bis(oxalato)borate (NaBOB), and the batteries had excellent room temperature cycle performance and high temperature cycle performance, and low high temperature gas generation.

[0175] The mass content of the first sodium salt in Examples 1 to 26 and 28 to 38 was 3% to 40% based on the total mass of the sodium salt, ethylene glycol ether-based solvent, and co-solvent, and the batteries had excellent room temperature cycle performance and high temperature cycle performance, and low high-temperature gas generation.

[0176] As can be seen from the comparison of Examples 1, 24-25 with Examples 23 and 26, the mass content of the first sodium salt was 5% to 30% based on the total mass of the sodium salt, ethylene glycol ether solvent, and co-solvent, which further improved the room temperature cycle performance and high temperature cycle performance of the battery and improved the electrochemical performance of the battery.

[0177] As can be seen from the comparison of Examples 1, 31 and 32 with Example 30, the mass content of the second sodium salt was 0.1% or more based on the total mass of the sodium salt, ethylene glycol ether solvent and co-solvent, which could improve the room temperature cycle performance and high temperature cycle performance of the battery and reduce the high temperature gas generation phenomenon of the battery.

[0178] As can be seen from the comparison between Examples 1 and 32 and Examples 30 to 31, the mass content of the second sodium salt was 1% or more based on the total mass of the sodium salt, ethylene glycol ether solvent, and co-solvent, which further improved the room temperature cycle performance and high temperature cycle performance of the battery and reduced the high temperature gas generation phenomenon of the battery.

[0179] As can be seen from the comparison between Examples 1 and 37 and Example 38, the negative electrode plate includes a negative electrode current collector and an undercoating formed on at least one side of the negative electrode current collector, and can improve the room temperature cycle performance and high temperature cycle performance of the battery, reduce the high temperature gas generation phenomenon of the battery, and improve the electrochemical performance and safety performance of the battery.

[0180] As can be seen from the comparison between Examples 1, 33-34 and Examples 35-36, the areal density of the undercoating is 5-50 g / m 2 This has improved the room temperature cycle performance and high temperature cycle performance of the battery, reduced the high temperature gas generation phenomenon of the battery, and improved the electrochemical performance and safety performance of the battery.

[0181] As can be seen from the comparison between Example 1 and Example 37, the sodium secondary battery is a negative electrode-less sodium metal battery, and can improve the room temperature cycle performance and high temperature cycle performance of the battery, reduce the high temperature gas generation phenomenon of the battery, and improve the electrochemical performance and safety performance of the battery.

[0182] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any embodiment that has substantially the same configuration as the technical idea and achieves the same effects within the scope of the technical solution of the present application is included within the technical scope of the present application. In addition, various modifications that a person skilled in the art can make to the embodiments without departing from the spirit of the present application, and other methods configured by combining some of the components of the embodiments, are also included within the scope of the present application. [Explanation of symbols]

[0183] 1 battery pack, 2 upper housing, 3 lower housing, 4 battery module, 5 sodium secondary battery, 51 case, 52 electrode assembly, 53 cover plate.

Claims

1. An electrolyte for a sodium secondary battery, the electrolyte comprising a diluent, the diluent having a general formula C n H 2n+2 and the value of n is 8 to 13.

2. 2. The electrolyte of claim 1, wherein the diluent comprises one or more of n-octane, n-nonane, n-decane, n-undecane, n-dodecane, n-tridecane, 2,3-dimethylheptane, 3-methylheptane, 4-methylheptane, and 3-ethylhexane, and optionally one or two of n-nonane and n-decane.

3. The electrolyte further comprises a co-solvent, the co-solvent comprising a compound represented by structural formula I: Here, R 1 is C 3-9 alkyl groups, R 2 is a halogen-substituted or unsubstituted C 1-3 3. The electrolyte according to claim 1, wherein the alkyl group is selected from alkyl groups.

4. The R 2 is -CF 3 , -CH 3 , -CH 2 -CF 3 , -CH 2 -CH 3 , -CF 2 -CF 3 and optionally one or more of -CF 2 -CF 3 , -CF 3 4. The electrolyte of claim 3, wherein the electrolyte is one or two of:

5. 5. The electrolyte of claim 3 or 4, wherein the co-solvent comprises one or more of methyl propyl ether, methyl butyl ether, methyl heptyl ether, ethyl propyl ether, 2-ethoxybutane, ethyl heptyl ether, ethyl amyl ether, methyl octyl ether, propyl butyl ether, propyl nonyl ether, trifluoromethyl heptyl ether, 1,1,2,2,2-pentafluoroethyl propyl ether, 2,2,2-trifluoroethyl butyl ether, and alternatively one or more of methyl butyl ether, methyl heptyl ether, ethyl propyl ether, ethyl heptyl ether, trifluoromethyl heptyl ether, 1,1,2,2,2-pentafluoroethyl propyl ether.

6. 6. The electrolyte according to any one of claims 3 to 5, characterized in that the molar ratio of the diluent to the co-solvent is between 1:7 and 7:1, and optionally between 1:5 and 5:

1.

7. The electrolyte according to claim 1 , wherein the electrolyte contains an ethylene glycol ether-based solvent.

8. 8. The electrolyte of claim 7, wherein the molar ratio of the ethylene glycol ether solvent to the diluent is 1:5 to 3:1, and optionally 1:3 to 1:

1.

9. 9. The electrolyte according to claim 7 or 8, wherein the ethylene glycol ether-based solvent comprises one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, and ethylene glycol dibutyl ether.

10. 10. The electrolyte of claim 1, further comprising a sodium salt, the sodium salt comprising one or two of a first sodium salt and a second sodium salt, the first sodium salt comprising one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, and sodium trifluoroacetate, and the second sodium salt comprising one or more of sodium difluoro(oxalato)borate, sodium bis(oxalato)borate, sodium tetraphenylborate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide.

11. 11. The electrolyte according to claim 10, wherein the mass content of the first sodium salt is 3% to 40%, and optionally 5% to 30%, based on the total mass of the sodium salt, the ethylene glycol ether-based solvent, and the co-solvent.

12. 12. The electrolyte according to claim 10 or 11, wherein the mass content of the second sodium salt is 0.1% or more, and optionally 1% or more, based on the total mass of the sodium salt, the ethylene glycol ether system and the co-solvent.

13. A sodium secondary battery comprising the electrolyte according to any one of claims 1 to 12.

14. 14. The sodium secondary battery according to claim 13, wherein the secondary battery includes a negative electrode plate, the negative electrode plate including a negative electrode current collector and an undercoating formed on at least one side of the negative electrode current collector.

15. The surface density of the undercoating is 5 to 50 g / m 2 15. The sodium secondary battery according to claim 14, wherein

16. 16. The sodium secondary battery according to claim 14, wherein the undercoating comprises one or more of a carbon coating, an alloy coating, and a metal oxide coating, and optionally is a carbon coating.

17. 17. The sodium secondary battery according to claim 14, wherein the undercoating contains one or more of superconducting carbon black, ketjen black, acetylene black, carbon nanotubes, and graphene.

18. 18. The sodium secondary battery according to claim 13, wherein the sodium secondary battery is a non-negative electrode sodium metal battery.

19. A power consuming device comprising the sodium secondary battery according to any one of claims 13 to 18.

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