Electrolyte and secondary battery

Abstract

An electrolyte and a secondary battery. The electrolyte comprises an additive, wherein the additive comprises a benzoxadiazole compound represented by formula (1). When used in a lithium metal secondary battery, the electrolyte is beneficial for improving the service life and electrical performance of the lithium metal secondary battery.

Description

Electrolyte and secondary battery

[0001] This application claims priority to the Chinese patent application No. 202410858648.6 filed on June 28, 2024, the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the field of battery, in particular to an electrolyte and a secondary battery. BACKGROUND

[0003] Lithium metal has an ultra-high theoretical specific capacity (3860 mAh / g) and an extremely low electrochemical potential (-3.04 V vs. SHE), and a lithium metal secondary battery with lithium metal as the negative electrode is considered to be a new generation of high-energy-density electrical energy storage device to upgrade lithium-ion batteries.

[0004] Currently, when the existing electrolyte is used in lithium metal secondary batteries, the following problems exist: (1) the SEI film (interface film) formed by the electrolyte on the surface of the lithium metal is prone to rupture, leading to continuous recombination of the SEI film, consumption of the electrolyte and active lithium, and also leading to reduced conductivity and reduced cycle efficiency; (2) lithium metal batteries are prone to produce lithium dendrites during the cycle process, and the lithium dendrites are prone to pierce the isolation film of the battery, leading to short circuit of the battery, etc. TECHNICAL PROBLEM TECHNICAL SOLUTION

[0005] Therefore, the present application provides an electrolyte and a lithium metal battery to solve at least one of the above technical problems.

[0006] In a first aspect, the embodiments of the present application provide an electrolyte for a secondary battery, the electrolyte comprising an additive, the additive comprising a benzoxadiazole compound represented by Formula 1,

[0007] wherein R1, R2, R3, R4 are each independently selected from hydrogen, halogen, nitro, nitrile, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy, substituted or unsubstituted C6-C10 aryl, substituted or unsubstituted C2-C6 alkenyl, substituted or unsubstituted C3-C6 alkynyl, substituted or unsubstituted C3-C10 cycloalkyl, substituted or unsubstituted C3-C10 cycloalkenyl, substituted or unsubstituted C2-C6 heterocyclyl, substituted or unsubstituted dimethylsulfonamide, and substituted or unsubstituted trimethylsilyl. 10 alkyl, substituted or unsubstituted C1-C6 alkoxy, substituted or unsubstituted C6-C10 aryl, substituted or unsubstituted C2-C6 alkenyl, substituted or unsubstituted C3-C6 alkynyl, substituted or unsubstituted C3-C10 cycloalkyl, substituted or unsubstituted C3-C10 cycloalkenyl, substituted or unsubstituted C2-C6 heterocyclyl, substituted or unsubstituted dimethylsulfonamide, and substituted or unsubstituted trimethylsilyl. 10 alkyl, substituted or unsubstituted C1-C6 alkoxy, substituted or unsubstituted C6-C10 aryl, substituted or unsubstituted C2-C6 alkenyl, substituted or unsubstituted C3-C6 alkynyl, substituted or unsubstituted C3-C10 cycloalkyl, substituted or unsubstituted C3-C10 cycloalkenyl, substituted or unsubstituted C2-C6 heterocyclyl, substituted or unsubstituted dimethylsulfonamide, and substituted or unsubstituted trimethylsilyl. 20 alkyl, substituted or unsubstituted C1-C6 alkoxy, substituted or unsubstituted C6-C10 aryl, substituted or unsubstituted C2-C6 alkenyl, substituted or unsubstituted C3-C6 alkynyl, substituted or unsubstituted C3-C10 cycloalkyl, substituted or unsubstituted C3-C10 cycloalkenyl, substituted or unsubstituted C2-C6 heterocyclyl, substituted or unsubstituted dimethylsulfonamide, and substituted or unsubstituted trimethylsilyl. 20 alkyl, substituted or unsubstituted C1-C6 alkoxy, substituted or unsubstituted C6-C10 aryl, substituted or unsubstituted C2-C6 alkenyl, substituted or unsubstituted C3-C6 alkynyl, substituted or unsubstituted C3-C10 cycloalkyl, substituted or unsubstituted C3-C10 cycloalkenyl, substituted or unsubstituted C2-C6 heterocyclyl, substituted or unsubstituted dimethylsulfonamide, and substituted or unsubstituted trimethylsilyl.

[0008] In some embodiments of the present application, R1, R2, R3, R4 are each independently selected from hydrogen, halogen, nitro, nitrile, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy, substituted or unsubstituted C6-C10 aryl, substituted or unsubstituted C2-C6 alkenyl, substituted or unsubstituted C3-C6 alkynyl, substituted or unsubstituted C3-C10 cycloalkyl, substituted or unsubstituted C3-C10 cycloalkenyl, substituted or unsubstituted C2-C6 heterocyclyl, substituted or unsubstituted dimethylsulfonamide, and substituted or unsubstituted trimethylsilyl.12 aryl, substituted or unsubstituted C2 to C6 alkenyl, substituted or unsubstituted C3 to C6 cycloalkyl, substituted or unsubstituted C3 to C6 cycloalkenyl, substituted or unsubstituted heterocyclyl, substituted or unsubstituted dimethylsulfonamide, substituted or unsubstituted trimethylsilyl. 10 aryl, substituted or unsubstituted C2 to C6 alkenyl, substituted or unsubstituted C3 to C6 cycloalkyl, substituted or unsubstituted C3 to C6 cycloalkenyl, substituted or unsubstituted heterocyclyl, substituted or unsubstituted dimethylsulfonamide, substituted or unsubstituted trimethylsilyl.

[0009] In some embodiments of the present application, R1, R4are each independently selected from hydrogen, fluorine, nitro, substituted or unsubstituted dimethylsulfonamide, substituted or unsubstituted C1 to C6 alkyl.

[0010] In some embodiments of the present application, at least one of R1, R2, R3, R4contains F atom.

[0011] In some embodiments of the present application, the substituent is selected from at least one of halogen, nitrile, C1 to C6 alkyl, C2 to C6 alkenyl, C1 to C6 alkoxy, C1 to C6 alkyl substituted or unsubstituted dimethylsulfonamide, alkyl substituted or unsubstituted trimethylsilyl, nitro.

[0012] In some embodiments of the present application, the additive is selected from at least one of the following compounds:

[0013] In some embodiments of the present application, the additive accounts for 0.01wt% to 3wt% of the electrolyte.

[0014] In some embodiments of the present application, the electrolyte further comprises a lithium salt and an organic solvent, the molar concentration of the lithium salt in the electrolyte is 0.2mol / L to 5mol / L.

[0015] In some embodiments of the present application, the lithium salt comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisdifluorosulfonimide, lithium bis-trifluoromethylsulfonimide, lithium (fluorosulfonyl) (n-perfluorobutylsulfonyl) imide, lithium bisoxalate borate, lithium difluorooxalate borate, lithium trifluoromethylsulfonate; and / or

[0016] The organic solvent comprises a carbonate solvent, the carbonate solvent comprises at least one of propylene carbonate, vinylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, 1,4-butanediol propyl carbonate; and / or

[0017] The organic solvent comprises an ether solvent, the ether solvent comprises at least one of ethylene glycol dimethyl ether, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane, dimethoxymethane, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, and diethylene glycol diethyl ether; and / or

[0018] The lithium salt includes lithium bis(trifluoromethanesulfonyl)imide, the organic solvent includes ethylene glycol dimethyl ether and 1,3-dioxolane, and the volume ratio of the ethylene glycol dimethyl ether and the 1,3-dioxolane is 1:1.

[0019] The second aspect of the application provides a secondary battery, which comprises a negative electrode, a positive electrode and the electrolyte, and the negative electrode comprises lithium metal. Advantages

[0020] The electrolyte provided by the application can effectively inhibit the reaction between the electrolyte and the lithium metal and the formation or growth of lithium dendrites when the electrolyte is used in a lithium metal secondary battery, thereby improving the service life of the lithium metal secondary battery. In addition, the inorganic component rich in Li3N can increase the ionic conductivity of the SEI layer, thereby improving the electrical performance of the lithium metal secondary battery. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative effort.

[0022] FIG. 1 is a cycle time curve of the battery in Example 1 and Comparative Example 1 of the application;

[0023] FIG. 2 is a morphology diagram of the lithium metal surface obtained by disassembling the battery after cycle test in Example 1 and Comparative Example 1 of the application. Embodiments of the application

[0024] The technical solutions in the embodiments of the application will be described clearly and completely in the following with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only some embodiments of the application, but not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the application. In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain the application, and are not used to limit the application.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting of the application. As used in this description, the singular forms "a", "an", and "the" include plural references unless the context clearly dictates otherwise. The term "and / or" includes any and all combinations of one or more of the associated listed items.

[0026] In the present application, the orientation words such as "upper" and "lower" refer to the upper and lower positions of the device in the actual use or working state, and specifically refer to the directions of the drawing surface in the drawings, unless otherwise specified. In addition, in the description of the present application, the term "comprising" means "including but not limited to". The terms first, second, third, etc. are only used as labels and do not impose numerical requirements or establish an order.

[0027] In the present application, "and / or" describes the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B, which can represent the following cases: A exists alone, A and B exist together, and B exists alone. Wherein A and B can be singular or plural.

[0028] In the present application, "at least one" means one or more, and "multiple" means two or more. "One or more", "at least one of the following" or the like means any combination of these items, including any combination of single item or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can represent a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, wherein a, b, and c can be single or multiple.

[0029] Various embodiments of the present application can exist in the form of a range; it should be understood that the description in the form of a range is only for the convenience and brevity, and should not be understood as a hard limit on the scope of the present application; therefore, it should be considered that the described range has been specifically disclosed all possible sub-ranges and single values within the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. In addition, whenever a numerical range is indicated in the present application, it refers to any cited number (fraction or integer) within the indicated range.

[0030] Currently, the existing electrolytes used in lithium metal secondary batteries have the following problems: (1) The SEI film (interface film) formed by the electrolyte on the lithium metal surface is prone to breakage, which leads to continuous recombination of the SEI film, consumes electrolyte and active lithium, and also reduces conductivity and cycle efficiency; (2) Lithium dendrites are prone to be generated during the cycle of lithium metal batteries. Lithium dendrites can easily pierce the battery's separator, which can cause the battery to short circuit.

[0031] In view of the above-mentioned technical problems in the prior art, this application provides a lithium metal secondary battery with a long service life, the secondary battery comprising a positive electrode, a negative electrode, and an electrolyte. The negative electrode comprises lithium metal. Exemplarily, the negative electrode is a lithium metal negative electrode or a lithium alloy negative electrode.

[0032] In this embodiment, the electrolyte includes an additive, which includes a 2,1,3-benzoxadiazole compound represented by Formula 1.

[0033] R1, R2, R3, and R4 are each independently selected from hydrogen, halogen, nitro, nitrile, substituted or unsubstituted C1 to C4 groups. 10 Alkyl, substituted or unsubstituted C1 to C 10 Alkoxy, substituted or unsubstituted C6 to C 20 Aryl, substituted or unsubstituted C2 to C6 alkenyl, substituted or unsubstituted C3 to C6 alkenyl 20 Heterocyclic group, substituted or unsubstituted dimethylsulfonamide group, substituted or unsubstituted trimethylsilyl group.

[0034] It should be noted that halogens in this application include fluorine (F), chlorine (Cl), bromine (Br), etc. For example, at least one of R1, R2, R3, and R4 is fluorine.

[0035] Among them, C1 to C 10 Alkyl refers to an alkyl group having 1 to 10 carbon atoms. Exemplarily, C1 to C1... 10 Alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, etc. Similarly, C1 to C6 alkyl groups refer to alkyl groups having 1 to 6 carbon atoms.

[0036] Similarly, C1 to C 10 Alkoxy groups refer to alkoxy groups having 1 to 10 carbon atoms. For example, C1-C... 10 Alkoxy groups include methoxy, ethoxy, propoxy, butoxy, etc.

[0037] Similarly, C6 to C 20 Aryl refers to an aryl group having 6 to 20 carbon atoms. For example, C6 to C2... 20 Aryl groups include phenyl, tolyl, xylyl, etc.

[0038] Similarly, C2 to C6 alkenyl refers to alkenyl groups having 2 to 6 carbon atoms. Exemplarily, C2 to C6 alkenyl includes vinyl, propenyl, butenyl, and the like.

[0039] Similarly, C3 to C 20 Heterocyclyl refers to oxiranyl, furanyl, thiophenyl, pyrrolyl, and the like having 3 to 20 carbon atoms.

[0040] In some embodiments of the present application, R1, R2, R3, R4 are each independently selected from hydrogen, halogen, nitro, nitrile, substituted or unsubstituted C1 to C6 alkyl, substituted or unsubstituted C1 to C6 alkoxy, substituted or unsubstituted C6 to C10 aryl, substituted or unsubstituted C2 to C6 alkenyl, substituted or unsubstituted C3 to C10 heterocyclyl, substituted or unsubstituted dimethylsulfonamide, and substituted or unsubstituted trimethylsilyl. 12 aryl, substituted or unsubstituted C2 to C6 alkenyl, substituted or unsubstituted C3 to C 10 heterocyclyl, substituted or unsubstituted dimethylsulfonamide, and substituted or unsubstituted trimethylsilyl.

[0041] In some embodiments of the present application, the substituents are at least one selected from halogen, nitrile, C1 to C6 alkyl, C2 to C6 alkenyl, C1 to C6 alkoxy, alkyl-substituted or unsubstituted dimethylsulfonamide, alkyl-substituted or unsubstituted trimethylsilyl, and nitro.

[0042] In some embodiments of the present application, R1, R4 are each independently selected from hydrogen, fluorine, nitro, substituted or unsubstituted dimethylsulfonamide, and substituted or unsubstituted C1 to C6 alkyl.

[0043] In some embodiments of the present application, at least one of R1, R2, R3, R4 contains F atom. In this way, the additive can contain both N atom and F atom, and the additive can be reduced to inorganic components such as Li3N, LiF, etc. on the surface of lithium metal. The inorganic components such as Li3N, LiF, etc. can increase the ion conductivity of the SEI layer, uniformly conduct lithium ions, thereby effectively inhibiting the growth of lithium dendrites and prolonging the life of lithium metal battery.

[0044] In some embodiments of the present application, the additive is at least one selected from the compounds shown in the following structural formulae:

[0045] In some embodiments of the present application, the additive accounts for 0.01wt% to 3wt% of the electrolyte. Further, the additive accounts for 0.1wt% to 2wt% of the electrolyte. It should be noted that if the additive accounts for less than 0.1wt% of the electrolyte, the effect of adding the additive to the electrolyte is not obvious. If the additive accounts for more than 2wt% of the electrolyte, the side reactions will be too many, which will seriously affect the performance of the battery with the electrolyte.

[0046] Exemplarily, the additive accounts for about 0.01 wt%, about 0.1 wt%, about 0.2 wt%, about 0.3 wt%, about 0.4 wt%, about 0.5 wt%, about 0.6 wt%, about 0.7 wt%, about 0.8 wt%, about 0.9 wt%, about 1.0 wt%, about 1.2 wt%, about 1.3 wt%, about 1.4 wt%, about 1.5 wt%, about 1.6 wt%, about 1.7 wt%, about 1.8 wt%, about 1.9 wt%, about 2 wt%, about 2.2 wt%, about 2.4 wt%, about 2.8 wt%, about 3.0 wt% of the electrolyte. It should be noted that the term "about" is used to describe and account for small variations. When used in conjunction with a number, the term can refer to a range of variation of less than or equal to ±10% of the number.

[0047] In some embodiments of the present application, the electrolyte further comprises a lithium salt, the molar concentration of the lithium salt in the electrolyte is 0.2 mol / L to 5 mol / L. Exemplarily, the molar concentration of the lithium salt in the electrolyte is about 0.2 mol / L, about 0.5 mol / L, about 1 mol / L, about 1.5 mol / L, about 2 mol / L, about 2.5 mol / L, about 3 mol / L, about 3.5 mol / L, about 4 mol / L, about 4.5 mol / L, about 5 mol / L.

[0048] In some embodiments of the present application, the lithium salt comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisdifluorosulfonimide, lithium bis-trifluoromethylsulfonimide, lithium (fluorosulfonyl)(n-perfluorobutylsulfonyl)imide, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium trifluoromethylsulfonate.

[0049] In some embodiments of the present application, the organic solvent comprises at least one of carbonates, ether solvents.

[0050] Further, the carbonate solvents comprise at least one of propylene carbonate, vinyl carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, 1,4-butylene carbonate.

[0051] Further, the ether solvents comprise at least one of ethylene glycol dimethyl ether, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane, dimethoxymethane, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, and diethylene glycol diethyl ether.

[0052] Embodiment 1

[0053] Preparation of electrolyte: In an argon-filled glove box, two organic solvents ethylene glycol dimethyl ether and 1,3-dioxolane were mixed in a volume ratio of 1:1 to obtain a mixed solvent. Lithium bis(trifluoromethylsulfonyl)imide and additive 1 were sequentially added to the mixed solvent and mixed uniformly to prepare a clear and transparent electrolyte. The concentration of lithium bis(trifluoromethylsulfonyl)imide in the electrolyte was 1 mol / L. The mass fraction of additive 1 in the electrolyte was 1wt% according to the mass ratio.

[0054] Preparation of symmetric battery: Under the inert atmosphere of the glove box, the water and oxygen contents were <0.1 PPM, and the negative shell, spring, gasket, lithium sheet, electrolyte, separator, lithium sheet, and positive shell were sequentially assembled according to the CR2032 button cell specification to assemble the button cell. The thickness of the lithium sheet was 20 pm, the diameter was 14 mm, the thickness of the separator was 12 pm PE separator, the diameter was 16 mm, and the amount of electrolyte used for each button cell was 40 pL. The assembly was completed by pressing at 800 kPa for 5 s to obtain the required secondary battery.

[0055] Example 2

[0056] The difference between it and example 1 is that:

[0057] Preparation of electrolyte: In an argon-filled glove box, three organic solvents vinyl carbonate, dimethyl carbonate, and methyl ethyl carbonate were mixed in a volume ratio of 1:1:1 to obtain a mixed solvent. Lithium hexafluorophosphate and additive 1 were sequentially added to the mixed solvent and mixed uniformly to prepare a clear and transparent electrolyte. The concentration of lithium hexafluorophosphate in the electrolyte was 1 mol / L. The mass fraction of additive 1 in the electrolyte was 1wt% according to the mass ratio.

[0058] Example 3

[0059] The difference between it and example 1 is that:

[0060] Preparation of electrolyte: In an argon-filled glove box, two organic solvents ethylene glycol dimethyl ether and 1,3-dioxolane were mixed in a volume ratio of 1:1 to obtain a mixed solvent. Lithium bis(trifluoromethylsulfonyl)imide and additive 2 were sequentially added to the mixed solvent and mixed uniformly to prepare a clear and transparent electrolyte. The concentration of lithium bis(trifluoromethylsulfonyl)imide was 1 mol / L, and the mass fraction of additive 2 was 1wt%.

[0061] Example 4

[0062] The difference between it and example 1 is that:

[0063] Preparation of electrolyte: in the argon-filled glove box, three organic solvents of vinyl carbonate: dimethyl carbonate: methyl ethyl carbonate with a volume ratio of 1:1:1 were mixed uniformly to obtain a mixed solvent. Lithium hexafluorophosphate and additive 2 were sequentially added to the mixed solvent and mixed uniformly to prepare a clear and transparent electrolyte. The concentration of lithium hexafluorophosphate was 1 mol / L, and the mass fraction of additive 2 was 1 wt%.

[0064] Example 5

[0065] The difference between it and example 1 is that:

[0066] Preparation of electrolyte: in the argon-filled glove box, two organic solvents of ethylene glycol dimethyl ether: 1,3-dioxolane with a volume ratio of 1:1 were mixed uniformly to obtain a mixed solvent. Lithium bis-trifluoromethyl sulfoximide and additive 3 were sequentially added to the mixed solvent and mixed uniformly to prepare a clear and transparent electrolyte. The concentration of lithium bis-trifluoromethyl sulfoximide was 1 mol / L, and the mass fraction of additive 3 was 1 wt%.

[0067] Example 6

[0068] The difference between it and example 1 is that:

[0069] Preparation of electrolyte: in the argon-filled glove box, three organic solvents of vinyl carbonate: dimethyl carbonate: methyl ethyl carbonate with a volume ratio of 1:1:1 were mixed uniformly to obtain a mixed solvent. Lithium hexafluorophosphate and additive 3 were sequentially added to the mixed solvent and mixed uniformly to prepare a clear and transparent electrolyte. The concentration of lithium hexafluorophosphate was 1 mol / L, and the mass fraction of additive 3 was 1 wt%.

[0070] Example 7

[0071] The difference between it and example 1 is that:

[0072] Preparation of electrolyte: in the argon-filled glove box, two organic solvents of ethylene glycol dimethyl ether and 1,3-dioxolane with a volume ratio of 1:1 were mixed uniformly to obtain a mixed solvent. Lithium bis-trifluoromethyl sulfoximide and additive 1 were sequentially added to the mixed solvent and mixed uniformly to prepare a clear and transparent electrolyte. The concentration of lithium bis-trifluoromethyl sulfoximide in the electrolyte was 1 mol / L. The mass fraction of additive 1 in the electrolyte was 0.1 wt% according to the mass ratio.

[0073] Example 8

[0074] The difference between it and example 1 is that:

[0075] Preparation of electrolyte: in an argon-filled glove box, two organic solvents ethylene glycol dimethyl ether and 1,3-dioxolane with a volume ratio of 1:1 were mixed uniformly to obtain a mixed solvent. Lithium bis(trifluoromethylsulfonyl)imide and additive 1 were sequentially added to the mixed solvent, and the mixture was uniformly mixed to prepare a clear and transparent electrolyte. The concentration of lithium bis(trifluoromethylsulfonyl)imide in the electrolyte was 1 mol / L. The mass fraction of additive 1 in the electrolyte was 0.6wt% according to the mass ratio.

[0076] Example 9

[0077] The difference between it and Example 1 is that:

[0078] Preparation of electrolyte: in an argon-filled glove box, two organic solvents ethylene glycol dimethyl ether and 1,3-dioxolane with a volume ratio of 1:1 were mixed uniformly to obtain a mixed solvent. Lithium bis(trifluoromethylsulfonyl)imide and additive 1 were sequentially added to the mixed solvent, and the mixture was uniformly mixed to prepare a clear and transparent electrolyte. The concentration of lithium bis(trifluoromethylsulfonyl)imide in the electrolyte was 1 mol / L. The mass fraction of additive 1 in the electrolyte was 1.5wt% according to the mass ratio.

[0079] Example 10

[0080] The difference between it and Example 1 is that:

[0081] Preparation of electrolyte: in an argon-filled glove box, two organic solvents ethylene glycol dimethyl ether and 1,3-dioxolane with a volume ratio of 1:1 were mixed uniformly to obtain a mixed solvent. Lithium bis(trifluoromethylsulfonyl)imide and additive 1 were sequentially added to the mixed solvent, and the mixture was uniformly mixed to prepare a clear and transparent electrolyte. The concentration of lithium bis(trifluoromethylsulfonyl)imide in the electrolyte was 1 mol / L. The mass fraction of additive 1 in the electrolyte was 2.0wt% according to the mass ratio.

[0082] Comparative Example 1

[0083] The difference between it and Example 1 is that:

[0084] Preparation of electrolyte: in an argon-filled glove box, two organic solvents ethylene glycol dimethyl ether and 1,3-dioxolane with a volume ratio of 1:1 were mixed uniformly to obtain a mixed solvent. Lithium bis(trifluoromethylsulfonyl)imide and additive 1 were sequentially added to the mixed solvent, and the mixture was uniformly mixed to prepare a clear and transparent electrolyte. The concentration of lithium bis(trifluoromethylsulfonyl)imide in the electrolyte was 1 mol / L. The mass fraction of additive 1 in the electrolyte was 2.0wt% according to the mass ratio.

[0085] Comparative Example 2

[0086] The difference between it and Example 1 is that:

[0087] Preparation of electrolyte: In an argon-filled glove box, mixed solvents were obtained by mixing ethylene carbonate: dimethyl carbonate: methyl ethyl carbonate at a volume ratio of 1:1:1. Lithium bis(trifluoromethylsulfonyl)imide was added to the mixed solvents in sequence, and the mixture was uniformly mixed to prepare a clear and transparent electrolyte. The concentration of lithium bis(trifluoromethylsulfonyl)imide in the electrolyte was 1 mol / L.

[0088] The compounds corresponding to the different additives in the examples are shown in Table 1.

[0089] Table 1

[0090] Battery performance test

[0091] The symmetrical batteries of Examples 1 to 10, and Comparative Examples 1 and 2 were tested at 25°C at a current density of 2 mA / cm 2 , a load of 2 mAh / cm 2 , and the time for the battery to undergo hard short circuit or polarization potential > 0.5V was the battery life. The test results are shown in Figure 1 and Table 2.

[0092] The test was performed at 25°C at a current density of 2 mA / cm 2 , a load of 2 mAh / cm 2 , and after 50 hours, the symmetrical battery was disassembled, the cycled lithium metal anode was taken out, and the lithium metal deposition morphology was observed using SEM, and the test results are shown in Figure 2.

[0093] Figure 1 is a cycle time-voltage curve of the secondary battery prepared in Experimental Example 1 and Comparative Example 1. As can be seen from Figure 1, the polarization potential of Comparative Example 1 is 50 mV, and after 20h of cycling, the polarization voltage rapidly increases until short circuit. The polarization potential of Example 1 is maintained at 50 mV for 300h.

[0094] Figure 2 is a SEM morphology diagram of the lithium metal surface after the battery prepared in Experimental Example 1 and Comparative Example 1 is cycled. As can be seen from Figure 2, after the lithium metal symmetrical battery prepared in Comparative Example 1 is cycled, the surface of the lithium metal electrode in contact with the electrolyte is loose and porous, and the deposition is very uneven, and a large amount of "dead lithium" is generated. After the lithium metal symmetrical battery of Experimental Example 1 is cycled, the surface of the lithium metal in contact with the electrolyte is smooth and uniform, and no "dead lithium" is generated.

[0095] Table 2

[0096] Note: " / " means not added.

[0097] According to the experimental results of FIG. 1, FIG. 2 and Table 2, it can be seen that the addition of the additive in the electrolyte in the present application can significantly improve the cycle life of the battery. One possible reason is that when the additive in the electrolyte is used in the lithium metal secondary battery, the additive can generate a stable and dense SEI film on the surface of the lithium metal, effectively inhibit the reaction between the electrolyte and the lithium metal, effectively inhibit the formation or growth of lithium dendrites, and thus improve the cycle stability and service life of the lithium metal secondary battery.

[0098] The above describes the technical solutions provided by the embodiments of the present application in detail, and the principles and implementation manners of the present application are described by applying specific examples. The above description of the embodiments is only used to help understand the method of the present application and its core idea; meanwhile, for those skilled in the art, according to the idea of the present application, the specific implementation manner and application range will be changed, and the above description of the present application should not be understood as a limitation.

Claims

1. An electrolyte for a secondary battery, the electrolyte comprising an additive, the additive comprising a benzoxadiazole compound represented by Formula 1, ###0000001### Formula 1 wherein R1, R2, R3, and R4 are each independently selected from hydrogen, halogen, nitro, nitrile, substituted or unsubstituted C1 to C4 groups. 10 Alkyl, substituted or unsubstituted C1 to C 10 Alkoxy, substituted or unsubstituted C6 to C 20 Aryl, substituted or unsubstituted C2 to C6 alkenyl, substituted or unsubstituted C3 to C6 alkenyl 20 Heterocyclic group, substituted or unsubstituted dimethylsulfonamide group, substituted or unsubstituted trimethylsilyl group.

2. The electrolyte of claim 1, wherein, R1, R2, R3, R4are each independently selected from the group consisting of hydrogen, halogen, nitro, nitrile, substituted or unsubstituted Ci to C6alkyl, substituted or unsubstituted Ci to C6alkoxy, substituted or unsubstituted C6to C10aryl, substituted or unsubstituted C2to C6alkenyl, substituted or unsubstituted C3to C6alkynyl, substituted or unsubstituted heterocyclyl, substituted or unsubstituted dimethylsulfonamide, substituted or unsubstituted trimethylsilyl. 12 R1, R2, R3, R4are each independently selected from the group consisting of hydrogen, halogen, nitro, nitrile, substituted or unsubstituted Ci to C6alkyl, substituted or unsubstituted Ci to C6alkoxy, substituted or unsubstituted C6to C10aryl, substituted or unsubstituted C2to C6alkenyl, substituted or unsubstituted C3to C6alkynyl, substituted or unsubstituted heterocyclyl, substituted or unsubstituted dimethylsulfonamide, substituted or unsubstituted trimethylsilyl. 10 R1, R2, R3, R4are each independently selected from the group consisting of hydrogen, halogen, nitro, nitrile, substituted or unsubstituted Ci to C6alkyl, 3. The electrolyte of claim 2, wherein, R1, R4 are each independently selected from the group consisting of hydrogen, fluorine, nitro, substituted or unsubstituted dimethylsulfonamide, substituted or unsubstituted C1 to C6 alkyl.

4. The electrolyte of claim 1, wherein, At least one of R1, R2, R3, R4 contains a F atom.

5. The electrolyte of claim 2, wherein, R1, R4 are each independently selected from the group consisting of hydrogen, substituted or unsubstituted C1 to C6 alkyl.

6. The electrolyte of any one of claims 1 to 5, wherein, The substituent is selected from at least one of halogen, nitrile, C1 to C6 alkyl, C2 to C6 alkenyl, C1 to C6 alkoxy, C1 to C6 alkyl-substituted or unsubstituted dimethylsulfonamide, alkyl-substituted or unsubstituted trimethylsilyl, nitro.

7. The electrolyte of claim 1, wherein, The additive is selected from at least one of the compounds shown in the following structural formulas:

8. The electrolyte of any one of claims 1 to 5, wherein, The additive accounts for 0.01wt% to 3wt% of the electrolyte.

9. The electrolyte of claim 8, wherein, The additive accounts for 0.1wt% to 2wt% of the electrolyte.

10. The electrolyte of claim 8, wherein, The electrolyte further comprises a lithium salt and an organic solvent, the molar concentration of the lithium salt in the electrolyte is 0.2mol / L to 5mol / L.

11. The electrolyte of claim 10, wherein, The molar concentration of the lithium salt in the electrolyte is 0.5mol / L to 1.5mol / L.

12. The electrolyte of claim 10, wherein, The lithium salt comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisdifluorosulfonimide, lithium bis-trifluoromethylsulfonimide, lithium (fluorosulfonyl)(n-perfluorobutylsulfonyl)imide, lithium bisoxalate borate, lithium difluorooxalate borate, lithium trifluoromethylsulfonate.

13. The electrolyte of claim 10, wherein, The organic solvent comprises a carbonate solvent, the carbonate solvent comprises at least one of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, 1,4-butanediol propyl carbonate.

14. The electrolyte of claim 10, wherein, The organic solvent comprises an ether solvent.

15. The electrolyte of claim 14, wherein, The ether solvent comprises at least one of ethylene glycol dimethyl ether, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane, dimethoxymethane, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, and diethylene glycol diethyl ether.

16. The electrolyte of claim 10, wherein, The lithium salt comprises lithium bis-trifluoromethylsulfonimide, the organic solvent comprises ethylene glycol dimethyl ether and 1,3-dioxolane, and the volume ratio of the ethylene glycol dimethyl ether to the 1,3-dioxolane is 1:

1.

17. The electrolyte of claim 16, wherein, The additive accounts for 0.6wt% to 1.5wt% of the electrolyte.

18. The electrolyte of claim 10, wherein, The lithium salt comprises lithium hexafluorophosphate, the organic solvent comprises ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate; in the organic solvent, the volume ratio of the ethylene carbonate:dimethyl carbonate:methyl ethyl carbonate is 1:1:

1.

19. A secondary battery, wherein, The secondary battery comprises a negative electrode, a positive electrode, and the electrolyte of any one of claims 1 to 18.

20. The secondary battery of claim 19, wherein, The negative electrode comprises a lithium metal negative electrode or a lithium alloy negative electrode.

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