Electrolyte, secondary battery, and electric device

Abstract

The application discloses an electrolyte, a secondary battery and a power utilization device. The electrolyte provided by the application takes a cyclic carbonate compound, a chain carbonate compound and a pyridine compound as a cosolvent, and limits the melting point of the pyridine compound to be less than or equal to -40 DEG C and the boiling point to be greater than or equal to 110 DEG C. The temperature range of the electrolyte is greatly widened, and the working temperature range is the widest, which is -70 DEG C to 100 DEG C.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and more particularly to an electrolyte, a secondary battery, and an electrical device. Background Technology

[0002] In recent years, with the increasingly wide application of lithium-ion batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, polar scientific research, aerospace and other fields.

[0003] Traditional lithium-ion batteries are often constrained by their limited operating temperature range, poor stability at high temperatures, and flammability risks; their performance degrades significantly at low temperatures.

[0004] Therefore, it is necessary to develop an electrolyte with a wide temperature range. Summary of the Invention

[0005] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the present invention proposes an electrolyte with a wide temperature range.

[0006] A second aspect of the present invention also provides a secondary battery.

[0007] A third aspect of the present invention also provides an electrical device.

[0008] The electrolyte according to a first aspect of the present invention comprises: lithium salt, cyclic carbonate compound, chain carbonate compound, and pyridine compound;

[0009] The melting point of the pyridine compound is ≤-40℃; the boiling point of the pyridine compound is ≥110℃.

[0010] The electrolyte according to embodiments of the present invention has at least the following beneficial effects:

[0011] This invention uses cyclic carbonate compounds, chain carbonate compounds, and pyridine compounds as co-solvents, and limits the melting point of the pyridine compounds to ≤-40℃ and boiling point to ≥110℃, thus greatly expanding its temperature range.

[0012] Furthermore, the pyridine compounds of this invention with specific melting and boiling points exhibit good solubility for lithium salts, low desolvation energy barriers, and excellent lithium ion transport at low temperatures; their structure is stable at high temperatures.

[0013] Furthermore, it can form eutectic mixtures with cyclic carbonate compounds, significantly lowering the overall freezing point of the electrolyte and preventing low-temperature crystallization. It also forms a homogeneous system through van der Waals forces and dipole-dipole interactions, preventing low-temperature phase separation.

[0014] Furthermore, it can form an azeotropic system with chain carbonate compounds, suppressing solvent evaporation and improving thermal stability.

[0015] According to some embodiments of the present invention, the boiling point of the pyridine compound is ≤300°C.

[0016] According to some embodiments of the present invention, the melting point of the pyridine compound is ≤-70°C.

[0017] According to some embodiments of the present invention, the melting point is obtained by testing with a microscopic melting point apparatus, and the boiling point is obtained by testing with a boiling point tube method.

[0018] According to some embodiments of the present invention, the content of the pyridine compound is 20% to 70% based on the total mass of the electrolyte. For example, it includes 20%, 30%, 40%, 45%, 50%, 60%, 70%, and any subrange consisting of two values.

[0019] According to some embodiments of the present invention, the content of the pyridine compound is 40% to 60% based on the total mass of the electrolyte. For example, it includes 40%, 45%, 50%, 55%, 60%, and any subrange consisting of two values.

[0020] According to some embodiments of the present invention, the pyridine compound is selected from at least one of 2-methylpyridine, 2,4-dimethylpyridine or 4-ethylpyridine.

[0021] According to some embodiments of the present invention, the lithium salt includes at least one selected from lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalateborate)borate (LiBOB), lithium difluorooxalateborate (LiDFOB), or lithium difluorophosphate (LiPO2F2). Therefore, the electrolyte of the present invention exhibits higher thermal stability.

[0022] According to some embodiments of the present invention, the amount of lithium salt used is 10% to 20% based on the total mass of the electrolyte. For example, it includes 10%, 12%, 14%, 18%, 20%, and any sub-range consisting of two values.

[0023] According to some embodiments of the present invention, the cyclic carbonate compounds include ethylene carbonate (EC) and / or propylene carbonate (PC).

[0024] According to some embodiments of the present invention, the chain carbonate compound includes diethyl carbonate (DEC) and / or methyl ethyl carbonate (EMC).

[0025] According to some embodiments of the present invention, the electrolyte further includes additives; the additives include at least one of film-forming additives, flame-retardant additives, and corrosion-resistant additives.

[0026] According to some embodiments of the present invention, the film-forming additive includes at least one selected from vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,3-propanesulfonate lactone (PS), propylene sulfonate lactone (PST), vinyl sulfate (DTD), vinyl disulfide (BiDTD), and ethylene sulfite (ES). Thus, the film-forming effect of the electrolyte on the electrode surface is improved by adding the film-forming agent.

[0027] According to some embodiments of the present invention, the flame retardant additive includes at least one selected from trimethyl phosphate (TMP), triethyl phosphate (TEP), tributyl phosphate (TBP), triphenyl phosphate (TPP), hexamethylphosphonon (HMPN), dimethyl phosphonomethyl ester (DMMP), diphenyl cresol diphenyl phosphate (CDP), diphenyl octyl phosphate (DPOF), diethyl vinylphosphonate (DEVP), diphenyl vinylphosphonate (DPVP), tripropynyl phosphate, ethoxy(pentafluoro)cyclotriphosphonon (PFPN), and pentafluorophenoxycyclotriphosphonon (POPFPN). Therefore, the flame retardant additive can improve the safety performance of the electrolyte.

[0028] According to some embodiments of the present invention, the corrosion inhibitor includes at least one selected from fluorinated ether (THF), boron trifluoride dimethyl ether, or boron trifluoride diethyl ether. Therefore, the corrosion inhibitor of the present invention not only possesses good chemical stability but also forms a synergistic effect with sulfonylimide lithium salts to jointly protect the positive electrode foil from corrosion, thereby further extending the battery's service life and improving its safety performance.

[0029] According to some embodiments of the present invention, the amount of the additive added is 1% to 20% based on the total mass of the electrolyte. For example, it can be selected from a subrange of 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, or any two of these values.

[0030] According to some embodiments of the present invention, the electrolyte is prepared by the following method:

[0031] The electrolyte is obtained by mixing lithium salts, cyclic carbonate compounds, chain carbonate compounds, pyridine compounds, and optionally additives in an argon-filled glove box.

[0032] A second aspect of the present invention provides a secondary battery comprising the electrolyte described in the first aspect of the present invention.

[0033] The secondary battery according to embodiments of the present invention has at least the following beneficial effects:

[0034] The secondary battery provided by this invention has a wide operating temperature range, and can operate under both low and high temperature conditions.

[0035] Furthermore, this secondary battery has high safety performance and cycle life.

[0036] According to some embodiments of the present invention, the secondary battery further includes a positive electrode, a separator, and an electrode sheet.

[0037] According to some embodiments of the present invention, the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0038] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0039] According to some embodiments of the present invention, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0040] According to some embodiments of the present invention, the positive electrode active material may be any positive electrode active material known in the art for use in batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites. In this application, the positive electrode active material can be a nickel-cobalt-manganese ternary material with the structural formula LiNi. x Co y Mn z O2, where 0.5≤x≤0.85, 0.01≤y≤0.2, 0≤z≤0.5, and x+y+z=1.

[0041] According to some embodiments of the present invention, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0042] According to some embodiments of the present invention, the positive electrode film layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0043] According to some embodiments of the present invention, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0044] According to some embodiments of the present invention, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0045] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0046] According to some embodiments of the present invention, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0047] According to some embodiments of the present invention, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, or tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more. In this application, the negative electrode active material may be selected from at least one of artificial graphite, natural graphite, soft carbon, hard carbon, or silicon-based materials.

[0048] According to some embodiments of the present invention, the negative electrode film layer may optionally include an adhesive. The adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), or carboxymethyl chitosan (CMCS).

[0049] According to some embodiments of the present invention, the negative electrode film layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0050] According to some embodiments of the present invention, the negative electrode film layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0051] According to some embodiments of the present invention, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0052] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0053] According to some embodiments of the present invention, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0054] According to some embodiments of the present invention, the positive electrode, the negative electrode, and the separator can be fabricated into an electrode assembly by a winding process or a stacking process.

[0055] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

[0056] Some of the raw materials used in the embodiments and comparative examples of this invention are as follows:

[0057] 2-Methylpyridine: Boiling point 128℃~129℃; Melting point -70℃;

[0058] 2,4-Dimethylpyridine: Boiling point 159℃; Melting point -60℃;

[0059] 4-Ethylpyridine: Boiling point 168℃; Melting point -91℃;

[0060] 2,3,5-Trifluoropyridine: Boiling point is 102℃. Attached Figure Description

[0061] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0062] Figure 1 This is a high and low temperature discharge curve of a lithium-ion battery prepared using the electrolyte of this invention.

[0063] Figure 2 The graph shows the cycle performance of a lithium-ion battery prepared using the electrolyte of this embodiment of the invention. Detailed Implementation

[0064] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0065] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0066] In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0067] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0068] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0069] Example 1

[0070] This example provides an electrolyte, the amounts of which are shown in Table 1, and its preparation method is as follows:

[0071] In an argon-filled glove box, ethylene carbonate (EC), diethyl carbonate (DEC), and 2-methylpyridine are mixed evenly, and then lithium bis(fluorosulfonyl)imide (LiFSI) is added. The mixture is magnetically stirred for 1 hour until it is completely dissolved. Then, fluoroethylene carbonate (FEC), vinylene carbonate (VC), trimethyl phosphate (TMP), and fluorinated ether (THF) are added and mixed evenly again to obtain the electrolyte.

[0072] Examples 2-21

[0073] This example provides a series of electrolytes, the amounts of each component of which are shown in Table 1, and their preparation methods are the same as in Example 1.

[0074] Table 1

[0075]

[0076]

[0077]

[0078] Comparative Example 1

[0079] This example provides an electrolyte whose component dosage and preparation method are the same as in Example 4, except that it does not contain pyridine compounds and is supplemented to 100% using DEC.

[0080] Comparative Example 2

[0081] This example provides an electrolyte whose component dosage and preparation method are the same as in Example 4, except that 2,3,5-trifluoropyridine with a low boiling point is used to replace 4-ethylpyridine in Example 4.

[0082] Performance testing

[0083] The electrolytes prepared in Examples 1-21 and Comparative Examples 1-2 of this invention were used to prepare secondary batteries, and the steps are as follows:

[0084] Preparation method of positive electrode sheet:

[0085] PVDF powder and NMP were mixed at a ratio of 1:20 to prepare a PVDF slurry. 0.02 parts by mass of PVDF, 0.03 parts by mass of conductive agent SP and 0.01 parts by mass of carbon nanotubes were added and stirred at 3000 rpm for 1 hour. Then, 0.94 parts by mass of commercially available nano LFP cathode material were added and stirred at 3200 rpm for 4 hours. The viscosity of the slurry was adjusted to between 5000-10000 mPas by adding NMP. After sieving, the cathode slurry was coated onto the current collector aluminum foil using a transfer roller coating machine. After drying at 120-130℃, a conventional cathode sheet was obtained.

[0086] Method for preparing negative electrode sheet:

[0087] Thickener CMC was added to deionized water at a mass ratio of 1:50 to prepare a slurry, wherein the proportion of CMC accounted for 2% of the dry powder of the negative electrode slurry (unless otherwise specified, the following proportions are based on the dry powder of the negative electrode). 0.02 parts by mass of CMC slurry, 0.03 parts by mass of conductive agent SP, and 0.01 parts by mass of carbon nanotubes were added. The mixture was first dispersed at 3000 rpm for 1 hour, then 0.92 parts by mass of commercially available graphite material was added, and the mixture was dispersed at 3200 rpm for 4 hours. Finally, 0.02 parts by mass of SBR (50% emulsion solids) and 0.05 parts by mass of NMP were added, and the mixture was stirred at 2000 rpm for 30 minutes. The viscosity of the slurry was adjusted to 2000-5000 mPas by adding deionized water. After sieving, the negative electrode slurry was coated onto the current collector copper foil using a transfer roller coater. After drying at 80-90℃, a conventional negative electrode sheet was obtained.

[0088] Separator: Polyimide separator (PI).

[0089] The prepared positive and negative electrode sheets are paired at an N / P ratio of approximately 1.1, and assembled into a cylindrical cell by winding with a separator. After baking at 100°C for 48 hours, the cells are injected with electrolyte, sealed, formed, and tested for capacity to obtain a lithium-ion battery.

[0090] The lithium-ion batteries prepared in the above embodiments and comparative examples were subjected to high and low temperature discharge performance tests; the results are shown in Table 2, and the test methods are as follows:

[0091] High and low temperature discharge (-70℃, -60℃, 80℃, 90℃, 100℃): Charge to 3.65V at 0.5C constant current and constant voltage at 25±5℃, let stand for 10 minutes, then discharge to 2.0V at 0.5C constant current, and record the discharge capacity as the room temperature discharge capacity; charge to 3.65V at 0.5C constant current and constant voltage again, place in a high and low temperature chamber for 8 hours (chamber settings: -70, -60, 80, 90, 100℃), and then discharge at the corresponding temperatures (0.1C discharge at -70 and -60℃; 0.2C discharge at 80, 90, and 100℃), and record the corresponding discharge capacity. The comparison with the room temperature capacity is the capacity retention rate at the corresponding temperature.

[0092] Cycle life: At (room temperature 25±5, 90℃±5℃), charge at 1C constant current and constant voltage to 3.65V, rest for 10min, then discharge at 1C to 2.0V (record the discharge capacity, which is the first cycle discharge capacity), rest for more than 10min to complete one charge-discharge cycle. Record the discharge capacity retention rate (discharge capacity / first cycle discharge capacity) to 80%, which is the corresponding cycle life.

[0093] Table 2

[0094]

[0095]

[0096] As can be seen from the data in Table 2, the lithium batteries prepared with the electrolytes provided in Examples 1 to 21 of the present invention have wide high and low temperature cycling performance, which greatly expands the working temperature range of the electrolytes of the present invention. Figure 1 The test results of Example 21 of the present invention show that the electrolyte of Example 21 has a capacity retention rate of 37.9% at 0.1C discharge at -70℃ and 80.7% at 0.2C discharge at 100℃.

[0097] Figure 2 The test results of Example 21 of the present invention show that the electrolyte of Example 21 has an 80% capacity retention rate after 2798 cycles at 25°C and an 80% capacity retention rate after 895 cycles at 90°C.

[0098] The electrolytes of Comparative Example 1 and Comparative Example 2 had poor high and low temperature cycling performance. Comparative Example 1 could not be measured at -60℃, and Comparative Example 2 could not be measured at -70℃.

[0099] The present invention has been described in detail above with reference to the embodiments of the invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. An electrolyte, characterized in that, include: Lithium salts, cyclic carbonates, chain carbonates, and pyridines; The melting point of the pyridine compounds is ≤-40℃; The pyridine compounds have a boiling point ≥110℃.

2. The electrolyte according to claim 1, characterized in that, The boiling point of the pyridine compound is ≤300℃.

3. The electrolyte according to claim 1, characterized in that, Based on the total mass of the electrolyte, the content of the pyridine compound is 20% to 70%.

4. The electrolyte according to claim 1, characterized in that, The pyridine compound is selected from at least one of 2-methylpyridine, 2,4-dimethylpyridine, or 4-ethylpyridine.

5. The electrolyte according to claim 1, characterized in that, The lithium salt includes at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalateborate), lithium difluorooxalateborate, or lithium difluorophosphate.

6. The electrolyte according to claim 1, characterized in that, The amount of lithium salt used is 10% to 20% based on the total mass of the electrolyte.

7. The electrolyte according to claim 1, characterized in that, The electrolyte also includes additives; the additives include at least one of film-forming additives, flame-retardant additives, and corrosion-resistant additives.

8. The electrolyte according to claim 7, characterized in that, Based on the total mass of the electrolyte, the amount of the additive is 1% to 20%.

9. A secondary battery, characterized in that, Includes the electrolyte as described in any one of claims 1 to 8.

10. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 9.

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