Low-temperature microemulsion electrolyte, preparation method and application thereof

Abstract

The application belongs to the technical field of secondary batteries, and more particularly relates to a low-temperature microemulsion electrolyte, a preparation method and application thereof. The low-temperature microemulsion electrolyte comprises an electrolyte salt, a symmetrical cyclic ether solvent, a highly chlorinated solvent insoluble in the symmetrical cyclic ether solvent, and a chlorinated ether solvent for dispersing the highly chlorinated solvent in the symmetrical cyclic ether solvent in the form of micelles. Through synergistic effect of the components, an electrolyte system with high ion conductivity, electrode interface stability and wide temperature range adaptability is constructed, effectively solving the core problems of kinetic sluggishness, poor interface stability and short cycle life of the secondary battery in an ultra-low temperature environment. The electrolyte remains liquid at -70 DEG C, and exhibits excellent cycle stability in a wide temperature range of -40 DEG C to 25 DEG C, giving the battery excellent wide temperature range adaptability, breaking the low-temperature performance bottleneck of the secondary battery, and having a broad application prospect.

Description

Technical Field

[0001] This application belongs to the field of secondary battery technology, and more specifically, relates to a low-temperature microemulsion electrolyte, its preparation method and application. Background Technology

[0002] Lithium-ion batteries, with their ultra-high theoretical specific capacity and extremely low electrochemical potential, have demonstrated irreplaceable application potential in the field of high-energy-density energy storage, especially in extreme environments such as national defense, space exploration, deep-sea operations, and transportation in frigid regions, where the demand for their low-temperature performance is increasingly urgent. However, existing lithium-ion batteries face serious performance degradation and safety hazards at temperatures of 0°C and below. The core issue lies in the insufficient low-temperature adaptability of the electrolyte. Currently used electrolyte systems in commercial and research applications, especially traditional electrolytes based on ethylene carbonate (EC), exhibit significantly increased viscosity and a sharp drop in ionic conductivity at low temperatures, hindering lithium-ion transport and exacerbating electrode polarization, leading to severe lithium plating reactions and lithium dendrite growth. Furthermore, the compatibility between the electrolyte and electrode interface deteriorates at low temperatures, and the stability of the solid electrolyte interphase (SEI) film is insufficient. This not only causes irreversible loss of active lithium but also induces a series of side reactions, further shortening battery cycle life and exacerbating safety hazards. Even though some ether-based electrolytes have been attempted for use in low-temperature scenarios due to their lower freezing point and viscosity, they often suffer from poor oxidation stability and high desolvation energy barriers, making it difficult to balance low-temperature performance with high voltage compatibility, which severely limits the large-scale application of lithium secondary batteries in low-temperature environments.

[0003] To address the aforementioned low-temperature bottleneck, researchers have developed various electrolyte design strategies. Among these, locally high-concentration electrolytes improve interfacial stability by modulating the lithium-ion solvation structure and inducing the formation of a low-resistivity SEI / CEI layer rich in inorganic matter; however, their preparation process is complex and costly. Weakly solvated electrolytes optimize the interaction between solvent molecules and lithium ions, lowering the desolvation energy barrier and thus enhancing interfacial transport kinetics at low temperatures. While their production cost is lower, it's difficult to simultaneously meet the requirements for low-temperature ionic conductivity and oxidation stability. Fluorinated carbonate / carboxylic acid ester electrolytes, with their unique interfacial reaction characteristics, can directly passivate lithium plating or construct stable electrode interfacial layers; however, they face challenges such as vigorous reaction with lithium metal and insufficient low-temperature ionic conductivity. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this application is to provide a low-temperature microemulsion electrolyte, its preparation method and application, which aims to solve the problems of existing electrolytes being prone to freezing at ultra-low temperatures (-50℃ and below), insufficient low-temperature ionic conductivity, interface instability, poor cycle performance and inability to operate stably for a long time.

[0005] To achieve the above objectives, in a first aspect, this application provides a low-temperature microemulsion electrolyte, comprising an electrolyte salt, a symmetrical cyclic ether solvent, a highly chlorinated solvent, and a chlorinated ether solvent;

[0006] Wherein, the highly chlorinated solvent is insoluble in the symmetrical cyclic ether solvent, and the chlorinated ether solvent is used to disperse the highly chlorinated solvent in the symmetrical cyclic ether solvent in the form of micelles; and the volume ratio of the chlorinated ether solvent to the highly chlorinated solvent is not less than 9:1.

[0007] Preferably, the sum of the volume percentages of the highly chlorinated solvent and the chlorinated ether solvent is 5% to 50%.

[0008] Preferably, the symmetrical cyclic ether solvent is a cyclic ether solvent having at least one symmetry element in its molecular structure, including a symmetry plane, symmetry axis, or symmetry center. Preferably, the symmetrical cyclic ether solvent is selected from one or more of the following: oxetane, tetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydropyran, 2,6-dimethyltetrahydropyran, 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, 12-crown ether-4, 15-crown ether-5, 18-crown ether-6, 2,2-dimethyloxetane, 2,2,5,5-tetramethyltetrahydrofuran, 2,2-dimethyl-1,3-dioxolane, 2,2,6,6-tetramethyltetrahydropyran, and dibenzo-18-crown ether-6.

[0009] Preferably, the highly chlorinated solvent is a chlorinated aliphatic hydrocarbon organic solvent in which the substitution rate of chlorine atoms for hydrogen atoms in the molecular structure is greater than or equal to 75%. Preferably, the highly chlorinated solvent is selected from one or more of carbon tetrachloride, chloroform, hexachloroethane, octachloropropane, decachlorobutane, tetradecylchlorohexane, tetrachloroethylene, trichloroethylene, hexachloropropylene, octachlorobutene, pentachloroethane, heptachloropropane, octachloroisobutane, pentachloropropylene, and hexachlorobutadiene.

[0010] Preferably, the chlorinated ether solvent is a chlorinated ether organic solvent in which the substitution rate of chlorine atoms for hydrogen atoms in the molecular structure is greater than or equal to 50%. Preferably, the chlorinated ether solvent is selected from 1,1,2,2-tetrachloroethyl-trichloromethyl ether, 1,1,2,3,3-pentachloropropyl-trichloromethyl ether, 1,1,2,2-tetrachloroethyl-2,2,3,3-tetrachloropropyl ether, pentachloroethyl-2,2,3,3-tetrachloropropyl ether, 1,1,2,2-tetrachloroethyl-1,1,2-trichloropropyl ether, 2,2,3,3-tetrachloropropyl-1,1,2,2-tetrachlorobutyl ether, 1,1,3,3-tetrachloropropyl-1,1,2,3,3-tetrachloropropyl-1,1,2,3-trichloropropyl ether, 2,2,3,3-tetrachloropropyl-1,1,2,3-tetrachlorobutyl ether, 1,1,3,3-tetrachloropropyl-1,1,2,3-trichloropropyl ether, etc. One or more of the following: 2-tetrachloroethyl ether, 1,1,2,2-tetrachloroethyl-2,6-dichlorophenyl ether, pentachloroethylphenyl ether, 1,1,2,2-tetrachloroethyl-2,4-dichlorophenyl ether, 1,1,3,3-tetrachloropropyl-trichloromethyl ether, 1,1,2,2-tetrachloroethyl-2,2-dichloroethyl ether, 3,3,3-trichloropropyl-2,2,3,3-tetrachloropropyl ether, 1,1,2,2-tetrachloroethyl-2,4,6-trichlorophenyl ether, and pentachloroethyl-2,6-dichlorophenyl ether.

[0011] Preferably, the electrolyte salt is a lithium salt or a potassium salt. Preferably, the molar concentration of the electrolyte salt in the low-temperature microemulsion electrolyte is 0.5 mol / L to 3 mol / L.

[0012] Preferably, the lithium salt is one or more selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium bisfluorosulfonylimide, lithium difluorooxalate borate, lithium bisoxalate borate, lithium perchlorate, lithium bistrifluoromethanesulfonylimide, and lithium nitrate.

[0013] Preferably, the potassium salt is one or more of potassium hexafluorophosphate, potassium perchlorate, potassium difluorosulfonyl imide, and potassium trifluoromethylsulfonate.

[0014] Secondly, this application provides a method for preparing the above-mentioned low-temperature microemulsion electrolyte, comprising the following steps:

[0015] S1. Mix the above electrolyte salt and the above symmetrical cyclic ether solvent to obtain a clear solution;

[0016] S2. Mix the above-mentioned clear solution and the above-mentioned highly chlorinated solvent to form a phase-separated system;

[0017] S3. Mix the above phase separation system with the above chloroether solvent to obtain the low-temperature microemulsion electrolyte.

[0018] Thirdly, this application provides a secondary battery comprising the aforementioned low-temperature microemulsion electrolyte.

[0019] Fourthly, this application provides an electrical device that includes the aforementioned secondary battery.

[0020] In summary, the technical solutions conceived in this application have the following main technical advantages compared with the prior art:

[0021] (1) The low-temperature microemulsion electrolyte provided in this application, through the synergistic effect of electrolyte salt, symmetrical cyclic ether solvent, highly chlorinated solvent insoluble in symmetrical cyclic ether solvent, and chlorinated ether solvent used to disperse the highly chlorinated solvent in the symmetrical cyclic ether solvent in the form of micelles, constructs a low-temperature microemulsion electrolyte system with high ionic conductivity, electrode interface compatibility and wide temperature range stability. This enables the electrolyte to maintain excellent cycle performance in a wide temperature range of -40℃ to 25℃, and endows the battery with high stability, long life and high reliability in ultra-low temperature environment. It effectively solves the core problems of slow kinetics, poor interface stability and short cycle life of secondary batteries in ultra-low temperature environment.

[0022] (2) By adding a symmetrical cyclic ether solvent and controlling its amount, this application utilizes its synergistic effect on molecular symmetry and weak solvent properties to significantly promote the dissociation of electrolyte salt, improve low-temperature ionic conductivity, avoid salting out, and at the same time significantly reduce the lithium-ion desolvation energy barrier and accelerate the electrode interface dynamics process, thereby synergistically improving the low-temperature performance of the battery from both ion transport and interface reaction aspects.

[0023] (3) By adding appropriate types of highly chlorinated solvents and chlorinated ether solvents and adjusting their ratio, this application successfully constructed a stable chlorinated microemulsion micelle structure, which can synergistically act on the electrode interface, guide the formation of a robust SEI film rich in inorganic matter on the negative electrode side, effectively suppress lithium dendrites and side reactions, and simultaneously synergistically construct a stable CEI film on the positive electrode side, enhancing the compatibility of the electrolyte and high-voltage positive electrode materials, and significantly improving the cycle stability and voltage tolerance of the battery from the perspective of electrode interface protection.

[0024] (4) Compared with commercial electrolytes, the batteries assembled based on the low-temperature microemulsion electrolyte provided in this application show significant technical advantages: the assembled Li||Li symmetric battery can cycle stably for more than 4000 hours at -20℃, and the cycle life is more than 3 times longer than that of traditional commercial electrolytes; the assembled Li||NMC811 full cell has a capacity utilization and cycle life of 3 times and 8 times that of traditional commercial electrolytes at -20℃, respectively; in addition, the assembled ampere-hour-level Li||NMC811 pouch battery can still maintain normal operation at ultra-low temperature of -50℃, showing excellent wide temperature range adaptability. Attached Figure Description

[0025] Figure 1 The size of the chlorinated micelles formed in the electrolyte prepared in Example 1 of this application;

[0026] Figure 2The electrolytes prepared in Example 1 and Comparative Example 1 of this application exhibit low-temperature performance at different temperatures; wherein the temperatures of contents (a), (b), (c), and (d) are -20°C, -40°C, -60°C, and -70°C, respectively.

[0027] Figure 3 The cycling performance of the Li||Li batteries assembled in Example 1 and Comparative Example 1 of this application at -20°C;

[0028] Figure 4 The cycling performance of the Li||NMC811 batteries assembled in Example 1 and Comparative Examples 1-2 of this application at 25°C and 1C rate is shown.

[0029] Figure 5 The cycling performance of the Li||NMC811 batteries assembled in Example 1 and Comparative Examples 1-2 of this application at -20°C and 0.5C rate is shown.

[0030] Figure 6 The cycling performance of the Li||NMC811 battery assembled in Example 1 of this application at -40°C and 0.2C rate is shown.

[0031] Figure 7 This is a discharge curve of the Li||NMC811 pouch battery assembled in Example 1 of this application after being charged at 25°C, at a low temperature (-50°C to -20°C) and a 0.1C rate. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0033] In the description of this application, it should be understood that the term "and / or" describes a relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The symbol " / " in this document indicates that the related objects are in an "or" relationship; for example, A / B means A or B.

[0034] In the description of the embodiments in this application, the words "exemplary" or "for example" are used to indicate that they are examples, illustrations, or descriptions. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design options. Specifically, the use of the words "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0035] In the description of the embodiments in this application, unless otherwise stated, "multiple" means two or more.

[0036] This application provides a low-temperature microemulsion electrolyte, comprising an electrolyte salt, a symmetrical cyclic ether solvent, a highly chlorinated solvent, and a chlorinated ether solvent;

[0037] The highly chlorinated solvent is insoluble in the symmetrical cyclic ether solvent, and the chlorinated ether solvent is used to disperse the highly chlorinated solvent in the symmetrical cyclic ether solvent in the form of micelles.

[0038] In some embodiments, the combined volume percentage of the highly chlorinated solvent and the chlorinated ether solvent in the aforementioned low-temperature microemulsion electrolyte is 5% to 50%. The inventors of this application have experimentally discovered that when the combined volume percentage of the highly chlorinated solvent and the chlorinated ether solvent is less than 5%, the capacity retention of the battery assembled from the low-temperature microemulsion electrolyte prepared based on this formulation deteriorates at different temperatures. This may be because the highly chlorinated solvent and the chlorinated ether solvent form too few microemulsion micelles, failing to form a robust SEI / CEI stable positive and negative electrode interface. When the combined volume percentage of the highly chlorinated solvent and the chlorinated ether solvent is greater than 50%, the operating temperature range of the battery assembled from the electrolyte prepared based on this formulation narrows. This may be because the highly chlorinated solvent and the chlorinated ether solvent form too many microemulsion micelles, hindering ion transport in the electrolyte phase and interface, leading to a significant decrease in battery kinetics and inability to function normally at -40°C.

[0039] In some embodiments, the volume ratio of chlorinated ether solvent to highly chlorinated solvent in the aforementioned low-temperature microemulsion electrolyte is not less than 9:1. From a cost perspective, chlorinated ether solvent is expensive, and excessive use increases the cost of the electrolyte. Therefore, the preferred volume ratio of chlorinated ether solvent to highly chlorinated solvent is (9~15):1, which allows the highly chlorinated solvent and chlorinated ether solvent to assemble into microemulsion micelles.

[0040] For example, in the aforementioned low-temperature microemulsion electrolyte, the sum of the volume ratios of the highly chlorinated solvent and the chlorinated ether solvent can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any combination of two of the above values. Specifically, the volume ratio of the chlorinated ether solvent to the highly chlorinated solvent can be 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, etc.

[0041] In some embodiments, the aforementioned symmetrical cyclic ether solvent is a cyclic ether solvent having at least one symmetry element among a symmetry plane, a symmetry axis, and a symmetry center in its molecular structure. In some embodiments, the aforementioned symmetrical cyclic ether solvent is selected from one or more of the following: oxetane, tetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydropyran, 2,6-dimethyltetrahydropyran, 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, 12-crown ether-4, 15-crown ether-5, 18-crown ether-6, 2,2-dimethyloxetane, 2,2,5,5-tetramethyltetrahydrofuran, 2,2-dimethyl-1,3-dioxolane, 2,2,6,6-tetramethyltetrahydropyran, and dibenzo-18-crown ether-6.

[0042] In some embodiments, the highly chlorinated solvent is a chlorinated aliphatic hydrocarbon organic solvent in which the substitution rate of chlorine atoms for hydrogen atoms in the molecular structure is greater than or equal to 75%. In some embodiments, the highly chlorinated solvent is selected from one or more of carbon tetrachloride, chloroform, hexachloroethane, octachloropropane, decachlorobutane, tetradecylchlorohexane, tetrachloroethylene, trichloroethylene, hexachloropropylene, octachlorobutene, pentachloroethane, heptachloropropane, octachloroisobutane, pentachloropropylene, and hexachlorobutadiene.

[0043] In some embodiments, the chlorinated ether solvent is a chlorinated ether organic solvent in which the substitution rate of chlorine atoms for hydrogen atoms in the molecular structure is greater than or equal to 50%. In some embodiments, the chlorinated ether solvent is selected from 1,1,2,2-tetrachloroethyl-trichloromethyl ether, 1,1,2,3,3-pentachloropropyl-trichloromethyl ether, 1,1,2,2-tetrachloroethyl-2,2,3,3-tetrachloropropyl ether, pentachloroethyl-2,2,3,3-tetrachloropropyl ether, 1,1,2,2-tetrachloroethyl-1,1,2-trichloropropyl ether, 2,2,3,3-tetrachloropropyl-1,1,2,2-tetrachlorobutyl ether, 1,1,3,3-tetrachloropropyl-1,1,2,3-trichloropropyl ether, 2,2,3,3-tetrachloropropyl-1,1,2,2-tetrachlorobutyl ether, 1,1,3,3-tetrachloropropyl- ... One or more of the following: 2,2-tetrachloroethyl ether, 1,1,2,2-tetrachloroethyl-2,6-dichlorophenyl ether, pentachloroethylphenyl ether, 1,1,2,2-tetrachloroethyl-2,4-dichlorophenyl ether, 1,1,3,3-tetrachloropropyl-trichloromethyl ether, 1,1,2,2-tetrachloroethyl-2,2-dichloroethyl ether, 3,3,3-trichloropropyl-2,2,3,3-tetrachloropropyl ether, 1,1,2,2-tetrachloroethyl-2,4,6-trichlorophenyl ether, and pentachloroethyl-2,6-dichlorophenyl ether.

[0044] In some embodiments, the chlorinated ether solvent can encapsulate the highly chlorinated solvent to form chlorinated micelles with a size of 50 nm to 120 nm inside the electrolyte.

[0045] It is understood that the low-temperature microemulsion electrolyte provided in this application is suitable for various secondary batteries, including commonly used lithium secondary batteries and potassium secondary batteries. It should also be understood that the low-temperature microemulsion electrolyte provided in this application can also be used in sodium secondary batteries, with the corresponding electrolyte salts being lithium salt, potassium salt, or sodium salt. The low-temperature microemulsion electrolyte provided in this application can be applied to different secondary batteries simply by adjusting the type of electrolyte salt, demonstrating good versatility.

[0046] When the low-temperature microemulsion electrolyte provided in this application is applied to a lithium secondary battery, the lithium salt may be one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium bisfluorosulfonylimide, lithium difluorooxalate borate, lithium bisoxalate borate, lithium perchlorate, lithium bistrifluoromethanesulfonylimide, and lithium nitrate, but not limited to these.

[0047] When the low-temperature microemulsion electrolyte provided in this application is applied to a potassium secondary battery, the potassium salt may be one or more of potassium hexafluorophosphate, potassium difluorosulfonamide, potassium perchlorate, and potassium trifluoromethylsulfonate, but is not limited to.

[0048] In some embodiments, the molar concentration of the electrolyte salt in the aforementioned low-temperature microemulsion electrolyte is 0.5 mol / L to 3 mol / L. Specifically, the molar concentration of the electrolyte salt can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, or any combination of two of the aforementioned values.

[0049] This application also provides a method for preparing the above-mentioned low-temperature microemulsion electrolyte, comprising the following steps:

[0050] S1. Mix the above electrolyte salt and the above symmetrical cyclic ether solvent to obtain a clear solution;

[0051] S2. Mix the above-mentioned clear solution and the above-mentioned highly chlorinated solvent to form a phase-separated system;

[0052] S3. Mix the above phase separation system with the above chloroether solvent to obtain the low-temperature microemulsion electrolyte.

[0053] On the other hand, this application also provides a secondary battery, including the aforementioned low-temperature microemulsion electrolyte.

[0054] In some embodiments, the battery described above can be a lithium secondary battery.

[0055] In some embodiments, the aforementioned secondary battery further includes a negative electrode. The combination of the negative electrode and the aforementioned low-temperature microemulsion electrolyte can significantly improve the uniformity of lithium metal deposition, enhance the interfacial properties of the negative electrode, and improve the kinetic and cycle performance of the lithium secondary battery.

[0056] In some embodiments, the negative electrode sheet may include a negative current collector. In some embodiments, the negative current collector may be a metal foil or a composite current collector. The composite current collector includes a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. For example, the metal foil may be, but is not limited to, copper foil. For example, the metal material of the composite current collector may be, but is not limited to, one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. For example, the polymer material base layer may be, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0057] In some embodiments, the negative electrode sheet further includes a conductive layer disposed on at least one side of the negative electrode current collector. The conductive layer includes a negative electrode conductive agent and a binder. Exemplarily, the negative electrode conductive agent includes, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Exemplarily, the negative electrode binder includes, but is not limited to, one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0058] In some embodiments, the secondary battery further includes a positive electrode sheet. In some embodiments, the positive electrode sheet may include a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and comprising a positive electrode active material. The positive electrode active material may be a positive electrode active material known in the art for lithium secondary batteries. Exemplarily, the positive electrode active material includes at least one of the following: layered structure positive electrode active materials (e.g., ternary, lithium nickel oxide / sodium, lithium cobalt oxide / sodium, lithium manganese oxide / sodium, lithium-rich / sodium layered, rock salt phase layered, etc.), olivine-type phosphate active materials, spinel structure positive electrode active materials (e.g., spinel lithium manganese oxide, spinel lithium nickel manganese oxide, lithium-rich spinel lithium manganese oxide, lithium nickel manganese oxide, etc.). Specifically, the layered structure positive electrode active materials include, but are not limited to, lithium cobalt oxide (LCO), lithium nickel oxide (LNO), lithium manganese oxide (LMO), and LiNi. 1 / 3 Mn 1 / 3 Co 1 / 3 O2 (NMC111), LiNi 0.8 Mn 0.1 Co 0.1 O2 (NMC811) and LiNi 0.5 Mn0.3 Co 0.2 One or more of O2 (NMC532).

[0059] In some embodiments, the aforementioned positive electrode film layer may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. Exemplary examples include, but are not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, and carbon nanofibers.

[0060] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode conductive agent. Exemplary examples include, but are not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0061] In some embodiments, the aforementioned secondary batteries can also be assembled into battery modules. This application does not limit the number of secondary batteries in a battery module; those skilled in the art can adjust this number according to the application and capacity of the battery module.

[0062] In some embodiments, the battery modules described above can be assembled into a battery pack. This application does not limit the number of battery modules in the battery pack; those skilled in the art can adjust this number according to the application and capacity of the battery modules.

[0063] This application also provides an electrical device, including at least one of the above-mentioned secondary battery, battery module or battery pack.

[0064] It should be understood that materials of the same or similar type, model, quality, properties, or function as the reagents and instruments used in the following embodiments can be used to implement this application. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available.

[0065] The following are examples and comparative examples:

[0066] Example 1

[0067] The method for preparing the low-temperature microemulsion electrolyte provided in this embodiment includes the following steps:

[0068] 0.187 g of lithium bis(fluorosulfonyl)imide and 0.67 mL of tetrahydropyran were stirred and mixed at room temperature to obtain a clear solution. The clear solution was mixed with 0.03 mL of tetradecylhexane, and a phase separation was observed. Then, 0.30 mL of 1,1,2,2-tetrachloroethyl-2,2,3,3-tetrachloropropyl ether was added dropwise while stirring, until the phase separation disappeared and a homogeneous solution was obtained, which is the low-temperature microemulsion electrolyte.

[0069] Dynamic light scattering tests were performed on the low-temperature microemulsion electrolyte, and micelle particles with an average diameter of 76 nm were observed in the electrolyte. Figure 1 This indicates that the chlorinated ether solvent added to the electrolyte can effectively encapsulate the highly chlorinated solvent and form micelle structures through self-assembly, thereby achieving uniform dispersion of the highly chlorinated solvent on a macroscopic scale and structural stability on a microscopic scale.

[0070] The performance of the above-mentioned low-temperature microemulsion electrolyte was tested:

[0071] (1) Low temperature performance: The low temperature microemulsion electrolyte prepared above was placed at low temperatures of -20℃, -40℃, -60℃ and -70℃ respectively, and the solidification was observed and photographed to evaluate its low temperature performance.

[0072] (2) Electrochemical performance: The low-temperature microemulsion electrolyte prepared above was used to assemble Li||Li batteries, Li||NMC811 batteries, and Li||NMC811 pouch batteries, wherein,

[0073] The assembly process of Li||Li battery is as follows: button cell batteries are assembled in a glove box with water content of less than 0.01ppm and oxygen content of less than 0.01ppm. The positive and negative electrodes are lithium metal sheets with a diameter of 12mm, and the electrolyte is the low-temperature microemulsion electrolyte mentioned above.

[0074] The assembly process of the Li||NMC811 battery is as follows: button cells are assembled in a glove box with a water content of less than 0.01ppm and an oxygen content of less than 0.01ppm. The positive electrode is an NMC811 sheet with a diameter of 8mm, the negative electrode is a lithium metal sheet with a diameter of 12mm, and the electrolyte is the low-temperature microemulsion electrolyte mentioned above.

[0075] The assembly process of the Li||NMC811 pouch battery is as follows: The pouch battery is assembled in a glove box with a water content of less than 0.01ppm and an oxygen content of less than 0.01ppm. The positive electrode is a 4cm×5cm NMC811 sheet, the negative electrode is a 4.5cm×5.5cm lithium metal sheet, the separator is a 5cm×6cm polypropylene separator, and the electrolyte is the above-mentioned low-temperature microemulsion electrolyte.

[0076] The assembled Li||Li batteries and Li||NMC811 batteries were placed in a high and low temperature test chamber with controlled test temperature, and cyclic tests were performed using a charge-discharge tester. The test current for the Li||Li batteries was 0.2 mA / cm. 2 The tested capacity is 0.2mAh / cm³. 2 The test voltage for the Li||NMC811 battery is 3~4.5V. The assembled Li||NMC811 pouch battery was charged to 4.5V at 25℃, placed in a high and low temperature test chamber to control the discharge temperature, and the discharge capacity was tested using a charge and discharge tester.

[0077] Comparative Example 1 (Commercial Electrolyte)

[0078] The commercial electrolyte provided in this comparative example is prepared by dissolving lithium hexafluorophosphate in ethylene carbonate and diethyl carbonate to form a homogeneous solution, which is the commercial electrolyte. The molar concentration of lithium hexafluorophosphate is 1 mol / L, and the volume ratio of ethylene carbonate to diethyl carbonate is 3:7.

[0079] The low-temperature performance and electrochemical performance of the electrolyte prepared in this comparative example were tested using the method provided in Example 1.

[0080] Comparative Example 2 (without highly chlorinated solvents)

[0081] The method for preparing the electrolyte provided in this comparative example includes the following steps:

[0082] 0.187 g of lithium bis(fluorosulfonyl)imide and 0.67 mL of tetrahydropyran were stirred and mixed at room temperature to obtain a clear solution. Then, 0.30 mL of 1,1,2,2-tetrachloroethyl-2,2,3,3-tetrachloropropyl ether was added dropwise to the above clear solution while stirring to prepare the electrolyte.

[0083] The low-temperature performance and electrochemical performance of the electrolyte prepared in this comparative example were tested using the method provided in Example 1.

[0084] Comparative Example 3 (without added chloroether solvent)

[0085] The method for preparing the electrolyte provided in this comparative example includes the following steps:

[0086] 0.187 g of lithium bis(fluorosulfonyl)imide and 0.67 mL of tetrahydropyran were stirred and mixed at room temperature to obtain a clear solution. Then, the clear solution was mixed with 0.03 mL of tetradecyl chloride to prepare the electrolyte.

[0087] Experiments revealed that the electrolyte exhibited a phase separation state, failing to meet the homogeneous usage conditions. Therefore, its low-temperature performance was not tested, nor was it assembled into a battery to test its electrochemical performance.

[0088] Comparative Example 4 (without added symmetrical cyclic ether solvent)

[0089] The method for preparing the electrolyte provided in this comparative example includes the following steps:

[0090] Mix 0.187 g of lithium difluorosulfonylimide and 0.03 mL of tetradecylhexane, and then add 0.30 mL of 1,1,2,2-tetrachloroethyl-2,2,3,3-tetrachloropropyl ether dropwise while stirring to prepare an electrolyte.

[0091] Experiments revealed that the lithium salt could not dissolve and the electrolyte was not conductive, therefore its low-temperature performance was not tested, nor was it assembled into a battery to test its electrochemical performance.

[0092] Comparative Example 5

[0093] 0.187 g of lithium bis(fluorosulfonyl)imide and 0.67 mL of tetrahydropyran were stirred and mixed at room temperature to obtain a clear solution. The clear solution was mixed with 0.03 mL of chloroethane, and no phase separation was observed. Then, 0.30 mL of 1,1,2,2-tetrachloroethyl-2,2,3,3-tetrachloropropyl ether was added dropwise while stirring to prepare the electrolyte.

[0094] Dynamic light scattering tests were performed on the prepared electrolyte, and no bell-shaped peak was observed, indicating that no micelles were formed in the electrolyte. The possible reason is that the chloroethane (a chlorinated solvent) added to the electrolyte formulation has a low substitution rate of chlorine atoms for hydrogen atoms (17%) in its molecular structure. This chlorinated solvent is highly polar and can directly dissolve in the symmetrical cyclic ether solvent tetrahydropyran, thus preventing the formation of chlorinated micelles in the electrolyte.

[0095] Comparative Example 6

[0096] 0.187 g of lithium bis(fluorosulfonyl)imide and 0.67 mL of tetrahydropyran were stirred and mixed at room temperature to obtain a clear solution. The clear solution was mixed with 0.03 mL of tetradecyl chloride, and a phase separation was observed. Then, 0.30 mL of ethyl-chloromethyl ether was added dropwise while stirring to prepare the electrolyte.

[0097] Experiments revealed that the electrolyte still exhibited phase separation, failing to meet the homogeneous usage requirements. The possible reason is that the ethyl-chloromethyl ether (a chloromethyl ether solvent) added to the electrolyte formulation has an excessively low chlorine-to-hydrogen substitution rate (12.5%). Furthermore, the polarity of this chloromethyl ether solvent is significantly higher than that of highly chloromethyl solvents, thus failing to solubilize the highly chloromethyl solvents and form a micellar structure.

[0098] Figure 2 Content (a), Figure 2 Content (b) Figure 2 Content (c) Figure 2Content (d) shows photographs of the low-temperature microemulsion electrolyte prepared in Example 1 and the commercial electrolyte prepared in Comparative Example 1 at -20°C, -40°C, -60°C, and -70°C, respectively. It can be seen that the commercial electrolyte solidifies at -40°C, while the low-temperature microemulsion electrolyte prepared in this application remains liquid at -70°C, exhibiting an excellent low freezing point and showing great potential for application in low-temperature lithium secondary batteries.

[0099] Figure 3 The figures show the cycling performance of the Li||Li batteries assembled in Example 1 and Comparative Example 1 at -20°C. It can be seen that the Li||Li battery assembled using the commercial electrolyte (Comparative Example 1) experiences a short circuit failure after approximately 1200 hours of cycling at -20°C, while the Li||Li battery assembled using the low-temperature microemulsion electrolyte prepared in Example 1 can cycle stably for over 4000 hours at -20°C. This indicates that the low-temperature microemulsion electrolyte provided in this application can effectively improve the cycling stability of lithium secondary batteries at low temperatures.

[0100] Figure 4 The figures show the cycling performance of the Li||NMC811 batteries assembled in Example 1 and Comparative Examples 1 and 2 at 25°C and 1C rate. It can be seen that the Li||NMC811 battery assembled using the commercial electrolyte (Comparative Example 1) experiences a sharp decrease in capacity during cycling, with a capacity retention of only 24% after 15 cycles; the Li||NMC811 battery assembled in Comparative Example 2 shows a capacity retention of only 67% after 190 cycles; while the Li||NMC811 battery assembled using the low-temperature microemulsion electrolyte prepared in Example 1 still maintains a capacity retention of 80% after 300 cycles, exhibiting excellent cycling stability. This indicates that the low-temperature microemulsion electrolyte provided in this application is well-suited for high-voltage cathode materials such as NMC811.

[0101] Figure 5 The figures show the cycling performance of the Li||NMC811 batteries assembled in Example 1 and Comparative Examples 1 and 2 at -20°C and 0.5C rate. It can be seen that the Li||NMC811 battery assembled using the commercial electrolyte (Comparative Example 1) experiences a sharp decrease in capacity during cycling, with a capacity retention of only 63% after 100 cycles; the Li||NMC811 battery assembled in Comparative Example 2 shows a capacity retention of only 70% after 400 cycles; while the Li||NMC811 battery assembled using the low-temperature microemulsion electrolyte prepared in Example 1 still maintains a capacity retention of 81% after 800 cycles, demonstrating excellent low-temperature cycling stability.

[0102] Figure 6The image shows the cycling performance of the Li||NMC811 battery assembled in Example 1 at -40°C and 0.2C rate. It can be seen that the Li||NMC811 battery assembled using the low-temperature microemulsion electrolyte prepared in Example 1 retains 87% of its capacity after 100 cycles, demonstrating excellent ultra-low temperature cycling stability.

[0103] Figure 7 The figure shows the discharge curves of the Li||NMC811 pouch battery assembled in Example 1 after charging at 25°C, within a temperature range of -50°C to -20°C at a rate of 0.1C. It can be seen that the Li||NMC811 pouch battery assembled using the low-temperature microemulsion electrolyte prepared in Example 1, after charging at 25°C, gradually decreases in discharge plateau as the test temperature decreases. This battery can still provide a high capacity of 1.4Ah at an ultra-low temperature of -50°C and a rate of 0.1C (approximately 53% of the theoretical capacity), indicating that the Li||NMC811 pouch battery assembled using the low-temperature microemulsion electrolyte prepared in this application can operate normally at an ultra-low temperature of -50°C.

[0104] Example 2

[0105] The method for preparing the low-temperature microemulsion electrolyte provided in this embodiment includes the following steps:

[0106] 0.187 g of lithium difluorosulfonylimide and 0.95 mL of tetrahydropyran were stirred and mixed at room temperature to obtain a clear solution. The clear solution was mixed with 0.005 mL of tetradecylhexane, and a phase separation was observed. Then, 0.045 mL of 1,1,2,2-tetrachloroethyl-2,2,3,3-tetrachloropropyl ether was added dropwise while stirring, until the phase separation disappeared and a homogeneous solution was obtained, which is the low-temperature microemulsion electrolyte.

[0107] The low-temperature microemulsion electrolyte prepared in this embodiment was placed at -70°C to observe whether it solidified. Then, the electrolyte was used to assemble a Li||NMC811 battery using the same method as in Example 1, and electrochemical tests were performed. The test results are shown in Table 1.

[0108] Example 3

[0109] The method for preparing the low-temperature microemulsion electrolyte provided in this embodiment includes the following steps:

[0110] 0.187 g of lithium difluorosulfonylimide and 0.50 mL of tetrahydropyran were stirred and mixed at room temperature to obtain a clear solution. The clear solution was mixed with 0.05 mL of tetradecylhexane, and a phase separation was observed. Then, 0.45 mL of 1,1,2,2-tetrachloroethyl-2,2,3,3-tetrachloropropyl ether was added dropwise while stirring, until the phase separation disappeared and a homogeneous solution was obtained, which is the low-temperature microemulsion electrolyte.

[0111] The low-temperature microemulsion electrolyte prepared in this embodiment was placed at -70°C to observe whether it solidified. Then, the electrolyte was used to assemble a Li||NMC811 battery using the same method as in Example 1, and electrochemical tests were performed. The test results are shown in Table 1.

[0112] Example 4

[0113] The method for preparing the low-temperature microemulsion electrolyte provided in this embodiment includes the following steps:

[0114] 0.187 g of lithium difluorosulfonylimide and 0.55 mL of 2,5-dimethyltetrahydrofuran were stirred and mixed at room temperature to obtain a clear solution. The clear solution was mixed with 0.03 mL of octachloropropane, and a phase separation was observed. Then, 0.42 mL of 1,1,2,2-tetrachloroethyl-trichloromethyl ether was added dropwise while stirring, until the phase separation disappeared and a homogeneous solution was obtained, which is the low-temperature microemulsion electrolyte.

[0115] The low-temperature microemulsion electrolyte prepared in this embodiment was placed at -70°C to observe whether it solidified. Then, the electrolyte was used to assemble a Li||NMC811 battery using the same method as in Example 1, and electrochemical tests were performed. The test results are shown in Table 1.

[0116] Example 5

[0117] The method for preparing the low-temperature microemulsion electrolyte provided in this embodiment includes the following steps:

[0118] 0.187 g of lithium bisfluorosulfonylimide and 0.63 mL of tetrahydrofuran were stirred and mixed at room temperature to obtain a clear solution. The clear solution was mixed with 0.03 mL of carbon tetrachloride, and a phase separation was observed. Then, 0.34 mL of 1,1,2,3,3-pentachloropropyl-trichloromethyl ether was added dropwise while stirring, which caused the phase separation to disappear, resulting in a homogeneous solution, which is the low-temperature microemulsion electrolyte.

[0119] The low-temperature microemulsion electrolyte prepared in this embodiment was placed at -70°C to observe whether it solidified. Then, the electrolyte was used to assemble a Li||NMC811 battery using the same method as in Example 1, and electrochemical tests were performed. The test results are shown in Table 1.

[0120] Example 6

[0121] The method for preparing the low-temperature microemulsion electrolyte provided in this embodiment includes the following steps:

[0122] 0.187 g of lithium difluorosulfonylimide and 0.65 mL of 2,6-dimethyltetrahydropyran were stirred and mixed at room temperature to obtain a clear solution. The clear solution was mixed with 0.03 mL of decachlorobutane, and a phase separation was observed. Then, 0.32 mL of 1,1,2,2-tetrachloroethyl-2,2,3,3-tetrachloropropyl ether was added dropwise while stirring, until the phase separation disappeared and a homogeneous solution was obtained, which is the low-temperature microemulsion electrolyte.

[0123] The low-temperature microemulsion electrolyte prepared in this embodiment was placed at -70°C to observe whether it solidified. Then, the electrolyte was used to assemble a Li||NMC811 battery using the same method as in Example 1, and electrochemical tests were performed. The test results are shown in Table 1.

[0124] Example 7

[0125] The method for preparing the low-temperature microemulsion electrolyte provided in this embodiment includes the following steps:

[0126] 0.0935 g of lithium difluorosulfonylimide and 0.86 mL of 1,3-dioxolane were stirred and mixed at room temperature to obtain a clear solution. The clear solution was mixed with 0.01 mL of tetradecylhexane, and a phase separation was observed. Then, 0.13 mL of pentachloroethyl-2,2,3,3-tetrachloropropyl ether was added dropwise while stirring, which caused the phase separation to disappear, resulting in a homogeneous solution, which is the low-temperature microemulsion electrolyte.

[0127] The low-temperature microemulsion electrolyte prepared in this embodiment was placed at -70°C to observe whether it solidified. Then, the electrolyte was used to assemble a Li||NMC811 battery using the same method as in Example 1, and electrochemical tests were performed. The test results are shown in Table 1.

[0128] Example 8

[0129] The method for preparing the low-temperature microemulsion electrolyte provided in this embodiment includes the following steps:

[0130] 0.374 g of lithium difluorosulfonylimide and 0.76 mL of 1,4-dioxane were stirred and mixed at room temperature to obtain a clear solution. The clear solution was mixed with 0.02 mL of tetrachloroethylene, and a phase separation was observed. Then, 0.22 mL of 1,1,2,2-tetrachloroethyl-2,6-dichlorophenyl ether was added dropwise while stirring, until the phase separation disappeared and a homogeneous solution was obtained, which is the low-temperature microemulsion electrolyte.

[0131] The low-temperature microemulsion electrolyte prepared in this embodiment was placed at -70°C to observe whether it solidified. Then, the electrolyte was used to assemble a Li||NMC811 battery using the same method as in Example 1, and electrochemical tests were performed. The test results are shown in Table 1.

[0132] Example 9

[0133] The method for preparing the low-temperature microemulsion electrolyte provided in this embodiment includes the following steps:

[0134] 0.561 g of lithium difluorosulfonylimide and 0.61 mL of 1,3,5-trioxane were stirred and mixed at room temperature to obtain a clear solution. The clear solution was then mixed with 0.03 mL of hexachloropropene, and a phase separation was observed. Then, 0.36 mL of pentachloroethyl phenyl ether was added dropwise while stirring until the phase separation disappeared, resulting in a homogeneous solution, which is the low-temperature microemulsion electrolyte.

[0135] The low-temperature microemulsion electrolyte prepared in this embodiment was placed at -70°C to observe whether it solidified. Then, the electrolyte was used to assemble a Li||NMC811 battery using the same method as in Example 1, and electrochemical tests were performed. The test results are shown in Table 1.

[0136] Example 10

[0137] The method for preparing the low-temperature microemulsion electrolyte provided in this embodiment includes the following steps:

[0138] 0.187 g of lithium difluorosulfonylimide and 0.62 mL of 12-crown ether-4 were stirred and mixed at room temperature to obtain a clear solution. The clear solution was mixed with 0.03 mL of octachlorobutene, and a phase separation was observed. Then, 0.35 mL of pentachloroethyl-2,2,3,3-tetrachloropropyl ether was added dropwise while stirring, until the phase separation disappeared and a homogeneous solution was obtained, which is the low-temperature microemulsion electrolyte.

[0139] The low-temperature microemulsion electrolyte prepared in this embodiment was placed at -70°C to observe whether it solidified. Then, the electrolyte was used to assemble a Li||NMC811 battery using the same method as in Example 1, and electrochemical tests were performed. The test results are shown in Table 1.

[0140] Table 1. Capacity retention of Li||NMC811 batteries assembled in Examples 1-10 and Comparative Examples 1-2 at different temperatures.

[0141]

[0142] As shown in Table 1, the low-temperature microemulsion electrolyte prepared in this application remains liquid at -70℃, exhibiting an excellent low freezing point. The Li||NMC811 battery assembled using the low-temperature microemulsion electrolyte prepared in this application demonstrates excellent low-temperature cycling performance, maintaining normal discharge operation and long-term stable operation even at ultra-low temperatures of -40℃. The reason for this may be that the symmetrical cyclic ether solvent added to the low-temperature microemulsion electrolyte provided in this application has sufficient dissociation capability for lithium salts due to its molecular symmetry. This not only improves ionic conductivity at low temperatures but also avoids lithium salt precipitation problems. Simultaneously, the weak solvation characteristics of the cyclic ether solvent lower the lithium-ion desolvation energy barrier, accelerating the electrode interface kinetics. Furthermore, the chlorinated microemulsion micelles formed by the highly chlorinated solvent and the chlorinated ether solvent guide the formation of a robust SEI layer rich in inorganic matter, effectively suppressing lithium dendrite growth and negative electrode interface side reactions, reducing irreversible loss of active lithium. Through the synergistic effect between the components, this electrolyte can be adapted to high-voltage cathode materials such as NMC811, and lithium secondary batteries assembled based on this electrolyte can still discharge normally at an ultra-low temperature of -50℃ and can cycle stably at an ultra-low temperature of -40℃.

[0143] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A low-temperature microemulsion electrolyte, characterized in that, Including electrolyte salts, symmetrical cyclic ether solvents, highly chlorinated solvents, and chlorinated ether solvents; Wherein, the highly chlorinated solvent is insoluble in the symmetrical cyclic ether solvent, and the chlorinated ether solvent is used to disperse the highly chlorinated solvent in the symmetrical cyclic ether solvent in the form of micelles; and the volume ratio of the chlorinated ether solvent to the highly chlorinated solvent is (9~15):

1. The highly chlorinated solvent is a chlorinated aliphatic hydrocarbon organic solvent in which the substitution rate of chlorine atoms for hydrogen atoms in the molecular structure is greater than or equal to 75%; the chlorinated ether solvent is a chlorinated ether organic solvent in which the substitution rate of chlorine atoms for hydrogen atoms in the molecular structure is greater than or equal to 50%.

2. The low-temperature microemulsion electrolyte according to claim 1, characterized in that, The combined volume percentage of the highly chlorinated solvent and the chlorinated ether solvent is 5% to 50%.

3. The low-temperature microemulsion electrolyte according to claim 1 or 2, characterized in that, The symmetrical cyclic ether solvent is a cyclic ether solvent with at least one symmetry element in its molecular structure, including a symmetry plane, symmetry axis, or symmetry center.

4. The low-temperature microemulsion electrolyte according to claim 3, characterized in that, The symmetrical cyclic ether solvent is selected from one or more of the following: oxetane, tetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydropyran, 2,6-dimethyltetrahydropyran, 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, 12-crown ether-4, 15-crown ether-5, 18-crown ether-6, 2,2-dimethyloxetane, 2,2,5,5-tetramethyltetrahydrofuran, 2,2-dimethyl-1,3-dioxolane, 2,2,6,6-tetramethyltetrahydropyran, and dibenzo-18-crown ether-6.

5. The low-temperature microemulsion electrolyte according to claim 1 or 2, characterized in that, The highly chlorinated solvent is selected from one or more of carbon tetrachloride, chloroform, hexachloroethane, octachloropropane, decachlorobutane, tetrachlorohexane, tetrachloroethylene, trichloroethylene, hexachloropropylene, octachlorobutene, pentachloroethane, heptachloropropane, octachloroisobutane, pentachloropropylene, and hexachlorobutadiene.

6. The low-temperature microemulsion electrolyte according to claim 1 or 2, characterized in that, The chloroether solvent is selected from 1,1,2,2-tetrachloroethyl-trichloromethyl ether, 1,1,2,3,3-pentachloropropyl-trichloromethyl ether, 1,1,2,2-tetrachloroethyl-2,2,3,3-tetrachloropropyl ether, pentachloroethyl-2,2,3,3-tetrachloropropyl ether, 1,1,2,2-tetrachloroethyl-1,1,2-trichloropropyl ether, 2,2,3,3-tetrachloropropyl-1,1,2,2-tetrachlorobutyl ether, 1,1,3,3-tetrachloropropyl-1,1,2,2- One or more of the following: tetrachloroethyl ether, 1,1,2,2-tetrachloroethyl-2,6-dichlorophenyl ether, pentachloroethylphenyl ether, 1,1,2,2-tetrachloroethyl-2,4-dichlorophenyl ether, 1,1,3,3-tetrachloropropyl-trichloromethyl ether, 1,1,2,2-tetrachloroethyl-2,2-dichloroethyl ether, 3,3,3-trichloropropyl-2,2,3,3-tetrachloropropyl ether, 1,1,2,2-tetrachloroethyl-2,4,6-trichlorophenyl ether, and pentachloroethyl-2,6-dichlorophenyl ether.

7. The low-temperature microemulsion electrolyte according to claim 1 or 2, characterized in that, The electrolyte salt is a lithium salt or a potassium salt; The lithium salt is one or more selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, and lithium nitrate; and / or, The potassium salt is one or more selected from potassium hexafluorophosphate, potassium perchlorate, potassium difluorosulfonyl imide, and potassium trifluoromethylsulfonate; and / or, The molar concentration of electrolyte salts in the low-temperature microemulsion electrolyte is 0.5 mol / L to 3 mol / L.

8. A method for preparing a low-temperature microemulsion electrolyte as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Mix the electrolyte salt and the symmetrical cyclic ether solvent to obtain a clear solution; S2. Mix the clarified solution and the highly chlorinated solvent to form a phase-separated system; S3. Mix the phase separation system and the chloroether solvent to obtain the low-temperature microemulsion electrolyte.

9. A secondary battery, characterized in that, Includes the low-temperature microemulsion electrolyte as described in any one of claims 1 to 7.

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

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