Wide-temperature-range electrolyte and preparation method thereof, battery and power-related equipment

Abstract

The invention provides a wide-temperature-range electrolyte and a preparation method thereof, a battery and electric equipment. Relates to the technical field of lithium batteries. The preparation method comprises the following steps: mixing fluoroethylene carbonate, perfluorohexanoic acid and diethyl tetrafluoroborate for reaction to obtain a functional solution; trimethyl borate and sulfuric acid are used for carrying out surface modification treatment on carbon nanofibers to form a B-CNF material; and embedding the B-CNF material into the hydrogen bond dynamic network of the functional solution to obtain the wide-temperature-range electrolyte. According to the preparation method, by constructing a hydrogen bond dynamic network and embedding the modified B-CNF material, the balance of low viscosity at low temperature and high stability at high temperature is realized, meanwhile, the ion conduction performance is improved, the performance of the battery in a wide temperature range is remarkably enhanced, and the high-temperature adaptability requirement is met.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a wide-temperature range electrolyte and a preparation method thereof, a battery, and electrical equipment. Background Art

[0002] As a highly efficient, rechargeable energy storage technology, lithium-ion batteries have been widely used in recent years in fields such as electric vehicles, portable electronic devices, and large-scale energy storage systems. Their core advantages lie in their high energy density, long cycle life, and relatively low self-discharge rate. However, the continuous expansion of these applications has placed higher demands on the performance of lithium-ion batteries, especially in terms of performance and service life under extreme temperature conditions. The operating temperature range and lifespan of batteries have become key issues in current research and applications, directly affecting their applicability and reliability in various environments.

[0003] In existing lithium-ion battery technology, traditional carbonate electrolytes are widely used in battery systems. However, this electrolyte faces significant performance bottlenecks at low temperatures (e.g., below -20°C). Due to a significant increase in viscosity, the conductivity drops sharply to below 0.5 mS / cm. Furthermore, the electrolyte tends to crystallize, destabilizing the electrode interface and severely affecting the battery's low-temperature electrical performance. Furthermore, high-temperature storage life is a challenge for traditional lithium-ion batteries. At high temperatures, the chemical stability of the electrolyte decreases, easily inducing side reactions and accelerating battery performance degradation. These factors combine to limit the low-temperature driving range and high-temperature storage life of electric vehicles, impacting the consumer experience and, to a certain extent, hindering the further promotion and application of electrification technologies such as electric vehicles.

[0004] In order to broaden the operating temperature range of batteries, the industry has tried a variety of improvement methods. For example, using ternary materials instead of lithium iron phosphate materials, using high-porosity diaphragms and high-conductivity electrolytes, etc. Although these methods have improved the low-temperature electrical performance of the battery to a certain extent, they have sacrificed the battery life at high temperatures and caused the battery consistency to deteriorate. On the other hand, traditional high-temperature storage life improvement strategies mainly rely on low-reactivity designs, such as using lithium iron phosphate instead of ternary materials, introducing composite additive electrolytes, etc. However, while these strategies improve high-temperature performance, they significantly deteriorate the low-temperature performance of the battery, making it difficult to achieve a balance in the battery's performance over a wide temperature range. At present, there are no battery cell technology elements on the market that can take into account both high and low temperature performance, which has become a key bottleneck restricting the further development of lithium-ion battery technology.

[0005] In summary, existing lithium-ion battery technology faces many challenges when dealing with extreme temperature conditions. The sharp drop in conductivity and destruction of the electrode interface at low temperatures, as well as the reduction in chemical stability and increase in side reactions at high temperatures, together lead to the decline in battery performance and shortened service life. Existing improvement methods can often only achieve a single improvement in low-temperature or high-temperature performance, and it is difficult to achieve a balance between high and low-temperature performance, resulting in limited applicability of batteries in different environments. The existence of these problems not only affects the consumer experience, but also hinders the further development and popularization of electrification technologies such as electric vehicles. There is an urgent need for an innovative technical solution that can simultaneously solve high and low-temperature performance problems.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of this application is to provide a wide-temperature range electrolyte and its preparation method, battery and electrical equipment. The preparation method achieves a balance between low viscosity at low temperature and high stability at high temperature by constructing a hydrogen bond dynamic network and embedding modified B-CNF material, while improving the ion conduction performance, significantly enhancing the performance of the battery in a wide temperature range, and meeting the high-temperature adaptability requirements.

[0008] In order to achieve the above-mentioned purpose of this application, the following technical solutions are specially adopted: In a first aspect, the present application provides a method for preparing a wide temperature range electrolyte, comprising: Fluoroethylene carbonate, perfluorohexanoic acid and diethyl tetrafluoroborate are mixed and reacted to obtain a functional solution with a dynamic hydrogen bond network; The carbon nanofibers were surface-modified using trimethyl borate and sulfuric acid to form B-CNF materials with surface defects and modified with boron functional groups. The B-CNF material is embedded in the hydrogen bond dynamic network of the functional solution containing lithium salt to obtain a wide temperature range electrolyte with three-dimensional lithium conductive channels.

[0009] In an optional embodiment, the mixing reaction of fluoroethylene carbonate, perfluorohexanoic acid and diethyl tetrafluoroborate to obtain a functional solution having a hydrogen bond dynamic network comprises: Mixing fluoroethylene carbonate, perfluorohexanoic acid, and diethyl tetrafluoroborate in a molar ratio of (0.5-1.5):(3.5-4.5):(7.5-8.5) to obtain a first mixed solution; The first mixed solution is subjected to a first heating and stirring treatment under reduced pressure to obtain the functional solution.

[0010] In an optional embodiment, the first heating and stirring treatment under reduced pressure has at least one of the following conditions: A. the stirring time is at least 8 hours; B. the heating temperature is 80°C; C. the first heating and stirring treatment is maintained in a reduced pressure state; D. the pressure during the first heating and stirring treatment is ≤10 -3 Pa; and / or, The dew point of the environment during the mixing process is ≤-60°C; and / or, The humidity in the environment during the mixing process is less than 0.1 ppm.

[0011] In an optional embodiment, the surface modification treatment includes: The carbon nanofibers are placed in a mixed solution of trimethyl borate and sulfuric acid, and refluxed under heating conditions to obtain nano high-flux carbon; The nano high-flux carbon is subjected to washing, drying and ball milling to obtain the B-CNF material.

[0012] In an optional embodiment, the temperature of the heating condition is 120° C.; and / or, The reflux reaction time is not less than 6 hours; and / or, The washing treatment is washing with water and / or an organic solvent at least 3 times; and / or, The drying process is a reduced pressure drying process; and / or, The average particle size of the B-CNF material after the ball milling treatment is ≤200 nm.

[0013] In an optional embodiment, the embedding of the B-CNF material into the hydrogen bond dynamic network of the functional solution containing lithium salt to obtain a wide temperature range electrolyte having three-dimensional lithium-conducting channels comprises: Premixing the lithium salt and the functional solution to obtain a second mixed solution; adding the B-CNF material to the second mixed liquid, and ultrasonically treating the mixture to obtain a mixed material; The mixed material is subjected to a second heating and stirring treatment under reduced pressure to obtain the wide temperature range electrolyte.

[0014] In an optional embodiment, the stirring speed of the mixing process is 800 rpm; and / or the time of the premixing process is not less than 10 minutes; and / or the concentration of the lithium salt in the wide temperature range electrolyte is 1M~5M; The concentration of the added B-CNF material in the wide temperature range electrolyte is 0.3wt%~0.5wt%; and / or the ultrasonic treatment time is not less than 30 minutes; and / or the pressure in the decompression state is ≤10 -3Pa; and / or, the heating temperature of the second heating and stirring treatment is 80° C.; and / or, the stirring time of the second heating and stirring treatment is not less than 2 hours.

[0015] In an optional embodiment, the lithium salt is a composite lithium salt prepared from lithium bis(trifluoromethylsulfonyl)imide and lithium difluorooxalatoborate; The preparation method of the composite lithium salt comprises: mixing lithium bis(trifluoromethylsulfonyl)imide and lithium difluorooxalatoborate, and performing ultrasonic dispersion treatment and stirring treatment to obtain the composite lithium salt; Wherein, the composite lithium salt has at least one of the following characteristics: A. The molar ratio of lithium bis(trifluoromethylsulfonyl)imide to lithium difluorooxalatoborate in the composite lithium salt is (3.5-4.5):(0.5-1.5); B. The conductivity of the composite lithium salt is greater than 4.5 ms / cm.

[0016] In a second aspect, the present application provides a wide temperature range electrolyte, which is prepared by the preparation method of the wide temperature range electrolyte as described in any of the aforementioned embodiments.

[0017] In a third aspect, the present application provides a battery comprising the wide temperature range electrolyte as described in the aforementioned embodiment.

[0018] In a fourth aspect, the present application provides an electrical device comprising a battery as described in the aforementioned embodiment.

[0019] Compared with the prior art, the present invention has the following advantages: The method for preparing a wide-temperature-range electrolyte involves reacting fluoroethylene carbonate, perfluorohexanoic acid, and diethyl tetrafluoroborate to form a functional solution with a dynamic hydrogen-bond network. This significantly reduces the viscosity of the electrolyte at low temperatures, improves the lithium ion transport efficiency, and thus enhances the low-temperature performance of the battery. Simultaneously, carbon nanofibers are surface-modified with trimethyl borate and sulfuric acid to form a boron-functionalized B-CNF material with surface defects. This material maintains structural and performance stability at high temperatures, reduces side reactions, and improves the high-temperature stability of the electrolyte. Furthermore, the B-CNF material is embedded in a functional solution containing a lithium salt to form a wide-temperature-range electrolyte with three-dimensional lithium-conducting channels, providing a path for rapid lithium ion transport and further improving the electrolyte's ion conductivity. This preparation method effectively balances high and low-temperature performance, resolving the difficulty of simultaneously meeting high and low-temperature requirements in existing technologies. It significantly improves the overall performance of the battery across a wide temperature range and is suitable for applications requiring high temperature adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0021] Figure 1 Schematic diagram of the process for preparing the wide temperature range electrolyte in the embodiment of the present application. DETAILED DESCRIPTION

[0022] The embodiments of the present invention will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all commercially available conventional products.

[0023] refer to Figure 1 In an embodiment of the present application, a method for preparing a wide temperature range electrolyte is provided, comprising: Step S1: mixing fluoroethylene carbonate, perfluorohexanoic acid and diethyl tetrafluoroborate to react to obtain a functional solution having a hydrogen bond dynamic network.

[0024] In this step, fluoroethylene carbonate (FEC), perfluorohexanoic acid (PFHA), and diethyl tetrafluoroborate (TFEB) are mixed and reacted in a certain ratio under specific conditions. This mixing reaction forms a functional solution with a dynamic hydrogen bond network.

[0025] A dynamic hydrogen bond network is a network structure formed by interconnected hydrogen bonds. Hydrogen bonds are weak chemical bonds, typically formed by electrostatic attraction between highly electronegative atoms (such as oxygen, nitrogen, and fluorine) and hydrogen atoms. The hydrogen bonds in a dynamic hydrogen bond network can constantly break and reform, making the entire network highly dynamic and adaptable.

[0026] The formation and breaking of hydrogen bonds are reversible, and this dynamic change occurs. The strength and number of hydrogen bonds vary under different temperatures and environments. For example, at low temperatures, hydrogen bonds may become more stable, while at high temperatures, they may break more easily. The dynamic hydrogen bond network is highly sensitive to temperature changes. At low temperatures, hydrogen bond strength may increase, thereby enhancing the network's stability; at high temperatures, hydrogen bond breaking may make the network more flexible. Furthermore, changes in one hydrogen bond in the hydrogen bond network can influence the structure and properties of surrounding hydrogen bonds. This synergistic effect gives hydrogen bond networks complex dynamic behavior.

[0027] In electrolytes, dynamic hydrogen bond networks can significantly enhance the electrolyte's ion conductivity. By designing electrolytes with dynamic hydrogen bonds, low viscosity can be maintained at low temperatures, thereby improving lithium-ion transport efficiency. At high temperatures, the dynamic reorganization of hydrogen bonds can reduce electrolyte volatilization and decomposition.

[0028] The dynamic hydrogen bond network is temperature-responsive, meaning hydrogen bonds can break and reform at different temperatures. This property allows the electrolyte to have a low viscosity at low temperatures (≤30 mPa·s, -40°C), maintaining good fluidity and facilitating lithium ion transport. It also results in a low vapor pressure at high temperatures (≤5 kPa, 80°C), which helps reduce electrolyte volatilization and decomposition, maintaining battery stability.

[0029] In the wide-temperature-range electrolyte provided in this embodiment, a dynamic hydrogen bond network is formed through a mixed reaction of fluoroethylene carbonate, perfluorohexanoic acid, and diethyl tetrafluoroborate. This network structure is temperature-responsive, dynamically adjusting the strength and number of hydrogen bonds at different temperatures, thereby optimizing the electrolyte's performance.

[0030] Step S2: using trimethyl borate and sulfuric acid to perform surface modification treatment on the carbon nanofibers to form a B-CNF material having surface defects and modified with boron functional groups.

[0031] In this step, the carbon nanofibers are surface modified so that they not only have surface defects but also have boron functional groups modified.

[0032] Among them, carbon nanofibers (CNF) are a type of carbon material with special structure and properties, usually a one-dimensional nanomaterial composed of carbon atoms in a graphitized or graphitized form.

[0033] After this surface modification, defects form on the carbon nanofiber surface and the fibers are modified with boron functional groups, becoming B-CNF materials. These surface defects and the presence of boron functional groups can generate strong interactions with lithium ions, thereby enhancing the adsorption capacity of lithium ions, providing more channels and sites for lithium ion transport, and helping to improve the conductivity of the electrolyte.

[0034] Step S3, embedding the B-CNF material into the hydrogen bond dynamic network of the functional solution containing lithium salt to obtain a wide temperature range electrolyte with three-dimensional lithium conductive channels.

[0035] In this step, the surface-modified B-CNF material is added to a functional solution containing lithium salt, and the B-CNF material is embedded in the hydrogen bond dynamic network through treatment methods such as stirring and ultrasound.

[0036] When embedded in a dynamic hydrogen bond network, B-CNF materials form three-dimensional lithium-conducting channels. This three-dimensional structure provides a more convenient and efficient path for lithium-ion transport, enabling lithium ions to move more quickly within the electrolyte, thereby further improving the electrolyte's ion conductivity and maintaining good conductivity over a wide temperature range (from low to high temperatures). This meets the requirements for lithium-ion batteries to be used under different temperature conditions and improves battery performance and service life.

[0037] In this example, a three-dimensional lithium-conducting channel is formed by embedding surface-modified boron-doped carbon nanofibers (B-CNFs) into a functional solution with a dynamic hydrogen-bonded network. This structure provides an efficient, continuous, and spatially organized channel for lithium-ion transport, significantly enhancing the electrolyte's ionic conductivity, particularly across a wide temperature range (low and high).

[0038] The mechanism of action of the three-dimensional lithium-conducting channels is that they provide a continuous transport path for lithium ions, thereby reducing the transport resistance of lithium ions in the electrolyte and significantly improving the ionic conductivity of the electrolyte. At the same time, the temperature responsiveness of the hydrogen bond dynamic network ensures that the electrolyte maintains a low viscosity at low temperatures and a low vapor pressure at high temperatures, thereby maintaining the stability of the electrolyte over a wide temperature range. Furthermore, the surface defects and boron functional groups of boron-doped carbon nanofibers (B-CNFs) can strongly interact with lithium ions, forming a stable interfacial layer, further enhancing the performance of the electrolyte under high and low temperature conditions.

[0039] In some embodiments, the step S1, mixing fluoroethylene carbonate, perfluorohexanoic acid, and diethyl tetrafluoroborate to obtain a functional solution having a hydrogen bond dynamic network, comprises: Step S11, mixing fluoroethylene carbonate, perfluorohexanoic acid, and diethyl tetrafluoroborate according to a molar ratio of (0.5-1.5):(3.5-4.5):(7.5-8.5) to obtain a first mixed solution; In this step, fluoroethylene carbonate (FEC), perfluorohexanoic acid (PFHA), and diethyl tetrafluoroborate (TFEB) are mixed at a specific molar ratio under specific reaction conditions. For example, fluoroethylene carbonate (FEC) (5 mmol), perfluorohexanoic acid (PFHA) (20 mmol), and diethyl tetrafluoroborate (TFEB) (40 mmol) are mixed.

[0040] The molar ratio of the fluoroethylene carbonate, perfluorohexanoic acid, and diethyl tetrafluoroborate can be (0.5-1.5):(3.5-4.5):(7.5-8.5). For example, the molar ratio of fluoroethylene carbonate can be 0.5, 1, 1.5, etc.; the molar ratio of perfluorohexanoic acid can be 3.5, 4, 4.5, etc.; and the molar ratio of diethyl tetrafluoroborate can be 7.5, 8, 8.5, etc.

[0041] This step can be performed in a container with protective gas, such as a glove box. The reason is that compounds such as fluoroethylene carbonate (FEC), perfluorohexanoic acid (PFHA) and diethyl tetrafluoroborate (TFEB) are generally sensitive to water and oxygen. Water and oxygen may react with these compounds, resulting in a decrease in the purity of the reaction products or the generation of unnecessary by-products. Carrying out the reaction in an anhydrous and oxygen-free environment can ensure the stability and reproducibility of the reaction. The presence of water and oxygen may interfere with the formation of hydrogen bonds or destroy the structure of the hydrogen bond network, thereby affecting the performance of the electrolyte.

[0042] Furthermore, the dew point of the environment during the mixing process is ≤-60° C. Furthermore, the humidity of the environment during the mixing process may be <0.1 ppm.

[0043] Step S12: subjecting the first mixed solution to a first heating and stirring treatment under reduced pressure to obtain the functional solution.

[0044] In this step, the first mixed liquid can be transferred to a vacuum reactor for treatment. The reduced pressure condition can be a condition under a specific pressure, for example, stirring treatment under near-vacuum conditions, so as to obtain a functional solution.

[0045] In this step, the pressure in the reactor can be controlled under specific conditions, for example, the reactor is kept under reduced pressure, with the pressure ≤ 10 -3 The heating temperature can be a constant temperature of 80°C with heating and stirring for at least 8 hours to form a hydrogen bond dynamic network having a temperature-responsive hydrogen bond breaking / reorganization capability, a low-temperature viscosity of ≤30 mPa·s (-40°C), and a high-temperature vapor pressure of ≤5 kPa (80°C).

[0046] In summary, the method steps in this embodiment provide a method for converting fluoroethylene carbonate, perfluorohexanoic acid and diethyl tetrafluoroborate into a functional solution having a hydrogen bond dynamic network by mixing and heating and stirring. The mixing uniformity ensures that the three compounds are fully mixed to provide uniform reactants for subsequent reactions. The reaction is carried out under a vacuum environment to avoid interference from impurities and moisture. In terms of temperature and time control, constant temperature stirring is performed at 80°C for 8 hours to ensure the full formation of the hydrogen bond dynamic network. The formed hydrogen bond dynamic network is temperature responsive and can maintain good ion conductivity in a wide temperature range, laying the foundation for the subsequent embedding of B-CNF materials and the formation of three-dimensional lithium-conducting channels.

[0047] In some embodiments, the step S2, surface modification treatment, comprises: Step S21 , placing the carbon nanofiber in a mixed solution of trimethyl borate and sulfuric acid, and subjecting the mixture to a reflux reaction under heating conditions to obtain nano high-flux carbon.

[0048] In this step, the carbon nanofibers are placed in a mixed solution of trimethyl borate and sulfuric acid, and refluxed under heating conditions to obtain nano high-flux carbon.

[0049] Carbon nanofibers (CNF) can be placed in a mixed solution of trimethyl borate (B(OCH3)3) and concentrated sulfuric acid (H2SO4). The volume ratio of the mixed solution can be 3:1.

[0050] Furthermore, a reflux reaction can be performed at 120°C for 6 hours. The 120°C temperature promotes the chemical reaction between trimethyl borate and sulfuric acid and the carbon nanofibers. The reflux reaction can be performed for 6 hours to ensure sufficient reaction progress and to form sufficient surface defects and boron functional groups on the carbon nanofiber surfaces.

[0051] Surface modification treatment with trimethyl borate and sulfuric acid creates defects on the carbon nanofiber surface and modifies it with boron functional groups. These surface defects and boron functional groups enhance the adsorption capacity of lithium ions and provide more active sites for lithium ion transport. After the reflux reaction, the surface structure of the carbon nanofiber changes, forming nano-high-flux carbon (B-CNF) with a boron content of 5-8at%.

[0052] Step S22, washing, drying and ball milling the nano high-flux carbon to obtain the B-CNF material.

[0053] In this step, the nano high-flux carbon is washed, dried and ball-milled to obtain the B-CNF material.

[0054] The washing treatment may be performed at least three times with water and / or an organic solvent. For example, the nano high-flux carbon can be washed three times with deionized water to remove surface impurities such as trimethyl borate and sulfuric acid. The nano high-flux carbon can then be washed three times with an organic solvent (such as ethanol) to further remove surface impurities.

[0055] The drying process may be a reduced-pressure drying process, for example, vacuum drying in an argon protective environment (dew point ≤ -60°C).

[0056] After drying, the nano high flux carbon needs to be tested for its graphitization degree (Id / Ig>1), particle size (Dv10>15nm, DV max <100 nm) and interlayer spacing (d002 is 0.35 nm~0.55 nm).

[0057] The ball milling treatment can be performed by ball milling the dried nano high-flux carbon. A planetary ball mill can be used, using zirconium oxide balls (3 mm in diameter), a ball milling speed of 500 rpm, and a ball milling time of at least 4 hours.

[0058] After ball milling, the agglomerate size (average particle size) of nano high-flux carbon should be ≤200 nm.

[0059] For example, carbon nanofibers (CNF) are used, which have a graphitization degree (Id / Ig > 1), a particle size (Dv10 > 20 nm, dV max <100nm), specific surface area 350 m 2 / g ~800 m 2 / g, d002 (0.35nm~0.55 nm), the carbon nanofibers were placed in a mixed solution of trimethyl borate and concentrated sulfuric acid, and refluxed at 120 ° C for 6 hours to form nano high-flux carbon, and the nano high-flux carbon was washed three times with deionized water and then washed three times with ethanol to remove impurities on the surface of the nano high-flux carbon, and then vacuum dried under argon protection (dew point ≤ -60 ° C). After drying, the graphitization degree (Id / Ig>1), particle size (Dv10>15nm, DV max <100nm), specific surface area 370 m 2 / g ~850m 2 / g, d002 is 0.35nm~0.55nm.

[0060] Among them, the nano high-flux carbon with a boron content of 3 wt% to 5 wt% has a boron content of 5 at% to 8 at%, a diameter of 90 ± 15 nm, and a molar volume density of borate groups grafted on the surface of 1.6 × 10 -3 mmol / m 2 ~5.5×10 -3 mmol / m2 , and after ball milling, a dispersion with an average size of ≤200nm is formed.

[0061] In some embodiments, the step S3 of embedding the B-CNF material into the hydrogen bond dynamic network of the functional solution containing lithium salt to obtain a wide temperature range electrolyte having three-dimensional lithium-conducting channels comprises: Step S31 : pre-mixing the lithium salt and the functional solution to obtain a second mixed solution.

[0062] In this step, the lithium salt and the functional solution are pre-mixed to obtain a second mixed solution. The lithium salt [such as lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and lithium difluorooxalatoborate (LiDFOB)] can be added to the prepared functional solution.

[0063] Furthermore, the pre-mixing treatment can be performed by magnetic stirring, wherein the stirring speed of the mixing treatment is 800 rpm; the time of the pre-mixing treatment is not less than 10 minutes to ensure that the lithium salt and the functional solution are fully mixed.

[0064] Furthermore, the concentration of the lithium salt in the wide temperature range electrolyte is 1M~5M; The premixing process allows the lithium salt to be evenly dispersed in the functional solution, providing a uniform mixing system for subsequent steps. The premixed solution can better combine with the B-CNF material, thereby improving the overall conductivity of the electrolyte.

[0065] Step S32: adding the B-CNF material to the second mixed liquid and performing ultrasonic treatment to obtain a mixed material.

[0066] In the above steps, the B-CNF material is added to the second mixed solution and ultrasonically treated to obtain a mixture. Specifically, the surface-modified B-CNF material (3-5 wt%) can be gradually added to the second mixed solution to avoid excessive concentration in some areas.

[0067] Furthermore, the concentration of the added B-CNF material in the wide temperature range electrolyte is 0.3 wt% to 0.5 wt%, for example, 0.3 wt%, 0.4 wt%, 0.5 wt%, and so on.

[0068] The mixed solution can be treated with ultrasound (500W, 40kHz), preferably for at least 30 minutes. Ultrasonic treatment can disrupt secondary agglomeration of the B-CNF material, resulting in the formation of monodisperse nanoparticles in the electrolyte. Ultrasonic treatment improves the B-CNF material's dispersion in the electrolyte, enhancing its stability and ionic conductivity.

[0069] Step S33 , subjecting the mixture to a second heating and stirring treatment under reduced pressure to obtain the wide temperature range electrolyte.

[0070] In the above steps, the mixture is subjected to a second heating and stirring treatment under reduced pressure to obtain a wide temperature range electrolyte.

[0071] The reduced pressure state may be a state close to vacuum, and further, the pressure of the reduced pressure state is ≤10 -3 Pa.

[0072] The specific operation can be carried out in a vacuum reactor. The mixed material after ultrasonic treatment is transferred to the vacuum reactor to ensure that the pressure in the reactor is controlled at ≤10 -3 Pa.

[0073] Furthermore, the heating temperature of the second heating and stirring treatment is 80° C. The stirring time of the second heating and stirring treatment is not less than 2 hours.

[0074] For example, heating and stirring at a constant temperature of 80°C for 2 hours ensures that the B-CNF material is fully embedded in the hydrogen bond dynamic network and that the reaction proceeds fully. Reduced pressure conditions allow the reaction to proceed in a vacuum environment to avoid interference from impurities and moisture.

[0075] Through heating and stirring, the B-CNF material is embedded in a dynamic hydrogen-bonded network, forming three-dimensional lithium-conducting channels. This structure provides an efficient and continuous transport path for lithium ions, significantly improving the ionic conductivity of the electrolyte. The resulting three-dimensional lithium-conducting channels enhance the electrolyte's performance over a wide temperature range, ensuring low viscosity at low temperatures and low vapor pressure at high temperatures, thereby improving the battery's low-temperature endurance and high-temperature storage life.

[0076] In summary, this example embeds B-CNF materials into a functional solution containing lithium salts. This involves premixing, ultrasonication, and heating and stirring to form three-dimensional lithium-conducting channels. These steps ensure that the B-CNF materials are evenly dispersed in the electrolyte and tightly integrated with the dynamic hydrogen bond network, significantly improving the performance of the wide-temperature electrolyte.

[0077] In some embodiments, the lithium salt is a composite lithium salt prepared from lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and lithium difluorooxalatoborate (LiDFOB); In this example, a composite lithium salt consisting of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and lithium difluorooxalatoborate (LiDFOB) was chosen because this combination significantly improves the electrolyte's ionic conductivity over a wide temperature range while optimizing its temperature adaptability. LiTFSI exhibits high conductivity and low viscosity at low temperatures, which helps improve lithium ion transport efficiency; while LiDFOB exhibits good thermal stability and reduces side reactions at high temperatures.

[0078] In addition, lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and lithium difluorooxalatoborate (LiDFOB) as dual-coordinate lithium salts can minimize the coordination number of the solvent, increase the redox window, and thus enhance the dual stability of the high-potential positive electrode and the low-potential negative electrode.

[0079] The synergistic effect of the two [lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and lithium difluorooxalatoborate (LiDFOB)] not only further enhances the electrolyte's ionic conductivity and redox window, but also forms a stable interface layer on the electrode surface, reducing interfacial impedance, thereby improving the battery's cycling stability and fast charge and discharge performance. The use of this composite lithium salt enables the electrolyte to maintain efficient and stable performance under both low and high temperature conditions, significantly improving the overall performance and service life of the lithium-ion battery.

[0080] The preparation method of the composite lithium salt comprises: mixing lithium bis(trifluoromethylsulfonyl)imide and lithium difluorooxalatoborate, and performing ultrasonic dispersion treatment and stirring treatment to obtain the composite lithium salt; Wherein, the composite lithium salt has at least one of the following characteristics: A. The molar ratio of lithium bis(trifluoromethylsulfonyl)imide to lithium difluorooxalatoborate in the composite lithium salt is (3.5-4.5):(0.5-1.5).

[0081] B. The conductivity of the composite lithium salt is greater than 4.5 ms / cm.

[0082] For example, LiTFSI (1.2 M) and LiDFOB (0.3 M) were added in batches, and ultrasonic dispersion (power 500 W, frequency 40 kHz) and magnetic stirring (speed 800 rpm) were alternately used for 3 hours to ensure that the conductivity was >4.5 ms / cm to obtain a composite lithium salt.

[0083] In the above, lithium bis(trifluoromethylsulfonyl)imide and lithium difluorooxalatoborate are prepared in a molar ratio of (3.5-4.5):(0.5-1.5). For example, the ratio of lithium bis(trifluoromethylsulfonyl)imide can be 3.5, 4, 4.5, etc.; the ratio of lithium bis(trifluoromethylsulfonyl)imide can be 0.5, 1, 1.5, etc.

[0084] In an embodiment of the present application, a wide temperature range electrolyte is provided, which is prepared by the preparation method of the wide temperature range electrolyte as described in any of the aforementioned embodiments.

[0085] In an embodiment of the present application, a battery is provided, comprising the wide temperature range electrolyte as described in the aforementioned embodiment.

[0086] In addition to the wide-temperature-range electrolyte, the above-mentioned battery may also include, but is not limited to, a positive electrode (including active material, conductive agent, binder, and aluminum foil current collector), a negative electrode (including active material, conductive agent, binder, and copper foil current collector), a separator (used to separate the positive and negative electrodes and allow lithium ions to pass through), a casing (providing packaging and physical protection), a current collector (used for current collection and conduction), and other components (such as tabs, safety valves, temperature sensors, etc.). These components work together to ensure efficient and safe operation of the battery over a wide temperature range, while also improving its overall performance and service life.

[0087] In an embodiment of the present application, an electrical device is provided, comprising the battery as described in the aforementioned embodiment.

[0088] The aforementioned "electrical equipment" refers to devices that use batteries (particularly those containing wide-temperature-range electrolytes) as their primary or auxiliary power source. These devices are widely used in various fields, including but not limited to electric vehicles, hybrid vehicles, portable electronic devices (such as smartphones, tablets, and laptops), wearable devices (such as smartwatches and health monitoring bracelets), medical devices (such as portable medical monitoring devices and pacemakers), energy storage systems (for grid energy storage and solar / wind energy storage), drones, power tools, and other equipment that requires efficient and reliable power support. By using batteries with wide-temperature-range electrolytes, these electrical equipment can maintain high performance and safety across a wider temperature range, thereby meeting the stringent requirements of different application scenarios.

[0089] The present invention is further described below by way of specific examples. However, it should be understood that these examples are merely provided for more detailed description and are not to be construed as limiting the present invention in any form.

[0090] Table 1. Comparison of main parameters in the examples and comparative examples

[0091] In Table 1, FEC stands for fluoroethylene carbonate; PFHA stands for perfluorohexanoic acid; TFEB stands for diethyl tetrafluoroborate; LiTFSI stands for lithium bis(trifluoromethylsulfonyl)imide; LiDFOB stands for lithium difluorooxalatoborate; and M stands for molar concentration, which represents the amount of substance contained per liter of solution.

[0092] Example 1 In this embodiment, a wide-temperature-range electrolyte was prepared, and a battery cell was obtained based on the wide-temperature-range electrolyte.

[0093] Experimental methods: (1) Preparation of functional solution: Mix fluoroethylene carbonate (FEC), perfluorohexanoic acid (PFHA), and diethyl tetrafluoroborate (TFEB), protect with argon (dew point ≤ -60 °C), and vacuum reactor (pressure ≤ 10 -3 Pa) in a constant temperature of 80°C with stirring for 8 hours to form a functional solution containing a dynamic hydrogen bond cross-linking network.

[0094] Fourier transform infrared spectroscopy (FTIR): at 3200 cm -1 ~3500cm -1 A broad peak (hydrogen bond OH stretching vibration) appears at , and the peak position blue-shifts by 10 cm at low temperature (-40 ° C). -1 , indicating that the hydrogen bond flexibility is enhanced‌.

[0095] Molecular dynamics simulation (MD): The average lifetime of hydrogen bonds decreased from 12 ps at 25°C to 4 ps at -40°C, proving that the dynamic reconstruction ability of hydrogen bonds is improved at low temperatures.

[0096] (2) Preparation of a composite lithium salt: In a glove box (water and oxygen content less than 10 ppm), LiTFSI (lithium bis(trifluoromethylsulfonyl)imide) and LiDFOB (lithium difluorooxalatoborate) were combined to obtain a composite lithium salt with a total molar concentration of 4 M. Alternating sonication (500 W, 40 kHz) and magnetic stirring (800 rpm) were used for 3 hours to ensure complete dissociation of the lithium salt. The electrolyte concentration reached 6.8 mS / cm at -40°C (conventional electrolyte: 0.1 mS / cm); at 80°C, it reached 14.2 mS / cm (conventional system: 18.5 mS / cm).

[0097] (3) Preparation of B-CNF material: In a reactor, 12 g of carbon nanofiber (CNF) with a graphitization degree (Id / Ig=1.52), a particle size (Dv10=20 nm, dV max =80nm), d002=0.4lnm, specific surface area=560m 2 / g, the carbon nanofibers were refluxed at 120 ° C for 6 hours in a mixed solution of 60 mL of trimethyl borate and 20 mL of concentrated sulfuric acid (the volume ratio of trimethyl borate and concentrated sulfuric acid in the mixed solution was 3:1) to obtain nano high-flux carbon with a boron doping amount of 6 at%; the B-CNFs were washed three times with deionized water and then washed three times with ethanol to remove surface impurities of the nano high-flux carbon, and vacuum dried under argon protection (dew point ≤ -60 ° C). After drying, the degree of graphitization (Id / Ig = 1.53), particle size (Dv10 = 18 nm, dVmax = 75 nm), d002 = 0.41 nm, and specific surface area = 580 m 2 / g.

[0098] After planetary ball milling (zirconia balls, 3 mm, 500 rpm, 4 hours), B-CNF material was obtained. Aggregate size was ≤200 nm (dynamic light scattering detection), and Raman spectrum: Id / Ig=0.92, indicating that surface defect sites and borate groups synergistically enhance lithium ion adsorption capacity.

[0099] X-ray photoelectron spectroscopy analysis: The B1s peak is located at 192.5 eV (BO bond), which is consistent with the F in the electrolyte. - The interaction energy is reduced to 0.25 eV (density functional theory calculation).

[0100] (4) Preparation of wide temperature range electrolyte: The functional solution obtained in step (1) and the composite lithium salt obtained in step (2) were premixed with magnetic stirring (800 rpm) for 10 minutes, and then B-CNF material (0.4 wt%) was gradually added to avoid excessive local concentration.

[0101] Ultrasonic treatment at 500W / 40kHz for 30 minutes was used to destroy the secondary agglomeration of B-CNF and promote its monodispersity in the electrolyte.

[0102] The mixture was transferred to a vacuum reactor (pressure ≤ 10 -3 Pa), and stirred at 80 °C for 2 h to embed B-CNF into a dynamic hydrogen bond network and form a three-dimensional lithium-conducting channel, thereby obtaining a wide temperature range electrolyte.

[0103] (5) Preparation of battery cells: A 20Ah square shell dry cell was prepared using a lithium manganese oxide system (active material loading of 97% + conductive agent 1.5% + PVDF 1.5%) for the positive electrode and a graphite system (active material loading of 96.5% + conductive agent 0.5% + (SBR + CMC) 3.0% in total) for the negative electrode. Among them, SBR is Styrene-Butadiene Rubber, CMC is Carboxymethyl Cellulose, and PVDF is Polyvinylidene Fluoride.

[0104] Example 2 In the examples, the preparation of a wide-temperature-range electrolyte and a battery cell prepared based on the wide-temperature-range electrolyte were respectively carried out.

[0105] Experimental methods: The method used in this embodiment is basically the same as that in Example 1, and the differences are with reference to the process parameters in Table 1.

[0106] Example 3 In this embodiment, a wide-temperature-range electrolyte was prepared, and a battery cell was obtained based on the wide-temperature-range electrolyte.

[0107] The experimental method is basically the same as that used in Example 1, with reference to the process parameters in Table 1 for differences.

[0108] Example 4 In this embodiment, a wide-temperature-range electrolyte was prepared, and a battery cell was obtained based on the wide-temperature-range electrolyte.

[0109] The experimental method is basically the same as that used in Example 1, except that in step (3), 72 g of carbon nanofiber (CNF) was refluxed at 120 °C for 6 h in 60 mL of trimethyl borate / 20 mL of concentrated sulfuric acid (volume ratio 3:1) to obtain nano high-flux carbon, and the boron doping amount was changed to 1 at%.

[0110] Example 5 In this embodiment, a wide-temperature-range electrolyte was prepared, and a battery cell was obtained based on the wide-temperature-range electrolyte.

[0111] The experimental method is basically the same as that used in Example 1, except that in step (3), 6 g of carbon nanofiber (CNF) is refluxed at 120°C for 6 hours in 60 mL of trimethyl borate / 20 mL of concentrated sulfuric acid (volume ratio 3:1) to obtain nano high-flux carbon, and the boron doping amount is changed to 12 at%.

[0112] Example 6 In this embodiment, a wide-temperature-range electrolyte was prepared, and a battery cell was obtained based on the wide-temperature-range electrolyte.

[0113] The experimental method is basically the same as that used in Example 1, except that the process parameters in Table 1 are used.

[0114] Comparative Example 1 This comparative example uses essentially the same method as Example 1, except that in step (3), 12 g of carbon nanofibers (CNF) are refluxed in 60 mL of trimethyl borate / 60 mL of concentrated sulfuric acid (volume ratio 1:1) at 120°C for 6 hours to obtain nano-high-flux carbon. In this example, due to excessive amounts of concentrated sulfuric acid, the temperature was locally too high during the preparation process, resulting in uneven boron doping in the material, with varying amounts of 3 at% to 30 at% in different locations.

[0115] Comparative Example 2 The method used in this comparative example is basically the same as that in Example 1, and the differences are shown in Table 1.

[0116] Comparative Example 3 The method used in this comparative example is basically the same as that in Example 1, except that a single lithium salt, 4.95 mol LiTFSI, is used.

[0117] Comparative Example 4 The method used in this comparative example is basically the same as that in Example 1, and the differences are shown in Table 1.

[0118] Comparative Example 5 In this embodiment, an electrolyte was prepared, and a battery cell was obtained based on the electrolyte.

[0119] The experimental method uses a conventional lithium manganese oxide electrolyte (the mass ratio of each component is: EC:EMC:VC:LiPF6=25.5:59.4:2:13.1), the parameters such as the molar concentration of the lithium salt are referred to Table 1, and the conductivity is 8.1mS / cm.

[0120] Comparative Example 6 In this embodiment, an electrolyte was prepared, and a battery cell was obtained based on the electrolyte.

[0121] The experimental method uses a conventional low-temperature electrolyte of lithium manganese oxide (the mass ratio of each component is: EC:EMC:DMC:VC:LiPF6:LiFSi=25:33.4:25:2:10.0:4.6). Parameters such as the molar concentration of the lithium salt are referred to Table 1, and the conductivity is 9.8mS / cm.

[0122] Test experiment: 1. Experimental materials and equipment: (1) Battery cells: The battery cells prepared in Examples 1 to 6 and Comparative Examples 1 to 6 were used.

[0123] (2) Test equipment: Electrochemical testing system: used to measure the battery's electrochemical performance parameters such as discharge DC resistance (DCR) and discharge capacity retention rate. It can accurately control the current, voltage and other conditions during the charge and discharge process and record relevant data.

[0124] Constant temperature chamber: used to simulate different temperature environments, such as -20℃, 45℃, 60℃, etc., to test the performance of the battery at different temperatures, ensure the stability and accuracy of the temperature, and keep the battery in the set temperature environment during the test.

[0125] Charge and discharge cycle tester: It is used in conjunction with the electrochemical testing system to perform battery cycle charge and discharge tests to evaluate performance indicators such as the battery's capacity maintenance during multiple charge and discharge processes.

[0126] 2. Test method: (1) Low temperature performance test: Each group of battery cells is placed in a constant temperature box set at -20°C. After the temperature of the battery cells stabilizes, a discharge test is performed using an electrochemical test system at a discharge rate of 1C.

[0127] The discharge DC internal resistance (DCR) of each group of batteries was recorded and compared with the initial internal resistance (R0) of the battery to obtain the ratio of the discharge DC internal resistance to R0. This ratio is used to evaluate the change in internal resistance of the battery at low temperatures and reflect the difficulty of processes such as ion transport within the battery.

[0128] At the same time, the capacity retention rate of each battery group when discharged to the termination voltage at -20°C is recorded, that is, the percentage of discharge capacity to rated capacity. This is to measure the discharge performance of the battery in a low-temperature environment and understand the proportion of electricity that the battery can release under low-temperature conditions. The -20°C 1C discharge test method is to charge the battery cell at room temperature (25±2°C) at 1C to 4.2V, cut off at 0.05C, and place it for 30 minutes. Then, discharge it at 1C to 2.7V and place it for 30 minutes. The initial capacity is recorded, and then the battery cell is fully charged. After fully charging, it is placed in a -20°C±2°C constant temperature charger and discharger for 6 hours. Then, it is discharged at 1C to 2.7V and the discharge capacity is recorded. The discharge capacity at -20°C is compared with the discharge capacity at room temperature to obtain the capacity retention rate.

[0129] The -20℃ DCR ​​test is to charge the battery cell at room temperature (25±2℃) at 1C to 4.2V, then cut off at 0.05C, let it sit for 30 minutes, then discharge it at 1C to 2.7V, let it sit for 30 minutes, record the initial capacity, and then fully charge it. After fully charging, put it in a -20℃±2℃ constant temperature charger and discharger and let it stand for 6 hours, then discharge it at 0.2C for 10 seconds and 1C for 1 second, and cycle it to 2.7V; record the discharge DC internal resistance of the full discharge SOC process, and take the discharge DC internal resistance at SOC50% for comparison.

[0130] (2) High-temperature storage performance test: Each group of fully charged battery cells was placed in a constant temperature box set at 60°C for a 7-day high-temperature storage test.

[0131] After storage, the battery cells are removed and the capacity retention rate is measured using an electrochemical testing system. This is the percentage of the battery capacity after storage to the battery capacity before storage, in order to evaluate the capacity loss of the battery after long-term storage in a high-temperature environment.

[0132] The battery is then charged and discharged for a cycle to restore it to its normal operating state, and its capacity recovery rate is measured again, which is the percentage of the battery capacity after recovery to the battery capacity before storage. This is used to understand the capacity ratio that can be recovered after a certain recovery treatment after high-temperature storage, reflecting the reversibility of the battery. The test method for 7-day full-charge storage at 60°C is to charge the battery cell at room temperature (25±2°C) at 1C to 4.2V, then cut off at 0.05C, leave it for 30 minutes, discharge it at 1C to 2.7V, leave it for 30 minutes, record the initial capacity, and then fully charge it. After full charging, place it in a 60°C±2°C constant temperature box for 7 days. After storage, cool it at room temperature for 6 hours, and cycle 3 times according to the initial capacity process. The smaller capacity of the second or third cycle is taken as the maintenance capacity, and compared with the initial capacity to obtain the capacity maintenance rate.

[0133] (3) Cycle life test: Each group of battery cells is subjected to a cyclic charge and discharge test under set temperature conditions (such as 45°C), and is cycled at a certain charge and discharge rate (such as 1C charge to 4.2V, 0.05C cut-off, 30 minutes standby, 1C discharge to 2.7V, 30 minutes standby) until the battery capacity retention rate reaches 80%.

[0134] The number of cycles when each group of batteries reaches a capacity retention rate of 80% is recorded to evaluate the cycle life of the battery under specific temperature conditions and reflect the stability of the battery during repeated charge and discharge.

[0135] 3. Test results: Table 2. Comparison of battery performance between examples and comparative examples

[0136] In Table 2, at -20°C, DCR(SOC50%)R0=36mΩ.

[0137] analyze: (1) Low temperature performance test: Discharge DC internal resistance (DCR): The discharge DC internal resistance of Examples 1-6 was all below 1 R0, with Example 2 having the lowest, at 0.41 R0. Comparative Examples 1-6 all exhibited a discharge DC internal resistance above 0.63 R0, with Comparative Example 5 having the highest, at R0. This demonstrates that the wide-temperature-range electrolyte of this application can significantly reduce the internal resistance of the battery and improve ion transport efficiency at low temperatures. This is because the application achieves a balance between low viscosity and high ion conductivity at low temperatures by constructing a dynamic hydrogen bond network and embedding modified B-CNF materials. The dynamic hydrogen bond network disintegrates hydrogen bonds at low temperatures, promoting the solvation of lithium ions at low temperatures. It also exhibits good flexibility and can quickly respond to ion transport requirements. LiTFSI has a high degree of dissociation, high ionic conductivity, and high kinetics, while the embedding of B-CNF materials further optimizes the ion transport pathway and reduces resistance to ion transport.

[0138] 1C discharge capacity retention rate: The 1C discharge capacity retention rates of Examples 1 to 6 are all above 86%, of which Example 2 has the highest 1C discharge capacity retention rate of 99%, while the 1C discharge capacity retention rates of Comparative Examples 1 to 6 are all below 92%, with Comparative Example 6 having the lowest 1C discharge capacity retention rate of 77%. This shows that the wide temperature range electrolyte of the present application can effectively maintain the discharge capacity of the battery at low temperatures and improve the low temperature performance of the battery. This is because the electrolyte of the present application has a lower viscosity and a higher ionic conductivity at low temperatures, which can ensure the rapid and stable transmission of lithium ions at low temperatures, thereby improving the discharge capacity retention rate of the battery.

[0139] (2) High temperature storage performance test: 60℃ 7-day storage capacity retention rate: The 60℃ 7-day storage capacity retention rates of Examples 1 to 6 are all above 91.2%, of which Example 2 has the highest 60℃ 7-day storage capacity retention rate of 96.9%, while the 60℃ 7-day storage capacity retention rates of Comparative Examples 1 to 6 are all lower than 93.6%, and the 60℃ 7-day storage capacity retention rate of Comparative Example 3 is the lowest, at 89.1%. This shows that the wide temperature range electrolyte of the present application can effectively maintain the capacity of the battery at high temperatures and reduce capacity loss. This is because the present application can increase the boiling point of the electrolyte at high temperatures through the presence of a dynamic hydrogen bond network, avoiding the production of gas due to side reactions of the electrolyte at high temperatures. The use of LiTFSI and LiDFOB double lithium salts can form a relatively stable two-fold coordination structure, which can effectively inhibit the decomposition of lithium salts at high temperatures, and the B-CNF material formed by surface modification treatment has good stability at high temperatures, which can reduce the occurrence of side reactions, thereby improving the high temperature stability of the electrolyte and thus improving the high temperature storage performance of the battery.

[0140] 60℃ 7-day storage capacity recovery rate: The 60℃ 7-day storage capacity recovery rates of Examples 1 to 6 are all above 93.3%, among which Example 2 has the highest 60℃ 7-day storage capacity recovery rate of 98.6%, while the 60℃ 7-day storage capacity recovery rates of Comparative Examples 1 to 6 are all lower than 93.6%, and the 60℃ 7-day storage capacity recovery rate of Comparative Example 3 is the lowest, at 90.9%. This shows that the wide temperature range electrolyte of the present application can better restore the capacity of the battery after high-temperature storage and improve the reversibility of the battery. This is because the electrolyte of the present application has a low vapor pressure and good chemical stability at high temperatures, which can reduce the volatilization and decomposition of the electrolyte, thereby better restoring the capacity of the battery after high-temperature storage.

[0141] (3) Cycle life test The number of cycles at 45°C to 80% capacity maintenance rate for Examples 1 to 6 is all above 532 cycles, among which Example 2 has the most cycles at 45°C to 80% capacity maintenance rate, which is 690 cycles, while the number of cycles at 45°C to 80% capacity maintenance rate for Comparative Examples 1 to 6 is all less than 530 cycles, and the number of cycles at 45°C to 80% capacity maintenance rate for Comparative Example 3 is the least, which is 420 cycles. This shows that the wide temperature range electrolyte of the present application can significantly improve the cycle life of the battery at 45°C and reduce the capacity attenuation during the cycle. This is because the electrolyte of the present application can maintain stable ion conductivity and electrode interface stability during the cycle, reduce side reactions and irreversible loss of lithium ions during the cycle, and thus improve the cycle life of the battery.

[0142] in conclusion: (1) Adjustment of the solvent ratio affects the formation of the hydrogen bond network: As can be seen from Examples 1 to 6, the functional solutions obtained by mixing different molar ratios of fluoroethylene carbonate (FEC), perfluorohexanoic acid (PFHA) and diethyl tetrafluoroborate (TFEB) have a significant effect on battery performance. When the molar ratio of FEC:PFHA:TFEB is 1:4:8 (Example 2), the low-temperature performance and high-temperature storage performance of the battery are both optimal, indicating that the hydrogen bond dynamic network formed at this time has the best ion conductivity and temperature adaptability. In Comparative Example 4, the molar ratio of FEC:PFHA:TFEB is 4:5:4. Compared with the example, the performance of the battery has declined, which further proves the importance of the solvent ratio on the formation of the hydrogen bond network.

[0143] (2) Advantages of the combination of lithium salt LiTFSI and LiDFOB: Examples 1 to 6 all use a composite lithium salt of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and lithium difluorooxalatoborate (LiDFOB). Compared with Comparative Examples 2 and 3, the low-temperature performance and high-temperature storage performance of the battery are significantly better than those of the battery using only a single lithium salt LiTFSI or a conventional lithium salt. This shows that LiTFSI has a high degree of dissociation and ionic conductivity, but the two-fold coordination of its anion with the solvent is unstable and easily induces side reactions; while LiDFOB can form a stable two-fold coordination structure with LiTFSI, inhibiting the decomposition of the lithium salt, thereby improving the electrochemical stability window of high voltage and high temperature, and improving the overall performance of the battery.

[0144] (3) Effect of boron doping amount and addition amount of B-CNF material on performance: The boron doping amount of B-CNF material in Examples 1 to 6 is about 6 at%, and the addition amount is between 0.3wt% and 0.5wt%, and the battery performance is good. However, the boron doping amount in Comparative Example 1 is uneven, resulting in a decrease in battery performance; the boron doping amounts in Comparative Examples 4 and 5 are 1 at% and 12 at%, respectively, and the battery performance is also reduced. This shows that when the boron doping amount is too low, the B-CNF material has no obvious effect on improving the interface and cannot effectively improve the ion conductivity; when the boron doping amount is too high, the porous structure of the B-CNF material may collapse and lose its function. At the same time, the addition amount of B-CNF material will also affect the performance of the electrolyte. Too little addition will affect the ionic conductivity, and too much addition will cause the electrolyte to settle and affect the stability. The addition amount of B-CNF material in Examples 1 to 6 has been optimized to fully exert its effect on improving the performance of the electrolyte and improve the low-temperature performance and high-temperature stability of the battery.

[0145] (4) Through the above analysis, it can be seen that the wide temperature range electrolyte and its preparation method of the present application can effectively solve the problem of poor performance of existing lithium-ion batteries under extreme temperature conditions. By constructing a hydrogen bond dynamic network and embedding modified B-CNF materials, a balance between low viscosity at low temperature and high stability at high temperature is achieved, while improving the ion conductivity performance, significantly enhancing the performance of the battery in a wide temperature range, and meeting the high temperature adaptability requirements. The electrolyte of the present application has low internal resistance and high discharge capacity retention at low temperatures, good capacity retention and recovery rate at high temperatures, and can maintain stable performance during the cycle process, extending the service life of the battery, and providing strong technical support for the application of lithium-ion batteries in a wider temperature range.

[0146] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a wide temperature range electrolyte, characterized in that: include: Fluoroethylene carbonate, perfluorohexanoic acid and diethyl tetrafluoroborate are mixed and reacted to obtain a functional solution with a dynamic hydrogen bond network; The carbon nanofibers were surface-modified using trimethyl borate and sulfuric acid to form B-CNF materials with surface defects and modified with boron functional groups. The B-CNF material is embedded in the hydrogen bond dynamic network of the functional solution containing lithium salt to obtain a wide temperature range electrolyte with three-dimensional lithium conductive channels.

2. The method for preparing a wide temperature range electrolyte according to claim 1, wherein: The method comprises mixing fluoroethylene carbonate, perfluorohexanoic acid and diethyl tetrafluoroborate to obtain a functional solution having a hydrogen bond dynamic network, comprising: Mixing fluoroethylene carbonate, perfluorohexanoic acid, and diethyl tetrafluoroborate in a molar ratio of (0.5-1.5):(3.5-4.5):(7.5-8.5) to obtain a first mixed solution; The first mixed solution is subjected to a first heating and stirring treatment under reduced pressure to obtain the functional solution.

3. The method for preparing a wide temperature range electrolyte according to claim 2, wherein: The first heating and stirring treatment under reduced pressure has at least one of the following conditions: A. the stirring time is at least 8 hours; B. the heating temperature is 80°C; C. the first heating and stirring treatment is maintained in a reduced pressure state; D. the pressure during the first heating and stirring treatment is ≤10 -3 Pa; and / or, The dew point of the environment during the mixing process is ≤-60°C; and / or, The humidity in the environment during the mixing process is less than 0.1 ppm.

4. The method for preparing a wide temperature range electrolyte according to claim 1, wherein: The surface modification treatment comprises: The carbon nanofibers are placed in a mixed solution of trimethyl borate and sulfuric acid, and refluxed under heating conditions to obtain nano high-flux carbon; The nano high-flux carbon is subjected to washing, drying and ball milling to obtain the B-CNF material.

5. The method for preparing a wide temperature range electrolyte according to claim 4, wherein: The heating condition is a temperature of 120° C.; and / or, The reflux reaction time is not less than 6 hours; and / or, The washing treatment is washing with water and / or an organic solvent at least 3 times; and / or, The drying process is a reduced pressure drying process; and / or, The average particle size of the B-CNF material after the ball milling treatment is ≤200 nm.

6. The method for preparing a wide temperature range electrolyte according to claim 1, wherein: The method of embedding the B-CNF material into the hydrogen bond dynamic network of the functional solution containing lithium salt to obtain a wide temperature range electrolyte having three-dimensional lithium-conducting channels comprises: Premixing the lithium salt and the functional solution to obtain a second mixed solution; adding the B-CNF material to the second mixed liquid, and ultrasonically treating the mixture to obtain a mixed material; The mixed material is subjected to a second heating and stirring treatment under reduced pressure to obtain the wide temperature range electrolyte.

7. The method for preparing a wide temperature range electrolyte according to claim 6, wherein: The stirring speed of the mixing process is 800 rpm; and / or, The pre-mixing treatment time is not less than 10 minutes; and / or, The concentration of the lithium salt in the wide temperature range electrolyte is 1M~5M; The concentration of the added B-CNF material in the wide temperature range electrolyte is 0.3wt% to 0.5wt%; and / or, The ultrasonic treatment time is not less than 30 minutes; and / or, The pressure in the decompression state is ≤10 -3 Pa; and / or, The heating temperature of the second heating and stirring treatment is 80° C.; and / or, The stirring time of the second heating and stirring treatment is not less than 2 hours.

8. The method for preparing a wide temperature range electrolyte according to claim 1, wherein: The lithium salt is a composite lithium salt prepared from lithium bis(trifluoromethylsulfonyl)imide and lithium difluorooxalatoborate; The preparation method of the composite lithium salt comprises: mixing lithium bis(trifluoromethylsulfonyl)imide and lithium difluorooxalatoborate, and performing ultrasonic dispersion treatment and stirring treatment to obtain the composite lithium salt; Wherein, the composite lithium salt has at least one of the following characteristics: A. The molar ratio of lithium bis(trifluoromethylsulfonyl)imide to lithium difluorooxalatoborate in the composite lithium salt is (3.5-4.5):(0.5-1.5); B. The conductivity of the composite lithium salt is greater than 4.5 ms / cm.

9. A wide temperature range electrolyte, characterized in that: The electrolyte is prepared by the method for preparing a wide temperature range electrolyte according to any one of claims 1 to 8.

10. A battery, characterized in that: Comprising the wide temperature range electrolyte as described in claim 9.

11. An electrical equipment, characterized in that: Comprising the battery of claim 10.

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