Electrolyte, single battery and energy storage device

Abstract

The invention provides an electrolyte, a single battery and an energy storage device. The electrolyte provided by the invention comprises an electrolyte salt, a first additive and a solvent, wherein the first additive is 2-first aryl-4-second aryl-5-third aryl imidazole.

Description

Technical Field

[0001] This application relates to the field of energy storage, specifically to an electrolyte, a single cell, and an energy storage device. Background Technology

[0002] With the development of the energy storage industry and the continuous advancement of lithium-ion battery technology, user scenarios such as wind and solar power generation are demanding lower lifespan degradation and longer service life for lithium-ion batteries.

[0003] During cycling, battery life degradation is primarily due to the reaction of lithium ions on the surface of the negative electrode, causing lithium to deposit as salts on the surface. On one hand, during charging, ester solvents are easily reduced on the low-potential surface of the negative electrode, reacting with lithium and consuming active lithium. On the other hand, lithium intercalation and deintercalation in the graphite negative electrode cause the interlayer spacing to continuously expand and shrink. This continuously stretches the solid electrolyte interphase (SEI) film on the surface of the negative electrode, exposing new graphite interfaces that come into contact with the electrolyte. The electrolyte then reacts continuously, leading to the loss of active lithium. These two side reactions result in rapid capacity decay and a short lifespan in batteries using this technology. Summary of the Invention

[0004] This application provides an electrolyte that, when applied to a single battery cell, can enable the single battery cell to have a higher high-temperature cycle capacity retention rate.

[0005] In a first aspect, embodiments of this application provide an electrolyte in which the mass fraction of 2-first aryl-4-second aryl-5-third arylimidazolium is 0.02% to 2%.

[0006] Furthermore, the mass fraction of 2-first aryl-4-second aryl-5-third arylimidazolium in the electrolyte is 0.2% to 0.7%.

[0007] Further, the first aryl group is at least one of phenyl, meta-substituted phenyl, para-substituted phenyl, and meta-para-substituted phenyl; the second aryl group is at least one of phenyl, meta-substituted phenyl, para-substituted phenyl, and meta-para-substituted phenyl; and the third aryl group is at least one of phenyl, meta-substituted phenyl, para-substituted phenyl, and meta-para-substituted phenyl.

[0008] Furthermore, in meta-substituted phenyl groups, the substituents are electron-withdrawing or conjugated groups; in para-substituted phenyl groups, the substituents are electron-withdrawing or conjugated groups; and in meta-para-substituted phenyl groups, the substituents are electron-withdrawing or conjugated groups.

[0009] Furthermore, the electron-withdrawing group includes one of halogen, trifluoromethyl, nitro, isocyanate, and isothiocyanate, and the conjugated group includes one of vinyl, ethynyl, and phenyl.

[0010] Further, the meta-substituted phenyl group includes one of the following: 3-halogen phenyl, 3-vinylphenyl, 3-ethynylphenyl, 3-trifluoromethylphenyl, 3-phenylphenyl, 3-nitrophenyl, 3-isocyanate phenyl, and 3-isothiocyanate phenyl;

[0011] The para-substituted phenyl group includes one of the following: 4-halogen phenyl, 4-vinylphenyl, 4-ethynylphenyl, 4-trifluoromethylphenyl, 4-phenylphenyl, 4-nitrophenyl, 4-isocyanate phenyl, and 4-isothiocyanate phenyl;

[0012] Meta- and para-substituted phenyl groups include one of the following: 3,4-dihalophenyl, 3,4-divinylphenyl, 3,4-diethynylphenyl, 3,4-ditrifluoromethylphenyl, 3,4-diphenylphenyl, 3,4-dinitrophenyl, 3,4-diisocyanate-based phenyl, 3,4-diisothiocyanate-based phenyl, 3,4,5-trihalophenyl, 3,4,5-trivinylphenyl, 3,4,5-triethynylphenyl, 3,4,5-tritrifluoromethylphenyl, 3,4,5-triphenylphenyl, 3,4,5-trinitrophenyl, 3,4,5-triisocyanate-based phenyl, and 3,4,5-triisothiocyanate-based phenyl.

[0013] Furthermore, the structural formula of 2-first aryl-4-second aryl-5-third arylimidazol is:

[0014]

[0015] Among them, R 1 H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups.

[0016] R 2 H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups.

[0017] R 3H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups.

[0018] R 4 H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups.

[0019] R 5 H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups.

[0020] R 6 H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups.

[0021] R 7 H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups.

[0022] R 8 H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups.

[0023] R 9 H, halogen, alkane with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy group with 1 to 5 carbon atoms, alkenyl group with 2 to 5 carbon atoms, alkynyl group with 2 to 5 carbon atoms, phenyl group, substituted phenyl group, nitro group, isocyanate group, isothiocyanate group.

[0024] Further, the first additive comprises at least one of: 2,4,5-triphenylimidazolium, 2,4,5-tris(4-fluorophenyl)imidazolium, 2,4,5-tris[(4-trifluoromethyl)phenyl]imidazolium, 2,4,5-tris(4-vinylphenyl)imidazolium, 2-phenylphenyl-4,5-diphenylimidazolium, 2,4,5-tris(4-isocyanate-phenyl)imidazolium, 2,4,5-tris(4-isothiocyanate-phenyl)imidazolium, and 2,4,5-tris(4-nitrophenyl)imidazolium.

[0025] Furthermore, the electrolyte also includes a second additive, which is at least one of cyclic carbonate additives and cyclic sulfate additives, and the mass fraction of the second additive in the electrolyte ranges from 0.1% to 5%.

[0026] Secondly, embodiments of this application also provide a single-cell battery, the single-cell battery comprising: the electrolyte, positive electrode, separator, and negative electrode as described in embodiments of this application.

[0027] Thirdly, embodiments of this application also provide an energy storage device, which includes at least the single-cell battery described in embodiments of this application.

[0028] The electrolyte in this embodiment includes a first additive, which is 2-first aryl-4-second aryl-5-third arylimidazolium. The first additive has three benzene rings and one imidazole ring, resulting in a lower LUMO energy level and a higher HOMO energy level, thus providing a narrower electrochemical window. This allows the first additive to preferentially undergo reduction on the surface of the negative electrode active layer compared to solvent molecules and conventional film-forming additives, participating in the formation of the SEI film and forming a nitrogen-rich SEI film. The nitrogen-rich SEI film exhibits higher temperature tolerance (i.e., better high-temperature tolerance), better protecting the negative electrode active layer at high temperatures. Therefore, adding the first additive to the electrolyte can significantly improve the high-temperature cycle capacity retention of a single battery cell. Furthermore, the N-3 atom in the imidazole ring of the first additive (i.e., the nitrogen atom on the imidazole ring that does not participate in double bond formation) has unconjugated lone pairs of electrons. The electron-donating conjugation effect of the benzene ring can enhance the basicity of the N-3 atom, enabling it to participate in Li... + The solvated structure makes it easier for the lithium to migrate to the surface of the negative electrode and undergo a reduction reaction. Furthermore, the interfacial film constructed by the first additive can reduce the side reactions at the interface between the positive and negative electrodes during the cycling of a single cell, reduce the consumption of active lithium, and thus enable the single cell to have a higher cycle capacity retention rate. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the structure of an energy storage system according to an embodiment of this application.

[0031] Figure 2 This is a schematic diagram of the structure of an energy storage system according to another embodiment of this application.

[0032] Figure 3 This is a schematic diagram of the structure of an energy storage system according to another embodiment of this application.

[0033] Figure 4 This is a schematic diagram of the structure of an energy storage device according to an embodiment of this application.

[0034] Figure 5 This is a schematic diagram of the structure of a single battery cell according to an embodiment of this application.

[0035] Figure 6 For the application of an embodiment of the single cell battery Figure 5 A schematic diagram of the cross-sectional structure along the AA direction.

[0036] Figure 7 This is a cross-sectional view of the positive electrode sheet according to an embodiment of this application.

[0037] Figure 8 This is a cross-sectional view of the negative electrode sheet according to one embodiment of the application.

[0038] Explanation of reference numerals in the attached figures:

[0039] 100 - Energy storage system; 110 - First power conversion device; 120 - First user load; 130 - Second user load; 140 - High-voltage cable; 150 - Second power conversion device; 160 - Photovoltaic-energy storage-charging station; 170 - Automobile; 200 - Energy storage device; 300 - Single cell battery; 310 - Positive electrode sheet; 311 - Positive current collector; 312 - Positive active layer; 320 - Separator; 330 - Negative electrode sheet; 331 - Negative current collector; 332 - Negative active layer; 340 - Housing; 350 - End cap assembly. Detailed Implementation

[0040] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0041] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0042] The technical solutions in the embodiments of this application will now be described with reference to the accompanying drawings.

[0043] It should be noted that, for ease of explanation, the same reference numerals denote the same components in the embodiments of this application, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments.

[0044] Because the energy we need is highly time- and space-dependent, in order to utilize energy rationally and improve energy efficiency, it is necessary to store one form of energy in the same way or by converting it into another, and then release it in a specific energy form based on future application needs. Currently, the main way to generate green electricity is to develop green energy sources such as photovoltaics and wind power to replace fossil fuels.

[0045] Currently, the generation of green electricity generally relies on solar, wind, and hydropower. However, wind and solar power are generally characterized by strong intermittency and large fluctuations, which can cause grid instability, insufficient power during peak demand periods, and excessive power during off-peak periods. Unstable voltage can also damage the power grid. Therefore, insufficient electricity demand or insufficient grid capacity may lead to the problem of "wind and solar curtailment." Solving these problems requires energy storage. This involves converting electrical energy into other forms of energy through physical or chemical means and storing it. When needed, this energy can be converted back into electrical energy and released. Simply put, energy storage is like a large "power bank," storing electrical energy when solar and wind power are abundant and releasing the stored electricity when needed.

[0046] Taking electrochemical energy storage as an example, this solution provides an energy storage device for use in energy storage systems. The energy storage device is equipped with a set of chemical batteries, which mainly use the chemical elements in the batteries as energy storage media. The charging and discharging process is accompanied by the chemical reaction or change of the energy storage media. Simply put, the electrical energy generated by wind and solar energy is stored in the chemical batteries. When the use of external electrical energy reaches its peak, the stored electricity is released for use, or transferred to places with a shortage of electricity for use.

[0047] Current energy storage applications are quite widespread, including generation-side energy storage, grid-side energy storage, and consumption-side energy storage. The corresponding types of energy storage devices include:

[0048] (1) Large-scale energy storage power stations (composed of multiple prefabricated energy storage modules) applied to wind power and photovoltaic power stations can help renewable energy power generation meet grid connection requirements and improve the utilization rate of renewable energy. As a high-quality active / reactive power source in the power supply side, the energy storage power station realizes the load matching of power in time and space, enhances the renewable energy absorption capacity, reduces instantaneous power changes, reduces the impact on the power grid, improves the problem of new energy power generation absorption, and is of great significance in power grid system backup, alleviating peak load power supply pressure and peak regulation and frequency regulation.

[0049] (2) The energy storage prefabricated cabin applied on the grid side mainly functions as peak regulation, frequency regulation and grid congestion relief. In terms of peak regulation, it can realize peak shaving and valley filling of electricity load, that is, charging the energy storage battery when the electricity load is low and releasing the stored electricity during the peak electricity load period, thereby achieving a balance between power production and consumption.

[0050] (3) Small energy storage cabinets applied to the electricity consumption side mainly function as self-consumption of electricity, peak-valley price arbitrage, capacity cost management, and improvement of power supply reliability. Depending on the application scenario, electricity consumption side energy storage can be divided into industrial and commercial energy storage cabinets, household energy storage devices, energy storage charging piles, etc., which are generally used in conjunction with distributed photovoltaics. Industrial and commercial users can use energy storage for peak-valley price arbitrage and capacity cost management. In the electricity market implementing peak-valley pricing, by charging the energy storage system when the electricity price is low and discharging the energy storage system when the electricity price is high, peak-valley price arbitrage can be achieved, reducing electricity costs. In addition, industrial enterprises subject to two-part tariffs can use energy storage systems to store energy during off-peak hours and discharge during peak loads, thereby reducing peak power and the maximum demand declared, achieving the goal of reducing capacity charges. Household photovoltaics with energy storage can improve the level of self-consumption of electricity. Due to high electricity prices and poor power supply stability, the demand for household photovoltaic installations is driven. Given that photovoltaic power generation occurs during the day, while user load is generally higher at night, configuring energy storage can better utilize photovoltaic power, improve self-consumption levels, and reduce electricity costs. Furthermore, energy storage is needed in areas such as communication base stations and data centers for backup power.

[0051] In some embodiments, see Figure 1 , Figure 1 This is a schematic diagram of the structure of an energy storage system 100 according to an embodiment of this application. Figure 1 The embodiments are illustrated using a home energy storage scenario in user-side energy storage as an example. The energy storage device 200 of this application is not limited to the home energy storage scenario.

[0052] This application provides an energy storage system 100, which includes a first power conversion device 110 (photovoltaic panel), a first user load 120 (household lighting fixture), a second user load 130 (e.g., household appliances such as air conditioners), and an energy storage device 200. The energy storage device 200 is a small energy storage box that can be wall-mounted on an outdoor wall. However, the energy storage device 200 is not limited to wall mounting and can also be placed in a user's residence in other ways. Specifically, the photovoltaic panel can convert solar energy into electrical energy during periods of low electricity prices, and the energy storage device 200 stores this electrical energy and supplies it to lighting fixtures and household appliances during peak electricity prices, or provides power during power outages / power interruptions.

[0053] In some embodiments, see Figure 2 , Figure 2 This is a schematic diagram of the structure of an energy storage system 100 according to another embodiment of this application, and this application Figure 2 The embodiments are illustrated using a shared energy storage scenario on the generation / distribution side as an example. The energy storage device 200 of this application is not limited to its generation / distribution side energy storage scenario.

[0054] This application provides an energy storage system 100, which includes: a high-voltage cable 140, a first power conversion device 110, a second power conversion device 150, and an energy storage device 200 provided in this application. In some embodiments of the power generation scenario, the second power conversion device 150 can be a wind power conversion device. Since the electricity generated by wind power conversion is volatile, random, and intermittent, the unstable electricity output by the wind power conversion device can be stored in the energy storage device 200 through grid connection. The energy storage device 200 is connected to the high-voltage cable 140 and outputs smooth electricity to the power consumption side of the distribution network, realizing peak shaving and frequency regulation, and stable grid operation; or, wind power conversion... The power conversion device is always connected to the high-voltage cable 140. Under normal power generation conditions, the power output of the wind power conversion device is supplied to the power consumption side of the distribution network through the high-voltage cable 140. When the current power load is low and the wind power conversion device generates excess power, the excess power is first stored in the energy storage device 200 to reduce wind and solar curtailment rates and improve the problem of new energy power generation consumption. When the power load is high, the power grid issues an instruction to transmit the power stored in the energy storage device 200 together with the high-voltage cable 140 in grid-connected mode to supply power to the power consumption side. This provides the power grid with various services such as peak shaving, frequency regulation, and backup, giving full play to the peak shaving role of the power grid, promoting peak shaving and valley filling, and alleviating the power supply pressure of the power grid.

[0055] In some embodiments on the distribution network side, the first power conversion device 110 can be a photovoltaic panel, and the energy storage device 200 is connected to the high-voltage cable 140 and installed downstream of the high-voltage cable 140 between the user load and the photovoltaic power conversion device. The electrical energy output by the photovoltaic power conversion device is stored in the energy storage device 200, which can respond in a timely manner to act as a backup power source when the power grid / distribution network fails; or, it can provide power supply support to alleviate line congestion when the high-voltage cable 140 transmission line is blocked, and to delay the economic pressure caused by the expansion of the power grid / distribution capacity when the power grid is planned to be expanded.

[0056] In some embodiments, see Figure 3 , Figure 3 This is a schematic diagram of the structure of an energy storage system 100 according to another embodiment of this application, and this application Figure 3 The embodiments are illustrated using an industrial and commercial energy storage scenario as an example. The energy storage device 200 of this application is not limited to industrial and commercial energy storage scenarios.

[0057] This application provides an energy storage system 100, which includes: an energy storage device 200, a high-voltage cable 140, a factory equipped with a first power conversion device 110, a photovoltaic-energy storage-charging station 160, and a vehicle 170. In some embodiments of industrial and commercial scenarios, the first power conversion device 110 can be a photovoltaic panel, which converts solar energy into electrical energy and stores it in the energy storage device 200 in the factory. In the event of a power grid failure, the energy storage device 200 provides power to ensure the safe and stable operation of the factory without interruption. Alternatively, when the factory's power load is high, the power grid issues an instruction to transmit the electricity stored in the energy storage device 200 in conjunction with the high-voltage cable 140 in a grid-connected mode to supply the factory with electricity, providing various services such as peak shaving / frequency regulation and backup for the power grid operation. In addition, the first power conversion device 110 can also convert solar energy into electrical energy and store it in the energy storage device 200 of the photovoltaic-energy storage-charging station 160, which can directly charge the vehicle 170, making it fast and convenient.

[0058] Optionally, the first power conversion device 110 may include, but is not limited to, a photovoltaic panel, and the second power conversion device 150 may include, but is not limited to, a wind power conversion device. The first power conversion device 110 and the second power conversion device 150 can convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy, and mechanical energy into electrical energy.

[0059] Please see Figure 4 , Figure 4 This is a schematic diagram of the structure of an energy storage device 200 according to an embodiment of this application.

[0060] Optionally, the energy storage device 200 includes one or more individual battery cells 300.

[0061] The term "multiple" refers to two or more, such as, but not limited to, 2, 5, 10, 30, 50, 100, 200, 300, 400, 800, 1000, etc. The number of individual battery cells 300 included in the energy storage device 200 can be determined based on the rated capacity of the individual battery cells 300 and the rated capacity to be achieved by the energy storage device 200.

[0062] Optionally, the energy storage device 200 can be used, but is not limited to, energy storage power stations, hydropower / thermal / wind power generation systems, solar power generation systems, mobile power systems, smart home systems, or temporary power supply systems, and is also applied in multiple fields such as data centers, military equipment, aerospace, charging piles, and electric vehicles.

[0063] Optionally, the energy storage device 200 may include, but is not limited to, battery integrated systems such as single-cell batteries, or battery modules, battery packs, battery clusters, power banks, energy storage cabinets / prefabricated energy storage containers, etc. In other words, when the energy storage device 200 includes a single-cell battery 300, the energy storage device 200 can exist in the form of a single-cell battery 300. When the energy storage device 200 includes multiple single-cell batteries 300, the multiple single-cell batteries 300 can be stacked, arranged, assembled, etc., to form battery integrated systems such as battery modules, battery packs, battery clusters, power banks, energy storage cabinets / energy storage containers; that is, the energy storage device 200 exists in the form of battery integrated systems such as battery modules, battery packs, battery clusters, power banks, energy storage cabinets / energy storage containers, etc. The actual application form of the energy storage device 200 provided in this application embodiment can be, but is not limited to, the listed products, and can also be other application forms. This application embodiment does not strictly limit the application form of the energy storage device 200. This application embodiment only illustrates the case where the energy storage device 200 is a multi-cell battery (i.e., multiple single-cell batteries 300).

[0064] Optionally, the single cell 300 can be, but is not limited to, at least one of cylindrical, square, prismatic, or other shaped cells.

[0065] Optionally, the single cell 300 can be a rechargeable battery, which refers to a single cell 300 that can be recharged after discharge to activate the active materials and continue to be used. The single cell 300 can be a lithium-ion battery, sodium-ion battery, sodium-lithium-ion battery, lithium metal battery, sodium metal battery, lithium-sulfur battery, magnesium-ion battery, nickel-metal hydride battery, nickel-cadmium battery, lead-acid battery, etc., and this application does not specifically limit it.

[0066] Understandably, the single cell 300 can be, but is not limited to, a sodium battery, a lithium battery, a magnesium battery, a nickel-hydrogen battery, a nickel-cadmium battery, a lead-acid battery, etc. In the following embodiments of this application, the single cell 300 is illustrated using a lithium battery as an example, and should not be construed as limiting the single cell 300 and electrolyte of the embodiments of this application.

[0067] Figure 5 This is a schematic diagram of the structure of a single cell battery 300 according to an embodiment of this application. Figure 6 For an embodiment of the application, a single cell 300 is provided. Figure 5 A schematic diagram of the cross-sectional structure along the AA direction.

[0068] Please see Figure 5 and Figure 6 This application provides a single-cell battery 300, which includes a positive electrode 310, a separator 320, a negative electrode 330, and an electrolyte.

[0069] Understandably, the positive electrode 310 and the negative electrode 330 are located on opposite sides of the separator 320, that is, the separator 320 is located between the positive electrode 310 and the negative electrode 330, separating the positive electrode 310 and the negative electrode 330.

[0070] It should be noted that the positive electrode 310, the separator 320, and the negative electrode 330 are all at least partially immersed in the electrolyte.

[0071] Understandably, the positive electrode 310, the separator 320, and the negative electrode 330 are sequentially stacked to form an electrode assembly. The electrode assembly can be, but is not limited to, a wound structure, a stacked structure, etc., and this application does not specifically limit it in this regard.

[0072] Figure 7 This is a cross-sectional view of the positive electrode 310 according to an embodiment of this application.

[0073] Please see Figure 7 Optionally, the positive electrode 310 further includes a positive current collector 311, and the positive active layer 312 is disposed on the surface of the positive current collector 311.

[0074] It should be noted that the positive electrode active layer 312 can be disposed on one or more surfaces (greater than or equal to two surfaces) of the positive electrode current collector 311. In the schematic diagram of the accompanying drawings of this application, the positive electrode active layer 312 is disposed on two opposite surfaces of the positive electrode current collector 311 as an example, which should not be construed as a limitation on the positive electrode active layer 312 and the positive electrode sheet 310 of the embodiments of this application.

[0075] Optionally, the positive current collector 311 can be, but is not limited to, an aluminum sheet, aluminum foil, etc.

[0076] Optionally, the positive electrode active layer 312 includes a positive electrode active material, a positive electrode conductive agent, a positive electrode binder, and a positive electrode thickener.

[0077] Optionally, the positive electrode conductive agent may be, but is not limited to, at least one of conductive carbon black (SP), acetylene black, carbon nanotubes, carbon fibers, graphene, etc.

[0078] Optionally, the positive electrode active material can be, but is not limited to, lithium iron phosphate.

[0079] Optionally, the positive electrode binder may be, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), polyhexanefluoropropylene, and polymerized styrene-butadiene rubber (SBR).

[0080] Optionally, the positive electrode thickener may be, but is not limited to, at least one of sodium carboxymethyl cellulose (CMC), polyacrylamide (PAM), and polymethyl methacrylate (PMA).

[0081] Optionally, the diaphragm 320 can be, but is not limited to, at least one of polypropylene membrane (PP membrane), polyethylene membrane (PE membrane), ceramic diaphragm, glass fiber membrane, etc.

[0082] Figure 8 This is a cross-sectional view of the negative electrode 330 according to an embodiment of the application.

[0083] Please see Figure 8 Optionally, the negative electrode 330 includes a negative electrode current collector 331 and a negative electrode active layer 332, wherein the negative electrode active layer 332 is disposed on the surface of the negative electrode current collector 331.

[0084] It should be noted that the negative electrode active layer 332 can be disposed on one or more surfaces (greater than or equal to two surfaces) of the negative electrode current collector 331. In the schematic diagram of the accompanying drawings of this application, the negative electrode active layer 332 is disposed on two opposite surfaces of the negative electrode current collector 331 as an example, which should not be construed as a limitation on the negative electrode active layer 332 and the negative electrode sheet 330 of the embodiments of this application.

[0085] Optionally, the negative current collector 331 can be, but is not limited to, at least one of copper foil, copper sheet, aluminum foil, and aluminum sheet.

[0086] Optionally, the negative electrode active layer 332 includes a negative electrode active material, a negative electrode conductive agent, a negative electrode binder, and a negative electrode thickener.

[0087] Optionally, the negative electrode active material can be, but is not limited to, graphite.

[0088] Optionally, the negative electrode conductive agent may be, but is not limited to, at least one of conductive carbon black (SP), acetylene black, carbon nanotubes, carbon fibers, graphene, etc.

[0089] Optionally, the negative electrode binder may be, but is not limited to, at least one of polyvinylidene fluoride, polyamide, polyacrylonitrile, polyacrylate, polyethylene ether, polymethyl methacrylate, polyhexafluoropropylene, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber, etc.

[0090] Optionally, the negative electrode thickener may be, but is not limited to, at least one of polyacrylamide (PAM) and polymethyl methacrylate (PMA).

[0091] Please see again Figure 5 and Figure 6 Optionally, the single-cell battery 300 further includes a housing 340 and an end cap assembly 350, the housing 340 and the end cap assembly 350 forming a closed receiving cavity (not shown) for housing the electrolyte, the positive electrode 310, the separator 320, and the negative electrode 330. Understandably, the end cap assembly 350 electrically connects the positive electrode 310 and the negative electrode 330, leading them out for electrical connection to external devices or other single-cell batteries 300.

[0092] With the development of the energy storage industry and the continuous advancement of lithium-ion battery technology, user scenarios such as wind and solar power generation are demanding lower lifespan degradation and longer service life for lithium-ion batteries.

[0093] During cycling, battery life degradation is primarily due to the reaction of lithium ions on the surface of the negative electrode, causing lithium to deposit as salts on the surface. On one hand, during charging, ester solvents are easily reduced on the low-potential surface of the negative electrode, reacting with lithium and consuming active lithium. On the other hand, lithium intercalation and deintercalation in the graphite negative electrode cause the interlayer spacing to continuously expand and shrink. This continuously stretches the solid electrolyte interphase (SEI) film on the surface of the negative electrode, exposing new graphite interfaces that come into contact with the electrolyte. The electrolyte then reacts continuously, leading to the loss of active lithium. These two side reactions result in rapid capacity decay and a short lifespan in batteries using this technology.

[0094] This application provides an electrolyte comprising an electrolyte salt, a first additive, and a solvent, wherein the first additive is 2-first aryl-4-second aryl-5-third arylimidazolium.

[0095] It should be noted that the first aryl, second aryl, and third aryl groups may be the same; they may be different; or they may be partially the same and partially different. For example, the first aryl, second aryl, and third aryl groups may all be the same; or the first aryl and second aryl groups may be the same, but the first aryl and third aryl groups may be different; or the first aryl and second aryl groups may be different, but the second aryl and third aryl groups may be the same.

[0096] The electrolyte in this embodiment includes a first additive, which is 2-first aryl-4-second aryl-5-third arylimidazolium. The first additive has three benzene rings and one imidazole ring, resulting in a lower LUMO energy level and a higher HOMO energy level, thus providing a narrower electrochemical window. This allows the first additive to preferentially undergo reduction on the surface of the negative electrode active layer 332 compared to solvent molecules and conventional film-forming additives, participating in the formation of the SEI film and forming a nitrogen-rich SEI film. The nitrogen-rich SEI film has higher temperature tolerance (i.e., better high-temperature tolerance), and can better protect the negative electrode active layer 332 at high temperatures. Therefore, adding the first additive to the electrolyte can significantly improve the high-temperature cycle capacity retention of the single-cell battery 300. Furthermore, the N-3 atom in the imidazole ring of the first additive (i.e., the nitrogen atom on the imidazole ring that does not participate in double bond formation) has unconjugated lone pairs of electrons. The electron-donating conjugation effect of the benzene ring can enhance the basicity of the N-3 atom, enabling it to participate in Li... + The solvated structure makes it easier for the lithium to migrate to the surface of the negative electrode 330 and undergo a reduction reaction. Furthermore, the interfacial film constructed by the first additive can reduce the side reactions at the interface between the positive electrode 310 and the negative electrode 330 during the cycling of the single cell 300, reduce the consumption of active lithium, and thus enable the single cell 300 to have a higher cycle capacity retention rate.

[0097] In some embodiments, the mass fraction of 2-first aryl-4-second aryl-5-third arylimidazolium in the electrolyte is 0.02% to 2%.

[0098] In the embodiments of this application, when the numerical range a to b is involved, unless otherwise specified, the numerical value can be any value between a and b, including the endpoint value a and the endpoint value b.

[0099] In the embodiments of this application, when referring to content, amount added, etc., unless otherwise specified, they all refer to mass content (i.e. mass fraction).

[0100] Specifically, the mass fraction of 2-first aryl-4-second aryl-5-third arylimidazolium in the electrolyte can be, but is not limited to, 0.02%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, etc.

[0101] In this embodiment, if the mass fraction of 2-first aryl-4-second aryl-5-third aryl imidazole in the electrolyte is too low, although 2-first aryl-4-second aryl-5-third aryl imidazole can improve the high-temperature stability of the SEI film of the single cell 300, the formed SEI film cannot effectively protect the negative electrode 330, resulting in poor improvement. If the mass fraction of 2-first aryl-4-second aryl-5-third aryl imidazole in the electrolyte is too high, the SEI film formed on the surface of the negative electrode active layer 332 of the negative electrode 330 will be too thick, increasing the impedance of the single cell 300, reducing the kinetic performance of the single cell 300, and easily causing lithium plating in the single cell 300 during cycling, consuming active lithium, and reducing the high-temperature cycle capacity retention rate of the single cell 300.

[0102] Furthermore, the mass fraction of 2-first aryl-4-second aryl-5-third aryl imidazole in the electrolyte is 0.2% to 0.7%. This allows 2-first aryl-4-second aryl-5-third aryl imidazole to better form a nitrogen-rich SEI film, improving the high-temperature stability of the SEI film, exhibiting a high high-temperature cycling capacity retention rate, and also enabling the SEI film to have a suitable thickness, resulting in low impedance and high kinetic performance.

[0103] In some embodiments, the first aryl group is at least one of phenyl, meta-substituted phenyl, para-substituted phenyl, and meta-para-substituted phenyl; the second aryl group is at least one of phenyl, meta-substituted phenyl, para-substituted phenyl, and meta-para-substituted phenyl; and the third aryl group is at least one of phenyl, meta-substituted phenyl, para-substituted phenyl, and meta-para-substituted phenyl.

[0104] It should be noted that the meta-substituted phenyl group can be, but is not limited to, at least one of 3-position substitution and 5-position substitution.

[0105] It should be noted that meta- and para-substituted phenyl refers to phenyl with substituents at both the meta and para positions; for example, 3,4-disubstituted phenyl and 3,4,5-trisubstituted phenyl.

[0106] Using a first additive with these substituents as an electrolyte additive allows for better preferential reduction of the first additive on the surface of the negative electrode active layer 332 of the negative electrode 330, resulting in a higher nitrogen content in the SEI film, improved high-temperature resistance of the SEI film, and enhanced high-temperature cycle capacity retention of the single cell 300. Furthermore, compared to 2-substituted phenyl and 3-substituted phenyl, phenyl and 4-substituted phenyl have lower steric hindrance, allowing for better surface reaction on the negative electrode 330 and further improving the high-temperature cycle capacity retention of the single cell 300. In other words, compared to a first additive with 2-substituted phenyl and 3-substituted phenyl, a first additive with phenyl and 4-substituted phenyl provides a better improvement in the high-temperature cycle capacity retention of the single cell 300.

[0107] In some embodiments, the substituent in meta-substituted phenyl groups is an electron-withdrawing group or a conjugated group; the substituent in para-substituted phenyl groups is an electron-withdrawing group or a conjugated group; and the substituent in meta-para-substituted phenyl groups is an electron-withdrawing group or a conjugated group.

[0108] In this embodiment, electron-withdrawing groups can better lower the LUMO energy level and raise the HOMO energy level of the first additive molecule, promoting the preferential reduction and decomposition of the first additive. This allows the first additive in the electrolyte to preferentially decompose and generate a nitrogen-containing SEI film, enhancing the density and mechanical strength of the SEI film and improving the cycle capacity retention of the single cell 300. Conjugated groups can give the first additive a lower LUMO energy level and a higher HOMO energy level, improving the stability and density of the SEI film, increasing the ionic conductivity of the SEI film, and improving the cycle capacity retention of the single cell 300.

[0109] In some embodiments, the electron-withdrawing group includes one of halogen, trifluoromethyl, nitro, isocyanate, and isothiocyanate.

[0110] In this embodiment, the halogen and trifluoromethyl fluorine atoms increase the LiF content in the SEI film, further enhancing its thermal stability and acid resistance, thus improving the 300-cycle high-temperature cycle capacity protection rate of the single-cell battery. The nitro group introduces Li3N into the formed SEI film, increasing its inorganic components, reducing its impedance, and improving its stability, thereby enhancing the 300-cycle high-temperature cycle capacity protection rate of the single-cell battery. Isocyanate or isothiocyanate groups can be reduced on the surface of the negative electrode 330 to form polyamide or polythioamide polymers, improving the stability of the SEI film. Furthermore, isothiocyanate groups may react to generate S-series lithium salt products (sulfide lithium salt products, such as Li2S, Li2SO3, Li2SO4, organic sulfides, etc.), thereby improving the chemical stability and mechanical properties of the SEI film, as well as its ionic conductivity and reducing interfacial impedance, further enhancing the 300-cycle high-temperature cycle capacity protection rate of the single-cell battery.

[0111] In some embodiments, the conjugated group includes one of vinyl, ethynyl, and phenyl.

[0112] In this embodiment, vinyl and acetylene groups can be reduced on the surface of the negative electrode 330 to generate products with a high degree of polymerization, which can further improve the stability of the SEI film and better enhance the high-temperature cycle capacity protection rate of the single cell after 300 cycles. The phenyl group is an inert group, which can enhance the stability of the molecular skeleton, thereby improving the high-temperature cycle capacity protection rate of the single cell after 300 cycles.

[0113] In some embodiments, the meta-substituted phenyl group includes one of: 3-halogen phenyl, 3-vinylphenyl, 3-ethynylphenyl, 3-trifluoromethylphenyl, 3-phenylphenyl, 3-nitrophenyl, 3-isocyanate phenyl, and 3-isothiocyanate phenyl;

[0114] The para-substituted phenyl group includes one of the following: 4-halogen phenyl, 4-vinylphenyl, 4-ethynylphenyl, 4-trifluoromethylphenyl, 4-phenylphenyl, 4-nitrophenyl, 4-isocyanate phenyl, and 4-isothiocyanate phenyl;

[0115] Meta- and para-substituted phenyl groups include one of the following: 3,4-dihalophenyl, 3,4-divinylphenyl, 3,4-diethynylphenyl, 3,4-ditrifluoromethylphenyl, 3,4-diphenylphenyl, 3,4-dinitrophenyl, 3,4-diisocyanate-based phenyl, 3,4-diisothiocyanate-based phenyl, 3,4,5-trihalophenyl, 3,4,5-trivinylphenyl, 3,4,5-triethynylphenyl, 3,4,5-tritrifluoromethylphenyl, 3,4,5-triphenylphenyl, 3,4,5-trinitrophenyl, 3,4,5-triisocyanate-based phenyl, and 3,4,5-triisothiocyanate-based phenyl.

[0116] Using a first additive with these substituents as an electrolyte additive allows for better preferential reduction of the first additive on the surface of the negative electrode active layer 332 of the negative electrode 330, resulting in a higher nitrogen content in the SEI film, improved high-temperature resistance of the SEI film, and enhanced high-temperature cycle capacity retention of the single cell 300. Furthermore, compared to 2-substituted phenyl and 3-substituted phenyl, phenyl and 4-substituted phenyl have lower steric hindrance, allowing for better surface reaction on the negative electrode 330 and further improving the high-temperature cycle capacity retention of the single cell 300. In other words, compared to a first additive with 2-substituted phenyl and 3-substituted phenyl, a first additive with phenyl and 4-substituted phenyl provides a better improvement in the high-temperature cycle capacity retention of the single cell 300.

[0117] In some embodiments, the structural formula of 2-first aryl-4-second aryl-5-third arylimidazol is:

[0118]

[0119] Among them, R 1 H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups.

[0120] R 2 H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups.

[0121] R 3H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups.

[0122] R 4 H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups.

[0123] R 5 H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups.

[0124] R 6 H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups.

[0125] R 7 H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups.

[0126] R 8 H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups.

[0127] R 9 H, halogen, alkane with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy group with 1 to 5 carbon atoms, alkenyl group with 2 to 5 carbon atoms, alkynyl group with 2 to 5 carbon atoms, phenyl group, substituted phenyl group, nitro group, isocyanate group, isothiocyanate group.

[0128] Understandably, the structural formula of the first aryl group is: The structural formula of the second aryl group is: The structural formula of the third aryl group is:

[0129] In this embodiment, the first additive with the above-described structure has a lower LUMO energy level and a higher HOMO energy level, resulting in a narrower electrochemical window. This allows the first additive to preferentially undergo reduction on the surface of the negative electrode active layer 332 before solvent molecules and conventional film-forming additives, participating in the formation of the SEI film and forming a nitrogen-rich SEI film. The nitrogen-rich SEI film has higher temperature tolerance (i.e., better high-temperature tolerance), and can better protect the negative electrode active layer 332 at high temperatures. Therefore, adding the first additive to the electrolyte can significantly improve the high-temperature cycle capacity retention of the single-cell battery 300. Furthermore, the N-3 atom in the imidazole ring of the first additive (i.e., the nitrogen atom on the imidazole ring that does not participate in double bond formation) has unconjugated lone pairs of electrons. The electron-donating conjugation effect of the benzene ring can enhance the basicity of the N-3 atom, enabling it to participate in the formation of the SEI film. + The solvated structure makes it easier for the lithium to migrate to the surface of the negative electrode 330 and undergo a reduction reaction. Furthermore, the interfacial film constructed by the first additive can reduce the side reactions at the interface between the positive electrode 310 and the negative electrode 330 during the cycling of the single cell 300, reduce the consumption of active lithium, and thus enable the single cell 300 to have a higher cycle capacity retention rate.

[0130] In some embodiments, the first additive includes: (2,4,5-Triphenylimidazole) (2,4,5-tris(4-fluorophenyl)imidazole),

[0131] (2,4,5-Tris[(4-trifluoromethyl)phenyl]imidazol),

[0132] (2,4,5-tris(4-vinylphenyl)imidazol),

[0133] (2-Phenylenyl-4,5-diphenylimidazole)

[0134] (2,4,5-Tris(4-isocyanatophenyl)imidazolium),

[0135] (2,4,5-tris(4-isothiocyanate-phenyl)imidazolium),

[0136] At least one of (2,4,5-tris(4-nitrophenyl)imidazole).

[0137] In this embodiment, compared to 2,4,5-triphenylimidazole, 2,4,5-tris(4-fluorophenyl)imidazole and 2,4,5-tris[(4-trifluoromethyl)phenyl]imidazole contain fluorine atoms at the para-position of the phenyl group, which can increase the LiF content in the SEI film, further increasing the thermal stability and acid resistance of the SEI film, and can better improve the high-temperature cycle capacity protection rate of the single cell after 300 cycles and 1000 cycles.

[0138] Compared to 2,4,5-triphenylimidazole, the phenyl-para-vinyl group of 2,4,5-tris(4-vinylphenyl)imidazole can be reduced on the surface of the negative electrode 330 to generate a product with a high degree of polymerization, which can further improve the stability of the SEI film and better improve the high-temperature cycle capacity protection rate of the single cell after 1000 cycles.

[0139] Compared to 2,4,5-triphenylimidazole, the phenyl group at the para-position of the phenyl group in 2-phenylphenyl-4,5-diphenylimidazole is an inert group, which can enhance the stability of the molecular skeleton and thus improve the high-temperature cycle capacity protection rate of the single cell after 300 cycles and 1000 cycles.

[0140] Compared to 2,4,5-triphenylimidazole, the isocyanate groups or isothiocyanate groups at the phenyl-para position of 2,4,5-tris(4-isocyanatophenyl)imidazole and 2,4,5-tris(4-isothiocyanatophenyl)imidazole can be reduced on the surface of the negative electrode 330 to form polyamide or polythioamide type polymers, improving the stability of the SEI film. In addition, the isothiocyanate groups may also react to form S-series lithium salt products (sulfide lithium salt products, such as Li2S, Li2SO3, Li2SO4, organic sulfides, etc.), thereby improving the chemical stability and mechanical properties of the SEI film, as well as improving the ionic conductivity of the SEI film and reducing the interfacial impedance, thus better improving the high-temperature cycle capacity protection rate of a single cell after 1000 cycles at 300 rpm.

[0141] Compared to 2,4,5-triphenylimidazole, 2,4,5-tris(4-nitrophenyl)imidazole has a nitro group at the para-position of the phenyl group, which allows the formed SEI film to contain Li3N, increasing the inorganic components of the SEI film, reducing the impedance of the SEI, and improving the stability of the SEI film, thereby improving the high-temperature cycle capacity protection rate of the single cell after 300 cycles and 1000 cycles.

[0142] In some embodiments, the electrolyte further includes a second additive, which is at least one of cyclic carbonate additives and cyclic sulfate additives.

[0143] Understandably, the second additive may include at least one of cyclic carbonate additives; the second additive may also include at least one of cyclic sulfate additives; the second additive may also include at least one of cyclic sulfate additives and at least one of cyclic sulfate additives.

[0144] In this embodiment, the second additive is used in conjunction with the first additive to help introduce more polymer organic layers and inorganic layers containing Li2CO3, Li2SO3, etc. into the SEI film. The increase in the content of inorganic layers in the SEI film helps to improve the thermal stability of the SEI film and further improves the cycle performance of the single cell 300.

[0145] Optionally, the mass fraction of the second additive in the electrolyte ranges from 0.1% to 5%. Specifically, the mass fraction of the second additive in the electrolyte can be, but is not limited to, 0.1%, 0.3%, 0.5%, 0.8%, 1.0%, 1.3%, 1.5%, 1.8%, 2.0%, 2.3%, 2.5%, 2.8%, 3.0%, 3.3%, 3.5%, 3.8%, 4.0%, 4.3%, 4.5%, 4.8%, and 5%. If the mass fraction of the second additive in the electrolyte is too low, the improvement on the thermal stability of the SEI film will be limited, the SEI film will be too monolithic, and the ionic conductivity will be low, which is not conducive to improving the cycle capacity retention rate of the single cell 300. If the mass fraction of the second additive in the electrolyte is too high, the impedance of the formed SEI film will be too high, which will easily lead to lithium plating and reduce the kinetic performance and cycle capacity retention rate of the single cell 300.

[0146] Optionally, the cyclic carbonate additive includes at least one of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and fluoroethylene carbonate (FEC).

[0147] Optionally, cyclic sulfate additives include vinyl sulfate (DTD), methylene methane disulfonate (MMDS), and vinyl disulfide (BiDTD).

[0148] Optionally, the electrolyte salt is a lithium salt. The lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalateborate)borate (LiBOB), lithium difluorodioxalate phosphate (LiODFP), lithium difluorooxalate borate (LiODFB), lithium difluorophosphate (LiPO2F2), and lithium trifluoromethanesulfonate (CF3SO3Li).

[0149] Optionally, the total molar concentration M of lithium salt in the electrolyte ranges from 0.7 mol / L to 1.4 mol / L. The total molar concentration M of lithium salt in the electrolyte can be, but is not limited to, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, etc. If the total molar concentration M of lithium salt is too small, the concentration of free ions in the electrolyte is too low, reducing the conductivity of the electrolyte and thus reducing the kinetic performance of the single-cell battery 300. If the total molar concentration M of lithium salt is too large, some electrolyte salt may remain undissociated, and the viscosity of the electrolyte will increase, which in turn reduces the conductivity of the electrolyte and also reduces the kinetic performance of the single-cell battery 300. When the total molar concentration M of lithium salt in the electrolyte is in the range of 0.7 mol / L ≤ M ≤ 1.4 mol / L, the electrolyte can have a high conductivity, thereby enabling the single cell 300 to have good kinetic performance.

[0150] Optionally, the solvent includes at least one of cyclic carbonates and chain carbonates. Cyclic carbonates have high dielectric constants and high ionic conductivity, enabling the formation of a stable SEI film on the surface of the negative electrode 330, but they have a relatively high viscosity. Chain carbonates have lower viscosity than cyclic carbonates, better electrochemical stability, and can improve the low-temperature performance of the electrolyte. Therefore, using a mixed solvent of cyclic and chain carbonates can give the electrolyte a suitable viscosity and low-temperature stability, and also allow the single-cell battery 300 using this electrolyte to form a better film.

[0151] Optionally, the cyclic carbonate may include, but is not limited to, at least one of ethylene carbonate (EC) and propylene carbonate (PC). Ethylene carbonate has a much higher dielectric constant than propylene carbonate, and therefore can better promote the formation of the SEI film.

[0152] Optionally, the chain carbonate may include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0153] Optionally, the solvent in the electrolyte has a mass fraction of 60 wt% to 85 wt%. Specifically, it can be, but is not limited to, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, etc.

[0154] Optionally, the solvent further includes at least one of ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, γ-butyrolactone, and 2,2-difluoroethyl acetate.

[0155] The electrolyte and single cell 300 of this application will be further described below through specific embodiments.

[0156] Examples 1 to 22

[0157] The preparation methods of the single cell 300 in each embodiment and comparative example include:

[0158] (1) Preparation of positive electrode 310: The positive electrode active material lithium iron phosphate (LiFePO4), conductive carbon black (positive electrode conductive agent, Super-P), and binder (positive electrode binder, PVDF) are dispersed in N-methylpyrrolidone (NMP) solvent according to a preset mass ratio and mixed evenly to obtain a positive electrode slurry; the positive electrode slurry is uniformly coated on the surface of the positive electrode current collector 311 aluminum foil, and the coating weight of the positive electrode slurry is 300mg / 1540.25mm. 2 After drying, cold pressing, slitting, and cutting, the positive electrode slurry solidifies to form the positive electrode active layer 312, resulting in the positive electrode sheet 310.

[0159] (2) Preparation of negative electrode sheet 330: Graphite (negative electrode active material), conductive carbon black (negative electrode conductive agent, Super-P), sodium carboxymethyl cellulose (negative electrode thickener, CMC), styrene-butadiene rubber latex (negative electrode binder SBR), and asphalt are dispersed in deionized water according to a preset mass ratio to obtain a negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector 331 copper foil. The coating weight of the negative electrode slurry is 144 mg / 1540.25 mm. 2 After drying, cold pressing, slitting, and cutting, the negative electrode slurry solidifies to form the negative electrode active layer 332, resulting in the negative electrode sheet 330.

[0160] (3) Preparation of electrolyte: In an argon atmosphere glove box with a moisture content ≤1ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed in a mass ratio of 1:1:2 to obtain a mixed solvent. Then, the dried electrolyte salt lithium hexafluorophosphate is dissolved in the mixed solvent and stirred until completely dissolved and homogeneous. The first additive and the second additive are added and stirred evenly to obtain the electrolyte. The molar concentration of lithium hexafluorophosphate in the electrolyte is 1 mol / L. The second additive includes: 1% VC, 0.5% FEC, 0.5% DTD, 0.1% MMDS, and 0.1% BiDTD. The types and amounts of the first additive in each embodiment are shown in Table 1 below.

[0161] (4) Preparation of diaphragm 320: 16μm polyethylene film (PE film) was used as diaphragm 320.

[0162] (5) Assembly of single cell 300 (soft pack battery): The positive electrode 310, separator 320 and negative electrode 330 are stacked in sequence to form an electrode assembly. After the electrode assembly is wound, a bare cell is obtained. After welding the tabs, the cell is assembled into the outer packaging. After injecting the above electrolyte, vacuum sealing, standing, formation, shaping, capacity testing, etc. are performed to finally prepare the single cell 300.

[0163] Comparative Example 1

[0164] The difference between this comparative example and Example 1 is that the electrolyte in this comparative example did not contain the first additive.

[0165] Comparative Example 2

[0166] The difference between this comparative example and Example 29 is that the electrolyte in this comparative example includes 0.5% 2-phenylimidazole.

[0167] Comparative Example 3

[0168] The difference between this comparative example and Example 29 is that the electrolyte in this comparative example includes 0.5% 2,4-diphenylimidazole.

[0169] Performance tests were conducted on the single cell 300 of each embodiment and comparative example:

[0170] (1) 45℃ Cyclic Performance Test: Under 45℃ conditions, the initialized single cell 300 was left to stand for 5 hours; then charged at a constant power rate of 1P to 3.65V, and left to stand for 10 minutes; then discharged at a constant power rate of 1P to 2.5V, and left to stand for 10 minutes; this one charge-discharge cycle is called one cycle or one cycle. The cyclic performance test of the single cell 300 was carried out with constant power charging at 1P and constant power discharging at 1P. The discharge capacity of the single cell 300 after 1000 cycles was recorded, and the cycle capacity retention rate of the single cell 300 after 1000 cycles was calculated.

[0171] Cycle capacity retention rate = (Discharge capacity in the 1000th cycle / Discharge capacity C0 in the 1st cycle) × 100%.

[0172] The initial discharge capacity percentage of each embodiment and comparative example cell 300 and the cycle capacity retention rate after 1000 cycles at 45°C and 1P charge / discharge rate are shown in Table 1 below.

[0173] Table 1 Performance parameters of the single cell 300 in each embodiment and comparative example

[0174]

[0175]

[0176] The test results from Examples 1 to 15 and Comparative Example 1 show that, in Comparative Example 1, without the addition of 2,4,5-triphenylimidazole (the first additive) to the electrolyte, the high-temperature cycle capacity retention rate of the single cell 300 after 1000 cycles is relatively low. This is because during the charge-discharge cycle of the single cell 300, along with the electrochemical process of charging and discharging, the SEI film expands and contracts. At this time, the SEI film has poor cycle stability at high temperatures, so the SEI film is constantly damaged and repaired. The process of forming the SEI film is the process of electrolyte components gaining and losing electrons on the surface of the negative electrode active material of the negative electrode 330. This process is accompanied by the loss of active lithium, which is irreversible. The decrease in the active lithium content leads to a decrease in the charge-discharge cycle capability of the single cell 300. Adding 2,4,5-triphenylimidazolium to the electrolyte can improve the high-temperature cycling capacity retention rate of a single cell after 1000 cycles. In Example 1, the mass fraction of 2,4,5-triphenylimidazolium in the electrolyte was relatively low; therefore, although the high-temperature cycling capacity retention rate of the single cell after 1000 cycles was improved, the improvement was minor. Although 2,4,5-triphenylimidazolium can improve the high-temperature stability of the SEI film, if the mass fraction of 2,4,5-triphenylimidazolium is too low, the formed SEI film cannot effectively protect the negative electrode 330. The test results from Examples 1 to 15 show that as the mass fraction of 2,4,5-triphenylimidazolium in the electrolyte increases, the high-temperature cycling capacity retention rate of the single cell after 1000 cycles first gradually increases and then gradually decreases. When an excessive amount of 2,4,5-triphenylimidazole is added to the electrolyte (as in Example 15), the high-temperature cycle capacity retention rate of the single cell 300 after 1000 cycles decreases significantly. This is because when the mass of the first additive in the electrolyte is too high, the SEI film formed on the surface of the negative electrode active layer 332 of the negative electrode 330 becomes too thick, increasing the impedance of the single cell 300, reducing its kinetic performance, and easily causing lithium deposition during cycling, consuming active lithium, and reducing the high-temperature cycle capacity retention rate of the single cell 300. When the mass fraction of the first additive in the electrolyte is 0.02% to 2%, the single cell 300 exhibits a higher high-temperature cycle capacity retention rate. When the mass fraction of the first additive in the electrolyte is 0.2% to 0.8%, the single cell 300 exhibits an even higher high-temperature cycle capacity retention rate.

[0177] Compared to Example 7, the single-cell batteries 300 of Examples 16 and 17 respectively added 2,4,5-tris(4-fluorophenyl)imidazole and 2,4,5-tris[(4-trifluoromethyl)phenyl]imidazole to the electrolyte. Compared to the single-cell battery 300 of Example 7, the high-temperature cycle capacity protection rates of the single-cell batteries 300 of Examples 16 and 17 after 1000 cycles were both higher. This is because the phenyl-para-position of 2,4,5-tris(4-fluorophenyl)imidazole and 2,4,5-tris[(4-trifluoromethyl)phenyl]imidazole contains fluorine atoms, which can increase the LiF content in the SEI film, further increasing the thermal stability and acid resistance of the SEI film, and improving the high-temperature cycle capacity protection rate of the single-cell battery 300 after 1000 cycles.

[0178] Compared to Example 7, the single-cell battery 300 of Example 18, with the addition of 2,4,5-tris(4-vinylphenyl)imidazolium to the electrolyte, exhibits a higher high-temperature cycle capacity protection rate after 1000 cycles compared to the single-cell battery 300 of Example 7. This is because the phenyl-para-vinyl group of 2,4,5-tris(4-vinylphenyl)imidazolium can be reduced on the surface of the negative electrode 330 to generate a highly polymerized product, which can further improve the stability of the SEI film, thereby increasing the high-temperature cycle capacity protection rate of the single-cell battery 300 after 1000 cycles.

[0179] Compared to Example 7, the single-cell battery 300 of Example 19, with the addition of 2-phenylphenyl-4,5-diphenylimidazole to the electrolyte, exhibits a higher high-temperature cycle capacity protection rate after 1000 cycles compared to the single-cell battery 300 of Example 7. This is because the phenyl group at the para-position of the phenyl group in 2-phenylphenyl-4,5-diphenylimidazole is an inert group, which enhances the stability of the molecular skeleton, thereby improving the high-temperature cycle capacity protection rate of the single-cell battery 300 after 1000 cycles. However, excessive phenyl substitution reduces the solubility of the first additive in the electrolyte; therefore, excessive phenyl substitution is not advisable.

[0180] Compared to Example 7, the single-cell batteries 300 of Examples 20 and 21 respectively added 2,4,5-tris(4-isocyanate-phenyl)imidazole and 2,4,5-tris(4-isothiocyanate-phenyl)imidazole to the electrolyte. Compared to the single-cell battery 300 of Example 7, the high-temperature cycle capacity protection rate of the single-cell batteries 300 of Examples 20 and 21 after 1000 cycles is higher. This is because the isocyanate group or isothiocyanate group at the phenyl-para position of 2,4,5-tris(4-isocyanatophenyl)imidazole can be reduced on the surface of the negative electrode 330 to form a polyamide or polythioamide type polymer, which improves the stability of the SEI film. In addition, the isothiocyanate group may also react to form S-series lithium salt products (sulfide lithium salt products, such as Li2S, Li2SO3, Li2SO4, organic sulfides, etc.), which can improve the chemical stability and mechanical properties of the SEI film, as well as improve the ionic conductivity of the SEI film and reduce the interfacial impedance, thereby better improving the high-temperature cycle capacity protection rate of the single cell after 1000 cycles at 300 rpm.

[0181] Compared to Example 7, the single-cell battery 300 of Example 22, with the addition of 2,4,5-tris(4-nitrophenyl)imidazolium to the electrolyte, exhibits a higher high-temperature cycle capacity protection rate after 1000 cycles compared to the single-cell battery 300 of Example 7. This is because the phenyl group at the para-position of 2,4,5-tris(4-nitrophenyl)imidazolium has a nitro group, which allows the formed SEI film to contain Li3N, increasing the inorganic component of the SEI film, reducing the SEI impedance, and improving the SEI film stability, thereby enhancing the high-temperature cycle capacity protection rate of the single-cell battery 300 after 1000 cycles.

[0182] As shown in the test results of Example 7, Comparative Example 2, and Comparative Example 3, compared to the schemes of Comparative Example 2 using 2-phenylimidazole as the first additive and Comparative Example 3 using 2,4-diphenylimidazole as the first additive, Example 7 using 2,4,5-triphenylimidazole as the first additive can result in a higher high-temperature cycle capacity retention rate for the single cell 300. This is because, compared to 2-phenylimidazole and 2,4-diphenylimidazole, the 2,4,5-triphenylimidazole of this application has a lower LUMO energy level, higher reducibility, and is more likely to react on the surface of the negative electrode 330 to form an SEI film. In addition, the large steric hindrance effect of the benzene ring in the SEI film helps to suppress the reaction between the SEI film and other substances, reduces the damage to the SEI film, helps to improve the stability of the SEI film, and improves the cycle performance of the single cell 300.

[0183] In this application, the terms "embodiment" and "implementation" mean that a specific feature, structure, or characteristic described in connection with an embodiment can be included in at least one embodiment of this application. The appearance of these phrases in various places in the specification does not necessarily refer to the same embodiment, nor are they independent or alternative embodiments mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this application can be combined with other embodiments. Furthermore, it should be understood that the features, structures, or characteristics described in the various embodiments of this application can be arbitrarily combined to form another embodiment that does not depart from the spirit and scope of the technical solution of this application, provided there is no contradiction between them.

[0184] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. An electrolyte, characterized in that, The electrolyte comprises an electrolyte salt, a first additive, and a solvent, wherein the first additive is 2-first aryl-4-second aryl-5-third arylimidazolium.

2. The electrolyte according to claim 1, characterized in that, The electrolyte contains 0.02% to 2% by mass of 2-first aryl-4-second aryl-5-third arylimidazolium.

3. The electrolyte according to claim 1, characterized in that, The electrolyte contains 0.2% to 0.7% by mass of 2-first aryl-4-second aryl-5-third aryl imidazole.

4. The electrolyte according to claim 1, characterized in that, The first aryl group is at least one of phenyl, meta-substituted phenyl, para-substituted phenyl, and meta-para-substituted phenyl; the second aryl group is at least one of phenyl, meta-substituted phenyl, para-substituted phenyl, and meta-para-substituted phenyl; and the third aryl group is at least one of phenyl, meta-substituted phenyl, para-substituted phenyl, and meta-para-substituted phenyl.

5. The electrolyte according to claim 4, characterized in that, In meta-substituted phenyl groups, the substituents are electron-withdrawing or conjugated groups; in para-substituted phenyl groups, the substituents are electron-withdrawing or conjugated groups; in meta-para-substituted phenyl groups, the substituents are electron-withdrawing or conjugated groups.

6. The electrolyte according to claim 5, characterized in that, The electron-withdrawing group includes one of halogen, trifluoromethyl, nitro, isocyanate, and isothiocyanate, and the conjugated group includes one of vinyl, ethynyl, and phenyl.

7. The electrolyte according to claim 4, characterized in that, The meta-substituted phenyl group includes one of the following: 3-halogen phenyl, 3-vinylphenyl, 3-ethynylphenyl, 3-trifluoromethylphenyl, 3-phenylphenyl, 3-nitrophenyl, 3-isocyanophenyl, and 3-isothiocyanophenyl. The para-substituted phenyl group includes one of the following: 4-halogen phenyl, 4-vinylphenyl, 4-ethynylphenyl, 4-trifluoromethylphenyl, 4-phenylphenyl, 4-nitrophenyl, 4-isocyanate phenyl, and 4-isothiocyanate phenyl; Meta- and para-substituted phenyl groups include one of the following: 3,4-dihalophenyl, 3,4-divinylphenyl, 3,4-diethynylphenyl, 3,4-ditrifluoromethylphenyl, 3,4-diphenylphenyl, 3,4-dinitrophenyl, 3,4-diisocyanate-based phenyl, 3,4-diisothiocyanate-based phenyl, 3,4,5-trihalophenyl, 3,4,5-trivinylphenyl, 3,4,5-triethynylphenyl, 3,4,5-tritrifluoromethylphenyl, 3,4,5-triphenylphenyl, 3,4,5-trinitrophenyl, 3,4,5-triisocyanate-based phenyl, and 3,4,5-triisothiocyanate-based phenyl.

8. The electrolyte according to claim 1, characterized in that, The structural formula of 2-first aryl-4-second aryl-5-tertaryl imidazole is: Among them, R 1 H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups. R 2 H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups. R 3 H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups. R 4 H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups. R 5 H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups. R 6 H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups. R 7 H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups. R 8 H, halogen, alkanes with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms, alkenyl groups with 2 to 5 carbon atoms, alkynyl groups with 2 to 5 carbon atoms, phenyl groups, substituted phenyl groups, nitro groups, isocyanate groups, and isothiocyanate groups. R 9 H, halogen, alkane with 1 to 5 carbon atoms, haloalkanes with 1 to 5 carbon atoms, alkoxy group with 1 to 5 carbon atoms, alkenyl group with 2 to 5 carbon atoms, alkynyl group with 2 to 5 carbon atoms, phenyl group, substituted phenyl group, nitro group, isocyanate group, isothiocyanate group.

9. The electrolyte according to claim 1, characterized in that, The first additive comprises at least one of the following: 2,4,5-triphenylimidazolium, 2,4,5-tris(4-fluorophenyl)imidazolium, 2,4,5-tris[(4-trifluoromethyl)phenyl]imidazolium, 2,4,5-tris(4-vinylphenyl)imidazolium, 2-phenylphenyl-4,5-diphenylimidazolium, 2,4,5-tris(4-isocyanate-phenyl)imidazolium, 2,4,5-tris(4-isothiocyanate-phenyl)imidazolium, and 2,4,5-tris(4-nitrophenyl)imidazolium.

10. The electrolyte according to any one of claims 1-9, characterized in that, The electrolyte further includes a second additive, which is at least one of cyclic carbonate additives and cyclic sulfate additives, and the mass fraction of the second additive in the electrolyte ranges from 0.1% to 5%.

11. A single-cell battery, characterized in that, The single cell includes: the electrolyte, positive electrode, separator, and negative electrode as described in any one of claims 1-10.

12. An energy storage device, characterized in that, The energy storage device includes at least one single battery cell as described in claim 11.

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