Electrolyte additive, electrolyte and battery

Abstract

This application relates to an electrolyte additive, an electrolyte, and a battery. The electrolyte additive includes a first additive and lithium trifluoromethanesulfinate; the first additive has a structural formula as shown in Formula (I): wherein the mass ratio of the first additive to the lithium trifluoromethanesulfinate in the electrolyte additive is 0.02 to 10. When added to the battery electrolyte, the electrolyte additive can effectively improve the battery's rate performance and high-temperature performance.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to an electrolyte additive, an electrolyte and a battery. Background Art

[0002] The rapid development and widespread adoption of various portable electronic devices, new energy electric vehicles, and energy storage systems in recent years has led to an increasingly urgent market demand for high-energy-density batteries. A new generation of high-voltage material systems, represented by high-nickel ternary materials (NCM / NCA) and lithium-rich manganese-based materials, has pushed lithium-ion battery energy densities past 300 Wh / kg. However, these upgrades in high-voltage material systems can lead to a series of battery performance issues, such as rapid capacity degradation under high-temperature conditions and increased polarization during high-rate charge and discharge. Summary of the Invention

[0003] The embodiments of the present application provide an electrolyte additive, an electrolyte, and a battery to at least partially solve the above-mentioned technical problems.

[0004] In order to achieve the above-mentioned object, according to the first aspect of the present application, there is provided an electrolyte additive, comprising a first additive and lithium trifluoromethanesulfinate; the structural formula of the first additive is shown in formula (I):

[0005] Formula (I),

[0006] Among the electrolyte additives, the mass ratio of the first additive to the lithium trifluoromethanesulfinate is 0.02-10.

[0007] Optionally, in the electrolyte additive, the mass ratio of the first additive to the lithium trifluoromethanesulfinate is 0.25-4.

[0008] According to a second aspect of the present application, an electrolyte is provided, comprising an electrolyte salt, a non-aqueous organic solvent, and the above-mentioned electrolyte additive; based on the total mass of the electrolyte, the mass proportion of the first additive is 0.01 wt%~5 wt%, and the mass proportion of the lithium trifluoromethanesulfinate is 0.05 wt%~3 wt%.

[0009] Optionally, based on the total mass of the electrolyte, the mass proportion of the first additive is 0.1 wt% to 1 wt%.

[0010] Optionally, based on the total mass of the electrolyte, the total mass of the first additive and the lithium trifluoromethanesulfinate accounts for 0.06 wt % to 8 wt %.

[0011] Optionally, based on the total mass of the electrolyte, the total mass of the first additive and the lithium trifluoromethanesulfinate accounts for 0.2 wt % to 6 wt %.

[0012] Optionally, the electrolyte includes, by weight, 7 to 18 parts of the electrolyte salt, 70 to 92 parts of the non-aqueous organic solvent, 0.01 to 5 parts of the first additive, and 0.05 to 3 parts of lithium trifluoromethanesulfinate.

[0013] Optionally, the electrolyte includes, by weight, 9 to 15 parts by weight of the electrolyte salt, 75 to 83 parts by weight of the non-aqueous organic solvent, 0.1 to 1 part by weight of the first additive, and 0.1 to 0.5 parts by weight of lithium trifluoromethanesulfinate.

[0014] Optionally, the electrolyte salt includes a lithium salt, and the lithium salt includes at least one of lithium hexafluorophosphate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(trifluoromethylsulfonylimide), and lithium bis(fluorosulfonylimide).

[0015] Optionally, the non-aqueous organic solvent includes at least one of a carbonate compound, a fluorinated compound of a carbonate compound, a carboxylate compound, and a fluorinated compound of a carboxylate compound.

[0016] According to a third aspect of the present application, a battery is provided, comprising a positive electrode sheet, a negative electrode sheet, a separator and the above-mentioned electrolyte.

[0017] Optionally, the positive electrode plate includes a positive electrode active material; the positive electrode active material includes LiNi 1-x- y Co x Mn y O2、LiNi 1-x-z Co x Al z At least one of O2, lithium nickel manganese oxide, lithium cobalt oxide, lithium-rich manganese base and lithium manganese oxide, wherein 0≤x≤1, 0≤y≤1, 0≤z≤1, and 0≤x+y≤1, 0≤x+z≤1.

[0018] Optionally, the negative electrode plate includes a negative electrode active material; the negative electrode active material includes at least one of artificial graphite, lithium metal, coated natural graphite, silicon-carbon negative electrode and silicon negative electrode.

[0019] Optionally, the charging cut-off voltage of the battery is greater than or equal to 4.3V to 4.8V.

[0020] The embodiment of the present application combines the first additive shown in formula (I) with lithium trifluoromethylsulfinate and applies it to the electrolyte. The synergistic effect of the sulfonyl fluoride group and the benzene ring in the first additive is utilized to form a dense CEI film on the positive electrode surface, thereby improving the problems of lattice oxygen release and transition metal dissolution in the high-voltage material system. At the same time, through the oxidative decomposition of the trifluoromethylsulfinate at the positive terminal and the interaction with the first additive, it can effectively inhibit the continuous decomposition and gas production of the electrolyte, alleviate the effect of the increase in SEI film interface impedance caused by the accumulation of by-products, and effectively reduce the Rct interface impedance. The CEI film is effectively formed under high voltage conditions, which inhibits the decomposition of the electrolyte and improves the cycle life and rate performance of the high-voltage battery.

[0021] In summary, by combining the first additive represented by formula (I) with lithium trifluoromethanesulfinate and applying it to the electrolyte, the performance shortcomings of the single component are compensated through the complementary mechanism of the oxidation-resistant composite membrane on the positive electrode side, forming a self-reinforcing interfacial membrane system and improving the rate performance of the battery system. In addition, the sulfonyl group of the first additive can also fix the non-aqueous organic solvent molecules in the electrolyte through strong hydrogen bonding, reducing the volatilization of the non-aqueous organic solvent at high temperatures. It also works together with the directional release of active lithium from lithium trifluoromethanesulfinate to enhance the thermodynamic stability of the SEI / CEI membrane, thereby improving the high-temperature performance of the battery system.

[0022] Other features and advantages of the present application will be described in detail in the subsequent detailed description. DETAILED DESCRIPTION

[0023] The following will be combined with the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of this application. In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain the present application and are not used to limit the present application.

[0024] In this application, unless otherwise indicated, directional terms such as "upper" and "lower" generally refer to the upper and lower parts of a device during actual use or operation; whereas "inner" and "outer" refer to the outline of a device. Furthermore, in the description of this application, the term "including" means "including but not limited to." Terms such as first, second, and third are used merely as labels and do not impose numerical requirements or establish a sequence.

[0025] In this application, "and / or" describes the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural.

[0026] In this application, "at least one" means one or more, and "plurality" means two or more. "One or more", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can each be single or plural.

[0027] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a hard limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numbers within the range. For example, the description of a range from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0028] With the continuous advancement of batteries (such as lithium-ion batteries), the development of high-energy density and high-capacity systems has become a core focus of the industry. A new generation of high-voltage material systems, represented by high-nickel ternary (NCM / NCA) and lithium-rich manganese-based materials, has pushed lithium-ion battery energy densities past 300 Wh / kg. However, these upgrades can lead to a series of battery performance issues, such as rapid capacity degradation under high-temperature conditions and increased polarization during high-rate charge and discharge.

[0029] The electrolyte is a crucial component of the battery, often called its "blood." It typically consists of electrolyte salts, solvents, and additives, and has a significant impact on battery performance. In the embodiments of this application, multiple additives are added to the electrolyte, which, through interaction, can improve the battery's rate performance and high-temperature performance.

[0030] Some embodiments of the present application provide a battery. Specifically, the battery includes a positive electrode sheet, a negative electrode sheet, a diaphragm and an electrolyte. Specifically, the positive electrode sheet and the negative electrode sheet are arranged opposite to each other, and the diaphragm is arranged between the positive electrode sheet and the negative electrode sheet to prevent the positive electrode sheet from contacting the negative electrode sheet and causing a short circuit. The electrolyte infiltrates the positive electrode sheet, the negative electrode sheet and the diaphragm. The electrolyte provides an ion channel during the charging and discharging process of the battery, enabling charge transfer between the positive electrode sheet and the negative electrode sheet, thereby completing the storage and release of energy. The battery can be used as a power source for an electrical device, and the electrical device can be but is not limited to a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, an electric tool, and the like. In the electrical device, the battery can be used as an operating power source or as a driving power source.

[0031] In some embodiments of the present application, the positive electrode plate includes a positive electrode active material. Optionally, the positive electrode plate includes a positive electrode film layer, which includes the positive electrode active material. As one example, the positive electrode plate also includes a positive electrode current collector, and the positive electrode film layer is disposed on the positive electrode current collector. In another example, the positive electrode plate is a self-supporting structure, and the positive electrode plate only includes the positive electrode film layer without a positive electrode current collector. Furthermore, the positive electrode film layer also includes a conductive agent and a binder. In the positive electrode plate, the conductive agent includes at least one of carbon black, graphite, carbon nanotubes (CNTs), graphene, and carbon fiber; the binder includes polyvinylidene fluoride (PVDF); and the positive electrode current collector includes aluminum foil.

[0032] In some embodiments of the present application, the positive electrode active material includes LiNi 1-x-y Co x Mn y O2、LiNi 1-x-z Co x Al z At least one of O2, lithium nickel manganese oxide, lithium cobalt oxide, lithium-rich manganese base and lithium manganese oxide, wherein 0≤x≤1, 0≤y≤1, 0≤z≤1, and 0≤x+y≤1, 0≤x+z≤1. The application of the above materials in batteries can effectively improve the energy density of the battery. As an example, x is any value of 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1 or a range of any two values; y is any value of 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1 or a range of any two values; z is any value of 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1 or a range of any two values.

[0033] In some embodiments, the negative electrode plate includes a negative electrode active material. Optionally, the negative electrode plate includes a negative electrode film layer, which includes the negative electrode active material. As one example, the negative electrode plate also includes a negative electrode current collector, with the negative electrode film layer disposed on the negative electrode current collector. In another example, the negative electrode plate is a self-supporting structure, comprising only the negative electrode film layer without a negative electrode current collector. Furthermore, the negative electrode film layer also includes a conductive agent and a binder. In the negative electrode plate, the conductive agent includes at least one of carbon black, graphite, carbon nanotubes (CNTs), graphene, and carbon fiber; the binder includes at least one of styrene-butadiene rubber (SBR) and polyacrylic acid (PAA); and the negative electrode current collector includes copper foil.

[0034] In some embodiments of the present application, the negative electrode active material includes at least one of artificial graphite, lithium metal, coated natural graphite, silicon-carbon negative electrode and silicon negative electrode.

[0035] In some embodiments of the present application, the battery has a charge cut-off voltage greater than or equal to 4.3V to 4.8V. The battery's charge cut-off voltage is related to the type of battery material. As an example, the battery's charge cut-off voltage is 4.3V, 4.4V, 4.5V, 4.6V, 4.7V, or 4.8V.

[0036] In some embodiments of the present application, the membrane material of the membrane includes at least one of polyethylene (PE) and polypropylene (PP).

[0037] In some embodiments of the present application, the battery is a secondary battery. Secondary batteries come in a variety of forms, including but not limited to single cells, battery modules, and battery packs. A secondary battery is a battery that can be recharged after discharge to activate its active materials and allow continued use. For example, the battery is a lithium-ion battery.

[0038] Some embodiments of the present application provide an electrolyte, and the above-mentioned battery includes the electrolyte. The electrolyte includes at least a non-aqueous organic solvent, an electrolyte salt, and an electrolyte additive. The electrolyte salt dissociates into cations and anions in the non-aqueous organic solvent, and the non-aqueous organic solvent provides a medium for the movement of ions, thereby achieving ion conduction. The type of electrolyte salt can be selected according to the type of battery. As an example, if the electrolyte salt is a lithium salt, the resulting electrolyte can be used in a lithium-ion battery. The type of non-aqueous organic solvent can also be selected according to the electrolyte salt.

[0039] In some embodiments of the present application, the electrolyte salt includes a lithium salt, and the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate, lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiODFB), lithium bis(trifluoromethylsulfonyl imide) (LiTFSI), and lithium bis(fluorosulfonyl imide) (LiFSI). Optionally, based on the total mass of the electrolyte, the mass percentage of the lithium salt is 10 wt% to 25 wt%. Increasing the content of the lithium salt in the electrolyte is beneficial to increasing the ionic conductivity of the electrolysis. However, the solubility of the lithium salt in the non-aqueous solvent is limited, and an excessive content of the lithium salt will increase the viscosity of the electrolyte. As an example, the mass percentage of the lithium salt in the electrolyte is any value of 10 wt%, 12 wt%, 14 wt%, 16 wt%, 18 wt%, 20 wt%, 22 wt%, 23 wt%, 24 wt%, and 25 wt%, or any two of the range values.

[0040] In some embodiments of the present application, the non-aqueous organic solvent includes at least one of a carbonate compound, a fluorinated carbonate compound, a carboxylate compound, and a fluorinated carboxylate compound. For example, the carbonate solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC); the fluorinated carbonate compound includes fluoroethylene carbonate (FEC); and the carboxylate compound includes at least one of ethyl acetate (EA), methyl acetate (MA), methyl propionate (MP), ethyl propionate (EP), and ethyl butyrate (EB).

[0041] Some embodiments of the present application provide an electrolyte additive, the electrolyte comprising the electrolyte additive. The electrolyte additive comprises a first additive and lithium trifluoromethanesulfinate; the first additive has a structural formula as shown in formula (I):

[0042] Formula (I),

[0043] Among the electrolyte additives, the mass ratio of the first additive to lithium trifluoromethanesulfinate is 0.02-10.

[0044] Specifically, the first additive is a benzenesulfonimide compound, and the CAS number of the first additive is 1622206-83-0. The structural formula of lithium trifluoromethanesulfinate is shown in formula (II):

[0045] Formula (II).

[0046] In the electrolyte additive, the first additive and lithium trifluoromethanesulfinate are mixed according to a mass ratio. As an example, the mass ratio of the first additive to lithium trifluoromethanesulfinate is 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 or a range value between any two of them.

[0047] Since the first additive contains sulfonyl fluoride groups and benzene rings, a dense CEI film is formed on the surface of the positive electrode active material through the synergistic effect of the sulfonyl fluoride groups and the benzene rings, which can improve the problems of lattice oxygen release and transition metal dissolution in high-voltage material systems. However, when the first additive is used as an electrolyte additive, a CEI film with a high proportion of rigid components such as FOS=O bonds (lithium sulfonate / lithium sulfate inorganic salts) and CF bonds (benzene ring fluorination products), a mixture of Li2SO4 (lithium sulfate) and LiF (lithium fluoride), and aromatic sulfonate polymers will be generated. Among them, Li2SO4 and LiF form an inorganic ceramic continuous phase, resulting in Li + When the migration energy barrier increases to greater than 0.75 eV, the aromatic sulfonate polymer will block the gaps between the inorganic particles, resulting in an increase in Rct and the initial interfacial impedance, further affecting the rate performance of the battery.

[0048] In this regard, the trifluoromethanesulfinate in lithium trifluoromethanesulfinate is oxidized and decomposed at the positive end, and its decomposition products (such as SO2, CHF3, etc.) are released in the form of gas. SO2 can react with Li2S produced by the decomposition of the first additive to form Li2SO3, filling the pores of the CEI membrane and reducing gas residues. Specifically: SO2+ Li2S→ Li2SO3 (solid-state deposition); the strong electronegativity of CHF3 can capture free electrons and inhibit the continuous decomposition and gas production of the electrolyte. At the same time, the decomposition products of lithium trifluoromethanesulfinate can release lithium ions (Li + ) is embedded in the negative electrode, alleviating the effect of the increase in SEI film interface impedance caused by the accumulation of by-products. The generated SEI film has high ionic conductivity (greater than 10 -10 S / cm), and can also reduce the Rct interface impedance (usually 120Ω·cm 2 ~150Ω·cm 2 Reduced to 72Ω·cm 2 ~90Ω·cm 2 ), and the Li +It can be directly embedded in the negative electrode to compensate for the active lithium consumed by the first additive in promoting the formation of the CEI film, further accelerate the directional replenishment of active lithium, and ultimately improve the ionic conductivity of the CEI film, improving the problem of increased interface impedance caused by the first additive.

[0049] However, lithium trifluoromethanesulfinate has limited antioxidant capacity for high-voltage cathodes (>4.3V), making it ineffective in forming a CEI film under high-voltage conditions. This leads to irreversible phase transitions in the cathode active material and electrolyte decomposition at high voltages. The benzene ring structure of the first additive provides steric hindrance, enhancing the mechanical strength of the CEI film and reducing electrolyte side reactions, effectively resolving the problem of lithium trifluoromethanesulfinate's inability to form an effective protective layer at high-voltage cathodes.

[0050] In other words, the combination of the first additive represented by formula (I) and lithium trifluoromethanesulfinate in the electrolyte compensates for the performance shortcomings of the individual components through the complementary mechanism of the oxidation-resistant composite membrane on the positive electrode side, forming a self-reinforcing interfacial membrane system and improving the rate performance of the battery system. Furthermore, the sulfonyl group of the first additive can also fix the non-aqueous organic solvent molecules in the electrolyte through strong hydrogen bonding, reducing the volatilization of the non-aqueous organic solvent at high temperatures. This, together with the directional release of active lithium from the lithium trifluoromethanesulfinate, enhances the thermodynamic stability of the SEI / CEI membrane, thereby improving the high-temperature performance of the battery system.

[0051] The present application achieves the following beneficial effects by using the first additive in combination with lithium trifluoromethanesulfinate:

[0052] (1) Complementarity between positive electrode protection and negative electrode optimization: the first additive focuses on high-voltage positive electrode stability, lithium trifluoromethanesulfinate focuses on negative electrode ion transport, and the dual membranes synergistically reduce the overall interface impedance.

[0053] (2) Electrochemical window expansion: The antioxidant property of the first additive broadens the operating voltage range of the electrolyte, while the oxidative decomposition characteristics of lithium trifluoromethanesulfinate balance the kinetic bottleneck. This together inhibits electrolyte decomposition and improves the cycle life and rate performance of high-voltage batteries.

[0054] It can be seen that by combining the first additive represented by formula (I) with lithium trifluoromethanesulfinate, the high-temperature performance and rate performance of the battery can be improved simultaneously, providing important technical support for the application of batteries in high-temperature, high-power scenarios such as electric vehicles and energy storage.

[0055] In some embodiments of the present application, the mass ratio of the first additive to lithium trifluoromethanesulfinate in the electrolyte additive is 0.25-4. As an example, the mass ratio of the first additive to lithium trifluoromethanesulfinate in the electrolyte additive is any one of 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0, or a range between any two of them. Within this range, the first additive and lithium trifluoromethanesulfinate can effectively produce a synergistic effect, improving the high temperature performance and rate performance of the battery.

[0056] In some embodiments of the present application, based on the total mass of the electrolyte, the mass proportion of the first additive is 0.01wt%~5wt%, and the mass proportion of lithium trifluoromethanesulfinate is 0.05wt%~3wt%. Within this range, there is a synergistic effect between the first additive and lithium trifluoromethanesulfinate, thereby improving the rate performance and high temperature performance of the battery. As an example, based on the total mass of the electrolyte, the mass proportion of the first additive is 0.01wt%, 0.05wt%, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt% and 5wt% or any two of the range values, and the mass proportion of lithium trifluoromethanesulfinate is 0.05wt%, 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt% and 3wt% or any two of the range values.

[0057] In some embodiments of the present application, the mass proportion of the first additive is 0.1wt% to 1wt% based on the total mass of the electrolyte. Within this range, the rate performance and high-temperature performance of the battery are good. As an example, the mass proportion of the first additive in the electrolyte is any one of 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt% and 1wt%, or any two of them.

[0058] In some embodiments of the present application, based on the total mass of the electrolyte, the total mass of the first additive and the lithium trifluoromethanesulfinate accounts for 0.06 wt % to 8 wt %. As an example, based on the total mass of the electrolyte, the total mass of the first additive and the lithium trifluoromethanesulfinate accounts for any one or two of 0.06 wt %, 0.1 wt %, 0.5 wt %, 1 wt %, 2 wt %, 3 wt %, 4 wt %, 5 wt %, 6 wt %, 7 wt %, and 8 wt %. Alternatively, based on the total mass of the electrolyte, the total mass of the first additive and the lithium trifluoromethanesulfinate accounts for 0.2 wt % to 6 wt %.

[0059] In some embodiments of the present application, the electrolyte includes, by weight, 7 to 18 parts of electrolyte salt, 70 to 92 parts of non-aqueous organic solvent, 0.01 to 5 parts of a first additive, and 0.05 to 3 parts of lithium trifluoromethanesulfinate. As an example, in the electrolyte, the weight of the electrolyte salt is 7 parts, 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, or 18 parts; the weight of the non-aqueous organic solvent is 70 parts, 71 parts, 72 parts, 73 parts, 74 parts, 75 parts, 76 parts, 77 parts, 78 parts, 79 parts, 80 parts, 81 parts, 82 parts, 83 parts by weight, 84 parts by weight, 85 parts by weight, 86 parts by weight, 87 parts by weight, 88 parts by weight, 89 parts by weight, 90 parts by weight, 91 parts by weight or 92 parts by weight; the weight of the first additive is 0.01 parts by weight, 0.05 parts by weight, 0.1 parts by weight, 0.5 parts by weight, 1 part by weight, 2 parts by weight, 3 parts by weight, 4 parts by weight or 5 parts by weight; the weight of lithium trifluoromethanesulfinate is 0.05 parts by weight, 0.1 parts by weight, 0.5 parts by weight, 1 part by weight, 2 parts by weight or 3 parts by weight. Optionally, the electrolyte includes, by weight, 9 to 15 parts by weight of an electrolyte salt, 75 to 83 parts by weight of a non-aqueous organic solvent, 0.1 to 1 parts by weight of the first additive, and 0.1 to 0.5 parts by weight of lithium trifluoromethanesulfinate.

[0060] The following describes the method in conjunction with specific embodiments.

[0061] Example 1

[0062] Preparation of positive electrode sheet: LiNi 0.9 Co 0.05 Mn 0.05 O2, conductive carbon black and carbon nanotubes, and binder polyvinylidene fluoride (PVDF) are added to N-methylpyrrolidone (NMP) in a mass ratio of 94.5:4:1.5 to make positive electrode slurry. The positive electrode slurry is coated on the upper and lower surfaces of aluminum foil and dried and then cold pressed. Then, it is trimmed, cut into pieces, and divided into strips to make positive electrode sheets.

[0063] Preparation of negative electrode sheets: Graphite-silicon carbon (capacity: 550 mAh / g) is mixed with conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener (CMC) in a mass ratio of 94.5:2:2:1 in deionized water to prepare a negative electrode slurry. The negative electrode slurry is coated on the upper and lower surfaces of copper foil and dried. It is then cold pressed, trimmed, cut into pieces, and slit into strips to make negative electrode sheets.

[0064] Preparation of the electrolyte: In a nitrogen-filled glove box (O2 <1ppm, H2O <1ppm), ethyl methyl carbonate (EMC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), and propylene carbonate (PC) were mixed in a mass ratio of 7:1:1:1 to prepare 84g of a non-aqueous organic solvent. 0.5g of the first additive and 0.5g of lithium trifluoromethylsulfinate were added as electrolyte additives to obtain a mixed solution. The mixed solution was sealed and packaged and placed in a freezer (10°C) for 2 hours. After removal, 8g of lithium hexafluorophosphate and 7g of lithium bis(fluorosulfonyl)imide were slowly added to the mixed solution in a nitrogen-filled glove box (O2 <1ppm, H2O <1ppm). After mixing, the electrolyte was prepared.

[0065] Isolation film: Polyethylene film is used as the isolation film.

[0066] Preparation of lithium-ion batteries: stack the positive electrode sheet, separator, and negative electrode sheet in order, with the separator placed between the positive and negative electrode sheets to isolate the positive and negative electrodes, wind to obtain a bare cell, weld the tabs, place the bare cell in an outer package, inject the above-prepared electrolyte into the dried cell, encapsulate, let stand, form, and shape, etc., to obtain a lithium-ion battery with a theoretical capacity of 1500mAh.

[0067] Example 2

[0068] The lithium ion battery preparation method of Example 2 differs from that of Example 1 in that the amount of the first additive in the electrolyte is 0.01 g, and the amount of the non-aqueous organic solvent is adjusted to 84.49 g, as shown in Table 1. Others are the same as in Example 1.

[0069] Example 3

[0070] The lithium ion battery preparation method of Example 3 differs from that of Example 1 in that the amount of the first additive in the electrolyte is 0.1 g, and the amount of the non-aqueous organic solvent is adjusted to 84.4 g, as shown in Table 1. Others are the same as in Example 1.

[0071] Example 4

[0072] The lithium ion battery preparation method of Example 4 differs from that of Example 1 in that the amount of the first additive in the electrolyte is 1 g, and the amount of the non-aqueous organic solvent is adjusted to 83.5 g, as shown in Table 1. Others are the same as in Example 1.

[0073] Example 5

[0074] The lithium ion battery preparation method of Example 5 differs from that of Example 1 in that the amount of the first additive in the electrolyte is 5 g, and the amount of the non-aqueous organic solvent is adjusted to 79.5 g, as shown in Table 1. Others are the same as in Example 1.

[0075] Example 6

[0076] The lithium ion battery preparation method of Example 6 differs from that of Example 1 in that the amount of lithium trifluoromethanesulfinate in the electrolyte is 0.05 g, and the amount of the non-aqueous organic solvent is adjusted to 84.45 g, as shown in Table 1. Others are the same as in Example 1.

[0077] Example 7

[0078] The lithium ion battery preparation method of Example 7 differs from that of Example 1 in that the amount of lithium trifluoromethanesulfinate in the electrolyte is 0.1 g, and the amount of the non-aqueous organic solvent is adjusted to 84.4 g, as shown in Table 1. Others are the same as in Example 1.

[0079] Example 8

[0080] The lithium ion battery preparation method of Example 8 differs from that of Example 1 in that the amount of lithium trifluoromethanesulfinate in the electrolyte is 1 g, and the amount of the non-aqueous organic solvent is adjusted to 83.5 g, as shown in Table 1. Others are the same as in Example 1.

[0081] Example 9

[0082] The lithium ion battery preparation method of Example 9 differs from that of Example 1 in that the amount of lithium trifluoromethanesulfinate in the electrolyte is 3 g, and the amount of the non-aqueous organic solvent is adjusted to 81.5 g, as shown in Table 1. Others are the same as in Example 1.

[0083] Example 10

[0084] The lithium ion battery preparation method of Example 10 differs from that of Example 1 in that the amount of the first additive in the electrolyte is 0.01 g, the amount of lithium trifluoromethanesulfinate is 0.05 g, and the amount of the non-aqueous organic solvent is adjusted to 84.94 g, as shown in Table 1. The rest is the same as in Example 1.

[0085] Example 11

[0086] The lithium ion battery preparation method of Example 11 differs from that of Example 1 in that the amount of the first additive in the electrolyte is 0.05 g, the amount of lithium trifluoromethanesulfinate is 0.05 g, and the amount of the non-aqueous organic solvent is adjusted to 84.9 g, as shown in Table 1. The rest is the same as in Example 1.

[0087] Example 12

[0088] The lithium ion battery preparation method of Example 12 differs from that of Example 1 in that the amount of the first additive in the electrolyte is 0.1 g, the amount of lithium trifluoromethanesulfinate is 0.1 g, and the amount of the non-aqueous organic solvent is adjusted to 84.8 g, as shown in Table 1. The rest is the same as in Example 1.

[0089] Example 13

[0090] The lithium ion battery preparation method of Example 13 differs from that of Example 1 in that the amount of the first additive in the electrolyte is 1 g, the amount of lithium trifluoromethanesulfinate is 1 g, and the amount of the non-aqueous organic solvent is adjusted to 83 g, as shown in Table 1. The rest is the same as in Example 1.

[0091] Example 14

[0092] The lithium ion battery preparation method of Example 14 differs from that of Example 1 in that the amount of the first additive in the electrolyte is 3 g, the amount of lithium trifluoromethanesulfinate is 3 g, and the amount of the non-aqueous organic solvent is adjusted to 79 g, as shown in Table 1. The rest is the same as in Example 1.

[0093] Example 15

[0094] The lithium ion battery preparation method of Example 15 is different from that of Example 1 in that the amount of the first additive in the electrolyte is 5 g, the amount of lithium trifluoromethanesulfinate is 3 g, and the amount of the non-aqueous organic solvent is adjusted to 77 g, as shown in Table 1. The rest is the same as Example 1.

[0095] Example 16

[0096] The lithium ion battery preparation method of Example 16 differs from that of Example 1 in that the amount of the first additive in the electrolyte is 0.2 g, and the amount of lithium trifluoromethanesulfinate is 0.8 g, as shown in Table 1. Other details are the same as those of Example 1.

[0097] Example 17

[0098] The lithium ion battery preparation method of Example 17 differs from that of Example 1 in that the amount of the first additive in the electrolyte is 0.8 g, and the amount of lithium trifluoromethanesulfinate is 0.2 g, as shown in Table 1. Other details are the same as those of Example 1.

[0099] Example 18

[0100] The difference between the lithium ion battery preparation method of Example 18 and that of Example 1 is that the positive electrode active material LiNi 0.9 Co 0.05 Mn 0.05 O2 replaced by LiNi 0.95 Co 0.02 Al 0.03 O2, as shown in Table 1, and the rest are the same as in Example 1.

[0101] Example 19

[0102] The difference between the lithium ion battery preparation method of Example 19 and that of Example 1 is that the positive electrode active material LiNi 0.9Co 0.05 Mn 0.05 O2 is replaced by lithium nickel manganese oxide, as shown in Table 1, and the rest is the same as in Example 1.

[0103] Example 20

[0104] The lithium ion battery preparation method of Example 20 differs from that of Example 1 in that the lithium salt in the electrolyte is replaced by 15 g of lithium hexafluorophosphate from 8 g of lithium hexafluorophosphate and 7 g of lithium bis(fluorosulfonyl)imide, as shown in Table 1. The rest is the same as in Example 1.

[0105] Example 21

[0106] The lithium ion battery preparation method of Example 21 differs from that of Example 1 in that the lithium salt in the electrolyte is replaced by 18 g of lithium hexafluorophosphate instead of 8 g of lithium hexafluorophosphate and 7 g of lithium bis(fluorosulfonyl)imide, and the amount of the non-aqueous organic solvent is adjusted to 81 g, as shown in Table 1. The rest is the same as in Example 1.

[0107] Example 22

[0108] The lithium ion battery preparation method of Example 22 differs from that of Example 1 in that the lithium salt in the electrolyte is replaced by 9 g of lithium hexafluorophosphate instead of 8 g of lithium hexafluorophosphate and 7 g of lithium bis(fluorosulfonyl)imide, and the amount of the non-aqueous organic solvent is adjusted to 90 g, as shown in Table 1. The rest is the same as in Example 1.

[0109] Example 23

[0110] The lithium ion battery preparation method of Example 23 differs from that of Example 1 in that the lithium salt in the electrolyte is replaced by 7 g of lithium hexafluorophosphate instead of 8 g of lithium hexafluorophosphate and 7 g of lithium bis(fluorosulfonyl)imide, and the amount of the non-aqueous organic solvent is adjusted to 92 g, as shown in Table 1. The rest is the same as in Example 1.

[0111] Example 24

[0112] The lithium ion battery preparation method of Example 24 differs from that of Example 1 in that the lithium salt in the electrolyte is replaced by 15 g of lithium bis(fluorosulfonyl)imide instead of 8 g of lithium hexafluorophosphate and 7 g of lithium bis(fluorosulfonyl)imide, as shown in Table 1. The rest is the same as in Example 1.

[0113] Example 25

[0114] The lithium-ion battery preparation method of Example 25 differs from that of Example 1 in that the negative electrode active material graphite-silicon carbon is replaced with silicon carbon, as shown in Table 1. Other details are the same as those of Example 1.

[0115] Example 26

[0116] The lithium-ion battery preparation method of Example 26 differs from that of Example 1 in that the negative electrode active material graphite-silicon carbon is replaced with graphite, as shown in Table 1. Other details are the same as those of Example 1.

[0117] Comparative Example 1

[0118] The lithium ion battery preparation method of Comparative Example 1 differs from that of Example 1 in that lithium trifluoromethanesulfinate is not added to the electrolyte, the total amount of electrolyte additives is 0.5 g, and the amount of non-aqueous organic solvent is adjusted to 84.5 g, as shown in Table 1. Other conditions are the same as those of Example 1.

[0119] Comparative Example 2

[0120] The lithium ion battery preparation method of Comparative Example 2 differs from that of Example 1 in that: the first additive is not added to the electrolyte, the total amount of the electrolyte additive is 0.5 g, and the amount of the non-aqueous organic solvent is adjusted to 84.5 g, as shown in Table 1. Others are the same as in Example 1.

[0121] Comparative Example 3

[0122] The lithium ion battery preparation method of Comparative Example 3 differs from that of Example 1 in that: lithium trifluoromethanesulfinate is not added to the electrolyte, but 1 g of the first additive is added, and the total amount of the electrolyte additive is 1 g, as shown in Table 1. Others are the same as in Example 1.

[0123] Comparative Example 4

[0124] The lithium ion battery preparation method of Comparative Example 4 differs from that of Example 1 in that: the first additive is not added to the electrolyte, but 1 g of lithium trifluoromethanesulfinate is added, and the total amount of the electrolyte additive is 1 g, as shown in Table 1. Other details are the same as in Example 1.

[0125] Comparative Example 5

[0126] The lithium ion battery preparation method of Comparative Example 5 differs from that of Example 1 in that: the first additive and lithium trifluoromethanesulfinate are not added to the electrolyte, the total amount of the electrolyte additive is 0 g, and the amount of the non-aqueous organic solvent is adjusted to 85 g, as shown in Table 1. Other conditions are the same as those of Example 1.

[0127] Table 1

[0128]

[0129] Performance testing:

[0130] The lithium-ion batteries obtained in Examples 1 to 26 and Comparative Examples 1 to 5 were tested for high-temperature cycle performance, high-temperature storage performance, DCIR and EIS performance before and after high-temperature storage, and rate performance. The test conditions are as follows, and the test results are shown in Table 2.

[0131] 1. High temperature cycle performance test:

[0132] The two lithium-ion batteries with the capacity divided by the upper clamping plate were placed in a preset temperature environment respectively, and charged to the upper limit cut-off voltage at a constant current and voltage of 1C / 1C, with a cut-off current of 0.05C. Then, they were discharged to the lower limit cut-off voltage at a constant current of 1C / 1C. This cycle was repeated, and the discharge capacity of the first cycle and the discharge capacity of the last cycle of the two lithium-ion batteries were recorded respectively. The capacity retention rate was calculated according to the following formula.

[0133] Capacity retention rate = discharge capacity of the last cycle / discharge capacity of the first cycle × 100%.

[0134] The capacity retention rate of lithium-ion batteries after 1000 cycles at high temperature (45°C) under 1C and 1C charge and discharge conditions was tested.

[0135] 2. High temperature storage test:

[0136] After removing the upper clamping plate from a lithium-ion battery with completed capacity separation, place it in an environment of 25°C and charge it at a constant current and constant voltage of 1C to the upper cut-off voltage, with a cut-off current of 0.05C. Then discharge it at a constant current of 1C to the lower cut-off voltage. Record the discharge capacity at this time as C0, and use a cell thickness tester to test the cell thickness before high-temperature storage, which is recorded as D1. The cell is then charged again at a constant current and constant voltage of 1C to the upper cutoff voltage, with a cutoff current of 0.05C. The fully charged battery is then placed in a 60°C constant temperature oven for 30 days, after which the battery is removed. The cell thickness after high-temperature storage is immediately tested using a cell thickness tester and recorded as D2. The battery is then placed in a 25°C environment for 2 hours, and then discharged at a constant current of 1C to the lower cutoff voltage in a 25°C environment. The discharge capacity at this time is recorded as C1. The battery is then charged at a constant current and constant voltage of 1C to the upper cutoff voltage, with a cutoff current of 0.05C, and then discharged at a constant current of 1C to the lower cutoff voltage. The discharge capacity at this time is recorded as C2.

[0137] Capacity retention rate = (C1 / C0) × 100%.

[0138] Capacity recovery rate = (C2 / C0) × 100%.

[0139] Thickness expansion rate = (D2-D1) / D1×100%.

[0140] 3. DCIR and EIS tests before and after high temperature storage:

[0141] Lithium-ion battery DCIR1 test before storage: Place the lithium-ion battery in a 25°C environment and charge it at a constant current of 0.5C to an upper cutoff voltage of 4.3V. Then, charge it at a constant voltage of 4.3V with a cutoff current of 0.05C. Then, discharge it at a constant current of 1C for 30 minutes (adjusted to 50% SOC, SOC refers to the battery's state of charge). Record the discharge voltage V0 at this time. Then, let the lithium-ion battery rest for 5 minutes and discharge it at a constant current of I1, corresponding to a 2C rate, for 30 seconds. Record the discharge voltage V1 at this time. Calculate the discharge DC internal resistance (DCIR1) before high-temperature storage: DCIR1 = (V0 - V1) / I1, in mΩ.

[0142] The DCIR2 test of lithium-ion batteries after storage: The above lithium-ion batteries were placed in a 60°C explosion-proof oven. After 30 days of storage, the batteries were removed and placed in a 25°C environment. They were charged at a constant current of 0.5C to an upper cutoff voltage of 4.3V. They were then charged at a constant voltage of 4.3V with a cutoff current of 0.05C. They were then discharged at a constant current of 1C for 30 minutes (adjusted to 50% SOC, where SOC refers to the battery's state of charge). The discharge voltage V2 at this time was recorded. The lithium-ion batteries were then left to rest for 5 minutes and discharged at a constant current of I1, corresponding to a 2C rate, for 30 seconds. The discharge voltage at this time was recorded as V3. The discharge DC internal resistance (DCIR2) after high-temperature storage was calculated as: DCIR2 = (V2 - V3) / I1, in mΩ.

[0143] Impedance growth rate (%) = (DCIR2-DCIR1) / DCIR1×100%.

[0144] ESI1 test of lithium-ion batteries before storage: The lithium-ion battery is placed in an environment of 25°C and charged to 50% SOC at a constant current and constant voltage of 1C for 30 minutes. The battery is then placed in an EIS electrochemical test cabinet (recording the open circuit voltage and setting the scanning frequency to 0.01 Hz–100 kHz). The Nyquist plot can be obtained. By analyzing the Nyquist plot with the help of Z-View software, Rct1 can be fitted.

[0145] ESI2 test of lithium-ion batteries before storage: Place the lithium-ion battery in an environment of 25°C, charge it to 50% SOC at 1C constant current and constant voltage for 30 minutes, and then place the battery in an EIS electrochemical test cabinet (record the open circuit voltage and set the scanning frequency to 0.01 Hz–100 kHz). The Nyquist diagram can be obtained by analyzing the Nyquist diagram with the help of Z-View software, and Rct2 can be fitted.

[0146] Rct impedance growth rate (%) = (Rct2-Rct1) / Rct1×100%.

[0147] 4. Rate performance test:

[0148] The two lithium-ion batteries with completed upper plate capacity separation were placed in a preset temperature environment respectively, and charged to the upper cut-off voltage at a constant current and constant voltage of 1C / 1C with a cut-off current of 0.05C, and then discharged to the lower cut-off voltage at a constant current of 1C / 1C for one cycle; charged to the upper cut-off voltage at a constant current and constant voltage of 3C / 3C with a cut-off current of 0.05C, and then discharged to the lower cut-off voltage at a constant current of 1C / 1C for three cycles, and the 1C discharge capacity of the two batteries at 1C and the last cycle of 1C discharge capacity were recorded respectively, and the relative 1C capacity retention rate was calculated according to the following formula.

[0149] Relative 1C capacity retention rate = 1C discharge capacity of the last cycle / 1C discharge capacity × 100%.

[0150] The relative 1C capacity retention rate of lithium-ion batteries after one cycle at room temperature (25°C) under 3C and 1C charge and discharge conditions was tested.

[0151] Table 2

[0152]

[0153] Compared with Comparative Examples 1 and 3, the rate performance and high-temperature performance of the battery provided in Example 1 are superior to those of the batteries provided in Comparative Examples 1 and 3. This is because the first additive and lithium trifluoromethylsulfinate were added to the electrolyte in Example 1, while the first additive was added to the electrolyte in Comparative Examples 1 and 3, but lithium trifluoromethylsulfinate was not added. Compared with Comparative Example 5, which did not add either the first additive or lithium trifluoromethylsulfinate, the rate performance and high-temperature performance of Comparative Example 5 were even worse.

[0154] Comparing Example 1 with Comparative Examples 2 and 4, the rate performance and high-temperature performance of the battery provided in Example 1 are superior to those of the batteries provided in Comparative Examples 2 and 4. This is because the electrolyte in Example 1 contains both the first additive and lithium trifluoromethanesulfinate, while the electrolytes in Comparative Examples 2 and 4 contain lithium trifluoromethanesulfinate but not the first additive. Comparing Comparative Examples 2 and 4 with Comparative Example 5, which does not contain either the first additive or lithium trifluoromethanesulfinate, the rate performance and high-temperature performance of Comparative Example 5 are even worse.

[0155] From the above, it can be seen that there is a synergistic effect between the first additive and lithium trifluoromethanesulfinate, thereby improving the rate performance and high temperature performance of the battery. Specifically, since the first additive contains sulfonyl fluoride groups and benzene rings, a dense CEI film is formed on the surface of the positive electrode active material through the synergistic effect of the sulfonyl fluoride groups and the benzene rings. This not only makes up for the limited antioxidant capacity of lithium trifluoromethanesulfinate for high-voltage positive electrodes and the inability to effectively form a CEI film, but also improves the problems of lattice oxygen release and transition metal dissolution in high-voltage material systems. The trifluoromethanesulfinate ion in lithium trifluoromethanesulfinate can be oxidized and decomposed at the positive terminal, and its decomposition products (such as SO2, CHF3, etc.) are released in the form of gas. SO2 can react with Li2S produced by the decomposition of the first additive to form Li2SO3, filling the pores of the CEI film and reducing gas residues; the strong electronegativity of CHF3 can capture free electrons and inhibit the continuous decomposition and gas production of the electrolyte. At the same time, the decomposition products of lithium trifluoromethanesulfinate can release lithium ions (Li + ) is embedded in the negative electrode, alleviating the effect of the increase in SEI film interface impedance caused by the accumulation of by-products. The generated SEI film has high ionic conductivity (greater than 10 -10 S / cm), can also reduce the Rct interface impedance, and the Li + It can be directly embedded in the negative electrode to compensate for the active lithium consumed by the first additive in promoting the formation of the CEI film, further accelerate the directional replenishment of active lithium, and ultimately improve the ionic conductivity of the CEI film, improving the problem of increased interface impedance caused by the first additive. In other words, the first additive and lithium trifluoromethylsulfinate can promote the formation of a dense and highly ionic conductive interface film on the positive and negative electrodes of the battery through synergistic action. This interface film can not only effectively prevent the electrolyte from undergoing side reactions on the electrodes at high temperatures, thereby improving the high-temperature performance of the battery, but also because the interface film can also reduce the interface impedance, thereby improving the rate performance of the battery. In addition, the sulfonyl group of the first additive can also fix the non-aqueous organic solvent molecules in the electrolyte through strong hydrogen bonding, reduce the volatilization of non-aqueous organic solvents at high temperatures, and work together with the directional release of active lithium in lithium trifluoromethylsulfinate to enhance the thermodynamic stability of the SEI / CEI film, further improving the high-temperature performance of the battery system.

[0156] Compared with Examples 1 to 5, the content of lithium trifluoromethanesulfinate in the electrolyte remains unchanged, but the content of the first additive in the electrolyte changes. Specifically, in Examples 2, 3, 1, 4, and 5, the mass ratios of the first additive to lithium trifluoromethanesulfinate are 0.01:0.5, 0.1:0.5, 0.5:0.5, 1:0.5, and 5:0.5, respectively, that is, the mass ratio of the two is 0.02 to 10. From the test results in Table 2, it can be seen that as the content of the first additive in the electrolyte increases, the capacity retention of the battery after 1000 cycles at 45°C first increases and then decreases; the capacity retention rate and capacity recovery rate of the battery after 30 days of storage at 60°C both first increase and then decrease, while the thickness expansion first decreases and then increases; the DCIR growth rate and Rct growth rate of the battery before and after high-temperature storage first decrease and then increase; the rate performance of the battery first improves and then deteriorates. The battery's high-temperature and rate performance are optimized when the mass ratio of the first additive to lithium trifluoromethanesulfinate is 0.5:0.5. However, in the electrolyte, if the first additive content is greater than the lithium trifluoromethanesulfinate content, or if the lithium trifluoromethanesulfinate content is greater than the first additive content, the battery's high-temperature and rate performance will be reduced to some extent. This is because a large difference between the first additive content and the lithium trifluoromethanesulfinate content in the electrolyte weakens the synergistic effect between the first additive and lithium trifluoromethanesulfinate, thereby reducing battery performance.

[0157] Compared with Example 1, Example 6 to Example 9, the content of the first additive in the electrolyte remains unchanged, while the content of lithium trifluoromethylsulfinate in the electrolyte changes. Specifically, in Example 6, Example 7, Example 1, Example 8, and Example 9, the mass ratios of the first additive to lithium trifluoromethylsulfinate are 0.5:0.05, 0.5:0.1, 0.5:0.5, 0.5:1, and 0.5:3, respectively. From the test results in Table 2, it can be seen that as the content of lithium trifluoromethylsulfinate in the electrolyte increases, the capacity retention of the battery after 1000 cycles at 45°C first increases and then decreases; the capacity retention rate and capacity recovery rate of the battery after 30 days of storage at 60°C both first increase and then decrease, while the thickness expansion first decreases and then increases; the DCIR growth rate and Rct growth rate of the battery before and after high-temperature storage first decrease and then increase; the rate performance of the battery first improves and then deteriorates. The battery's high-temperature and rate performance are optimized when the mass ratio of the first additive to lithium trifluoromethanesulfinate is 0.5:0.5. However, in the electrolyte, if the first additive content is greater than the lithium trifluoromethanesulfinate content, or if the lithium trifluoromethanesulfinate content is greater than the first additive content, the battery's high-temperature and rate performance will be reduced to some extent. This is because a large difference between the first additive content and the lithium trifluoromethanesulfinate content in the electrolyte weakens the synergistic effect between the first additive and lithium trifluoromethanesulfinate, thereby reducing battery performance.

[0158] From the test results in Table 2, it can be seen that among Examples 1 to 9, the high temperature performance and rate performance of the battery of Example 1 are the best, when the mass ratio of the first additive and lithium trifluoromethanesulfinate in the electrolyte is 0.5:0.5; when the mass ratio of the first additive and lithium trifluoromethanesulfinate in the electrolyte is controlled to be 0.5:0.5, 0.1:0.5, 1:0.5, 0.5:0.05, 0.5:0.1, 0.5:1, and 0.5:3, the capacity retention rate of the battery after 1000 cycles at 45°C is greater than 81.5%; the capacity retention rate and capacity recovery rate of the battery after storage for 30 days at 60°C are greater than 78.5% and 79.5%, respectively, and the thickness expansion rate is less than 6.8%; before and after high temperature storage, the DCIR growth rate of the battery is less than 85%, and the Rct growth rate is less than 56%; the 1C capacity retention rate of the battery is greater than 93.5%, and the 3C capacity retention rate is greater than 88%.

[0159] Compared with Example 10, Example 3 reduces the content of the first additive and the content of lithium trifluoromethanesulfinate in the electrolyte in equal proportions. The total content of the first additive and lithium trifluoromethanesulfinate in the electrolyte decreases from 0.6wt% to 0.06wt%. The high temperature performance and rate performance of the battery are both reduced. This shows that an excessive total content of the first additive and lithium trifluoromethanesulfinate in the electrolyte is not conducive to improving battery performance, and it is necessary to control the total content of the first additive and lithium trifluoromethanesulfinate in the electrolyte.

[0160] Compared with Example 1 and Example 11 to Example 14, the mass ratio of the first additive to lithium trifluoromethylsulfinate is 1:1, but the total amount of the first additive and lithium trifluoromethylsulfinate in the electrolyte changes. As the total amount of the first additive and lithium trifluoromethylsulfinate increases, the high temperature performance and rate performance of the battery first improve and then deteriorate. This is because increasing the total content of the first additive and lithium trifluoromethylsulfinate in the electrolyte is not only beneficial to improving the film formation effect of the SEI film and the CEI film, but an excessive total content of the first additive and lithium trifluoromethylsulfinate in the electrolyte will cause changes in the acidity and viscosity of the electrolyte, thereby deteriorating the performance of the electrolyte and decreasing the battery performance. Among the above-mentioned Examples 1 and 11 to 14, the high temperature performance and rate performance of the battery of Example 1 are the best, when the total content of the first additive and lithium trifluoromethanesulfinate in the electrolyte is 1wt%; when the total content of the first additive and lithium trifluoromethanesulfinate in the electrolyte is controlled to be 0.2wt% to 6wt%, the capacity retention rate of the battery after 1000 cycles at 45°C is greater than 81%; the capacity retention rate and capacity recovery rate of the battery after storage at 60°C for 30 days are greater than 78% and 79%, respectively, and the thickness expansion rate is less than 7%; before and after high temperature storage, the DCIR growth rate of the battery is less than 85%, and the Rct growth rate is less than 55.5%; the 1C capacity retention rate of the battery is greater than 93%, and the 3C capacity retention rate is greater than 87%.

[0161] Compared with Example 9, Example 14 and Example 15, the content of lithium trifluoromethylsulfinate in the electrolyte remains unchanged, the content of the first additive in the electrolyte increases, and the total content of the first additive and lithium trifluoromethylsulfinate in the electrolyte increases from 3.5wt% to 8wt%. The high temperature performance and rate performance of the battery first improve and then deteriorate, among which Example 14 has the best performance among the three. This is because the difference between the content of the first additive and the content of lithium trifluoromethylsulfinate in the electrolyte of Example 9 is too large, which makes it difficult for the first additive and lithium trifluoromethylsulfinate to effectively produce a synergistic effect; the total content of the first additive and lithium trifluoromethylsulfinate in the electrolyte of Example 15 is too large, especially the redundant content of part of the first additive, which leads to the deterioration of the performance of the electrolyte and the reduction of battery performance.

[0162] Compared with Example 1, Example 16, and Example 17, the total amount of the first additive and lithium trifluoromethylsulfinate in the electrolyte remains unchanged, and the mass ratio of the first additive to the lithium trifluoromethylsulfinate changes. As can be seen from the results in Table 2, when the mass ratio of the first additive to the lithium trifluoromethylsulfinate is 0.5:0.5, the first additive and the lithium trifluoromethylsulfinate can effectively produce a synergistic effect, and the high temperature performance and rate performance of the battery are optimized. However, in the electrolyte, the content of the first additive is greater than the content of the lithium trifluoromethylsulfinate, or the content of the lithium trifluoromethylsulfinate is greater than the content of the first additive. Both will affect the synergistic cooperation between the two to a certain extent, thereby reducing the high temperature performance and rate performance of the battery.

[0163] Compared with Example 1, Example 18 and Example 19, the positive electrode active material of the battery has changed. The results show that the high temperature performance and rate performance of the batteries in Example 1, Example 18 and Example 19 are better, which shows that the electrolyte additive provided in the examples of this application can be applied to a variety of positive electrode material systems and optimize the performance of the battery.

[0164] Compared with Example 1, Example 20 and Example 24, the type of lithium salt in the electrolyte has changed. The results show that the high temperature performance and rate performance of the batteries in Example 1, Example 20 and Example 24 are better, which shows that the electrolyte additive provided in the examples of the present application can be used in electrolytes containing different lithium salts and optimize the performance of the battery.

[0165] Further comparing Examples 20 to 23, the type of lithium salt in the electrolyte is the same, but the content of lithium salt in the electrolyte changes. As the content of lithium salt in the electrolyte increases, the high temperature performance and rate performance of the battery are improved. This is because increasing the content of lithium salt is beneficial to improving the ionic conductivity of the electrolyte and promoting the growth of the interfacial film.

[0166] Compared with Example 1, Example 25 and Example 26, the negative electrode active material of the battery has changed. The results show that the high temperature performance and rate performance of the batteries in Example 1, Example 25 and Example 26 are better, which shows that the electrolyte additive provided in the examples of this application can be applied to a variety of negative electrode material systems and optimize the performance of the battery.

[0167] The above is a detailed introduction to the embodiments of the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. At the same time, for those skilled in the art, based on the ideas of the present application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. An electrolyte, characterized in that: The electrolyte comprises an electrolyte salt, a non-aqueous organic solvent and an electrolyte additive, wherein the electrolyte additive comprises a first additive and lithium trifluoromethanesulfinate; the structural formula of the first additive is shown in formula (I): Formula (I), Wherein, in the electrolyte additive, the mass ratio of the first additive to the lithium trifluoromethanesulfinate is 0.02-10; Based on the total mass of the electrolyte, the mass proportion of the first additive is 0.01 wt% to 5 wt%, and the mass proportion of the lithium trifluoromethanesulfinate is 0.05 wt% to 3 wt%.

2. The electrolyte according to claim 1, characterized in that In the electrolyte additive, the mass ratio of the first additive to the lithium trifluoromethanesulfinate is 0.25-4.

3. The electrolyte according to claim 1, characterized in that Based on the total mass of the electrolyte, the mass proportion of the first additive is 0.1 wt % to 1 wt %.

4. The electrolyte according to claim 1, characterized in that Based on the total mass of the electrolyte, the total mass of the first additive and the lithium trifluoromethanesulfinate accounts for 0.06 wt % to 8 wt %.

5. The electrolyte according to claim 4, characterized in that Based on the total mass of the electrolyte, the total mass of the first additive and the lithium trifluoromethanesulfinate accounts for 0.2 wt % to 6 wt %.

6. The electrolyte according to claim 1, characterized in that The electrolyte includes, by weight, 7 to 18 parts of the electrolyte salt, 70 to 92 parts of the non-aqueous organic solvent, 0.01 to 5 parts of the first additive, and 0.05 to 3 parts of lithium trifluoromethanesulfinate.

7. The electrolyte according to claim 6, characterized in that The electrolyte includes, by weight, 9 to 15 parts of the electrolyte salt, 75 to 83 parts of the non-aqueous organic solvent, 0.1 to 1 parts of the first additive, and 0.1 to 0.5 parts of lithium trifluoromethanesulfinate.

8. The electrolyte according to any one of claims 1 to 7, characterized in that The electrolyte salt includes a lithium salt, and the lithium salt includes at least one of lithium hexafluorophosphate, lithium perchlorate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium bistrifluoromethylsulfonyl imide and lithium bisfluorosulfonyl imide; and / or, The non-aqueous organic solvent includes at least one of a carbonate compound, a fluorinated product of a carbonate compound, a carboxylate compound, and a fluorinated product of a carboxylate compound.

9. A battery, characterized in that: The battery comprises a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte according to any one of claims 1 to 8.

10. The battery according to claim 9, characterized in that The positive electrode sheet includes a positive electrode active material; the positive electrode active material includes LiNi 1-x-y Co x Mn y O2、LiNi 1-x-z Co x Al z At least one of O2, lithium nickel manganese oxide, lithium cobalt oxide, lithium-rich manganese-based and lithium manganese oxide, wherein 0≤x≤1, 0≤y≤1, 0≤z≤1, and 0≤x+y≤1, 0≤x+z≤1; and / or, The negative electrode plate includes a negative electrode active material; the negative electrode active material includes at least one of artificial graphite, lithium metal, coated natural graphite, silicon-carbon material and silicon material.

11. The battery according to claim 9, characterized in that The charging cut-off voltage of the battery is greater than or equal to 4.3V to 4.8V.

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