A battery monomer, a preparation method thereof, a battery device, and an energy storage device

Abstract

The application relates to the field of secondary batteries, and provides a battery monomer, a preparation method of the battery monomer, a battery device and an energy storage device. In the battery monomer, an electrolyte comprises a cyanopyridine additive, a sulfonyl fluoride additive and an amine additive, at least the initial efficiency of the battery monomer can be improved, and the capacity attenuation and internal resistance increase of the battery monomer can be well inhibited, so that the use performance of the battery monomer is improved.

Description

Technical Field

[0001] This application relates to the field of secondary batteries, and in particular to a battery cell and its preparation method, battery device, and energy storage device. Background Technology

[0002] During the formation of a secondary battery, the active lithium of the positive electrode and substances in the electrolyte are consumed to form an SEI (Solid Electrolyte Interface) film. The SEI film can protect the negative electrode material.

[0003] However, the initial formation of the SEI film irreversibly consumes active lithium, resulting in a low initial efficiency (i.e., first-time efficiency) of the secondary battery, directly reducing the energy density of the secondary battery. Moreover, during cycling, especially under high current charging and discharging or high and low temperature environments, the SEI is prone to rupture. This leads to the continuous decomposition of the electrolyte in the secondary battery and the repeated growth of the SEI film, which continuously consumes active lithium and electrolyte, resulting in accelerated capacity decay and increased internal resistance of the secondary battery, affecting the performance of the secondary battery. Summary of the Invention

[0004] This application provides a battery cell and its preparation method, battery device, and energy storage device, which at least helps to improve the initial efficiency of the battery cell, and can also effectively suppress the capacity decay and internal resistance increase of the battery cell, thereby improving the performance of the battery cell.

[0005] The first aspect of this application provides a battery cell, including a cell assembly, the cell assembly including a positive electrode, a separator and a negative electrode; a housing, the cell assembly being located inside the housing; an electrolyte, the electrolyte being located inside the housing; the electrolyte including additives, the additives including cyanopyridine additives, sulfonyl fluoride additives and amine additives; The general structural formula of cyanopyridine additives is shown in Formula I below:

[0006] R1, R2, and R3 are each independently selected from any one of hydrogen atom, C1-C4 alkyl, C1-C4 alkoxy, halogen or cyano, and at least one of R1, R2, and R3 is cyano; The general structural formula of sulfonyl fluoride additives is shown in Formula II below:

[0007] R4 is selected from any one of aryl or C2-C6 hydrocarbon groups containing unsaturated bonds, wherein the aryl group includes at least one of substituted or unsubstituted thiophene, furanyl, phenyl or pyridinyl, and the substituent is at least one of halogen or C1-C3 alkyl. The general structural formula of amine additives is shown in Formula III below:

[0008] R5, R6, and R7 are each independently selected from any one of hydrogen atoms, C1-C6 alkyl groups, or C1-C6 alkoxyalkyl groups, and R5, R6, and R7 are not all hydrogen atoms at the same time.

[0009] A second aspect of this application also provides a method for preparing the above-mentioned battery cell, comprising: placing a cell assembly and an electrolyte in a housing; performing a formation step; wherein the formation step includes a first charging step, a second charging step, and a third charging step performed sequentially, wherein the first charging step charges to a first cutoff voltage, the second charging step charges to a second cutoff voltage, and the third charging step charges to a third cutoff voltage, wherein the first cutoff voltage is less than the second cutoff voltage, and the second cutoff voltage is less than the third cutoff voltage.

[0010] A third aspect of this application also provides a battery device comprising the aforementioned battery cell, or a battery cell prepared by the aforementioned method for preparing the battery cell.

[0011] A fourth aspect of this application also provides an energy storage device, including the aforementioned battery device, which is used to store electrical energy.

[0012] The technical solution provided in this application has at least the following advantages: In the battery cell of this application, the electrolyte contains cyanopyridine additives, sulfonyl fluoride additives, and amine additives. During formation, all three additives are sequentially reduced and then combined to form an SEI composite film. The protective films formed by the three different additives have different characteristics, ensuring that the SEI composite film formed by their combined action has both good flexibility and good mechanical strength. Attached Figure Description

[0013] One or more embodiments are illustrated by way of example with corresponding pictures in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Unless otherwise stated, the pictures in the accompanying drawings do not constitute a limitation on scale. In order to more clearly illustrate the technical solutions in the embodiments of this application or in the conventional technology, 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.

[0014] Figure 1 This is a process flow diagram of the battery cell manufacturing process provided in the embodiments of this application. Detailed Implementation

[0015] As the background technology indicates, the initial growth of the SEI film leads to excessive loss in the initial efficiency and energy density of the secondary battery. Furthermore, during cycling, especially under high-current charge / discharge and high / low temperature conditions, the SEI film repeatedly ruptures and grows, continuously consuming active lithium and electrolyte, resulting in a decline in the performance of the battery cells. This is because the negative electrode material (such as graphite particles) undergoes significant volume changes (approximately 10%) during cycling, while traditional SEI films have limited mechanical properties, being either too brittle or too soft, making them prone to rupture when negative electrode materials like graphite repeatedly expand and contract.

[0016] Currently, there are technical solutions to improve the performance of SEI films by adding film-forming additives to the electrolyte, such as adding vinylene carbonate (VC) and fluoroethylene carbonate (FEC). However, it is still difficult to achieve a balance between the mechanical strength and elasticity of the SEI film. For example, although VC can form a polyVC-based SEI film with a certain degree of elasticity, its mechanical strength is insufficient; FEC can form a hard SEI film rich in LiFe, but it has poor elasticity and is too brittle.

[0017] Based on this, this application provides a battery cell, its preparation method, a battery device, and an energy storage device. In the battery cell of this application, the additives contained in the electrolyte can form an SEI film with high mechanical strength and good elasticity during the formation process, which can significantly reduce the number of SEI film rupture and growth cycles, thereby inhibiting the capacity decay and internal resistance increase of the battery cell, which is beneficial to improving the performance of the battery cell, and can also improve the first efficiency and energy density of the secondary battery.

[0018] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined. Similarly, "multiple sets" refers to two or more sets (including two sets), and "multiple pieces" refers to two or more pieces (including two pieces).

[0019] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0020] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. In addition, the character " / " in this document generally indicates that the related objects before and after it have an "or" relationship.

[0021] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application. For example, if the device or element in the illustration is inverted, then the element described as "below," "under," "below," or "bottom" of other elements or features will be oriented "above" or "top" of other elements or features. Therefore, the term "below" may cover both above and below orientation depending on the context in which the term is used, which will be obvious to those skilled in the art. Materials may be oriented in other ways (e.g., rotated 90 degrees, inverted, flipped), and the spatial relative descriptive terms used herein may be interpreted accordingly.

[0022] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0023] In the description of embodiments of this application, the terms "about," "approximately," "roughly," or "about" for referring to a specific parameter include numerical values, and those skilled in the art will understand that the deviation from the numerical value is within the acceptable tolerance of the specific parameter. For example, "about" or "about" for a numerical value may include additional numerical values ​​that are in the range of 90.0% to 110.0% of the numerical value, such as in the range of 95.0% to 105.0%, 97.5% to 102.5%, 99.0% to 101.0%, 99.5% to 100.5%, or 99.9% to 100.1%.

[0024] In the accompanying drawings corresponding to the embodiments of this application, the thickness and area of ​​the layers are enlarged for better understanding and ease of description. Furthermore, when describing a component as "generally" formed on another component, it means that the component is not formed on the entire surface (or front surface) of the other component, nor is it formed on a portion of the edge of the entire surface.

[0025] In the description of the embodiments of this application, when a component "includes" another component, other components are not excluded unless otherwise stated, and other components may be further included. The formation or provision of a second component above or on a first component, or on the surface of a first component, or on one side of a first component, may include embodiments where the first and second components are in direct contact, and may also include embodiments where an additional component may be present between the first and second components, thereby preventing direct contact between the first and second components. For simplicity and clarity, various components may be drawn at different scales. In the drawings, some layers / components may be omitted for simplicity. Unless otherwise specified, the formation or provision of a second component on the surface of a first component refers to direct contact between the first and second components. The term "component" may refer to a layer, film, region, portion, structure, etc.

[0026] The terminology used in the description of the various embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various embodiments and the appended claims, the term "component" is also intended to include the plural form unless the context clearly indicates otherwise. Components include layers, films, regions, or plates, etc.

[0027] The embodiments of this application will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0028] This application provides a battery cell, including a cell assembly, a casing, and an electrolyte. The cell assembly and electrolyte are located inside the casing, and the cell assembly includes a positive electrode, a separator, and a negative electrode.

[0029] In this embodiment, the electrolyte serves as a carrier for ion transport, effectively conducting ions. The electrolyte primarily comprises lithium salts, non-aqueous solvents, and additives. In this application, the additives in the electrolyte include cyanopyridine additives, sulfonyl fluoride additives, and amine additives. The general structural formula of the cyanopyridine additives is shown in Formula I below:

[0030] R1, R2, and R3 are each independently selected from any one of hydrogen atom, C1-C4 alkyl, C1-C4 alkoxy, halogen or cyano, and at least one of R1, R2, and R3 is a cyano group.

[0031] The general structural formula of sulfonyl fluoride additives is shown in Formula II below:

[0032] R4 is selected from any one of aryl or C2-C6 hydrocarbon groups containing unsaturated bonds. The aryl group includes at least one of substituted or unsubstituted thiophene, furanyl, phenyl or pyridinyl, and the substituent is at least one of halogen or C1-C3 alkyl.

[0033] The general structural formula of amine additives is shown in Formula III below:

[0034] R5, R6, and R7 are each independently selected from any one of hydrogen atoms, C1-C6 alkyl groups, or C1-C6 alkoxyalkyl groups, and R5, R6, and R7 are not all hydrogen atoms at the same time.

[0035] In the battery cell of this application, during formation, the three additives are sequentially reduced to form protective films, which are then combined to form an SEI composite film. The protective films formed by the three different additives have different characteristics, ensuring that the SEI composite film formed by their combined action has both good flexibility and good mechanical strength. Of course, in the actual formation process, the sequential formation of the three additives is also ensured by controlling the cutoff voltage, as detailed later in this application.

[0036] Among the additives, cyanopyridine additives are the most reactive and are preferentially reduced to form a film during the formation process. After film formation, cyanopyridine additives can block electrons, not only suppressing subsequent side reactions at high potentials but also improving the initial efficiency of the battery cell. Although cyanopyridine additives effectively block electrons after film formation, other additives and metal ions (such as Li)... + It can still pass through, therefore the subsequent sulfonyl fluoride additives will form a film on the inner surface of the cyanopyridine additive film (i.e., the surface near the negative electrode), and the sulfonyl fluoride additives will react with Li. +Together, they form a LiF / Li₂S rich film, which possesses high ionic conductivity and mechanical strength, acting as the main framework of the SEI film and ensuring its good mechanical strength. Finally, the amine additive also penetrates the cyanopyridine additive film and forms a film between the cyanopyridine additive film and the LiF / Li₂S rich film. This film has good elasticity and, being located in the middle of the SEI composite film, can buffer the volume surface of the SEI composite film, maintaining interfacial stability and making the SEI film less prone to breakage.

[0037] Through the combined action of cyanopyridine additives, sulfonyl fluoride additives, and amine additives, the resulting SEI composite film possesses both good mechanical strength and elasticity, making it less prone to repeated rupture and growth due to the expansion and contraction of the negative electrode material. Furthermore, the battery cells of this application exhibit high initial efficiency and minimal energy density loss after formation.

[0038] It should be noted that traditional SEI films are deposited and grown layer by layer from the surface (inner) of the negative electrode to the electrolyte (outer), with the later-formed material covering the surface of the earlier-formed material. However, in this application, because cyanopyridine additives allow other additives and Li to form the film, the process is different. + Therefore, in the process of forming the SEI composite film, the battery cells of this application do not grow layer by layer from the inside out. The cyanopyridine additives that react first form the film on the outermost side, the sulfonyl fluoride additives that react later form the film on the inner side, and the amine additives that react last form the film in between the two.

[0039] In addition, in some embodiments of this application, besides the three additives mentioned above, other additives, such as FEC, can be added as needed. If FEC is added, the amines will play a "proton acceptor" and "kinetic regulation" role during film formation, regulating the decomposition of FEC and causing it to decompose and react with Li in the electrolyte. + The reaction produces fine, uniform LiF nanocrystals. These LiF particles are embedded in the organic polymer matrix that the amine additive molecules may form. Moreover, the density of LiF gradually decreases from the inside out, thus forming a gradient distribution.

[0040] In some embodiments of this application, in order to take into account other properties such as ion transport performance of the electrolyte, the mass content of the additive is 0.5% to 5% based on the mass of the electrolyte; specifically, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, etc., or within the range of any two of the above values.

[0041] In some embodiments of this application, the mass ratio of cyanopyridine additives, sulfonyl fluoride additives, and amine additives is (0.3~0.8):1:(0.1~0.5), which enables the formation of an SEI film with suitable thickness and good protective properties. If the proportion of cyanopyridine additives is too low, it will be difficult to form a complete and dense protective film initially, leading to an increased risk of substrate exposure; if the proportion of cyanopyridine additives is too high, the subsequently formed SEI composite film may be too thick, resulting in a sharp increase in impedance. Sulfonyl fluoride additives serve as a core component, with their proportion fixed as a baseline to ensure that the SEI composite film has sufficient flexibility and sulfur / fluorine-containing stable components. If the proportion of amine additives is too low, it can easily lead to insufficient flexibility of the SEI composite film; if the proportion of amine additives is too high, it may result in an excessively thick SEI composite film or too much organic component, reducing the electron blocking ability.

[0042] As an example, this application lists specific types of cyanopyridine additives, sulfonyl fluoride additives, and amine additives, as follows: Cyanopyridine additives include at least one of the following compounds:

[0043] Acyl fluoride additives include at least one of the following compounds: .

[0044] Amine additives include at least one of the following compounds: .

[0045] As described above, the electrolyte contains, in addition to additives, solvents and lithium salts. This application does not impose any particular restrictions on the types and amounts of non-aqueous solvents and lithium salts, as long as they meet the objectives of this application.

[0046] For example, in this application, the non-aqueous solvent may include, but is not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds or cyclic carbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (EMC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. Other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. During the formation process, non-aqueous solvents may also undergo partial reduction, generating lithium carbonate, lithium alkoxy, etc. These products constitute the bottom layer of the SEI composite film, directly contacting the negative electrode material (such as graphite) and filling the pores between the inorganic framework.

[0047] In this application, the lithium salt may include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), lithium difluorooxalato)borate (LiDFOB), or lithium difluoroborate. This application does not impose any particular limitation on the content of the lithium salt in the electrolyte, as long as the purpose of this application is achieved. For example, based on the mass of the electrolyte, the mass percentage of the lithium salt is 8% to 15%. This application does not impose any particular limitation on non-aqueous solvents, as long as the purpose of this application is achieved.

[0048] Apart from the electrolyte, this application does not have any special requirements for components such as the positive electrode, negative electrode, and separator, as long as they can meet the purpose of this application. As an example, specific examples are given below.

[0049] Positive electrode sheet The positive electrode includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector. Specifically, in this application, the positive active layer can be disposed on one surface or on two surfaces along the thickness direction of the positive current collector. Furthermore, in this application, the "surface of the positive current collector" can be the entire area of ​​the positive current collector or only a portion thereof; there are no particular limitations, as long as the purpose of this application is achieved.

[0050] The components in the positive electrode active layer generally include positive electrode active material, positive electrode conductive agent, and positive electrode binder. Typically, the content of the positive electrode active material is 85wt%~95wt%, the positive electrode conductive agent is 1wt%~8wt%, and the binder is 2wt%~8wt%. The positive electrode active material can be any material capable of reversibly intercalating and deintercalating Li. + Na + Materials containing alkali metal ions are used to ensure the normal charging and discharging of individual battery cells. For example, positive electrode active materials include, but are not limited to, at least one of layered oxide positive electrode materials, spinel structure positive electrode materials, polyanion positive electrode materials, and lithium-rich manganese-based positive electrode materials; alternatively, high-voltage systems with a working voltage greater than or equal to 4.3V can be selected, such as high-nickel ternary materials, high-voltage spinel materials, lithium manganese phosphate, or lithium-rich manganese-based materials. Layered oxide positive electrode materials include, but are not limited to, LiCoO2 and LiNi. 1-x-y Co x Mn y At least one of O2, LiNiCoAlO2, etc., and spinel structure cathode materials include, but are not limited to, LiMn2O4, LiNi 0.5 Mn 1.5 At least one of O4, etc., and polyanionic cathode materials including but not limited to at least one of LiFePO4, LiMnPO4, Li3V2(PO4)3, etc.; high-nickel ternary materials such as LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.15 Al 0.05 O2 (NCA) and other compounds possess operating voltages of 4.3V~4.6V and high specific capacity, making them ideal cathode choices for high-voltage lithium metal batteries. High-voltage spinel LiNi... 0.5 Mn 1.5 O4 has an operating voltage of up to 4.7V, perfectly matching its high voltage stability. Lithium manganese iron phosphate, as an emerging high-voltage phosphate material, combines safety and high-voltage characteristics.

[0051] Positive conductive agents include, but are not limited to, at least one of the following: acetylene black, Super-P carbon black, amorphous carbon such as needle coke, carbon nanotubes, or graphene. Positive electrode binders include, but are not limited to, any one or at least two of the following: resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubber-like polymers such as styrene-butadiene rubber (SBR), nitrile rubber (NBR), fluororubber, isoprene rubber, polybutadiene rubber, and ethylene-propylene rubber; thermoplastic elastomers such as styrene-butadiene-styrene block copolymers or their hydrides, ethylene-propylene-diene terpolymers (EPDM), styrene-ethylene-butadiene-ethylene copolymers, and styrene-isoprene-styrene block copolymers or their hydrides; soft resin-like polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorinated polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; and polymer compositions with ion conductivity of alkali metal ions (especially lithium ions).

[0052] Positive electrode binders include, but are not limited to, any one or at least two of the following: resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubber-like polymers such as styrene-butadiene rubber (SBR), nitrile rubber (NBR), fluororubber, isoprene rubber, polybutadiene rubber, and ethylene-propylene rubber; thermoplastic elastomers such as styrene-butadiene-styrene block copolymers or their hydrides, ethylene-propylene-diene terpolymers (EPDM), styrene-ethylene-butadiene-ethylene copolymers, and styrene-isoprene-styrene block copolymers or their hydrides; soft resin-like polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorinated polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; and polymer compositions with ion conductivity of alkali metal ions (especially lithium ions).

[0053] In the positive electrode sheet, there are no particular restrictions on the type of positive current collector; it can be any known material suitable for use as a positive current collector. Materials for the positive current collector include, but are not limited to, metals such as aluminum, stainless steel, nickel plating, titanium, and tantalum. Furthermore, to reduce the electronic contact resistance between the positive current collector and the positive active material layer, conductive additives or conductive coatings can be applied to the surface of the positive current collector. Conductive additives include, but are not limited to, carbon and precious metals such as gold, platinum, and silver. The conductive coating can be a mixture of inorganic oxides, conductive agents, and positive electrode binders.

[0054] In preparing the positive electrode sheet, the components of the aforementioned positive active material layer can be dissolved or dispersed in a liquid solvent to form a positive electrode slurry. This slurry is then coated onto a positive current collector and dried, thereby forming the positive active material layer on the current collector, thus obtaining the positive electrode sheet. When preparing the positive electrode sheet using this method, there are no particular limitations on the solvent in the positive electrode slurry, as long as it can dissolve or disperse the aforementioned components. Specifically, the solvent in the positive electrode slurry includes, but is not limited to, N-methylpyrrolidone (NMP) and ethylene carbonate (EC). Alternatively, in preparing the positive electrode sheet, the components of the positive active material layer can be dry-mixed to form a sheet, which is then pressed onto the positive current collector.

[0055] Negative electrode sheet The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The composition of the negative electrode active material layer includes the negative electrode sheet active material. That is, in this application, the negative electrode active material layer can be disposed on one surface or on two surfaces in the thickness direction of the negative electrode current collector. Moreover, in this application, the "surface of the negative electrode current collector" can be the entire area of ​​the negative electrode current collector or a part of the negative electrode current collector. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0056] The negative electrode active material layer generally contains a negative electrode active material, and this application does not impose any particular limitation on the negative electrode active material. Specifically, the negative electrode active material may include at least one of carbon materials or silicon-based materials. More specifically, carbon materials include, but are not limited to, at least one of natural graphite, artificial graphite, mesophase microcarbon spheres, hard carbon, or soft carbon; silicon-based materials include, but are not limited to, at least one of silicon, silicon-oxygen composite materials, or silicon-carbon composite materials.

[0057] In some embodiments, the negative electrode active material layer typically also contains a negative electrode conductive agent. This application does not particularly limit the type of negative electrode conductive agent, as long as it achieves the purpose of this application. For example, negative electrode conductive agents include, but are not limited to, at least one of acetylene black, Ketjen black, carbon nanotubes, carbon fibers, carbon dots, or graphene.

[0058] In some embodiments, the negative electrode active material layer may also contain a negative electrode binder and a thickener. This application does not impose any particular limitation on the types of negative electrode binders and thickeners, as long as they can achieve the purpose of this application. For example, the negative electrode binder may include, but is not limited to, at least one of polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, or acrylated styrene-butadiene rubber; the thickener in the negative electrode slurry may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose.

[0059] In the negative electrode sheet, the material of the negative electrode current collector includes, but is not limited to, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal, etc., and this application does not have any particular limitations. Among them, the conductive metal includes, but is not limited to, copper, nickel, or titanium, and the material of the polymer substrate includes, but is not limited to, at least one of polyethylene, polypropylene, ethylene propylene copolymer, polyethylene terephthalate, polyethylene terephthalate, or poly(p-phenylene terephthalamide).

[0060] Furthermore, this application does not impose any particular limitations on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 12 μm, and the thickness of the single-sided negative electrode active material layer is 30 μm to 160 μm.

[0061] Furthermore, similar to the preparation of the positive electrode sheet, the preparation of the negative electrode sheet can be achieved either by preparing a negative electrode slurry, coating the slurry onto a negative electrode current collector, and drying it to form a negative electrode active material layer on the current collector, thus obtaining the negative electrode sheet; or by dry mixing the components of the negative electrode active material layer to form a sheet, which is then pressed onto the negative electrode current collector to form the negative electrode active material layer, thereby obtaining the negative electrode sheet. The solvent in the negative electrode slurry includes any one of aqueous solvents and organic solvents. Aqueous solvents include, but are not limited to, mixtures of alcohol and water or water itself. Organic solvents include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide. In some other embodiments, when using aqueous solvents, the negative electrode slurry composition may also include a thickener and styrene-butadiene rubber (SBR) emulsion to slurry the negative electrode slurry, thereby adjusting its viscosity. The types of thickeners in the positive electrode slurry include, but are not limited to, at least one of carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and their salts.

[0062] Separating membrane To prevent short circuits, a separator is typically placed between the positive and negative electrodes. In this case, the electrolyte of this application is typically used after penetrating into the separator.

[0063] This application does not impose any particular limitations on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application. The separator material may be a resin, glass fiber, inorganic material, etc., formed from a material stable to the electrolyte of this application. In some embodiments, the separator includes a porous sheet or non-woven fabric-like material with excellent liquid retention properties. Examples of resin or glass fiber separator materials include, but are not limited to, polyolefins, aromatic polyamides, polyimide (PI), polyamide (PA), polytetrafluoroethylene, polyethersulfone, spandex, or aramid. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-mentioned separator materials can be used alone or in any combination.

[0064] The separator can also be a material formed by laminating the above-mentioned materials, examples of which include, but are not limited to, a three-layer separator formed by laminating polypropylene, polyethylene, and polypropylene in that order.

[0065] Inorganic materials include, but are not limited to, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.). The forms of inorganic materials include, but are not limited to, particulate or fibrous forms.

[0066] The separator can be in the form of a thin film, including but not limited to non-woven fabric, woven fabric, and microporous membranes. In the thin film form, the pore size of the separator is 0.01 μm to 1 μm, and the thickness is 5 μm to 50 μm. In addition to the above-mentioned independent thin film separators, the following separators can also be used: separators formed by using a resin-based adhesive to form a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or negative electrode, for example, a separator formed by using fluororesin as an adhesive to form a porous layer of alumina particles with a particle size of less than 1 μm on both sides of the positive electrode.

[0067] The thickness of the separator is arbitrary. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. When the thickness of the separator is within the above ranges, insulation and mechanical strength can be ensured, and the rate performance and energy density of the battery cells can be guaranteed.

[0068] In this application, the diaphragm may include a substrate and a surface treatment layer. The substrate may be a nonwoven fabric or composite membrane with a porous structure, and the material of the substrate may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. For example, the inorganic layer includes inorganic particles and a binder. This application does not have any particular limitation on the aforementioned inorganic particles, and may include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. This application does not have any particular limitation on the aforementioned binders, and may include at least one of the aforementioned binders. The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0069] The battery cells in this application embodiment can be packaged in various forms such as button cells, pouch cells, and hard-shell cells. The operating voltage range is between 1.7V and 2.8V, and the operating temperature range is between -20℃ and 60℃. The battery cells in this application embodiment can achieve large-capacity energy storage, meeting the needs of long-term energy storage, achieving long-term energy storage of 4 hours or more. For example, they can be applied to energy storage scenarios such as 5 hours, 6 hours, and 8 hours. Long-term energy storage means being able to continuously discharge at rated power for 4 hours or even longer, or achieving large-scale, low-cost energy storage for several days or months.

[0070] Accordingly, another embodiment of this application also provides a method for preparing a battery cell, which can be used to manufacture the battery cell provided in the above embodiments. The method for preparing a battery cell according to another embodiment of this application will be described in detail below with reference to the accompanying drawings. For parts that are the same as or corresponding to the previous embodiment, please refer to the corresponding descriptions of the foregoing embodiments; detailed descriptions will not be repeated below.

[0071] The process flow diagram of the battery cell manufacturing process in this application embodiment is as follows: Figure 1 As shown, the specific steps include the following: S100. The positive electrode, separator and negative electrode are arranged in sequence to form a cell assembly.

[0072] In this step, the positive electrode, separator, and negative electrode are arranged sequentially to avoid short circuits caused by short-circuiting the positive and negative electrodes. Furthermore, when forming the battery cell assembly, it can be arranged either in a stacked or wound configuration; this application does not have any particular requirements in this regard.

[0073] S200, prepare the electrolyte.

[0074] In this step, the electrolyte composition is as described above in this application. Electrolyte preparation is typically carried out in a glove box with moisture and oxygen content below 0.1 ppm. Generally, the lithium salt is dissolved in a base solvent, and then additives are added. Typically, additives are added in a specific order to avoid side reactions during preparation.

[0075] Taking a solution containing FEC and the three additives mentioned above as an example, when preparing the electrolyte, FEC is added first. This ensures that FEC is evenly dispersed in the electrolyte, which is beneficial for a wider distribution of LiF in the SEI composite membrane later. Then, sulfonyl fluoride additives are added to help maintain the stability of the electrolyte system. Next, amine additives are added, which begin to interact weakly with FEC, pre-regulating its decomposition kinetics. Finally, the most reactive cyanopyridine additive is added to reduce its consumption during storage. If FEC is not present, the additives can also be added in the above order.

[0076] S300, Place the cell assembly and electrolyte inside the housing.

[0077] After the cell assembly and electrolyte are placed in the casing, the electrolyte will wet the cell assembly to ensure that the subsequent formation process can proceed normally.

[0078] S400, proceed with the formation step.

[0079] As can be seen from the foregoing content of this application, in this step, the three additives can be sequentially film-forming by controlling the cutoff voltage. Specifically, the formation step includes a first charging step, a second charging step, and a third charging step performed sequentially. The first charging step charges to the first cutoff voltage, the second charging step charges to the second cutoff voltage, and the third charging step charges to the third cutoff voltage. The first cutoff voltage is lower than the second cutoff voltage, and the second cutoff voltage is lower than the third cutoff voltage.

[0080] It should be noted that, in the subsequent content of this application, the voltage in a single battery cell mainly comes from the potential difference between the negative electrode and the lithium metal reference electrode.

[0081] In the first charging step, the first cutoff voltage is typically 2.2V~2.6V, while the lithium ion insertion / extraction potential of positive electrode active materials such as lithium iron phosphate is approximately 3.4V. Therefore, the positive electrode provides almost no lithium source, and lithium hardly forms a film on the negative electrode. This is the reduction window for the most reactive cyanopyridine additives. In the first charging step, the charging rate is typically in the range of 0.01C~0.02C, and the charging current naturally decays during charging. This process ensures that the reduction / polymerization reaction of cyanopyridine can proceed fully and completely, forming a highly covered and dense SEI composite film. This film acts as a barrier to electrons, suppressing side reactions at subsequent high potentials and improving the initial efficiency of the battery cell. In the first charging step, when the current decreases to 0.005C, it means that the reaction at that potential is essentially complete.

[0082] In the second charging step, the potential of the negative electrode plate is further reduced (relative to Li). + The second cutoff voltage is typically 3.0V to 3.2V, with a charging rate of 0.05C to 0.3C. This stage is the preferential reduction range for sulfonyl fluoride additives. Under the protection of the outer layer of the SEI composite film, non-solvent molecules remain stable, while sulfonyl fluoride additives can penetrate the surface of the outer negative electrode material and then decompose. Taking 2-thiophene sulfonyl fluoride (i.e., formula II-1) as an example, during the decomposition process, the SF bond breaks to generate LiF, and the thiophene ring participates in the reaction to form an inorganic inner layer rich in LiF and Li2S; this layer constitutes the main framework of the SEI film and has high ionic conductivity and mechanical strength.

[0083] In the third charging step, a more complex reaction occurs, involving not only amine additives but also non-aqueous solvents, all participating in the formation of the SEI composite film. The third cutoff voltage is typically 3.65V, and the charging rate is usually 0.05C~0.1C.

[0084] On one hand, amine additives can penetrate the outer layer of the SEI composite film, reaching the space between the inner and outer layers, and then forming a highly elastic film. If the additive contains FEC, the amine additive will also regulate the decomposition of FEC and react with Li. + The reaction generates fine, uniform LiF nanocrystals. These LiF particles are embedded in the organic polymer matrix that may be formed by the amine additive molecules themselves, and the density of LiF gradually decreases from the inside out, thus forming a gradient distribution. On the other hand, at the lowest potential, the basic solvents EC and EMC undergo reduction, generating components such as lithium carbonate and lithium alkoxy. These products constitute the bottom layer of the SEI composite film, directly contacting the negative electrode material and filling the gaps between the inorganic framework. In addition, lithium ions begin to reversibly intercalate into the negative electrode sheet. Since the SEI composite film has been formed, the damage to the negative electrode material structure caused by lithium ion intercalation is minimized, and almost no additional active lithium is used to repair the broken SEI film. Through the preparation method of this application, the construction of an SEI composite film in a battery cell is completed. The formed SEI composite film has both good mechanical strength and good elasticity, which can effectively suppress the capacity decay and internal resistance increase of the battery cell, thereby improving the performance of the secondary battery.

[0085] This application also provides a battery device, which includes the aforementioned battery cell. The battery device may also include one or more of a battery module, a battery pack, and an energy storage battery.

[0086] This application also provides an energy storage device, including the aforementioned battery device, which is used to store electrical energy. The energy storage device includes, but is not limited to, residential energy storage cabinets, commercial energy storage cabinets, energy storage containers, energy storage racks, energy storage power stations, energy storage battery packs, or portable energy storage systems. The energy storage device may also include an energy management system (EMS), a battery management system (BMS), and a power conversion system (PCS).

[0087] This application also provides an electrical device, including the aforementioned battery device, which is used to provide electrical energy. The electrical device includes, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0088] The technical solution of this application will be described in detail below with reference to specific embodiments and comparative examples.

[0089] Example 1 <Preparation of Electrolyte> raw material: Base solvents: EC / EMC / DEC, with a volume ratio of 3:5:2.

[0090] Lithium salts: LiPF6, battery grade, purity ≥99.95%; LiDFOB: battery grade, purity ≥99.9%.

[0091] Cyanopyridine additives: 3-Cyanopyridine (Formula I-4): Custom-synthesized, purity ≥99.5%. Dry under vacuum at 60°C for 12 hours before use.

[0092] Sulfonyl fluoride additive: 2-Thiophenesulfonyl fluoride (Formula II-1): Custom-synthesized, purity ≥99%. Sensitive to water and air; weighed in a glove box.

[0093] Amine additive: Bis(2-methoxyethyl)amine (Formula III-3): reagent grade, purity ≥99.8%. It is hygroscopic and oxidizable. Before use, it needs to be purified by vacuum distillation after reflux with calcium hydride and stored in a sealed container.

[0094] First, dissolve LiPF6 in a base solvent, keeping the system temperature below 30°C. After the LiPF6 is completely dissolved, add LiDFOB and continue stirring until the system is completely clear and transparent. Then, add formulas I-4, III-3, and II-1 in sequence to obtain the electrolyte. The contents of LiPF6 and LiDFOB are 14% and 1.8%, respectively. The specific contents of the additives are shown in Table 1, and the remainder is the base solvent.

[0095] <Preparation of Battery Cell Components> The positive electrode, separator, and negative electrode are sequentially arranged and wound to form a battery cell assembly.

[0096] In the positive electrode, lithium iron phosphate is used as the positive active material; in the negative electrode, graphite is used as the negative active material, and a polypropylene / polyethylene / polypropylene three-layer composite structure is used as the separator.

[0097] <Assembling battery cells> The battery cell assembly and electrolyte are placed inside the housing and left to stand so that the electrolyte wets the battery cell assembly.

[0098] <Transformation Steps> The first charging step, the second charging step, and the third charging step are performed sequentially.

[0099] The first charging step charges the battery to the first cutoff voltage of 2.6V, with a charging rate of 0.02C.

[0100] The second charging step charges the battery to the second cutoff voltage of 3.2V, with a charging rate of 0.3C.

[0101] The third charging step charges the battery to the second cutoff voltage of 3.65V, with a charging rate of 0.1C.

[0102] Examples 2 to 5 Compared to Example 1, the main difference is that the type and content of cyanopyridine additives are changed when preparing the electrolyte, as shown in Table 1.

[0103] Examples 6 to 9 Compared to Example 1, the main difference is that the type and content of sulfonyl fluoride additives are changed when preparing the electrolyte, as shown in Table 1.

[0104] Examples 10-13 Compared to Example 1, the main difference is that the type and content of amine additives are changed when preparing the electrolyte, as shown in Table 1.

[0105] Examples 14-17 Compared to Example 1, the main difference is that the content of the three additives is changed, as shown in Table 1.

[0106] Example 18 Compared to Example 1, the main difference is that the following formation steps are used.

[0107] <Transformation Steps> The first charging step, the second charging step, and the third charging step are performed sequentially.

[0108] The first charging step charges the battery to the first cutoff voltage of 2.2V, with a charging rate of 0.01C.

[0109] The second charging step charges the battery to the second cutoff voltage of 3.0V, with a charging rate of 0.05C.

[0110] The third charging step charges the battery to the second cutoff voltage of 3.65V, with a charging rate of 0.05C.

[0111] Comparative Examples 1 to 3 Compared to Example 1, the main difference is that the types and amounts of additives are changed when preparing the electrolyte, as shown in Table 1.

[0112] Comparative Example 4 Compared to Example 1, the electrolyte was prepared using the following method.

[0113] <Preparation of Electrolyte> First, LiPF6 was dissolved in a base solvent, keeping the system temperature below 30°C. After the LiPF6 was completely dissolved, LiDFOB was added, and stirring continued until the system was completely clear and transparent. Then, the additive FEC was added to obtain the electrolyte. The contents of LiPF6 and LiDFOB were 14% and 1.8%, respectively, and the specific contents of the additive FEC are shown in Table 1. The remainder was the base solvent.

[0114] Comparative Example 5 Compared to Example 1, the electrolyte was prepared using the following method.

[0115] <Preparation of Electrolyte> First, dissolve LiPF6 in a base solvent, keeping the system temperature below 30°C. After the LiPF6 is completely dissolved, add LiDFOB and continue stirring until the system is completely clear and transparent. Then add the additive VC to obtain the electrolyte. The contents of LiPF6 and LiDFOB are 14% and 1.8%, respectively, and the specific contents of the additive VC are shown in Table 1. The remainder is the base solvent.

[0116] Table 1

[0117] Test methods and equipment First-effect test At (25±2)℃, newly prepared, uncycled batteries were subjected to their first charge-discharge cycle at a current of 0.1 or 0.2C. First-cycle efficiency = (First discharge capacity / First charge capacity) × 100% Energy retention rate after 2000 cycles The battery was placed in a constant temperature chamber at (25±2)℃ and charged and discharged at 0.5P power with a voltage range of 2.5V~3.65V. The cycle retention rate was recorded after 2000 cycles.

[0118] Internal resistance growth test At 50% SOC, the 1kHz AC internal resistance was tested using a Hioki BT4560 battery tester.

[0119] Energy density test At an ambient temperature of (25±2)℃, the battery cells were left to stand for a sufficient time (2h) to allow the temperature to stabilize. They were then charged and discharged at a constant power of 0.5P with a voltage range of 2.5~3.65V. The discharge capacity at this time was recorded.

[0120] The test results are shown in Table 2.

[0121] Table 2

[0122] As can be seen from the above, in the battery cells of this application, the cyanopyridine additives, sulfonyl fluoride additives, and amine additives work together to form an SEI composite film with high mechanical strength and good flexibility, thereby improving the performance and initial efficiency of the battery cell. In particular, as can be seen from the examples and Comparative Examples 1 to 3, all three additives are indispensable; otherwise, it is impossible to form an SEI film with both good mechanical strength and good elasticity, which would lead to a decrease in the initial efficiency of the battery cell, accelerated capacity decay, and a significant increase in internal resistance.

[0123] In particular, as can be seen from Examples 1 to 15, when the mass ratio of cyanopyridine additives, sulfonyl fluoride additives and amine additives is in the range of (0.3~0.8):1:(0.1~0.5), the performance and first efficiency of the battery cell can be improved more effectively.

[0124] Those skilled in the art will understand that the above embodiments are specific examples of implementing this application, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of this application. Any person skilled in the art can make various alterations and modifications without departing from the spirit and scope of this application; therefore, the scope of protection of this application should be determined by the scope defined in the claims.

Claims

1. A battery cell, characterized in that, include: A battery cell assembly, the battery cell assembly comprising a positive electrode, a separator, and a negative electrode; The housing, in which the battery cell assembly is located; Electrolyte, wherein the electrolyte is located within the housing; The electrolyte includes additives, including cyanopyridine additives, sulfonyl fluoride additives, and amine additives; The general structural formula of the cyanopyridine additive is shown in Formula I below: R1, R2, and R3 are each independently selected from any one of hydrogen atom, C1-C4 alkyl, C1-C4 alkoxy, halogen or cyano, and at least one of R1, R2, and R3 is cyano; The general structural formula of the sulfonyl fluoride additive is shown in Formula II below: R4 is selected from any one of aryl or C2-C6 hydrocarbon groups containing unsaturated bonds, wherein the aryl group includes at least one of substituted or unsubstituted thiophene, furanyl, phenyl or pyridinyl, and the substituent is at least one of halogen or C1-C3 alkyl. The general structural formula of the amine additive is shown in Formula III below: R5, R6, and R7 are each independently selected from any one of hydrogen atoms, C1-C6 alkyl groups, or C1-C6 alkoxyalkyl groups, and R5, R6, and R7 are not all hydrogen atoms at the same time. The battery cell undergoes a formation step; wherein the formation step includes a first charging step, a second charging step, and a third charging step performed sequentially, wherein the first charging step charges to a first cutoff voltage, the second charging step charges to a second cutoff voltage, and the third charging step charges to a third cutoff voltage, wherein the first cutoff voltage is less than the second cutoff voltage, and the second cutoff voltage is less than the third cutoff voltage.

2. The battery cell according to claim 1, characterized in that, Based on the mass of the electrolyte, the mass content of the additive is 0.5% to 5%.

3. The battery cell according to claim 1 or 2, characterized in that, Based on the mass of the electrolyte, the mass contents of the cyanopyridine additive, the sulfonyl fluoride additive, and the amine additive are 0.5%~2%, 0.2%~1.5%, and 0.2%~1%, respectively; and / or, The mass ratio of the cyanopyridine additive, the sulfonyl fluoride additive, and the amine additive is (0.3~0.8):1:(0.1~0.5).

4. The battery cell according to claim 1, characterized in that, The cyanopyridine additives include at least one of the following compounds: 。 5. The battery cell according to claim 1, characterized in that, The sulfonyl fluoride additives include at least one of the following compounds: 。 6. The battery cell according to claim 1, characterized in that, The amine additive includes at least one of the following compounds: 。 7. A method for preparing a battery cell as described in any one of claims 1 to 6, characterized in that, include: The battery cell assembly and the electrolyte are placed inside the housing; Perform the formation step; The formation step includes a first charging step, a second charging step, and a third charging step performed sequentially. The first charging step charges to a first cutoff voltage, the second charging step charges to a second cutoff voltage, and the third charging step charges to a third cutoff voltage. The first cutoff voltage is less than the second cutoff voltage, and the second cutoff voltage is less than the third cutoff voltage.

8. The method for preparing a battery cell according to claim 7, characterized in that, The first cutoff voltage is 2.2V~2.6V; The second cutoff voltage is 3.0V~3.2V; The third cutoff voltage is 3.65V.

9. A battery device, characterized in that, It includes battery cells as described in any one of claims 1 to 6, or battery cells prepared by the method described in any one of claims 7 to 8.

10. An energy storage device, characterized in that, Includes the battery device as described in claim 9, wherein the battery device is used to store electrical energy.

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