Battery monomer and electric equipment

Abstract

The invention discloses a battery monomer and electric equipment. The battery monomer comprises a positive pole piece, a negative pole piece, an isolating membrane and electrolyte, the electrolyte comprises a lithium salt, a solvent and an additive, the solvent comprises carboxylic ester; the additive comprises vinylene carbonate, fluorine-containing anhydride and derivatives thereof; and the mass percent a of the carboxylic ester in the electrolyte is more than or equal to 10% and less than or equal to 80%. Carboxylic ester, vinylene carbonate, fluorine-containing anhydride and derivatives thereof in the electrolyte are matched with one another, so that the cycle life of the battery monomer is prolonged, and meanwhile, the battery monomer is kept to have relatively good quick charge performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to battery cells and electrical equipment. Background Technology

[0002] Lithium-ion batteries are widely used in wireless communication, transportation, aerospace and other fields due to their advantages such as high energy density, long cycle life, low self-discharge rate, fast charging capability and wide operating temperature range. With the continuous progress and development of technology, lithium-ion batteries will continue to play an important role and drive innovation in energy storage technology.

[0003] For lithium batteries, cycle life and charging rate are key factors affecting their development. Summary of the Invention

[0004] This application provides a battery cell and an electrical device to improve the cycle life of the battery cell.

[0005] To address the aforementioned technical problems, the first aspect of this application provides a battery cell comprising: a positive electrode, a negative electrode, a separator, and an electrolyte; the electrolyte comprises a lithium salt, a solvent, and additives; the solvent comprises a carboxylic acid ester; the additives comprise vinylene carbonate (VC), a fluoro anhydride, and its derivatives; the mass percentage of the carboxylic acid ester in the electrolyte is a, where 10% ≤ a ≤ 80%.

[0006] The electrolyte comprises carboxylic acid esters, vinylene carbonate, and fluorescent anhydrides and their derivatives. The carboxylic acid esters exhibit good compatibility with the electrolyte components, and their mass percentage in the electrolyte is 'a', with 10% ≤ a ≤ 80%. This results in a low-viscosity electrolyte that facilitates freer ion movement. Vinylene carbonate enhances the stability of the SEI film on the negative electrode surface, while fluorescent anhydrides and their derivatives form a stable negative electrode interface rich in inorganic LiF, further increasing the stability of the SEI film and reducing the continuous decomposition of the electrolyte during lithium-ion secondary batteries during cycling. Through the synergistic effect of carboxylic acid esters, vinylene carbonate, and fluorescent anhydrides and their derivatives, the cycle life of lithium-ion secondary batteries is improved while maintaining good fast-charging performance.

[0007] In one implementation, 10% ≤ a ≤ 50%.

[0008] By setting the mass percentage of carboxylic acid ester in the electrolyte to 'a', where 10% ≤ a ≤ 50%, the electrolyte achieves lower viscosity and higher conductivity, which is beneficial for maintaining the high efficiency and rapid charging and discharging of lithium-ion secondary batteries. Simultaneously, in combination with vinylene carbonate, fluoroanhydride, and their derivatives, the cycle life of lithium-ion secondary batteries is improved, while maintaining good fast-charging performance.

[0009] In one embodiment, the mass ratio of fluoro anhydride and its derivatives to vinylene carbonate is 1.7%-200%.

[0010] Through the above settings, while improving the cycle life of lithium-ion secondary batteries, ethylene carbonate and fluoro anhydride and its derivatives can effectively improve the poor lithium conductivity caused by the excessive thickness and density of the decomposition products of ethylene carbonate. In other words, reducing the influence of ethylene carbonate on lithium conductivity helps to reduce the DC resistance (DCR) of lithium-ion secondary batteries, reduce energy loss during charging and discharging, and help maintain good fast-charging performance of lithium-ion secondary batteries.

[0011] In one embodiment, the mass ratio of fluoro anhydride and its derivatives to vinylene carbonate is 5%-25%.

[0012] Through the above settings, while improving the cycle life of lithium-ion secondary batteries, ethylene carbonate and fluoro anhydride and its derivatives can effectively improve the poor lithium conductivity caused by the excessive thickness and density of the decomposition products of ethylene carbonate. In other words, reducing the influence of ethylene carbonate on lithium conductivity helps to reduce the DC resistance (DCR) of lithium-ion secondary batteries, reduce energy loss during charging and discharging, and help maintain good fast-charging performance of lithium-ion secondary batteries.

[0013] In one embodiment, the mass percentage of vinylene carbonate in the electrolyte is b, where 1% ≤ b ≤ 15%.

[0014] By setting the mass percentage of vinylene carbonate in the electrolyte as described above, the amount of vinylene carbonate added to the electrolyte is more suitable, which is beneficial to increase the stability of SEI film formation, reduce the decomposition of carboxylic acid esters in the electrolyte during cycling, reduce the occurrence of side reactions, and help the electrolyte maintain stable performance during battery charging and discharging, thereby extending the cycle life of lithium-ion secondary batteries.

[0015] In one embodiment, the mass percentage of the fluoro anhydride and its derivatives in the electrolyte is c, where 0.05% ≤ c ≤ 10%.

[0016] By setting the mass percentage of fluoroanhydride and its derivatives in the electrolyte to c, where 0.05% ≤ c ≤ 10%, the addition amount of fluoroanhydride and its derivatives in the electrolyte is more suitable. This is beneficial for increasing the stability of the SEI film formation, reducing the decomposition of carboxylic acid esters in the electrolyte during cycling, reducing the occurrence of side reactions, and improving the cycle life of lithium-ion secondary batteries. At the same time, it can improve the poor lithium conductivity caused by the excessive thickness and density of the decomposition products of vinylene carbonate. That is, reducing the influence of vinylene carbonate on lithium conductivity is beneficial for reducing the DC resistance (DCR) of lithium-ion secondary batteries, reducing energy loss during charging and discharging, maintaining a faster charging and discharging rate, and maintaining good fast-charging performance of lithium-ion secondary batteries.

[0017] In one embodiment, the lithium salt constitutes 10%-20% by mass in the electrolyte.

[0018] By setting the mass percentage of lithium salt in the electrolyte as described above, the concentration of lithium salt and the number of lithium ions in the electrolyte are suitable. During the charging and discharging process, lithium ions are transported smoothly, which is beneficial to improving the cycle life of lithium-ion secondary batteries and maintaining good fast charging performance of lithium-ion secondary batteries.

[0019] In one embodiment, the structural formula of the fluoroanhydride and its derivatives is as follows:

[0020] Wherein, R1 includes one of hydrogen, an alkyl group having 1-10 carbon atoms, and a fluoroalkane having 1-10 carbon atoms; R2 includes one of hydrogen, an alkyl group having 1-10 carbon atoms, and a fluoroalkane having 1-10 carbon atoms; the number of fluorine atoms in R1 is n1, 0≤n1≤11; the number of fluorine atoms in R2 is n2, 0≤n2≤11; at least one of R1 and R2 includes fluorine atoms.

[0021] By including fluorine atoms in at least one of R1 and R2, where the number of fluorine atoms in R1 is n1 (0 ≤ n1 ≤ 11) and the number of fluorine atoms in R2 is n2 (0 ≤ n2 ≤ 11), a greater amount of lithium fluoride can be formed on the surface of the negative electrode, improving the stability of the SEI film and extending the cycle life of the lithium-ion secondary battery. Furthermore, by setting the number of carbon atoms in both R1 and R2 to 1-10, various components containing fluoroanhydride and its derivatives can also enhance the cycle life of lithium-ion secondary batteries.

[0022] In one implementation, 3 ≤ n1 ≤ 5, and / or, 3 ≤ n2 ≤ 5.

[0023] The number of fluorine atoms in R1 is n1, where 3≤n1≤5, and the number of fluorine atoms in R2 is n2, where 3≤n2≤5. This allows for the formation of more lithium fluoride on the surface of the negative electrode, improving the stability of the SEI film and enhancing the cycle life of the lithium-ion secondary battery.

[0024] In one embodiment, the fluoroanhydride and its derivatives include at least one of pentafluoropropionic anhydride, difluoroacetic anhydride, and trifluoroacetic anhydride.

[0025] By adding at least one of the above-mentioned materials containing fluoro anhydride and its derivatives to the electrolyte, the stability of the SEI film can be effectively improved, thereby enhancing the cycle life of lithium-ion secondary batteries.

[0026] In one embodiment, the structural formula of the carboxylic acid ester is:

[0027]

[0028] R3 includes one of hydrogen and an alkyl group having 1-10 carbon atoms; R4 includes one of hydrogen and an alkyl group having 1-10 carbon atoms.

[0029] By setting R3 and R4 as described above, the carbon chain length of the carboxylic acid ester is more suitable, which is beneficial to improving the electronic conductivity of the electrolyte, reducing the internal resistance of the lithium-ion secondary battery, and maintaining a faster charge and discharge rate of the lithium-ion secondary battery.

[0030] In one embodiment, the carboxylic acid ester includes at least one of ethyl acetate, propyl acetate, and propyl propionate.

[0031] By selecting at least one of the aforementioned materials as the solvent for the carboxylic acid ester, the electrolyte achieves higher conductivity, which is beneficial for maintaining a faster charge and discharge rate in the lithium-ion secondary battery.

[0032] In one embodiment, the solvent further includes carbonate, which has a mass percentage of 4.8%-85% in the electrolyte.

[0033] The solvent also includes carbonates. Carbonate solvents have high polarity and good polarity, which can dissolve lithium salts and additives well. Carbonates have very high electrochemical stability, which can effectively reduce electrolyte decomposition, thereby extending the cycle life of lithium-ion secondary batteries.

[0034] In one embodiment, the carbonate includes at least one of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and fluoroethylene carbonate.

[0035] By using at least one of the aforementioned materials as a solvent for the electrolyte, the lithium salt and additives can be effectively dissolved, reducing electrolyte decomposition and thus extending the cycle life of the lithium-ion secondary battery.

[0036] In one embodiment, the conductivity of the electrolyte is d, where 7 mS / cm ≤ d ≤ 20 mS / cm.

[0037] By setting the conductivity of the electrolyte within the aforementioned range, it is beneficial to improve the transport capacity of lithium ions in the electrolyte and reduce side reactions in the lithium-ion battery, thereby improving the cycle life of the lithium-ion battery.

[0038] In one embodiment, the conductivity of the electrolyte is 10 mS / cm ≤ d ≤ 15 mS / cm.

[0039] By setting the conductivity of the electrolyte within the above range, lithium ions can be kept to have a fast transport capacity in the electrolyte, while the side reactions of lithium-ion batteries can be significantly reduced, thereby improving the cycle life of lithium-ion batteries.

[0040] In one embodiment, the negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one side of the negative current collector. The negative active layer includes a negative active material, which includes graphite, and the specific surface area of ​​the graphite is 0.5 m². 2 / g-10m 2 / g.

[0041] By setting the specific surface area of ​​graphite as described above, it is beneficial for sufficient contact between graphite and electrolyte; it helps to form a stable SEI film, reduces the occurrence of side reactions, thereby improving the cycle stability of the battery, reducing the decomposition of electrolyte during the cycle, and improving the cycle life of lithium-ion secondary batteries.

[0042] In one embodiment, the positive electrode includes a positive current collector and a positive active layer disposed on at least one side of the positive current collector. The positive active layer includes a positive active material, which includes lithium iron phosphate.

[0043] For lithium iron phosphate systems, the electrolyte solvent includes carboxylic acid esters, and the additives include vinylene carbonate and fluoro anhydrides and their derivatives, which can effectively improve the cycle life of lithium-ion secondary batteries while maintaining good fast-charging performance.

[0044] A second aspect of this application provides an electrical device comprising a battery cell as described in any of the preceding claims. The electrical device has at least the same advantages as the battery cell.

[0045] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0047] Figure 1 This is a schematic diagram of the structure of the lithium-ion secondary battery provided in the embodiments of this application;

[0048] Figure 2 This is an exploded structural diagram of a battery cell provided in an embodiment of this application;

[0049] Figure 3 This is a schematic diagram of the vehicle structure provided in an embodiment of this application.

[0050] Label Explanation:

[0051] Lithium-ion secondary battery 100, housing 10, first part 11, second part 12, battery cell 20, end cap 21, electrode terminal 21a, shell 22, cell assembly 23, tab 23a, controller 200, motor 300, vehicle 1000. Detailed Implementation

[0052] To make the objectives, technical solutions, and effects of this application clearer and more explicit, the embodiments of the technical solutions of this application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of this application, and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0053] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0054] 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, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces), unless otherwise explicitly specified.

[0055] 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.

[0056] 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: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0057] Quantities, ratios, and other numerical values ​​are presented in range format in this document. It should be understood that this range format is for convenience and brevity and should be interpreted flexibly to include not only numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0058] Unless otherwise specified, all steps of this application may be performed sequentially, randomly, or in parallel, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially, or steps (a) and (b) may be performed simultaneously in parallel. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b), etc.

[0059] To improve fast-charging performance, lithium-ion rechargeable batteries typically use high-conductivity electrolytes to enhance lithium-ion transport rates. These high-conductivity electrolytes often contain low-molecular-weight linear ester solvents, such as carboxylic acid esters, which reduce electrolyte viscosity, increase conductivity, and accelerate lithium-ion movement. However, carboxylic acid ester solvents are generally susceptible to oxidation and reduction, and are prone to decomposition and side reactions during battery formation, aging, and subsequent cycle storage, reducing the cycle life of lithium-ion rechargeable batteries. Furthermore, the electrochemical interface (SEI film) formed by carboxylic acid ester solvents on the negative electrode is not dense enough and is unstable, leading to continuous electrolyte decomposition and further reducing the cycle life of lithium-ion rechargeable batteries.

[0060] Therefore, embodiments of this application provide a battery cell and an electrical device to improve the cycle life of the battery cell.

[0061] Please see Figure 1 , Figure 1 This is a schematic diagram of the structure of the lithium-ion secondary battery provided in the embodiments of this application.

[0062] The lithium-ion secondary battery 100 includes a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10.

[0063] The housing 10 provides a space for accommodating the battery cell 20, and can adopt various structures. In some embodiments, the housing 10 may include a first part 11 and a second part 12, which overlap each other, and together define a space for accommodating the battery cell 20. The second part 12 may be a hollow structure with one open end, and the first part 11 may be a plate-like structure, covering the open side of the second part 12 so that the first part 11 and the second part 12 together define the space; alternatively, the first part 11 and the second part 12 may both be hollow structures with one open side, with the open side of the first part 11 covering the open side of the second part 12. Of course, the housing 10 formed by the first part 11 and the second part 12 can be of various shapes, such as a cylinder, a cuboid, etc.

[0064] In a lithium-ion secondary battery 100, there can be multiple battery cells 20. These multiple battery cells 20 can be connected in series, in parallel, or in a mixed configuration. A mixed configuration means that multiple battery cells 20 are connected in both series and parallel configurations. Multiple battery cells 20 can be directly connected in series, in parallel, or in a mixed configuration, and then the entire assembly of the multiple battery cells 20 is housed within a housing 10. Alternatively, the lithium-ion secondary battery 100 can also be composed of multiple battery cells 20 first connected in series, in parallel, or in a mixed configuration to form a battery module, and then multiple battery modules are connected in series, in parallel, or in a mixed configuration to form a whole, which is then housed within a housing 10.

[0065] The lithium-ion secondary battery 100 may also include other structures, for example, the lithium-ion secondary battery 100 may also include a busbar for realizing electrical connection between multiple battery cells 20.

[0066] Each battery cell 20 can be a secondary battery. The battery cell 20 can be cylindrical, flat, cuboid, or other shapes.

[0067] Please see Figure 2 , Figure 2 This is an exploded structural diagram of a lithium-ion secondary battery cell provided in an embodiment of this application.

[0068] Battery cell 20 refers to the smallest unit that makes up a lithium-ion secondary battery 100. For example... Figure 2 As shown, the battery cell 20 includes an end cap 21, a housing 22, a cell assembly 23, and other functional components.

[0069] End cap 21 refers to a component that covers the opening of housing 22 to isolate the internal environment of battery cell 20 from the external environment. In any case, the shape of end cap 21 can be adapted to the shape of housing 22 to fit it. Optionally, end cap 21 can be made of a material with a certain hardness and strength (such as aluminum alloy), so that end cap 21 is less prone to deformation under pressure and impact, enabling battery cell 20 to have higher structural strength and improved stability.

[0070] The end cap 21 may be provided with functional components such as electrode terminals 21a. The electrode terminals 21a can be used to electrically connect with the cell assembly 23 for outputting or inputting electrical energy of the battery cell 20. In some embodiments, the end cap 21 may also be provided with a pressure relief mechanism for releasing internal pressure when the internal pressure or temperature of the battery cell 20 reaches a threshold.

[0071] The end cap 21 can be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. This application embodiment does not impose any special restrictions on this.

[0072] In some embodiments, an insulating element may be provided on the inner side of the end cap 21. The insulating element can be used to isolate the electrical connection components within the housing 22 from the end cap 21 to reduce the risk of short circuits. For example, the insulating element may be made of plastic, rubber, etc.

[0073] The housing 22 is a component used to cooperate with the end cap 21 to form the internal environment of the battery cell 20. This internal environment can accommodate the cell assembly 23, electrolyte, and other components. The housing 22 and the end cap 21 can be independent components. An opening can be provided on the housing 22, and the end cap 21 can be used to close the opening to form the internal environment of the battery cell 20. Alternatively, the end cap 21 and the housing 22 can be integrated. Specifically, the end cap 21 and the housing 22 can form a common connecting surface before other components are inserted into the housing. When it is necessary to encapsulate the interior of the housing 22, the end cap 21 closes the housing 22. The housing 22 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 22 can be determined according to the specific shape and size of the cell assembly 23. The material of the housing 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. This application embodiment does not impose any special limitations on this.

[0074] The cell assembly 23 is the component in the battery cell 20 where the electrochemical reaction occurs. The casing 22 may contain one or more cell assemblies 23. The cell assembly 23 includes a positive electrode, a negative electrode, and a separator. The separator is located between the positive and negative electrode. The positive and negative electrode are wound or stacked to form the cell assembly 23. The portions of the positive and negative electrode with active material constitute the main body of the cell assembly 23, while the portions without active material each constitute a tab 23a. The positive and negative tabs may be located together at one end of the main body or at opposite ends. During the charging and discharging process of the lithium-ion secondary battery 100, the positive and negative active materials react with the electrolyte, and the tabs 23a connect to the electrode terminals 21a to form a current loop.

[0075] In one embodiment, the electrolyte includes a lithium salt, a solvent, and an additive; the solvent includes a carboxylic acid ester; the additive includes vinylene carbonate (VC), fluoro anhydride, and its derivatives; the mass percentage of the carboxylic acid ester in the electrolyte is a, where 10% ≤ a ≤ 80%.

[0076] Lithium salts are compounds containing lithium ions that act as carriers of these ions in electrolytes, migrating between the positive and negative electrodes. Solvents serve as dissolving media, ensuring the lithium salts are uniformly distributed throughout the electrolyte. Additives are used to improve the electrochemical performance of the electrolyte system.

[0077] The mass percentage of carboxylic acid esters in the electrolyte is the proportion of the mass of carboxylic acid esters in the total mass of the electrolyte. The mass percentage of carboxylic acid esters in the electrolyte can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc., or it can be a range of any two of the above values, such as 10%-20%, 10%-60%, etc.

[0078] By including carboxylic acid esters as the solvent, which have good solubility and can be effectively compatible with other electrolyte components, and with the carboxylic acid ester having a mass percentage of 'a' in the electrolyte (10% ≤ a ≤ 80%), the electrolyte has a low viscosity. The low viscosity electrolyte formed by the carboxylic acid ester helps ions move more freely in the electrolyte, increases the electrolyte conductivity, accelerates the movement of lithium ions, reduces energy loss, and helps maintain the lithium-ion secondary battery with relatively efficient and rapid charging and discharging.

[0079] Because the electrochemical interface (SEI film) formed by carboxylic acid ester solvents on the negative electrode is not dense enough and is unstable, it can lead to continuous decomposition of the electrolyte. Furthermore, carboxylic acid esters are generally susceptible to oxidation and reduction, and are prone to decomposition and side reactions during battery formation, aging, and subsequent cycle storage, thus reducing the cycle life of lithium-ion secondary batteries. Adding vinylene carbonate to the electrolyte effectively enhances the stability of the SEI film formation on the negative electrode surface, reduces the continuous decomposition of the electrolyte during cycling, and helps the electrolyte maintain stable performance during battery charge and discharge, thereby extending the cycle life of lithium-ion secondary batteries. By incorporating additives including fluoro anhydrides and their derivatives, a stable negative electrode interface rich in inorganic LiF is formed, further increasing the stability of the SEI film formation, reducing the decomposition of carboxylic acid esters in the electrolyte during cycling, reducing side reactions, and ultimately improving the cycle life of lithium-ion secondary batteries.

[0080] The decomposition products of fluoroanhydrides and their derivatives are inorganic substances. As components of the SEI film, they exhibit good lithium conductivity, mitigating the poor lithium conductivity caused by the excessive thickness and density of vinylene carbonate decomposition products. This helps reduce the DC resistance (DCR) of lithium-ion secondary batteries, minimizing energy loss during charge and discharge, maintaining a fast charge and discharge rate, and ensuring good fast-charging performance. Furthermore, fluoroanhydrides and their derivatives have high oxidation potentials, resulting in excellent high-voltage stability.

[0081] The combination of carboxylic acid esters, vinylene carbonate, fluoro anhydrides and their derivatives in the electrolyte improves the cycle life of lithium-ion secondary batteries while maintaining good fast-charging performance.

[0082] It should be noted that the qualitative and quantitative analysis of lithium salts and lithium salt additives in the electrolyte, including ion chromatography and FTIR methods, is based on the standards JY / T 020-1996 and GB / T 6040-2002. The organic components in the electrolyte are quantitatively analyzed by gas chromatography, based on the standard GB / T 9722-2006.

[0083] In one implementation, 10% ≤ a ≤ 50%.

[0084] By setting the mass percentage of carboxylic acid ester in the electrolyte to 'a', where 10% ≤ a ≤ 50%, the electrolyte achieves lower viscosity and higher conductivity, which is beneficial for maintaining efficient and rapid charge-discharge of the lithium-ion secondary battery. Simultaneously, it works in conjunction with vinylene carbonate, fluoro anhydride, and their derivatives to improve the cycle life of the lithium-ion secondary battery while maintaining good rapid charge-discharge performance. The mass percentage of carboxylic acid ester in the electrolyte can be 10%, 13%, 15%, 17%, 20%, 24%, 25%, 30%, 32%, 35%, 38%, 40%, 43%, 45%, 47%, 50%, etc., or a range of any two of the above values, such as 10%-30%, 13%-47%, etc.

[0085] In one embodiment, the mass ratio of fluoro anhydride and its derivatives to vinylene carbonate is 1.7%-200%.

[0086] Through the above settings, while improving the cycle life of lithium-ion secondary batteries, ethylene carbonate and fluoro anhydrides and their derivatives can effectively improve the poor lithium conductivity caused by the excessive thickness and density of the decomposition products of ethylene carbonate. In other words, reducing the influence of ethylene carbonate on lithium conductivity helps to reduce the DC resistance (DCR) of lithium-ion secondary batteries, reduce energy loss during the charging and discharging process, and help maintain a faster charging and discharging rate for lithium-ion secondary batteries. The mass ratio of fluoro anhydride and its derivatives to vinylene carbonate can be 1.7%, 2%, 5%, 10%, 12%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 110%, 120%, 130%, 140%, 150%, 160%, 170%, 180%, 190%, 200%, etc., or it can be a range of any two of the above values, such as 2%-50%, 5%-100%, etc.

[0087] In one embodiment, the mass ratio of fluoro anhydride and its derivatives to vinylene carbonate is 5%-25%.

[0088] Through the above settings, while improving the cycle life of lithium-ion secondary batteries, ethylene carbonate and fluoroanhydrides and their derivatives can effectively mitigate the poor lithium conductivity caused by the excessive thickness and density of ethylene carbonate decomposition products. In other words, reducing the impact of ethylene carbonate on lithium conductivity helps lower the DC resistance (DCR) of the lithium-ion secondary battery, reduces energy loss during charging and discharging, and helps maintain a faster charge and discharge rate. The mass ratio of fluoroanhydrides and their derivatives to ethylene carbonate can be 5%, 8%, 10%, 12%, 15%, 20%, 23%, 25%, etc., or a range of any two of the above values, such as 5%-20%, 10%-23%, etc.

[0089] In one embodiment, the mass percentage of vinylene carbonate in the electrolyte is b, where 1% ≤ b ≤ 15%.

[0090] The mass percentage of vinylene carbonate in the electrolyte is the proportion of the mass of vinylene carbonate in the total mass of the electrolyte. The mass percentage of vinylene carbonate in the electrolyte can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc., or it can be a range of any two of the above values, such as 1%-10%, 2%-14%, etc.

[0091] By setting the mass percentage of vinylene carbonate in the electrolyte as described above, the amount of vinylene carbonate added to the electrolyte is more suitable, which is beneficial to increase the stability of SEI film formation, reduce the decomposition of carboxylic acid esters in the electrolyte during cycling, reduce the occurrence of side reactions, and help the electrolyte maintain stable performance during battery charging and discharging, thereby extending the cycle life of lithium-ion secondary batteries.

[0092] In one embodiment, the mass percentage of the fluoro anhydride and its derivatives in the electrolyte is c, where 0.05% ≤ c ≤ 10%.

[0093] The mass percentage of fluoroanhydrides and their derivatives in the electrolyte is the proportion of the mass of fluoroanhydrides and their derivatives in the total mass of the electrolyte. The mass percentage of fluoroanhydrides and their derivatives in the electrolyte can be 0.05%, 0.1%, 0.25%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc., or it can be a range of any two of the above values, such as 0.1%-4%, 2%-7%, 0.25%-1%, etc.

[0094] By setting the mass percentage of fluoroanhydride and its derivatives in the electrolyte to c, where 0.05% ≤ c ≤ 10%, the addition amount of fluoroanhydride and its derivatives in the electrolyte is more suitable. This is beneficial for increasing the stability of the SEI film formation, reducing the decomposition of carboxylic acid esters in the electrolyte during cycling, reducing the occurrence of side reactions, and improving the cycle life of lithium-ion secondary batteries. At the same time, it can improve the poor lithium conductivity caused by the excessive thickness and density of the decomposition products of vinylene carbonate. That is, reducing the influence of vinylene carbonate on lithium conductivity is beneficial for reducing the DC resistance (DCR) of lithium-ion secondary batteries, reducing energy loss during the charging and discharging process, and maintaining a faster charging and discharging rate for lithium-ion secondary batteries.

[0095] In one embodiment, the lithium salt has a mass percentage of 10%-20% in the electrolyte.

[0096] The mass percentage of lithium salt in the electrolyte is the proportion of the lithium salt's mass in the total mass of the electrolyte. The mass percentage of lithium salt in the electrolyte can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc., or it can be a range of any two of the above values, such as 13%-19%, 10%-16%, etc.

[0097] By setting the mass percentage of lithium salt in the electrolyte as described above, the concentration of lithium salt and the number of lithium ions in the electrolyte are more suitable. During the charging and discharging process, lithium ions are transported smoothly, which is beneficial to improving the cycle life of lithium-ion secondary batteries and maintaining a fast charging rate.

[0098] In one embodiment, the structural formula of the fluoroanhydride and its derivatives is as follows:

[0099] Wherein, R1 includes one of hydrogen, an alkyl group having 1-10 carbon atoms, and a fluoroalkane having 1-10 carbon atoms; R2 includes one of hydrogen, an alkyl group having 1-10 carbon atoms, and a fluoroalkane having 1-10 carbon atoms; the number of fluorine atoms in R1 is n1, 0≤n1≤11; the number of fluorine atoms in R2 is n2, 0≤n2≤11; at least one of R1 and R2 includes fluorine atoms.

[0100] By including fluorine atoms in at least one of R1 and R2, where the number of fluorine atoms in R1 is n1 (0 ≤ n1 ≤ 11) and the number of fluorine atoms in R2 is n2 (0 ≤ n2 ≤ 11), a greater amount of lithium fluoride can be formed on the surface of the negative electrode, improving the stability of the SEI film and extending the cycle life of the lithium-ion secondary battery. Furthermore, by setting the number of carbon atoms in both R1 and R2 to 1-10, various components containing fluoroanhydride and its derivatives can also enhance the cycle life of lithium-ion secondary batteries.

[0101] The number of fluorine atoms in R1 can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, etc., or a range consisting of any two of the above values, for example, 3≤n1≤11, 0≤n1≤6, etc. The number of fluorine atoms in R2 can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, etc., or a range consisting of any two of the above values, for example, 3≤n1≤11, 0≤n1≤6, etc. The number of carbon atoms in R1 can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc., or a range consisting of any two of the above values, for example, 1-3, 2-5, etc. The number of carbon atoms in R2 can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc., or a range consisting of any two of the above values, for example, 4-10, 2-5, etc.

[0102] In one implementation, 3 ≤ n1 ≤ 5, and / or, 3 ≤ n2 ≤ 5.

[0103] The number of fluorine atoms in R1 is n1, where 3 ≤ n1 ≤ 5, and the number of fluorine atoms in R2 is n2, where 3 ≤ n2 ≤ 5. This allows for the formation of more lithium fluoride on the surface of the negative electrode, improving the stability of the SEI film and extending the cycle life of the lithium-ion secondary battery. The number of fluorine atoms in R1 can be 3, 4, or 5, etc. The number of fluorine atoms in R2 can also be 3, 4, or 5, etc.

[0104] In one embodiment, R1 has 1-3 carbon atoms, and / or R2 has 1-3 carbon atoms.

[0105] By setting the number of carbon atoms in R1 and R2 as described above, the chain length of the fluoroanhydride and its derivatives is suitable, which is beneficial to improving the electrochemical performance of the electrolyte. The number of carbon atoms in R1 can be 1, 2, 3, etc. The number of carbon atoms in R2 can be 1, 2, 3, etc.

[0106] In one embodiment, the fluoroanhydride and its derivatives include at least one of pentafluoropropionic anhydride, difluoroacetic anhydride, and trifluoroacetic anhydride.

[0107] By adding at least one of the above-mentioned materials containing fluoro anhydride and its derivatives to the electrolyte, the stability of the SEI film can be effectively improved, thereby enhancing the cycle life of lithium-ion secondary batteries.

[0108] In one embodiment, the structural formula of the carboxylic acid ester is:

[0109] R3 includes one of hydrogen and an alkyl group having 1-10 carbon atoms; R4 includes one of hydrogen and an alkyl group having 1-10 carbon atoms.

[0110] By setting R3 and R4 as described above, the carbon chain length of the carboxylic acid ester is more suitable, which is beneficial to improving the electronic conductivity of the electrolyte, reducing the internal resistance of the lithium-ion secondary battery, and maintaining a faster charge and discharge rate. The number of carbon atoms in R3 can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or any range of two of the above values, such as 1-3, 2-5, etc. The number of carbon atoms in R4 can also be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or any range of two of the above values, such as 4-10, 2-5, etc.

[0111] In one embodiment, R3 has 1-3 carbon atoms, and / or R4 has 1-4 carbon atoms.

[0112] By setting the number of carbon atoms in R3 and R4 as described above, the carbon chain length of the carboxylic acid ester is more suitable, which is beneficial to improving the electronic conductivity of the electrolyte, reducing the internal resistance of the lithium-ion secondary battery, and maintaining a faster charge and discharge rate. The number of carbon atoms in R1 can be 1, 2, or 3, etc. The number of carbon atoms in R2 can also be 1, 2, or 3, etc.

[0113] In one embodiment, the carboxylic acid ester includes at least one of ethyl acetate, propyl acetate, and propyl propionate.

[0114] By selecting at least one of the aforementioned materials as the solvent for the carboxylic acid ester, the electrolyte achieves higher conductivity, which is beneficial for maintaining a faster charge and discharge rate in the lithium-ion secondary battery.

[0115] In one embodiment, the solvent further includes carbonate, which has a mass percentage of 4.8%-85% in the electrolyte.

[0116] The mass percentage of carbonate in the electrolyte is the proportion of the mass of carbonate in the total mass of the electrolyte. The mass percentage of carbonate in the electrolyte can be 4.8%, 5%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 85%, etc., or it can be a range of any two of the above values, such as 13%-30%, 20%-80%, etc.

[0117] The solvent also includes carbonates. Carbonate solvents have high polarity and good polarity, which can dissolve lithium salts and additives well. Carbonates have very high electrochemical stability, which can effectively reduce electrolyte decomposition, thereby extending the cycle life of lithium-ion secondary batteries.

[0118] In one embodiment, the carbonate includes at least one of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and fluoroethylene carbonate (FEC).

[0119] By using at least one of the aforementioned materials as a solvent for the electrolyte, the lithium salt and additives can be effectively dissolved, reducing electrolyte decomposition and thus extending the cycle life of the lithium-ion secondary battery.

[0120] In one embodiment, the conductivity of the electrolyte is d, where 7 mS / cm ≤ d ≤ 20 mS / cm.

[0121] Electrolyte conductivity refers to the ability of active ions to conduct within the electrolyte. Higher conductivity indicates greater conductivity, which is beneficial for maintaining a faster charge / discharge rate in lithium-ion batteries. Electrolyte conductivity at 25°C can be tested using any known method. For example, a conductivity testing method may include: heating the test sample and standard liquid to 25°C (±0.1°C); calibrating the testing instrument (Leici DDSJ-308F) using two standard liquids at an ambient temperature of 25°C (±0.5°C); after calibration and electrode cleaning, vertically immersing the test sample electrode in the test liquid to begin testing; and recording the results after the data has stabilized for at least 10 seconds.

[0122] By setting the electrolyte conductivity within the aforementioned range, it is beneficial to improve the lithium-ion transport capacity in the electrolyte and reduce side reactions in the lithium-ion battery, thereby improving the cycle life of the lithium-ion battery while maintaining good fast-charging performance of the lithium-ion rechargeable battery. The electrolyte conductivity can be 7 mS / cm, 8 mS / cm, 9 mS / cm, 10 mS / cm, 11 mS / cm, 12 mS / cm, 13 mS / cm, 14 mS / cm, 15 mS / cm, 16 mS / cm, 17 mS / cm, 18 mS / cm, 19 mS / cm, 20 mS / cm, etc., or it can be a range of any two of the above values, for example, 7 mS / cm ≤ d ≤ 15 mS / cm, 10 mS / cm ≤ d ≤ 19 mS / cm, etc.

[0123] In one embodiment, the conductivity of the electrolyte is 10 mS / cm ≤ d ≤ 15 mS / cm.

[0124] By setting the electrolyte conductivity within the aforementioned range, the rapid transport capability of lithium ions in the electrolyte is maintained, while side reactions in the lithium-ion battery are significantly reduced, thereby improving the cycle life of the lithium-ion battery and ensuring good fast-charging performance of the lithium-ion rechargeable battery. The electrolyte conductivity can be 10 mS / cm, 11 mS / cm, 12 mS / cm, 13 mS / cm, 14 mS / cm, 15 mS / cm, etc., or a range consisting of any two of the above values, for example, 10 mS / cm ≤ d ≤ 14 mS / cm, 12 mS / cm ≤ d ≤ 15 mS / cm, etc.

[0125] In one embodiment, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0126] In one embodiment, the negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one side of the negative current collector. The negative active layer includes a negative active material, which includes graphite, and the specific surface area of ​​the graphite is 0.5 m². 2 / g-10m 2 / g.

[0127] The specific surface area of ​​graphite is tested using the gas adsorption BET method, according to the national standard GB / T19587-2004. The specific surface area of ​​graphite can be as low as 0.5 m². 2 / g, 1m 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g, etc., can also be a range consisting of any two of the above values, for example, 0.5m. 2 / g-7m 2 / g、2m 2 / g-10m 2 / g etc.

[0128] By setting the specific surface area of ​​graphite as described above, it is beneficial for sufficient contact between graphite and electrolyte; it helps to form a stable SEI film, reduces the occurrence of side reactions, thereby improving the cycle stability of the battery, reducing electrolyte decomposition during cycling, and extending the cycle life of lithium-ion secondary batteries. The graphite can be at least one of natural graphite or artificial graphite.

[0129] In other embodiments, the negative electrode active material may be any battery negative electrode active material known in the art, other than graphite. As an example, the negative electrode active material may include at least one of the following materials: soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys.

[0130] In one embodiment, the negative electrode current collector may be a metal foil or a composite negative electrode current collector. Optionally, copper foil may be used as the metal foil. Optionally, the composite negative electrode current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite negative electrode current collector may be formed by forming a metal material on the polymer material substrate; the metal material may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy; the polymer material may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0131] In one embodiment, the negative electrode active layer may optionally include a negative electrode binder. The negative electrode binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0132] In one embodiment, the negative electrode active layer may optionally include a negative electrode conductive agent. The negative electrode conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0133] In one embodiment, the negative electrode active layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0134] In one embodiment, the positive electrode includes a positive current collector and a positive active layer disposed on at least one side of the positive current collector. The positive active layer includes a positive active material, which includes lithium iron phosphate.

[0135] For lithium iron phosphate systems, the electrolyte solvent includes carboxylic acid esters, and the additives include vinylene carbonate and fluoro anhydrides and their derivatives, which can effectively improve the cycle life of lithium-ion secondary batteries while maintaining good fast-charging performance.

[0136] In one embodiment, the positive electrode current collector may be a metal foil or a composite positive electrode current collector. Optionally, aluminum foil may be used as the metal foil. Optionally, the composite positive electrode current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite positive electrode current collector may be formed by forming a metal material on the polymer material substrate; the metal material may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy; the polymer material may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0137] In one embodiment, the positive electrode active layer may optionally include a positive electrode binder. The negative electrode binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0138] In one embodiment, the positive electrode active layer may optionally include a positive electrode conductive agent. The negative electrode conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0139] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0140] In one embodiment, the positive electrode, negative electrode, and separator can be manufactured into a cell assembly 23 by a winding process or a stacking process.

[0141] In one specific embodiment, the negative electrode active material includes graphite, and the specific surface area of ​​graphite is 0.5 m². 2 / g-10m 2 / g; the positive electrode active material includes lithium iron phosphate; the electrolyte includes lithium salt, solvent and additives; the solvent includes carboxylic acid ester; the additives include vinylene carbonate, fluoro anhydride and its derivatives; the mass percentage of carboxylic acid ester in the electrolyte is a, 10% ≤ a ≤ 80%. Lithium-ion secondary batteries have a long cycle life and good fast charging capability.

[0142] The lithium-ion secondary battery disclosed in this application can be used in electrical devices that use batteries as a power source or in various energy storage systems that use batteries as energy storage elements. Electrical devices include the lithium-ion secondary batteries provided in the above embodiments. Electrical devices can be, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0143] For ease of explanation, the following embodiments use a vehicle 1000 as an example of an electrical device according to an embodiment of this application. Please refer to... Figure 3 , Figure 3 This is a schematic diagram of the vehicle structure provided in an embodiment of this application.

[0144] Vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A lithium-ion secondary battery 100 is installed inside vehicle 1000, which can be located at the bottom, front, or rear of vehicle 1000. The lithium-ion secondary battery 100 can be used to power vehicle 1000; for example, it can serve as the operating power source for vehicle 1000. Vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 controls the lithium-ion secondary battery 100 to supply power to the motor 300, for example, to meet the power needs of vehicle 1000 during starting, navigation, and driving.

[0145] In some embodiments of this application, the lithium-ion secondary battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0146] To make the technical problems, technical solutions, and beneficial effects solved by the embodiments of this application clearer, the following will provide a more detailed description in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0147] The preparation process of Example 1 is as follows:

[0148] (1) Preparation of positive electrode sheet:

[0149] (a) Obtain the positive current collector aluminum foil with a thickness of 13 μm.

[0150] (b) Lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 98:1:1. N-methylpyrrolidone was added, and the mixture was stirred for 6 hours to obtain a positive electrode active slurry with a solid content of 50 wt%. The positive electrode active slurry was then coated onto the surface of the aluminum foil used as a positive electrode current collector.

[0151] (c) After drying and rolling, a positive electrode active layer with a thickness of 35 μm is formed, and a positive electrode sheet is obtained.

[0152] (2) Preparation of negative electrode sheet:

[0153] (a) Obtain a negative electrode current collector copper foil with a thickness of 6 μm.

[0154] (b) The negative electrode active material graphite, conductive agent acetylene black, binder styrene-butadiene latex (SBR), and dispersant sodium carboxymethyl cellulose (CMC-Na) were mixed and dispersed in deionized water at a mass ratio of 97:1:1:1. After stirring and mixing evenly, a negative electrode active slurry was prepared with a solid content of 50%. The negative electrode active slurry was then prepared at a concentration of 7 mg / cm³. 2 The coating density is uniformly coated on the negative electrode current collector copper foil, and after drying and rolling, a 60μm negative electrode active layer is formed to obtain the negative electrode sheet.

[0155] (3) Preparation of electrolyte:

[0156] An organic solvent was prepared by mixing carbonate and carboxylic acid ester at a mass ratio of 74.75:10. LiPF6 was dissolved in the organic solvent to prepare a 10% (w / w) LiPF6 solution. Ethylene carbonate (VC) was added to bring its mass fraction to 5%, and fluoro anhydride and its derivatives were added to bring their mass fraction to 0.25%. The carbonate consisted of EC and EMC, with an EC:EMC ratio of 3:7 (w / w).

[0157] (4) Separating membrane:

[0158] A 7μm polyethylene film was used as the separator.

[0159] (5) Assembly:

[0160] The positive electrode, separator, and negative electrode are wound together, wrapped in an aluminum shell, and then injected with the prepared electrolyte. After formation, aging, and other processes, the battery is obtained and then subjected to subsequent testing.

[0161] After the above steps (1)-(5), a lithium-ion secondary battery is obtained.

[0162] The preparation process of the lithium-ion secondary batteries in other embodiments and comparative examples is similar to that in Example 1, and the different parameters can be found in Table 1.

[0163] The relevant parameter testing process for the embodiments and comparative examples of this application is as follows:

[0164] 1. Test methods for each component in the electrolyte and its dosage

[0165] (1) Organic molecular testing method: Organic components are quantitatively analyzed by gas chromatography, according to national standard GB / T 9722-2006.

[0166] (2) Inorganic salt test method: lithium salt composition analysis of electrolyte, national standard GB / T 6040-2002.

[0167] 2. Electrolyte conductivity

[0168] The test sample and standard liquid were kept at a constant temperature of 25℃ (±0.1℃). The instrument (Leici DDSJ-308F) was calibrated using two standard liquids at an ambient temperature of 25℃ (±0.5℃). After calibration and cleaning of the electrodes, the test sample electrode was vertically placed into the test liquid to start the test. The test results were recorded after the data stabilized for more than 10 seconds.

[0169] 3. Specific surface area of ​​graphite

[0170] Gas adsorption BET method for specific surface area analysis, testing according to national standard GB / T 19587-2004.

[0171] 4. Cycle life

[0172] At 60℃, the battery is charged to 3.8V at a 1C rate and then charged at a constant voltage to 0.05C. After standing for 10 minutes, it is discharged to 2.0V at a 1C rate. This is recorded as one charge-discharge cycle. The discharge capacity of each cycle is tested. The above charge-discharge cycle is repeated until the battery capacity decays to 80% of the initial capacity. The number of cycles N at this point is recorded as the cycle life of the battery.

[0173] 5. Low-temperature fast charging performance

[0174] At -10℃, the battery was charged at a constant current of 0.33C to the charging cutoff voltage of 3.8V, then charged at a constant voltage to a current of 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.33C to the discharge cutoff voltage of 2V. Its actual capacity was recorded as C0.

[0175] Then, the battery was sequentially charged at constant current rates of 2C0, 1.8C0, 1.6C0, 1.4C0, 1.2C0, 1.0C0, 0.8C0, 0.75C0, 0.7C0, 0.65C0, 0.6C0, 0.5C0, 0.4C0, 0.25C0, 0.15C0, and 0.05C0 until the full battery charging cutoff voltage of 3.8V or the negative terminal cutoff potential (whichever comes first). After each charging, the battery was discharged at 0.33C0 until the full battery discharge cutoff voltage of 2V. The charging rates were recorded at 10%, 20%, 30%, ... 80% SOC. The negative electrode potential corresponding to the state of charge (SOC) is plotted at different rates. Linear fitting yields the charging rate corresponding to a negative electrode potential of 0V at different SOC states. This charging rate is the charging window for that SOC state, denoted as C10%SOC, C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, and C80%SOC. Using the formula (60 / C25%SOC + 60 / C30%SOC + 60 / C35%SOC + 60 / C40%SOC) × 10%, the charging time T for charging the battery from 20%SOC to 40%SOC is calculated. A shorter charging time T indicates better fast-charging performance of the secondary battery.

[0176] The relevant parameter testing process for the embodiments and comparative examples of this application is as follows:

[0177]

[0178]

[0179] By comparing Examples 1-17 with Comparative Example 1, when the mass percentage a of carboxylic acid ester in the electrolyte is 10% ≤ a ≤ 80%, the addition of fluoro anhydride and its derivatives to the electrolyte can improve the cycle performance of lithium-ion secondary batteries while maintaining good fast-charging performance.

[0180] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A battery cell, characterized in that, include: Positive electrode, negative electrode, separator, and electrolyte; The electrolyte comprises lithium salt, solvent, and additives; the solvent comprises carboxylic acid esters; the additives comprise vinylene carbonate, fluoro anhydrides, and their derivatives; the mass percentage of the carboxylic acid ester in the electrolyte is a, where 10% ≤ a ≤ 80%.

2. The battery cell according to claim 1, characterized in that, 10％≤a≤50％。 3. The battery cell according to claim 1 or 2, characterized in that, The mass ratio of the fluoro anhydride and its derivatives to the vinylene carbonate is 1.7%-200%.

4. The battery cell according to any one of claims 1 to 3, characterized in that, The mass ratio of the fluoro anhydride and its derivatives to the vinylene carbonate is 5%-25%.

5. The battery cell according to any one of claims 1 to 4, characterized in that, The mass percentage of the vinylene carbonate in the electrolyte is b, where 1% ≤ b ≤ 15%.

6. The battery cell according to any one of claims 1 to 5, characterized in that, The mass percentage of the fluoro anhydride and its derivatives in the electrolyte is c, where 0.05% ≤ c ≤ 10%.

7. The battery cell according to any one of claims 1 to 6, characterized in that, The lithium salt constitutes 10%-20% by mass in the electrolyte.

8. The battery cell according to any one of claims 1 to 7, characterized in that, The structural formulas of the fluoro anhydrides and their derivatives are as follows: Wherein, R1 includes one of hydrogen, an alkyl group having 1-10 carbon atoms, and a fluoroalkane having 1-10 carbon atoms; R2 includes one of hydrogen, an alkyl group having 1-10 carbon atoms, and a fluoroalkane having 1-10 carbon atoms; the number of fluorine atoms in R1 is n1, 0≤n1≤11; the number of fluorine atoms in R2 is n2, 0≤n2≤11; at least one of R1 and R2 includes fluorine atoms.

9. The battery cell according to claim 8, characterized in that, 3≤n1≤5, and / or, 3≤n2≤5.

10. The battery cell according to claim 8 or 9, characterized in that, The fluoro anhydrides and their derivatives include at least one of pentafluoropropionic anhydride, difluoroacetic anhydride, and trifluoroacetic anhydride.

11. The battery cell according to any one of claims 1 to 10, characterized in that, The structural formula of the carboxylic acid ester is: R3 includes one of hydrogen and an alkyl group having 1-10 carbon atoms; R4 includes one of hydrogen and an alkyl group having 1-10 carbon atoms.

12. The battery cell according to claim 11, characterized in that, The carboxylic acid ester includes at least one of ethyl acetate, propyl acetate, and propyl propionate.

13. The battery cell according to any one of claims 1 to 12, characterized in that, The solvent also includes carbonates, which constitute 4.8%-85% by mass in the electrolyte.

14. The battery cell according to claim 13, characterized in that, The carbonate includes at least one of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and fluoroethylene carbonate.

15. The battery cell according to any one of claims 1 to 14, characterized in that, The conductivity of the electrolyte is d, 7 mS / cm ≤ d ≤ 20 mS / cm.

16. The battery cell according to any one of claims 1 to 15, characterized in that, 10mS / cm≤d≤15mS / cm.

17. The battery cell according to any one of claims 1 to 16, characterized in that, The negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one side of the negative current collector. The negative active layer includes a negative active material, which includes graphite, and the specific surface area of ​​the graphite is 0.5 m². 2 / g-10m 2 / g.

18. The battery cell according to any one of claims 1 to 17, characterized in that, The positive electrode includes a positive current collector and a positive active layer disposed on at least one side of the positive current collector. The positive active layer includes a positive active material, and the positive active material includes lithium iron phosphate.

19. An electrical appliance, characterized in that, Includes the battery cell as described in any one of claims 1 to 18.

Images