Electrolytic solution, battery cell and preparation method therefor, battery, and electrical device

Abstract

An electrolytic solution, a battery cell and a preparation method therefor, a battery, and an electrical device. The electrolytic solution comprises an electrolyte salt and an additive; the electrolyte salt comprises a first electrolyte salt shown in formula (1), and the additive comprises a first additive shown in formula (2); the content by weight of the first electrolyte salt in the electrolytic solution is denoted as x, the content by weight of the first additive in the electrolytic solution is denoted as y, and the content is calculated on the basis of the total weight of the electrolytic solution, wherein 50≤x / y≤500. The electrolytic solution can improve the cycle performance and dynamic performance of the battery.

Description

Electrolyte, battery cell and preparation method thereof, battery and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202310771021.2 filed on June 27, 2023, entitled “Electrolyte, battery cell and preparation method thereof, battery and electrical device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to an electrolyte, a battery cell and a preparation method thereof, a battery and an electrical device. Background Art

[0004] In recent years, batteries have been widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. The electrolyte, as a key component of a battery, affects its performance. The above statements are intended only to provide background information related to this application and do not necessarily constitute prior art.

[0005] Summary of the Invention

[0006] The present application provides an electrolyte, a battery cell and a preparation method thereof, a battery and an electrical device, which can improve the cycle performance and dynamic performance of the battery.

[0007] In a first aspect, the present application provides an electrolyte solution comprising an electrolyte salt and an additive.

[0008] The electrolyte salt includes a first electrolyte salt represented by formula (1), R1 and R2 each independently include a fluorine atom or a C1-C6 fluoroalkyl group, and M1 includes one or more of Li, Na, and K.

[0009] The additive includes a first additive represented by formula (2), and R3 and R4 independently include a fluorine atom and a C1-C6 fluoroalkyl group.

[0010] The weight content of the first electrolyte salt in the electrolyte is denoted as x, and the weight content of the first additive in the electrolyte is denoted as y, both based on the total weight of the electrolyte, and 50≤x / y≤500.

[0011] The inventors have found that by making the electrolyte include the first additive shown in formula (2) and adjusting the weight content x of the first electrolyte salt and the weight content y of the first additive in the electrolyte so that they satisfy 50≤x / y≤500, the dissolution of soluble products formed after the corrosion reaction between the first electrolyte salt and the positive electrode collector into the electrolyte can be reduced, thereby reducing the corrosion of the positive electrode collector and improving the cycle performance of the battery, especially the cycle performance in a high temperature environment. It can also reduce the internal resistance of the battery and improve the dynamic performance of the battery.

[0012] In any embodiment, 100≤x / y≤400, optionally, 125≤x / y≤300.

[0013] In any embodiment, 1%≤x≤15%, optionally, 7%≤x≤12%.

[0014] In any embodiment, 0.01%≤y≤0.20%, optionally, 0.025%≤y≤0.10%.

[0015] In any embodiment, R1 and R2 independently include a fluorine atom, a trifluoromethyl group, a pentafluoroethyl group, a heptafluoropropyl group, or a nonafluorobutyl group. Optionally, at least one of R1 and R2 represents a fluorine atom.

[0016] When R1 and R2 are within the above range, it is also helpful to form a thinner interface film, thereby helping to reduce the interface ion impedance, reduce the internal resistance of the battery, and improve the dynamic performance of the battery.

[0017] In any embodiment, R3 and R4 independently include a fluorine atom, a trifluoromethyl group, a pentafluoroethyl group, a heptafluoropropyl group, or a nonafluorobutyl group. Optionally, at least one of R3 and R4 represents a fluorine atom.

[0018] When R3 and R4 are within the above range, it is also helpful to form a thinner interface film, thereby helping to reduce the interface ion impedance, reduce the internal resistance of the battery, and improve the dynamic performance of the battery.

[0019] In any embodiment, the first electrolyte salt includes one or more of the following:

[0020] Optionally, the first electrolyte salt includes one or more of A1 to A7:

[0021] When the first electrolyte salt is within the above range, it has higher thermal stability and is less susceptible to hydrolysis, which helps further improve the conductivity of the electrolyte, thereby further improving the battery's cycling performance. Furthermore, when the first electrolyte salt is within the above range, it helps form a thinner interfacial film, reducing interfacial ionic impedance, thereby reducing the battery's internal resistance and improving the battery's kinetic performance.

[0022] In any embodiment, the first additive includes one or more of B1 to B5:

[0023] When the first additive is within the above range, it exhibits higher thermal stability and is less susceptible to hydrolysis, further improving the conductivity of the electrolyte and thus the battery's cycling performance. Furthermore, when the first additive is within the above range, it helps form a thinner interfacial film, reducing interfacial ionic impedance, thereby reducing the battery's internal resistance and improving its kinetic performance.

[0024] In any embodiment, the anion of the first electrolyte salt represented by formula (1) is the same as the anion of the first additive represented by formula (2).

[0025] In any embodiment, the electrolyte further includes a second electrolyte salt, and the second electrolyte salt includes one or more of the following:

[0026] M2 includes one or more of Li, Na, and K, and may optionally include one or more of Li and Na.

[0027] The second electrolyte salt can passivate the positive electrode current collector, for example, forming a poorly soluble product such as LiF, thereby protecting the positive electrode current collector and reducing corrosion of the positive electrode current collector by the first electrolyte salt. Therefore, when the electrolyte also includes a second electrolyte salt, the cycle performance of the battery can be further improved.

[0028] In any embodiment, the weight content of the second electrolyte salt in the electrolyte is denoted as m, and based on the total weight of the electrolyte, m / (x+m) is greater than or equal to 15%. By adjusting the content of the second electrolyte salt, the electrolyte can also have both high conductivity and low viscosity, thereby further improving the cycle performance of the battery.

[0029] In any embodiment, the electrolyte further comprises a second additive represented by formula (3),

[0030] R5 includes a fluorine atom or a C1-C6 fluoroalkyl group, and M3 includes one or more of Li, Na, and K, and may optionally include one or more of Li and Na.

[0031] The second additive represented by formula (3) has high thermal stability and helps to form a thinner and more flexible interface film, thereby helping to further improve the cycle performance and / or kinetic performance of the battery.

[0032] In any embodiment, the weight content of the second additive in the electrolyte is denoted as n, based on the total weight of the electrolyte, 0.01%≤n≤1%.

[0033] In any embodiment, the second additive includes one or more of the following:

[0034] Optionally, the second additive includes one or more of D1 to D6:

[0035] In any embodiment, the electrolyte further comprises a third additive represented by formula (4),

[0036] M4 includes one or more of Li, Na, and K, and may optionally include one or more of Li and Na.

[0037] When the electrolyte further includes a third additive, the storage performance, cycle performance and / or kinetic performance of the battery can be improved.

[0038] In any embodiment, the weight content of the third additive in the electrolyte is denoted as p, and based on the total weight of the electrolyte, 0.01%≤p≤1%.

[0039] In any embodiment, the electrolyte further includes a non-aqueous solvent, and the non-aqueous solvent includes one or more of cyclic carbonates, chain carbonates, and carboxylates.

[0040] In any embodiment, the weight content of the cyclic carbonate in the non-aqueous solvent is denoted as a, and based on the total weight of the non-aqueous solvent, 1%≤a≤35%.

[0041] In any embodiment, the weight content of the linear carbonate in the non-aqueous solvent is denoted as b, and based on the total weight of the non-aqueous solvent, 65%≤b≤99%.

[0042] In any embodiment, the weight content of the carboxylic acid ester in the non-aqueous solvent is denoted as c, based on the total weight of the non-aqueous solvent, 0≤c≤30%.

[0043] A second aspect of the present application provides a battery cell comprising a positive electrode sheet, a negative electrode sheet, and the electrolyte of the first aspect of the present application.

[0044] In any embodiment, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, the positive electrode film layer includes a first positive electrode active material, and the voltage platform of the first positive electrode active material is greater than or equal to 3.6V. The first positive electrode active material has a high voltage platform, which is beneficial to improve the energy density of the battery, but its thermal stability and cycle stability are generally poor. The first positive electrode active material with a high voltage platform is used in combination with the electrolyte provided in this application, which can give full play to the advantages of the first positive electrode active material with a high voltage platform, thereby enabling the battery to have both high energy density and good cycle performance.

[0045] In any embodiment, the first positive electrode active material includes one or more of lithium cobalt oxide, lithium nickel cobalt manganese ternary material, lithium nickel cobalt aluminum ternary material, and modified compounds thereof.

[0046] In any embodiment, the weight content of the first positive electrode active material in the positive electrode film layer is greater than or equal to 50%, based on the total weight of the positive electrode film layer.

[0047] In any embodiment, the positive electrode current collector includes aluminum foil, aluminum alloy foil, aluminum mesh, aluminum alloy mesh, or a composite current collector having a surface containing aluminum or aluminum alloy.

[0048] In any embodiment, the negative electrode plate includes one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials and lithium titanate.

[0049] The third aspect of the present application provides a method for preparing a battery cell, comprising the following steps: providing a battery container comprising a positive electrode sheet and a negative electrode sheet; injecting the electrolyte of the first aspect of the present application into the battery container to obtain a battery cell.

[0050] A fourth aspect of the present application provides a battery, comprising the battery cell of the first aspect of the present application or the battery cell prepared by the preparation method of the second aspect of the present application.

[0051] A fifth aspect of the present application provides an electrical device comprising the battery of the fourth aspect of the present application.

[0052] The electric device of the present application includes the battery provided by the present application, and thus has at least the same advantages as the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] To more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive effort.

[0054] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0055] FIG. 2 is an exploded schematic diagram of an embodiment of the battery cell of FIG. 1 .

[0056] FIG3 is a schematic diagram of an embodiment of a battery module of the present application.

[0057] FIG4 is a schematic diagram of an embodiment of a battery pack of the present application.

[0058] FIG. 5 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 4 .

[0059] FIG6 is a schematic diagram of an embodiment of an electric device including the battery of the present application as a power source.

[0060] In the accompanying drawings, which are not necessarily drawn to scale, reference numerals are as follows: 1 battery pack, 2 upper housing, 3 lower housing, 4 battery module, 5 battery cell, 51 housing, 52 electrode assembly, 53 cover plate. DETAILED DESCRIPTION

[0061] Below, the embodiments of the electrolyte, battery cells and their preparation methods, batteries and electrical devices of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0062] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0063] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0064] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

[0065] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further 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 may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0066] Unless otherwise specified, in this application, the terms "first", "second", "third", etc. are used to distinguish different objects rather than to describe a specific order or a primary-secondary relationship.

[0067] In this application, the terms "plurality" and "multiple" refer to two or more.

[0068] Unless otherwise specified, the terms used in this application have the common meanings that are commonly understood by those skilled in the art.

[0069] Unless otherwise stated, the numerical values ​​of the various parameters mentioned in this application can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of this application. Unless otherwise stated, the test temperature of each parameter is 25°C.

[0070] In the present application, "fluoroalkyl" may be a partially fluorinated alkyl or a fully fluorinated alkyl, and includes fluorinated straight-chain alkyl and fluorinated branched-chain alkyl.

[0071] In various embodiments, the C1-C6 fluoroalkyl group, ie, the fluoroalkyl group, may contain 1-6 carbon atoms.

[0072] Throughout this specification, substituents of compounds are disclosed in groups or ranges. It is expressly intended that this description includes each individual subcombination of members of these groups and ranges. For example, it is expressly intended that the term "C1-C6 fluoroalkyl" individually discloses C1, C2, C3, C4, C5, C6, C1-C6, C1-C5, C1-C4, C1-C3, C1-C2, C2-C6, C2-C5, C2-C4, C2-C3, C3-C6, C3-C5, C3-C4, C4-C6, C4-C5, C5-C6 fluoroalkyl.

[0073] The battery mentioned in the embodiments of the present application may be a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in the present application may include a battery cell, a battery module, or a battery pack.

[0074] A battery cell is the smallest unit of a battery, independently capable of charging and discharging. A battery cell can be cylindrical, flat, rectangular, or in other shapes, though this is not a limitation in the present invention. Figure 1 shows a battery cell 5 with a rectangular structure as an example.

[0075] When there are multiple battery cells, the multiple battery cells are connected in series, in parallel, or in mixed series via a busbar. In some embodiments, the battery may be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module. In some embodiments, the battery may be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed in the housing. In some embodiments, the housing may serve as part of the vehicle's chassis structure. For example, a portion of the housing may form at least a portion of the vehicle's floor, or a portion of the housing may form at least a portion of the vehicle's crossbeam or longitudinal beam.

[0076] In some embodiments, the battery may be an energy storage device, including an energy storage container, an energy storage cabinet, and the like.

[0077] A battery cell generally includes an electrode assembly. The electrode assembly generally includes a positive electrode sheet and a negative electrode sheet. The electrode assembly can be a wound structure or a stacked structure, which is not limited in the present embodiment.

[0078] The battery cell may also include an outer packaging, which can be used to encapsulate the electrode assembly and electrolyte. The outer packaging can be a hard shell, such as a hard plastic shell, aluminum shell, steel shell, etc. The outer packaging can also be a soft package, such as a bag-type soft package. The soft package can be made of plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0079] In some embodiments, as shown in Figure 2, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, which together form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening, thereby sealing the receiving cavity. The electrode assembly 52 is enclosed in the receiving cavity. The number of electrode assemblies 52 contained in a battery cell 5 can be one or more, and can be adjusted according to needs.

[0080] In some embodiments, battery cells can be assembled into a battery module. The number of battery cells contained in a battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module. Figure 3 is a schematic diagram of a battery module 4 as an example. As shown in Figure 3, in the battery module 4, multiple battery cells 5 can be arranged in sequence along the length of the battery module 4. Of course, they can also be arranged in any other manner. The multiple battery cells 5 can further be fixed by fasteners.

[0081] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0082] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0083] Figures 4 and 5 are schematic diagrams of an exemplary battery pack 1. As shown in Figures 4 and 5, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing comprises an upper housing 2 and a lower housing 3. The upper housing 2 covers the lower housing 3 and forms an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 may be arranged in any manner within the housing.

[0084] The electrolyte is one of the key factors affecting battery performance. Currently, the most widely commercially used electrolyte system is a mixed carbonate solution of lithium hexafluorophosphate. However, lithium hexafluorophosphate has poor thermal stability and decomposes to form PF5 at higher temperatures. PF5 has strong Lewis acidity, which reacts with the lone electron pairs on the oxygen atoms in non-aqueous solvent molecules, causing the non-aqueous solvent to decompose. Furthermore, PF5 is highly sensitive to trace amounts of water in the electrolyte, generating HF upon contact with water, which can cause battery performance degradation.

[0085] In view of this, the inventors improved the electrolyte.

[0086] The electrolyte provided in the embodiments of the present application can be used in battery cells.

[0087] The electrolyte provided in the embodiment of the present application includes an electrolyte salt and an additive.

[0088] The electrolyte salt includes a first electrolyte salt represented by formula (1), R1 and R2 each independently include a fluorine atom or a C1-C6 fluoroalkyl group, and M1 includes one or more of Li, Na, and K.

[0089] The additive includes a first additive represented by formula (2), and R3 and R4 each independently include a fluorine atom or a C1-C6 fluoroalkyl group.

[0090] The weight content of the first electrolyte salt in the electrolyte is recorded as x, and the weight content of the first additive in the electrolyte is recorded as y, both based on the total weight of the electrolyte, and 50≤x / y≤500.

[0091] The first electrolyte salt represented by formula (1) has the characteristics of high thermal stability and non-hydrolysis. In addition, the anion of the first electrolyte salt represented by formula (1) is a weakly coordinated anion centered on N, containing a conjugated group and a fluorine atom and / or a fluoroalkyl group with strong electron-attracting properties, the anion charge is highly delocalized, and the anion is closely related to M1. + The interaction between the first electrolyte salt and the positive electrode is weak. Therefore, the first electrolyte salt also has a low lattice energy and is easy to dissociate, which also helps to improve the conductivity of the electrolyte and provide good power performance of the battery. However, the first electrolyte salt is prone to corroding the positive electrode current collector, such as aluminum foil, at high voltages (e.g., voltages above 4V), and this corrosion becomes more obvious at high temperatures.

[0092] The main function of the positive electrode current collector is to provide an electron channel for the electrochemical reaction, accelerate charge transfer, and reduce electrochemical polarization. Corrosion of the positive electrode current collector will cause irreversible capacity loss of the battery and affect the reliability of the battery. The soluble products formed after corrosion will contaminate the electrolyte and aggravate the decomposition of the electrolyte. As the corrosion reaction continues, the high concentration of soluble Al in the electrolyte will 3+ It will also migrate to the negative electrode and be reduced and deposited. 3+ The aluminum metal formed after reduction will be deposited on the negative electrode active material, such as the graphite surface, which will block the diffusion channel of lithium ions and affect the extraction and insertion of lithium ions. In addition, during the use of the battery, the stability and density of the solid electrolyte interface film on the surface of the negative electrode active material may be worse than the initial state of the battery. At this time, the aluminum metal that is continuously dissolved after the positive electrode current collector is corroded will be deposited on the negative electrode active material, which will block the diffusion channel of lithium ions and affect the extraction and insertion of lithium ions. 3+ This will have a serious impact on battery performance, such as deteriorating the battery's cycle performance and kinetic performance. In addition, the soluble products formed after corrosion will increase battery polarization, exacerbate lithium plating at the negative electrode, and reduce battery reliability.

[0093] The inventors have found that by making the electrolyte include the first additive shown in formula (2) and adjusting the weight content x of the first electrolyte salt and the weight content y of the first additive in the electrolyte so that they satisfy 50≤x / y≤500, the dissolution of soluble products formed after the corrosion reaction between the first electrolyte salt and the positive electrode collector into the electrolyte can be reduced, thereby reducing the corrosion of the positive electrode collector and improving the cycle performance of the battery, especially the cycle performance in a high temperature environment. It can also reduce the internal resistance of the battery and improve the dynamic performance of the battery.

[0094] The inventors have found that when x / y is greater than 500, the content of the first electrolyte salt in the electrolyte is high and the content of the first additive is low. At this time, the first additive is insufficient to reduce the dissolution of the soluble product formed by the corrosion reaction between the first electrolyte salt and the positive electrode collector into the electrolyte, thereby failing to reduce the corrosion of the positive electrode collector, thereby resulting in poor improvement of the battery cycle performance and no obvious effect on reducing the internal resistance of the battery. When x / y is less than 50, the content of the first electrolyte salt in the electrolyte is low and the content of the first additive is high. At this time, the Al in the electrolyte is 3+ The content will also be higher, a lot of Al 3+ Will migrate to the negative electrode and reduce and deposit. 3+ The reduction potential of aluminum is higher, so aluminum metal will be preferentially reduced and deposited on the negative electrode active material, such as the surface of graphite, which will also affect the extraction and insertion of lithium ions and affect the cycle performance and kinetic performance of the battery.

[0095] In some embodiments, x / y may be 50, 75, 100, 125, 150, 200, 250, 300, 350, 400, or any range thereof, preferably, 100≤x / y≤400, and more preferably, 125≤x / y≤300.

[0096] In some embodiments, 1%≤x≤15%, for example, 1%, 2%, 3%, 5%, 7%, 10%, 12%, 15%, or any range thereof. Alternatively, 5%≤x≤12%, 7%≤x≤12%.

[0097] In some embodiments, 0.01%≤y≤0.20%, for example, it can be 0.01%, 0.02%, 0.025%, 0.03%, 0.04%, 0.05%, 0.08%, 0.10%, 0.12%, 0.15%, 0.20%, or a range consisting of any of the above values. Optionally, 0.02%≤y≤0.20%, 0.02%≤y≤0.15%, 0.02%≤y≤0.12%, 0.02%≤y≤0.10%, 0.02%≤y≤0.08%, 0.025%≤y≤0.15%, 0.025%≤y≤0.12%, 0.025%≤y≤0.10%, 0.025%≤y≤0.08%, 0.04%≤y≤0.15%, 0.04%≤y≤0.12%, 0.04%≤y≤0.10%, 0.04%≤y≤0.08%, 0.05%≤y≤0.15%, 0.05%≤y≤0.12%, 0.05%≤y≤0.10%, 0.05%≤y≤0.08%.

[0098] In some embodiments, R1 and R2 may each independently include a fluorine atom, a trifluoromethyl group, a pentafluoroethyl group, a heptafluoropropyl group, or a nonafluorobutyl group. Alternatively, at least one of R1 and R2 represents a fluorine atom.

[0099] When R1 and R2 are within the above range, it is also helpful to form a thinner interface film, thereby helping to reduce the interface ion impedance, reduce the internal resistance of the battery, and improve the dynamic performance of the battery.

[0100] In some embodiments, M1 may include one or more of Li and Na. Alternatively, M1 may include Li.

[0101] In some embodiments, the first electrolyte salt may include one or more of the following:

[0102] In some embodiments, the first electrolyte salt may include one or more of the following:

[0103] In some embodiments, the first electrolyte salt may include one or more of A1 to A7:

[0104] Alternatively, the first electrolyte salt may include one or more of A1 to A4.

[0105] Optionally, the first electrolyte salt may include one or more of A1 and A3.

[0106] When the first electrolyte salt is within the above range, it has higher thermal stability and is less susceptible to hydrolysis, which helps further improve the conductivity of the electrolyte, thereby further improving the battery's cycling performance. Furthermore, when the first electrolyte salt is within the above range, it helps form a thinner interfacial film, reducing interfacial ionic impedance, thereby reducing the battery's internal resistance and improving the battery's kinetic performance.

[0107] In some embodiments, R3 and R4 can each independently include a fluorine atom, a trifluoromethyl group, a pentafluoroethyl group, a heptafluoropropyl group, or a nonafluorobutyl group. Alternatively, at least one of R3 and R4 represents a fluorine atom.

[0108] When R3 and R4 are within the above range, it is also helpful to form a thinner interface film, thereby helping to reduce the interface ion impedance, reduce the internal resistance of the battery, and improve the dynamic performance of the battery.

[0109] In some embodiments, the first additive may include one or more of B1 to B5:

[0110] Alternatively, the first additive may include one or more of B1 to B4.

[0111] Optionally, the first additive may include one or more of B1 and B3.

[0112] When the first additive is within the above range, it exhibits higher thermal stability and is less susceptible to hydrolysis, further improving the conductivity of the electrolyte and thus the battery's cycling performance. Furthermore, when the first additive is within the above range, it helps form a thinner interfacial film, reducing interfacial ionic impedance, thereby reducing the battery's internal resistance and improving its kinetic performance.

[0113] In some embodiments, the anion of the first electrolyte salt represented by formula (1) is the same as the anion of the first additive represented by formula (2).

[0114] In some embodiments, the electrolyte may further include a second electrolyte salt, which may include one or more of the following:

[0115] M2 includes one or more of Li, Na, and K.

[0116] The second electrolyte salt can passivate the positive electrode current collector, for example, forming a poorly soluble product such as LiF, thereby protecting the positive electrode current collector and reducing corrosion of the positive electrode current collector by the first electrolyte salt. Therefore, when the electrolyte also includes a second electrolyte salt, the cycle performance of the battery can be further improved.

[0117] Optionally, M2 includes one or more of Li and Na.

[0118] Optionally, M2 includes Li.

[0119] In some embodiments, the second electrolyte salt may include one or more of the following:

[0120] In some embodiments, the weight content of the second electrolyte salt in the electrolyte is recorded as m, and based on the total weight of the electrolyte, m / (x+m) can be greater than or equal to 15%. Optionally, m / (x+m) can be greater than or equal to 30%, greater than or equal to 40%, greater than or equal to 50%, or greater than or equal to 60%.

[0121] By adjusting the content of the second electrolyte salt, the electrolyte can also have both high conductivity and low viscosity, thereby further improving the cycle performance of the battery.

[0122] In some embodiments, the electrolyte may further include a second additive represented by formula (3), wherein R5 includes a fluorine atom or a C1-C6 fluoroalkyl group, and M3 includes one or more of Li, Na, and K.

[0123] The second additive represented by formula (3) has high thermal stability and helps to form a thinner and more flexible interface film, thereby helping to further improve the cycle performance and / or kinetic performance of the battery.

[0124] In some embodiments, the weight content of the second additive in the electrolyte is denoted as n, based on the total weight of the electrolyte, 0.01%≤n≤1%, optionally, 0.01%≤n≤0.5%.

[0125] In some embodiments, R5 may include a fluorine atom, a trifluoromethyl group, a pentafluoroethyl group, a heptafluoropropyl group, or a nonafluorobutyl group, and may optionally include a fluorine atom, a trifluoromethyl group, or a pentafluoroethyl group.

[0126] When R5 is within the above range, it also helps to form a thinner interface film, thereby further reducing the interface ion impedance, reducing the battery internal resistance, and improving the battery's kinetic performance.

[0127] In some embodiments, M3 includes one or more of Li and Na.

[0128] In some embodiments, M3 includes Li.

[0129] In some embodiments, the second additive may include one or more of the following:

[0130] Optionally, the second additive may include one or more of D1 to D6:

[0131] In some embodiments, the electrolyte may further include a third additive represented by formula (4), wherein M4 includes one or more of Li, Na, and K.

[0132] The third additive usually decomposes in the electrolyte earlier than the non-aqueous solvent, thereby forming a low-impedance interface film at the positive electrode. This interface film can protect the positive electrode active material, reduce the oxidative decomposition of the electrolyte on the positive electrode surface, reduce the gas production of the battery, improve the high-temperature storage performance of the battery, and also reduce the charge transfer resistance of the positive electrode, thereby improving the cycle performance and / or kinetic performance of the positive electrode. At the same time, the third additive can also form a low-impedance interface film at the negative electrode, protecting the negative electrode active material and reducing the reductive decomposition of the electrolyte on the negative electrode surface. Therefore, when the electrolyte also includes the third additive, the storage performance, cycle performance and / or kinetic performance of the battery can also be improved.

[0133] In some embodiments, the weight content of the third additive in the electrolyte is denoted as p, based on the total weight of the electrolyte, 0.01%≤p≤1%, optionally, 0.01%≤p≤0.5%.

[0134] In some embodiments, M4 includes one or more of Li and Na.

[0135] In some embodiments, M4 includes Li.

[0136] In some embodiments, the electrolyte may further include other additives, for example, additives for improving the overcharge performance of the battery, additives for improving the low-temperature power performance of the battery, etc., which are not limited in the embodiments of the present application.

[0137] In some embodiments, the electrolyte further includes a non-aqueous solvent, and the non-aqueous solvent may include one or more of cyclic carbonates, chain carbonates, and carboxylates.

[0138] In some embodiments, the cyclic carbonate may include one or more of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0139] In some embodiments, the linear carbonate may include one or more of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), and ethylpropyl carbonate (EPC).

[0140] In some embodiments, the carboxylic acid ester may include one or more of methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), and ethyl butyrate (EB).

[0141] In some embodiments, the non-aqueous solvent may include a cyclic carbonate and a chain carbonate. Cyclic carbonates have a higher dielectric constant and can increase the conductivity of the electrolyte, while chain carbonates have a lower viscosity and can reduce the viscosity of the electrolyte. Therefore, when the non-aqueous solvent includes both a cyclic carbonate and a chain carbonate, it helps the electrolyte have a suitable viscosity and conductivity, thereby facilitating the transport of lithium ions.

[0142] Optionally, the weight content of the cyclic carbonate in the non-aqueous solvent is recorded as a, based on the total weight of the non-aqueous solvent, 1%≤a≤35%, optionally, 3%≤a≤30%.

[0143] Optionally, the weight content of the linear carbonate in the non-aqueous solvent is recorded as b, based on the total weight of the non-aqueous solvent, 65%≤b≤99%, optionally, 66%≤a≤94%.

[0144] In some embodiments, the weight content of the carboxylate in the non-aqueous solvent is denoted as c, and based on the total weight of the non-aqueous solvent, 0 ≤ c ≤ 30%, optionally 1% ≤ c ≤ 20%. The carboxylate helps the electrolyte have a suitable viscosity and conductivity, thereby facilitating the transport of lithium ions.

[0145] In some embodiments, the non-aqueous solvent may further include other solvents other than cyclic carbonates, linear carbonates, and carboxylates. As an example, other solvents may include sulfone solvents such as sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0146] The electrolyte provided in the embodiments of the present application can be referred to as an electrolyte solution after being uniformly mixed. The electrolyte solution can be prepared according to conventional methods in the art. For example, the non-aqueous solvent, various electrolyte salts, various additives, and other components can be uniformly mixed to obtain the electrolyte solution. The order in which the various materials are added is not particularly limited. For example, the electrolyte salts, additives, and other components can be added to the non-aqueous solvent and mixed uniformly to obtain the electrolyte solution.

[0147] The components and their contents in the electrolyte can be measured according to methods known in the art. For example, they can be measured by gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), etc. Electrolyte salts and some additives usually dissociate into cations and anions in non-aqueous solvents, so the content of each component can also be measured by detecting the content of cations and / or anions.

[0148] [Positive electrode]

[0149] The battery cell also includes a positive electrode plate.

[0150] The positive electrode sheet includes a positive electrode current collector and a positive electrode film disposed on at least one surface of the positive electrode current collector. For example, the positive electrode current collector has two surfaces that face each other in the thickness direction, and the positive electrode film is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0151] The positive electrode current collector may include aluminum foil, aluminum alloy foil, aluminum mesh, aluminum alloy mesh, or a composite current collector having aluminum or aluminum alloy on its surface.

[0152] In order to improve the corrosion resistance and strength of the positive electrode current collector, optionally, an aluminum foil with a purity of 99.99% or more is used.

[0153] An aluminum alloy can be an alloy of aluminum and other metal elements or non-metal elements. Aluminum alloy foil may contain, in addition to aluminum, other metal elements and / or non-metal elements. For example, the other metal elements may include at least one of iron, magnesium, zinc, manganese, tin, lithium, sodium, silver, gold, gallium, indium, and platinum, and the non-metal elements may include at least one of silicon, boron, and carbon. For example, the aluminum alloy foil may be an Al-Fe alloy foil, an Al-Mn alloy foil, or an Al-Mg alloy foil. The aluminum alloy foil may contain aluminum by weight in an amount of 95% to 99.5%, more preferably 98% to 99.5%.

[0154] In the present application, the aluminum foil and aluminum alloy foil may be a continuous non-porous foil, a perforated foil, a foam foil, etc., and the embodiments of the present application are not limited thereto.

[0155] In this application, the aluminum mesh and aluminum alloy mesh may be a woven structure, which is not limited in the embodiments of this application. The wires in the aluminum mesh and aluminum alloy mesh may contain other metal wires and / or non-metallic wires (such as carbon fiber) in addition to aluminum wire and aluminum alloy wire, which is not limited in the embodiments of this application.

[0156] The composite current collector may include a base layer and a metal material layer formed on at least one surface of the base layer, wherein the metal material layer includes aluminum or an aluminum alloy.

[0157] The base layer and the metal material layer can be bonded together by an adhesive to form a composite current collector. Alternatively, the metal material can be evaporated on the surface of the base layer to form a composite current collector.

[0158] As an example, the base layer may include a polymer material base layer or other metal material base layers.

[0159] As an example, the polymer material base layer may include a polymer material, and further, may include one or more of an inorganic conductive filler and an inorganic non-conductive filler.

[0160] The polymer material may include one or more of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polypropylene (PP), polyethylene (PE), polypropylene, polyvinyl chloride, polytetrafluoroethylene, polyvinylidene fluoride, polyamide, polyimide, aramid, epoxy resin, phenolic resin, silicone rubber, polycarbonate, cellulose, polyformaldehyde, polyvinyl alcohol, and polyethylene glycol, and the embodiments of the present application are not limited to this.

[0161] The inorganic conductive filler may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, and the present embodiment is not limited thereto. The inorganic non-conductive filler may include one or more of ceramic materials and glass materials, and the present embodiment is not limited thereto.

[0162] The positive electrode film typically contains a positive electrode active material, an optional binder, and an optional conductive agent. The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional binder, an optional conductive agent, and any other components in a solvent and stirring until uniformly mixed.

[0163] The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.

[0164] As an example, the binder for the positive electrode film layer may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0165] As an example, the conductive agent used for the positive electrode film layer may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0166] In some embodiments, the positive electrode active material may include a first positive electrode active material, and a voltage platform of the first positive electrode active material is greater than or equal to 3.6V.

[0167] The first cathode active material has a high voltage platform, which is beneficial for improving the energy density of the battery, but its thermal stability and cycling stability are generally poor. Combining the first cathode active material with a high voltage platform with the electrolyte provided in the embodiments of this application can fully utilize the advantages of the first cathode active material with a high voltage platform, thereby enabling the battery to achieve both high energy density and good cycling performance.

[0168] The voltage platform of the first positive electrode active material has a well-known meaning in the art, which generally refers to the voltage value corresponding to the stable section where the discharge voltage does not change significantly in the battery voltage-capacity curve (charge-discharge curve) or the voltage value maintained for the longest time during the discharge process; it can also be obtained through the differential capacity curve. The position of the peak in the differential capacity curve indicates that the charge-discharge curve has a voltage platform.

[0169] During testing, the first positive electrode active material can be assembled into a button battery for charge and discharge testing, and the charge and discharge rate can be 0.1C.

[0170] In some embodiments, the first positive electrode active material may include one or more of lithium cobalt oxide, lithium nickel cobalt manganese ternary material, lithium nickel cobalt aluminum ternary material, and modified compounds thereof.

[0171] In some embodiments, the first cathode active material may include a general formula of Li a Ni b Co c M1 d M2 e O f A g One or more of the ternary materials and modified compounds thereof. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 0≤e<1, 1≤f≤2, 0≤g≤1, M1 includes Mn and / or Al, M2 includes one or more of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes one or more of N, F, S and Cl.

[0172] High-nickel-content cathode active materials have a high voltage platform and high gram capacity, which are beneficial for improving the energy density of the battery. However, they have poor thermal stability and cycle stability. Combining high-nickel-content cathode active materials with the electrolyte provided in the examples of this application can fully utilize the advantages of high-nickel-content cathode active materials, thereby enabling the battery to achieve both high energy density and good cycle performance.

[0173] As an example, the first positive active material may include LiNi 0.5 Co 0.2 Mn 0.3O2(NCM523),LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622),LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.15 Al 0.05 O2, and one or more of their respective modified compounds.

[0174] In some embodiments, the positive electrode active material may further include a second positive electrode active material, the second positive electrode active material including one or more of a lithium-containing phosphate and a modified compound thereof. As an example, the lithium-containing phosphate may include one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and modified compounds thereof.

[0175] The modifying compounds of each of the above-mentioned positive electrode active materials may be doped and / or surface-coated to modify the positive electrode active materials. For example, the coating layer may be a carbon coating layer. The carbon coating layer helps stabilize the surface of the positive electrode active material, further reduces the charge transfer resistance of the positive electrode active material, and improves the kinetic properties of the positive electrode active material. Optionally, the carbon coating layer includes amorphous carbon, such as soft carbon, hard carbon, or a combination thereof.

[0176] In some embodiments, the weight percentage of the first positive electrode active material may be greater than or equal to 50%, based on the total weight of the positive electrode film layer, for example, the weight percentage of the first positive electrode active material may be 50%, 60%, 70%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any range thereof. Alternatively, the weight percentage of the first positive electrode active material may be 50% to 99%, 60% to 99%, 70% to 99%, 80% to 99%, 85% to 99%, 90% to 99%, 95% to 99%, 80% to 98%, 85% to 98%, 90% to 98%, 95% to 98%, 80% to 97%, 85% to 97%, 90% to 97%, or 95% to 97%.

[0177] [Negative electrode]

[0178] The battery cell includes a negative electrode plate.

[0179] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film disposed on at least one surface of the negative electrode current collector. For example, the negative electrode current collector has two opposing surfaces in the thickness direction of the negative electrode current collector, and the negative electrode film is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0180] The negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0181] The negative electrode film typically contains a negative electrode active material, an optional binder, an optional conductive agent, and other optional additives. The negative electrode film is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring them uniformly.

[0182] The solvent may be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0183] As an example, the binder for the negative electrode film layer may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA) and carboxymethyl chitosan (CMCS).

[0184] As an example, the conductive agent for the negative electrode film layer may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Other optional additives may include thickeners (e.g., sodium carboxymethyl cellulose CMC), PTC thermistor materials, etc.

[0185] The negative electrode active material may be a material known in the art. As an example, the negative electrode active material may include one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials and lithium titanate. Silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite and silicon alloy materials. Tin-based materials may include one or more of elemental tin, tin oxide and tin alloy materials. The present application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0186] [Isolation film]

[0187] The battery cell also includes a separator.

[0188] The separator is provided between the positive electrode and the negative electrode to isolate the electrodes. The present application does not particularly limit the type of separator, and any known porous structure membrane with good chemical and mechanical stability can be selected.

[0189] In some embodiments, the material of the isolation membrane can include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different.

[0190] Preparation method

[0191] The embodiments of the present application also provide a method for preparing a battery cell.

[0192] The method comprises the following steps: providing a battery container comprising a positive electrode sheet and a negative electrode sheet; injecting the electrolyte provided in an embodiment of the present application into the battery container to obtain a battery cell.

[0193] In some embodiments, the battery container further includes a separator.

[0194] In some embodiments, the method may further include the following steps: forming an electrode assembly by winding the positive electrode sheet, the separator and the negative electrode sheet through a winding process and / or a lamination process, and placing the electrode assembly in a battery container.

[0195] The battery container can be an outer packaging. The outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging can also be a soft package, such as a bag-type soft package. The soft package can be made of plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0196] In some embodiments, after the electrolyte provided in the embodiments of the present application is injected into the battery container, it may be subjected to processes such as standing and formation to obtain a battery cell.

[0197] Multiple battery cells can be further connected in series, parallel, or hybrid to form a battery module. Multiple battery modules can also be connected in series, parallel, or hybrid to form a battery pack. In some embodiments, multiple battery cells can also be directly connected to form a battery pack.

[0198] Electrical devices

[0199] The present application also provides an electrical device, which includes a battery provided in the present application. The battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0200] The electrical device can select the type of battery according to its usage requirements, such as a battery cell, a battery module or a battery pack.

[0201] Figure 6 is a schematic diagram of an exemplary electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this device, a battery pack or battery module may be used.

[0202] As another example, an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0203] Example

[0204] The following examples describe the present disclosure in more detail and are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise indicated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used directly without further processing, and all instruments used in the examples are commercially available.

[0205] Examples 1-19 and Comparative Examples 1-3 were prepared according to the following method.

[0206] Preparation of positive electrode

[0207] The positive electrode active material LiNi0.8 Co 0.1 Mn 0.1 O2, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in an appropriate amount of solvent NMP in a weight ratio of 97.5:1.4:1.1 to form a uniform positive electrode slurry; the positive electrode slurry is evenly coated on the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, the positive electrode sheet is obtained.

[0208] Preparation of negative electrode sheet

[0209] The negative electrode active material graphite, binder styrene-butadiene rubber (SBR), thickener sodium carboxymethyl cellulose (CMC-Na), and conductive agent carbon black (Super P) are fully stirred and mixed in an appropriate amount of solvent deionized water in a weight ratio of 96.2:1.8:1.2:0.8 to form a uniform negative electrode slurry; the negative electrode slurry is evenly coated on the surface of the negative electrode current collector copper foil, and after drying and cold pressing, the negative electrode sheet is obtained.

[0210] Isolation film

[0211] A porous polyethylene (PE) film is used as the separator.

[0212] Preparation of electrolyte

[0213] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed uniformly in a weight ratio of 3:5:2 to obtain a non-aqueous solvent. The electrolyte salts and additives listed in Table 1 were dissolved in the non-aqueous solvent according to the weight contents shown in Table 1, and stirred uniformly to obtain an electrolyte solution.

[0214] In Table 1, the weight content of the first electrolyte salt is recorded as x, the weight content of the second electrolyte salt is recorded as m, and the weight content of the first additive is recorded as y, all based on the total weight of the electrolyte.

[0215] In Table 1, “ / ” indicates that the electrolyte does not include the corresponding component.

[0216] The electrolyte salts and additives in Examples 1 to 19 are abbreviated as follows.

[0217] Battery preparation

[0218] The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in order to obtain an electrode assembly; the electrode assembly is placed in an outer package, injected with the above-mentioned electrolyte, and after packaging, standing, formation and other processes, a battery is obtained.

[0219] Test section

[0220] (1) Cyclic performance test

[0221] At 45°C, charge the battery at a constant current of 1C to 4.3V. Continue constant voltage charging until the current reaches 0.05C. At this point, the battery is fully charged. Record the charge capacity at this point, which is the charge capacity of the first cycle. After the battery rests for 5 minutes, discharge it at a constant current of 1C to 2.8V. This constitutes one charge-discharge cycle. Record the discharge capacity at this point, which is the discharge capacity of the first cycle. Perform the battery cyclic charge-discharge test as described above, and record the discharge capacity after each cycle. Capacity retention (%) of the battery after 600 cycles at 45°C = discharge capacity after 600 cycles / discharge capacity after the first cycle × 100%.

[0222] (2) Initial DC internal resistance test of the battery

[0223] At 25°C, charge the battery at a constant current of 1C to 4.3V. Continue constant voltage charging until the current reaches 0.05C, at which point the battery is fully charged. Discharge the battery at a constant current of 0.5C and adjust the battery to 50% SOC. The battery voltage at this point is recorded as U1. Discharge the battery at a constant current of 4C I1 for 30 seconds, using 0.1-second sampling. The voltage at the end of discharge is recorded as U2. The discharge DC internal resistance of the battery at 50% SOC represents the initial DC internal resistance of the battery. The initial DC internal resistance of the battery (mΩ) = (U1-U2) / I1.

[0224] The test results are shown in Table 1.

[0225] Table 1

[0226] From the test results in Table 1, it can be seen that by making the electrolyte include the first electrolyte salt represented by formula (1) and the first additive represented by formula (2), and adjusting the weight content x of the first electrolyte salt and the weight content y of the first additive so that they satisfy 50≤x / y≤500, the dissolution of soluble products formed after the corrosion reaction between the first electrolyte salt and the positive electrode collector into the electrolyte can be reduced, thereby reducing the corrosion of the positive electrode collector and improving the cycle performance of the battery. At the same time, the initial DC internal resistance of the battery can be reduced, and the kinetic performance of the battery can be improved.

[0227] From the test results in Table 1, it can be seen that by further adjusting the range of x / y, the cycle performance of the battery can be further improved and the initial DC internal resistance of the battery can be further reduced.

[0228] From the test results in Table 1, it can be seen that by further adjusting the range of m / (x+m), the cycle performance of the battery can be further improved and the initial DC internal resistance of the battery can be further reduced.

[0229] In Examples 20-22, the second additive and the third additive shown in Table 2 were further added to the electrolyte prepared in Example 4. The weight content of the second additive was recorded as n, and the weight content of the third additive was recorded as p, both based on the total weight of the electrolyte.

[0230] The electrolyte salts and additives in Examples 20-22 are abbreviated as follows.

[0231] Table 2

[0232] From the test results in Table 2, it can be seen that by further including a suitable amount of the second additive and / or the third additive in the electrolyte, the cycle performance of the battery can be further improved and the initial DC internal resistance of the battery can be further reduced.

[0233] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. An electrolyte, wherein The electrolyte includes an electrolyte salt and an additive; The electrolyte salt comprises a first electrolyte salt represented by formula (1), R1 and R2 each independently comprise a fluorine atom or a C1-C6 fluoroalkyl group, and M1 comprises one or more of Li, Na, and K; The additive includes a first additive represented by formula (2), R3 and R4 independently include a fluorine atom and a C1-C6 fluoroalkyl group; The weight content of the first electrolyte salt in the electrolyte is recorded as x, and the weight content of the first additive in the electrolyte is recorded as y, both based on the total weight of the electrolyte, and 50≤x / y≤500.

2. The electrolyte according to claim 1, wherein 100≤x / y≤400, optionally, 125≤x / y≤300.

3. The electrolyte according to claim 1 or 2, wherein 1%≤x≤15%, optionally, 7%≤x≤12%; and / or, 0.01%≤y≤0.20%, optionally, 0.025%≤y≤0.10%.

4. The electrolyte according to any one of claims 1 to 3, wherein R1 and R2 independently include fluorine atoms, trifluoromethyl groups, pentafluoroethyl groups, heptafluoropropyl groups, and nonafluorobutyl groups. Optionally, at least one of R1 and R2 represents a fluorine atom; and / or, R3 and R4 independently include a fluorine atom, a trifluoromethyl group, a pentafluoroethyl group, a heptafluoropropyl group, or a nonafluorobutyl group. Optionally, at least one of R3 and R4 represents a fluorine atom.

5. The electrolyte according to any one of claims 1 to 4, wherein: The first electrolyte salt includes one or more of the following: Optionally, the first electrolyte salt includes one or more of A1 to A7: The first additive includes one or more of B1 to B5:

6. The electrolyte according to any one of claims 1 to 5, wherein The anion of the first electrolyte salt represented by formula (1) is the same as the anion of the first additive represented by formula (2).

7. The electrolyte according to any one of claims 1 to 6, wherein: The electrolyte further includes a second electrolyte salt, wherein the second electrolyte salt includes one or more of the following: M2 includes one or more of Li, Na, and K, and may be selected to include one or more of Li and Na; Optionally, the weight content of the second electrolyte salt in the electrolyte is denoted as m, and based on the total weight of the electrolyte, m / (x+m) is greater than or equal to 15%.

8. The electrolyte according to any one of claims 1 to 7, wherein: The electrolyte further comprises a second additive represented by formula (3), R5 includes a fluorine atom or a C1-C6 fluoroalkyl group, and M3 includes one or more of Li, Na, and K, and may be selected to include one or more of Li and Na; Optionally, the weight content of the second additive in the electrolyte is denoted as n, and based on the total weight of the electrolyte, 0.01%≤n≤1%.

9. The electrolyte according to claim 8, wherein The second additive includes one or more of the following: Optionally, the second additive includes one or more of D1 to D6:

10. The electrolyte according to any one of claims 1 to 9, wherein: The electrolyte further comprises a third additive represented by formula (4), M4 includes one or more of Li, Na, and K, and may be selected to include one or more of Li and Na; Optionally, the weight content of the third additive in the electrolyte is denoted as p, and based on the total weight of the electrolyte, 0.01%≤p≤1%.

11. The electrolyte according to any one of claims 1 to 10, wherein: The electrolyte further includes a non-aqueous solvent, and the non-aqueous solvent includes one or more of cyclic carbonate, chain carbonate, and carboxylate; Optionally, the weight content of the cyclic carbonate in the non-aqueous solvent is denoted as a, based on the total weight of the non-aqueous solvent, 1%≤a≤35%; and / or, Optionally, the weight content of the linear carbonate in the non-aqueous solvent is denoted as b, based on the total weight of the non-aqueous solvent, 65%≤b≤99%; and / or, Optionally, the weight content of the carboxylic acid ester in the non-aqueous solvent is denoted as c, based on the total weight of the non-aqueous solvent, 0≤c≤30%.

12. A battery cell comprising a positive electrode sheet, a negative electrode sheet and the electrolyte according to any one of claims 1 to 11.

13. The battery cell according to claim 12, wherein: The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer includes a first positive electrode active material, and the voltage platform of the first positive electrode active material is greater than or equal to 3.6V; Optionally, the first positive electrode active material includes one or more of lithium cobalt oxide, lithium nickel cobalt manganese ternary material, lithium nickel cobalt aluminum ternary material, and their respective modified compounds; and / or, Optionally, the weight content of the first positive electrode active material in the positive electrode film layer is greater than or equal to 50%, based on the total weight of the positive electrode film layer; Optionally, the positive electrode current collector includes aluminum foil, aluminum alloy foil, aluminum mesh, aluminum alloy mesh, or a composite current collector whose surface contains aluminum or aluminum alloy.

14. The battery cell according to claim 12 or 13, wherein: The negative electrode plate includes one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials and lithium titanate.

15. A method for preparing a battery cell, comprising the following steps: Providing a battery container including a positive electrode sheet and a negative electrode sheet; The electrolyte according to any one of claims 1 to 11 is injected into the battery container to obtain a battery cell. 16 . A battery, comprising the battery cell according to any one of claims 12 to 14 or the battery cell prepared by the preparation method according to claim 15 .

17. An electrical device comprising the battery according to claim 16.

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