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

Abstract

The application provides an electrolyte, a battery monomer and a preparation method thereof, a battery and a power utilization device. The electrolyte comprises a non-aqueous solvent and an electrolyte salt, the non-aqueous solvent comprises ethylene carbonate, the weight content of the ethylene carbonate in the non-aqueous solvent is denoted as x, and is based on the total weight of the non-aqueous solvent; the electrolyte salt comprises a first electrolyte salt shown in formula (1) and a second electrolyte salt shown in formula (2), and the weight content of the first electrolyte salt in the electrolyte is denoted as y, the weight content of the second electrolyte salt is denoted as z, and is based on the total weight of the electrolyte; R1 and R2 each independently comprise a fluorine atom and a C1-C6 fluoroalkyl group, R3 comprises a fluorine atom and a C1-C6 fluoroalkyl group, M1 and M2 each independently comprise one or more of Li, Na and K; 5%≤x≤25%, 0.75≤x / y≤5 and 120≤x / z≤3000.

Description

Technical Field

[0001] This application relates to an electrolyte, a battery cell and its preparation method, a battery and an electrical device. Background Technology

[0002] In recent years, batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. Electrolyte, as a crucial component of batteries, affects battery performance through its composition. The above statements are for providing background information related to this application only and do not necessarily constitute prior art. Summary of the Invention

[0003] This application provides an electrolyte, a battery cell and its preparation method, a battery and an electrical device, which can improve the high-temperature cycle performance of the battery.

[0004] The first aspect of this application provides an electrolyte comprising a non-aqueous solvent and an electrolyte salt, wherein the non-aqueous solvent comprises ethylene carbonate, and the weight content of the ethylene carbonate in the non-aqueous solvent is denoted as x, based on the total weight of the non-aqueous solvent; the electrolyte salt comprises a first electrolyte salt as shown in formula (1) and a second electrolyte salt as shown in formula (2), and the weight content of the first electrolyte salt in the electrolyte is denoted as y, and the weight content of the second electrolyte salt is denoted as z, based on the total weight of the electrolyte; R1 and R2 each independently comprise fluorine atoms and C1-C6 fluoroalkyl groups, R3 comprises fluorine atoms and C1-C6 fluoroalkyl groups, M1 and M2 each independently comprise one or more of Li, Na, and K; 5% ≤ x ≤ 25%, 0.75 ≤ x / y ≤ 5 and 120 ≤ x / z ≤ 3000.

[0005]

[0006] The inventors discovered that by using a low content of EC (5%-25% of the total weight of non-aqueous solvent) in combination with the first electrolyte salt shown in formula (1) and the second electrolyte salt shown in formula (2), and by reasonably adjusting the content relationship between the three, the battery can have good high-temperature cycle performance.

[0007] In any embodiment, 8% ≤ x ≤ 20%, and optionally, 10% ≤ x ≤ 18%. By adjusting the weight content x of EC in the non-aqueous solvent within the above range, the high-temperature cycling performance of the battery can be further improved.

[0008] In any embodiment, 0.86 ≤ x / y ≤ 3, and optionally, 1 ≤ x / y ≤ 2. This allows for better synergistic effects between the EC and the first electrolyte salt, and further improves the high-temperature cycling performance of the battery.

[0009] In any embodiment, 160 ≤ x / z ≤ 1500, and optionally, 300 ≤ x / z ≤ 1200. This allows for better utilization of the synergistic effect between the EC and the second electrolyte salt, and further improves the high-temperature cycling performance of the battery.

[0010] In any embodiment, 2.4% ≤ y ≤ 18%, and optionally, 6% ≤ y ≤ 12%. By adjusting the weight content y of the first electrolyte salt in the electrolyte within the above range, the high-temperature cycle performance of the battery can be further improved.

[0011] In any embodiment, 0.004% ≤ z ≤ 0.10%, and optionally, 0.008% ≤ z ≤ 0.075%. By adjusting the weight content z of the second electrolyte salt in the electrolyte within the above range, the high-temperature cycle performance of the battery can be further improved.

[0012] In any embodiment, 10% ≤ x ≤ 18%, 1 ≤ x / y ≤ 2, 300 ≤ x / z ≤ 1200, 6% ≤ y ≤ 12%, and 0.008% ≤ z ≤ 0.075%. This allows for better synergistic effects between the EC, the first electrolyte salt, and the second electrolyte salt, and further improves the high-temperature cycling performance of the battery.

[0013] In any embodiment, R1 and R2 independently comprise fluorine atoms, trifluoromethyl, pentafluoroethyl, heptafluoropropyl, and nonafluorobutyl, respectively. When R1 and R2 are within the above range, it also helps to form a thinner interface film, thereby helping to reduce interfacial ionic impedance and improve the kinetic performance of the battery.

[0014] In any embodiment, R3 includes fluorine atoms, trifluoromethyl, or pentafluoroethyl. When R3 is within the above range, it also helps to form a thinner interface film, thereby helping to reduce interfacial ionic impedance and improve the kinetic performance of the battery.

[0015] In any embodiment, the first electrolyte salt includes one or more of the following:

[0016]

[0017] When the first electrolyte salt is within the above range, it has higher thermal stability and is less prone to hydrolysis, which helps to improve the ionic conductivity of the electrolyte, thereby helping to further improve the high-temperature cycle performance of the battery; in addition, it also helps to form a thinner interfacial film, which in turn helps to reduce interfacial ionic impedance and improve the kinetic performance of the battery.

[0018] In any embodiment, the second electrolyte salt comprises one or more of the following:

[0019]

[0020] When the second electrolyte salt is within the above range, it has higher thermal stability and can better regulate the content of inorganic and organic components in the interface film, which helps to obtain a thinner and more flexible interface film, thereby helping to further improve the high-temperature cycle performance of the battery. In addition, it also helps to reduce the interfacial ion impedance and improve the kinetic performance of the battery.

[0021] In any embodiment, M1 includes one or both of Li and Na, and may be selected as Li.

[0022] In any embodiment, M2 includes one or both of Li and Na, and may be selected as Li.

[0023] In any embodiment, the non-aqueous solvent further includes chain carbonates. Chain carbonates can adjust the viscosity of the electrolyte, thereby further improving the ionic conductivity of the electrolyte and contributing to improved high-temperature cycle performance of the battery.

[0024] In any embodiment, the weight content of the chain carbonate in the non-aqueous solvent is denoted as m, and based on the total weight of the non-aqueous solvent, m ≥ 70%.

[0025] In any embodiment, the chain carbonate includes one or more of ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate.

[0026] In any embodiment, the non-aqueous solvent further includes propylene carbonate.

[0027] In any embodiment, the weight content of propylene carbonate in the non-aqueous solvent is denoted as n, and based on the total weight of the non-aqueous solvent, 0 < n ≤ 5%.

[0028] In any embodiment, the electrolyte further includes a third electrolyte salt as shown in formula (3), where M3 includes one or more of Li, Na, and K.

[0029]

[0030] The third electrolyte salt shown in formula (3) has appropriate solubility, high ionic conductivity, and a wide electrochemical window in non-aqueous solvents. This can improve the ionic conductivity of the electrolyte and passivate the positive electrode current collector, reducing the corrosion of the positive electrode current collector by the first electrolyte salt. Therefore, when the electrolyte also includes the third electrolyte salt shown in formula (3), it helps to further improve the high-temperature cycle performance of the battery.

[0031] In any embodiment, M3 includes one or both of Li and Na, and may be selected as Li.

[0032] In any embodiment, the weight content of the third electrolyte salt in the electrolyte is denoted as p, and based on the total weight of the electrolyte, 10% ≤ y + p ≤ 25%. This allows the electrolyte to have high ionic conductivity and low viscosity, thereby further improving the high-temperature cycle performance of the battery.

[0033] In any embodiment, the electrolyte further includes a fourth electrolyte salt as shown in formula (4), where M4 includes one or more of Li, Na, and K.

[0034]

[0035] The fourth electrolyte salt shown in formula (4) typically decomposes earlier in the electrolyte than in the non-aqueous solvent, thereby generating a low-resistance interfacial film at the positive electrode. This interfacial film protects the positive electrode active material, reduces oxidative decomposition of the electrolyte on the positive electrode surface, decreases battery gas production, improves the battery's high-temperature storage performance, and also reduces the charge transfer resistance of the positive electrode, improving its kinetic performance. Simultaneously, the fourth electrolyte salt shown in formula (4) can also generate a low-resistance interfacial 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 fourth electrolyte salt shown in formula (4), it can further improve the battery's high-temperature storage performance and / or kinetic performance.

[0036] In any embodiment, M4 includes one or both of Li and Na, and may be selected as Li.

[0037] In any embodiment, the weight content of the fourth electrolyte salt in the electrolyte is denoted as q, and based on the total weight of the electrolyte, 0 < q ≤ 0.5%, or optionally, 0.1% ≤ q ≤ 0.4%.

[0038] In any embodiment, the electrolyte further includes additives, which include one or both of 1,3-propanesulfonyl lactone and fluoroethylene carbonate.

[0039] PS and FEC can form an interface film at the negative electrode, improving the stability of the negative electrode interface film. This can better protect the negative electrode active material, reduce side reactions between the negative electrode active material and the electrolyte, and improve the high-temperature cycle performance of the battery.

[0040] In any embodiment, the weight content of the additive in the electrolyte is denoted as r, and based on the total weight of the electrolyte, 0 < r ≤ 3%.

[0041] The second aspect of this application provides a battery cell, including a positive electrode, a negative electrode, a separator, and an electrolyte according to the first aspect of this application.

[0042] In any embodiment, the battery cell includes a lithium secondary battery cell.

[0043] In any embodiment, the positive electrode sheet includes a first positive electrode active material, the first positive electrode active material including materials with the general formula Li. a Ni b Co c M d O e A f The active material comprises one or more lithium transition metal oxides and their modified compounds, wherein 0.8 ≤ a ≤ 1.2, 0.8 ≤ b < 1, 0 < c < 0.2, 0 < d < 0.2, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M includes one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A includes one or more of N, F, S, and Cl. High-nickel-content cathode active materials possess high voltage plateaus and high specific capacity, which is beneficial for improving battery energy density; however, they exhibit poor thermal stability and cycle stability. Combining high-nickel-content cathode active materials with the electrolyte provided in the embodiments of this application can fully leverage the advantages of high-nickel-content cathode active materials, thereby enabling the battery to possess both high energy density and good high-temperature cycle performance.

[0044] In any embodiment, the negative electrode sheet includes one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.

[0045] The third aspect of this application provides a method for preparing a battery cell, comprising the following steps: providing a battery container including a positive electrode, a negative electrode and a separator; injecting the electrolyte of the first aspect of this application into the battery container to obtain a battery cell.

[0046] The fourth aspect of this application provides a battery, including a battery cell according to the second aspect of this application or a battery cell prepared by the preparation method according to the third aspect of this application.

[0047] The fifth aspect of this application provides an electrical device, including the battery of the fourth aspect of this application.

[0048] The electrical device of this application includes the battery provided in this application, and therefore has at least the same advantages as the battery. Attached Figure Description

[0049] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0050] Figure 1This is a schematic diagram of one embodiment of the battery cell of this application.

[0051] Figure 2 yes Figure 1 An exploded view of the implementation method of the battery cell.

[0052] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0053] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0054] Figure 5 yes Figure 4 An exploded view of an embodiment of the battery pack shown.

[0055] Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses the battery of this application as a power source.

[0056] The accompanying drawings are not necessarily drawn to scale. The reference numerals are explained as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Individual battery cell, 51 Housing, 52 Electrode assembly, 53 Cover plate. Detailed Implementation

[0057] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the electrolyte, battery cell, preparation method thereof, battery, and power device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0058] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0059] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0060] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0061] Unless otherwise specified, all steps in this 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 it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0062] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0063] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0064] Unless otherwise specified, in this application, the terms "first," "second," "third," "fourth," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0065] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0066] Unless otherwise stated, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0067] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in the embodiments of this application. Unless otherwise stated, the test temperature for each parameter is 25°C.

[0068] In this application, "fluoroalkyl" can be a partially fluorinated alkyl group or a fully fluorinated alkyl group. Fluorinated alkyl groups encompass both fluorinated straight-chain alkyl groups and fluorinated branched-chain alkyl groups.

[0069] In various embodiments, C1-C6 fluoroalkyl groups, i.e., fluoroalkyl groups, may contain 1-6 carbon atoms.

[0070] Throughout this specification, substituents of compounds are disclosed by groups or ranges. It is expressly intended that such description include each individual sub-combination 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.

[0071] The battery mentioned in the embodiments of this application can be a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application can include battery cells, battery modules, or battery packs.

[0072] A battery cell is the smallest unit that makes up a battery, and it can independently perform the functions of charging and discharging. A battery cell can be cylindrical, cuboid, or other shapes, etc., and the embodiments of this application are not limited in this respect. Figure 1 The example shown is a rectangular battery cell 5.

[0073] When there are multiple battery cells, they are connected in series, parallel, or mixed via a busbar. In some embodiments, the battery can be a battery module; when there are multiple battery cells, they are arranged and fixed to form a battery module. In some embodiments, the battery can be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed within the housing. In some embodiments, the housing can be part of the vehicle's chassis structure. For example, a portion of the housing can be at least part of the vehicle's floor, or a portion of the housing can be at least part of the vehicle's crossbeams and longitudinal beams.

[0074] In some embodiments, the battery can be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0075] A single battery cell generally includes an electrode assembly and an electrolyte. The electrode assembly typically includes a positive electrode and a negative electrode, and can be a wound structure or a stacked structure; the embodiments of this application are not limited in this regard.

[0076] The battery cell may also include an outer packaging, which can be used to encapsulate the electrode components and electrolyte. The outer packaging can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging can also be a flexible package, such as a pouch-type flexible package. The material of the flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0077] In some embodiments, such as Figure 2 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. Electrode assemblies 52 are encapsulated in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, and can be adjusted as needed.

[0078] In some embodiments, individual battery cells can be assembled into a battery module, and the number of individual battery cells contained in the battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module. Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3As shown, in battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0079] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0080] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0081] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing includes an upper housing 2 and a lower housing 3. The upper housing 2 covers the lower housing 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the housing.

[0082] Electrolyte is one of the key factors affecting battery performance. As people's requirements for battery energy density are getting higher and higher, ternary materials, especially high-nickel ternary materials, have attracted widespread attention due to their high voltage platform and high specific capacity. However, the thermal stability and cycle stability of ternary materials are not excellent enough. At the same time, the side reactions between the electrolyte and the positive electrode active material will increase under high temperature and high voltage, which will affect the use of the battery.

[0083] In view of this, the inventors improved the electrolyte.

[0084] The electrolyte provided in this application embodiment can be used in a battery cell. The battery cell can be a lithium secondary battery cell.

[0085] The electrolyte comprises a non-aqueous solvent and an electrolyte salt. The non-aqueous solvent comprises ethylene carbonate (EC), and the weight content of ethylene carbonate in the non-aqueous solvent is denoted as x, based on the total weight of the non-aqueous solvent; the electrolyte salt comprises a first electrolyte salt as shown in formula (1) and a second electrolyte salt as shown in formula (2), and the weight content of the first electrolyte salt in the electrolyte is denoted as y, and the weight content of the second electrolyte salt is denoted as z, based on the total weight of the electrolyte; R1 and R2 independently comprise fluorine atoms and C1-C6 fluoroalkyl groups, respectively, R3 comprises fluorine atoms and C1-C6 fluoroalkyl groups, and M1 and M2 independently comprise one or more of Li, Na, and K, respectively; 5% ≤ x ≤ 25%, 0.75 ≤ x / y ≤ 5 and 120 ≤ x / z ≤ 3000.

[0086]

[0087] EC (electrolyte) is widely used as a non-aqueous solvent in electrolytes due to its high dielectric constant. Currently, the weight content of EC in commercial battery electrolytes is typically above 30%, which enables the electrolyte to have high ionic conductivity. However, EC is unstable at high temperatures, and a high EC content can negatively impact the high-temperature performance of the battery.

[0088] The inventors discovered that by using a low content of EC (5%-25% of the total weight of non-aqueous solvent) in combination with the first electrolyte salt shown in formula (1) and the second electrolyte salt shown in formula (2), and by reasonably adjusting the content relationship between the three, the battery can have good high-temperature cycle performance.

[0089] Compared with the electrolytes of currently commercially available batteries, the electrolyte provided in this application embodiment has a lower content of EC, which is 5%-25% of the total weight of non-aqueous solvents. This can reduce the adverse effects of high EC content on the high-temperature performance of the battery.

[0090] The first electrolyte salt shown in formula (1) has high thermal stability and is not easily hydrolyzed, which helps to form a thermally stable interfacial film on the surface of the negative electrode active material, thereby reducing side reactions between the negative electrode active material and the electrolyte. In addition, the anion of the first electrolyte salt is a weakly coordinated anion centered on N, containing conjugated groups and strongly electron-withdrawing fluorine atoms and / or fluoroalkyl groups. The anion charge is highly delocalized, and the interaction between the anion and the metal M1 ion is weak. Therefore, the first electrolyte salt also has a low lattice energy and is easy to dissociate, which also helps to improve the ionic conductivity of the electrolyte and reduce the viscosity of the electrolyte.

[0091] However, the first electrolyte salt is prone to corroding the positive electrode current collector (e.g., aluminum foil), which increases the side reactions between the positive electrode active material and the electrolyte, and thus easily affects the high-temperature cycle performance of the battery.

[0092] The inventors discovered that by including the first electrolyte salt shown in formula (1) in the electrolyte and adjusting the relationship between the weight content x of EC in the non-aqueous solvent and the weight content y of the first electrolyte salt in the electrolyte to satisfy 0.75≤x / y≤5, the synergistic effect of EC and the first electrolyte salt can be fully utilized. Using the first electrolyte salt in the electrolyte can improve the thermal stability of the electrolyte, reduce hydrolysis, and compensate for the insufficient ionic conductivity of the electrolyte due to the low content of EC. The anions of EC and the first electrolyte salt have a certain binding force, which can reduce the corrosion of the positive electrode current collector by the first electrolyte salt, and further reduce the side reactions between the positive electrode active material and the electrolyte. Therefore, by adjusting 0.75≤x / y≤5, the battery can have good high-temperature cycle performance.

[0093] When x / y is less than 0.75, the content of EC in the non-aqueous solvent is relatively low while the content of the first electrolyte salt in the electrolyte is relatively high. At this time, some of the anions of the first electrolyte salt cannot combine with EC molecules, which leads to a more severe corrosion effect of the anions of the first electrolyte salt on the positive electrode current collector under high temperature and high voltage, which in turn deteriorates the high temperature cycle performance of the battery.

[0094] When x / y is greater than 5, the content of EC in the non-aqueous solvent is relatively high while the content of the first electrolyte salt in the electrolyte is relatively low. At this time, there are more free EC molecules in the electrolyte, which will also deteriorate the high-temperature cycle performance of the battery.

[0095] In some embodiments, optionally, 0.86 ≤ x / y ≤ 3, 1 ≤ x / y ≤ 2. This allows for better synergistic effects between the EC and the first electrolyte salt, and further improves the battery's high-temperature cycling performance.

[0096] The second electrolyte salt shown in formula (2) has high thermal stability, which can improve the charge-discharge characteristics of the battery at high temperatures. Simultaneously, the second electrolyte salt can form a film on the surface of both the negative and positive electrode active materials, and can also adjust the composition of the interfacial film, thereby reducing side reactions between the negative electrode active material and the electrolyte, as well as between the positive electrode active material and the electrolyte. However, the second electrolyte salt has low ionic conductivity, and when its content is too high, it increases the content of inorganic components in the interfacial film, leading to decreased flexibility and a tendency for cracking after multiple charge-discharge cycles, which in turn deteriorates the battery's high-temperature cycle performance.

[0097] The inventors discovered that by including a second electrolyte salt as shown in formula (2) in the electrolyte and adjusting the relationship between the weight content x of EC in the non-aqueous solvent and the weight content z of the second electrolyte salt in the electrolyte to satisfy 120≤x / z≤3000, the synergistic effect of EC and the second electrolyte salt can be fully utilized. By using an appropriate amount of the second electrolyte salt, the composition of the interfacial film can be adjusted, resulting in an interfacial film with appropriate amounts of inorganic and organic components. This leads to a dense, uniform, and flexible interfacial film, which can provide long-term protection for the active materials and reduce side reactions between the negative electrode active material and the electrolyte, as well as between the positive electrode active material and the electrolyte. Therefore, by adjusting 120≤x / z≤3000, the cycle stability of the battery can be improved, resulting in a longer high-temperature cycle life.

[0098] When x / z is less than 120, the content of EC in the non-aqueous solvent is relatively low while the content of the second electrolyte salt in the electrolyte is relatively high. At this time, the content of inorganic components in the interface film formed on the surface of the negative electrode active material is high. Inorganic components are usually more rigid, which leads to poor elasticity and flexibility of the interface film, which in turn deteriorates the high-temperature cycle performance of the battery.

[0099] When x / y is greater than 3000, the content of EC in the non-aqueous solvent is relatively high while the content of the second electrolyte salt in the electrolyte is relatively low. At this time, the content of organic components in the interface film formed on the surface of the negative electrode active material is high. At high temperature, the organic components in the interface film are more likely to dissolve into the electrolyte, which will also deteriorate the high-temperature cycle performance of the battery.

[0100] In some embodiments, optionally, 160≤x / z≤1500, 300≤x / z≤1200, 400≤x / z≤1000, and 400≤x / z≤800. This allows for better utilization of the synergistic effect between the EC and the second electrolyte salt, and further improves the high-temperature cycling performance of the battery.

[0101] In some embodiments, optionally, 8% ≤ x ≤ 20%, 10% ≤ x ≤ 18%. By adjusting the weight content x of EC in the non-aqueous solvent within the above range, the high-temperature cycle performance of the battery can be further improved.

[0102] In some embodiments, optionally, 2.4% ≤ y ≤ 18%, 4% ≤ y ≤ 15%, 6% ≤ y ≤ 12%, and 6% ≤ y ≤ 10%. By adjusting the weight content y of the first electrolyte salt in the electrolyte within the above range, the high-temperature cycle performance of the battery can be further improved.

[0103] In some embodiments, optionally, 0.004% ≤ z ≤ 0.10%, 0.008% ≤ z ≤ 0.075%, 0.01% ≤ z ≤ 0.06%, and 0.01% ≤ z ≤ 0.04%. By adjusting the weight content z of the second electrolyte salt in the electrolyte to the above range, the high-temperature cycle performance of the battery can be further improved.

[0104] In some embodiments, 10% ≤ x ≤ 18%, 1 ≤ x / y ≤ 2, 300 ≤ x / z ≤ 1200, 6% ≤ y ≤ 12%, and 0.008% ≤ z ≤ 0.075%. This allows for better synergistic effects between the EC, the first electrolyte salt, and the second electrolyte salt, and further improves the high-temperature cycling performance of the battery.

[0105] M1 includes one or more of Li, Na, and K. In some embodiments, M1 may include one or both of Li and Na, and may be Li.

[0106] M2 includes one or more of Li, Na, and K. In some embodiments, M2 may include one or both of Li and Na, optionally Li.

[0107] In some embodiments, R1 and R2 may each independently include fluorine atoms, trifluoromethyl, pentafluoroethyl, heptafluoropropyl, and nonafluorobutyl. When R1 and R2 are within the above range, it also helps to form a thinner interface film, thereby helping to reduce interfacial ionic impedance and improve the kinetic performance of the battery.

[0108] In some embodiments, the first electrolyte salt may include one or more of the following:

[0109]

[0110] In some embodiments, the first electrolyte salt may include one or more of A1 to A7:

[0111]

[0112] When the first electrolyte salt is within the above range, it has higher thermal stability and is less prone to hydrolysis, which helps to improve the ionic conductivity of the electrolyte, thereby helping to further improve the high-temperature cycle performance of the battery; in addition, it also helps to form a thinner interfacial film, which in turn helps to reduce interfacial ionic impedance and improve the kinetic performance of the battery.

[0113] In some embodiments, R3 may include fluorine atoms, trifluoromethyl, or pentafluoroethyl. When R3 is within the above range, it also helps to form a thinner interface film, thereby helping to reduce interfacial ionic impedance and improve the kinetic performance of the battery.

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

[0115]

[0116] In some embodiments, the second electrolyte salt may include one or more of B1 to B6:

[0117]

[0118] When the second electrolyte salt is within the above range, it has higher thermal stability and can better regulate the content of inorganic and organic components in the interface film, which helps to obtain a thinner and more flexible interface film, thereby helping to further improve the high-temperature cycle performance of the battery. In addition, it also helps to reduce the interfacial ion impedance and improve the kinetic performance of the battery.

[0119] In some embodiments, the non-aqueous solvent may also include chain carbonates. Chain carbonates can adjust the viscosity of the electrolyte, thereby further improving the ionic conductivity of the electrolyte and contributing to improved high-temperature cycle performance of the battery.

[0120] In some embodiments, the weight content of the chain carbonate in the non-aqueous solvent is denoted as m, and based on the total weight of the non-aqueous solvent, m ≥ 70%. For example, m can be a range of 75%, 78%, 80%, 82%, 85%, 88%, 90%, 95%, or any combination thereof. Optionally, 70% ≤ m ≤ 95%, 75% ≤ m ≤ 95%, 75% ≤ m ≤ 90%, 80% ≤ m ≤ 90%, and 82% ≤ m ≤ 88%.

[0121] In some embodiments, the chain carbonate may include one or more of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC). Optionally, the chain carbonate may include one or more of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dimethyl carbonate (DMC).

[0122] In some embodiments, the non-aqueous solvent may further include propylene carbonate. Optionally, the weight content of propylene carbonate in the non-aqueous solvent is denoted as n, and based on the total weight of the non-aqueous solvent, 0 < n ≤ 5%.

[0123] In some embodiments, the non-aqueous solvent may also include other solvents, such as 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), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). The embodiments of this application are not limited in this respect.

[0124] In some embodiments, the electrolyte may further include a third electrolyte salt as shown in formula (3), where M3 includes one or more of Li, Na, and K. Optionally, M3 includes one or two of Li and Na, and more preferably Li.

[0125]

[0126] The third electrolyte salt shown in formula (3) has appropriate solubility, high ionic conductivity, and a wide electrochemical window in non-aqueous solvents. This can improve the ionic conductivity of the electrolyte and passivate the positive electrode current collector, reducing the corrosion of the positive electrode current collector by the first electrolyte salt. Therefore, when the electrolyte also includes the third electrolyte salt shown in formula (3), it helps to further improve the high-temperature cycle performance of the battery.

[0127] In some embodiments, the weight content of the third electrolyte salt in the electrolyte is denoted as p, and based on the total weight of the electrolyte, 10% ≤ y + p ≤ 25%, or optionally, 12% ≤ y + p ≤ 20%. This allows the electrolyte to have high ionic conductivity and low viscosity, thereby further improving the high-temperature cycle performance of the battery.

[0128] In some embodiments, the electrolyte may further include a fourth electrolyte salt as shown in formula (4), where M4 includes one or more of Li, Na, and K. Optionally, M4 includes one or two of Li and Na, and more preferably Li.

[0129]

[0130] The fourth electrolyte salt shown in formula (4) typically decomposes earlier in the electrolyte than in the non-aqueous solvent, thereby generating a low-resistance interfacial film at the positive electrode. This interfacial film protects the positive electrode active material, reduces oxidative decomposition of the electrolyte on the positive electrode surface, decreases battery gas production, improves the battery's high-temperature storage performance, and also reduces the charge transfer resistance of the positive electrode, improving its kinetic performance. Simultaneously, the fourth electrolyte salt shown in formula (4) can also generate a low-resistance interfacial 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 fourth electrolyte salt shown in formula (4), it can further improve the battery's high-temperature storage performance and / or kinetic performance.

[0131] In some embodiments, the weight content of the fourth electrolyte salt in the electrolyte is denoted as q, and based on the total weight of the electrolyte, 0 < q ≤ 0.5%, and optionally, 0.1% ≤ q ≤ 0.4%.

[0132] In some embodiments, the electrolyte may also include other electrolyte salts. For example, the anion of the electrolyte salt may also include perchlorate anion (ClO4). - ), hexafluoroarsenate anion (AsF6) - ), difluorooxalate borate anion (DFOB) - ), dioxaborate anion (BOB) - ), difluorodioxanol phosphate anion (DFOP) - ) and tetrafluorooxalate phosphate anion (TFOP) -One or more of the following; the cation of the electrolyte salt may include Li + Na + K + One or more of them, optionally including Li + Na + One or two of them, or Li can be selected. + .

[0133] In some embodiments, the electrolyte may also include additives, which may include one or both of 1,3-propanesulfonyl lactone (PS) and fluoroethylene carbonate (FEC).

[0134] PS and FEC can form an interface film at the negative electrode, improving the stability of the negative electrode interface film. This can better protect the negative electrode active material, reduce side reactions between the negative electrode active material and the electrolyte, and improve the high-temperature cycle performance of the battery.

[0135] PS can also improve the flexibility of the positive electrode interface film, enabling the battery to remain stable during long-term cycling; PS can also reduce the amount of gas produced by the battery and improve the battery's high-temperature storage performance.

[0136] The LUMO energy of FEC is much lower than that of EC, so its decomposition in the electrolyte usually occurs earlier than in non-aqueous solvents. This reduces electrolyte decomposition, lowers battery gas production, and improves the battery's high-temperature storage performance. FEC can also increase the content of inorganic components in the negative electrode interface film, thereby improving the mechanical strength of the negative electrode interface film and thus improving its cycle stability. FEC also helps to form a thin and stable interface film on the negative electrode, reducing ion diffusion resistance and low-temperature resistance of the negative electrode interface film, thus improving the battery's low-temperature performance.

[0137] In some embodiments, the weight content of the additive in the electrolyte is denoted as r, and based on the total weight of the electrolyte, 0 < r ≤ 3%.

[0138] In some embodiments, the electrolyte may also include other additives, such as additives that improve battery overcharge performance or additives that improve battery low-temperature power performance, etc., which are not limited in this application.

[0139] The electrolyte provided in this application embodiment can be prepared according to conventional methods in the art. For example, a non-aqueous solvent, an electrolyte salt, and optional additives can be mixed evenly to obtain an electrolyte. There are no particular restrictions on the order of addition of the materials. For example, the electrolyte salt and optional additives can be added to a non-aqueous solvent and mixed evenly to obtain an electrolyte.

[0140] The components and their contents in the electrolyte can be determined according to methods known in the art. For example, they can be determined by gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), etc.

[0141] [Positive electrode plate]

[0142] A single battery cell also includes a positive electrode plate.

[0143] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is located on either or both of the two opposite surfaces of the positive current collector.

[0144] The positive electrode current collector can be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil can be used. The composite current collector may include a polymer material substrate and a metal material layer formed on at least one surface of the polymer material substrate. As an example, the metal material may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0145] The positive electrode film typically comprises a positive electrode active material, as well as optional binders and optional conductive agents. The positive electrode film is usually 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, optional binder, optional conductive agent, and any other components in a solvent and stirring until homogeneous.

[0146] The solvent can be N-methylpyrrolidone (NMP), but is not limited to this.

[0147] As an example, the binder used for the positive electrode film may include one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0148] As an example, the conductive agent used for the positive electrode film may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0149] In some embodiments, the positive electrode active material may include a first positive electrode active material. The first positive electrode active material may include materials with the general formula Li. a Nib Co c M d O e A f One or more of lithium transition metal oxides and their modified compounds. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M includes one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes one or more of N, F, S and Cl.

[0150] Optionally, 0.8 ≤ b < 1, 0 < c < 0.2, 0 < d < 0.2. High-nickel-content cathode active materials have a high voltage plateau and high specific capacity, which is beneficial for improving the energy density of the battery, but their thermal stability and cycle stability are poor. Combining high-nickel-content cathode active materials with the electrolyte provided in the embodiments of this application can fully utilize the advantages of high-nickel-content cathode active materials, thereby enabling the battery to have both high energy density and good high-temperature cycle performance.

[0151] As an example, the first positive electrode active material may include LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(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.

[0152] The modifying compounds for the aforementioned positive electrode active materials can be those used for doping and / or surface coating modification of the positive electrode active materials. For example, the coating layer can be a carbon coating layer. A carbon coating layer helps stabilize the surface of the positive electrode active material and further reduces its charge transfer impedance, thereby improving its kinetic performance. Optionally, the carbon coating layer includes amorphous carbon, such as soft carbon, hard carbon, or combinations thereof.

[0153] Li a Ni b Co c M d O e A fIt can be prepared according to conventional methods in the art. An exemplary preparation method is as follows: a lithium source, a nickel source, a cobalt source, an M-element precursor, and optionally an A-element precursor are mixed and then sintered. The sintering atmosphere can be an oxygen-containing atmosphere, such as an air atmosphere or an oxygen atmosphere. The O2 concentration of the sintering atmosphere is, for example, 70% to 100%. The sintering temperature and sintering time can be adjusted according to actual conditions. As an example, the lithium source includes, but is not limited to, one or more of lithium oxide (Li2O), lithium phosphate (Li3PO4), lithium dihydrogen phosphate (LiH2PO4), lithium acetate (CH3COOLi), lithium hydroxide (LiOH), lithium carbonate (Li2CO3), and lithium nitrate (LiNO3). As an example, the nickel source includes, but is not limited to, one or more of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate. As an example, the cobalt source includes, but is not limited to, one or more of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate. As an example, the M-element precursor includes, but is not limited to, one or more of oxides of the M-element, nitrate compounds, carbonate compounds, hydroxides, and acetate compounds. As an example, precursors of element A include, but are not limited to, one or more of the following: ammonium fluoride, lithium fluoride, hydrogen fluoride, ammonium chloride, lithium chloride, hydrogen chloride, ammonium nitrate, ammonium nitrite, ammonium carbonate, ammonium bicarbonate, ammonium phosphate, phosphoric acid, ammonium sulfate, ammonium bisulfate, ammonium bisulfite, ammonium sulfite, ammonium hydrogen sulfide, hydrogen sulfide, lithium sulfide, ammonium sulfide, and elemental sulfur.

[0154] In some embodiments, the positive electrode active material does not exclude materials with the molecular formula Li. a Ni b Co c M d O e A f In addition to lithium transition metal oxides and their modified compounds, other components may be included in the positive electrode active material. For example, the positive electrode active material may also include a second positive electrode active material, which may include one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium-containing phosphates, and their respective modified compounds. As an example, lithium-containing phosphates may include one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds.

[0155] In some embodiments, the weight percentage of the first positive electrode active material can be from 80% to 99%, based on the total weight of the positive electrode film layer. For example, the weight percentage of the first positive electrode active material can be a range consisting of 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any value above. Optionally, the weight percentage of the first positive electrode active material can be 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%.

[0156] In some embodiments, the specific surface area of ​​the positive electrode active material can be 0.3-3 m². 2 / g. When the specific surface area of ​​the positive electrode active material is within the above range, the positive electrode active material can have good kinetic properties and reduce side reactions at high temperatures, thereby enabling the battery to have good high-temperature cycle performance and kinetic performance.

[0157] The specific surface area of ​​the positive electrode active material is a well-known concept in the art and can be measured using instruments and methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017, and calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0158] In some embodiments, the compaction density of the positive electrode sheet can be 2.9-3.6 g / cm³. 3 When the compaction density of the positive electrode sheet is within the above range, the positive electrode sheet can have good conductivity and good electrolyte wettability, thereby enabling the battery to have good high-temperature cycle performance and kinetic performance.

[0159] The compaction density of the positive electrode sheet is a term known in the art and can be measured using instruments and methods known in the art. The compaction density of the positive electrode sheet = the areal density of the positive electrode film layer / the thickness of the positive electrode film layer. The thickness of the positive electrode film layer is a term known in the art and can be measured using instruments and methods known in the art, such as a micrometer. The areal density of the positive electrode film layer is a term known in the art and can be measured using instruments and methods known in the art. For example, a single-sided coated and cold-pressed positive electrode sheet (if it is a double-sided coated positive electrode sheet, the positive electrode film layer on one side can be wiped off first) can be cut into small circular pieces with an area of ​​S1, weighed, and recorded as M1; then, the positive electrode film layer of the weighed positive electrode sheet is wiped off, and the weight of the positive current collector is weighed and recorded as M0; the areal density of the positive electrode sheet = (M1 - M0) / S1.

[0160] [Negative electrode plate]

[0161] A single battery cell includes a negative electrode plate.

[0162] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is located on either or both of the two opposite surfaces of the negative current collector.

[0163] The negative electrode current collector can be a metal foil or a composite current collector. As an example of a metal foil, copper foil can be used. The composite current collector may include a polymer substrate and a metal material layer formed on at least one surface of the polymer substrate. As an example, the metal material may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0164] The negative electrode film typically comprises a negative electrode active material, optional binder, optional conductive agent, and other optional additives. The negative electrode film is usually formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry coating is typically formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous.

[0165] The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0166] As an example, the binder used for the negative electrode membrane may include one or more of the following: styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne 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).

[0167] As an example, the conductive agent used for the negative electrode film 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-Na), PTC thermistor materials, etc.

[0168] The negative electrode active material may be one or more materials known in the art. As examples, 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 composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide, and tin alloys. This 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.

[0169] [Isolation membrane]

[0170] The battery cell also includes a separator.

[0171] The separator is positioned between the positive and negative electrodes to provide isolation. This application does not impose any particular restrictions on the type of separator; any known porous membrane with good chemical and mechanical stability can be selected.

[0172] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0173] Preparation method

[0174] This application also provides a method for preparing battery cells.

[0175] The method includes the following steps: providing a battery container including a positive electrode, a negative electrode, and a separator; and injecting the electrolyte provided in the embodiments of this application into the battery container including the positive electrode, the negative electrode, and the separator.

[0176] In some embodiments, the method may further include the following steps: forming an electrode assembly by winding and / or stacking a positive electrode sheet, a separator, and a negative electrode sheet, and placing the electrode assembly inside a battery container.

[0177] The battery container can be an outer packaging. The outer packaging can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging can also be a flexible package, such as a pouch. The material of the flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0178] Multiple battery cells can be further connected in series, parallel, or a combination thereof to form a battery module. Multiple battery modules can also be connected in series, parallel, or a combination thereof to form a battery pack. In some embodiments, multiple battery cells can also be directly connected to form a battery pack.

[0179] Electrical appliances

[0180] This application also provides an electrical device, which includes the battery provided in this application embodiment. The battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can be, but is not limited to, mobile devices (such as mobile phones, tablets, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0181] Electrical devices can choose the type of battery according to their usage needs, such as individual battery cells, battery modules, or battery packs.

[0182] Figure 6 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0183] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0184] Example

[0185] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0186] Examples 1-26 and Comparative Examples 1-7 were prepared according to the following method.

[0187] Preparation of positive electrode sheet

[0188] LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 97.5:1.4:1.1 to form a uniform positive electrode slurry. The positive electrode slurry is then uniformly coated onto the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained.

[0189] Preparation of negative electrode sheet

[0190] The negative electrode active material graphite, the binder styrene-butadiene rubber (SBR), the thickener sodium carboxymethyl cellulose (CMC-Na), and the conductive agent carbon black (Super P) are mixed thoroughly in an appropriate amount of deionized water at a weight ratio of 96.2:1.8:1.2:0.8 to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the surface of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet is obtained.

[0191] Separating membrane

[0192] Porous polyethylene (PE) membrane is used as the separator.

[0193] Preparation of electrolyte

[0194] Ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed evenly according to the weight contents shown in Table 1 to obtain a non-aqueous solvent. The electrolyte salts shown in Table 1 were dissolved in the above non-aqueous solvent according to the weight contents shown in Table 1, and stirred evenly to obtain an electrolyte solution.

[0195] In Table 1, the weight content of EC is denoted as x, the weight content of PC is denoted as n, and the sum of the weight contents of EMC and DEC is denoted as m. All are based on the total weight of non-aqueous solvents, and the weight ratio of EMC and DEC is 1:1.

[0196] In Table 1, the weight content of the first electrolyte salt is denoted as y, the weight content of the second electrolyte salt is denoted as z, and the weight content of the third electrolyte salt is denoted as p, all based on the total weight of the electrolyte.

[0197] In Table 1, " / " indicates that the corresponding component was not added to the electrolyte.

[0198] Battery manufacturing

[0199] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly. The electrode assembly is placed in an outer packaging, injected with the electrolyte, and after processes such as encapsulation, settling, and formation, a battery is obtained.

[0200] Test section

[0201] (1) High-temperature cycling performance test

[0202] At 45℃, the battery is charged at a constant current of 1C to 4.3V, and then charged at a constant voltage until the current reaches 0.05C. At this point, the battery is fully charged, and the charging capacity is recorded as the first charge capacity. After the battery is left to rest for 5 minutes, it is discharged at a constant current of 1C to 2.8V. This completes one charge-discharge cycle, and the discharge capacity is recorded as the first discharge capacity. The battery is subjected to cyclic charge-discharge tests using the above method, and the discharge capacity after each cycle is recorded. The battery capacity retention rate (%) after 600 cycles at 45℃ = discharge capacity after 600 cycles / discharge capacity of the first cycle × 100%.

[0203] (2) Battery high-temperature storage performance test

[0204] At 60℃, the battery is charged at a constant current of 1C to 4.3V, and then charged at a constant voltage until the current reaches 0.05C. The volume of the battery at this point is measured using the water displacement method and recorded as V0. The battery is then placed in a 60℃ constant temperature chamber and stored for 30 days. After this period, the volume of the battery is measured again using the water displacement method and recorded as V1. The volume expansion rate (%) of the battery after 30 days of storage at 60℃ is calculated as [(V1-V0) / V0]×100%.

[0205] Table 1 presents the test results for Examples 1-26 and Comparative Examples 1-7.

[0206] Table 1

[0207]

[0208]

[0209] As can be seen from the test results in Table 1, by using a low content of EC in combination with the first electrolyte salt shown in Formula (1) and the second electrolyte salt shown in Formula (2), and by reasonably adjusting the content relationship between the three to satisfy 0.75≤x / y≤5 and 120≤x / z≤3000, the battery can have good high-temperature cycle performance.

[0210] Examples 27-29

[0211] The battery preparation method is similar to that in Example 4, except for the preparation of the electrolyte. In Table 2, the weight content of the fourth electrolyte salt is denoted as q, and the weight content of the additive is denoted as r, both based on the total weight of the electrolyte. " / " indicates that the corresponding component was not added to the electrolyte.

[0212] Example 27 adds 0.2% LiPO2F2 to the electrolyte provided in Example 4.

[0213] Example 28 adds 0.2% LiPO2F2 and 1% PS to the electrolyte provided in Example 4.

[0214] Example 29 adds 0.2% LiPO2F2 and 1% FEC to the electrolyte provided in Example 4.

[0215] Table 2

[0216]

[0217] As can be seen from the test results in Table 2, adding an appropriate amount of the fourth electrolyte salt and / or additives to the electrolyte can further improve the high-temperature cycle performance of the battery and further improve its high-temperature storage performance.

[0218] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. An electrolyte comprising a non-aqueous solvent and an electrolyte salt, wherein, The non-aqueous solvent includes ethylene carbonate, and the weight content of the ethylene carbonate in the non-aqueous solvent is denoted as x, based on the total weight of the non-aqueous solvent; The electrolyte salt includes a first electrolyte salt as shown in formula (1) and a second electrolyte salt as shown in formula (2), and the weight content of the first electrolyte salt in the electrolyte is denoted as y, and the weight content of the second electrolyte salt is denoted as z, based on the total weight of the electrolyte; Equation (1) Equation (2) R1 and R2 each independently include a fluorine atom and a C1-C6 fluoroalkyl group, R3 includes a fluorine atom and a C1-C6 fluoroalkyl group, and M1 and M2 each independently include one or more of Li, Na, and K. Where 5%≤x≤25%, 0.75≤x / y≤5 and 120≤x / z≤3000; The non-aqueous solvent also includes chain carbonates, and the weight content of the chain carbonates in the non-aqueous solvent is denoted as m. Based on the total weight of the non-aqueous solvent, m ≥ 70%.

2. The electrolyte according to claim 1, wherein, 8%≤x≤20%; and / or, 0.86 ≤ x / y ≤ 3; and / or, 160≤x / z≤1500.

3. The electrolyte according to claim 2, wherein, 10%≤x≤18%。 4. The electrolyte according to claim 2, wherein, 1≤x / y≤2.

5. The electrolyte according to claim 2, wherein, 300≤x / z≤1200.

6. The electrolyte according to claim 2, wherein, 2.4%≤y≤18%; and / or, 0.004%≤z≤0.10%。 7. The electrolyte according to claim 2, wherein, 6%≤y≤12%。 8. The electrolyte according to claim 2, wherein, 0.008%≤z≤0.075%。 9. The electrolyte according to claim 1, wherein, 10%≤x≤18%, 1≤x / y≤2, 300≤x / z≤1200, 6%≤y≤12%, and 0.008%≤z≤0.075%.

10. The electrolyte according to claim 1, wherein, R1 and R2 each independently include a fluorine atom, a trifluoromethyl atom, a pentafluoroethyl atom, a heptafluoropropyl atom, and a nonafluorobutyl atom; and / or, R3 includes fluorine atoms, trifluoromethyl, and pentafluoroethyl.

11. The electrolyte according to claim 1, wherein, The first electrolyte salt includes one or more of the following: ; and / or, The second electrolyte salt includes one or more of the following: 。 12. The electrolyte according to claim 1, wherein, M1 includes one or both of Li and Na; and / or, M2 includes one or both of Li and Na.

13. The electrolyte according to claim 1, wherein, M1 includes Li.

14. The electrolyte according to claim 1, wherein, M2 includes Li.

15. The electrolyte according to claim 1, wherein the chain carbonate comprises one or more of ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate.

16. The electrolyte according to claim 1, wherein, The non-aqueous solvent also includes propylene carbonate.

17. The electrolyte according to claim 16, wherein, Let n be the weight content of propylene carbonate in the non-aqueous solvent. Based on the total weight of the non-aqueous solvent, 0 < n ≤ 5%.

18. The electrolyte according to claim 1, wherein, The electrolyte also includes a third electrolyte salt as shown in formula (3). Equation (3) M3 includes one or more of Li, Na, and K.

19. The electrolyte according to claim 18, wherein, M3 includes one or both of Li and Na.

20. The electrolyte according to claim 18, wherein, M3 includes Li.

21. The electrolyte according to claim 18, wherein, The weight content of the third electrolyte salt in the electrolyte is denoted as p. Based on the total weight of the electrolyte, 10% ≤ y + p ≤ 25%.

22. The electrolyte according to claim 1, wherein, The electrolyte also includes the fourth electrolyte salt shown in formula (4). Equation (4) M4 includes one or more of Li, Na, and K.

23. The electrolyte according to claim 22, wherein, M4 includes one or both of Li and Na.

24. The electrolyte according to claim 22, wherein, M4 includes Li.

25. The electrolyte according to claim 22, wherein, The weight content of the fourth electrolyte salt in the electrolyte is denoted as q. Based on the total weight of the electrolyte, 0 < q ≤ 0.5%.

26. The electrolyte according to claim 25, wherein, 0.1%≤q≤0.4%。 27. The electrolyte according to claim 1, wherein, The electrolyte also includes additives, which include one or two of 1,3-propanesulfonyl lactone and fluoroethylene carbonate.

28. The electrolyte according to claim 27, wherein, The weight content of the additive in the electrolyte is denoted as r, and based on the total weight of the electrolyte, 0 < r ≤ 3%.

29. A battery cell comprising a positive electrode, a negative electrode, a separator, and an electrolyte as described in any one of claims 1-28.

30. The battery cell according to claim 29, wherein, The battery cell includes a lithium secondary battery cell.

31. The battery cell according to claim 29, wherein, The positive electrode sheet includes a first positive electrode active material, the first positive electrode active material comprising a general formula Li a Ni b Co c M d O e A f One or more of lithium transition metal oxides and their modified compounds, wherein 0.8 ≤ a ≤ 1.2, 0.8 ≤ b < 1, 0 < c < 0.2, 0 < d < 0.2, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M includes one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes one or more of N, F, S and Cl; and / or, The negative electrode sheet includes one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.

32. A method for preparing a single battery cell, comprising the following steps: Provides battery containers including positive electrode plates, negative electrode plates, and separators; The electrolyte according to any one of claims 1-28 is injected into the battery container to obtain a single battery cell.

33. A battery comprising a battery cell according to any one of claims 29-31 or a battery cell prepared by the preparation method according to claim 32.

34. An electrical device comprising the battery of claim 33.

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