Electrolyte, secondary battery, and electric device

Abstract

The application relates to an electrolyte, a secondary battery and a power utilization device, wherein the electrolyte comprises a first additive, a second additive and a third additive; the first additive comprises an inorganic salt containing elements; the second additive comprises a compound containing an unsaturated bond, the reduction potential of the compound containing the unsaturated bond is greater than or equal to 0.8 V (Li + / Li); and the third additive comprises a compound containing an amide group; by adding the first additive, the second additive and the third additive in the electrolyte, the high-temperature performance and the low-temperature performance of the secondary battery can be simultaneously improved.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to an electrolyte, a secondary battery, and an electrical device. Background Technology

[0002] The statements herein are provided only as background information in connection with this application and do not necessarily constitute prior art.

[0003] In recent years, lithium-ion batteries have demonstrated advantages such as high open-circuit voltage, high energy density, long lifespan, no memory effect, no pollution, and low self-discharge. They are widely used in energy storage systems for hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. With the development of lithium-ion batteries, higher performance requirements have been placed on them. However, in related technologies, it is difficult for lithium-ion batteries to simultaneously achieve high-temperature and low-temperature performance, which to some extent limits their application. Summary of the Invention

[0004] This application provides an electrolyte that can simultaneously achieve both high-temperature and low-temperature performance of a secondary battery, and also provides a secondary battery and an electrical device.

[0005] To achieve the above objectives, the first aspect of this application provides an electrolyte comprising:

[0006] The first additive includes an inorganic salt containing fluorine.

[0007] The second additive comprises a compound containing unsaturated bonds, wherein the reduction potential of the unsaturated compound is ≥0.8V (Li). + / Li); and

[0008] The third additive includes compounds containing amide groups.

[0009] The second additive includes a reduction potential ≥0.8V (Li +Compounds containing unsaturated bonds (e.g., those with a lithium oxide layer) can undergo a reduction reaction on the negative electrode surface during battery formation to generate polymers, forming an SEI film to passivate the negative electrode. This prevents direct contact between the solvent and the negative electrode, thus avoiding continuous side reactions and achieving excellent passivation of the negative electrode, improving the battery's high-temperature performance. The first additive includes compounds containing fluorine, which decompose at the negative electrode to form an SEI film containing fluorine-type inorganic compounds. This film has a wider band gap and higher ionic conductivity, enhancing the ion-conducting ability of the SEI film, lowering the lithium-ion diffusion barrier, facilitating lithium-ion transport, and reducing low-temperature interfacial charge transfer impedance, thereby improving low-temperature performance. Lithium ions in the electrolyte combine with solvent molecules and anions to form solvated lithium ions. During charging, these solvated lithium ions migrate towards the negative electrode. Upon reaching the SEI film, they desolvate and pass through the SEI film to embed into the negative electrode. The third additive includes compounds containing amide groups, thus also participating in the formation of the solvation structure. The negatively charged nitrogen in the amide group strongly interacts with lithium ions. The third additive can replace cyclic esters, reducing the amount of cyclic esters in the solvation structure, significantly lowering the activity energy of the lithium ion desolvation process, and facilitating desolvation, thereby improving low-temperature kinetics. Therefore, this application, by adding the first, second, and third additives to the electrolyte, achieves a synergistic effect, simultaneously improving both the high-temperature and low-temperature performance of the secondary battery.

[0010] In some embodiments, the first additive has a mass percentage of A in the electrolyte, the second additive has a mass percentage of B in the electrolyte, and the third additive has a mass percentage of C in the electrolyte, wherein A, B, and C satisfy: 2% ≤ (A+C) / B ≤ 120%;

[0011] Optionally, 5% ≤ (A+C) / B ≤ 55%.

[0012] In some embodiments, 0.01 ≤ A ≤ 1.

[0013] In some embodiments, 0.5 ≤ B ≤ 10.

[0014] In some embodiments, 0.01 ≤ C ≤ 0.1.

[0015] In some embodiments, the fluorine element accounts for ≥8% of the mass of the inorganic salt;

[0016] Optionally, the first additive includes one or more of difluorophosphate, tetrafluoroborate, and fluorosulfonate containing element M, wherein element M includes one or more of Li, Na, K, and Cs.

[0017] In some embodiments, the second additive comprises a cyclic compound containing unsaturated bonds;

[0018] Optionally, the second additive includes one or more of vinylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfate, and vinyl disulfate.

[0019] In some embodiments, the third additive comprises one or more compounds represented by formulas (I) and (II):

[0020]

[0021] R1 and R2 each independently include any one of hydrogen, methyl and ethyl, and R3 includes C3-C6 alkyl groups;

[0022] Optionally, the third additive includes one or more of N,N-dimethylformamide and N-methylpyrrolidone.

[0023] In some embodiments, the electrolyte further comprises a cyclic ester solvent;

[0024] Optionally, the cyclic ester solvent includes one or more of ethylene carbonate and propylene carbonate;

[0025] Further optionally, the ethylene carbonate in the electrolyte has a mass percentage of D%, and the C and D satisfy 0.01% ≤ C / D ≤ 1%.

[0026] Alternatively, 5 ≤ D ≤ 35.

[0027] In some embodiments, the electrolyte further comprises a lithium salt;

[0028] Optionally, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, and lithium bistrifluoromethylsulfonylimide;

[0029] Optionally, the lithium salt accounts for 5%-15% of the mass of the electrolyte.

[0030] A second aspect of this application provides a secondary battery, including the electrolyte of the first aspect of this application.

[0031] The secondary battery of this application has both excellent high-temperature performance and low-temperature performance.

[0032] In some embodiments, the secondary battery includes a negative electrode sheet, the negative electrode sheet includes a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode active material; the areal density of the negative electrode active material layer is Eg / m³. 2 The specific surface area of ​​the negative electrode active material is Fm. 2 / g, wherein the mass percentage of the negative electrode active material in the negative electrode active material layer is L;

[0033] The second additive accounts for B% of the mass of the electrolyte;

[0034] The following conditions must be met: B, E, F, and L satisfy the condition: 0.5% ≤ B / (E*F*L) ≤ 12%.

[0035] In some embodiments, 80 ≤ E ≤ 150.

[0036] In some embodiments, 0.5 ≤ F ≤ 5.

[0037] In some embodiments, 93% ≤ L ≤ 98%.

[0038] A third aspect of this application provides an electrical device, including at least one of the electrolyte of the first aspect of this application and the secondary battery of the second aspect of this application.

[0039] The electrical device of this application includes the secondary battery provided in this application, and therefore has at least the same advantages as the secondary battery.

[0040] Details of one or more embodiments of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims. Attached Figure Description

[0041] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0042] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0043] Figure 2 for Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0044] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0045] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0046] Figure 5 for Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0047] Figure 6This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0048] Explanation of reference numerals in the attached figures:

[0049] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Cover plate; 6 Electrical device. Detailed Implementation

[0050] Hereinafter, some embodiments of the electrolyte, secondary battery, and electrical device of this application are described in detail with appropriate reference to the accompanying drawings. However, some unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy 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.

[0051] The "range" disclosed in this application can be defined in the form of 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; any endpoint can be independently included or excluded, and they can be combined arbitrarily, meaning 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 ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also 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" and "5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when describing a parameter as an integer ≥ 2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 for that parameter. For instance, when describing a parameter as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0052] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0053] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0054] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0055] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can 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.

[0056] In this application, open-ended technical features or solutions described using terms such as "containing," "comprising," or "including" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, if A includes a1, a2, and a3, it may also include other members or exclude additional members unless otherwise specified. This can be considered as providing both the feature or solution that "A consists of a1, a2, and a3" and the feature or solution that "A includes not only a1, a2, and a3, but also other members." In this application, unless otherwise specified, A (e.g., B) indicates that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0057] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0058] Among related technologies, lithium-ion batteries are difficult to balance high-temperature and low-temperature performance simultaneously, which limits their application to some extent.

[0059] To address the aforementioned issues, this application provides an electrolyte in which a first additive, a second additive, and a third additive are simultaneously added to improve both the high-temperature and low-temperature performance of a secondary battery.

[0060] The first aspect of this application provides an electrolyte comprising a first additive, a second additive, and a third additive; the first additive comprises an inorganic salt containing fluorine; the second additive comprises a compound containing unsaturated bonds, wherein the reduction potential of the compound containing unsaturated bonds is ≥0.8V (Li). + / Li); the third additive includes compounds containing amide groups.

[0061] Understandably, the second additive includes a reduction potential ≥0.8V (Li + Compounds containing unsaturated bonds (e.g., those with a lithium oxide layer) can undergo a reduction reaction on the negative electrode surface during battery formation to generate polymers, forming an SEI film to passivate the negative electrode. This prevents direct contact between the solvent and the negative electrode, thus avoiding continuous side reactions and achieving excellent passivation of the negative electrode, improving the battery's high-temperature performance. The first additive includes compounds containing fluorine, which decompose at the negative electrode to form an SEI film containing fluorine-type inorganic compounds. This film has a wider band gap and higher ionic conductivity, enhancing the ion-conducting ability of the SEI film, lowering the lithium-ion diffusion barrier, facilitating lithium-ion transport, and reducing low-temperature interfacial charge transfer impedance, thereby improving low-temperature performance. Lithium ions in the electrolyte combine with solvent molecules and anions to form solvated lithium ions. During charging, these solvated lithium ions migrate towards the negative electrode. Upon reaching the SEI film, they desolvate and pass through the SEI film to embed into the negative electrode. The third additive includes compounds containing amide groups, thus also participating in the formation of the solvation structure. The negatively charged nitrogen in the amide group strongly interacts with lithium ions. The third additive can replace cyclic esters, reducing the amount of cyclic esters in the solvation structure, significantly lowering the activity energy of the lithium ion desolvation process, and facilitating desolvation, thereby improving low-temperature kinetics. Therefore, this application, by adding the first, second, and third additives to the electrolyte, can simultaneously improve the high-temperature and low-temperature performance of the secondary battery.

[0062] In some embodiments, the first additive has a mass percentage of A in the electrolyte, the second additive has a mass percentage of B in the electrolyte, and the third additive has a mass percentage of C in the electrolyte, wherein A, B, and C satisfy: 2% ≤ (A+C) / B ≤ 120%. As an example, (A+C) / B can be, but is not limited to, 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 105%, 110%, 115%, 120%, or any range between any two of the above values. When A, B, and C satisfy the above relationship, the high-temperature and low-temperature performance of the secondary battery can be significantly improved simultaneously; when (A+C) / B is below the above range, the improvement in the low-temperature performance of the secondary battery is limited; when (A+C) / B is above the above range, the improvement in the high-temperature performance of the secondary battery is limited.

[0063] In some alternative implementations, 5% ≤ (A+C) / B ≤ 55%.

[0064] It should be noted that A% refers to the mass percentage of the first additive in the electrolyte of the battery cell after formation or after further charge-discharge cycling. B% refers to the mass percentage of the second additive in the electrolyte of the battery cell after formation or after further charge-discharge cycling. C% refers to the mass percentage of the third additive in the electrolyte of the battery cell after formation or after further charge-discharge cycling. "Battery cell after formation" refers to a fresh battery cell formed after formation, which has not yet undergone further charge-discharge cycling.

[0065] In some possible implementations, 0.01 ≤ A ≤ 1; for example, A can be, but is not limited to, 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, or a range between any two of the above values. When the mass percentage (A%) of the first additive in the electrolyte is less than 0.1%, it may not effectively improve the low-temperature performance of the secondary battery. During battery cycling, as lithium insertion and extraction occur at the negative electrode, the negative electrode expands and contracts, resulting in significant changes in its volume. Due to the poor mechanical stability of inorganic SEI films, they are prone to rupture when the negative electrode volume changes significantly, exposing new active sites and continuously inducing side reactions. Therefore, when the mass percentage (A%) of the first additive in the electrolyte is higher than 1%, its effect on improving the high-temperature cycling performance of the secondary battery may show a decreasing trend.

[0066] In some possible embodiments, 0.5 ≤ B ≤ 10; for example, B can be, but is not limited to, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or any range between any two of the above values. When the mass percentage (B%) of the second additive in the electrolyte is less than 1%, it may not effectively improve the high-temperature performance of the secondary battery; since the formation of the SEI film by the second additive will lead to an increase in battery impedance, especially a significant increase in low-temperature impedance, when the mass percentage (B%) of the second additive in the electrolyte is greater than 10%, it may be detrimental to low-temperature discharge performance.

[0067] In some possible embodiments, 0.01 ≤ C ≤ 0.1; for example, C can be, but is not limited to, 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, 0.095, 0.1, or any two of the above values. When the mass percentage (C%) of the third additive in the electrolyte is less than 0.01%, it may not effectively improve the low-temperature performance of the secondary battery; because the third additive itself has poor electrochemical stability, it is prone to reduction side reactions at the negative electrode, affecting the stability of the SEI film. At high temperatures, the reduction side reactions are aggravated. Therefore, when the mass percentage (C%) of the third additive in the electrolyte is greater than 0.1%, it may affect the high-temperature cycle life of the battery.

[0068] As an example, the mass percentage (A%) of the first additive mentioned above in the electrolyte can be determined by referring to the ion chromatography analysis method in JY / T0575-2020.

[0069] The mass percentage (B%) of the second additive in the electrolyte and the mass percentage (C%) of the third additive in the electrolyte mentioned above can be determined by referring to GB / T9722-2006 Chemical Reagents Gas Chromatography.

[0070] In some embodiments, the mass percentage of fluorine in the inorganic salt is ≥8%; for example, it can be, but is not limited to, 8%, 10%, 13%, 15%, 17%, 20%, 23%, 25%, 27%, 30%, 40%, 50%, 60%, 70%, 80%, or any two of the above values. When the mass percentage of fluorine in the inorganic salt is within the above range, it can effectively increase the fluoride content in the SEI membrane, which is beneficial to improving the ionic conductivity of the SEI membrane.

[0071] As an example, the mass percentage of fluorine in inorganic salts mentioned above can be determined by referring to JY / T 0567-2020 Inductively Coupled Plasma Emission Spectrometry.

[0072] In some embodiments, the first additive includes one or more of difluorophosphate, tetrafluoroborate, and fluorosulfonate containing element M, wherein element M includes one or more of Li, Na, K, and Cs.

[0073] In some embodiments, the first additive includes one or more of lithium difluorophosphate, lithium tetrafluoroborate, and lithium fluorosulfonate.

[0074] In some embodiments, the second additive comprises a cyclic compound containing unsaturated bonds; it is readily reduced at the negative electrode to form an oligomer.

[0075] As one possible implementation, the second additive includes one or more of vinylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfate, and vinyl disulfate.

[0076] In some embodiments, the third additive comprises one or more compounds represented by formulas (I) and (II):

[0077]

[0078] R1 and R2 each independently include any one of hydrogen, methyl and ethyl, and R3 includes C3-C6 alkyl groups.

[0079] As one possible implementation, the third additive includes one or more of N,N-dimethylformamide and N-methylpyrrolidone.

[0080] In some embodiments, the electrolyte also contains a cyclic ester solvent.

[0081] In some possible implementations, the cyclic ester solvent includes one or more of ethylene carbonate and propylene carbonate.

[0082] Ethylene carbonate has a high dielectric constant, can dissociate lithium salts, and improve the conductivity of the electrolyte; at the same time, ethylene carbonate can undergo a reduction reaction, and its product Li2CO3 has good thermal stability, which can improve the high-temperature cycle performance of the battery to a certain extent.

[0083] In some possible implementations, the mass percentage of ethylene carbonate in the electrolyte is D%, and C and D satisfy 0.01% ≤ C / D ≤ 1%; for example, C / D can be, but is not limited to, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1%, or any range between any two of the above values. Because ethylene carbonate occupies the inner layer of the solvation structure in the electrolyte, its high dielectric constant also increases the intermolecular orientation forces, leading to an increase in the phase transition point and viscosity of the electrolyte. At low temperatures, the viscosity increases sharply, affecting the lithium-ion desolvation process. Since desolvation is the rate-determining step for charge transfer in the electrolyte at low temperatures, an excessively high mass proportion of ethylene carbonate in the electrolyte will deteriorate the battery's low-temperature performance. A third additive can also participate in the formation of the solvation structure, thereby reducing the amount of ethylene carbonate in the solvation structure and improving low-temperature kinetics. Therefore, the amounts of ethylene carbonate and the third additive can be adjusted to simultaneously improve both low-temperature and high-temperature performance. When the C / D ratio is within the above range, both low-temperature and high-temperature performance of the battery are better; when the C / D ratio is below the above range, the improvement in low-temperature performance may be limited; when the C / D ratio is above the above range, the improvement in high-temperature performance may be limited.

[0084] In some possible implementations, the mass percentage of ethylene carbonate in the electrolyte is D%, 5 ≤ D ≤ 35; for example, D can be, but is not limited to, 5, 7, 10, 12, 15, 17, 20, 22, 25, 27, 30, 32, 35, or any two of the above values. When the mass percentage of ethylene carbonate in the electrolyte is less than 5%, the effect on improving the conductivity of the electrolyte may be limited; when the mass percentage of ethylene carbonate in the electrolyte is greater than 35%, the electrolyte viscosity is high and the low-temperature conductivity is low, which may deteriorate the low-temperature performance of the battery.

[0085] As an example, the mass percentage (D%) of ethylene carbonate in the electrolyte and the mass ratio (C / D) of the third additive to ethylene carbonate mentioned above can be determined with reference to GB / T9722-2006.

[0086] It should be noted that the D% mentioned above refers to the mass percentage of ethylene carbonate in the electrolyte of the battery cell obtained after formation or after further charge-discharge cycling. C / D refers to the mass ratio of the third additive to ethylene carbonate in the battery cell obtained after formation or after further charge-discharge cycling. "Battery cell obtained after formation" refers to a fresh battery cell made after formation, which has not undergone further charge-discharge cycling.

[0087] In some implementations, the electrolyte also contains lithium salts.

[0088] Optionally, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, and lithium bistrifluoromethylsulfonylimide.

[0089] In some possible implementations, the lithium salt constitutes 5%-15% of the electrolyte by mass; for example, it can be, but is not limited to, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or any two of the above values. The lithium salt dissociates into ions in the electrolyte, acting as a transport medium during charging and discharging. As the lithium salt concentration increases, the number of lithium ions in the electrolyte increases, and the electrolyte conductivity increases. When the mass percentage of the lithium salt in the electrolyte is within the above-mentioned range, the electrolyte conductivity is relatively high. When the mass percentage of the lithium salt in the electrolyte is higher than the above-mentioned range, the electrolyte viscosity will increase excessively, increasing the resistance to lithium ion transport, and the electrolyte conductivity will actually decrease.

[0090] It should be noted that the mass percentage of lithium salt in the electrolyte mentioned above refers to the mass percentage of lithium salt in the electrolyte in the battery cell obtained after formation or in the battery cell after further charge-discharge cycles. "Battery cell obtained after formation" refers to a fresh battery cell made after formation, which has not undergone further charge-discharge cycles.

[0091] As an example, the mass percentage of lithium salt in the electrolyte mentioned above can be determined by referring to the JY / T 0575-2020 ion chromatography analysis method.

[0092] In some embodiments, the lithium salt in the electrolyte may also include one or more of lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0093] In some embodiments, the solvent in the electrolyte may also include propylene carbonate (PC). ), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethylene carbonate Fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0094] In some embodiments, the additives in the electrolyte may also include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0095] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate (TFPC), etc.

[0096] A second aspect of this application provides a secondary battery, including the electrolyte of the first aspect of this application. The secondary battery of this application exhibits excellent high-temperature and low-temperature performance.

[0097] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte in the solution conducts ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0098] Negative electrode sheet

[0099] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0100] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0101] In some embodiments, the secondary battery includes a negative electrode sheet, which includes a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode active material; the areal density of the negative electrode active material layer is Eg / m³. 2 The specific surface area of ​​the negative electrode active material is Fm 2 / g, the mass percentage of the negative electrode active material in the negative electrode active material layer is L; the mass percentage of the second additive in the electrolyte is B%; B, E, F, and L satisfy: 0.5% ≤ B / (E*F*L) ≤ 12%. As an example, B / (E*F*L) can be, but is not limited to, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, or any two of the above values.

[0102] It should be noted that the mass percentage of negative electrode active material in the negative electrode active material layer mentioned above refers to the mass percentage of negative electrode active material in the negative electrode active material layer in the battery cell obtained after formation or in the battery cell after further charge-discharge cycles. "Battery cell obtained after formation" refers to a fresh battery cell made after formation, which has not undergone further charge-discharge cycles.

[0103] The active material is a porous material with a larger actual surface area and specific surface area. E*F*L represents the actual surface area of ​​the active material per unit area on the electrode sheet. The second additive mainly gains electrons on the specific surface of the negative electrode active material to form a film. The larger the specific surface area, the more second additive is required. Since excessive second additive is detrimental to low-temperature charge-discharge performance, the B, E, F, and L values ​​need to be controlled. When the value of B / (E*F*L) is within the above range, the secondary battery has good high-temperature cycle performance and low-temperature performance. When the value of B / (E*F*L) is higher than the above range, it indicates that the content of the second additive is too high, and the SEI film will be too thick, which may affect the low-temperature performance of the battery. When the value of B / (E*F*L) is lower than the above range, it indicates that the second additive is insufficient to form a film on the specific surface of the negative electrode material, and the exposed active sites will continue to react with the electrolyte, which may affect the high-temperature cycle performance of the battery.

[0104] In some implementations, 80 ≤ E ≤ 150; for example, E can be, but is not limited to, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150 or any two of the above values.

[0105] As an example, the areal density of the negative electrode active material layer mentioned above can be determined by the following method: Discharge the battery at 0.1C to 2.0V, disassemble the battery, and take the areal density per unit area V (100cm²). 2The negative electrode sheet is immersed in DMC for 48 hours, and then dried at 60℃ and -80kPa. The mass m1 is measured. Then the slurry is scraped off and the mass m2 of the substrate is measured. If it is a single-sided coating, the areal density of the negative electrode active material layer is (m1-m2) / V. If it is a double-sided coating, the areal density of the negative electrode active material layer is (m1-m2) / 2 / V.

[0106] In some implementations, 0.5 ≤ F ≤ 5; for example, F can be, but is not limited to, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or any two of the above values.

[0107] As an example, the specific surface area of ​​the aforementioned negative electrode active material can be determined by referring to GB / T 19587-2017 Gas Adsorption BET Method.

[0108] In some implementations, 95% ≤ L ≤ 99%; for example, L can be, but is not limited to, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99% or any two of the above values.

[0109] As an example, the mass percentage of the aforementioned negative electrode active material in the negative electrode active material layer can be determined using the following method:

[0110] The battery was charged at a constant current of 0.1C to 3.8V, and then charged at a constant voltage until the battery was ≤0.05C. At this point, the graphite active material of the negative electrode was fully intercalated with lithium, forming a LiC6 compound. The lithium content in the negative electrode film was tested according to the inductively coupled plasma atomic emission spectrometry method of EPA6010D-2018. Based on this, the content of the negative electrode active material in the negative electrode film was calculated, thus obtaining its mass percentage in the negative electrode active material layer.

[0111] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be obtained by forming a metal material on the polymeric material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymeric material substrate in the negative electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0112] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0113] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0114] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0115] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0116] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto at least one surface of a negative electrode current collector, and then obtaining the negative electrode sheet through processes such as drying and cold pressing. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt%-60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000-10000 mPa·s. The compacted density of the negative electrode sheet can be 1.0 g / cm³. 3 -2.0g / cm 3 .

[0117] Positive electrode sheet

[0118] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector.

[0119] In some embodiments, the positive electrode active material may further include one or more of ternary materials and lithium manganese iron phosphate materials; wherein, the ternary materials include Lix(NiaCobMnc)1-dMdO2-yAy (x is 0.2-1.2) and / or LixAa(NiaCobMnc)1-dMdO2-yAy (x+a is 0.2-1.2); the lithium manganese iron phosphate materials include LiaMn1-yByP1-zCzO4-nDn (a is 0-1.1) and / or LiaAxMn1-yByP1-zCzO4-nDn (a+x is 0-1.1).

[0120] It should be noted that the above limitation on x includes the molar content of Li under different charge and discharge states of the battery (typically the battery voltage is between 2-5V).

[0121] Understandably, lithium (Li) is intercalated and deintercalated during the charging and discharging process of a battery, and the Li content in the positive electrode varies depending on the state of discharge. Unless otherwise specified, the Li content in the examples of positive electrode materials listed in this application refers to the initial state of the material. When a positive electrode material is applied to a positive electrode in a battery system, the Li content in the positive electrode material typically changes after charge-discharge cycles. The Li content can be measured using molar content, but is not limited to this. Regarding "Li content refers to the initial state of the material," the initial state of the material refers to its state before being added to the positive electrode slurry. It is understood that new materials obtained by appropriately modifying the listed positive electrode materials are also within the scope of positive electrode materials. The aforementioned appropriate modification refers to acceptable modification methods for the positive electrode material; non-limiting examples include coating modification.

[0122] In the examples of cathode materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause changes in the molar content of oxygen, and the actual O content will fluctuate. The O content can be measured in molar content, but is not limited to this.

[0123] As a non-limiting example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0124] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be obtained by forming a metal material on a polymeric material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymeric material substrate in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0125] In some embodiments, the positive electrode active material may also be a known positive electrode active material for batteries. As a non-limiting example, the positive electrode active material may also include one or more of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, one or more of lithium cobalt oxides (such as LiCoO2), lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds. Non-limiting examples of lithium-containing phosphates with an olivine structure include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium manganese iron phosphate and carbon composites. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 Examples of lithium nickel cobalt aluminum oxides include LiNi, etc. 0.85 Co 0.15 Al 0.05 O2.

[0126] In some embodiments, the positive electrode active material layer may optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0127] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0128] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto at least one surface of the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing, and other processes. The solvent can be selected from, but is not limited to, any of the solvents described in the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface or both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40wt%-80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000-25000 mPa·s. When coating the positive electrode slurry, the areal density per unit area of ​​the coating, based on dry weight (excluding solvent), can be 15-35 mg / cm³. 2 The compaction density of the positive electrode sheet can be 2-3 g / cm³. 3 .

[0129] Separating membrane

[0130] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0131] 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, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0132] In some embodiments, the thickness of the isolation membrane is 6-40 μm, optionally 12-20 μm.

[0133] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0134] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0135] In some embodiments, the outer packaging of the secondary battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0136] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0137] In this application, unless otherwise specified, "cell battery" refers to the basic unit capable of converting chemical energy into electrical energy, and generally includes at least a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the battery, active ions move back and forth between the positive and negative electrode plates, inserting and extracting. The electrolyte acts as a conductor for the active ions between the positive and negative electrode plates.

[0138] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 The example shown is a square-structured battery cell 5.

[0139] In some of these embodiments, reference is made to Figure 2The 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 forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to actual needs.

[0140] Secondary batteries can be battery modules or battery packs.

[0141] A battery module includes at least one battery cell. The number of battery cells in a battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0142] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 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.

[0143] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0144] 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 one or more. Those skilled in the art can select an appropriate number according to the application and capacity of the battery pack.

[0145] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0146] In addition, this application also provides an electrical device, which includes the secondary battery provided in this application. The secondary 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 may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to.

[0147] As an electrical device, a rechargeable battery can be selected based on its usage requirements.

[0148] Figure 6 Here is an example of an electrical device 6. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0149] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0150] Example

[0151] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where the technology or conditions are not specified in the embodiments, they are performed according to the technology or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0152] Preparation of primary and secondary batteries

[0153] Example 1

[0154] 1) Preparation of the positive electrode sheet

[0155] The positive electrode material LiFePO4, polyvinylidene fluoride (PVDF), and carbon black (SP) are mixed with the solvent dimethyl sulfoxide in a mass ratio of 96:3:1. After stirring, a uniformly dispersed positive electrode slurry is obtained. The positive electrode slurry is uniformly coated on both surfaces of an aluminum foil. After drying, cold pressing, and cutting, the positive electrode sheet is obtained.

[0156] 2) Preparation of negative electrode sheet

[0157] Artificial graphite, carbon black (SP), styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) were mixed in a mass ratio of 96:1.5:1.5:1. Deionized water was added, and the mixture was stirred to obtain a uniformly dispersed negative electrode slurry. This slurry was then evenly coated onto both surfaces of a copper foil. After drying, cold pressing, and cutting, the negative electrode sheet was obtained. The specific surface area of ​​the artificial graphite, the negative electrode active material, was 1 m². 2 / g, the coating surface density of the negative electrode active material is 90g / m². 2 .

[0158] 3) Separating membrane

[0159] Polyethylene film is used as the separation membrane.

[0160] 4) Preparation of electrolyte

[0161] In an argon-atmospheric glove box, ethylene carbonate (EC, as solvent), dimethyl carbonate (DMC, as solvent), ethyl methyl carbonate (EMC, as solvent), diethyl carbonate (DEC, as solvent), vinylene carbonate (VC, as second additive), lithium difluorophosphate (LiPO2F2, as first additive), N-methylpyrrolidone (NMP, as third additive), and lithium hexafluorophosphate (LiPF6, as lithium salt) are mixed and dissolved by mass percentage to obtain an electrolyte.

[0162] 5) Preparation of battery cells

[0163] The positive electrode, negative electrode, and separator are made into an electrode assembly by winding or stacking processes, and then placed in a shell made of aluminum, aluminum-plastic film, etc. After the electrolyte is injected, subjected to high-temperature standing, formation, and capacity testing, a secondary battery is obtained.

[0164] The liquid retention coefficient of a single battery cell is 3g / Ah.

[0165] Example 2-24

[0166] The main differences between the preparation methods of the secondary batteries in Examples 2-24 and the preparation methods of the secondary batteries in Example 1 are: at least one of the following: the mass percentage of solvent in the electrolyte, the type and / or amount of the first additive, the type and / or amount of the second additive, the type and / or amount of the third additive, the specific surface area of ​​the negative electrode active material, the coating unit areal density of the negative electrode active material, and the mass percentage of the negative electrode active material in the negative electrode active material layer, as shown in Table 1.

[0167] Comparative Example 1

[0168] Comparative Example 1 did not contain the first, second, and third additives, as detailed in Table 1.

[0169] Comparative Example 2

[0170] The electrolyte of Comparative Example 2 did not contain the second additive, but only the first and third additives were added, as detailed in Table 1.

[0171] Comparative Example 3

[0172] The electrolyte of Comparative Example 3 did not contain the first additive, but only the second and third additives were added, as detailed in Table 1.

[0173] Comparative Example 4

[0174] No third additive was added to the electrolyte of Comparative Example 4; only the first and second additives were added, as detailed in Table 1.

[0175] The secondary batteries obtained in the above embodiments and comparative examples were subjected to parameter tests including at least the following:

[0176] The mass percentages of EC, DMC, EMC, DEC, first additive, second additive, third additive, and lithium salt in the electrolyte are used to calculate (A+C) / B, C / D, and B / (E*F*L). See Table 1 for details.

[0177] The parameter settings for the above embodiments and comparative examples are shown in Table 1.

[0178] Table 1

[0179]

[0180]

[0181] In Table 1, n represents the percentage of the mass of the second lithium salt relative to the mass of the first lithium salt, T represents the thickness of the positive electrode sheet, A% represents the mass percentage of the first additive in the electrolyte, B% represents the mass percentage of the second additive in the electrolyte, C% represents the mass percentage of the third additive in the electrolyte, D% represents the mass percentage of ethylene carbonate in the electrolyte, VC represents vinylene carbonate, PS represents 1,3-propanesulfonate lactone, DTD represents vinyl sulfate, BDTD represents ethylene disulfate, NMP represents N-methylpyrrolidone, DMP represents N,N-dimethylformamide, E represents the coating areal density of the negative electrode active material, F represents the specific surface area of ​​the negative electrode active material, and L represents the mass percentage of the negative electrode active material in the negative electrode active material layer.

[0182] The mass percentage of the first additive mentioned above in the electrolyte was determined according to the ion chromatography analysis method in JY / T 0575-2020.

[0183] The mass percentage of the second and third additives mentioned above in the electrolyte was determined according to GB / T9722-2006 Chemical Reagents Gas Chromatography.

[0184] The mass percentage of EC in the electrolyte and the mass ratio of the third additive to ethylene carbonate (C / D) mentioned above were determined by gas chromatography using chemical reagents in GB / T9722-2006.

[0185] The mass percentage of lithium salt in the electrolyte mentioned above was determined according to the ion chromatography analysis method in JY / T 0575-2020.

[0186] The specific surface area of ​​the aforementioned negative electrode active material was determined according to the gas adsorption BET method in GB / T 19587-2017.

[0187] The areal density per unit area of ​​the aforementioned negative electrode active material was determined using the following method: the battery was discharged at 0.1C to 2.0V, the battery was disassembled, and the areal density per unit area V (100cm²) was measured. 2 The negative electrode sheet was soaked in DMC for 48 hours, and then dried at 60℃ and -80kPa. The mass m1 was measured. The slurry was then scraped off, and the mass m2 of the substrate was measured. The coating density of the negative electrode active material was calculated based on the formula (m1-m2) / 2 / V.

[0188] The mass percentage of the aforementioned negative electrode active material in the negative electrode active material layer was determined using the following method: the battery was charged at a constant current of 0.1C to 3.8V, and then charged at a constant voltage until the battery was ≤0.05C. At this point, the graphite of the negative electrode active material was fully intercalated with lithium, forming a LiC6 compound. The lithium content in the negative electrode film layer was tested using the inductively coupled plasma atomic emission spectrometry method (EPA6010D-2018), and the graphite content in the negative electrode film layer was calculated accordingly, thus obtaining its mass percentage in the negative electrode active material layer.

[0189] II. Battery Cell Performance Testing

[0190] 1. Determination of high-temperature cycling performance at 60℃

[0191] At 60°C, the secondary batteries of each embodiment and comparative example were charged at a constant current of 0.5C to the upper voltage limit of 3.8V, and then charged at a constant voltage to a current of 0.05C. The batteries were then allowed to stand for 5 minutes and discharged at a constant current of 1 / 3C to 2.0V. This was the first charge-discharge cycle of the battery, and the discharge capacity of this cycle was recorded as D1. The batteries were then subjected to cyclic charge-discharge tests using the above method, and the capacity Dn at the nth cycle was recorded. The capacity retention rate was then Dn / D1. The number of cycles when the capacity retention rate reached 80% was recorded.

[0192] 2. Testing of low-temperature cycling performance at -10℃

[0193] At -10°C, the batteries of each embodiment and comparative example were charged at a constant current of 0.2C to the upper voltage limit of 3.8V, and then charged at a constant voltage to a current of 0.05C. The batteries were then allowed to stand for 5 minutes and discharged at a constant current of 1 / 3C to 2.0V. This was the first charge-discharge cycle of the battery, and the discharge capacity of this cycle was recorded as the discharge capacity D1 of the battery in the first cycle. The discharge capacity of the nth cycle was Dn, and the capacity retention rate was Dn / D1. The number of cycles when the battery capacity retention rate was 80% was recorded.

[0194] The performance test results of the above embodiments and comparative examples are shown in Table 2.

[0195] Table 2

[0196]

[0197]

[0198] A comparison of the results from Examples 1-24 and Comparative Examples 1-4 shows that by simultaneously adding the first additive, the second additive, and the third additive to the electrolyte provided in this application, the high-temperature performance and low-temperature performance of the secondary battery can be improved simultaneously. Furthermore, a comparison of the results from Examples 1-21 and Examples 22-23 shows that by adjusting the amounts of the first additive, the second additive, and the third additive so that the amounts of the three additives satisfy 2% ≤ (A+C) / B ≤ 120%, the high-temperature performance and low-temperature performance of the secondary battery can be improved simultaneously.

[0199] The main difference between Example 24 and Examples 1 and 10-11 is that EC was not added to the electrolyte in Example 24. EC has a high dielectric constant, can dissociate lithium salt, improve electrolyte conductivity, and can also undergo a reduction reaction to obtain Li2CO3, a product with good thermal stability, which improves the high-temperature cycle performance of the battery to a certain extent. However, due to the sharp increase in EC viscosity at low temperatures, the electrolyte viscosity may be high and the conductivity may be reduced, affecting the low-temperature performance. EC, in combination with a third additive, can improve the low-temperature performance of the battery. Therefore, based on the comparison of the results of Example 24 with Examples 1 and 10-11, it can be seen that adding EC to the electrolyte can further improve the high-temperature and low-temperature performance of the battery cells.

[0200] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0201] 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, characterized in that, The electrolyte comprises: The first additive includes an inorganic salt containing fluorine. The second additive comprises a compound containing unsaturated bonds, wherein the reduction potential of the unsaturated compound is ≥0.8V (Li). + / Li); and The third additive comprises a compound containing an amide group; the third additive comprises the following formulas (I) and (I). One or more of the compounds shown: 、 R1 and R2 each independently include any one of hydrogen, methyl and ethyl, and R3 includes C3-C6 alkylene groups; The first additive has a mass percentage of A in the electrolyte, the second additive has a mass percentage of B in the electrolyte, and the third additive has a mass percentage of C in the electrolyte, with 0.01≤A≤0.5, 0.5≤B≤3, and 0.05≤C≤0.1; A, B, and C satisfy: 2%≤(A+C) / B≤120%.

2. The electrolyte as described in claim 1, characterized in that, 5%≤(A+C) / B≤55%.

3. The electrolyte as described in claim 1, characterized in that, The fluorine element accounts for ≥8% of the mass of the inorganic salt.

4. The electrolyte as described in claim 3, characterized in that, The first additive includes one or more of difluorophosphate, tetrafluoroborate and fluorosulfonate containing element M, wherein element M includes one or more of Li, Na, K and Cs.

5. The electrolyte as described in claim 1, characterized in that, The second additive includes cyclic compounds containing unsaturated bonds.

6. The electrolyte as described in claim 5, characterized in that, The second additive includes one or more of vinylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfate, and vinyl disulfate.

7. The electrolyte as described in claim 1, characterized in that, The third additive includes one or more of N,N-dimethylformamide and N-methylpyrrolidone.

8. The electrolyte as described in claim 1, characterized in that, The electrolyte also contains a cyclic ester solvent.

9. The electrolyte as described in claim 8, characterized in that, The cyclic ester solvent includes one or more of ethylene carbonate and propylene carbonate.

10. The electrolyte as described in claim 9, characterized in that, The ethylene carbonate in the electrolyte has a mass percentage of D, and the C and D satisfy 0.01%≤C / D≤1%.

11. The electrolyte as described in claim 10, characterized in that, 5≤D≤35。 12. The electrolyte according to any one of claims 1 to 11, characterized in that, The electrolyte also contains lithium salts.

13. The electrolyte as described in claim 12, characterized in that, The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

14. The electrolyte as described in claim 12, characterized in that, The lithium salt accounts for 5%-15% of the mass of the electrolyte.

15. A secondary battery, characterized in that, Includes the electrolyte as described in any one of claims 1 to 14.

16. The secondary battery as described in claim 15, characterized in that, The secondary battery includes a negative electrode sheet, the negative electrode sheet includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material; the areal density of the negative electrode active material layer is Eg / m³. 2 The specific surface area of ​​the negative electrode active material is Fm. 2 / g, wherein the mass percentage of the negative electrode active material in the negative electrode active material layer is L; The second additive accounts for B% of the mass of the electrolyte. The following conditions must be met: B, E, F, and L satisfy: 0.5% ≤ B / (E*F*L) ≤ 12%.

17. The secondary battery as described in claim 16, characterized in that, 80≤E≤150。 18. The secondary battery as described in claim 16, characterized in that, 0.5≤F≤5。 19. The secondary battery according to any one of claims 16 to 18, characterized in that, 93%≤L≤98%。 20. An electrical appliance, characterized in that, It includes at least one of the electrolyte as described in any one of claims 1 to 14 and the secondary battery as described in any one of claims 15 to 19.

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