Electrolyte, secondary battery, and electrical apparatus

Abstract

An electrolyte, a secondary battery, and an electrical apparatus. The electrolyte includes a first additive, a second additive, and a third additive. The first additive comprises an element-containing inorganic salt, the second additive comprises an unsaturated bond-containing compound, the reduction potential of the unsaturated bond-containing compound being greater than or equal to 0.8V (Li+ / Li), and the third additive comprises an amide group-containing compound. The first additive, the second additive and the third additive are added into the electrolyte, so as to improve both high-temperature performance and low-temperature performance of a secondary battery.

Description

Electrolyte, secondary battery and electrical device

[0001] This application refers to Chinese patent application No. 202311276886.8, filed on September 28, 2023, entitled “Electrolyte, Secondary Battery and Electrical Device,” which is incorporated herein by reference in its entirety. Technical Field

[0002] The present application relates to the technical field of secondary batteries, and in particular to an electrolyte, a secondary battery, and an electrical device. Background Art

[0003] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0004] In recent years, lithium-ion batteries, with their advantages of high open-circuit voltage, high energy density, long service life, no memory effect, no pollution, and low self-discharge, have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. With the development of lithium-ion batteries, higher performance requirements have been placed on them. However, in related technologies, lithium-ion batteries have difficulty in achieving both high-temperature and low-temperature performance, which to some extent limits their application.

[0005] Summary of the Invention

[0006] The present application is made in view of the above-mentioned problems, and its purpose includes providing an electrolyte solution that can achieve both high-temperature performance and low-temperature performance of a secondary battery, and also provides a secondary battery and an electrical device.

[0007] In order to achieve the above-mentioned object, the first aspect of the present application provides an electrolyte, the electrolyte comprising:

[0008] a first additive comprising an inorganic salt containing fluorine;

[0009] The second additive comprises a compound containing an unsaturated bond, wherein the reduction potential of the compound containing an unsaturated bond is ≥ 0.8 V (Li + / Li); and

[0010] The third additive includes a compound containing an amide group.

[0011] The second additive includes a reduction potential ≥ 0.8 V (Li +The first additive comprises a compound containing fluorine (Fe / Li) and containing unsaturated bonds. This compound undergoes a reduction reaction on the negative electrode surface during battery formation to form a polymer, forming a SEI film that passivates the negative electrode, thereby preventing continuous side reactions caused by direct contact between the solvent and the negative electrode. This achieves excellent negative electrode passivation and improves the battery's high-temperature performance. The first additive comprises a compound containing fluorine, which decomposes at the negative electrode to form an SEI film containing F-based inorganic compounds. This SEI film has a wider band gap and higher ionic conductivity, which can enhance the SEI film's ion conductivity, reduce the lithium ion diffusion barrier, facilitate lithium ion transport, and reduce the low-temperature interfacial charge transfer impedance, thereby improving low-temperature performance. The lithium ions in the electrolyte will combine with solvent molecules and anions to form solvated lithium ions. During charging, the solvated lithium ions migrate toward the negative electrode. When they reach the SEI membrane, the lithium ions are desolvated and penetrate the SEI membrane to embed into the negative electrode. The third additive includes a compound containing an amide group, so it can also participate in the formation of a solvation structure. The negatively charged N in the amide group interacts strongly with the lithium ions. The third additive can replace the cyclic ester, reducing the amount of cyclic ester in the solvation structure. It can significantly reduce the active energy of the lithium ion desolvation process, making it easier to desolvate, thereby improving low-temperature kinetics. Therefore, the present application adds the first additive, the second additive, and the third additive to the electrolyte, and the three play a synergistic role to simultaneously improve the high-temperature performance and low-temperature performance of the secondary battery.

[0012] In some embodiments, the mass proportion of the first additive in the electrolyte is A%, the mass proportion of the second additive in the electrolyte is B%, and the mass proportion of the third additive in the electrolyte is C%, and A, B, and C satisfy: 2%≤(A+C) / B≤120%;

[0013] Optionally, 5%≤(A+C) / B≤55%.

[0014] In some embodiments, 0.01≤A≤1.

[0015] In some embodiments, 0.5≤B≤10.

[0016] In some embodiments, 0.01≤C≤0.1.

[0017] In some embodiments, the mass percentage of the fluorine element in the inorganic salt is ≥8%;

[0018] Optionally, the first additive includes one or more of difluorophosphate, tetrafluoroborate and fluorosulfonate containing an M element, and the M element includes one or more of Li, Na, K and Cs.

[0019] In some embodiments, the second additive includes a cyclic compound containing an unsaturated bond;

[0020] Optionally, the second additive includes one or more of vinylene carbonate, 1,3-propane sultone, vinyl sulfate and vinyl bissulfate.

[0021] In some embodiments, the third additive includes one or more compounds represented by the following formulas (I) and (II):

[0022] wherein R1 and R2 each independently include any one of hydrogen, methyl and ethyl, and R3 includes a C3-C6 alkyl group;

[0023] Optionally, the third additive includes one or more of N,N-dimethylformamide and N-methylpyrrolidone.

[0024] In some embodiments, the electrolyte further comprises a cyclic ester solvent;

[0025] Optionally, the cyclic ester solvent includes one or more of ethylene carbonate and propylene carbonate;

[0026] Further optionally, the mass proportion of the ethylene carbonate in the electrolyte is D%, and C and D satisfy 0.01%≤C / D≤1%;

[0027] Further optionally, 5≤D≤35.

[0028] In some embodiments, the electrolyte further comprises a lithium salt;

[0029] Optionally, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide;

[0030] Optionally, the lithium salt accounts for 5%-15% by mass in the electrolyte.

[0031] A second aspect of the present application provides a secondary battery comprising the electrolyte of the first aspect of the present application.

[0032] The secondary battery of the present application has both excellent high-temperature performance and low-temperature performance.

[0033] In some embodiments, the secondary battery includes a negative electrode plate, the negative electrode plate includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material; the surface density of the negative electrode active material layer is Eg / m 2 , the specific surface area of ​​the negative electrode active material is Fm 2 / g, the mass proportion of the negative electrode active material in the negative electrode active material layer is L;

[0034] The mass proportion of the second additive in the electrolyte is B%;

[0035] The B, E, F and L satisfy: 0.5%≤B / (E*F*L)≤12%.

[0036] In some embodiments, 80≤E≤150.

[0037] In some embodiments, 0.5≤F≤5.

[0038] In some embodiments, 93%≤L≤98%.

[0039] A third aspect of the present application provides an electrical device comprising at least one of the electrolyte of the first aspect of the present application and the secondary battery of the second aspect of the present application.

[0040] The electric device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery.

[0041] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more of the accompanying drawings. The additional details or examples used to describe the accompanying drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes currently understood for these applications. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the accompanying drawings:

[0043] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0044] FIG. 2 is an exploded view of the battery cell according to one embodiment of the present application shown in FIG. 1 .

[0045] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0046] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0047] FIG5 is an exploded view of the battery pack shown in FIG4 according to an embodiment of the present application.

[0048] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0049] Explanation of the accompanying symbols: 1. battery pack; 2. upper box; 3. lower box; 4. battery module; 5. battery cell; 51. shell; 52. electrode assembly; 53. cover plate; 6. electrical device. DETAILED DESCRIPTION

[0050] Below, some embodiments of the electrolyte, secondary battery and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0051] " scope " disclosed in the present application can be limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and any end value can be included or not included independently, and can be arbitrarily combined, that is, any lower limit can form a scope with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 are also listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is merely an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to listing the parameter as, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on. For example, when a parameter is expressed as an integer selected from "2-10", this is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0052] In this application, "a plurality of" or "a plurality of" refers to a number greater than or equal to 2 unless otherwise specified. For example, "one or more" means one or more than or equal to two.

[0053] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0054] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor does it necessarily refer to independent or alternative embodiments that are mutually exclusive with other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments. References to "implementations" herein have a similar understanding.

[0055] It will be appreciated by those skilled in the art that, in the methods of various embodiments or examples, the order in which the steps are written does not imply a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible inherent logic. Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0056] In this application, in the open technical features or technical solutions described with words such as "contain", "include", and "include", unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions that also include additional members in addition to the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2, and a3" and the feature or solution of "A includes not only a1, a2, and a3, but also other members". In this application, unless otherwise specified, A (such as B) means 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, the terms "optionally," "optional," and "optional" are optional and refer to either option being present or absent. If a technical solution contains multiple "options," each option is considered independent unless otherwise specified and there are no conflicts or constraints.

[0058] In related technologies, it is difficult for lithium-ion batteries to simultaneously take into account both high-temperature performance and low-temperature performance, which to a certain extent limits the application of lithium-ion batteries.

[0059] Based on the above problems, the present application provides an electrolyte, to which a first additive, a second additive and a third additive are added simultaneously, so as to simultaneously improve the high temperature performance and the low temperature performance of the secondary battery.

[0060] The first aspect of the present application provides an electrolyte, the 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 an unsaturated bond, the reduction potential of the compound containing an unsaturated bond being ≥ 0.8 V (Li + / Li); the third additive includes a compound containing an amide group.

[0061] It is understood that the second additive includes a reduction potential ≥ 0.8 V (Li + The first additive comprises a compound containing fluorine (Fe / Li) and containing unsaturated bonds. This compound undergoes a reduction reaction on the negative electrode surface during battery formation to form a polymer, forming a SEI film that passivates the negative electrode, thereby preventing continuous side reactions caused by direct contact between the solvent and the negative electrode. This achieves excellent negative electrode passivation and improves the battery's high-temperature performance. The first additive comprises a compound containing fluorine, which decomposes at the negative electrode to form an SEI film containing F-based inorganic compounds. This SEI film has a wider band gap and higher ionic conductivity, which can enhance the SEI film's ion conductivity, reduce the lithium ion diffusion barrier, facilitate lithium ion transport, and reduce the low-temperature interfacial charge transfer impedance, thereby improving low-temperature performance. The lithium ions in the electrolyte will combine with solvent molecules and anions to form solvated lithium ions. During charging, the solvated lithium ions migrate toward the negative electrode. When they reach the SEI membrane, the lithium ions are desolvated and penetrate the SEI membrane to embed into the negative electrode. The third additive includes a compound containing an amide group, so it can also participate in the formation of a solvation structure. The negatively charged nitrogen in the amide group strongly interacts with the lithium ions. The third additive can replace the cyclic ester, reducing the amount of cyclic ester in the solvation structure. It can significantly reduce the active energy of the lithium ion desolvation process, making it easier to desolvate, thereby improving low-temperature kinetics. Therefore, the present application can simultaneously improve the high-temperature performance and low-temperature performance of the secondary battery by adding the first additive, the second additive, and the third additive to the electrolyte.

[0062] In some embodiments, the mass proportion of the first additive in the electrolyte is A%, the mass proportion of the second additive in the electrolyte is B, and the mass proportion of the third additive in the electrolyte is C. A, B, and C satisfy the following: 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 a range between any two of the above values. When A, B and C satisfy the above relationship, the high-temperature performance and low-temperature performance of the secondary battery can be significantly improved at the same time; when (A+C) / B is lower than the above range, the improvement of the low-temperature performance of the secondary battery is limited; when (A+C) / B is higher than the above range, the improvement of the high-temperature performance of the secondary battery is limited.

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

[0064] It should be noted that A% refers to the mass proportion of the first additive in the electrolyte in the battery cell produced after formation or in the battery cell after further charge and discharge cycles. B% refers to the mass proportion of the second additive in the electrolyte in the battery cell produced after formation or in the battery cell after further charge and discharge cycles. C% refers to the mass proportion of the third additive in the electrolyte in the battery cell produced after formation or in the battery cell after further charge and discharge cycles. "Battery cell produced after formation" refers to a fresh battery cell produced after formation that has not been subjected to further charge and discharge cycles.

[0065] In some possible embodiments, 0.01≤A≤1; for example, A may 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 proportion (A%) of the first additive in the electrolyte is lower than 0.1%, it may not be able to effectively improve the low-temperature performance of the secondary battery; because during the battery cycle, as the negative electrode deintercalates and deintercalates lithium, the negative electrode expands and contracts, and the volume of the negative electrode changes significantly; since the inorganic SEI film has poor mechanical stability, it is easy to rupture when the volume of the negative electrode changes significantly, exposing new active sites and continuously inducing side reactions. Therefore, when the mass proportion (A%) of the first additive in the electrolyte is higher than 1%, the effect of improving the high-temperature cycle performance of the secondary battery may show a downward 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 a range between any two of the foregoing 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. Because the formation of an SEI film by the second additive will increase the battery impedance, especially at low temperatures, the increase in low-temperature impedance is more significant. Therefore, 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 a range between any two of the above values. When the mass proportion (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 electrochemical stability of the third additive itself is poor, it is easy to cause a reduction side reaction at the negative electrode, affecting the stability of the SEI film. The reduction side reaction is aggravated at high temperature. Therefore, when the mass proportion (C%) of the third additive in the electrolyte is higher than 0.1%, it may affect the high-temperature cycle life of the battery.

[0068] As an example, the mass proportion (A%) of the first additive mentioned above in the electrolyte can be determined by referring to the ion chromatography analysis method JY / T 0575-2020.

[0069] The mass percentage of the second additive in the electrolyte (B%) and the mass percentage of the third additive in the electrolyte (C%) mentioned above can be determined by referring to the chemical reagent gas chromatography method in GB / T9722-2006.

[0070] In some embodiments, the weight 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 a range between any two of the foregoing values. When the weight percentage of fluorine in the inorganic salt is within the above range, it can effectively increase the fluoride content in the SEI film, thereby improving the ionic conductivity of the SEI film.

[0071] As an example, the mass proportion of the above-mentioned fluorine element in the inorganic salt can be determined by referring to the JY / T 0567-2020 inductively coupled plasma optical emission spectrometry analysis method.

[0072] In some embodiments, the first additive includes one or more of difluorophosphate, tetrafluoroborate, and fluorosulfonate containing an M element, and the M element 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 includes a cyclic compound containing an unsaturated bond, which is easily reduced at the negative electrode to form an oligomer.

[0075] As a possible implementation, the second additive includes one or more of vinylene carbonate, 1,3-propane sultone, vinyl sulfate, and vinyl bissulfate.

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

[0077] Wherein, R1 and R2 each independently include any one of hydrogen, methyl and ethyl, and R3 includes C3-C6 alkyl.

[0078] As a possible implementation, the third additive includes one or more of N,N-dimethylformamide and N-methylpyrrolidone.

[0079] In some embodiments, the electrolyte further comprises a cyclic ester solvent.

[0080] In some possible embodiments, the cyclic ester solvent includes one or more of ethylene carbonate and propylene carbonate.

[0081] Ethylene carbonate has a high dielectric constant and can dissociate lithium salts to 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.

[0082] In some possible embodiments, the mass proportion 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 a range between any two of the above values. Since ethylene carbonate occupies the inner layer of the electrolyte's solvation structure, its high dielectric constant also increases the orientational forces between molecules, leading to an increase in the electrolyte's phase transition point and viscosity. At low temperatures, the viscosity increases dramatically and affects the desolvation process of lithium ions, which is the rate-determining step for charge transfer in the electrolyte at low temperatures. Therefore, when the mass proportion of ethylene carbonate in the electrolyte is too high, the low-temperature performance of the battery will deteriorate. The 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 amount of ethylene carbonate and the third additive can be adjusted to simultaneously take into account both the low-temperature and high-temperature performance of the battery. When the C / D ratio is within the above range, both the low-temperature and high-temperature performance of the battery are better. When the C / D ratio is lower than the above range, the low-temperature performance of the battery may be limited. When the C / D ratio is higher than the above range, the high-temperature performance of the battery may be limited.

[0083] In some possible embodiments, the weight percentage of ethylene carbonate in the electrolyte is D%, with 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 a range between any two of the foregoing values. When the weight percentage of ethylene carbonate in the electrolyte is less than 5%, the effect of improving the electrolyte conductivity may be limited. When the weight 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.

[0084] As an example, the mass proportion (D%) of the above-mentioned ethylene carbonate in the electrolyte and the mass ratio (C / D) of the third additive to ethylene carbonate can be determined with reference to GB / T9722-2006.

[0085] It should be noted that the D% mentioned above refers to the mass fraction of ethylene carbonate in the electrolyte in a battery cell produced after formation or after further charge-discharge cycling. C / D refers to the mass ratio of the third additive to ethylene carbonate in a battery cell produced after formation or after further charge-discharge cycling. "Battery cells produced after formation" refers to fresh battery cells produced after formation that have not been subjected to further charge-discharge cycling.

[0086] In some embodiments, the electrolyte further comprises a lithium salt.

[0087] Optionally, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

[0088] In some possible embodiments, the mass percentage of lithium salt in the electrolyte is 5%-15%; for example, it can be, but is not limited to, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a range between any two of the above values. Lithium salt dissociates into ions in the electrolyte, acting as a transmission medium during the charge and discharge process; 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 lithium salt in the electrolyte is within the above range, the electrolyte conductivity is high. When the mass percentage of lithium salt in the electrolyte is higher than the above range, the viscosity of the electrolyte will increase excessively, the lithium ion transmission resistance will increase, and the electrolyte conductivity will decrease.

[0089] It should be noted that the aforementioned percentage by mass of lithium salt in the electrolyte refers to the percentage by mass of lithium salt in the battery cell produced after formation or in the battery cell after further charge and discharge cycles. "Battery cell produced after formation" refers to fresh battery cells produced after formation and not subjected to further charge and discharge cycles.

[0090] As an example, the mass proportion of the above-mentioned lithium salt in the electrolyte can be determined by referring to the ion chromatography analysis method JY / T 0575-2020.

[0091] 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 difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorodioxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0092] In some embodiments, the solvent in the electrolyte may further include propylene carbonate (PC, ), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate One or more of 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.

[0093] In some embodiments, the additives in the electrolyte may also include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery properties, such as additives that improve the battery's overcharge performance, additives that improve the battery's high or low temperature performance, etc.

[0094] In some embodiments, the additives in the electrolyte may further include, but are not limited to, one or more of difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0095] The second aspect of the present application provides a secondary battery comprising the electrolyte of the first aspect of the present application. The secondary battery of the present application has both excellent high-temperature performance and low-temperature performance.

[0096] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolytes in the electrolyte conduct ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0097] Negative electrode

[0098] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0099] As a non-limiting example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two facing surfaces of the negative electrode current collector.

[0100] In some embodiments, 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 surface density of the negative electrode active material layer is Eg / m 2 , the specific surface area of ​​the negative electrode active material is Fm 2 / g, the mass proportion of the negative electrode active material in the negative electrode active material layer is L; the mass proportion of the second additive in the electrolyte is B%; B, E, F, and L satisfy the following: 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 a range between any two of the above values.

[0101] It should be noted that the aforementioned percentage by mass of the negative electrode active material in the negative electrode active material layer refers to the percentage by mass of the negative electrode active material in the battery cell produced after formation or in the battery cell after further charge and discharge cycles. "Battery cell produced after formation" refers to a fresh battery cell produced after formation that has not been subjected to further charge and discharge cycles.

[0102] The active material is a porous material with a larger true surface area and specific surface area. E*F*L represents the true surface area of ​​the active material per unit area of ​​the active sheet. The second additive is mainly reduced by electrons to form a film on the specific surface area of ​​the negative electrode active material. The larger the specific surface area, the more second additive is required. Since too much second additive is not conducive to low-temperature charge and discharge performance, it is necessary to regulate the B value, E value, F value, and L value. 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, the SEI film will be too thick, and the low-temperature performance of the battery may be affected. When the value of B / (E*F*L) is lower than the above range, it indicates that the second additive is insufficient to fully form a film on the specific surface area of ​​the negative electrode material. The exposed active sites will continue to undergo side reactions with the electrolyte, and the high-temperature cycle performance of the battery may be affected.

[0103] In some embodiments, 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 a range between any two of the above values.

[0104] As an example, the surface density of the negative electrode active material layer mentioned above can be measured by the following method: discharge the battery at 0.1C to 2.0V, disassemble the battery, and take the surface density per unit area V (100cm 2) is immersed in DMC for 48 hours, and then the electrode is dried at 60°C and -80kPa, and the mass m1 is weighed; then the slurry is scraped off and the mass m2 of the substrate is weighed; if it is single-sided coating, the surface density of the negative electrode active material layer is (m1-m2) / V, and if it is double-sided coating, the surface density of the negative electrode active material layer is (m1-m2) / 2 / V.

[0105] In some embodiments, 0.5≤F≤5; for example, F may be, but is not limited to, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or a range between any two of the above values.

[0106] As an example, the specific surface area of ​​the negative electrode active material mentioned above can be measured by referring to the gas adsorption BET method in GB / T 19587-2017.

[0107] In some embodiments, 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 a range between any two of the above values.

[0108] As an example, the mass proportion of the above-mentioned negative electrode active material in the negative electrode active material layer can be measured using the following method:

[0109] The battery is charged at a constant current of 0.1C to 3.8V, and then charged at a constant voltage to ≤0.05C. At this time, the negative electrode active material graphite is fully embedded with lithium to form a LiC6 compound; referring to EPA6010D-2018 inductively coupled plasma spectrometry, the lithium content in the negative electrode film layer is tested, and the content of the negative electrode active material in the negative electrode film layer is calculated based on this, thereby obtaining its mass proportion in the negative electrode active material layer.

[0110] 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 polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0111] In some of these embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. 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, lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional 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.

[0112] In some embodiments, the negative electrode active material layer may further 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).

[0113] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0114] In some embodiments, the negative electrode active material layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0115] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode collector coated with the negative electrode slurry can be a single surface of the negative electrode collector or two surfaces of the negative electrode 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 2000mPa·s-10000mPa·s. The compaction density of the negative electrode sheet can be 1.0g / cm 3 -2.0g / cm 3 .

[0116] Positive electrode

[0117] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.

[0118] In some embodiments, the positive electrode active material may also include one or more of a ternary material and a lithium iron manganese phosphate material; wherein the ternary material includes 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 iron manganese phosphate material includes LiaMn1-yByP1-zCzO4-nDn (a is 0-1.1) and / or LiaAxMn1-yByP1-zCzO4-nDn (a+x is 0-1.1).

[0119] It should be noted that the above definition of x includes the molar content of Li in different charge and discharge states of the battery (usually the battery voltage is between 2-5V).

[0120] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charge and discharge process, and the content of Li in the positive electrode plate is different when the battery is discharged to different states. In the list of positive electrode materials in this application, unless otherwise specified, the Li content is the initial state of the material. The positive electrode material is applied to the positive electrode plate in the battery system, and after the charge and discharge cycle, the Li content in the positive electrode material contained in the plate will usually change. Among them, the Li content can be measured by molar content, but is not limited to this. Regarding "the Li content is the initial state of the material", the initial state of the material refers to the state before the material is added to the positive electrode slurry. It is understandable that new materials obtained by appropriate modification on the basis of the listed positive electrode materials are also within the scope of positive electrode materials. The aforementioned appropriate modification refers to acceptable modification methods for positive electrode materials, and non-limiting examples include coating modification.

[0121] In the examples of positive electrode materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual O content will fluctuate. The O content can be measured by molar content, but is not limited to this.

[0122] As a non-limiting example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on either or both of the two facing surfaces of the positive electrode current collector.

[0123] 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 polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0124] In some embodiments, the positive electrode active material may also be a positive electrode active material for batteries known in the art. As non-limiting examples, the positive electrode active material may also include one or more of the following materials: olivine-structured lithium-containing phosphates, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as battery positive electrode active materials 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 may include, but are not limited to, one or more of lithium cobalt oxide (such as LiCoO2), lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Non-limiting examples of olivine-structured lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. 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 referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.85 Co 0.15 Al 0.05 O2.

[0125] In some embodiments, the positive electrode active material layer may further optionally include a binder. As non-limiting examples, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0126] In some embodiments, the positive electrode active material layer may further include a conductive agent. As non-limiting examples, 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.

[0127] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on at least one side of the positive electrode current collector, and after drying, cold pressing, and other processes, the positive electrode sheet can be obtained. The type of solvent can be selected from but not limited to any of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector or on both surfaces of the positive electrode current collector. The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector or on 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 5000mPa·s-25000mPa·s. When applying the positive electrode slurry, the coating unit area density based on dry weight (excluding solvent) can be 15 mg / cm 2 -35mg / cm 2 The compaction density of the positive electrode can be 2g / cm 3 -3g / cm 3 .

[0128] Isolation film

[0129] The present application has no particular limitation on the type of isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0130] In some embodiments, the material of the separator may include one or more of glass fiber, non-woven 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.

[0131] In some embodiments, the isolation film has a thickness of 6 μm-40 μm, and optionally 12 μm-20 μm.

[0132] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0133] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0134] In some embodiments, the outer packaging of the secondary battery can be a hard 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 shell, such as a pouch-type soft shell. The material of the soft shell can be plastic. Further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0135] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0136] In this application, unless otherwise specified, a "battery cell" refers to a basic unit that can achieve the mutual conversion of chemical energy and electrical energy. Further, generally speaking, it includes at least a positive electrode plate, a negative electrode plate, and an electrolyte. During the battery's charge and discharge process, active ions are embedded in and out of the positive and negative electrode plates. The electrolyte plays the role of conducting active ions between the positive and negative electrode plates.

[0137] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG1 shows a battery cell 5 with a square structure as an example.

[0138] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to actual needs.

[0139] The secondary battery may be a battery module or a battery pack.

[0140] A battery module includes at least one battery cell. The number of battery cells contained 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.

[0141] FIG3 shows an example battery module 4. Referring to FIG3 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0142] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0143] In some embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select an appropriate number based on the application and capacity of the battery pack.

[0144] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0145] In addition, the present application also provides an electrical device, which includes the secondary battery provided in the present application. The secondary battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can include, but is not limited to, mobile devices, electric vehicles, electric trains, ships, satellites, energy storage systems, etc. Among them, mobile devices can be, for example, mobile phones, laptops, etc.; electric vehicles can 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 these.

[0146] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0147] Figure 6 shows an example of an electric device 6. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0148] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0149] Example

[0150] Below, the embodiment of the present application is described. The embodiment described below is exemplary, is only used to explain the present application, and is not to be construed as limiting the present application. Where the technology or conditions are not specified in the embodiment, the technology or conditions described in the literature in this area or the product instructions are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0151] Preparation of 1. Secondary Battery

[0152] Example 1

[0153] 1). Preparation of positive electrode

[0154] The positive electrode materials LiFePO4, polyvinylidene fluoride (PVDF), and carbon black (SP) are mixed with the solvent dimethyl sulfoxide in a mass ratio of 96:3:1, and stirred to obtain a uniformly dispersed positive electrode slurry. The positive electrode slurry is evenly coated on both surfaces of the aluminum foil, and then dried, cold pressed, and cut to obtain the positive electrode sheet.

[0155] 2). Preparation of negative electrode sheet

[0156] Artificial graphite: carbon black (SP): styrene-butadiene rubber (SBR): sodium carboxymethyl cellulose (CMC) were mixed in a mass ratio of 96:1.5:1.5:1, deionized water was added, and a uniformly dispersed negative electrode slurry was obtained by stirring. The negative electrode slurry was evenly coated on both surfaces of the copper foil, and the negative electrode sheet was obtained after drying, cold pressing, and cutting. The specific surface area of ​​the negative electrode active material artificial graphite is 1m 2 / g, and the coating unit area density of the negative electrode active material is 90g / m 2 .

[0157] 3). Isolation film

[0158] Polyethylene film is used as the isolation film.

[0159] 4). Preparation of electrolyte

[0160] In an argon atmosphere glove box, ethylene carbonate (EC, as a solvent), dimethyl carbonate (DMC, as a solvent), ethyl methyl carbonate (EMC, as a solvent), diethyl carbonate (DEC, as a solvent), vinylene carbonate (VC, as a second additive), lithium difluorophosphate (LiPO2F2, as a first additive), N-methylpyrrolidone (NMP, as a third additive), and lithium hexafluorophosphate (LiPF6, as a lithium salt) were mixed and dissolved in percentage by mass to obtain an electrolyte.

[0161] 5). Preparation of battery cells

[0162] The positive electrode sheet, negative electrode sheet and separator are made into an electrode assembly through a winding process or a lamination process, and placed in a shell made of aluminum shell, aluminum-plastic film, etc. After the above-mentioned electrolyte is injected, left to stand at high temperature, formed, and capacity divided, a secondary battery is obtained.

[0163] The battery cell's liquid retention coefficient is 3g / Ah.

[0164] Examples 2-24

[0165] The main difference between the preparation method of the secondary battery in Examples 2-24 and the preparation method of the secondary battery in Example 1 is that at least one of the mass percentage of the 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 surface density of the negative electrode active material, and the mass proportion of the negative electrode active material in the negative electrode active material layer is different, as shown in Table 1.

[0166] Comparative Example 1

[0167] In Comparative Example 1, the first additive, the second additive, and the third additive were not added. See Table 1 for details.

[0168] Comparative Example 2

[0169] The second additive was not added to the electrolyte of Comparative Example 2, and only the first additive and the third additive were added. See Table 1 for details.

[0170] Comparative Example 3

[0171] The first additive was not added to the electrolyte of Comparative Example 3, and only the second additive and the third additive were added. See Table 1 for details.

[0172] Comparative Example 4

[0173] The electrolyte of Comparative Example 4 did not contain the third additive, but only contained the first additive and the second additive.

[0174] The secondary batteries prepared in the above embodiments and comparative examples were subjected to parameter tests including at least the following items:

[0175] The mass percentages of EC, DMC, EMC, DEC, the first additive, the second additive, the third additive, and the lithium salt in the electrolyte are calculated as (A+C) / B, C / D, and B / (E*F*L). See Table 1 for details.

[0176] The parameter settings of the above embodiments and comparative examples are shown in Table 1.

[0177] Table 1

[0178] In Table 1, n represents the percentage of the mass of the second lithium salt to the mass of the first lithium salt, T represents the thickness of the positive electrode sheet, A% represents the mass proportion of the first additive in the electrolyte, B% represents the mass proportion of the second additive in the electrolyte, C% represents the mass proportion of the third additive in the electrolyte, D% represents the mass proportion of ethylene carbonate in the electrolyte, VC represents vinylene carbonate, PS represents 1,3-propane sultone, DTD represents vinyl sulfate, BDTD represents diethylene sulfate, NMP represents N-methylpyrrolidone, DMP represents N,N-dimethylformamide, E represents the coating unit area density of the negative electrode active material, F represents the specific surface area of ​​the negative electrode active material, and L represents the mass proportion of the negative electrode active material in the negative electrode active material layer.

[0179] The mass proportion of the first additive mentioned above in the electrolyte is determined with reference to the ion chromatography analysis method JY / T 0575-2020.

[0180] The mass proportions of the second additive and the third additive mentioned above in the electrolyte are determined by referring to the chemical reagent gas chromatography method in GB / T9722-2006.

[0181] The mass proportion of EC in the electrolyte and the mass ratio of the third additive to ethylene carbonate (C / D) mentioned above were determined by referring to the chemical reagent gas chromatography method in GB / T9722-2006.

[0182] The mass proportion of the above-mentioned lithium salt in the electrolyte is determined with reference to the JY / T 0575-2020 ion chromatography analysis method.

[0183] The specific surface area of ​​the negative electrode active material mentioned above is measured with reference to the gas adsorption BET method in GB / T 19587-2017.

[0184] The coating unit area density of the negative electrode active material mentioned above was measured by the following method: the battery was discharged to 2.0V at 0.1C, the battery was disassembled, and the unit area V (100cm 2 ) was immersed in DMC for 48 h, and then the electrode was dried at 60°C and -80 kPa, and the mass m1 was weighed; then the slurry was scraped off and the mass m2 of the substrate was weighed; the coating surface density of the negative electrode active material was calculated based on the formula (m1-m2) / 2 / V.

[0185] The mass proportion of the above-mentioned negative electrode active material in the negative electrode active material layer is determined by the following method: the battery is charged at a constant current of 0.1C to 3.8V, and then charged at a constant voltage to the battery ≤0.05C. At this time, the negative electrode active material graphite is fully embedded with lithium to form a LiC6 compound; referring to EPA6010D-2018 inductively coupled plasma spectrometry, the lithium content in the negative electrode film layer is tested, and the graphite content in the negative electrode film layer is calculated based on this, thereby obtaining its mass proportion in the negative electrode active material layer.

[0186] 2. Battery Cell Performance Test

[0187] 1.60℃ high temperature cycle performance determination

[0188] At 60°C, the secondary batteries of each embodiment and comparative example were charged at a constant current of 0.5C to a voltage upper limit of 3.8V, then charged at a constant voltage to a current of 0.05C. The batteries were allowed to rest for 5 minutes and then 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 at this time was recorded as the discharge capacity of the first cycle, D1. The batteries were subjected to cyclic charge and discharge tests according to the above method, and the capacity Dn at the nth cycle was recorded. The capacity retention rate was Dn / D1. The number of cycles at which the capacity retention rate reached 80% was recorded.

[0189] 2. -10℃ low temperature cycle performance test

[0190] At -10°C, the batteries of each Example and Comparative Example were charged at a constant current of 0.2C to a voltage upper limit of 3.8V, then charged at a constant voltage to a current of 0.05C. The batteries were allowed to rest for 5 minutes and then 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 at this time was recorded as the discharge capacity of the first cycle, D1. The discharge capacity of the nth cycle was Dn, and the capacity retention rate was Dn / D1. The number of cycles at which the battery capacity retention rate reached 80% was recorded.

[0191] The performance test results of the above embodiments and comparative examples are shown in Table 2.

[0192] Table 2

[0193] Comparing the results of Examples 1-24 and Comparative Examples 1-4, it can be seen that by simultaneously adding the first, second, and third additives to the electrolyte provided by this application, both the high-temperature and low-temperature performance of the secondary battery can be improved. Furthermore, comparing the results of Examples 1-21 and Examples 22-23, it can be seen that by adjusting the amounts of the first, second, and third additives so that the amounts of the three additives satisfy 2% ≤ (A + C) / B ≤ 120%, both the high-temperature and low-temperature performance of the secondary battery can be improved.

[0194] The main difference between Example 24 and Example 1 and Examples 10-11 is that: EC is not added to the electrolyte of Example 24; EC has a higher dielectric constant, can dissociate lithium salts, improve the conductivity of the electrolyte, and can also undergo a reduction reaction to obtain a product Li2CO3 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, it may cause the electrolyte viscosity to be high and the conductivity to decrease, affecting the low-temperature performance, and EC can improve the low-temperature performance of the battery at the same time by combining with the third additive; therefore, based on the comparison of the results of Example 24 with Examples 1 and Examples 10-11, it can be seen that adding EC to the electrolyte can further improve the high-temperature performance and low-temperature performance of the battery cell.

[0195] The above description of the various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced with each other and will not be repeated herein for the sake of brevity.

[0196] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. An electrolyte, comprising: A first additive, wherein the first additive comprises an inorganic salt containing fluorine element; The second additive comprises a compound containing an unsaturated bond, wherein the reduction potential of the compound containing an unsaturated bond is ≥ 0.8 V (Li + / Li); as well as The third additive includes a compound containing an amide group.

2. The electrolyte according to claim 1, wherein the mass proportion of the first additive in the electrolyte is A%, the mass proportion of the second additive in the electrolyte is B%, the mass proportion of the third additive in the electrolyte is C%, and A, B and C satisfy: 2%≤(A+C) / B≤120%; Optionally, 5%≤(A+C) / B≤55%.

3. The electrolyte of claim 2, wherein 0.01≤A≤1.

4. The electrolyte according to any one of claims 2 to 3, wherein 0.5≤B≤10.

5. The electrolyte according to any one of claims 2 to 4, wherein 0.01≤C≤0.

1.

6. The electrolyte according to any one of claims 1 to 5, wherein the mass proportion of the fluorine element in the inorganic salt is ≥ 8%; Optionally, the first additive includes one or more of difluorophosphates, tetrafluoroborate and fluorosulfonate containing an M element, and the M element includes one or more of Li, Na, K and Cs.

7. The electrolyte according to any one of claims 1 to 6, wherein the second additive comprises a cyclic compound containing an unsaturated bond; Optionally, the second additive includes one or more of vinylene carbonate, 1,3-propane sultone, vinyl sulfate and vinyl bissulfate.

8. The electrolyte according to any one of claims 1 to 7, wherein the third additive comprises one or more of the compounds represented by the following formulae (I) and (II): in, R1 and R2 each independently include any one of hydrogen, methyl and ethyl, and R3 includes C3-C6 alkylene; Optionally, the third additive includes one or more of N,N-dimethylformamide and N-methylpyrrolidone.

9. The electrolyte according to any one of claims 2 to 8, wherein the electrolyte further comprises a cyclic ester solvent; Optionally, the cyclic ester solvent includes one or more of ethylene carbonate and propylene carbonate; Further optionally, the mass proportion of the ethylene carbonate in the electrolyte is D%, and C and D satisfy 0.01%≤C / D≤1%; Further optionally, 5≤D≤35.

10. The electrolyte according to any one of claims 1 to 9, wherein the electrolyte further comprises a lithium salt; Optionally, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide; Optionally, the lithium salt accounts for 5%-15% by mass in the electrolyte.

11. A secondary battery comprising the electrolyte according to any one of claims 1 to 10.

12. The secondary battery according to claim 11, wherein the secondary battery comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material; the surface density of the negative electrode active material layer is Eg / m 2 , the specific surface area of ​​the negative electrode active material is Fm 2 / g, the mass proportion of the negative electrode active material in the negative electrode active material layer is L; The mass proportion of the second additive in the electrolyte is B%; The B, E, F and L satisfy: 0.5%≤B / (E*F*L)≤12%. 13 . The secondary battery according to claim 12 , wherein 80≤E≤150. 14 . The secondary battery according to claim 12 , wherein 0.5≤F≤5. 15 . The secondary battery according to claim 12 , wherein 93%≤L≤98%. 16 . An electrical device comprising at least one of the electrolyte according to claim 1 and the secondary battery according to claim 11 .

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