Electrolyte solution, secondary battery, and electric device

Abstract

The invention relates to an electrolyte, a secondary battery and an electric device. The electrolyte comprises a first additive, a second additive and a third additive, the first additive comprises inorganic salt containing elements; the second additive comprises a compound containing an unsaturated bond, and the reduction potential of the compound containing the unsaturated bond is larger than or equal to 0.8 V (Li < + > / Li); the third additive comprises a compound containing an amide group; by adding the first additive, the second additive and the third additive into the electrolyte, the high-temperature performance and the low-temperature performance of the secondary battery can be improved at the same time.

Description

Technical Field

[0001] 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

[0002] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] In recent years, lithium-ion batteries have the advantages of high open-circuit voltage, high energy density, long service life, no memory effect, no pollution and low self-discharge. They are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. With the development of lithium-ion batteries, higher requirements are also put forward for their performance. However, in related technologies, it is difficult for lithium-ion batteries to take into account both high-temperature performance and low-temperature performance at the same time, which limits the application of lithium-ion batteries to a certain extent. Summary of the invention

[0004] The present application provides an electrolyte that can take into account both the high-temperature performance and the low-temperature performance of a secondary battery, and also provides a secondary battery and an electrical device.

[0005] In order to achieve the above object, the first aspect of the present application provides an electrolyte, the electrolyte comprising:

[0006] A first additive, wherein the first additive comprises an inorganic salt containing fluorine element;

[0007] 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

[0008] The third additive includes a compound containing an amide group.

[0009] The second additive includes a reduction potential ≥ 0.8V (Li + / Li) and containing unsaturated bonds, which can undergo a reduction reaction on the negative electrode surface to generate polymers during battery formation, forming a SEI film to passivate the negative electrode, thereby avoiding the solvent and the negative electrode from continuously causing side reactions in direct contact, achieving an excellent passivation effect on the negative electrode and improving the high-temperature performance of the battery. The first additive includes a compound containing fluorine, which will form an SEI film containing F-type inorganic compounds when decomposed at the negative electrode, which has a wider band gap and higher ionic conductivity, can improve the ion conductivity of the SEI film, reduce the lithium ion diffusion barrier, facilitate lithium ion transportation, and reduce the low-temperature interface charge transfer impedance, thereby improving the low-temperature performance. The lithium ions in the electrolyte will combine with the solvent molecules and anions to form solvated lithium ions. When charging, the solvated lithium ions migrate to the negative electrode. When reaching 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, which 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.

[0010] 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%, the mass proportion of the third additive in the electrolyte is C%, and 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 mass percentage of the fluorine element in the inorganic salt is ≥ 8%;

[0016] 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.

[0017] In some embodiments, the second additive includes a cyclic compound containing an unsaturated bond;

[0018] Optionally, the second additive includes one or more of vinylene carbonate, 1,3-propane sultone, vinyl sulfate and vinyl bissulfate.

[0019] In some embodiments, the third additive includes one or more of the compounds represented by the following formulae (I) and (II):

[0020]

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

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

[0026] Further optionally, 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 bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide;

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

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

[0031] The secondary battery of the present application has 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, 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;

[0033] The mass proportion of the second additive in the electrolyte is B%;

[0034] The B, E, F and L satisfy: 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 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.

[0039] 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.

[0040] 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 specification, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to better describe and illustrate the embodiments or examples provided by the present application, reference may be made to one or more drawings. The additional details or examples used to describe the 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 of these applications currently understood. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0042] Figure 1 It is a schematic diagram of a battery cell according to an embodiment of the present application.

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

[0044] Figure 3 It is a schematic diagram of a battery module according to one embodiment of the present application.

[0045] Figure 4 A schematic diagram of a battery pack according to an embodiment of the present application.

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

[0047] Figure 6FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0048] Description of reference numerals:

[0049] 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 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 structure 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 descriptions 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 a 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 a special range. The scope limited in this way can be including end values ​​or excluding end values, and any end value can be included or not included independently, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 listed, and if the maximum range values ​​3,4 and 5 are also listed, 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 real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation for these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed 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 the present application, "plurality", "multiple" and the like, unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" means one or greater 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] Reference to "embodiments" herein means 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 the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. The "implementation methods" mentioned herein have a similar understanding.

[0055] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which each step is written does not mean 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 internal logic. If there is no special explanation, all steps of the present application can 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 also include step (c), indicating that step (c) can 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 the present application, in the open technical features or technical solutions described by the words "contain", "include", "comprise", etc., 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 including 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 not only includes a1, a2 and a3, but also includes other members". In the present 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, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

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

[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 improve both the high temperature performance and the low temperature performance of a 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 ≥ 0.8V (Li + / Li) and containing unsaturated bonds, which can undergo a reduction reaction on the negative electrode surface to generate polymers during battery formation, forming a SEI film to passivate the negative electrode, thereby avoiding the solvent and the negative electrode from continuously causing side reactions in direct contact, achieving an excellent passivation effect on the negative electrode and improving the high-temperature performance of the battery. The first additive includes a compound containing fluorine, which will form an SEI film containing F-type inorganic compounds when decomposed at the negative electrode, which has a wider band gap and higher ionic conductivity, can improve the ion conductivity of the SEI film, reduce the lithium ion diffusion barrier, facilitate lithium ion transportation, and reduce the low-temperature interface charge transfer impedance, thereby improving the low-temperature performance. The lithium ions in the electrolyte will combine with the solvent molecules and anions to form solvated lithium ions. When charging, the solvated lithium ions migrate to the negative electrode. When reaching 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, which 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%, and 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 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 obtained 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 obtained 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 obtained after formation or in the battery cell after further charge and discharge cycles. "Battery cell obtained after formation" refers to a fresh battery cell obtained after formation, which has not been further charged and discharged.

[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; during the battery cycle, as the negative electrode deintercalates and releases 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 improvement effect on 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 may 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 above values. When the mass proportion (B%) of the second additive in the electrolyte is less than 1%, the high temperature performance of the secondary battery may not be effectively improved; since the second additive will increase the battery impedance after forming the SEI film, especially the increase in low temperature impedance is more obvious, when the mass proportion (B%) of the second additive in the electrolyte is higher than 10%, it may be detrimental to the 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 lower than 0.01%, the low temperature performance of the secondary battery may not be effectively improved; due to the poor electrochemical stability of the third additive itself, it is easy to cause reduction side reactions at the negative electrode, affecting the stability of the SEI film, and the reduction side reactions are aggravated at high temperatures. Therefore, when the mass proportion (C%) of the third additive in the electrolyte is higher than 0.1%, the high temperature cycle life of the battery may be affected.

[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 of JY / T0575-2020.

[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 GB / T9722-2006 chemical reagent gas chromatography method.

[0070] In some embodiments, the mass percentage of fluorine in the inorganic salt is ≥ 8%; for example, it can be but 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 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 film, which is beneficial to 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 inductively coupled plasma emission spectrometry analysis method JY / T 0567-2020.

[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 of the compounds represented by the following formulae (I) and (II):

[0077]

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

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

[0080] In some embodiments, the electrolyte further comprises a cyclic ester solvent.

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

[0082] 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.

[0083] 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 will occupy the inner layer of the electrolyte solvation structure, the high dielectric constant also increases the orientation force between molecules, which leads to an increase in the phase transition point and viscosity of the electrolyte; the viscosity increases sharply at low temperatures and affects the desolvation process of lithium ions, and the desolvation process is the rate-determining step of the charge transfer of 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 be deteriorated; 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 dynamics; therefore, the amount of ethylene carbonate and the third additive can be adjusted to take into account both the low-temperature performance and the high-temperature performance of the battery. When C / D is within the above range, the low-temperature performance and high-temperature performance of the battery are both good; when C / D is lower than the above range, the low-temperature performance of the battery may be limited; when C / D is higher than the above range, the high-temperature performance of the battery may be limited.

[0084] In some possible embodiments, 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 a range between any two of the above values. When the mass percentage of ethylene carbonate in the electrolyte is less than 5%, the effect of improving the conductivity of the electrolyte may be limited; when the mass percentage of ethylene carbonate in the electrolyte is higher than 35%, the viscosity of the electrolyte is large and the low-temperature conductivity is low, which may deteriorate the low-temperature performance of the battery.

[0085] 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.

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

[0087] In some embodiments, the electrolyte further comprises a lithium salt.

[0088] Optionally, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

[0089] In some possible embodiments, the mass proportion of lithium salt in the electrolyte is 5%-15%; for example, it can be but 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 ions in the electrolyte and acts as a transmission medium during the charge and discharge process; as the concentration of lithium salt increases, the number of lithium ions in the electrolyte increases, and the conductivity of the electrolyte increases. When the mass proportion of lithium salt in the electrolyte is within the above range, the conductivity of the electrolyte is high. When the mass proportion of lithium salt in the electrolyte is higher than the above range, the viscosity of the electrolyte will increase too much, the lithium ion transmission resistance will increase, and the conductivity of the electrolyte will decrease instead.

[0090] It should be noted that the mass proportion of lithium salt in the electrolyte mentioned above refers to the mass proportion of lithium salt in the electrolyte in the battery cell obtained after formation or in the battery cell after further charge and discharge cycles. "Battery cell obtained after formation" refers to fresh battery cells produced after formation, which have not been further charged and discharged.

[0091] 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.

[0092] In some of the 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 difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0093] In some embodiments, the solvent in the electrolyte may also 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), ethylene 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, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0094] In some of the 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 performance of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high or low temperature performance of the battery, etc.

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

[0096] 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.

[0097] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte in the electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0098] Negative electrode

[0099] 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.

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

[0102] It should be noted that the mass proportion of the negative electrode active material in the negative electrode active material layer mentioned above refers to the mass proportion of the 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 and discharge cycles. "Battery cell obtained after formation" refers to a fresh battery cell obtained after formation, which has not been further charged and discharged.

[0103] The active material is a porous material, and its real surface and specific surface area are larger. E*F*L represents the real surface area of ​​the active material per unit surface area on the positive sheet. The second additive is mainly reduced by electrons to form a film on the specific surface of the negative electrode active material. The larger the specific surface area, the more second additives are needed. 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 at the same time; 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 much, 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 not enough to fully form a film on the specific surface of the negative electrode material, and the exposed active sites will continue to react with the electrolyte, and the high-temperature cycle performance of the battery may be affected.

[0104] In some embodiments, 80≤E≤150; for example, E may 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.

[0105] 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 unit area V (100cm 2) is immersed in DMC for 48 hours, then the electrode is dried at 60°C and -80 kPa, 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.

[0106] 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.

[0107] 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 of GB / T 19587-2017.

[0108] 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.

[0109] As an example, the mass proportion of the above-mentioned negative electrode active material in the negative electrode active material layer can be measured by the following method:

[0110] 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; refer to EPA6010D-2018 inductively coupled plasma spectrometry to test the lithium content in the negative electrode film layer, 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.

[0111] In some of the 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.

[0112] In some of the embodiments, the negative electrode active material may adopt the negative electrode active material for batteries 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. The silicon-based material may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include one or more of elemental tin, tin oxide compounds, 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.

[0113] 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).

[0114] 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.

[0115] In some of the embodiments, the negative electrode active material layer may further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0116] In some of the 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 surface 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 on a single surface of the negative electrode collector or on both 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 2000-10000mPa·s. The compaction density of the negative electrode sheet can be 1.0g / cm 3 -2.0g / cm 3 .

[0117] Positive electrode

[0118] 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.

[0119] 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).

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

[0121] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charging and discharging 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 content of Li 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 content of Li in the positive electrode material contained in the plate usually changes. Among them, the content of Li can be measured by molar content, but is not limited to this. Regarding "the content of Li 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 the new material obtained by appropriate modification on the basis of the listed positive electrode materials is also within the scope of the positive electrode material. The aforementioned appropriate modification refers to the acceptable modification method for the positive electrode material, and non-limiting examples include coating modification.

[0122] In the list of positive electrode materials in this application, the content of oxygen (O) is only a theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual content of O will fluctuate. Among them, the content of O can be measured by molar content, but is not limited to this.

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

[0124] In some of the 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.

[0125] In some of the embodiments, the positive electrode active material may also use a positive electrode active material for a battery known in the art. 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, the present application is not limited to these materials, and other traditional 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. Among them, 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 lithium-containing phosphates with an olivine structure 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.

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

[0127] 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.

[0128] In some of the embodiments, the positive electrode sheet can be prepared in the following manner: 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 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 one of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode 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 5000-25000mPa·s. When applying the positive electrode slurry, the coating unit area density based on dry weight (excluding solvent) can be 15-35 mg / cm 2 The compaction density of the positive electrode can be 2-3g / cm 3 .

[0129] Isolation film

[0130] The present application has no particular limitation on the type of isolation membrane, and any known porous isolation membrane with good chemical stability and mechanical stability can be selected.

[0131] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane 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 isolation film has a thickness of 6-40 μm, and optionally 12-20 μm.

[0133] In some of the embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly by a winding process or a lamination process.

[0134] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0135] 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 package, such as a bag-type soft package. The material of the soft package can be plastic, and further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

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

[0137] In this application, unless otherwise specified, "battery cell" refers to a basic unit that can realize the mutual conversion of chemical energy and electrical energy, and further, generally speaking, at least includes a positive electrode sheet, a negative electrode sheet and an electrolyte. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0138] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 1 The battery cell 5 is a square structure as an example.

[0139] In some of these embodiments, reference Figure 2, the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate 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 form 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 infiltrated 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.

[0140] The secondary battery may be a battery module or a battery pack.

[0141] The battery module includes at least one battery cell. The number of battery cells contained in the battery module can be one or more, and those skilled in the art can select a suitable number according to the application and capacity of the battery module.

[0142] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0143] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0144] In some of the 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 a suitable number according to the application and capacity of the battery pack.

[0145] Figure 4 and Figure 5 1 is a battery pack 1 as an example. Figure 4 and Figure 5 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0146] In addition, the present application also provides an electrical device, which includes a secondary battery provided by 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 may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto. Among them, the mobile device may be, for example, a mobile phone, a laptop computer, etc.; the electric vehicle may be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but are not limited thereto.

[0147] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0148] Figure 6 The power consumption device 6 is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the power consumption device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module can be used.

[0149] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0150] Example

[0151] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If the techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0152] 1. Preparation of secondary batteries

[0153] Example 1

[0154] 1). Preparation of positive electrode

[0155] 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 a positive electrode sheet.

[0156] 2). Preparation of negative electrode

[0157] Artificial graphite: carbon black (SP): styrene-butadiene rubber (SBR): sodium hydroxymethyl cellulose (CMC) are mixed in a mass ratio of 96:1.5:1.5:1, deionized water is added, and a uniformly dispersed negative electrode slurry is obtained by stirring. The negative electrode slurry is evenly coated on both surfaces of the copper foil, and the negative electrode sheet is obtained by drying, cold pressing, and cutting. The specific surface area of ​​the negative electrode active material artificial graphite is 1m 2 / g, the coating unit surface density of the negative electrode active material is 90g / m 2 .

[0158] 3). Isolation film

[0159] A polyethylene film is used as the isolation film.

[0160] 4). Preparation of electrolyte

[0161] In an argon atmosphere 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 the second additive), lithium difluorophosphate (LiPO2F2, as the first additive), N-methylpyrrolidone (NMP, as the third additive), and lithium hexafluorophosphate (LiPF6, as lithium salt) were mixed and dissolved in percentage by mass to obtain an electrolyte.

[0162] 5). Preparation of battery cells

[0163] The positive electrode sheet, the negative electrode sheet and the separator are made into an electrode assembly through a winding process or a lamination process, and placed in a casing made of an aluminum shell, an aluminum-plastic film, etc. After the above-mentioned electrolyte is injected, left to stand at high temperature, formed, and divided into volumes, a secondary battery is obtained.

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

[0165] Example 2-24

[0166] The difference between the preparation method of the secondary battery in Examples 2-24 and the preparation method of the secondary battery in Example 1 mainly lies in: 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.

[0167] Comparative Example 1

[0168] In Comparative Example 1, the first additive, the second additive and the third additive were not added, as shown in Table 1 for details.

[0169] Comparative Example 2

[0170] The second additive was not added to the electrolyte of Comparative Example 2, and only the first additive and the third additive were added, as shown in Table 1 for details.

[0171] Comparative Example 3

[0172] The first additive was not added to the electrolyte of Comparative Example 3, and only the second additive and the third additive were added, as shown in Table 1 for details.

[0173] Comparative Example 4

[0174] The third additive was not added to the electrolyte of Comparative Example 4, and only the first additive and the second additive were added, as shown in Table 1 for details.

[0175] The secondary batteries prepared in the above embodiments and comparative examples were tested for parameters including at least the following items:

[0176] 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), as shown in Table 1 for details.

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

[0178] Table 1

[0179]

[0180]

[0181] Among them, 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 divinyl sulfate, NMP represents N-methylpyrrolidone, DMP represents N,N-dimethylformamide, E represents the coating unit surface 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.

[0182] The mass proportion of the first additive mentioned above in the electrolyte is determined by referring to the ion chromatography analysis method JY / T 0575-2020.

[0183] 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 of GB / T9722-2006.

[0184] The mass proportion of EC in the electrolyte and the mass ratio of the third additive to ethylene carbonate (C / D) mentioned above are determined by referring to the chemical reagent gas chromatography method of GB / T9722-2006.

[0185] The mass proportion of the above-mentioned lithium salt in the electrolyte is determined by referring to the ion chromatography analysis method JY / T 0575-2020.

[0186] The specific surface area of ​​the negative electrode active material mentioned above is measured with reference to the gas adsorption BET method of GB / T 19587-2017.

[0187] The coating unit area density of the negative electrode active material mentioned above was determined by the following method: the battery was discharged at 0.1C to 2.0V, the battery was disassembled, and the unit area V (100cm 2 ) was immersed in DMC for 48 hours, 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.

[0188] 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; refer to EPA6010D-2018 inductively coupled plasma spectrometry to test the lithium content in the negative electrode film layer, 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.

[0189] 2. Battery Cell Performance Test

[0190] 1.60℃ high temperature cycle performance determination

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

[0192] 2. -10℃ low temperature cycle performance test

[0193] At -10°C, the batteries of the embodiments and comparative examples were charged at a constant current of 0.2C to an upper voltage limit of 3.8V, and then charged at a constant voltage to a current of 0.05C; the batteries were left to stand for 5 minutes, and discharged at a constant current of 1 / 3C to 2.0V. This was the first charge and discharge cycle of the battery, and the discharge capacity of this time was recorded as the discharge capacity D1 of the first cycle of the battery. 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] From the comparison of the results of Examples 1-24 and Comparative Examples 1-4, it can be seen that by adding the first additive, the second additive and the third additive simultaneously to the electrolyte provided by the present application, the high temperature performance and the low temperature performance of the secondary battery can be improved simultaneously. Further, from the comparison of the results of Examples 1-21 and Examples 22-23, it can be seen that by adjusting the amounts of the first additive, the second additive and the third additive, the amounts of the three additives satisfy 2%≤(A+C) / B≤120%, the high temperature performance and the low temperature performance of the secondary battery can be improved simultaneously.

[0199] The main difference between Example 24 and Example 1 and Examples 10-11 is that: EC is not added to the electrolyte in 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, thereby improving 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, while 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.

[0200] The above description of various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced to each other, and for the sake of brevity, they will not be repeated herein.

[0201] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. An electrolyte, characterized in that: The electrolyte comprises: 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, characterized in that 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 according to claim 2, characterized in that 0.01≤A≤1。 4. The electrolyte according to any one of claims 2 to 3, characterized in that 0.5≤B≤10。 5. The electrolyte according to any one of claims 2 to 4, characterized in that 0.01≤C≤0.1。 6. The electrolyte according to any one of claims 1 to 5, characterized in that The mass percentage 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, characterized in that The second additive includes 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, characterized in that The third additive includes one or more of the compounds represented by the following formulas (I) and (II): Wherein, 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, characterized in that 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, characterized in that 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, characterized in that: 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 plate, the negative electrode plate 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, characterized in that: 80≤E≤150。 14. The secondary battery according to any one of claims 12 to 13, characterized in that: 0.5≤F≤5。 15. The secondary battery according to any one of claims 12 to 14, characterized in that: 93％≤L≤98％。 16. An electrical device, characterized in that: The invention comprises at least one of the electrolyte according to any one of claims 1 to 10 and the secondary battery according to any one of claims 11 to 15.

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