Electrolyte and preparation method thereof, secondary battery and electric device

Abstract

The invention relates to an electrolyte and a preparation method thereof, a secondary battery and an electric device. The electrolyte comprises an electrolyte salt, a first solvent and a composite flame retardant, the composite flame retardant comprises a flame retardant and a gel polymer, the flame retardant is located in internal pores of the gel polymer, the electrolyte salt is dissolved in the first solvent, and the composite flame retardant is dispersed in the first solvent. The electrolyte is applied to the secondary battery, the service life of the battery is prolonged, and the damage degree caused by thermal runaway of the battery is reduced.

Description

Technical Field

[0001] The present application relates to the field of new energy technology, and in particular to an electrolyte and a preparation method thereof, 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, the application scope of secondary batteries such as lithium-ion batteries has become increasingly wide. For example, 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. The electrolyte is an important component of lithium-ion batteries. At present, the commercial electrolyte of power batteries is flammable. When the battery has thermal runaway, the combustion of the electrolyte will increase the safety hazard. With the great development of lithium-ion batteries, it is very important to reduce the degree of damage caused by thermal runaway of batteries. Summary of the invention

[0004] The present application provides an electrolyte capable of reducing the degree of damage caused by thermal runaway of a battery, a preparation method thereof, a secondary battery, and an electrical device.

[0005] In order to achieve the above-mentioned objectives, the first aspect of the present application provides an electrolyte, comprising an electrolyte salt, a first solvent and a composite flame retardant, wherein the composite flame retardant comprises a flame retardant and a gel polymer, the flame retardant is located in the internal pores of the gel polymer, the electrolyte salt is dissolved in the first solvent, and the composite flame retardant is dispersed in the first solvent.

[0006] Therefore, the above-mentioned electrolyte of the present application adds the flame retardant and the gel polymer to the electrolyte in the form of a composite flame retardant, the composite flame retardant is dispersed as a whole in the first solvent of the electrolyte, and the flame retardant in the composite flame retardant is located in the internal pores of the gel polymer, so that the flame retardant can be inhibited from directly contacting the surface of the electrode and inhibiting the problem of side reactions of the flame retardant on the surface of the electrode; at the same time, when the battery temperature is too high, the gel polymer of the composite flame retardant in the electrolyte can be further cured at high temperature to form a cross-linked cured polymer to block the conduction and play a preliminary role in preventing thermal runaway, especially in the overcharging stage; as the temperature continues to rise, the battery cell fails and burns, and the flame retardant in the composite flame retardant absorbs the free radicals generated during the combustion process, thereby blocking the continuous reaction of the combustion, and playing a further role in flame retardancy and preventing thermal runaway. Such multi-faceted synergy is conducive to extending the battery life and reducing the degree of damage caused by thermal runaway of the battery.

[0007] In some embodiments of the present application, the electrolyte satisfies at least one of the following conditions:

[0008] (1) In the electrolyte, the mass content of the composite flame retardant is 1% to 10%;

[0009] (2) In the composite flame retardant, the mass content of the flame retardant is 30% to 70%;

[0010] (3) In the electrolyte solution, the concentration of the electrolyte salt is 0.5 to 1.5 mol / L.

[0011] In some embodiments of the present application, the electrolyte satisfies at least one of the following conditions:

[0012] (1) In the electrolyte, the mass content of the composite flame retardant is 2% to 6%;

[0013] (2) In the components of the composite flame retardant other than the solvent, the mass content of the flame retardant is 40% to 60%;

[0014] (3) In the electrolyte solution, the concentration of the electrolyte salt is 0.8 to 1.2 mol / L.

[0015] In some embodiments of the present application, the electrolyte satisfies at least one of the following conditions:

[0016] (1) The flame retardant includes a phosphate flame retardant,

[0017] (2) The components of the gel polymer include a main polymer and a second solvent;

[0018] (3) The dynamic viscosity of the electrolyte is 3.5 to 5 cp.

[0019] In some embodiments of the present application, the electrolyte satisfies at least one of the following conditions:

[0020] (1) The flame retardant comprises at least one of halogenated phosphates, halogenated phosphites and halogenated phosphonates;

[0021] (2) the host polymer has a carbonyl group;

[0022] (3) The second solvent includes a carbonate solvent.

[0023] In some embodiments of the present application, the electrolyte satisfies at least one of the following conditions:

[0024] (1) The flame retardant comprises at least one of triethyl 2-fluoro-2-phosphoryl acetate and bis(2,2,2-trifluoroethyl)methyl phosphate;

[0025] (2) The host polymer includes an ester polymer.

[0026] In some embodiments of the present application, the electrolyte satisfies at least one of the following conditions:

[0027] (1) The electrolyte salt includes at least one of an electrolyte lithium salt and an electrolyte sodium salt;

[0028] (2) the first solvent includes at least one of an ester solvent, an ether solvent and a sulfone solvent;

[0029] (3) The ionic conductivity of the electrolyte is 4 to 10 mS / cm.

[0030] The second aspect of the present application also provides a method for preparing any of the above-mentioned electrolytes, comprising the following steps:

[0031] The flame retardant and the raw material for preparing the gel polymer are mixed and subjected to a curing reaction to obtain the composite flame retardant;

[0032] The composite flame retardant, the electrolyte salt and the first solvent are stirred and mixed to form the electrolyte solution.

[0033] In some embodiments of the present application, the stirring step is controlled so that the dynamic viscosity of the electrolyte is controlled within a range of 3.5 to 5 cp.

[0034] In some embodiments of the present application, the raw materials for preparing the gel polymer include polymer monomers and initiators.

[0035] In some embodiments of the present application, the preparation method satisfies at least one of the following conditions:

[0036] (1) The polymer monomer includes an ester monomer;

[0037] (2) The mass ratio of the polymer monomer to the flame retardant is (1-5):1;

[0038] (3) The mass ratio of the polymer monomer to the initiator is (10-20):1.

[0039] A second aspect of the present application provides a secondary battery, comprising a positive electrode plate, a negative electrode plate and an electrolyte as described above, wherein the electrolyte is disposed between the positive electrode plate and the negative electrode plate.

[0040] In some embodiments of the present application, the negative electrode plate includes a carbon-based negative electrode active material; optionally, the carbon-based negative electrode active material includes at least one of artificial graphite, natural graphite, soft carbon and hard carbon.

[0041] A third aspect of the present application provides an electrical device, comprising any of the secondary batteries described above.

[0042] 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.

[0043] 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

[0044] 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:

[0045] Figure 1 It is a schematic diagram of a battery cell according to an embodiment of the present application.

[0046] Figure 2 for Figure 1 An exploded view of a battery cell according to an embodiment of the present application is shown.

[0047] Figure 3 It is a schematic diagram of a battery module according to one embodiment of the present application.

[0048] Figure 4 A schematic diagram of a battery pack according to an embodiment of the present application.

[0049] Figure 5 for Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0050] Figure 6 FIG. 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.

[0051] Description of reference numerals:

[0052] 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

[0053] Below, some embodiments of the electrolyte and its preparation method, 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 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.

[0054] "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.

[0055] 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.

[0056] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] The secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0062] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, and an electrolyte. The electrolyte is located between the positive electrode sheet and the negative electrode sheet. During the battery charging and discharging process, active ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet.

[0063] Electrolyte

[0064] The electrolyte is located between the positive electrode sheet and the negative electrode sheet, and plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet.

[0065] An embodiment of the present application provides an electrolyte, including an electrolyte salt, a first solvent and a composite flame retardant, wherein the composite flame retardant includes a flame retardant and a gel polymer, the flame retardant is located in the internal pores of the gel polymer, the electrolyte salt is dissolved in the first solvent, and the composite flame retardant is dispersed in the first solvent.

[0066] In order to achieve the flame retardant effect, the traditional technology is to directly add the flame retardant and disperse it in the electrolyte. This method is simple and easy, but during the operation of the battery, the flame retardant components in the prepared electrolyte will migrate to the surface of the electrode due to the action of the electric field. Due to the high reducing property of the electrode surface, side reactions will occur. For example, phosphate flame retardants are prone to produce gas, which will cause the battery cell to swell, thereby affecting the long-term life of the battery.

[0067] It is worth noting that the gel polymer in the composite flame retardant includes a polymer and a second solvent filled in the polymer, and the gel polymer is in a swollen state in the electrolyte. The polymer in the gel polymer is a mesh structure with certain physical support and structural stability. When the flame retardant is dispersed in the gel polymer formed by the polymer, the flame retardant is confined in the internal pores of the gel polymer, and the polymer framework can inhibit the free diffusion of the flame retardant, thereby preventing the flame retardant from diffusing in the liquid electrolyte to the electrode surface to cause electrochemical side reactions.

[0068] Without wishing to be limited to any theory, the above-mentioned electrolyte of the present application adds the flame retardant and the gel polymer to the electrolyte in the form of a composite flame retardant, the composite flame retardant is dispersed as a whole in the first solvent of the electrolyte, and the flame retardant in the composite flame retardant is located in the internal pores of the gel polymer, so that the flame retardant can be inhibited from directly contacting the surface of the pole piece, and the problem of the flame retardant having side reactions on the surface of the pole piece can be inhibited; at the same time, when the battery temperature is too high, the gel polymer of the composite flame retardant in the electrolyte can be further cured at high temperature to form a cross-linked cured polymer to block the conduction and play a preliminary role in preventing thermal runaway, especially in the overcharging stage; as the temperature continues to rise, the battery cell fails and burns, and the flame retardant in the composite flame retardant absorbs the free radicals generated in the combustion process, thereby blocking the continuous reaction of the combustion, and playing a further role in flame retardancy and preventing thermal runaway. Such multi-faceted synergy is conducive to extending the battery life and reducing the degree of damage caused by thermal runaway of the battery.

[0069] In some embodiments, the first solvent includes at least one of an ester solvent, an ether solvent, and a sulfone solvent.

[0070] As an example, the ester solvent may include at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), γ-butyrolactone (BL), 1,3-propane sultone (1,3-PS), methyl formate, methyl acetate, ethyl acetate (EA), propyl acetate, methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB) and ethyl butyrate (EB).

[0071] As an example, the ether solvent may include at least one of ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TRGDME), tetraethylene glycol dimethyl ether (TEGDME), and 1,3-dioxolane (DOL).

[0072] As an example, the sulfone solvent includes one or more of dimethyl sulfoxide (DMSO), sulfolane, methyl ethyl sulfone, and diethyl sulfone.

[0073] In some embodiments, in the electrolyte, the mass content of the composite flame retardant is 1% to 10%, optionally 2% to 6%, optionally 3% to 5%. As an example, the mass content of the composite flame retardant can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%. Controlling the composite flame retardant in the electrolyte within this range can achieve a good ion transmission effect while taking into account a good flame retardant effect.

[0074] In some embodiments, in the components of the composite flame retardant other than the solvent, the mass content of the flame retardant is 30% to 70%, and can be optionally 40% to 60%. As an example, in the composite flame retardant, the mass content of the flame retardant can be 30%, 40%, 50%, 60%, 70%. The components other than the solvent in the composite flame retardant include the flame retardant and the main polymer in the gel polymer, but do not include the solvent.

[0075] The mass content of the composite flame retardant in the electrolyte and the mass content of the flame retardant in the composite flame retardant can be analyzed and determined by conventional organic analysis methods such as nuclear magnetic resonance, liquid chromatography, gas chromatography-mass spectrometry, and plasma chromatography.

[0076] The gel polymer in the composite flame retardant provides a framework for the flame retardant, binds the flame retardant molecules, and prevents the flame retardant from diffusing to the surface of the electrode to cause electrochemical side reactions. Due to the limited internal space of the polymer and the need to take into account the life of the battery cell, the mass content of the flame retardant in the composite flame retardant is further controlled within the above range to take into account both good flame retardant properties and battery cell life.

[0077] In some embodiments, the flame retardant includes a phosphate flame retardant, such as a halogenated phosphate flame retardant. Further, the flame retardant includes at least one of a halogenated phosphate, a halogenated phosphite, and a halogenated phosphonate; optionally, the flame retardant includes at least one of triethyl 2-fluoro-2-phosphorylacetate and bis(2,2,2-trifluoroethyl)methyl phosphate. The flame retardant containing both halogen and P flame retardant elements has a better flame retardant effect.

[0078] In some embodiments, the components of the gel polymer include a main polymer and a second solvent, wherein the main polymer is a cross-linked polymer.

[0079] Optionally, the main polymer has a carbonyl group (C=O); the carbonyl group can have good compatibility with the electrolyte salt in the electrolyte, ensuring that the electrolyte can maintain a high ionic conductivity and a good interface contact effect, so that the gel polymer can build a stable interface at the negative electrode interface, promote uniform lithium deposition at the negative electrode and inhibit the growth of lithium dendrites. It is understood that the main polymer includes but is not limited to polymers with carbonyl groups, and can also be polymers without carbonyl groups, such as polyolefins such as polydivinylbenzene.

[0080] Optionally, the main polymer includes an ester polymer; more optionally, the main polymer includes a carboxylate polymer; more optionally, the polymer includes at least one of polyethylene glycol dimethacrylate, polypentaerythritol tetraacrylate and ethylene glycol dimethacrylate-pentaerythritol tetraacrylate copolymer.

[0081] Optionally, the second solvent comprises a carbonate solvent.

[0082] In some embodiments, in the electrolyte, the concentration of the electrolyte salt is 0.5-1.5 mol / L, and can be 0.8-1.5 mol / L, 0.8-1.2 mol / L. As an example, in the electrolyte, the concentration of the electrolyte salt can be 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.5 mol / L.

[0083] In some of these embodiments, the electrolyte salt includes at least one of an electrolyte lithium salt and an electrolyte sodium salt.

[0084] In some of the embodiments, the electrolyte lithium salt in the electrolyte salt may also include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorobisoxalate phosphate (LiDFOP) and lithium tetrafluorooxalate phosphate (LiTFOP).

[0085] In some of the embodiments, the electrolyte sodium salt in the electrolyte salt may also include one or more of sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium hexafluorophosphate (NaPF6), sodium hexafluoroarsenate (NaAsF6), sodium trifluoroacetate (CF3COONa), sodium tetraphenylborate (NaB(C6H5)4), sodium trifluoromethylsulfonate (NaSO3CF3), sodium bis(fluorosulfonyl)imide (Na[(FSO2)2N]) or sodium bis(trifluoromethylsulfonyl)imide (Na[(CF3SO2)2N]).

[0086] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0087] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0088] In some embodiments, the dynamic viscosity of the electrolyte is between 3.5 and 5 cp, for example, 3.5 cp, 4 cp, 4.5 cp, and 5 cp; 3.5 cp to 4 cp may be selected. The dynamic viscosity of the electrolyte is related to the degree of crosslinking of the gel polymer, which can reflect the degree of formation of the gel network structure. Generally speaking, when other conditions remain unchanged, the higher the degree of crosslinking of the gel polymer, the greater the dynamic viscosity of the electrolyte. The dynamic viscosity of the electrolyte is controlled within this range. On the one hand, the gel polymer has a better gel network structure, and on the other hand, the electrolyte as a whole has better fluidity.

[0089] In some embodiments, the ion conductivity of the electrolyte is 4-10 mS / cm. Such an electrolyte has good ion transport capability.

[0090] As an example, ionic conductivity can be measured by a conductivity meter.

[0091] Another embodiment of the present application further provides a method for preparing the above electrolyte. The preparation method comprises the following steps S10 to S20:

[0092] S10, mixing the flame retardant and the raw material for preparing the gel polymer and causing a curing reaction to occur to obtain a composite flame retardant.

[0093] In some embodiments, the raw materials for preparing the gel polymer include polymer monomers and initiators. Furthermore, the raw materials for preparing the gel polymer also include the second solvent mentioned above.

[0094] Optionally, the polymer monomer includes a comonomer, and the comonomer includes but is not limited to an ester monomer and an olefin monomer.

[0095] Optionally, the comonomer includes at least one of methyl methacrylate, methyl acrylate, ethyl methacrylate, ethyl acrylate, n-butyl methacrylate, butyl acrylate, n-octyl methacrylate, n-octyl acrylate, vinyl acetate, vinylene carbonate, acrylonitrile, vinyl ethylene carbonate, triethylene glycol dimethacrylate, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, allyl methacrylate, divinylbenzene, polyvinyl alcohol, hexafluoropropylene, trichloroethylene, tetrafluoroethylene, chlorotrifluoroethylene and styrene.

[0096] Optionally, the initiator used to initiate polymerization of the comonomer to form a polymer includes at least one of a persulfate initiator, an azo initiator and an organic peroxide initiator; more optionally, the azo initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile and dimethyl azobisisobutyrate.

[0097] Optionally, the mass ratio of the polymer monomer to the flame retardant is (1-5):1, for example, 1:1, 1:2, 1:3, 1:4, 1:5.

[0098] Optionally, the mass ratio of the polymer monomer to the initiator is (10-20):1, for example, 10:1, 15:1, 20:1.

[0099] Optionally, the solid content (mass content) in the solution obtained by mixing the polymer monomer, the flame retardant, the initiator and the second solvent is 2% to 20%, for example, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%. The solid content refers to the mass content of the polymer monomer, the flame retardant and the initiator in the obtained solution. The composite flame retardant obtained after curing is in a gel state, which is filled with a large amount of the second solvent.

[0100] In some embodiments, the curing reaction conditions in S10 include curing at a temperature of 70 to 120°C for 10 to 60 minutes. The temperature of the heating curing may be 70°C, 75°C, 80°C, 85°C, 90°C, 100°C, 110°C, 120°C, and may be 90 to 100°C, or a range of any two of the above values. The heating curing time may be 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes, and may be 20 to 40 minutes, or a range of any two of the above values.

[0101] It can be understood that in some examples, all the products obtained in step S10 can be directly put into step S20.

[0102] S20, stirring and mixing the composite flame retardant, the electrolyte salt, and the first solvent to form an electrolyte solution.

[0103] The preparation method of the above-mentioned electrolyte is to first mix the flame retardant and the raw materials for preparing the gel polymer and perform a curing reaction to obtain a composite flame retardant; then mix the composite flame retardant with the electrolyte salt and the first solvent under stirring conditions, and control the electrolyte to have good fluidity through stirring.

[0104] In some of the embodiments, the stirring step is controlled so that the dynamic viscosity of the electrolyte is controlled within a range of 3.5 to 5 cp.

[0105] Positive electrode

[0106] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector.

[0107] 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 film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0108] 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 and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be obtained by forming a metal material on a polymer material substrate. 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. Non-limiting examples of the polymer material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE) and the like.

[0109] In some embodiments, the positive electrode film layer may include a positive electrode active material layer. The positive electrode active material layer contains positive electrode active materials.

[0110] The positive electrode active material may be a positive electrode active material for a battery known in the art. As a non-limiting example, the positive electrode active material may include one or more of the following materials: lithium-containing phosphates of 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, nickel cobalt manganese ternary positive electrode materials (or lithium nickel cobalt manganese oxide), lithium nickel cobalt aluminum oxide, and its modified compounds.

[0111] 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.

[0112] 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 aluminum oxides may include LiNi 0.85 Co 0.15 Al 0.05 O2.

[0113] Non-limiting examples of nickel-cobalt-manganese ternary positive electrode materials (or lithium nickel-cobalt-manganese oxides) may include LiNi 1 / 3Co 1 / 3 Mn 1 / 3O2 (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 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc. It is understandable that the nickel-cobalt-manganese ternary positive electrode material may also be doped with other metal elements.

[0114] 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 active material is different when the battery is discharged to different states. In the enumeration of positive electrode active materials in this application, unless otherwise specified, the content of Li is the initial state of the material. The positive electrode active 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 active 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 active materials is also within the scope of positive electrode active materials. The aforementioned appropriate modification refers to the acceptable modification method for the positive electrode active material, and non-limiting examples include coating modification.

[0115] In the list of positive electrode active 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.

[0116] In some embodiments, the positive electrode active material may further include a sodium ion active material.

[0117] As an example, the sodium ion active material may include one or more of the following materials: one or more of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, the present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium ion batteries may also be used.

[0118] As an optional technical solution of the present application, in the sodium transition metal oxide, the transition metal may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Non-limiting examples of sodium transition metal oxides may include Na x MO2, wherein M may include one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, 0<x≤1.

[0119] As an optional technical solution of the present application, the polyanionic compound can be a compound having sodium ions, transition metal ions and tetrahedral (YO4) n- A class of compounds with anionic units. Transition metals may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y may be one or more of P, S and Si; n represents (YO4) n- valence state.

[0120] Polyanionic compounds can also be those with sodium ions, transition metal ions, tetrahedral (YO4) n- A class of compounds containing anion units and halogen anions. Transition metals may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y may be one or more of P, S and Si, and n represents (YO4) n- valence state; the halogen can be one or more of F, Cl and Br.

[0121] Polyanionic compounds can also be sodium ions, tetrahedral (YO4) n- Anion unit, polyhedral unit (ZO y ) m+ and an optional halogen anion. Y can be one or more of P, S and Si, and n represents (YO4) n- valence state; Z represents a transition metal, which may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; m represents (ZO y ) m+ valence state; the halogen can be one or more of F, Cl and Br.

[0122] Polyanionic compounds may include NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, referred to as NVP), Na4Fe3(PO4)2 (P2O7), NaM'PO4F and Na3(VO y )2(PO4)2F 3-2y(0≤y≤1) or more. Wherein, M' in NaM'PO4F may include one or more of V, Fe, Mn and Ni.

[0123] Prussian blue compounds can be sodium ions, transition metal ions and cyanide ions (CN - ). The transition metal may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Non-limiting examples of Prussian blue compounds may include Na a Me b Me' c (CN)6, wherein Me and Me' can be independently one or more of Ni, Cu, Fe, Mn, Co and Zn, 0<a≤2, 0<b<1, 0<c<1.

[0124] 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.

[0125] 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.

[0126] In some of the embodiments, in the positive electrode active material layer, the mass content of the positive electrode active material is 75% to 98%.

[0127] In some of the embodiments, in the positive electrode active material layer, the mass content of the conductive agent is 0.1% to 15%.

[0128] In some of the embodiments, in the positive electrode active material layer, the binder has a mass content of 0.5% to 15%.

[0129] 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.

[0130] 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% to 80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 to 25000 mPa·s. When coating the positive electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 15 to 35 mg / cm 2 The compaction density of the positive electrode sheet can be 3.0 to 3.6 g / cm 3 , can be selected as 3.3~3.5g / cm 3 .

[0131] Negative electrode

[0132] Generally, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector.

[0133] As a non-limiting example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0134] 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.

[0135] Further, the negative electrode film layer may include a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode active material.

[0136] 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: carbon-based negative electrode active materials such as 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 oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide compounds, and tin alloys. However, 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.

[0137] Optionally, the negative electrode active material includes a carbon-based negative electrode active material, and the carbon-based negative electrode active material includes at least one of artificial graphite, natural graphite, soft carbon and hard carbon. The above electrolyte is particularly suitable for negative electrode plates containing carbon-based negative electrode active materials. This is because the traditional technology of directly adding flame retardants to the electrolyte has poor compatibility with negative electrode plates, especially carbon-based negative electrode active materials, due to the high viscosity of flame retardants. Therefore, although the flame retardant can improve the flame retardancy of the electrolyte after addition, it will reduce the ionic conductivity of the electrolyte and greatly shorten the battery cycle life. Therefore, the electrolyte of the present application first fixes the flame retardant in the form of a polymer within the framework of the formed polymer, which can inhibit the excessive reaction of the single molecule flame retardant with the components in the electrolyte to a certain extent, thereby extending its service life.

[0138] 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).

[0139] 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.

[0140] 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)).

[0141] In some of the embodiments, in the negative electrode film layer, the mass content of the positive electrode active material is 75% to 98%.

[0142] In some of the embodiments, in the negative electrode film layer, the mass content of the conductive agent is 0.1% to 15%.

[0143] In some of the embodiments, in the negative electrode film layer, the mass content of the binder is 0.5% to 15%.

[0144] 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 surface of the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0145] The negative electrode current collector surface coated with the negative electrode slurry may be on a single surface of the negative electrode current collector or on both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry may be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature may be adjusted to 2000-10000mPa·s.

[0146] Isolation film

[0147] The isolation membrane is set between the positive electrode plate and the negative electrode plate, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0148] 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.

[0149] In some embodiments, the thickness of the isolation film is 6 μm to 40 μm, and may be 12 μm to 20 μm.

[0150] 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.

[0151] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0152] 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.

[0153] The secondary battery includes at least one battery cell. The secondary battery may include one or more battery cells. In one example, the secondary battery may also be a battery cell.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] The secondary battery may be a battery cell 5 , a battery module 4 or a battery pack 1 .

[0158] 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.

[0159] 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.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] 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.

[0164] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0165] 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.

[0166] 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.

[0167] The following are specific embodiments.

[0168] 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.

[0169] Example 1

[0170] 1) Preparation of positive electrode

[0171] The positive electrode active material NCM 333 , conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are uniformly mixed in a proper amount of solvent N-methylpyrrolidone (NMP) in a mass ratio of 96.2:2.7:1.1 to obtain a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector aluminum foil, and a positive electrode active material layer with a thickness of 140 μm is formed through drying, cold pressing, slitting, cutting and other processes to obtain a positive electrode sheet.

[0172] 2) Preparation of negative electrode sheet

[0173] The negative electrode active material artificial graphite, the conductive agent carbon black (Super P), the binder styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) were mixed uniformly in a proper amount of solvent deionized water at a mass ratio of 96.4:0.7:1.8:1.1 to obtain a negative electrode slurry; the negative electrode slurry was coated on the negative electrode current collector copper foil, and a negative electrode active material layer with a thickness of 110 μm was formed through drying, cold pressing, slitting and cutting processes to obtain a negative electrode sheet.

[0174] 3) Isolation film

[0175] A 12μm thick polypropylene isolation film was selected.

[0176] 4) Preparation of electrolyte

[0177] 4.1 Selection of flame retardant: The flame retardant is triethyl 2-fluoro-2-phosphoryl acetate; the polymerization monomer is ethylene glycol dimethacrylate, pentaerythritol tetraacrylate; the initiator is 2,2-azobisisobutyronitrile;

[0178] 4.2 Preparation of composite flame retardant (polymerization gelation of flame retardant): The flame retardant 2-fluoro-2-phosphorylacetate triethyl ester, the polymer monomer ethylene glycol dimethacrylate, the pentaerythritol tetraacrylate and the initiator azobisisobutyronitrile in a mass ratio of 2:1:1:0.1 were dissolved in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (mass ratio of 1:1) to prepare a solution in which the first four components (flame retardant, polymer monomer and initiator) accounted for 8% by mass. The solution was stirred at room temperature until dissolved and heated at 60°C for 12 hours to gelate to obtain a gel composite flame retardant.

[0179] 4.3 Preparation of electrolyte: Continue to add the mixed solvent (EC / EMC) in the same amount and mass ratio as in 4.2 to the above-mentioned gel composite flame retardant, and then add lithium hexafluorophosphate (LiPF6) to prepare an electrolyte with a LiPF6 concentration of 1.1 mol / L, stir and adjust the dynamic viscosity of the mixed solution to 4 cP to obtain a finished electrolyte.

[0180] 5) Preparation of secondary batteries

[0181] The positive electrode sheet, the separator, and the negative electrode sheet are stacked and wound in order to obtain an electrode assembly; the electrode assembly is placed in an outer package, and after drying, the electrolyte is injected, and after vacuum packaging, standing, forming, shaping and other processes, a secondary battery is obtained.

[0182] The secondary batteries of Examples 2 to 18 and the secondary battery of Example 1 are prepared in a similar manner, except that different electrolytes are used. Please refer to Table 1 for the specific differences.

[0183] Comparative Example 1

[0184] It is basically the same as Example 1, except that the preparation steps of the electrolyte are different. The step of pre-polymerization and gelation of the flame retardant in 4.2 is omitted, and the flame retardant 2-fluoro-2-phosphoryl acetate triethyl, the polymerization monomer ethylene glycol dimethacrylate, pentaerythritol tetraacrylate and the initiator azobisisobutyronitrile with a mass ratio of 2:1:1:0.1 are directly dissolved in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (mass ratio 1:1), and lithium hexafluorophosphate (LiPF6) is continuously added to prepare an electrolyte with a LiPF6 concentration of 1.1 mol / L, and the finished electrolyte is obtained after stirring.

[0185] Accordingly, in the preparation process of the secondary battery, after the electrolyte is injected, it is heated to 80° C. and kept warm for 24 hours so that the finished electrolyte can be completely solidified in situ.

[0186] Comparative Example 2

[0187] The method is basically the same as Example 1, except that the preparation steps of the composite flame retardant are different, which are as follows: the flame retardant triethyl 2-fluoro-2-phosphorylacetate, polyethylene glycol dimethacrylate and water are mixed to obtain a mixed solution, wherein the mass ratio of the flame retardant to polyethyl methacrylate in the mixed solution is 1:1; the mixed solution is then spray-granulated and dried to obtain core-shell composite flame retardant particles in which the polyethyl methacrylate shell layer coats the flame retardant.

[0188] Comparative Example 3

[0189] It is basically the same as Example 1, except that the preparation steps of the composite flame retardant are different, specifically, the polymerized monomer ethylene glycol dimethacrylate in Example 1 is replaced by styrene of equal mass.

[0190] 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.

[0191] The following is a performance test.

[0192] (1) Flame retardant performance test:

[0193] In the first step, the gel solidifies to block the internal conductive path, and the effect can be evaluated by overcharge abuse effect:

[0194] Perform overcharge abuse test on the battery cell: First, fully charge the battery cell to 100% SOC, and perform overcharge test at a 1 / 3C charging rate until the battery cell cannot be charged further or thermal runaway occurs. Record the corresponding short-circuit SOC or failure when charging cannot be continued as the evaluation standard. The lower the short-circuit SOC, the better.

[0195] The second step is the flame retardant's effect, which can be evaluated by the hot box abuse effect:

[0196] Perform hot box abuse test on the battery cell: first charge the battery cell to 100% SOC, heat the battery cell at a temperature rise rate of 5℃ / min, and after heating to 55℃, keep the temperature for 30 minutes every 5℃ rise until the battery cell thermal runaway, and record the state of thermal runaway, such as whether there is open flame burning or the intensity of burning (such as explosion and other behaviors for evaluation). In this application, the degree of burning intensity is divided from low to high: smoking without open flame, open flame extinguished quickly, and open flame extinguished slowly.

[0197] (2) Cyclic performance test:

[0198] The battery was charged to 4.25V at a constant current of 0.5C at 25°C, then charged at a constant voltage of 4.25V until the current dropped to 0.05C, and then discharged to 2.8V at a constant current of 0.5C to obtain the first cycle discharge capacity (Cd1); this charging and discharging was repeated until the nth cycle, and the discharge capacity of the battery after n cycles was obtained, recorded as Cdn.

[0199] Capacity retention rate = discharge capacity after n cycles (Cdn) / first cycle discharge capacity (Cd1). According to this formula, the number of cycles n corresponding to a capacity retention rate of 80% is obtained.

[0200] Some parameters and performance test results of the above embodiments and comparative examples are shown in Table 1 below.

[0201] In Table 1, the mass content of the composite flame retardant refers to the mass content of the composite flame retardant in the electrolyte, which can be represented by the mass of the raw materials used to prepare the composite flame retardant to represent the mass of the composite flame retardant, thereby obtaining the mass content of the composite flame retardant in the electrolyte.

[0202] Table 1

[0203]

[0204]

[0205]

[0206] It should be noted that the number of cycles n corresponding to 80% in Table 1 is the result of rounding off the units digit to an integer multiple of 10.

[0207] It can be seen from Table 1 that the flame retardant in the electrolyte in the injection state in Comparative Example 1 is not confined in the network structure, which will trigger side reactions and lead to reduced cycle performance. The time required for in-situ curing after injection is prolonged and the low fluidity of the electrolyte after curing will also reduce the cycle performance. In addition, the battery in Comparative Example 1 has a higher short-circuit SOC corresponding to the overcharge test, indicating that its ability to prevent thermal runaway in the early stage is relatively low.

[0208] The composite flame retardant used in Comparative Example 2 is a core-shell structure, which does not contain the gel polymer in the embodiment of the present application. The overcharge test results show that all 10 test samples fail, indicating that it cannot play the role of preventing thermal runaway in the overcharge stage of the embodiment of the present application. Therefore, the combustion intensity of Comparative Example 2 in the hot box abuse test is greater than that of Comparative Example 1 and Comparative Example 3.

[0209] Comparative Example 3 uses a linear polymer to replace the gel polymer in the embodiment of the present application. The results show that its effect in preventing thermal runaway in the overcharge stage is not as good as the gel polymer. Some of its batteries fail in the overcharge abuse test, with 4 failures out of 10 test samples and a failure probability of 40%.

[0210] The electrolyte used in each embodiment adds the flame retardant and the gel polymer to the electrolyte in the form of a composite flame retardant. When the battery temperature is too high, the gel polymer of the composite flame retardant in the electrolyte can be further cured at high temperature to form a cross-linked cured polymer to block conduction and play a preliminary role in preventing thermal runaway, especially in the overcharging stage. As the temperature continues to rise, the battery cell fails and burns, and the flame retardant in the composite flame retardant absorbs the free radicals generated during the combustion process, thereby blocking the continuous reaction of combustion and playing a further role in flame retardancy and preventing thermal runaway. Such multi-faceted synergy is conducive to extending the battery life and reducing the degree of damage caused by thermal runaway of the battery.

[0211] 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 invention comprises an electrolyte salt, a first solvent and a composite flame retardant, wherein the composite flame retardant comprises a flame retardant and a gel polymer, the flame retardant is located in the internal pores of the gel polymer, the electrolyte salt is dissolved in the first solvent, and the composite flame retardant is dispersed in the first solvent.

2. The electrolyte according to claim 1, characterized in that The electrolyte satisfies at least one of the following conditions: (1) In the electrolyte, the mass content of the composite flame retardant is 1% to 10%; (2) In the composite flame retardant, the mass content of the flame retardant is 30% to 70%; (3) In the electrolyte solution, the concentration of the electrolyte salt is 0.5 to 1.5 mol / L.

3. The electrolyte according to claim 2, characterized in that The electrolyte satisfies at least one of the following conditions: (1) In the electrolyte, the mass content of the composite flame retardant is 2% to 6%; (2) In the components of the composite flame retardant other than the solvent, the mass content of the flame retardant is 40% to 60%; (3) In the electrolyte solution, the concentration of the electrolyte salt is 0.8 to 1.2 mol / L.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The electrolyte satisfies at least one of the following conditions: (1) The flame retardant includes a phosphate flame retardant, (2) The components of the gel polymer include a main polymer and a second solvent; (3) The dynamic viscosity of the electrolyte is 3.5 to 5 cp.

5. The electrolyte according to claim 4, characterized in that The electrolyte satisfies at least one of the following conditions: (1) The flame retardant comprises at least one of halogenated phosphates, halogenated phosphites and halogenated phosphonates; (2) the host polymer has a carbonyl group; (3) The second solvent includes a carbonate solvent.

6. The electrolyte according to claim 5, characterized in that The electrolyte satisfies at least one of the following conditions: (1) The flame retardant comprises at least one of triethyl 2-fluoro-2-phosphoryl acetate and bis(2,2,2-trifluoroethyl)methyl phosphate; (2) The host polymer includes an ester polymer.

7. The electrolyte according to any one of claims 1 to 3, 5 to 6, characterized in that: The electrolyte satisfies at least one of the following conditions: (1) The electrolyte salt includes at least one of an electrolyte lithium salt and an electrolyte sodium salt; (2) the first solvent includes at least one of an ester solvent, an ether solvent and a sulfone solvent; (3) The ionic conductivity of the electrolyte is 4 to 10 mS / cm.

8. The method for preparing an electrolyte according to any one of claims 1 to 7, characterized in that: The steps include: The flame retardant and the raw material for preparing the gel polymer are mixed and subjected to a curing reaction to obtain the composite flame retardant; The composite flame retardant, the electrolyte salt and the first solvent are stirred and mixed to form the electrolyte solution.

9. The method for preparing an electrolyte according to claim 8, characterized in that: The stirring step is controlled so that the dynamic viscosity of the electrolyte is controlled within 3.5-5 cp.

10. The method for preparing an electrolyte according to any one of claims 8 to 9, characterized in that: The raw materials for preparing the gel polymer include polymer monomers and initiators.

11. The method for preparing an electrolyte according to claim 10, characterized in that: The preparation method satisfies at least one of the following conditions: (1) The polymer monomer includes an ester monomer; (2) The mass ratio of the polymer monomer to the flame retardant is (1-5):1; (3) The mass ratio of the polymer monomer to the initiator is (10-20):

1.

12. A secondary battery, characterized in that: It comprises a positive electrode sheet, a negative electrode sheet and the electrolyte according to any one of claims 1 to 6, wherein the electrolyte is arranged between the positive electrode sheet and the negative electrode sheet.

13. The secondary battery according to claim 12, characterized in that: The negative electrode plate includes a carbon-based negative electrode active material; optionally, the carbon-based negative electrode active material includes at least one of artificial graphite, natural graphite, soft carbon and hard carbon.

14. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 12 to 13.

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