Secondary battery and preparation method therefor, and electric device

Abstract

A secondary battery and a preparation method therefor, and an electric device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte solution, a gel electrolyte, and a separator that is arranged between the positive electrode sheet and the negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode active material layer; the gel electrolyte is at least located between the negative electrode active material layer and the separator and within pores in both the negative electrode active material layer and the separator; and the electrolyte solution contains a nitrile additive. Therefore, the high-temperature storage performance and cycling performance of a secondary battery are effectively improved.

Description

Secondary battery, preparation method thereof, and power-consuming device

[0001] Cross-references

[0002] This application refers to Chinese patent application No. 202410008428.4, filed on January 2, 2024, entitled “Secondary battery, preparation method thereof, and electrical device”, which is incorporated into this application in its entirety by reference. Technical Field

[0003] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery, a preparation method thereof, and an electrical device thereof. Background Art

[0004] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0005] Secondary batteries, with their advantages of high operating voltage, light weight, and lack of memory effect, have been widely used in mobile phones, digital cameras, laptops, electric vehicles, power tools, and other fields. With the rapid development of these industries, the performance requirements for secondary batteries are becoming increasingly demanding. Improving the high-temperature storage and cycling performance of traditional secondary batteries is a pressing technical challenge.

[0006] Summary of the Invention

[0007] The present application provides a secondary battery, a preparation method thereof, and an electrical device, aiming to improve the high-temperature storage performance and cycle performance of the secondary battery.

[0008] In a first aspect of the present application, a secondary battery is provided, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, a gel electrolyte, and a separator disposed between the positive electrode sheet and the negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode active material layer, the gel electrolyte is located at least between the negative electrode active material layer and the separator, within the pores of the negative electrode active material layer, and within the pores of the separator, and the electrolyte contains a nitrile additive.

[0009] In the above-mentioned secondary battery, the nitrile additive can effectively stabilize the structure of the positive electrode plate, improve the high-temperature storage performance of the positive electrode plate, and reduce the gas production of the positive electrode plate. Since the nitrile additive in the electrolyte mainly diffuses into the interior of the negative electrode active material layer through the large surface of the negative electrode active material layer, and there is at least gel electrolyte between the negative electrode active material layer and the isolation membrane, in the pores of the negative electrode active material layer, and in the pores of the isolation membrane, the gel electrolyte can increase the diffusion path of the nitrile additive to the negative electrode active material layer, reduce the diffusion of the nitrile additive, reduce the damage of the nitrile additive to the negative electrode active material layer, and improve the protection effect of the negative electrode active material layer, thereby effectively improving the high-temperature storage performance and cycle performance of the secondary battery.

[0010] In some embodiments, the mass proportion of the nitrile additive in the electrolyte is 0.1%-20%, thereby further improving the high-temperature storage performance and cycle performance of the secondary battery.

[0011] In some embodiments, the mass proportion of the nitrile additive in the electrolyte is 0.5%-10%, thereby further improving the high-temperature storage performance and cycle performance of the secondary battery.

[0012] In some embodiments, the nitrile additive comprises one or more of acetonitrile, propionitrile, butyronitrile, pivalonitrile, capronitrile, malononitrile, succinonitrile, glutaronitrile, and adiponitrile. Selecting the above types of nitrile additives is beneficial to further improve the high temperature storage performance and cycle performance of the secondary battery.

[0013] In some embodiments, the porosity of the separator is 32%-45%, thereby further improving the high-temperature storage performance and cycle performance of the secondary battery while also taking into account the rate performance of the secondary battery.

[0014] In some embodiments, the porosity of the separator is 37%-42%, thereby further improving the high-temperature storage performance and cycle performance of the secondary battery while also taking into account the rate performance of the secondary battery.

[0015] In some embodiments, the gel electrolyte comprises a polymer whose monomers include acrylate monomers. The cross-linked network formed by the polymerization of the acrylate monomers has good elasticity and can adapt to the volume changes of the negative electrode during charge and discharge, thereby further improving the cycle performance of the secondary battery.

[0016] In some embodiments, the number of repeating structural units in the acrylic ester monomer is 50 to 2000. Controlling the number of repeating structural units in the acrylic ester monomer within the above range helps reduce damage to the negative electrode active material layer caused by the nitrile additive, improves the protective effect of the negative electrode active material layer, and thus further enhances the high-temperature storage performance and cycle performance of the secondary battery.

[0017] In some embodiments, the number of repeating structural units in the acrylic acid ester monomer is 200 to 800. This further helps reduce the damage of the nitrile additive to the negative electrode active material layer, improves the protection effect of the negative electrode active material layer, and further improves the high-temperature storage performance and cycle performance of the secondary battery.

[0018] In some embodiments, the acrylate monomer includes one or more of pentaerythritol tetraacrylate, polyethylene glycol diacrylate, triethylene glycol dimethacrylate, trimethylolpropane triacrylate, and ethoxylated trimethylolpropane triacrylate. These acrylate monomers have excellent stability and processability, and the resulting polymers possess good elasticity, adapting to the volume changes of the negative electrode during the charge and discharge process of the secondary battery, thereby further improving the cycling performance of the secondary battery. Alternatively, the acrylate monomer includes polyethylene glycol diacrylate.

[0019] In some embodiments, the gel electrolyte further includes an organic solvent, including a carbonate-based organic solvent, including a linear carbonate-based organic solvent and a fluorocarbon-based organic solvent, wherein the mass ratio of the linear carbonate-based organic solvent to the fluorocarbon-based organic solvent is 1:1-5:1. This allows for the formation of a more film-forming SEI (solid electrolyte interface) film, which also improves wettability with the separator and negative electrode active material layer, further enhancing the cycling performance of the secondary battery.

[0020] In some embodiments, the thickness of the gel electrolyte between the negative electrode active material layer and the separator is 0.1 μm to 5 μm. This allows for close contact between the negative electrode and the separator, which helps improve the conduction rate of active ions and thus the rate performance of the secondary battery.

[0021] In some embodiments, the gel electrolyte is also located on the surface of the separator away from the negative electrode active material layer, thereby further improving the high-temperature storage performance and cycle performance of the secondary battery.

[0022] In some embodiments, the gel electrolyte is located within the pores of the negative electrode active material layer and the pores of the separator, and the gel electrolyte wraps around the surfaces of the separator and the negative electrode sheet. This helps further improve the high-temperature storage performance and cycle performance of the secondary battery.

[0023] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer contains a positive active material, and the positive active material includes one or more of lithium cobalt oxide, lithium nickel manganese oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. This helps further improve the high-temperature storage performance and cycle performance of the secondary battery.

[0024] In a second aspect of the present application, a method for preparing a secondary battery is provided, comprising the following steps:

[0025] Covering the isolation film on the surface of the negative electrode active material layer of the negative electrode plate to obtain a composite layer;

[0026] Infiltrating the composite layer with a gel precursor solution and solidifying the gel precursor solution to form a gel electrolyte, wherein the gel electrolyte is located at least between the negative electrode active material layer and the separator, within the pores of the negative electrode active material layer, and within the pores of the separator, to obtain a composite intermediate containing the gel electrolyte;

[0027] Laminating the positive electrode sheet to the composite intermediate so that the positive electrode sheet is located on one side of the separator of the composite intermediate;

[0028] The interface between the positive electrode sheet and the composite intermediate and the positive electrode sheet after lamination are infiltrated with an electrolyte containing a nitrile additive.

[0029] In this way, secondary batteries can be prepared simply, which is beneficial to the mass production of secondary batteries and expands the selection range of electrolytes. At the same time, the concentration of nitrile additives can be increased, and the performance improvement effect of the positive electrode sheet can be enhanced, thereby further improving the high-temperature storage performance and cycle performance of the secondary battery.

[0030] In some embodiments, the gel precursor solution contains polymer monomers, and the weight percentage of the polymer monomers in the gel precursor solution is 10%-20%, thereby further improving the high-temperature storage performance and cycle performance of the secondary battery.

[0031] The third aspect of the present application provides an electrical device comprising at least one of the secondary battery described in the first aspect of the present application and the secondary battery prepared by the preparation method described in the second aspect of the present application.

[0032] 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.

[0033] 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

[0034] In order to better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more of the accompanying drawings. The additional details or examples used to describe the accompanying drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes currently understood for these applications. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the accompanying drawings:

[0035] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0036] FIG. 2 is an exploded view of the battery cell according to one embodiment of the present application shown in FIG. 1 .

[0037] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0038] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0039] FIG5 is an exploded view of the battery pack shown in FIG4 according to an embodiment of the present application.

[0040] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0041] Description of reference numerals:

[0042] 1. Battery pack; 2. Upper box; 3. Lower box; 4. Battery module; 5. Battery cell; 5. Casing; 5. Electrode assembly; 5. Cover; 6. Electrical device. DETAILED DESCRIPTION

[0043] Below, some embodiments of the secondary battery, its preparation method, and the electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same 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.

[0044] " scope " disclosed in the present application can be limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and any end value can be included or not included independently, and can be arbitrarily combined, that is, any lower limit can form a scope with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 are also listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is merely an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to listing the parameter as, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on. For example, when a parameter is expressed as an integer selected from "2-10", this is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0045] In this application, "a plurality of" or "a plurality of" refers to a number greater than or equal to 2 unless otherwise specified. For example, "one or more" means one or more than or equal to two.

[0046] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0047] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor does it necessarily refer to independent or alternative embodiments that are mutually exclusive with other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments. References to "implementations" herein have a similar understanding.

[0048] It will be appreciated by those skilled in the art that, in the methods of various embodiments or examples, the order in which the steps are written does not imply a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible inherent logic. Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0049] In this application, in open technical features or technical solutions described with words such as "contain", "include", and "include", unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions that also include additional members in addition to the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2, and a3" and the feature or solution of "A includes not only a1, a2, and a3, but also other members". In this application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0050] In this application, the terms "optionally," "optional," and "optional" are optional and refer to either option being present or absent. If a technical solution contains multiple "options," each option is considered independent unless otherwise specified and there are no conflicts or constraints.

[0051] Improving the performance of traditional secondary batteries is essential to meet the rapid growth of industries such as mobile phones, laptops, and electric vehicles. Currently, introducing appropriate additives is one of the most cost-effective methods for improving secondary battery performance. However, while some additives can improve the stability of the positive electrode, they can also damage the negative electrode, causing capacity degradation in the secondary battery. Consequently, their application in secondary batteries is significantly limited.

[0052] In view of this, the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, a gel electrolyte, and a separator arranged between the positive electrode sheet and the negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode active material layer, the gel electrolyte is located at least between the negative electrode active material layer and the separator, within the pores of the negative electrode active material layer, and within the pores of the separator, and the electrolyte contains a nitrile additive; the nitrile additive in the secondary battery can effectively stabilize the structure of the positive electrode sheet, improve the high-temperature storage performance of the positive electrode sheet, and reduce gas production of the positive electrode sheet. Since the nitrile additive in the electrolyte mainly diffuses into the interior of the negative electrode active material layer through the large surface of the negative electrode active material layer, and the gel electrolyte is at least provided between the negative electrode active material layer and the separator, within the pores of the negative electrode active material layer, and within the pores of the separator, the gel electrolyte can increase the diffusion path of the nitrile additive to the negative electrode active material layer, reduce the diffusion of the nitrile additive, reduce the damage of the nitrile additive to the negative electrode active material layer, and improve the protection effect on the negative electrode active material layer, thereby effectively improving the high-temperature storage performance and cycle performance of the secondary battery.

[0053] secondary batteries

[0054] One embodiment of the present application provides a secondary battery, including a positive electrode sheet, a negative electrode sheet, an electrolyte, a gel electrolyte, and a separator arranged between the positive electrode sheet and the negative electrode sheet, the negative electrode sheet includes a negative electrode active material layer, the gel electrolyte is located at least between the negative electrode active material layer and the separator, within the pores of the negative electrode active material layer, and within the pores of the separator, and the electrolyte contains a nitrile additive.

[0055] In the above-mentioned secondary battery, the nitrile additive can effectively stabilize the structure of the positive electrode plate, improve the high-temperature storage performance of the positive electrode plate, and reduce the gas production of the positive electrode plate. Since the nitrile additive in the electrolyte mainly diffuses into the interior of the negative electrode active material layer through the large surface of the negative electrode active material layer, and there is at least gel electrolyte between the negative electrode active material layer and the isolation membrane, in the pores of the negative electrode active material layer, and in the pores of the isolation membrane, the gel electrolyte can increase the diffusion path of the nitrile additive to the negative electrode active material layer, reduce the diffusion of the nitrile additive, reduce the damage of the nitrile additive to the negative electrode active material layer, and improve the protection effect of the negative electrode active material layer, thereby effectively improving the high-temperature storage performance and cycle performance of the secondary battery.

[0056] Optionally, a scanning electron microscope (SEM) can be used to observe the cross-section of the negative electrode sheet and the separator to determine the relative positions of the gel electrolyte, the negative electrode sheet, and the separator. High performance liquid chromatography or nuclear magnetic resonance spectroscopy can be used to determine the type of nitrile additives in the electrolyte. The high performance liquid chromatography method can be specifically tested in accordance with the provisions of the relevant test methods in GB / T 26792-2019, and the nuclear magnetic resonance spectroscopy method can be tested in accordance with the provisions of the relevant test methods in GB / T 34059-2017.

[0057] In some embodiments, the mass percentage of the nitrile additive in the electrolyte is 0.1%-20%. This can further improve the high-temperature storage performance and cycle performance of the secondary battery. It is understood that the mass percentage of the nitrile additive in the electrolyte includes, but is not limited to, 0.1%, 0.5%, 1%, 3%, 5%, 8%, 10%, 13%, 15%, 18%, and 20%. Furthermore, the mass percentage of the nitrile additive in the electrolyte is 0.5%-10%.

[0058] Optionally, the mass proportion of nitrile additives in the electrolyte can be determined by high performance liquid chromatography, and the specific detection method can be referred to the provisions of the relevant detection method in GB / T 26792-2019.

[0059] In some embodiments, the nitrile additive comprises one or more of acetonitrile, propionitrile, butyronitrile, pivalonitrile, capronitrile, malononitrile, succinonitrile, glutaronitrile, and adiponitrile. Selecting the above types of nitrile additives is beneficial to further improve the high temperature storage performance and cycle performance of the secondary battery.

[0060] In some embodiments, the porosity of the separator is 32%-45%. This can effectively reduce the diffusion of nitrile additives to the surface of the negative electrode, while taking into account the transmission rate of active ions, thereby further improving the high-temperature storage performance and cycle performance of the secondary battery, while taking into account the rate performance of the secondary battery. It is understood that the porosity of the separator includes but is not limited to: 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, and 45%. Furthermore, the porosity of the separator is 37%-42%.

[0061] In some embodiments, the material of the isolation membrane includes one or more of polyamide, polyamideimide, polyketone, polyaryletherketone, polysulfone, polyphenylene sulfide, polyphenylene oxide, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl chloride, polyolefin, perfluoroalkoxyalkane, polyester, liquid crystal polymer, polyoxymethylene, acrylonitrile styrene acrylate, styrene acrylonitrile, acrylonitrile butadiene styrene, polybenzimidazole, polyparaphenylene copolymer, polyacrylonitrile, polyethyleneimine, ethylene tetrafluoroethylene, polychlorotrifluoroethylene, aramid, and polyetherimide. Optionally, the isolation membrane can 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 can be the same or different, without particular limitation.

[0062] In some embodiments, the isolation film has a thickness of 6 μm-40 μm, and optionally 12 μm-20 μm.

[0063] In this application, the unit "μm" means micrometer.

[0064] In some embodiments, the gel electrolyte includes a polymer whose monomers include acrylate monomers. Acrylate monomers have good stability and processability, and the resulting polymer has good elasticity, which can adapt to the volume changes of the negative electrode during the charge and discharge process of the secondary battery, thereby further improving the cycle performance of the secondary battery.

[0065] In some embodiments, the number of repeating structural units in the acrylate monomer is 50-2000. Controlling the number of repeating structural units in the acrylate monomer within the above range is conducive to reducing the damage of the nitrile additive to the negative electrode active material layer, improving the protection effect of the negative electrode active material layer, and thus further improving the high-temperature storage performance and cycle performance of the secondary battery. It is understood that the number of repeating structural units in the acrylate monomer includes but is not limited to: 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, 1400, 1600, 1800, 2000. Optionally, the number of repeating structural units in the acrylate monomer is 200-800.

[0066] In some embodiments, the acrylate monomer includes one or more of pentaerythritol tetraacrylate (PETA), polyethylene glycol diacrylate (PEGDA), triethylene glycol dimethacrylate, trimethylolpropane triacrylate, and ethoxylated trimethylolpropane triacrylate. Alternatively, the acrylate monomer includes polyethylene glycol diacrylate (PEGDA).

[0067] In some embodiments, the gel electrolyte further includes an organic solvent, and the organic solvent includes one or more of a carbonate organic solvent, a carboxylate organic solvent, and an ether organic solvent.

[0068] In some embodiments, the gel electrolyte further comprises an organic solvent, and the organic solvent comprises a carbonate organic solvent. Optionally, the organic solvent further comprises one or more of a carboxylate organic solvent and an ether organic solvent.

[0069] In some embodiments, the carbonate organic solvent includes a linear carbonate organic solvent and a fluorinated carbonate organic solvent. This can form a SEI (solid electrolyte interface) film with better film-forming properties and better wettability for the separator and the negative electrode active material layer, further improving the cycle performance of the secondary battery.

[0070] In some embodiments, the mass ratio of the linear carbonate organic solvent to the fluorocarbonate organic solvent is 1:1-5:1. This can further improve the cycle performance of the secondary battery. Optionally, the linear carbonate organic solvent includes one or more of ethyl methyl carbonate and dimethyl carbonate, and the fluorocarbonate organic solvent includes fluoroethylene carbonate.

[0071] In some embodiments, the linear carbonate organic solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, diphenyl carbonate, dibutyl carbonate, and butylene carbonate.

[0072] In some embodiments, the fluorocarbonate-based organic solvent includes fluoroethylene carbonate.

[0073] In some embodiments, the carboxylate organic solvent includes one or more of propyl butyrate, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, isopropyl propionate, and ethyl butyrate.

[0074] In some embodiments, the ether organic solvent includes one or more of methyl ether, propyl ether, butyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyltetrahydrofuran, diphenyl ether and crown ether.

[0075] In some embodiments, the gel electrolyte further includes a first electrolyte salt.

[0076] In some embodiments, the first electrolyte salt includes a lithium salt. Optionally, the lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorooxalatoborate (LiDFOB), and lithium perchlorate (LiClO4).

[0077] In some embodiments, the thickness of the gel electrolyte located between the negative electrode active material layer and the separator is 0.1 μm-5 μm. As a result, the negative electrode plate and the separator can be in close contact, which is beneficial to improving the conduction rate of active ions, thereby improving the rate performance of the secondary battery. It is understood that the thickness of the gel electrolyte located between the negative electrode active material layer and the separator includes but is not limited to: 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm.

[0078] In some embodiments, the gel electrolyte is further located on the surface of the separator away from the negative electrode active material layer.

[0079] In some embodiments, the thickness of the gel electrolyte located on the surface of the separator away from the negative electrode active material layer is 1 μm to 3 μm.

[0080] In some embodiments, the gel electrolyte is located in the pores of the negative electrode active material layer and the pores of the separator, and the gel electrolyte is wrapped around the surfaces of the separator and the negative electrode sheet.

[0081] In some embodiments, 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.

[0082] As a non-limiting example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two facing surfaces of the negative electrode current collector.

[0083] In some embodiments, the negative electrode active material layer includes a negative electrode active material. Optionally, the negative electrode active material includes one or more of a carbon-based material and a silicon-based material. Optionally, the carbon-based material may include graphite. Further optionally, the graphite may include one or more of artificial graphite and natural graphite. Alternatively, the silicon-based material may include one or more of elemental silicon, a silicon-oxygen compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy.

[0084] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0085] 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).

[0086] 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.

[0087] In some embodiments, the negative electrode active material layer may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0088] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or two surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt%-60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000mPa·s-10000mPa·s. When coating the negative electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75g / m 2 -220g / m 2 The compaction density of the negative electrode can be 1.0g / cm 3 -1.8g / cm 3 .

[0089] In this application, the unit "mPa·s" refers to millipascal·second, and the unit "g / m 2 " refers to grams per square meter, the unit is "g / cm 3 ” refers to grams per cubic centimeter.

[0090] In some embodiments, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, the positive electrode active material layer contains a positive electrode active material, and the positive electrode active material includes one or more of lithium cobalt oxide, lithium nickel manganese oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and their respective modified compounds. Nitrile additives can reach the surface of the positive electrode active material from the electrolyte, reduce the dissolution and gas production of transition metal ions in the positive electrode active material, thereby further improving the high temperature storage performance and cycle performance of the secondary battery. Non-limiting examples of lithium cobalt oxide can include but are not limited to LiCoO2; non-limiting examples of lithium nickel manganese oxide can include but are not limited to LiNi 0.5 Mn 1.5 O4、LiNi 0.5 Mn 0.5 O2, etc.; non-limiting examples of lithium manganese oxides may include but are not limited to LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include but are not limited to 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 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.; Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.8 Co 0.15 Al 0.05 O2.

[0091] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charge and discharge process, and the content of Li in the positive electrode plate is different when the battery is discharged to different states. In the list of positive electrode 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 positive electrode plate will usually change. 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 new materials obtained by appropriate modification on the basis of the listed positive electrode active materials are also within the scope of positive electrode active materials. The aforementioned appropriate modification refers to acceptable modification methods for positive electrode active materials, and non-limiting examples include coating modification.

[0092] In the examples of positive electrode active materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual O content will fluctuate. The O content can be measured by molar content, but is not limited to this.

[0093] As a non-limiting example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on either or both of the two facing surfaces of the positive electrode current collector.

[0094] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0095] In some embodiments, the positive electrode active material layer may further optionally include a binder. As non-limiting examples, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0096] 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.

[0097] In some embodiments, a positive electrode sheet can be prepared by dispersing the components for preparing the positive electrode sheet, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry on at least one side of a positive electrode current collector, and performing drying, cold pressing, and other processes to obtain a positive electrode sheet. The type of solvent can be selected from, but not limited to, any of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface of the positive electrode current collector or both surfaces of the positive electrode current collector. The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface of the positive electrode current collector or both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40 wt% to 80 wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 mPa·s to 25000 mPa·s. When applying the positive electrode slurry, the coating unit area density based on dry weight (excluding solvent) can be 15 mg / cm 2 -35mg / cm 2 The compaction density of the positive electrode can be 3.0g / cm 3 -3.6g / cm 3 , optional 3.3g / cm 3 -3.5g / cm 3 .

[0098] In this application, the unit "mg / cm 2 ” refers to mg / cm2.

[0099] In some embodiments, the electrolyte includes a second electrolyte salt and a solvent.

[0100] In some embodiments, the second electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorodioxalatophosphate (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP).

[0101] In some embodiments, the solvent may include ethylene carbonate (EC, ), propylene carbonate (PC, ), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate One or more of fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0102] In some embodiments, the electrolyte may optionally include other additives. For example, the other additives may include 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, and additives that improve battery high or low temperature performance.

[0103] In some embodiments, other additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0104] Another embodiment of the present application provides a method for preparing the secondary battery described above, comprising the following steps:

[0105] Covering the isolation film on the surface of the negative electrode active material layer of the negative electrode plate to obtain a composite layer;

[0106] Infiltrating the composite layer with a gel precursor solution, solidifying the gel precursor solution to form a gel electrolyte, and obtaining a composite intermediate containing the gel electrolyte;

[0107] Laminating the positive electrode sheet to the composite intermediate so that the positive electrode sheet is located on the separator side of the composite intermediate;

[0108] The electrolyte is used to wet the interface between the positive electrode sheet and the composite intermediate and the positive electrode sheet after bonding.

[0109] Thus, secondary batteries can be simply prepared, facilitating mass production of secondary batteries. Furthermore, in the composite intermediate obtained by the preparation method of the above embodiment, the negative electrode plate, separator, and gel electrolyte can form an integrated structure. The gel electrolyte can increase the diffusion path of the nitrile additive to the surface of the negative electrode plate, effectively improving the protection of the negative electrode. The positive electrode plate can be independently infiltrated with a specially designed electrolyte containing the nitrile additive, thereby expanding the range of electrolyte options and increasing the concentration of the nitrile additive, thereby enhancing the performance improvement effect of the positive electrode plate, thereby further improving the high-temperature storage performance and cycle performance of the secondary battery.

[0110] In some embodiments, the gel precursor solution contains polymer monomers, and the weight percentage of the polymer monomers in the gel precursor solution is 10%-20%. It is understood that the weight percentage of the polymer monomers in the gel precursor solution includes, but is not limited to, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, and 20%.

[0111] In some embodiments, the gel precursor solution further comprises an organic solvent, a first electrolyte salt, and an initiator.

[0112] In some embodiments, the mass proportion of the initiator in the gel precursor solution is 0.03%-0.4%. It is understood that the mass proportion of the initiator in the gel precursor solution includes but is not limited to: 0.03%, 0.05%, 0.07%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, and 0.4%.

[0113] In some embodiments, the initiator comprises an azo-based initiator.

[0114] In some embodiments, the azo initiator includes one or more of azobisisobutyronitrile, dimethyl azobisisobutyrate, and azobisisoheptanenitrile.

[0115] Yet another embodiment of the present application provides an electrical device including the secondary battery of the present application.

[0116] In addition, the secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0117] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0118] Positive electrode

[0119] The above-mentioned positive electrode sheet of this application is used.

[0120] Negative electrode

[0121] The above-mentioned negative electrode sheet of this application is used.

[0122] Isolation film

[0123] The isolation film described above is used.

[0124] electrolytes

[0125] The above-mentioned electrolyte of this application is used.

[0126] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0127] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0128] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft shell, such as a pouch-type soft shell. The material of the soft shell can be plastic. Further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0129] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0130] In this application, unless otherwise specified, a "battery cell" refers to a basic unit that can achieve the mutual conversion of chemical energy and electrical energy. Further, generally speaking, it includes at least a positive electrode plate, a negative electrode plate, and an electrolyte. During the battery's charge and discharge process, active ions are embedded in and out of the positive and negative electrode plates. The electrolyte plays the role of conducting active ions between the positive and negative electrode plates.

[0131] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG1 shows a battery cell 5 with a square structure as an example.

[0132] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and 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 be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is 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.

[0133] The secondary battery may be a battery module 4 or a battery pack 1 .

[0134] A battery module includes at least one battery cell. The number of battery cells contained in a battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0135] FIG3 shows an example battery module 4. Referring to FIG3 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0136] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0137] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select an appropriate number based on the application and capacity of the battery pack.

[0138] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0139] In addition, the present application also provides an electrical device, which includes the secondary battery provided in the present application. The secondary battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can include, but is not limited to, mobile devices, electric vehicles, electric trains, ships, satellites, energy storage systems, etc. Among them, mobile devices can be, for example, mobile phones, laptops, etc.; electric vehicles can be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to these.

[0140] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0141] Figure 6 shows an example of an electric device 6. The electric device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module can be used.

[0142] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0143] Below, the embodiment of the present application is described. The embodiment described below is exemplary, is only used to explain the present application, and is not to be construed as limiting the present application. Where the technology or conditions are not specified in the embodiment, the technology or conditions described in the literature in this area or the product instructions are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0144] Example 1

[0145] (1) Preparation of negative electrode sheet

[0146] A silicon-carbon composite negative electrode material (silicon content 20%), a conductive agent (acetylene black), and a binder (carboxymethyl cellulose) were mixed in a mass ratio of 97wt%:2wt%:1wt%, and deionized water was added and stirred evenly to obtain a negative electrode slurry; the negative electrode slurry was coated on both sides of the copper foil, dried, cold pressed, and punched to obtain a negative electrode sheet, wherein the coating amount per unit area on both sides was 0.117g / 1540.25mm 2 , the negative electrode active material layer is located on both sides of the negative electrode current collector (copper foil). In this application, the unit "g" refers to grams, and the unit "mm 2 ” refers to square millimeters.

[0147] (2) Preparation of gel precursor solution

[0148] Fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) were prepared in a mass ratio of 2:3:1 and stirred to obtain a negative electrode base electrolyte. The negative electrode base electrolyte, polyethylene glycol diacrylate (PEGDA700), and initiator azobisisobutyronitrile (AIBN) were mixed in a mass ratio of 85:15:0.3 to obtain a gel precursor solution. The acrylate monomer (i.e., polyethylene glycol diacrylate) accounted for 15% by weight of the gel precursor solution.

[0149] (3) Isolation film

[0150] A polyolefin separator coated with aluminum oxide layers on both sides was selected, and its porosity was 40%.

[0151] (4) Preparation of composite intermediates

[0152] The separator and negative electrode sheet are laminated and placed in an aluminum-plastic film, so that the separator covers the surface of the negative electrode active material layer. A gel precursor solution is injected at a ratio of 1.8 grams per ampere-hour (g / Ah), and negative pressure is applied for 5 minutes. The film is then heat-sealed for 6 hours. The aluminum-plastic film is then fixed with a clamp under a pressure of 0.5 megapascals (MPa). The film is then heated in an oven at 70 degrees Celsius for 10 hours to cure the gel electrolyte. The separator and negative electrode sheet are removed from the aluminum-plastic film to obtain a composite intermediate containing a gel electrolyte. The gel electrolyte is located within the pores of the separator and the pores of the negative electrode active material layer, and the gel electrolyte wraps around the separator and the surface of the negative electrode sheet. The thickness of the gel electrolyte between the negative electrode active material layer and the separator is 0.8 μm, and the thickness of the gel electrolyte on the surface of the separator away from the negative electrode active material layer is 2 μm.

[0153] (5) Preparation of positive electrode sheet

[0154] Lithium cobalt oxide (LiCoO2), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were mixed thoroughly in an N-methylpyrrolidone (NMP) solvent system at a weight ratio of 94:3:3, and then coated on both sides of the aluminum foil. The foil was dried and cold pressed to obtain a positive electrode sheet, which was then cut into corresponding sizes for later use. The coating amount per unit area on both sides was 0.38 g / 1540.25 mm 2 .

[0155] (6) Preparation of electrolyte

[0156] The carbonate solvents ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed in a volume ratio of EC:DEC:EMC = 1:1:1 and stirred evenly. 1.0 mol / L of lithium hexafluorophosphate was then added to dissolve the mixture. Succinonitrile additive was then added and stirred evenly to obtain an electrolyte containing a nitrile additive. The nitrile additive accounted for 5% by weight of the electrolyte.

[0157] (7) Preparation of lithium-ion batteries

[0158] The positive electrode sheet was laminated to the composite intermediate, with the positive electrode sheet positioned on the separator side of the composite intermediate, i.e., the separator was positioned between the positive and negative electrode sheets. An electrolyte solution containing a nitrile additive was injected at a rate of 1.0 g / Ah, and the electrolyte was used to soak the interface between the positive electrode sheet and the composite intermediate, as well as the positive electrode sheet. The battery was then packaged under negative pressure and soaked for 12 hours to obtain a lithium-ion battery.

[0159] Example 2-20

[0160] The method is basically the same as Example 1, except that the mass ratio of the nitrile additive in the electrolyte, the porosity of the isolation membrane, the type of acrylate monomer in the gel precursor, the number of repeating structural units in the acrylate monomer, the mass ratio of the acrylate monomer in the gel precursor, the mass ratio of the base electrolyte, the acrylate monomer and the initiator in the gel precursor, and the type of the organic solvent in the gel precursor are changed, as described in Table 1.

[0161] The mass ratio of fluoroethylene carbonate, ethyl methyl carbonate, and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) in the gel precursor solution of Example 18 is 1:1:1.

[0162] Comparative Example 1

[0163] (1) Preparation of negative electrode sheet

[0164] A silicon-carbon composite negative electrode material (silicon content 20%), a conductive agent (acetylene black), and a binder (carboxymethyl cellulose) were mixed in a mass ratio of 97wt%:2wt%:1wt%, and deionized water was added and stirred evenly to obtain a negative electrode slurry; the negative electrode slurry was coated on both sides of the copper foil, dried, cold pressed, and punched to obtain a negative electrode sheet, wherein the coating amount per unit area on both sides was 0.117g / 1540.25mm 2 .

[0165] (2) Isolation film

[0166] A polyolefin separator coated with aluminum oxide layers on both sides was selected, and its porosity was 40%.

[0167] (3) Preparation of positive electrode sheet

[0168] Lithium cobalt oxide (LiCoO2), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were mixed thoroughly in an N-methylpyrrolidone (NMP) solvent system at a weight ratio of 94:3:3, and then coated on both sides of the aluminum foil. The foil was dried and cold pressed to obtain a positive electrode sheet, which was then cut into corresponding sizes for later use. The coating amount per unit area on both sides was 0.38 g / 1540.25 mm 2 .

[0169] (4) Preparation of electrolyte

[0170] The carbonate solvents ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed in a volume ratio of EC:DEC:EMC = 1:1:1 and stirred evenly. 1.0 mol / L lithium hexafluorophosphate was then added to dissolve the mixture. A 5% by mass fraction (based on the total weight of the electrolyte containing the nitrile additive) of succinonitrile additive was then added and stirred evenly to obtain an electrolyte containing the nitrile additive.

[0171] (5) Preparation of lithium-ion batteries

[0172] The negative electrode sheet, separator, and positive electrode sheet were stacked, with the separator positioned between the positive and negative electrodes. An electrolyte solution containing a nitrile additive was injected at a rate of 1.6 g / Ah. The battery was then sealed under negative pressure and allowed to soak for 12 hours to produce a lithium-ion battery.

[0173] Performance Testing

[0174] (1) High temperature storage test

[0175] At 45°C, the lithium-ion battery was charged to 4.5 volts (V) at a rate of 0.5C, then charged at a constant voltage until the current dropped below 0.05C. It was then discharged to 2.5V at a rate of 0.5C. The initial discharge capacity was recorded as C1. The lithium-ion battery was adjusted to 100% SOC and stored at 45°C. After 30 days, the charge and discharge cycle was repeated using the same procedure. The discharge capacity was recorded as C2.

[0176] High temperature storage capacity retention rate (%) = C2 / C1×100%.

[0177] (2) Cyclic performance test

[0178] At 45°C, charge the lithium-ion battery to 4.5V at a rate of 0.5C, then charge at a constant voltage until the current is less than 0.05C, and then discharge it to 2.5V at a rate of 0.5C. Perform a cycle test in this full-charge-discharge form until the discharge capacity of the lithium-ion battery decays to 80% of the initial capacity, and record the number of cycles at this time.

[0179] The product parameters and performance test results of each embodiment and each comparative example are shown in Table 1 and Table 2, wherein “ / ” represents the absence of the substance or parameter.

[0180] Table 1

[0181] Table 2

[0182] It can be seen from Tables 1 and 2 that compared with Comparative Example 1, the high-temperature storage capacity retention rate of the batteries of Examples 1-20 and the number of cycles in which the discharge capacity of the batteries decays to 80% of the initial capacity at 45°C are significantly higher, indicating that the combined use of the positive electrode sheet, the negative electrode sheet, the isolation membrane, the gel electrolyte and the electrolyte containing nitrile additives in the secondary batteries of Examples 1-20 of the present application effectively improves the high-temperature storage performance and cycle performance of the secondary batteries.

[0183] The above description of the various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced with each other and will not be repeated herein for the sake of brevity.

[0184] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery, comprising a positive electrode plate, a negative electrode plate, an electrolytic solution, a gel electrolyte, and a separator disposed between the positive electrode plate and the negative electrode plate. The negative electrode plate includes a negative active material layer. The gel electrolyte is at least located between the negative active material layer and the separator, in the pores of the negative active material layer, and in the pores of the separator. The electrolytic solution contains a nitrile additive.

2. The secondary battery according to claim 1, wherein, The mass ratio of the nitrile additive in the electrolytic solution is 0.1%-20%.

3. The secondary battery according to claim 1 or 2, wherein The mass ratio of the nitrile additive in the electrolytic solution is 0.5%-10%.

4. The secondary battery according to any one of claims 1 to 3, wherein, The nitrile additive includes one or more of acetonitrile, propionitrile, butyronitrile, pivalonitrile, hexanenitrile, malononitrile, succinonitrile, glutaronitrile, and adiponitrile.

5. The secondary battery according to any one of claims 1 to 4, wherein, The porosity of the separator is 32%-45%.

6. The secondary battery according to any one of claims 1 to 5, wherein, The porosity of the separator is 37%-42%.

7. The secondary battery according to any one of claims 1 to 6, wherein, The gel electrolyte contains a polymer, and the monomers of the polymer include acrylate monomers.

8. The secondary battery according to claim 7, wherein, The number of repeating structural units in the acrylate monomer is 50-2000.

9. The secondary battery according to claim 7 or 8, wherein The number of repeating structural units in the acrylate monomer is 200-800.

10. The secondary battery according to any one of claims 7 to 9, wherein, The acrylate monomer includes one or more of pentaerythritol tetraacrylate, polyethylene glycol diacrylate, triethylene glycol dimethacrylate, trimethylolpropane triacrylate, and ethoxylated trimethylolpropane triacrylate.

11. The secondary battery according to any one of claims 1 to 10, wherein, The gel electrolyte further contains an organic solvent. The organic solvent includes a carbonate organic solvent. The carbonate organic solvent includes a chain carbonate organic solvent and a fluorinated carbonate organic solvent. The mass ratio of the chain carbonate organic solvent to the fluorinated carbonate organic solvent is 1:1-5:

1.

12. The secondary battery according to any one of claims 1 to 11, wherein, The thickness of the gel electrolyte located between the negative active material layer and the separator is 0.1 μm-5 μm.

13. The secondary battery according to any one of claims 1 to 12, wherein, The gel electrolyte is also located on the surface of the separator away from the negative active material layer.

14. The secondary battery according to any one of claims 1 to 13, wherein, The gel electrolyte is in the pores of the negative active material layer and in the pores of the separator, and the gel electrolyte wraps around the surfaces of the separator and the negative electrode plate.

15. The secondary battery according to any one of claims 1 to 14, wherein, The positive electrode plate includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer contains a positive active material. The positive active material includes one or more of lithium cobalt oxide, lithium nickel manganese oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds.

16. A method for preparing a secondary battery, comprising the following steps: Cover the separator on the surface of the negative active material layer of the negative electrode plate to obtain a composite layer; Infiltrate the composite layer with a gel precursor solution to cure the gel precursor solution to form the gel electrolyte. The gel electrolyte is at least located between the negative active material layer and the separator, in the pores of the negative active material layer, and in the pores of the separator, to obtain a composite intermediate containing the gel electrolyte; Bond the positive electrode plate to the composite intermediate so that the positive electrode plate is on the separator side of the composite intermediate; Infiltrate the interface between the positive electrode sheet and the composite intermediate and the positive electrode sheet after lamination with an electrolyte containing a nitrile additive.

17. The preparation method according to claim 16, wherein, The gel precursor solution contains monomers of a polymer, and the mass percentage of the monomers of the polymer in the gel precursor solution is 10%-20%.

18. An electrical device includes at least one of the secondary batteries according to any one of claims 1 to 15 and the secondary battery prepared by the preparation method according to any one of claims 16 to 17.

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