Polymer gel electrolyte, secondary battery and electric device

Abstract

The present application relates to a polymer gel electrolyte, a secondary battery and an electric device. The polymer gel electrolyte comprises a polymer framework and an electrolyte solution located in gaps of the polymer framework, wherein the polymer framework comprises a cyclic group. The polymer gel electrolyte has a high ionic conductivity and a high ion migration number, and can make the internal resistance (DCR) of the battery relatively small.

Description

Polymer gel electrolyte, secondary battery, and electrical device

[0001] Related applications

[0002] This application claims priority to Chinese patent application number 2024101697399, filed on February 6, 2024, entitled “Polymer Gel Electrolyte and Secondary Battery, Electrical Device,” the entire text of which is hereby incorporated by reference. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a polymer gel electrolyte, a secondary battery, and an electrical device. Background Art

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

[0005] In recent years, batteries have been widely used in energy storage power systems such as hydropower, thermal, wind and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields, and their application scope is becoming more and more extensive.

[0006] The electrolyte materials used in batteries can be divided into liquid electrolytes (electrolytes) and solid electrolytes. Among them, polymer electrolytes have attracted much attention due to their excellent processability and good interfacial contact properties, and are currently the only commercial solid electrolyte material. Early polymer electrolytes did not contain solvents and relied solely on the movement of polymer chains to drive lithium ion transport, but their ionic conductivity was low. Therefore, in recent years, there have been methods to bind the electrolyte in the polymer skeleton to form a polymer electrolyte similar to a gel substance, which can be called a polymer gel electrolyte. Compared with early polymer electrolytes, the ionic conductivity has been greatly improved. However, compared with liquid electrolytes, there is still a certain gap, especially under high-rate discharge conditions, the internal resistance of the battery (DCR) is large, and the ionic conductivity and ion transport characteristics such as ion mobility need to be further improved.

[0007] Summary of the Invention

[0008] The present application provides a polymer gel electrolyte having high ionic conductivity and ion transference number, thereby reducing the internal resistance (DCR) of the battery, as well as a secondary battery and an electrical device comprising the polymer gel electrolyte.

[0009] In a first aspect of the present application, a polymer gel electrolyte is provided, comprising a polymer skeleton and an electrolyte located in the gaps of the polymer skeleton, wherein the polymer skeleton comprises a cyclic group, and the cyclic group comprises one or more structures represented by the following formulae (I), (II), (III), and (IV):

[0010] wherein R0 includes one or more of H, C1-C5 hydrocarbon group, fluorinated C1-C5 hydrocarbon group and C3-C10 ester group;

[0011] n1 includes integers from 0 to 10;

[0012] n2 includes integers from 0 to 10;

[0013] m includes integers from 0 to 5;

[0014] q includes integers from 0 to 5.

[0015] The polymer gel electrolyte adopts a polymer skeleton containing specific cyclic groups, which can improve the ionic conductivity and ion transference number, thereby slowing down the deterioration of DCR.

[0016] In some embodiments, R0 includes one or more of H and C3-C10 ester groups; and / or,

[0017] n1 includes 0, 1, 2, 3 or 4; and / or,

[0018] n2 includes 0, 1, 2, 3 or 4; and / or,

[0019] m includes 0 or 1; and / or,

[0020] q includes 0, 1 or 2.

[0021] In some embodiments, the cyclic group includes one or more of the structures shown in the following formulae (I-1), (II-1), (II-2), (III-1) and (IV-1):

[0022] In some embodiments, the infrared spectrum of the polymer backbone includes a peak at 1220 cm -1 ~1320cm -1 The CN stretching vibration peak is located at 1655 cm -1 ~1750cm -1 The C=O stretching vibration peak.

[0023] In some embodiments, the mass percentage of the cyclic groups in the polymer backbone is 1% to 20%. Reasonable control of the mass percentage of the cyclic groups in the polymer backbone can further improve the ionic conductivity and ion transference number of the electrolyte. Furthermore, the mass percentage of the cyclic groups in the polymer backbone is 5% to 15%.

[0024] In some embodiments, the polymer backbone comprises a cross-linked polymer having a three-dimensional network structure.

[0025] In some embodiments, the cross-linked polymer having a three-dimensional network structure includes a polymer obtained by copolymerizing a monomer containing a cyclic group and a cross-linking agent; the monomer containing a cyclic group includes one or more structures represented by the following formulas (1), (2), (3) and (4):

[0026] Wherein, R0, n1, n2, m and q are defined as above.

[0027] In some embodiments, the cyclic group-containing monomer includes one or more of maleimide, 6-vinyl-2-piperidone, N-vinylpyrrolidone, 7-vinyl-hexahydropyrrolazin-3-one, N-vinylcaprolactam and 4-allyl-5-oxopyrrolidine-2-carboxylic acid methyl ester.

[0028] In some embodiments, the cross-linking agent comprises a carbon-carbon double bond in its chemical formula.

[0029] In some embodiments, the number of carbon-carbon double bonds in the chemical formula of the cross-linking agent is P, and P ≥ 3. Using a cross-linking agent with ≥ 3 carbon-carbon double bonds has high reactivity, which is conducive to forming a structurally stable polymer backbone, thereby facilitating the interaction between the polymer backbone and the electrolyte.

[0030] In some embodiments, 3≤P≤6. Reasonable control of the number of carbon-carbon double bonds stabilizes the polymer skeleton, improves ionic conductivity and ion migration number, and also provides relatively suitable fluidity, which is beneficial for material filling and infiltration before polymerization in secondary batteries.

[0031] In some embodiments, the crosslinking agent includes an acrylate crosslinking agent. This crosslinking agent can react quickly with the monomer, and the copolymer system has a high liquid retention capacity, thereby further improving ionic conductivity and slowing down the deterioration of DCR.

[0032] In some embodiments, the crosslinking agent includes one or more of isopentaerythritol tetraacrylate, di(trimethylolpropane) tetraacrylate, polydipentaerythritol hexaacrylate, trimethylolpropane triacrylate, and pentaerythritol triacrylate.

[0033] In some embodiments, the mass ratio of the cyclic group-containing monomer to the crosslinker is (0.01-0.25):1. This allows for the formation of a gel electrolyte with moderate flexibility while also improving ionic conductivity and ion transference number. Furthermore, the mass ratio of the cyclic group-containing monomer to the crosslinker is (0.05-0.18):1.

[0034] In some embodiments, the solvent of the electrolyte includes one or more of a carbonate solvent and an ether solvent.

[0035] In some embodiments, the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, and fluoroethylene carbonate; and / or

[0036] The ether solvent includes one or more of ethylene glycol dimethyl ether, tetrahydrofuran, dioxolane, methyl nonafluoro-n-butyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, octafluoropentyl-tetrafluoroethyl ether, 1,2-bis(cyanoethoxy)ethane, diphenyl ether and 18-crown-6.

[0037] In some embodiments, the mass ratio of the electrolyte to the polymer skeleton is 200% to 5000%. The polymer gel electrolyte thus formed has moderate hardness, good contact with the positive and negative electrodes, and high ionic conductivity and lithium ion transference number.

[0038] In some embodiments, the polymer gel electrolyte has at least one of the following features (1) to (2):

[0039] (1) Ionic conductivity is 0.5mS / cm to 10mS / cm;

[0040] (2) The lithium ion migration number is 0.3 to 0.8.

[0041] In some embodiments, the polymer gel electrolyte has at least one of the following features (1) to (2):

[0042] (1) Ionic conductivity is 4mS / cm to 9mS / cm;

[0043] (2) The lithium ion migration number is 0.3 to 0.5.

[0044] A second aspect of the present application provides a secondary battery comprising the polymer gel electrolyte described in the first aspect.

[0045] The electric device of the present application includes the polymer gel electrolyte provided by the present application, and thus has at least the same advantages as the polymer gel electrolyte.

[0046] A third aspect of the present application provides an electrical device comprising the secondary battery according to the second aspect of the present application.

[0047] 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.

[0048] 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

[0049] 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:

[0050] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0051] FIG2 is an exploded view of a battery cell according to an embodiment of the present application shown in FIG1 ;

[0052] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0053] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0054] FIG5 is an exploded view of the battery pack shown in FIG4 according to an embodiment of the present application;

[0055] FIG6 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application;

[0056] FIG7 is a SEM morphology image of a polymer gel electrolyte according to one embodiment of the present application;

[0057] Description of reference numerals:

[0058] 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

[0059] Below, some embodiments of the polymer gel electrolyte and its preparation method, secondary battery, and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be 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 understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0060] The "ranges" disclosed in this application can be defined in the form of lower limits and upper limits. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. Ranges defined in this way can be inclusive or exclusive of the end values, any end value can be included or excluded independently, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4, and 5 are also listed, the following ranges are all expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" is an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply 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.

[0061] 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.

[0062] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0063] 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.

[0064] 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.

[0065] In this application, in the open technical features or technical solutions described with words such as "contain", "include", and "include", unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions that also include additional members in addition to the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2, and a3" and the feature or solution of "A includes not only a1, a2, and a3, but also other members". In this application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0066] 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.

[0067] In this application, "*" indicates the attachment site of a group in the polymer backbone.

[0068] Some examples of the present application provide a polymer gel electrolyte, comprising a polymer skeleton and an electrolyte located in the gaps of the polymer skeleton, wherein the polymer skeleton comprises a cyclic group, and the cyclic group comprises one or more structures represented by the following formulas (I), (II), (III), and (IV):

[0069] wherein R0 includes one or more of H, C1-C5 hydrocarbon group, fluorinated C1-C5 hydrocarbon group and C3-C10 ester group;

[0070] n1 includes integers from 0 to 10;

[0071] n2 includes integers from 0 to 10;

[0072] m includes integers from 0 to 5;

[0073] q includes integers from 0 to 5.

[0074] It can be understood that n1, n2, m, and q being 0 means that the groups at both ends are directly bonded by single bonds.

[0075] Compared with solvent-free polymer electrolytes, the presence of electrolyte in polymer gel electrolytes can improve the ion transport properties of the electrolyte. At the same time, during the charge and discharge process, as the volume changes due to the insertion and extraction of lithium ions, whether the electrolyte can be stably present in the polymer skeleton is one of the keys to further improve the ion transport properties. The polymer skeleton of the above polymer gel electrolyte contains specific cyclic groups:

[0076] On the one hand, the cyclic group can promote the dissociation of the electrolyte lithium salt, improve the ion transport of the polymer electrolyte, especially the ion transference number, and thus slow down the deterioration of the DCR. The possible mechanism is that the cyclic group can effectively weaken the Coulomb attraction between the anion and cation of the electrolyte salt, thereby helping to weaken the binding strength between the two, thereby promoting the dissociation of the electrolyte salt. At the same time, it can also form hydrogen bonds with the anion of the electrolyte salt to promote ion migration.

[0077] On the other hand, the cyclic group can enhance the binding ability between the polymer skeleton and the electrolyte solvent. The possible principle is that the cyclic group has similar compatibility with the electrolyte solvent, and compared with the chain amide group, the cyclic group has a larger dielectric constant, better solubility in the electrolyte solvent than the chain amide, and a strong binding force with the electrolyte solvent, so it has a strong liquid retention ability, which can reduce the electrolyte being squeezed out due to the expansion of the battery cell during the application of the battery; at the same time, it can also reduce the reduction reaction of the electrolyte solvent on the negative electrode side, thereby reducing the consumption of the electrolyte, achieving better ionic conductivity and slowing down the deterioration of DCR.

[0078] In summary, the above-mentioned polymer gel electrolyte can improve the ionic conductivity and ion transference number by introducing cyclic groups into the polymer skeleton to interact with the electrolyte, thereby slowing down the deterioration of DCR.

[0079] Without limitation, "C1-C5 hydrocarbon group" includes, but is not limited to, C1 hydrocarbon group, C2 hydrocarbon group, C3 hydrocarbon group, C4 hydrocarbon group, C5 hydrocarbon group, or a range between any two of the foregoing. Furthermore, C1-C5 hydrocarbon group includes C1-C5 alkyl group.

[0080] Without limitation, "fluorinated C1-C5 hydrocarbon group" includes, but is not limited to, fluorinated C1 hydrocarbon group, fluorinated C2 hydrocarbon group, fluorinated C3 hydrocarbon group, fluorinated C4 hydrocarbon group, fluorinated C5 hydrocarbon group, or a range between any two of the foregoing. Furthermore, fluorinated C1-C5 hydrocarbon group includes fluorinated C1-C5 alkyl group. The number of "fluorinated" groups is not limited, and can be, for example, 1 to 10.

[0081] Without limitation, “C3-C10 ester group” includes but is not limited to: C3 ester group, C4 ester group, C5 ester group, C6 ester group, C7 ester group, C8 ester group, C9 ester group, C10 ester group or a range between any two of the foregoing.

[0082] In some examples, R0 includes one or more of H and a C3-C10 ester group.

[0083] Without limitation, n1 includes 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or a range between any two of the foregoing. Further, n1 includes 0, 1, 2, 3 or 4.

[0084] Without limitation, n2 includes 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or a range between any two of the foregoing. Further, n2 includes 0, 1, 2, 3 or 4.

[0085] Without limitation, m includes 0, 1, 2, 3, 4, 5, or a range between any two of the foregoing. Further, m includes 0 or 1.

[0086] Without limitation, q includes 0, 1, 2, 3, 4, 5 or a range between any two of the foregoing. Further, q includes 0, 1 or 2.

[0087] In some examples, the cyclic group includes one or more of the structures shown in the following formulae (I-1), (II-1), (II-2), (III-1) and (IV-1):

[0088] In some examples, the infrared spectrum of the polymer backbone includes a peak at 1220 cm -1 ~1320cm -1 The CN stretching vibration peak is located at 1655 cm -1 ~1750cm -1 The C=O stretching vibration peak of the infrared spectrum reflects the presence of the cyclic group. In addition, without limitation, the infrared spectrum of the polymer skeleton may also include a peak at 3100 cm -1 ~3500cm -1 The NH stretching vibration peak at or including 3000 cm -1 ~3700cm -1Furthermore, the infrared spectrum of the polymer skeleton has a peak at 3100 cm -1 ~3500cm -1 There is no NH stretching vibration peak in the range, that is, there is a substituent on the N of the cyclic group, which can further improve the ionic conductivity and ion migration number of the electrolyte.

[0089] In some examples, the mass percentage of the cyclic group in the polymer backbone is 1% to 20%. Reasonable control of the mass percentage of the cyclic group in the polymer backbone can further improve the ionic conductivity and ion migration number of the electrolyte. Specifically, the mass percentage of the cyclic group includes but is not limited to: 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% or a range between the foregoing. Further, the mass percentage of the cyclic group is 5% to 15%.

[0090] Without limitation, the mass percentage of the cyclic groups in the polymer backbone can be obtained by testing as follows:

[0091] The secondary battery is disassembled, and the polymer gel electrolyte is collected. After being crushed, the polymer gel electrolyte is washed with a DMC solvent for multiple times and then dried in an oven to obtain a polymer skeleton. The polymer skeleton is tested by Fourier transform infrared spectroscopy (FT-IR), and the ratio of the two C=O stretching vibration peak areas x (C=O stretching vibration peak (small area) of the monomer containing a cyclic group in the polymer skeleton / C=O stretching vibration peak (large area) of the cross-linking agent in the polymer skeleton) is calculated, that is, the ratio of the number of C=O in the monomer containing a cyclic group to the number of C=O in the cross-linking agent in the polymer skeleton. The number of C=O in the cross-linking agent in the polymer skeleton (that is, the number of cross-linking groups (such as double bonds) in the cross-linking agent) is taken as 1, and x is the number of C=O in the monomer containing a cyclic group. Combined with the molecular weight range of the monomer containing a cyclic group and the cross-linking agent, the mass percentage of the two is obtained, and then the molecular weight (M) of the monomer containing a cyclic group is obtained. m ) and the molecular weight of the cross-linker (M c The mass percentage of the cyclic groups in the polymer backbone is calculated as follows:

[0092] x*M1 / (M2+x*M1)

[0093] Among them, M1 is M m The ratio of M2 to n, where n refers to the number of amide carbonyl groups in the cyclic group; M2 is M c The ratio of m to m refers to the number of crosslinking groups in the crosslinker.

[0094] In some examples, the polymer backbone comprises polyacrylate structural units. It is understood that the polyacrylate structural units can be obtained by double bond opening polymerization of an acrylate crosslinking agent.

[0095] In some examples, the polymer backbone comprises a cross-linked polymer having a three-dimensional network structure. Furthermore, the cross-linked polymer having a three-dimensional network structure comprises a polymer obtained by copolymerizing a monomer containing a cyclic group with a cross-linking agent; the monomer containing a cyclic group comprises one or more structures represented by the following formulas (1), (2), (3) and (4):

[0096] Wherein, R0, n1, n2, m and q are defined as above.

[0097] In some examples, the cyclic group includes one or more of the structures shown in the following formulae (1-1), (2-1), (2-2), (3-1) and (4-1):

[0098] In some examples, the cyclic group-containing monomer includes one or more of maleimide, 6-vinyl-2-piperidone, N-vinylpyrrolidone, 7-vinyl-hexahydropyrrolazin-3-one, N-vinylcaprolactam and methyl-4-allyl-5-oxopyrrolidine-2-carboxylate.

[0099] In some examples, the chemical formula of the crosslinker includes a carbon-carbon double bond. Furthermore, the number of carbon-carbon double bonds in the chemical formula of the crosslinker is P, where P ≥ 3. Using a crosslinker with ≥ 3 carbon-carbon double bonds exhibits high reactivity, facilitates the formation of a structurally stable polymer backbone, and thus enhances the interaction between the polymer backbone and the electrolyte.

[0100] In some examples, 3 ≤ P ≤ 6. Reasonable control of the number of carbon-carbon double bonds stabilizes the polymer backbone, improves ionic conductivity and ion mobility, and provides suitable fluidity, facilitating material filling and impregnation prior to polymerization in secondary batteries. Specifically, the number of carbon-carbon double bonds P in the chemical formula of the crosslinker includes, but is not limited to, 3, 4, 5, or 6.

[0101] In some examples, the crosslinker is an acrylate crosslinker, which reacts quickly with the monomer and provides a high liquid retention capacity for the copolymer system, thereby further improving ionic conductivity and slowing down DCR degradation.

[0102] Without limitation, the crosslinking agent includes one or more of isopentaerythritol tetraacrylate, di(trimethylolpropane) tetraacrylate, polydipentaerythritol hexaacrylate, trimethylolpropane triacrylate, and pentaerythritol triacrylate.

[0103] In some examples, the infrared spectrum of the polymer backbone includes a peak at 1220 cm -1 ~1320cm -1 The CN stretching vibration peak is located at 1655 cm -1 ~1750cm -1 The C=O stretching vibration peak is located at 1655cm without restriction. -1 ~1750cm -1 The C=O stretching vibration peaks include two, corresponding to the C=O stretching vibration peak of the cyclic group in the polymer skeleton and the C=O stretching vibration peak of the acrylate crosslinking agent.

[0104] In some examples, the mass ratio of the monomer containing a cyclic group to the cross-linking agent is (0.01 to 0.25): 1. In this way, on the one hand, a gel electrolyte with moderate flexibility can be formed; on the other hand, it is beneficial to improve the ionic conductivity and the ion migration number. Specifically, the mass ratio of the monomer containing a cyclic group to the cross-linking agent includes but is not limited to: 0.01: 1, 0.05: 1, 0.07: 1, 0.11: 1, 0.14: 1, 0.15: 1, 0.18: 1, 0.2: 1, 0.24: 1, 0.25: 1 or a range between the foregoing two. Further, the mass ratio of the monomer containing a cyclic group to the cross-linking agent is (0.05 to 0.18): 1.

[0105] In some examples, the solvent of the electrolyte includes one or more of a carbonate solvent and an ether solvent. It is understandable that for lithium-ion batteries, carbonate solvents are mainly used as solvents, while for lithium metal batteries, ether solvents are mainly used.

[0106] In some examples, the electrolyte solvent is a carbonate solvent, which has a stronger interaction with the polymer backbone, thereby improving ionic conductivity and ion transference number.

[0107] Without limitation, the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate and fluoroethylene carbonate.

[0108] Without limitation, the ether solvent includes one or more of ethylene glycol dimethyl ether, tetrahydrofuran, dioxolane, methyl nonafluoro-n-butyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, octafluoropentyl-tetrafluoroethyl ether, 1,2-bis(cyanoethoxy)ethane, diphenyl ether and 18-crown-6.

[0109] In some examples, the mass percentage of the electrolyte is 200% to 5000% based on the total mass of the cyclic group-containing monomer and the cross-linking agent. The polymer gel electrolyte formed in this way has moderate hardness, can contact well with the positive and negative electrodes, and also has high ionic conductivity and lithium ion migration number. Specifically, the mass percentage of the electrolyte includes but is not limited to: 200%, 400%, 600%, 1000%, 1500%, 2000%, 2500%, 3000%, 3500%, 4000%, 4500%, 5000% or a range between the foregoing two. Furthermore, the mass percentage of the electrolyte is 400% to 600%.

[0110] In addition, without limitation, the concentration of the lithium salt in the electrolyte is 0.5 M to 3 M. The types of lithium salts include, but are not limited to, one or more of lithium hexafluorophosphate, tetrafluoroboric acid, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalatoborate, lithium perchlorate, and lithium bis(oxalatoborate).

[0111] In some examples, the ionic conductivity of the polymer gel electrolyte is 0.5 millisiemens / cm (mS / cm) to 10 mS / cm. Specifically, the ionic conductivity of the polymer gel electrolyte includes but is not limited to: 0.5 mS / cm, 1 mS / cm, 2 mS / cm, 3 mS / cm, 4 mS / cm, 4.1 mS / cm, 4.2 mS / cm, 4.5 mS / cm, 4.8 mS / cm, 5.9 mS / cm, 6.1 mS / cm, 6.2 mS / cm, 6.5 mS / cm, 7.1 mS / cm, 7.3 mS / cm, 7.5 mS / cm, 7.8 mS / cm, 8 mS / cm, 8.1 mS / cm, 8.2 mS / cm, 8.3 mS / cm, 8.5 mS / cm, 9 mS / cm, 9.5 mS / cm, 10 mS / cm, or a range therebetween. Furthermore, the ionic conductivity is 4 mS / cm to 9 mS / cm.

[0112] In some examples, the lithium ion transference number of the polymer gel electrolyte is 0.3 to 0.8. Specifically, the lithium ion transference number of the polymer gel electrolyte includes but is not limited to: 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.4, 0.41, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, or a range therebetween. Furthermore, the lithium ion transference number is 0.3 to 0.5.

[0113] Another aspect of the present application provides a method for preparing a polymer gel electrolyte, comprising the following steps:

[0114] The polymer gel electrolyte is prepared by mixing a monomer containing a cyclic group, a cross-linking agent and an electrolyte and performing a polymerization reaction.

[0115] The above-described preparation method involves polymerizing a cyclic group-containing monomer and a cross-linking agent to form a polymer backbone, while simultaneously binding the electrolyte within the polymer backbone. The resulting polymer gel electrolyte has similar design and advantages to the aforementioned polymer gel electrolytes, and will not be further elaborated here. Furthermore, this preparation method produces the polymer gel electrolyte in a single-step reaction, making it simple to operate and amenable to industrial implementation.

[0116] In some examples, the cyclic group-containing monomer contains one carbon-carbon double bond. Having only one carbon-carbon double bond allows the cyclic group to be located pendant or to one side of the polymer backbone (i.e., not directly on the central axis of the backbone) after polymerization. This gives it greater freedom of movement, allowing for better contact with the electrolyte, and improving ionic conductivity and ion transference number.

[0117] In some examples, the cyclic group-containing monomer includes one or more of the structures shown in the following formulae (1), (2), (3) and (4):

[0118] wherein R0 includes one or more of H, C1-C5 hydrocarbon group, fluorinated C1-C5 hydrocarbon group and C3-C10 ester group;

[0119] n1 includes integers from 0 to 10;

[0120] n2 includes integers from 0 to 10;

[0121] m includes integers from 0 to 5;

[0122] q includes integers from 0 to 5.

[0123] Without limitation, "C1-C5 hydrocarbon group" includes, but is not limited to, C1 hydrocarbon group, C2 hydrocarbon group, C3 hydrocarbon group, C4 hydrocarbon group, C5 hydrocarbon group, or a range between any two of the foregoing. Furthermore, C1-C5 hydrocarbon group includes C1-C5 alkyl group.

[0124] Without limitation, "fluorinated C1-C5 hydrocarbon group" includes, but is not limited to, fluorinated C1 hydrocarbon group, fluorinated C2 hydrocarbon group, fluorinated C3 hydrocarbon group, fluorinated C4 hydrocarbon group, fluorinated C5 hydrocarbon group, or a range between any two of the foregoing. Furthermore, fluorinated C1-C5 hydrocarbon group includes fluorinated C1-C5 alkyl group. The number of "fluorinated" groups is not limited, and can be, for example, 1 to 10.

[0125] Without limitation, “C3-C10 ester group” includes but is not limited to: C3 ester group, C4 ester group, C5 ester group, C6 ester group, C7 ester group, C8 ester group, C9 ester group, C10 ester group or a range between any two of the foregoing.

[0126] In some examples, R0 includes one or more of H and a C3-C10 ester group.

[0127] Without limitation, n1 includes 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or a range between any two of the foregoing. Further, n1 includes 0, 1, 2, 3 or 4.

[0128] Without limitation, n2 includes 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or a range between any two of the foregoing. Further, n2 includes 0, 1, 2, 3 or 4.

[0129] Without limitation, m includes 0, 1, 2, 3, 4, 5, or a range between any two of the foregoing. Further, m includes 0 or 1.

[0130] Without limitation, q includes 0, 1, 2, 3, 4, 5 or a range between any two of the foregoing. Further, q includes 0, 1 or 2.

[0131] In some examples, the cyclic group-containing monomer includes one or more compounds represented by the following formulae (1-1), (2-1), (3-2), (4-1) and (IV-1):

[0132] In some examples, the monomer containing a cyclic group includes one or more of the compounds shown in formula (2-1), (2-2), (3-1) and (4-1). In this way, after the monomer is polymerized, the cyclic group is located on the side chain of the polymer main chain and is more flexible, thereby better contacting the electrolyte, improving the ion conductivity and the ion migration number. Further, the monomer containing a cyclic group includes one or more of the compounds shown in formula 3-1) and 4-1). Setting the double bond on the amino group, or further cyclizing the amino group, on the one hand, can improve the solubility of the monomer in the electrolyte, and on the other hand, can improve the electrochemical stability of the polymer skeleton, while also reducing the possibility of side reactions between the amino group and the electrolyte, thereby reducing the consumption of the electrolyte and improving the ion conductivity and the ion migration number.

[0133] Without limitation, the monomer containing a cyclic group includes maleimide 6-vinyl-2-piperidone N-vinyl pyrrolidone 7-Vinyl-hexahydropyrrolizin-3-one N-vinylcaprolactam and methyl 4-allyl-5-oxopyrrolidine-2-carboxylate One or more of .

[0134] In some examples, the chemical formula of the crosslinker includes a carbon-carbon double bond. Furthermore, the number of carbon-carbon double bonds in the chemical formula of the crosslinker is P, where P ≥ 3. Using a crosslinker with ≥ 3 carbon-carbon double bonds exhibits high reactivity, facilitates the formation of a structurally stable polymer backbone, and thus facilitates interaction between the polymer backbone and the electrolyte.

[0135] In some examples, 3 ≤ P ≤ 6. Reasonable control of the number of carbon-carbon double bonds stabilizes the polymer backbone, improves ionic conductivity and ion mobility, and provides suitable fluidity, facilitating material filling and impregnation prior to polymerization in secondary batteries. Specifically, the number of carbon-carbon double bonds P in the chemical formula of the crosslinker includes, but is not limited to, 3, 4, 5, or 6.

[0136] In some examples, the crosslinker is an acrylate crosslinker, which reacts quickly with the monomer and provides a high liquid retention capacity for the copolymer system, thereby further improving ionic conductivity and slowing down DCR degradation.

[0137] Without limitation, the crosslinking agent includes one or more of isopentaerythritol tetraacrylate, di(trimethylolpropane) tetraacrylate, polydipentaerythritol hexaacrylate, trimethylolpropane triacrylate, and pentaerythritol triacrylate.

[0138] In some examples, the mass ratio of the monomer containing a cyclic group to the cross-linking agent is (0.01 to 0.25): 1. In this way, on the one hand, a gel electrolyte with moderate flexibility can be formed; on the other hand, it is beneficial to improve the ionic conductivity and the ion migration number. Specifically, the mass ratio of the monomer containing a cyclic group to the cross-linking agent includes but is not limited to: 0.01: 1, 0.05: 1, 0.07: 1, 0.11: 1, 0.14: 1, 0.15: 1, 0.18: 1, 0.2: 1, 0.24: 1, 0.25: 1 or a range between the foregoing two. Further, the mass ratio of the monomer containing a cyclic group to the cross-linking agent is (0.05 to 0.18): 1.

[0139] In some examples, the electrolyte solvent includes one or more of a carbonate solvent and an ether solvent. In some examples, the electrolyte solvent is a carbonate solvent. Such solvents interact more strongly with the polymer backbone, thereby improving ionic conductivity and ion transference number.

[0140] Without limitation, the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate and fluoroethylene carbonate.

[0141] Without limitation, the ether solvent includes one or more of ethylene glycol dimethyl ether, tetrahydrofuran, dioxolane, methyl nonafluoro-n-butyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, octafluoropentyl-tetrafluoroethyl ether, 1,2-bis(cyanoethoxy)ethane, diphenyl ether and 18-crown-6.

[0142] In some examples, the mass percentage of the electrolyte is 200% to 5000% based on the total mass of the cyclic group-containing monomer and the cross-linking agent. The polymer gel electrolyte formed in this way has moderate hardness, can contact well with the positive and negative electrodes, and also has high ionic conductivity and lithium ion migration number. Specifically, the mass percentage of the electrolyte includes but is not limited to: 200%, 400%, 600%, 1000%, 1500%, 2000%, 2500%, 3000%, 3500%, 4000%, 4500%, 5000% or a range between the foregoing two. Furthermore, the mass percentage of the electrolyte is 400% to 600%.

[0143] In addition, without limitation, the concentration of the lithium salt in the electrolyte is 0.5 molar concentration (mol / L, M) to 3 M. The types of lithium salts include, but are not limited to, one or more of lithium hexafluorophosphate, tetrafluoroboric acid, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalatoborate, lithium perchlorate, and lithium bis(oxalatoborate). Without limitation, the polymerization reaction method can be at least one of free radical polymerization and radiation polymerization.

[0144] In some examples, the polymerization reaction is free radical polymerization. Accordingly, the mixing process further includes adding an initiator to initiate the free radical polymerization.

[0145] Without limitation, the initiator includes one or more of azobisisobutyronitrile, azobisisovaleronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, azobiscyclohexylcarbonitrile, benzoyl peroxide, lauroyl peroxide, tert-butyl benzoyl peroxide and methyl ethyl ketone peroxide.

[0146] In some examples, the mass percentage of the initiator is 0.05% to 2% based on the total mass of the cyclic group-containing monomer and the cross-linking agent. Specifically, the mass percentage of the initiator includes, but is not limited to, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 2%, or a range therebetween.

[0147] Without limitation, the polymerization reaction temperature is 50 degrees Celsius (° C.) to 80° C., and the polymerization reaction time is 1 hour (h) to 15 hours. Specifically, the temperature includes, but is not limited to, 50° C., 55° C., 60° C., 65° C., 70° C., 75° C., 80° C., or a range therebetween; and the polymerization reaction time includes, but is not limited to, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 7 hours, 10 hours, 12 hours, 15 hours, or a range therebetween.

[0148] In some examples, the polymerization reaction is radiation polymerization. Further, the radiation polymerization includes one or both of electron beam polymerization and gamma ray polymerization. Without limitation, radiation is applied during the polymerization reaction at a radiation dose of 50 kilogray (kGy) to 250 kGy.

[0149] Other examples of the present application further provide a secondary battery comprising the polymer gel electrolyte described above or a polymer gel electrolyte prepared by the preparation method described above. The secondary battery employs the polymer gel electrolyte, which has high ionic conductivity and ion transference number, resulting in a low DCR value for the secondary battery.

[0150] Other examples of the present application further provide an electric device including the secondary battery as described above.

[0151] In addition, the secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0152] 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 embedded in and extracted from the positive and negative electrodes. The electrolyte, typically a polymer gel electrolyte as described above, 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.

[0153] Positive electrode

[0154] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charge and discharge process, and the content of Li in the positive electrode plate is different when the battery is discharged to different states. In the list of positive electrode materials in this application, unless otherwise specified, the Li content is the initial state of the material. The positive electrode material is applied to the positive electrode plate in the battery system, and after the charge and discharge cycle, the Li content in the positive electrode material contained in the plate will usually change. Among them, the Li content can be measured by molar content, but is not limited to this. Regarding "the Li content is the initial state of the material", the initial state of the material refers to the state before the material is added to the positive electrode slurry. It is understandable that new materials obtained by appropriate modification on the basis of the listed positive electrode materials are also within the scope of positive electrode materials. The aforementioned appropriate modification refers to acceptable modification methods for positive electrode materials, and non-limiting examples include coating modification.

[0155] In the examples of positive electrode materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual O content will fluctuate. The O content can be measured by molar content, but is not limited to this.

[0156] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material.

[0157] 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.

[0158] 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.

[0159] In some embodiments, the positive electrode active material may be a positive electrode active material for a battery that is well known in the art. As a non-limiting example, the positive electrode active material may include one or more of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide (such as LiCoO2), lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Non-limiting examples of olivine-structured lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.8 Co 0.15 Al 0.05 O2.

[0160] 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.

[0161] 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.

[0162] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on at least one side of the positive electrode current collector, and after drying, cold pressing, and other processes, the positive electrode sheet can be obtained. The type of solvent can be selected from, but not limited to, any of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector or on both surfaces of the positive electrode current collector. The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector or on both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40 wt% to 80 wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 millipascals·second (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 / cm2 (mg / cm 2 )~35mg / cm 2 The compacted density of the positive electrode can be 3.0 g / cm3 (g / cm 3 )~3.6g / cm 3 , optional 3.3g / cm 3 ~3.5g / cm 3 .

[0163] Negative electrode

[0164] 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.

[0165] 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.

[0166] 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.

[0167] In some of these embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0168] 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).

[0169] 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.

[0170] In some embodiments, the negative electrode active material layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0171] 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 on both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000mPa·s to 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 .

[0172] electrolytes

[0173] The electrolyte has the function of conducting ions between the positive electrode and the negative electrode. The present application adopts the polymer gel electrolyte as described above.

[0174] In some embodiments, the electrolyte may optionally include additives. For example, the 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.

[0175] In some embodiments, the 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.

[0176] Isolation film

[0177] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0178] In some embodiments, the material of the separator may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0179] In some embodiments, the isolation film has a thickness of 6 to 40 μm, and may optionally be 12 to 20 μm.

[0180] 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.

[0181] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0182] 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.

[0183] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0184] 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.

[0185] 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.

[0186] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to actual needs.

[0187] The secondary battery may be a battery module 4 or a battery pack 1 .

[0188] 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.

[0189] 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.

[0190] 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.

[0191] In some embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select an appropriate number based on the application and capacity of the battery pack.

[0192] 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.

[0193] 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.

[0194] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0195] Figure 6 shows an example of an electric device 6. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0196] 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.

[0197] 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.

[0198] Example 1

[0199] This embodiment is a lithium-ion secondary battery using a polymer gel electrolyte, and the preparation method is as follows:

[0200] (1) Dry cell preparation:

[0201] 1) Preparation of positive electrode sheet

[0202] The positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM 622 ), conductive carbon black SP and binder PVDF are dispersed in solvent NMP in a weight ratio of 98:1:1 and mixed evenly to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on both sides of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained, wherein the coating amount per unit area on both sides is 0.27g / 1540.25mm 2 .

[0203] 2) Preparation of negative electrode sheet

[0204] The negative electrode active material graphite, thickener sodium carboxymethyl cellulose, binder styrene butadiene rubber, and conductive agent acetylene black were mixed in a mass ratio of 97:1:1:1, and deionized water was added to obtain a negative electrode slurry under the action of a vacuum mixer; the negative electrode slurry was evenly coated on both sides of the copper foil; the copper foil was dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then cold pressed and cut to obtain a negative electrode sheet, wherein the coating amount per unit area on both sides was 0.17g / 1540.25mm 2 .

[0205] 3) Isolation film

[0206] A 12μm thick polypropylene isolation film was selected.

[0207] (2) Preparation of polymer gel electrolyte: N-vinyl pyrrolidone (0.11 g), pentamethylenetetraacrylate (1 g), azobisisoheptonitrile (0.02 g), and 1 M LiPF6 electrolyte (4.44 g, solvent: EC-DMC (1:1, v:v)) were mixed uniformly at room temperature to obtain a clear and transparent precursor solution (the test example was tested with this precursor solution).

[0208] (3) Preparation of secondary battery: stack the positive electrode sheet, isolation film and negative electrode sheet in order, so that the isolation film is between the positive and negative electrode sheets to play an isolating role, and then wind them into a square bare cell, put them into aluminum plastic film, bake them to remove water, and inject the precursor solution prepared in step (2) (injection volume 5g / Ah). The cell is sealed and fully infiltrated, and then heated in an oven at 60℃ for 2h to carry out polymerization reaction, thereby obtaining a lithium-ion secondary battery based on polymer-based gel electrolyte.

[0209] Examples 2 to 5 vary the mass percentage of the cyclic groups in the polymer backbone based on Example 1 by adjusting the mass ratio of the monomer to the cross-linking agent. Other parameters are the same as those in Example 1.

[0210] Examples 6 to 9 change the type of monomer containing cyclic groups for preparing the polymer backbone based on Example 1, and adjust the mass ratio of the monomer to the cross-linking agent accordingly so that the mass percentage of the cyclic groups in the polymer backbone remains consistent with that in Example 1. The other parameters are the same as those in Example 1.

[0211] Examples 10-11 are based on Example 1, except that the type of cross-linking agent used to prepare the polymer backbone is changed, and the other parameters are the same as those of Example 1.

[0212] Examples 12 to 16 vary the percentage of the electrolyte relative to the mass of the polymer backbone (i.e., the sum of the masses of the monomer containing a cyclic group and the cross-linking agent) based on Example 1, and adjust the mass of the lithium salt accordingly so that its concentration in the electrolyte remains unchanged. The remaining parameters are the same as in Example 1.

[0213] Comparative Example 1: Based on Example 1, the type of monomer used to prepare the polymer backbone was changed to hexamethylenebisacrylamide, and the other parameters were the same as those in Example 1.

[0214] The main differences between the preparation methods of the lithium ion secondary batteries of Examples 2 to 16 and Comparative Example 1 and Example 1 are summarized in Table 1 below.

[0215] Table 1

[0216] Among them, the infrared spectrum characteristic peaks of the polymer skeleton can be obtained by the following method:

[0217] The secondary batteries of Examples 1-16 and Comparative Example 1 were disassembled, and the polymer gel electrolytes were collected. After crushing, they were washed with DMC solvent several times and then dried in an oven to obtain polymer skeletons. The polymer skeletons were tested by Fourier transform infrared spectroscopy (FT-IR). Taking Example 1 as an example, the 1724 cm -1 The C=O stretching vibration peak of the crosslinking agent is 1692 cm -1 The C=O stretching vibration peak belonging to the cyclic group is 1264 cm -1 The CN stretching vibration peak belongs to the cyclic group.

[0218] Test example:

[0219] (1) 10 mL of the precursor solution of Example 1 was heated in an oven at 60° C. for 2 h to perform a polymerization reaction, and then cooled to room temperature to obtain a gel sample. After freeze-drying, the morphology was observed by SEM. The results are shown in FIG7 , which shows that the monomer and the cross-linking agent formed a polymer skeleton structure.

[0220] (2) Test method for ionic conductivity of polymer gel electrolyte

[0221] The test temperature was 25°C. The ion conductivity instrument probe was completely immersed in a container containing 10 mL of the precursor solution. After sealing, it was heated in an oven at 60°C for 2 hours to perform a polymerization reaction. After cooling to room temperature, the measurement was performed.

[0222] (3) Test method for lithium ion transference number of polymer gel electrolyte

[0223] Assemble the Li-Li symmetrical button cell. During the process, the precursor solution is dripped in. After sealing, the button cell is heated in a 60℃ oven for 2 hours to perform polymerization reaction. Then, an electrochemical impedance spectroscopy (EIS) test is performed between 1Hz and 1MHz. The impedance value R0 is obtained from the impedance spectrum. Then, a 20mV bias (ΔV) is applied and the initial current I0 is recorded. After the current stabilizes, the stable current I is recorded. ss ; Then perform the electrochemical impedance spectroscopy (EIS) test again between 1Hz and 1MHz to calculate R ss According to the formula, the ion migration number t can be calculated + .

[0224] (3) Test method for DCR of lithium-ion secondary batteries

[0225] The test temperature is 25°C. The prepared lithium-ion secondary battery is first charged to 4.25V at a rate of 0.33C, and then discharged to 2.8V to obtain the first-week discharge specific capacity (Cd1). Then, the battery is discharged at a rate of 0.33C to modulate the SOC to 50%, and then discharged at a DC rate of 2C for 30 seconds. The voltage change during the DC discharge at a rate of 2C for 30 seconds is recorded. The resistance value at 50% SOC (State of Charge) can be obtained through the ratio of voltage to average current.

[0226] The test results are shown in Table 2 below.

[0227] Table 2

[0228] It can be seen that compared with Comparative Example 1, the embodiment can effectively improve the ion conductivity and ion transport characteristics such as the ion transfer number by introducing a cyclic group into the polymer skeleton, and the battery internal resistance (DCR) is smaller.

[0229] From the comparison between Example 1 and Examples 2 to 5, it can be seen that reasonable control of the mass percentage of the cyclic groups in the polymer backbone can improve the ionic conductivity and ion transference number of the electrolyte.

[0230] From the comparison between Example 1 and Examples 6 to 9, it can be seen that the presence of a substituent on the nitrogen of the cyclic group can further improve the ionic conductivity and ion transference number of the electrolyte.

[0231] From the comparison between Example 1 and Examples 10 to 11, it can be seen that the ionic conductivity and the ion transference number can be improved by properly controlling the number of carbon-carbon double bonds.

[0232] From the comparison between Example 1 and Examples 12 to 16, it can be seen that reasonable control of the mass percentage of the electrolyte is beneficial to improving the ionic conductivity and the ion transference number.

[0233] 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.

[0234] 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 polymer gel electrolyte comprising a polymer backbone and an electrolyte located in gaps within the polymer backbone, wherein the polymer backbone comprises a cyclic group, wherein the cyclic group comprises one or more of the structures represented by the following formulae (I), (II), (III), and (IV): in, R0 includes one or more of H, C1-C5 hydrocarbon group, fluorinated C1-C5 hydrocarbon group and C3-C10 ester group; n1 includes integers from 0 to 10; n2 includes integers from 0 to 10; m includes integers from 0 to 5; q includes integers from 0 to 5.

2. The polymer gel electrolyte according to claim 1, wherein Have one or more of the following characteristics: (1) R0 includes one or more of H and C3-C10 ester groups; (2) n1 includes 0, 1, 2, 3 or 4; (3) n2 includes 0, 1, 2, 3 or 4; (4) m includes 0 or 1; (5)q includes 0, 1 or 2.

3. The polymer gel electrolyte according to claim 1 or 2, wherein The cyclic group includes one or more structures represented by the following formulae (I-1), (II-1), (II-2), (III-1) and (IV-1):

4. The polymer gel electrolyte according to any one of claims 1 to 3, wherein The infrared spectrum of the polymer backbone includes a -1 ~1320cm -1 The CN stretching vibration peak is located at 1655 cm -1 ~1750cm -1 The C=O stretching vibration peak.

5. The polymer gel electrolyte according to any one of claims 1 to 4, wherein In the polymer skeleton, the mass percentage of the cyclic group is 1% to 20%.

6. The polymer gel electrolyte according to claim 5, wherein In the polymer skeleton, the mass percentage of the cyclic group is 5% to 15%.

7. The polymer gel electrolyte according to any one of claims 1 to 6, wherein The polymer backbone includes a cross-linked polymer having a three-dimensional network structure.

8. The polymer gel electrolyte according to claim 7, wherein The cross-linked polymer having a three-dimensional network structure includes a polymer obtained by copolymerizing a monomer containing a cyclic group and a cross-linking agent; the monomer containing a cyclic group includes one or more structures represented by the following formulas (1), (2), (3) and (4): Wherein, R0, n1, n2, m and q are defined the same as any one of claims 1 to 2.

9. The polymer gel electrolyte according to claim 8, wherein The cyclic group-containing monomer includes one or more of maleimide, 6-vinyl-2-piperidone, N-vinyl pyrrolidone, 7-vinyl-hexahydropyrrolazin-3-one, N-vinyl caprolactam and 4-allyl-5-oxopyrrolidine-2-carboxylic acid methyl ester.

10. The polymer gel electrolyte according to claim 8 or 9, wherein The chemical formula of the cross-linking agent contains a carbon-carbon double bond.

11. The polymer gel electrolyte according to claim 10, wherein The number of carbon-carbon double bonds in the chemical formula of the cross-linking agent is P, and P≥3.

12. The polymer gel electrolyte according to claim 11, wherein 3≤P≤6。 13. The polymer gel electrolyte according to any one of claims 8 to 12, wherein The cross-linking agent includes an acrylate cross-linking agent.

14. The polymer gel electrolyte according to claim 13, wherein The crosslinking agent includes one or more of isopentaerythritol tetraacrylate, di(trimethylolpropane) tetraacrylate, polydipentaerythritol hexaacrylate, trimethylolpropane triacrylate, and pentaerythritol triacrylate.

15. The polymer gel electrolyte according to any one of claims 8 to 14, wherein The mass ratio of the monomer containing a cyclic group to the cross-linking agent is (0.01-0.25):

1.

16. The polymer gel electrolyte according to claim 15, wherein The mass ratio of the monomer containing a cyclic group to the cross-linking agent is (0.05-0.18):

1.

17. The polymer gel electrolyte according to any one of claims 1 to 16, wherein The solvent of the electrolyte includes one or more of a carbonate solvent and an ether solvent.

18. The polymer gel electrolyte according to claim 17, wherein Have one or more of the following characteristics: (1) The carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, and fluoroethylene carbonate; (2) The ether solvent includes one or more of ethylene glycol dimethyl ether, tetrahydrofuran, dioxolane, methyl nonafluorobutyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, octafluoropentyl-tetrafluoroethyl ether, 1,2-bis(cyanoethoxy)ethane, diphenyl ether and 18-crown-6.

19. The polymer gel electrolyte according to any one of claims 1 to 18, wherein The mass ratio of the electrolyte to the polymer skeleton is 200% to 5000%.

20. The polymer gel electrolyte according to any one of claims 1 to 19, wherein The polymer gel electrolyte has at least one of the following characteristics (1) to (2): (1) Ionic conductivity is 0.5mS / cm to 10mS / cm; (2) The lithium ion migration number is 0.3 to 0.

8.

21. The polymer gel electrolyte according to claim 20, wherein The polymer gel electrolyte has at least one of the following characteristics (1) to (2): (1) Ionic conductivity is 4mS / cm to 9mS / cm; (2) The lithium ion migration number is 0.3 to 0.

5.

22. A secondary battery comprising the polymer gel electrolyte according to any one of claims 1 to 21.

23. An electric device comprising the secondary battery according to claim 22.

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