CN117423897A - Composition for preparing gel polymer electrolyte, secondary battery and electronic device - Google Patents

Abstract

The present application provides a composition for preparing a gel polymer electrolyte, a secondary battery and an electronic device. The composition includes: a star branched multi-arm polymer, a cross-linking agent, an electrolyte salt and an organic solvent. According to the present application, the star-branched multi-arm polymer and the cross-linking agent in the composition can initiate a polymerization reaction to form a cross-linked polymer. Due to the special structure of the star-branched multi-arm polymer, the cross-linked polymer The formed network structure has a larger pore structure, and the electrolyte formed by the organic solvent in which the electrolyte salt is dissolved can be restricted in the network structure of the cross-linked polymer, thereby obtaining a gel polymer electrolyte. The gel polymer The electrolyte can reduce side reactions between the electrolyte and active materials, and can obtain a uniform flow of active ions, which can improve the cycle performance of lithium metal batteries.

Description

Composition for preparing gel polymer electrolyte, secondary battery and electronic device

Technical Field

The present application relates to the field of battery technology, and in particular to a composition for preparing a gel polymer electrolyte, a secondary battery and an electronic device.

Background Art

Secondary batteries represented by lithium-ion batteries are widely used in digital electronic products, energy storage, drones, power tools, electric vehicles and other products due to their high energy density, long cycle life, high safety, fast charging capability and other characteristics. Lithium metal batteries with lithium metal as the negative electrode material have high energy density, but the metal lithium is prone to side reactions with the electrolyte, the growth of lithium dendrites during the cycle, and the accumulation of "dead lithium", which leads to reduced cycle performance of lithium metal batteries and limits their application. Therefore, it is necessary to improve the cycle performance of lithium metal batteries.

Summary of the invention

The present application provides a composition for preparing a gel polymer electrolyte, a secondary battery and an electronic device, aiming to improve the cycle performance of a lithium metal battery by obtaining a gel polymer electrolyte capable of uniform active ion flow.

In a first aspect, the present application provides a composition for preparing a gel polymer electrolyte, comprising: a star-branched multi-arm polymer, a crosslinking agent, an electrolyte salt and an organic solvent; wherein the number of arms in the star-branched multi-arm polymer is 3, 4 or 5, and the arms are independently represented by _R1 represents a linear or branched alkylene group having 1 to 5 carbon atoms, _R2 represents a methacrylate group, an acrylate group, R' represents a linear or branched alkylene group having 1 to 5 carbon atoms, and m represents an integer from 20 to 80; _R2 of at least one arm of the star-branched multi-arm polymer represents

According to the present application, the star-branched multi-arm polymer and the cross-linking agent in the composition can be initiated to undergo a polymerization reaction to form a cross-linked polymer. Due to the special structure of the star-branched multi-arm polymer, the network structure formed by the cross-linked polymer has a relatively large pore structure, and the electrolyte formed by the organic solvent dissolved with the electrolyte salt can be confined in the network structure of the cross-linked polymer, thereby obtaining a gel polymer electrolyte, thereby inhibiting the side reaction between the electrolyte and the active material, and obtaining a uniform active ion flow; at the same time, due to the alkoxy segments, amide groups and ester groups contained in the star-branched multi-arm polymer, the ionic conductivity can be improved, wherein the amide group can also have the function of further homogenizing the active ion flow by fixing the anions, thereby improving the cycle performance of the lithium metal battery.

In some embodiments, the star-branched multi-arm polymer satisfies at least one of the following conditions: 1) the weight average molecular weight of the star-branched multi-arm polymer is not less than 5000; 2) the number of arms is 3 or 4; 3) _R1 represents a linear or nonlinear alkylene group having 2 to 4 carbon atoms; 4) _R2 of the arms all represent

In some embodiments, the crosslinking agent includes at least one of a vinyl functional group, an acryl functional group, an aziridine functional group, and a thiol functional group, and the number of the functional groups is 3, 4, or 5.

In some embodiments, the cross-linking agent may be represented by Formula I,

Wherein, _R3 and _R4 each independently represent a linear or branched alkylene group having 1 to 5 carbon atoms, _R5 represents a vinyl group and its derivative groups, a propenyl group and its derivative groups, an aziridine group and its derivative groups or a mercapto group, x is 0 or 1, and y is an integer from 0 to 4.

In some embodiments, the cross-linking agent satisfies at least one of the following conditions: 1) x is 1; 2) y is an integer from 0 to 2;

In some embodiments, the electrolyte salt includes a lithium salt and/or a sodium salt; the lithium salt includes at least one of _LiPF6 , _LiBF6 , _LiClO4 , lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorophosphate, lithium difluorobis(oxalatophosphate) and lithium _{tetrafluorooxalatophosphate} ; the sodium salt includes at least one of _NaPF6 , _{NaClO4 , NaBCl4} , _NaSO3CF3 and _Na ( _CH3 ) _C6H4SO3 .

In some embodiments, the organic solvent includes at least one of an ether-based solvent, a carbonate solvent, a nitrile solvent, and an ionic liquid solvent. The ether-based solvent includes at least one of ethylene glycol dimethyl ether, 1,4-dioxane, diethylene glycol dimethyl ether, ethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, methyltetrahydrofuran, and a fluoroether solvent. The carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, and a fluorocarbonate solvent. The nitrile solvent includes acetonitrile, propionitrile, succinonitrile, and a fluoronitrile solvent. At least one of the ionic liquid solvents includes anions and cations, the anions include bis(trifluoromethanesulfonyl)imide ions, bis(fluoromethanesulfonyl)imide ions, hexafluorophosphate ions, boron tetrafluoride ions, nitrate ions, acetate ions, perchlorate ions, hydrogen sulfate ions, dihydrogen phosphate ions, halogen anions, p-toluenesulfonate ions, trifluoromethanesulfonate ions, trifluoroacetate ions, and tetrachloroaluminum anions, and the cations include at least one of imidazole cations, quaternary ammonium ions, pyrrolidine cations, pyridinium cations, piperidinium cations, and quaternary phosphonium cations.

In some embodiments, the composition satisfies at least one of the following conditions: 1) the mass percentage of the star-branched multi-arm polymer in the composition is 1% to 10%; 2) the mass percentage of the cross-linking agent in the composition is 0.1% to 10%; 3) the mass percentage of the electrolyte salt in the composition is 1% to 90%; 4) the mass percentage of the organic solvent in the composition is 1% to 90%.

In some embodiments, an initiator is further included, and the mass percentage of the initiator in the composition is 0.1% to 2%. The initiator includes at least one of an organic peroxide initiator, an inorganic peroxide initiator and an azo initiator. The organic peroxide initiator includes at least one of dibenzoyl peroxide, lauroyl peroxide, isopropylbenzene hydroperoxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, diisopropylbenzene peroxide, tert-butyl perbenzoate, tert-butyl pervalerate, methyl ethyl ketone peroxide, cyclohexanone peroxide, diisopropyl peroxydicarbonate and dicyclohexyl peroxydicarbonate. The inorganic peroxide initiator includes at least one of potassium persulfate, sodium persulfate and ammonium persulfate. The azo initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile and dimethyl azobisisobutyrate.

In a second aspect, the present application provides a secondary battery, comprising: a positive electrode plate, a negative electrode plate, a separator, and a gel polymer electrolyte obtained by initiating a polymerization reaction of the composition according to any embodiment of the first aspect.

In a third aspect, the present application provides an electronic device, comprising: a secondary battery according to any embodiment of the second aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

FIG. 1( a ) is a morphology of lithium metal deposition on the surface of the negative electrode plate in Comparative Examples 1-3.

Figure 1(b) is a morphology of lithium metal deposition on the surface of the negative electrode plate in Example 1-1.

FIG. 2 is the cycle performance test results of Example 1-1 and Comparative Example 1-3.

FIG3 is a DSC curve of the gel electrolyte obtained in Example 1-1.

FIG. 4( a ) is a diagram showing the impact test results of the battery cells in Comparative Examples 1-3.

FIG4( b ) is the result of the battery cell impact test in Example 1-1.

FIG4( c ) is the hot box test results of comparative examples 1-3.

FIG4( d ) is the hot box test result of Example 1-1.

DETAILED DESCRIPTION

The various embodiments or implementation schemes in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments.

In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the implementation or example are included in at least one implementation or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same implementation or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more implementations or examples in a suitable manner.

In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

In the present application, the secondary battery may include a lithium ion battery, a lithium sulfur battery, a sodium lithium ion battery, a sodium ion battery or a magnesium ion battery, etc., which is not limited in the embodiments of the present application. The battery may be cylindrical, flat, rectangular or other shapes, etc., which is not limited in the embodiments of the present application.

As described in the background technology above, metallic lithium is prone to side reactions with the electrolyte, the growth of lithium dendrites during the cycle, and the accumulation of "dead lithium", which leads to reduced cycle performance of lithium metal batteries.

The following is an analysis of the problems existing in lithium metal batteries, such as: 1) Side reactions between fresh lithium metal and electrolyte. Because lithium metal has an extremely high Fermi energy level, lithium metal without solid electrolyte membrane (SEI) coverage can spontaneously undergo redox reactions with most electrolytes when in contact, which not only leads to low coulombic efficiency, but also leads to continuous loss of negative electrode active materials and electrolytes, resulting in low coulombic efficiency and continuous attenuation of cycle capacity and kinetics. 2) Uneven lithium deposition/extraction leads to the growth of lithium dendrites and the continuous accumulation of "dead lithium" during the cycle, resulting in the continuous consumption of active lithium and the risk of lithium dendrites penetrating the diaphragm, causing the battery to short-circuit and catch fire. During the charging process, lithium metal undergoes a deposition reaction at the negative electrode, and the lithium ion transport in the electrolyte and at the interface usually determines the location and deposition morphology of lithium deposition. When the lithium ion flow in the electrolyte is concentrated at certain points, or when the SEI on the surface of lithium metal breaks, the deposition of metallic lithium will be concentrated at these locations, resulting in uneven lithium deposition and the formation of a loose lithium deposition layer, which further aggravates the interfacial side reactions between lithium and electrolyte; it may even form lithium dendrites that pierce the diaphragm, causing short circuits in the battery cells and serious safety hazards. In addition, loose lithium is more likely to form dead lithium with interrupted electronic pathways during lithium extraction, and the dead lithium layer continues to accumulate during the cycle, which not only causes the tortuosity of the lithium negative electrode surface to increase, but also affects the dynamics. 3) The pulverization of the pole piece caused by the drastic change in the volume of the lithium negative electrode during the cycle and the accumulation of dead lithium further aggravate the side reactions between metallic lithium and the electrolyte and the uneven deposition of lithium, which in turn leads to the accelerated decay of battery capacity and dynamics.

In order to solve the above problems, the following methods are mainly used in related technologies:

1) Electrolyte optimization: Although the side reaction between electrolyte and lithium metal can be reduced by optimizing the solvation structure and composition of the electrolyte, the problem of uneven lithium ion flow in the liquid electrolyte itself still exists, which is more likely to cause uneven lithium deposition. Moreover, due to the high fluidity of the liquid, when loose and porous lithium deposits appear at the negative electrode, the flowing electrolyte will immediately contact them and cause side reactions, resulting in deterioration of battery performance.

2) Artificial interface coating, in advance, covers the surface of lithium metal with one or more layers of protective layer with lithium ion conductivity by physical or chemical methods. While conducting lithium ions, it isolates the electrolyte from direct contact with lithium metal, thereby reducing side reactions. If the protective layer has high mechanical strength, it can also inhibit the growth of lithium dendrites. However, due to the rapid volume change of the anode during the charging and discharging process, these materials with higher hardness covering the surface of the anode are prone to rupture, resulting in a continuous decrease in effectiveness.

3) Solid electrolytes. The self-limiting characteristics of solid electrolytes can greatly slow down the occurrence of side reactions and reduce the content of liquid electrolyte in the battery cell, which can greatly improve the safety performance of lithium metal batteries. However, there are many problems that need to be solved in solid electrolytes, whether oxides, sulfides or polymers, among which interface problems and ion conductivity problems are particularly prominent. Therefore, the commercialization of solid electrolytes is still greatly limited.

Based on this, the present application provides a composition for preparing a gel polymer electrolyte, a secondary battery and an electronic device. The gel polymer electrolyte prepared using the above composition can uniformly flow active ions and improve the cycle performance of lithium metal batteries. The embodiments of the present application are described in detail below.

In a first aspect, the present application provides a composition for preparing a gel polymer electrolyte, comprising: a star-branched multi-arm polymer, a crosslinking agent, an electrolyte salt and an organic solvent; wherein the number of arms in the star-branched multi-arm polymer is 3, 4 or 5, and the arms are independently represented by _R1 represents a linear or branched alkylene group having 1 to 5 carbon atoms, _R2 represents a methacrylate group, an acrylate group, R' represents a linear or branched alkylene group having 1 to 5 carbon atoms, and m represents an integer from 20 to 80; _R2 of at least one arm in the star-branched multi-arm polymer represents

According to the present application, the composition includes a star-branched multi-arm polymer, a cross-linking agent, an electrolyte salt and an organic solvent, wherein the organic solvent is used to dissolve and disperse other components in the composition and provide an environment for the polymerization reaction, the electrolyte salt provides active ions for the gel polymer electrolyte, the star-branched multi-arm polymer and the cross-linking agent can initiate a polymerization reaction to form a cross-linked polymer, and the cross-linked polymer can limit the organic solvent dissolved with the electrolyte salt, thereby forming a gel polymer electrolyte.

The structure of the star-branched multi-arm polymer is further defined in the present application. It should be noted that the star-branched multi-arm polymer has a well-known meaning in the art, and refers to a type of branched structure polymer formed by connecting more than 3 linear polymer branches (i.e., arms) to the same center. In the composition, the number of arms of the star-branched multi-arm polymer is 3, 4 or 5, and the structure of the arm is defined. When the number of arms is more than 3, since each arm has the ability to polymerize and extend, the cross-linked polymer thus formed has a network structure with a larger pore size, which can gel a large amount of electrolyte, restrict the electrolyte to the network structure, reduce the free electrolyte in the gel polymer electrolyte, and then reduce the side reaction of the electrolyte with the active material. At the same time, the electrolyte restricted in the network structure can obtain a more uniform active ion flow; if the number of arms is too large, the cross-linking density of the cross-linked polymer will be too large, which is not conducive to the transmission of active ions in the gel polymer electrolyte.

The arms are independently represented as Wherein m represents an integer from 20 to 80. The repeated alkoxy chain segments -OR ₁ - in the arm can increase the arm length, thereby controlling the pore size in the cross-linked polymer. The large pore size can not only make the gel polymer electrolyte solidify more electrolyte, but also be compatible with electrolytes with special solvation structures (such as high concentration, local high concentration electrolytes) without phase separation, thereby improving the ionic conductivity of the gel polymer electrolyte while reducing the content of free electrolyte therein and inhibiting side reactions with metallic lithium. On the other hand, the alkoxy chain segments can inhibit the crystallization of polymer branches, thereby improving the flexibility and elasticity of the polymer and reducing the glass transition temperature of the gel polymer electrolyte, so that the electrolyte still has good ionic conductivity at a lower temperature. In addition, the polar oxygen atoms can improve the ionic conductivity. For example, m can be 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80.

_R2 represents a methacrylate group, an acrylate group, The unsaturated double bond enables the polymer to extend, and the ester group can improve the affinity of the polymer with organic solvents, thereby improving the ionic conductivity of the gel polymer electrolyte. At the same time, R ₂ of at least one arm represents The amide group can fix anions and increase the number of ion migration, thereby playing a role in homogenizing the active ion flow. In addition, the amide group can cooperate with the above-mentioned alkoxy chain segment to further reduce the glass transition temperature of the gel polymer electrolyte, so that the gel polymer electrolyte has a wider amorphous temperature range, so that the electrolyte still has good ionic conductivity at a lower temperature. For example, R ₂ represents

The gel polymer electrolyte prepared from the composition provided by the present application can reduce the content of free electrolyte in the electrolyte by limiting the electrolyte in the network structure, inhibit the side reaction between the electrolyte and metallic lithium, and can homogenize the active ion flow, thereby promoting uniform lithium deposition and reducing lithium dendrites, thereby significantly improving the cycle performance of lithium metal batteries. At the same time, the above effects can also improve the coulombic efficiency and safety performance of lithium metal batteries.

It should also be noted that, in this context, the gel polymer electrolyte prepared by the composition provided in the present application includes but is not limited to applications in lithium metal batteries, and can also be used as an electrolyte for other secondary batteries in the art, by inhibiting side reactions between the electrolyte and the active material and homogenizing the active ion flow, which can correspondingly improve the cycle performance of the secondary battery.

The star-branched multi-arm polymer includes but is not limited to being purchased directly through commercial channels or synthesized by known methods. For example, an intermediate containing an arm structure can be first synthesized and then reacted with a corresponding coupling agent to obtain a star-branched multi-arm polymer. When the number of arms is 3, the coupling agent can be propylene glycol, and when the number of arms is 4, the coupling agent can be pentaerythritol.

It should be noted that the structures of the arms in the star-branched multi-arm polymer may be the same or different.

In some embodiments, the weight average molecular weight of the star-branched multi-arm polymer is not less than 5000. The cross-linked polymer obtained at this time can restrict more electrolytes, further reduce the content of free electrolytes in the gel polymer electrolyte, and thus improve the cycle performance of the lithium metal battery.

The weight average molecular weight of the star-branched multi-arm polymer has a well-known meaning in the art and can be detected according to methods and instruments known in the art. For example, the weight average molecular weight of the star-branched multi-arm polymer can be determined by GPC (gel permeation chromatography). The unit of weight average molecular weight is Dalton, which can generally be omitted.

In some embodiments, the number of arms in the star-branched multi-arm polymer is 3 or 4. In this case, the cross-linked polymer obtained has a more suitable cross-linking density, which reduces the free electrolyte content in the gel polymer electrolyte, obtains a more uniform active ion flow, and has better ion conductivity.

In some embodiments, _R1 represents a linear or nonlinear alkylene group having 2 to 4 carbon atoms. In this case, the obtained cross-linked polymer has better flexibility, the gel polymer electrolyte has a wider amorphous temperature range, and has better ionic conductivity at low temperatures.

In some embodiments, the _R2 of the arms are all represented At this time, each arm of the star-branched multi-arm polymer contains an amide group, which can better homogenize the active ion flow, further improve the lithium metal deposition morphology, inhibit the formation of lithium dendrites, and further improve the cycle performance and safety performance of lithium metal batteries.

In some embodiments, the crosslinking agent includes at least one of a vinyl functional group, an propylene functional group, an aziridine functional group, and a thiol functional group, and the number of the functional groups is 3, 4, or 5. The crosslinking agent may include the above-mentioned functional groups to quickly respond to the polymerization reaction initiated by free radicals, which is conducive to the rapid crosslinking of the star-branched multi-arm polymer and the increase of the crosslinking density.

In some embodiments, the cross-linking agent may be represented by Formula I,

Wherein, _R3 and _R4 each independently represent a linear or branched alkylene group having 1 to 5 carbon atoms, _R5 represents a vinyl group and its derivative groups, a propenyl group and its derivative groups, an aziridine group and its derivative groups or a mercapto group, x is 0 or 1, and y is an integer from 0 to 4.

In some of the above embodiments, the specific structure of the cross-linking agent is specifically defined, and the cross-linking agent can be cross-linked with the star-branched multi-arm polymer in the four branch directions, and the four branches are shorter than the arms of the star-branched multi-arm polymer. Therefore, the cross-linking agent is more densely distributed in the three-dimensional network structure, which is beneficial to the rapid spatial transmission and response of the polymerization reaction initiated by free radicals, and thus has a faster cross-linking speed. At the same time, a cross-linked polymer with a better cross-linking density is obtained, the three-dimensional network structure is improved, the free electrolyte content is further reduced, and the ionic conductivity of the gel polymer electrolyte is improved.

In some embodiments, x is 1. Each branch of the cross-linking agent also has an ester group, and since the ester group has better compatibility with the organic solvent in the composition, the dispersibility of the cross-linking agent in the composition can be improved, and at the same time, it has a better limiting effect on the electrolyte in the network structure, and phase separation is not easy to occur. In addition, the polar ester group is also beneficial to improving the ionic conductivity of the gel polymer electrolyte.

In some embodiments, y is an integer from 0 to 2. In this case, the crosslinking agent can respond faster to the polymerization reaction initiated by free radicals, so that the star-branched multi-arm polymer in the composition can be crosslinked and polymerized faster, thereby obtaining a gel polymer electrolyte.

In some embodiments, the electrolyte salt includes a lithium salt and/or a sodium salt; the lithium salt includes at least one of LiPF ₆ , LiBF ₆ , LiClO ₄ , lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorophosphate, lithium difluorobis(oxalate phosphate) and lithium tetrafluorooxalate phosphate; the sodium salt includes at least one of NaPF ₆ , NaClO ₄ , NaBCl ₄ , NaSO ₃ CF ₃ and Na(CH ₃ )C ₆ H ₄ SO _3. Since the gel polymer electrolyte formed by the above composition is not only applicable to lithium metal batteries, but also to other types of secondary batteries, the electrolyte salt can be selected according to actual needs. In addition, there is no particular limitation on the type of electrolyte salt, which can include but is not limited to the above-mentioned types, and any electrolyte salt known in the art that can be used for secondary battery electrolytes can also be used.

In some embodiments, the organic solvent includes at least one of an ether-based solvent, a carbonate solvent, a nitrile solvent, and an ionic liquid solvent. The ether-based solvent includes at least one of ethylene glycol dimethyl ether, 1,4-dioxane, diethylene glycol dimethyl ether, ethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, methyltetrahydrofuran, and a fluoroether solvent. The carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, and a fluorocarbonate solvent. The nitrile solvent includes acetonitrile, propionitrile, succinonitrile, and a fluoronitrile solvent. At least one, the ionic liquid solvent includes anions and cations, the anions include bis(trifluoromethanesulfonyl)imide ions, bis(fluoromethanesulfonyl)imide ions, hexafluorophosphate ions, boron tetrafluoride ions, nitrate ions, acetate ions, perchlorate ions, hydrogen sulfate ions, dihydrogen phosphate ions, halogen anions, p-toluenesulfonate ions, trifluoromethanesulfonate ions, trifluoroacetate ions, at least one of tetrachloroaluminum anions, and the cations include imidazole cations, quaternary ammonium ions, pyrrolidine cations, pyridine cations, piperidine cations, and at least one of quaternary phosphonium cations. Since the three-dimensional network structure in the gel polymer electrolyte formed by the above composition has a larger pore size, there is no special restriction on the type of organic solvent, and it can be selected according to actual needs. Similarly, the organic solvent is not limited to the above-mentioned ones, and any organic solvent known in the art that can be used for secondary battery electrolytes can also be used.

In some embodiments, the composition satisfies at least one of the following conditions: 1) the mass percentage of the star-branched multi-arm polymer in the composition is 1% to 10%; 2) the mass percentage of the cross-linking agent in the composition is 0.1% to 10%; 3) the mass percentage of the electrolyte salt in the composition is 1% to 90%; 4) the mass percentage of the organic solvent in the composition is 1% to 90%.

In some of the above embodiments, the mass percentage of each component in the composition is further defined. It can be understood that due to the special structure of the star-branched multi-arm polymer, the cross-linked polymer obtained by cross-linking can solidify a large amount of electrolyte, so the mass percentage of each component in the composition can be adjusted within a large range, and those skilled in the art can choose according to actual needs. For example, the mass percentage of the star-branched multi-arm polymer in the composition can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or within the range composed of any of the above values, preferably, it can be 3% to 6%; the mass percentage of the cross-linking agent in the composition can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or within the range composed of any of the above values, preferably, it can be 0.1 to 5%; the mass percentage of the electrolyte salt in the composition can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39 %, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69% ,70%,71%,7 2%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, or any range formed by the above values, preferably, it can be 10% to 70%; the mass percentage of the organic solvent in the composition can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 5%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, or any range consisting of the above values, preferably, it can be 20% to 90%.

In some embodiments, an initiator is further included, and the mass percentage of the initiator in the composition is 0.1% to 2%. The initiator includes at least one of an organic peroxide initiator, an inorganic peroxide initiator and an azo initiator. The organic peroxide initiator includes dibenzoyl peroxide, lauroyl peroxide, isopropylbenzene hydroperoxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, diisopropylbenzene peroxide, tert-butyl perbenzoate, tert-butyl pervalerate, methyl ethyl ketone peroxide, cyclohexanone peroxide, diisopropyl peroxydicarbonate and dicyclohexyl peroxydicarbonate. The inorganic peroxide initiator includes at least one of potassium persulfate, sodium persulfate and ammonium persulfate. The azo initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile and dimethyl azobisisobutyrate.

In some of the above embodiments, the composition also includes an initiator, which is used to cause the star-branched multi-arm polymer and the crosslinking agent in the composition to be induced to undergo a crosslinking polymerization reaction under milder conditions. In the above embodiments, there is no particular limitation on the type of initiator, and the initiator may include but is not limited to the above-mentioned types, and an initiator known in the art that can be used to initiate a free radical chain reaction may also be selected, and those skilled in the art may select according to implementation needs.

In some embodiments, the composition may optionally include additives, for example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

In some embodiments, the composition can be prepared in the following manner: the components included in the above composition are directly mixed to obtain the composition.

Secondary battery

In a second aspect, the present application provides a secondary battery, comprising: a positive electrode plate, a negative electrode plate, a separator, and a gel polymer electrolyte obtained by initiating a polymerization reaction of the composition according to any embodiment of the first aspect.

According to the present application, since the secondary battery includes a gel polymer electrolyte obtained by initiating a polymerization reaction of the composition according to any embodiment of the first aspect, it has the beneficial effects of the first aspect. At the same time, since the gel polymer electrolyte is generally amorphous and has low strength, a separator is required to isolate the positive electrode sheet and the negative electrode sheet to prevent short circuit.

In some embodiments, the conditions for initiating the polymerization reaction may include heating, electron beam, or γ-ray treatment for a certain period of time. As an example, the conditions for initiating the polymerization reaction may be reacting at a temperature above 60° C. for more than 6 hours.

In some embodiments, the polymerization reaction is carried out under inert conditions. Since the polymerization reaction is a free radical chain reaction, oxygen in the air will block the polymerization reaction. Therefore, under inert conditions, the star-branched multi-arm polymer and the crosslinking agent react more fully. The inert conditions can be sealed conditions or in an inert gas environment.

In some embodiments, the glass transition temperature of the gel polymer electrolyte may be below -57.6°C.

The glass transition temperature of the gel polymer electrolyte has a well-known meaning in the art and can be measured using methods and instruments known in the art, for example, using a differential scanning calorimeter.

In some embodiments, the ionic conductivity of the gel polymer electrolyte is 10 ⁻³ to 10 ⁻⁴ S/cm.

[Positive electrode]

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

As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

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 and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the positive electrode active material may be a positive electrode active material for a battery known in the art. As an example, the positive electrode active material may include at least one 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 positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxide (such as LiCoO ₂ ), lithium nickel oxide (such as LiNiO ₂ ), lithium manganese oxide (such as LiMnO ₂ , LiMn ₂ O ₄ ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (also referred to as NCM ₃₃₃ ), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (also referred to as NCM ₅₂₃ ), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (also referred to as NCM ₂₁₁ ), LiNi _0.6 Co _0.2 Mn _0.2 O 2 (also referred to as NCM _{622 ), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (also referred to as NCM 811 )} , and LiNi _0.8 Co _0.2 Mn _0.2 O ₂ (also referred to as NCM ₈₁₁ ), lithium nickel cobalt aluminum oxide (such as LiNi _0.85 Co _0.15 Al _0.05 O ₂ ) and modified compounds thereof. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO ₄ (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO ₄ ), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

In some embodiments, the positive electrode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

In some embodiments, the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[Negative electrode]

In some embodiments, the negative electrode plate may be lithium or a lithium alloy. For example, lithium is directly used as the negative electrode plate, in which case lithium serves as the negative electrode active material and also acts as a current collector.

In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. 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 formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: lithium, lithium alloy, artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more.

In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one 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).

In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

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 (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[Isolation film]

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

In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. 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.

In some embodiments, the isolation film has a thickness of 7 to 16 μm.

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.

In some embodiments, the secondary battery includes an outer package, and after the outer package encapsulates the electrode assembly and the composition, the composition is initiated to undergo a polymerization reaction to form a gel polymer electrolyte in situ.

In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

In some embodiments, the secondary battery may be a lithium metal battery.

Electronic devices

In a third aspect, the present application provides an electronic device, comprising: a secondary battery according to any embodiment of the second aspect.

According to the present application, since the electronic device includes the secondary battery of any embodiment of the second aspect, the electronic device has the beneficial effects of the third aspect.

The electronic device of the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device can include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used that do not indicate the manufacturer are all conventional products that can be obtained commercially.

Cycle performance test: The battery is charged and discharged at 60 degrees Celsius at a rate of 0.1C for one cycle, and then charged and discharged at room temperature. The current in the cross-current charging stage is 0.3C, the cut-off voltage is, and the cut-off current in the constant voltage charging stage is 0.05C, and the cut-off voltage is 3.9V. The cross-current discharge rate is 1C, and the discharge cut-off voltage is 2.7V. Taking the discharge capacity of the third cycle as the benchmark (100%), the discharge capacity retention rate of different cycle numbers can be obtained, and the cycle capacity change curve can be drawn, and the battery cycle number when the discharge capacity retention rate is 80% can be recorded.

Coulomb efficiency test: The battery is charged and discharged at 60 degrees Celsius at a rate of 0.1C for one cycle, and then charged and discharged at room temperature. The current in the cross-current charging stage is 0.3C, the cut-off voltage is, and the cut-off current in the constant voltage charging stage is 0.05C, and the cut-off voltage is 3.9V. The cross-current discharge rate is 1C, and the discharge cut-off voltage is 2.7V. The coulomb efficiency of each cycle is obtained by dividing the discharge capacity of each cycle by the charging capacity.

Impact test: After the battery cell is cycled for 50 times, it is charged to 100% SOC. In the test environment of 20±5℃, the sample is placed on the test table, and a round bar with a diameter of 15.8mm is placed at the center of the wide surface of the sample. The longitudinal axis of the cylindrical, bagged, and columnar samples is parallel to the surface of the plate and perpendicular to the longitudinal axis of the round bar. A 9.1±0.1kg heavy hammer is used to drop vertically and freely from a height of 610±25mm, and falls on the intersection of the round bar and the sample. During this process, the battery cell is qualified if it does not catch fire or explode.

Hot box test: After the battery cell is cycled fifty times and charged to 100% SOC, the battery cell is placed in a test box. The temperature inside the test box is raised to the set temperature at a rate of 5±2℃ per minute and maintained for 30 minutes. During this process, the battery cell is qualified if it does not catch fire or explode.

Example 1-1

1. Preparation of negative electrode

The negative electrode plate uses a commercial lithium-copper composite strip with a thickness of 50um, which is directly punched into (18mm) specifications for use.

2. Preparation of positive electrode

The positive electrode active material lithium iron phosphate (LiFePO ₄ ), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed at a weight ratio of 97.5:1.0:1.5, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 0.75, and stirred evenly. The slurry was evenly coated on the positive electrode current collector aluminum foil and dried at 90°C to obtain a positive electrode sheet. The loading capacity was 1mAh/cm ^2. After coating, the sheet was cut into (14mm) specifications for standby use.

3. Preparation of composition for preparing gel polymer electrolyte

In a dry argon atmosphere, dioxolane (DOL) and dimethyl ether (DME) were first mixed in a volume ratio of 1:1, and then lithium salt LiTFSI was added to an organic solvent to obtain an electrolyte (LDD) with a lithium salt concentration of 1 mol/L. 10 g of the prepared electrolyte LDD was taken, 0.28 g of a star-branched multi-arm polymer, 0.0195 g of a cross-linking agent and 0.006 g of an initiator azobisisobutyronitrile (AIBN) were added and completely dissolved to obtain a composition, wherein the arms in the star-branched multi-arm polymer are represented by Other parameters are shown in Table 1. The cross-linking agent can be represented by Formula I, and the specific parameters are shown in Table 1.

4. Diaphragm Preparation

Industrial PE diaphragm (9 microns thick) was selected as the diaphragm, and the diaphragm was cut into 22 mm specifications for standby use.

5. Cell preparation

The lithium copper composite strip prepared in step 1 is used as the negative electrode, the lithium iron phosphate prepared in step 2 is used as the positive electrode, and the composition in step 3 is prepared in step 4. After being assembled into a button battery in a glove box, the battery is allowed to stand for 12 hours until the composition is completely soaked, and then the battery is placed in a 60 degree Celsius oven for curing for more than 6 hours before testing.

Examples 1-2 to 1-10, Comparative Example 1-1, Comparative Example 1-2

It is substantially the same as Example 1-1, except that the star-branched multi-arm polymer and the cross-linking agent in step 3 are different, see Table 1 for details.

Comparative Examples 1-3

It is substantially the same as Example 1-3, except that the star-branched multi-arm polymer, the cross-linking agent and the initiator are not added to the composition, that is, the electrolyte LDD is directly used as the electrolyte.

The battery cells obtained from Examples 1-1 to 1-10 and Comparative Examples 1-1 to 1-3 were subjected to cycle performance tests, and the results are shown in Table 1.

Table 1

Note: Formula II is

According to Table 1, the battery cells obtained in each embodiment have better cycle performance than the comparative example. Among them, in comparative example 1-1, the arm of the star-branched multi-arm polymer does not contain an amide group, and the obtained gel polymer electrolyte has a poor effect of homogenizing the ion flow, thereby affecting the cycle performance of the battery; in comparative example 1-2, the arm length of the star-branched multi-arm polymer is too short, which may result in a smaller pore structure in the formed network structure, which cannot affect the transmission of ions and thus affect the cycle performance of the battery.

According to Examples 1-1 to 1-4, the number of arms of the star-branched multi-arm polymer has a certain influence on the cycle performance of the battery. When the number of arms is 3 or 4, the cycle performance of the battery is better.

According to Examples 1-1, 1-5 to 1-7, the arm length of the star-branched multi-arm polymer has a certain influence on the cycle performance of the battery. When R1 is ethylene and m is 40 to 80, the cycle performance of the battery is better.

According to Examples 1-1, 1-8 to 1-10, the type of cross-linking agent has a certain influence on the cycle performance of the battery. When the cross-linking agent has an ester group and a small molecular weight, the cycle performance of the battery is better.

In addition, a scanning electron microscope was used to detect the surface morphology of the negative electrode plates after cycling of the battery cells obtained in Example 1-1 and Comparative Example 1-3, and the results are shown in Figure 1, wherein (a) is a morphology of lithium metal deposition on the surface of the negative electrode plates in Comparative Example 1-3, showing a loose and porous deposition morphology, and (b) is a morphology of lithium metal deposition on the surface of the negative electrode plates in Example 1-1, showing a dense and flat block lithium deposition morphology with fewer holes and dendritic deposition morphology, which is beneficial to preventing dendrite growth and reducing surface side reactions. The above deposition morphology results show that the use of the gel electrolyte of the present application can effectively improve the uniformity of lithium deposition.

The cycle performance test results of Example 1-1 and Comparative Example 1-3 are shown in Figure 2. It can be seen from the figure that the liquid electrolyte short-circuits after only 59 cls of cycling at a high rate of 0.5C/1C, while the gel electrolyte of the present application can be cycled for more than 200 cls, and the cycle performance is greatly improved. The results show that the gel electrolyte in the present application can greatly improve the short circuit and cycle performance of the battery cell.

The gel electrolyte obtained in Example 1-1 was tested using a differential scanning calorimeter (DSC). The DSC curve is shown in FIG3 . Its glass transition temperature is about −57.6° C., indicating that it is amorphous in a wide temperature range and can still maintain good ionic conductivity at a relatively low temperature.

The battery cells obtained in Example 1-1 and Comparative Example 1-3 were subjected to impact tests and hot box tests, and the results are shown in Figure 4, where (a) is the impact test result of Comparative Example 1-3, with a pass rate of 1/3, (b) is the impact test result of Example 1-1, with a pass rate of 3/3, (c) is the hot box test result of Comparative Example 1-3, with a pass rate of 0/3, and (d) is the hot box test result of Example 1-1, with a pass rate of 3/3. The results show that the gel electrolyte in this application can greatly improve the safety performance of the battery cell.

Example 2-1 to Example 2-8

It is basically the same as Example 1-1, and the only difference is that some parameters are different. The specific differences are shown in Table 2.

It should be noted that the mass percentage of the star-branched multi-arm polymer in the composition is controlled by adjusting the addition of the electrolyte LDD, and the mass percentages of the crosslinking agent and the initiator remain unchanged.

The battery cells obtained from Examples 2-1 to 2-8 and Comparative Examples 1-3 were subjected to cycle performance tests, coulomb efficiency tests, and hot box tests at different temperatures. The results are shown in Table 2.

Table 2

According to Table 2, the battery cells obtained in each embodiment have improved cycle performance, coulombic efficiency and thermal stability compared with the comparative example.

According to Examples 2-1 to 2-5, the higher the content of the star-branched multi-arm polymer, the better the thermal stability; when the mass percentage is 3% to 6%, the coulombic efficiency of the battery is higher; when the mass percentage is 4% to 6%, the cycle performance of the battery is better.

According to Examples 2-3 and 2-6, the use of different organic solvents has a certain influence on the cycle performance, coulombic efficiency and thermal stability of the battery.

According to Examples 2-3, 2-7, and 2-8, the use of different electrolytes has little effect on the thermal stability of the battery, but has a certain effect on the cycle performance and coulombic efficiency of the battery.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims (12)

1. A composition for preparing a gel polymer electrolyte, characterized in that it comprises: a star-branched multi-arm polymer, a crosslinking agent, an electrolyte salt and an organic solvent; Wherein, in the star-branched multi-arm polymer, the number of arms is 3, 4 or 5, and the arms are independently represented as _R1 represents a linear or branched alkylene group having 1 to 5 carbon atoms, _R2 represents a methacrylate group, an acrylate group, R' represents a linear or branched alkylene group having 1 to 5 carbon atoms, and m represents an integer of 20 to 80; _R2 of at least one arm of the star-branched multi-arm polymer is 2. according to the composition of claim 1, it is characterized in that, described star-shaped branched multi-arm polymer satisfies at least one of the following conditions: 1) The weight average molecular weight of the star-branched multi-arm polymer is not less than 5000; 2) The number of arms is 3 or 4; 3) R ₁ represents a linear or non-linear alkylene group having 2 to 4 carbon atoms; 4) _R2 of the arms are all 3. according to the composition of claim 1, it is characterized in that the crosslinking agent comprises at least one of a vinyl functional group, a propenyl functional group, an aziridine functional group and a sulfhydryl functional group, and the number of the functional group is 3,4 or 5. 4. The composition according to claim 1, characterized in that the crosslinking agent can be represented by formula I, wherein R ₃ and R ₄ each independently represent a linear or branched alkylene group having 1 to 5 carbon atoms, R ₅ represents a vinyl group and its derivative groups, a propenyl group and its derivative groups, an aziridine group and its derivative groups or a mercapto group, x is 0 or 1, and y is an integer from 0 to 4. 5. The composition according to claim 3, characterized in that the cross-linking agent satisfies at least one of the following conditions: 1) x is 1; 2) y is an integer from 0 to 2. 6. The composition according to claim 1, characterized in that the electrolyte salt comprises a lithium salt and/or a sodium salt; the lithium salt comprises at least one of LiPF ₆ , LiBF ₆ , LiClO ₄ , lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorophosphate, lithium difluorobis(oxalatophosphate) and lithium tetrafluorooxalatophosphate; the sodium salt comprises at least one of NaPF ₆ , NaClO ₄ , NaBCl ₄ , NaSO ₃ CF ₃ and Na(CH ₃ )C ₆ H ₄ SO ₃ . 7. The composition according to claim 1, characterized in that the organic solvent comprises at least one of an ether-based solvent, a carbonate solvent, a nitrile solvent, and an ionic liquid solvent. The ether-based solvent includes at least one of ethylene glycol dimethyl ether, 1,4-dioxane, diethylene glycol dimethyl ether, ethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, methyltetrahydrofuran and fluoroether solvents. The carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate and fluorocarbonate solvents. The nitrile solvent includes at least one of acetonitrile, propionitrile, succinonitrile, and a fluoronitrile solvent. The ionic liquid solvent includes anions and cations, wherein the anions include at least one of bis(trifluoromethanesulfonyl)imide ions, bis(fluoromethanesulfonyl)imide ions, hexafluorophosphate ions, boron tetrafluoride ions, nitrate ions, acetate ions, perchlorate ions, hydrogen sulfate ions, dihydrogen phosphate ions, halogen anions, p-toluenesulfonate ions, trifluoromethanesulfonate ions, trifluoroacetate ions, and tetrachloroaluminum anions, and the cations include at least one of imidazole cations, quaternary ammonium ions, pyrrolidine cations, pyridine cations, piperidinium cations, and quaternary phosphonium cations. 8. The composition according to any one of claims 1 to 7, characterized in that the composition satisfies at least one of the following conditions: 1) The mass percentage of the star-branched multi-arm polymer in the composition is 1% to 10%; 2) The mass percentage of the cross-linking agent in the composition is 0.1% to 10%; 3) The mass percentage of the electrolyte salt in the composition is 1% to 90%; 4) The mass percentage of the organic solvent in the composition is 1% to 90%. 9. The gel polymer electrolyte composition according to claim 8, characterized in that the gel polymer electrolyte composition satisfies at least one of the following conditions: 1) The mass percentage of the star-branched multi-arm polymer in the composition is 3% to 6%; 2) The mass percentage of the cross-linking agent in the composition is 0.1% to 5%; 3) The mass percentage of the electrolyte salt in the composition is 10% to 70%; 4) The mass percentage of the organic solvent in the composition is 20% to 90%. 10. The composition according to any one of claims 1 to 7, characterized in that it further comprises an initiator, wherein the mass percentage of the initiator in the composition is 0.1% to 2%, and the initiator comprises at least one of an organic peroxide initiator, an inorganic peroxide initiator and an azo initiator. The organic peroxide initiator comprises at least one of dibenzoyl peroxide, lauroyl peroxide, cumene hydroperoxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, diisopropyl peroxide, tert-butyl perbenzoate, tert-butyl pervalerate, methyl ethyl ketone peroxide, cyclohexanone peroxide, diisopropyl peroxydicarbonate and dicyclohexyl peroxydicarbonate. The inorganic peroxide initiator comprises at least one of potassium persulfate, sodium persulfate and ammonium persulfate, The azo initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile and dimethyl azobisisobutyrate. 11. A secondary battery, comprising: a positive electrode sheet, a negative electrode sheet, a separator, and a gel polymer electrolyte obtained by initiating a polymerization reaction of the composition according to any one of claims 1 to 10. 12 . An electronic device, comprising: the secondary battery according to claim 11 .