Gel polymer electrolyte with core-shell structure as well as preparation method and application of gel polymer electrolyte

Abstract

The invention provides a core-shell structured gel polymer electrolyte and a preparation method and application thereof.The core-shell structured gel polymer electrolyte comprises a core-shell structured nanofiber, the core-shell structured nanofiber comprises a core layer and a shell layer, the core layer comprises a polyvinylidene fluoride-hexafluoropropylene copolymer and inorganic nanoparticles, and the shell layer comprises a shell layer and a polyvinylidene fluoride-hexafluoropropylene copolymer; the polyvinylidene fluoride-hexafluoropropylene copolymer and the inorganic nanoparticles are connected through a silane coupling agent; the shell layer comprises a polyacrylate polymer. The gel polymer electrolyte based on the core-shell structure solves the technical problem that the gel polymer electrolyte in the prior art is difficult to consider ionic conductivity, mechanical strength and interfacial compatibility between the electrolyte and an electrode material at the same time.

Description

Technical Field

[0001] The present invention relates to the field of lithium-ion batteries, and in particular, to a gel polymer electrolyte with a core-shell structure, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium-ion batteries have high energy density and long cycle life, and are widely used in various portable electronic devices. With the rapid development of new energy vehicles and energy storage devices, the demand for high-performance lithium-ion batteries is increasing. In the research of battery technology, the research of electrolyte materials has become a hot spot. The electrolyte plays a crucial role in the battery, and its performance directly affects the performance of the battery. The conductivity, polarization, electrochemical stability, safety, and stability of the electrolyte are key factors affecting the battery performance.

[0003] At present, electrolyte materials are mainly divided into two categories: liquid electrolytes and solid electrolytes. In liquid electrolytes, lithium salts are dissolved in organic solvents. Traditional lithium-ion batteries using liquid electrolytes have safety problems caused by leakage of organic electrolytes. Although solid electrolytes can overcome the safety hazards of liquid electrolytes, their ionic conductivity is much lower than that of liquid electrolytes, which limits their application in lithium-ion batteries.

[0004] Gel polymer electrolytes absorb liquid electrolytes based on the cross-linked structure formed by chemical bonds or physical forces in a polymer matrix, combining the high ionic conductivity of liquid electrolytes and the low risk of electrolyte leakage of solid electrolytes. Gel polymer electrolytes based on polyvinylidene fluoride (PVDF) have good electrochemical properties because they have strong electron-withdrawing functional groups and high dielectric constants, which are beneficial to the dissolution of lithium salts and the transport of high-concentration charge carriers, and are widely used as the matrix of gel polymers. However, gel polymer electrolytes based on PVDF have their disadvantages. For example, their semi-crystalline structure has relatively low ionic conductivity and poor interfacial compatibility with electrode materials. In addition, in gel polymer electrolytes, after the polymer backbone material adsorbs liquid electrolyte to form a gel state, the polymer mainly plays a mechanical support role, and lithium ions are mainly conducted through the adsorbed liquid electrolyte, so that its room-temperature ionic conductivity can be close to that of liquid electrolytes, and its mechanical strength is reduced due to the presence of liquid electrolyte adsorbed in the polymer matrix and porous structure. Therefore, the existing gel polymer electrolytes have technical problems that it is difficult to balance ionic conductivity, mechanical strength, and interfacial compatibility between the electrolyte and electrode materials. Summary of the Invention

[0005] The main object of the present invention is to provide a gel polymer electrolyte with a core-shell structure, a preparation method thereof, and an application thereof, so as to solve the technical problems that the existing gel polymer electrolytes are difficult to balance ionic conductivity, mechanical strength, and interfacial compatibility between the electrolyte and electrode materials.

[0006] To achieve the above object, the present invention provides a gel polymer electrolyte with a core-shell structure, comprising: nanofibers with a core-shell structure, the nanofibers with a core-shell structure comprising a core layer and a shell layer, the core layer comprising a polyvinylidene fluoride-hexafluoropropylene copolymer and inorganic nanoparticles, the polyvinylidene fluoride-hexafluoropropylene copolymer and the inorganic nanoparticles being connected by a silane coupling agent; the shell layer comprising a polyacrylate polymer.

[0007] Further, the polyacrylate polymer is selected from one or more of polymethyl methacrylate, polyethyl methacrylate, ethylene glycol polyacrylate, poly(methyl trifluoracrylate), poly(trifluoroethyl methacrylate), and poly(methyl trifluoracrylate).

[0008] Further, the inorganic nanoparticles are selected from one or more of nano-silica, titanium dioxide, zirconium dioxide, aluminum trioxide, and zinc oxide.

[0009] Further, the D50 particle size of the nanoparticles is 10 nm to 100 nm.

[0010] Preferably, the D50 particle size of the nanoparticles is 10 nm to 30 nm.

[0011] Further, the silane coupling agent is selected from one or more of 1H,1H,2H,2H-perfluorooctyltrimethoxysilane, vinyltriethoxysilane, 1H,1H,2H,2H-perfluorodecyltrimethoxysilane, vinyltrimethoxysilane, (heptadecafluoro-1,1,2,2-tetradecyl)trimethoxysilane, and vinyltris(β-methoxyethoxy)silane.

[0012] Further, the weight ratio of the polyvinylidene fluoride-hexafluoropropylene copolymer to the inorganic nanoparticles is (20 to 240):1.

[0013] Further, the weight ratio of the inorganic nanoparticles to the silane coupling agent is (1 to 2):(1 to 7).

[0014] Preferably, the weight ratio of the inorganic nanoparticles to the silane coupling agent is (1 to 2):(1 to 2).

[0015] Further, the weight ratio of the polyvinylidene fluoride-hexafluoropropylene copolymer to the polyacrylate polymer is (1 to 4):1.

[0016] Further, the diameter of the nanofibers with a core-shell structure is 100 nm to 300 nm.

[0017] According to another aspect of the present invention, a method for preparing a gel polymer electrolyte with a core-shell structure is provided, comprising the following steps:

[0018] Mix polyvinylidene fluoride - hexafluoropropylene copolymer, inorganic nanoparticles, silane coupling agent and a first solvent and react to obtain a core layer spinning solution;

[0019] Mix a polyacrylate polymer and a second solvent to obtain a shell layer spinning solution;

[0020] Use coaxial electrospinning technology to make the core layer spinning solution and the shell layer spinning solution into a core - shell structured gel polymer electrolyte.

[0021] Furthermore, first stir and mix polyvinylidene fluoride - hexafluoropropylene copolymer, inorganic nanoparticles, silane coupling agent and the first solvent at room temperature, then heat and react at 45°C - 65°C for 4h - 5h, and after the reaction is completed, let it stand for 0.5h - 2h to obtain the core layer spinning solution.

[0022] Furthermore, first ultrasonically dissolve the polyacrylate polymer in the second solvent, then stir and mix for 0.5h - 2h, and after mixing is completed, let it stand for 0.5h - 2h to obtain the shell layer spinning solution.

[0023] Furthermore, the first solvent and the second solvent are each independently selected from the mixture of at least one of N,N - dimethylacetamide, N,N - dimethylformamide, N - methylpyrrolidone and acetone.

[0024] Furthermore, the weight ratio of polyvinylidene fluoride - hexafluoropropylene copolymer to the first solvent is 1:(4 - 20).

[0025] Furthermore, the weight ratio of polyacrylate polymer to the second solvent is 1:(4 - 20).

[0026] Preferably, the first solvent and the second solvent have the same composition.

[0027] More preferably, both the first solvent and the second solvent are obtained by mixing at least one of N,N - dimethylacetamide, N,N - dimethylformamide, N - methylpyrrolidone and acetone in a volume ratio of (3 - 7):(3 - 7).

[0028] According to another aspect of the present invention, there is provided a lithium - ion battery, including the core - shell structured gel polymer electrolyte as above or a core - shell structured gel polymer electrolyte prepared by the preparation method of the core - shell structured gel polymer electrolyte as above.

[0029] Applying the technical solution of the present invention, nanofibers with a core-shell structure are used. The core-shell structure respectively adopts two different polymers, namely polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and polyacrylate polymer. By utilizing the advantages of different polymer materials and compounding inorganic nanoparticles in the core layer to synergistically improve the performance of the gel polymer electrolyte, the performance such as ionic conductivity, mechanical strength, and interfacial compatibility with electrode materials is improved simultaneously. On the one hand, using polyacrylate polymer as the shell material is beneficial to improving the interfacial compatibility between the gel polymer electrolyte layer and the electrode material. Using PVDF-HFP as the core material can reduce its direct contact with components such as solvents in the liquid electrolyte, provide a strong skeleton support for the gel polymer electrolyte, and improve the mechanical properties of the gel polymer electrolyte. Inorganic nano-fillers are compounded and connected at the molecular chain ends of the core material PVDF-HFP, and polyacrylate polymer is used as the shell material for compounding to improve the toughness of the material, which is beneficial to obtaining a gel polymer electrolyte with high mechanical properties. On the other hand, PVDF-HFP as the core material itself has a relatively high ionic conductivity. By compounding and connecting inorganic nano-fillers, its ionic conductivity can be further improved; by introducing inorganic nanoparticles into the core material PVDF-HFP, the crystallinity of PVDF-HFP can also be reduced, and the ionic conductivity of PVDF-HFP can be improved; by introducing inorganic nanoparticles into the core material PVDF-HFP to improve the mechanical strength, it is beneficial to avoid the reduction of the ionic conductivity of polyacrylate polymer caused by the mixing of crystalline substances in the polyacrylate polymer electrolyte, and the shell material polyacrylate polymer distributed along the core nanofibers can provide a three-dimensional ordered channel for lithium ion transport based on the complexation-dissociation effect, improving the ionic conductivity of the gel polymer electrolyte. Moreover, polyacrylate polymer has strong adhesion. As the shell material, it can adhere to the core nanofibers, which is beneficial to film formation; the diameter of the nanofibers with a core-shell structure is at the nanoscale and has a high specific surface area. A large van der Waals force can be generated between the nanofibers, which is beneficial to mutual attraction and entanglement to form a stable membrane structure. And using polyacrylate polymer as the shell material makes the surface of the nanofibers contain a certain amount of hydroxyl groups, which is beneficial to the combination of nanofibers through hydrogen bonds and improves the stability of the membrane structure. Description of the Drawings

[0030] The specification drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0031] Figure 1 Shows the SEM image of the gel polymer electrolyte with a core-shell structure prepared in Example 1;

[0032] Figure 2 The SEM image of the gel polymer electrolyte with a core-shell structure prepared in Example 2 is shown;

[0033] Figure 3 The SEM image of the gel polymer electrolyte with a core-shell structure prepared in Example 3 is shown;

[0034] Figure 4 The SEM image of the gel polymer electrolyte with a core-shell structure prepared in Example 4 is shown. Detailed implementation manners

[0035] It should be noted that, without conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0036] As described in the background art, there are technical problems in the prior art that it is difficult for gel polymer electrolytes to balance ion conductivity, mechanical strength, and the interfacial compatibility between the electrolyte and the electrode material. For example, for gel polymer electrolytes, if the mechanical strength is poor, lithium dendrites are likely to pierce through the electrolyte membrane, leading to potential battery short circuits and even explosions. If the ion conductivity is low, there will be insufficient channels for lithium ion transmission, thereby reducing the electrochemical performance such as the charge-discharge cycle performance of the battery. To solve the above problems, according to one aspect of the present invention, a gel polymer electrolyte with a core-shell structure is provided, including: nanofibers with a core-shell structure, the nanofibers with a core-shell structure include a core layer and a shell layer, the core layer includes a polyvinylidene fluoride-hexafluoropropylene copolymer and inorganic nanoparticles, and the polyvinylidene fluoride-hexafluoropropylene copolymer and the inorganic nanoparticles are connected by a silane coupling agent; the shell layer includes a polyacrylate polymer.

[0037] PVDF-HFP is beneficial to the dissolution of lithium salts and the transmission of high-concentration lithium ions due to its strong electron-withdrawing functional group (-C-F) and high dielectric constant, and thus has good electrochemical performance. However, its semi-crystalline structure itself leads to relatively low ion conductivity and poor interfacial compatibility with electrode materials; in addition, its mechanical strength is prone to decrease during use due to the absorption of liquid electrolyte and the existence of a porous structure. Polyacrylate polymers have good shape stability, high ion conductivity, and good interfacial compatibility with electrode materials, but they are brittle, difficult to form films, and if crystalline substances are mixed in polyacrylate polymers, their ion conductivity is likely to decrease.

[0038] Based on the gel polymer electrolyte with a core-shell structure of the present invention, nanofibers with a core-shell structure are adopted. The core-shell structure respectively uses two different polymers, namely poly(vinylidene fluoride-hexafluoropropylene) copolymer (PVDF-HFP) and polyacrylate polymer. By utilizing the advantages of different polymer materials and compounding inorganic nanoparticles in the core layer to synergistically improve the performance of the gel polymer electrolyte, the performance such as ionic conductivity, mechanical strength, and interfacial compatibility with electrode materials is improved simultaneously. On the one hand, using polyacrylate polymer as the shell material is beneficial to improving the interfacial compatibility between the gel polymer electrolyte layer and the electrode material. Using PVDF-HFP as the core material can reduce its direct contact with components such as solvents in the liquid electrolyte, provide a strong skeleton support for the gel polymer electrolyte, and improve the mechanical properties of the gel polymer electrolyte. Compounding and connecting inorganic nano-fillers at the molecular chain ends of the core material PVDF-HFP and using polyacrylate polymer as the shell material for compounding to improve the material toughness are conducive to obtaining a gel polymer electrolyte with high mechanical properties. On the other hand, PVDF-HFP as the core material itself has a relatively high ionic conductivity. Its ionic conductivity can be further improved by compounding and connecting inorganic nano-fillers; by introducing inorganic nanoparticles into the core material PVDF-HFP, the crystallinity of PVDF-HFP can also be reduced, and the ionic conductivity of PVDF-HFP can be improved; by introducing inorganic nanoparticles into the core material PVDF-HFP to improve the mechanical strength, it is beneficial to avoid the reduction of the ionic conductivity of polyacrylate polymer caused by the mixing of crystalline substances in the polyacrylate polymer electrolyte. Moreover, the shell material polyacrylate polymer distributed along the core layer nanofibers can provide a three-dimensional ordered channel for lithium ion transport based on the complexation-dissociation effect, improving the ionic conductivity of the gel polymer electrolyte. Furthermore, polyacrylate polymer has strong adhesion. As the shell material, it can adhere to the core layer nanofibers, which is beneficial to film formation; the diameter of the nanofibers with a core-shell structure is at the nanoscale, having a high specific surface area. Large van der Waals forces can be generated between the nanofibers, which is beneficial to mutual attraction and entanglement to form a stable membrane structure. And using polyacrylate polymer as the shell material makes the surface of the nanofibers contain a certain amount of hydroxyl groups, which is beneficial to the hydrogen bond combination between the nanofibers and improves the stability of the membrane structure.

[0039] In some embodiments, the polyacrylate polymer is selected from one or more of polymethyl methacrylate, polyethyl methacrylate, ethylene glycol polyacrylate, poly(methyl trifluoroacrylate), poly(ethyl trifluoromethacrylate), poly(methyl trifluoroacrylate), but is not limited to the above polyacrylate polymers. The above polyacrylate polymers have good electrolyte compatibility, good interfacial compatibility with electrode materials, and ionic conductivity. Selecting the above polyacrylate polymers as the shell material can improve the interfacial compatibility between the gel polymer electrolyte and the electrode material, maintain a high ionic conductivity, and enhance the mechanical stability of the gel polymer electrolyte. It can be understood that different polyacrylate polymers have different polarities and side chain structures, which can affect their solubility and interaction with lithium salts, thereby affecting the performance of the gel polymer electrolyte. For example, poly(methyl trifluoroacrylate) has high thermal stability and chemical stability and is suitable for high-temperature conditions, while polyethyl methacrylate and ethylene glycol polyacrylate have better flexibility and electrolyte adsorption capacity. Those skilled in the art can further select the corresponding polyacrylate polymers according to needs.

[0040] The addition of inorganic nanoparticles can improve the ionic conductivity and mechanical properties of the gel polymer electrolyte. Through the interaction between groups such as Lewis acid sites on the surface and lithium salt anions, it can promote the dissociation of lithium salts and then release free lithium ions, thereby increasing the ionic conductivity of lithium salts. In some embodiments, the inorganic nanoparticles are selected from one or more of nano-silica, titanium dioxide, zirconium dioxide, aluminum trioxide, and zinc oxide. The above inorganic nanoparticles such as nano-silica, titanium dioxide, zirconium dioxide, etc. can promote the dissociation of lithium salts and increase the ionic conductivity. At the same time, the high modulus of these inorganic nanoparticles can enhance the mechanical strength of the gel polymer electrolyte.

[0041] The nano-scale particle size of the inorganic nanoparticles is beneficial to the full combination and uniform dispersion of the inorganic nanoparticles with the polymer matrix, reducing local stress concentration and improving the uniformity and stability of the performance of the gel polymer electrolyte. In some embodiments, the D50 particle size of the nanoparticles is 10 nm to 100 nm, preferably 10 nm to 30 nm, which is beneficial to the uniform dispersion of the inorganic nanoparticles and reduces the risk of swelling and fragmentation of the core layer material during use, improving the ionic conductivity, mechanical strength, and stability of the gel polymer electrolyte.

[0042] Silane coupling agents have organic functional groups at one end that can react with, physically adsorb, or be compatible with organic polymers (such as amino groups (-NH2), epoxy groups (-O-C-CH2-CH3), methacryloyl groups (-CH2-CO-C-CH2-CH3), mercapto groups (-SH), vinyl groups (-CH=CH2), alkyl chains, etc.), and inorganic functional groups at the other end that can react with surface hydroxyl groups (-OH) or other active groups on inorganic materials, such as alkoxy groups (-OR), thus establishing a bridge between organic polymers and inorganic materials and achieving the fusion of their interfaces. In some embodiments, the silane coupling agent is selected from one or more of 1H,1H,2H,2H-perfluorooctyltrimethoxysilane, vinyltriethoxysilane, 1H,1H,2H,2H-perfluorodecyltrimethoxysilane, vinyltrimethoxysilane, (heptadecafluoro-1,1,2,2-tetradecyl)trimethoxysilane, vinyltris(β-methoxyethoxy)silane, but is not limited to the above silane coupling agents. Using the above silane coupling agents is beneficial for inorganic nanoparticles to be evenly dispersed in the polymer matrix, reducing interfacial stress and improving the uniformity, stability, and mechanical strength of the gel polymer electrolyte.

[0043] The polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) is the core layer material of the gel polymer electrolyte, and the weight ratio of it to the inorganic nanoparticles affects the internal structure and properties of the nanofibers of the formed core-shell structure, thereby affecting the ionic conductivity, mechanical strength, film-forming performance, and flexibility of the gel polymer electrolyte. In some embodiments, the weight ratio of the polyvinylidene fluoride-hexafluoropropylene copolymer to the inorganic nanoparticles is (20-240):1. At the above weight ratio, it is beneficial to obtain higher ionic conductivity and mechanical strength.

[0044] The weight ratio between the inorganic nanoparticles and the silane coupling agent affects the degree of surface modification of the inorganic nanoparticles and the stability of the interfacial bonding between the inorganic nanoparticles and the organic polymer. In some embodiments, the weight ratio of the inorganic nanoparticles to the silane coupling agent is (1-2):(1-7) so that the surfaces of the inorganic particles are fully modified and dispersed in the polyvinylidene fluoride-hexafluoropropylene copolymer, improving the mechanical strength and ionic conductivity of the core-shell structured gel polymer electrolyte; preferably (1-2):(1-2).

[0045] The weight ratio of the polyvinylidene fluoride - hexafluoropropylene copolymer to the polyacrylate polymer affects the thickness and properties of the core layer and the shell layer. A higher PVDF - HFP is beneficial for obtaining a stronger mechanical skeleton and a higher electrolyte retention capacity, while a higher proportion of the polyacrylate polymer is beneficial for obtaining higher interfacial compatibility and ionic conductivity. In some embodiments, the weight ratio of the polyvinylidene fluoride - hexafluoropropylene copolymer to the polyacrylate polymer is (1 - 4):1. Under the above weight ratio, it is beneficial to obtain a gel polymer electrolyte with high ionic conductivity, mechanical properties, and interfacial compatibility.

[0046] In some embodiments, the diameter of the core - shell structured nanofibers is 100 nm to 300 nm. The diameter of the nanofibers affects the pore size, pore size distribution, and porosity of the gel polymer electrolyte film formation. A smaller diameter of the nanofibers is beneficial for reducing the pore size of the formed film, increasing the specific surface area and porosity of the film. However, a smaller diameter of the nanofibers can increase the agglomeration between the fibers and the tightness of stacking, thereby reducing the porosity. The nanofibers within the above diameter range are beneficial for obtaining a film product with a smaller film pore size and a higher porosity, which can provide a shorter migration path for lithium - ion transport and is beneficial for improving the lithium - ion transport efficiency.

[0047] According to another aspect of the present invention, there is also provided a method for preparing a gel polymer electrolyte with a core - shell structure, including the following steps:

[0048] Mix and react the polyvinylidene fluoride - hexafluoropropylene copolymer, inorganic nanoparticles, silane coupling agent, and a first solvent to obtain a core - layer spinning solution;

[0049] Mix the polyacrylate polymer and a second solvent to obtain a shell - layer spinning solution;

[0050] Use coaxial electrospinning technology to make the core - layer spinning solution and the shell - layer spinning solution into a gel polymer electrolyte with a core - shell structure.

[0051] Based on the method of the present invention, the coaxial electrospinning technology can control the formation of the core - shell structure, realizing the complementary advantages of the core - layer material and the shell - layer material, and a gel polymer electrolyte with high ionic conductivity, high mechanical strength, and good interfacial compatibility can be prepared; in addition, by using the coaxial electrospinning technology, by controlling the core - layer fiber diameter, shell - layer fiber diameter, core - layer thickness, shell - layer thickness, and spinning time, precise regulation of structural characteristics such as the membrane porosity, membrane pore size, uniformity of the membrane pore size that affect the lithium - ion transport channel, and membrane thickness that affects the energy density of the assembled battery can be achieved, which is beneficial for the consistency control of the gel polymer electrolyte membrane product with a core - shell structure, and the preparation process is simple and efficient, suitable for large - scale industrial production.

[0052] In some embodiments, first, a poly(vinylidene fluoride - hexafluoropropylene) copolymer, inorganic nanoparticles, a silane coupling agent, and a first solvent are stirred and mixed at room temperature, and then heated and reacted at 45°C to 65°C for 4 h to 5 h. After the reaction is completed, it is left standing for 0.5 h to 2 h to obtain a core layer spinning solution; in the process of preparing the core layer spinning solution, first, the poly(vinylidene fluoride - hexafluoropropylene) copolymer (PVDF - HFP), inorganic nanoparticles, a silane coupling agent, and a first solvent are mixed to preliminarily disperse and dissolve the components. Subsequently, it is heated and reacted at a temperature of 45°C to 65°C for 4 h to 5 h to promote the reaction between the inorganic end of the silane coupling agent and the active groups such as hydroxyl groups on the surface of the inorganic nanoparticles, and its organic end interacts with PVDF - HFP molecules to form intermolecular entanglement or cross - linking. After the reaction is completed, the slurry needs to be left standing for 0.5 h to 2 h so that the bubbles in the reaction system can escape, improving the uniformity and stability of the prepared gel polymer electrolyte, and thus enhancing the electrochemical stability of the gel polymer electrolyte; preferably, the stirring is mechanical stirring to improve the efficiency of dispersion and dissolution. Specifically, a high - speed rotating stirring device such as a stirring paddle, a magnetic stirrer, or a mechanical stirrer can be used for high - intensity stirring operations.

[0053] In some embodiments, a polyacrylate polymer is ultrasonically dissolved in a second solvent first, and then stirred and mixed for 0.5 h to 2 h. After the mixing is completed, it is left standing for 0.5 h to 2 h to obtain a shell layer spinning solution; ultrasonic dissolution and stirring are used to prepare the shell layer spinning solution so that the polyacrylate polymer can be fully dissolved and uniformly dispersed in the solvent to form a stable and homogeneous shell layer spinning solution, which is beneficial to forming a stable shell layer structure during the coaxial electrospinning process and improving the electrochemical stability and mechanical stability of the gel polymer electrolyte; preferably, the stirring is strong mechanical stirring to improve the efficiency of dispersion. Specifically, a high - speed rotating stirring device such as a stirring paddle, a magnetic stirrer, or a mechanical stirrer can be used for high - intensity stirring operations.

[0054] In some embodiments, the first solvent and the second solvent are each independently selected from at least one of N,N - dimethylacetamide, N,N - dimethylformamide, N - methylpyrrolidone and acetone; using the above solvents is beneficial for the dissolution of the poly(vinylidene fluoride - hexafluoropropylene) copolymer and the polyacrylate polymer and the formation of a uniform spinning solution, and the prepared spinning solution has appropriate rheology for subsequent electrospinning to prepare core - shell structured nanofibers; preferably, the first solvent and the second solvent have the same composition. Using the same mixed solvent as the core layer solvent and the shell layer solvent respectively is beneficial for reducing the risk of sedimentation when the polymers dissolved in the core layer solvent and the shell layer solvent are mixed and coagulation at the spinneret of the syringe, thereby blocking the spinneret; more preferably, both the first solvent and the second solvent are obtained by mixing at least one of N,N - dimethylacetamide, N,N - dimethylformamide, N - methylpyrrolidone and acetone in a volume ratio of (3 - 7):(3 - 7).

[0055] In some embodiments, the weight ratio of the polyvinylidene fluoride - hexafluoropropylene copolymer to the first solvent is 1:(4 - 20), which is conducive to the formation of nanofibers with a uniform core - shell structure.

[0056] In some embodiments, the weight ratio of the polyacrylate polymer to the second solvent is 1:(4 - 20), which is conducive to the formation of nanofibers with a uniform core - shell structure.

[0057] In some embodiments, the parameters of coaxial electrospinning include: the flow rate ratio of the core - layer spinning solution to the shell - layer spinning solution is (1 - 20):1, the electrospinning voltage is 10 kV - 30 kV, the injection speed of the syringe is 0.05 mm / min - 1 mm / min, the rotational speed of the receiver is 400 rpm / min - 600 rpm / min, the humidity is 10% - 30%, and the distance between the spinneret and the receiver is 5 cm - 20 cm.

[0058] According to another aspect of the present invention, a lithium - ion battery is provided, which includes the gel polymer electrolyte with the core - shell structure as above or the gel polymer electrolyte with the core - shell structure prepared by the preparation method of the gel polymer electrolyte with the core - shell structure as above. The gel polymer electrolyte based on the core - shell structure of the present invention has both high ionic conductivity, high mechanical strength, and good interfacial compatibility between the electrolyte and the electrode material, which is conducive to obtaining high - performance lithium - ion batteries. For example, the gel polymer electrolyte with high ionic conductivity is conducive to promoting the rapid transport of ions inside the battery, so that the active sites on the electrode material can be more fully utilized, enabling the battery to exhibit better rate performance during rapid charge and discharge, while reducing the internal resistance, thereby improving the energy conversion efficiency of the battery, increasing the energy density of the battery, further reducing the polarization of the electrode material, and reducing the heat accumulation inside the battery, thus contributing to improving the charge - discharge cycle stability and lifespan; good mechanical properties are conducive to preventing the deformation or damage of the gel polymer electrolyte during the charge and discharge process of the battery, conducive to improving the stability of the interface between the electrode material and the gel polymer electrolyte, reducing the loss of active substances and the occurrence of side reactions, and conducive to improving the charge - discharge cycle stability and the first Coulomb efficiency; good interfacial compatibility between the gel polymer electrolyte and the electrode material (such as a high - specific - capacity silicon - based negative electrode) means that the gel polymer electrolyte can form a stable contact interface with the electrode material, which is conducive to reducing the interfacial resistance inside the battery, improving the charge - discharge cycle stability. At the same time, good interfacial compatibility is conducive to the insertion and extraction of lithium ions in the electrode material, thereby improving the first Coulomb efficiency.

[0059] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0060] Example 1

[0061] A preparation method of a gel polymer electrolyte with a core-shell structure, comprising the following steps:

[0062] Step 1, 3.5 g of acetone and 8.2 g of N,N-dimethylformamide are mechanically stirred for 0.5 h to fully mix them to form a core layer solvent, and a shell layer solvent is prepared according to the same composition and method.

[0063] Step 2, 2.4 g of PVDF-HFP is weighed and added to the core layer solvent, and mechanically stirred at room temperature for 2 h to completely dissolve and uniformly mix the PVDF-HFP (Shanghai Aladdin Biochemical Technology Co., Ltd., P304908) to obtain a core layer solution; 0.01 g of silica particles with a D50 particle size of 15 nm and 0.01 g of 1H,1H,2H,2H-perfluorooctyltrimethoxysilane are added to the core layer solution, first mechanically stirred at room temperature for 1 h, and then continuously mechanically stirred in a water bath at 55 °C for 4 h to fully couple the polyvinylidene fluoride-hexafluoropropylene copolymer, inorganic nanoparticles, and silane coupling agent. After standing for 0.5 h to remove bubbles, a core layer spinning solution is obtained.

[0064] Step 3, 0.6 g of polymethyl methacrylate is weighed and added to the shell layer solvent, first ultrasonically treated for 2 h to completely dissolve it and then mechanically stirred for 1 h to fully mix it. After standing for 0.5 h to remove bubbles, a shell layer spinning solution is obtained.

[0065] Step 4, the core layer spinning solution and the shell layer spinning solution are respectively placed in a core layer syringe and a shell layer syringe, and the parameter conditions are set as follows: the flow rate ratio of the core layer spinning solution to the shell layer spinning solution is 1, the environmental humidity is 20%, the spinning voltage is 22 kV, the syringe pushing speed is 1 mm / min, the receiver rotation speed is 500 rpm / min, and the distance between the spinneret and the receiver is 5 cm; coaxial electrospinning is started, and the mixed spinning solution is stretched into nanofiber filaments under the action of a high-voltage electrostatic field and wound on the receiver to form a gel polymer electrolyte with a core-shell structure, and the average membrane thickness is 22 μm.

[0066] Example 2

[0067] A preparation method of a gel polymer electrolyte with a core-shell structure, comprising the following steps:

[0068] Step 1, 7 g of acetone and 3 g of N,N-dimethylformamide are mechanically stirred for 0.5 h to fully mix them to form a core layer solvent, and a shell layer solvent is prepared according to the same composition and method.

[0069] Step 2: Weigh 2.5 g of PVDF-HFP and add it to the core layer solvent. Mechanically stir at room temperature for 2 h until all of the PVDF-HFP (Shanghai Aladdin Biochemical Technology Co., Ltd., P304908) is dissolved and evenly mixed to obtain the core layer solution; weigh 0.125 g of silica particles with a D50 particle size of 15 nm and 0.25 g of 1H,1H,2H,2H-perfluorodecyltrimethoxysilane and add them to the core layer solution. First, mechanically stir at room temperature for 1 h, and then continuously mechanically stir in a 45 °C water bath for 5 h to fully couple the polyvinylidene fluoride-hexafluoropropylene copolymer, inorganic nanoparticles, and silane coupling agent. Let it stand for 0.5 h to remove bubbles and obtain the core layer spinning solution.

[0070] Step 3: Weigh 2.5 g of polyethyl methacrylate and add it to the shell layer solvent. First, ultrasonically treat for 2.5 h until it is completely dissolved, and then mechanically stir for 1 h to fully mix it. Let it stand for 0.5 h to remove bubbles and obtain the shell layer spinning solution.

[0071] Step 4: Place the core layer spinning solution and the shell layer spinning solution in the core layer syringe pump and the shell layer syringe pump respectively. Set the parameter conditions as follows: the flow rate ratio of the core layer spinning solution to the shell layer spinning solution is 1, the ambient humidity is 20%, the spinning voltage is 22 kV, the syringe pump propulsion speed is 0.3 mm / min, the receiver rotation speed is 500 rpm / min, and the distance between the spinneret and the receiver is 15 cm; start coaxial electrospinning, and under the action of a high-voltage electrostatic field, stretch the mixed spinning solution into nanofibers and wind them on the receiver to form a core-shell structured gel polymer electrolyte with a membrane average thickness of 25 μm.

[0072] Example 3

[0073] A preparation method of a core-shell structured gel polymer electrolyte, comprising the following steps:

[0074] Step 1: Mechanically stir 6.1 g of acetone and 6.1 g of N,N-dimethylformamide for 0.5 h to fully mix them to prepare the core layer solvent, and prepare the shell layer solvent according to the same composition and method.

[0075] Step 2: Weigh 1.83 g of PVDF-HFP and add it to the core layer solvent. Mechanically stir at room temperature for 2 h until all of the PVDF-HFP (Shanghai Aladdin Biochemical Technology Co., Ltd., P304908) is dissolved and evenly mixed to obtain the core layer solution; weigh 0.05 g of titanium dioxide particles with a D50 particle size of 25 nm and 0.05 g of vinyltriethoxysilane and add them to the core layer solution. First, mechanically stir at room temperature for 1 h, and then continuously mechanically stir in a 65 °C water bath for 4 h to fully couple the polyvinylidene fluoride-hexafluoropropylene copolymer, inorganic nanoparticles, and silane coupling agent. Let it stand for 1 h to remove bubbles and obtain the core layer spinning solution;

[0076] Step 3: Weigh 1.85 g of poly(ethylene glycol acrylate) and add it to the shell solvent. First, ultrasonically treat it for 2.5 h to completely dissolve it, and then mechanically stir it for 1 h to fully mix it. Let it stand for 0.5 h to remove bubbles, obtaining the shell spinning solution.

[0077] Step 4: Place the core spinning solution and the shell spinning solution in the core syringe pump and the shell syringe pump respectively. Set the parameter conditions as follows: the flow rate ratio of the core spinning solution to the shell spinning solution is 1, the ambient humidity is 20%, the spinning voltage is 22 kV, the advancing speed of the syringe pump is 0.05 mm / min, the rotational speed of the receiver is 500 rpm / min, and the distance between the spinneret and the receiver is 20 cm. Start coaxial electrospinning, and under the action of a high-voltage electrostatic field, the mixed spinning solution is stretched into nanofiber filaments and wound around the receiver to form a core-shell structured gel polymer electrolyte, with the average thickness of the membrane being 19 μm.

[0078] Example 4

[0079] A preparation method of a core-shell structured gel polymer electrolyte, comprising the following steps:

[0080] Step 1: Mechanically stir 7.0 g of acetone and 4.9 g of N,N-dimethylformamide for 0.5 h to fully mix them to prepare the core solvent, and prepare the shell solvent according to the same composition and method.

[0081] Step 2: Weigh 2.38 g of PVDF-HFP (Shanghai Aladdin Biochemical Technology Co., Ltd., P304908) and add it to the core solvent. Mechanically stir it at room temperature for 2 h to completely dissolve and uniformly mix PVDF-HFP, obtaining the core solution. Weigh 0.1 g of zirconia particles with a D50 particle size of 20 nm and 0.65 g of vinyltrimethoxysilane and add them to the core solution. First, mechanically stir it at room temperature for 1 h, and then continuously mechanically stir it in a 45 °C water bath for 5 h to fully couple the poly(vinylidene fluoride-hexafluoropropylene) copolymer, inorganic nanoparticles, and silane coupling agent. Let it stand for 0.5 h to remove bubbles, and then obtain a uniform core spinning solution.

[0082] Step 3: Weigh 1.2 g of poly(methyl trifluoracrylate) and add it to the shell solvent. First, ultrasonically treat it for 2 h to completely dissolve it, and then mechanically stir it for 1 h to fully mix it. Let it stand for 0.5 h to remove bubbles, obtaining the shell spinning solution.

[0083] Step 4: Place the core layer spinning solution and the shell layer spinning solution in the core layer syringe pump and the shell layer syringe pump respectively. Set the parameter conditions as follows: the flow rate ratio of the core layer spinning solution to the shell layer spinning solution is 1, the environmental humidity is 20%, the spinning voltage is 22 kV, the advancing speed of the syringe pump is 0.6 mm / min, the rotational speed of the receiver is 500 rpm / min, and the distance between the spinneret and the receiver is 9 cm. Start coaxial electrospinning, and the mixed spinning solution is stretched into nanofibers under the action of a high-voltage electrostatic field and wound around the receiver to form a core-shell structured gel polymer electrolyte with an average membrane thickness of 18 μm.

[0084] Example 5

[0085] The difference from Example 3 is only that the addition amount of titanium dioxide particles is 0.092 g (i.e., the weight ratio of polyvinylidene fluoride-hexafluoropropylene copolymer to inorganic nanoparticles is 20:1).

[0086] Example 6

[0087] The difference from Example 3 is only that the addition amount of titanium dioxide particles is 0.0076 g (i.e., the weight ratio of polyvinylidene fluoride-hexafluoropropylene copolymer to inorganic nanoparticles is 240:1).

[0088] Example 7

[0089] The difference from Example 3 is only that the addition amount of titanium dioxide particles is 0.0061 g (i.e., the weight ratio of polyvinylidene fluoride-hexafluoropropylene copolymer to inorganic nanoparticles is 300:1).

[0090] Example 8

[0091] The difference from Example 3 is only that the addition amount of ethylene glycol polyacrylate is 0.23 g (i.e., the weight ratio of polyvinylidene fluoride-hexafluoropropylene copolymer to polyacrylate polymer is 8:1).

[0092] Example 9

[0093] The difference from Example 3 is only that the D50 particle size of titanium dioxide particles is 60 nm.

[0094] Comparative Example 1

[0095] The difference from Example 3 is only that the shell layer structure is not prepared. The specific steps are as follows:

[0096] Step 1: Mechanically stir 6.1 g of acetone and 6.1 g of N,N-dimethylformamide for 0.5 h to fully mix them to form a solvent.

[0097] Step 2: Weigh 1.83 g of PVDF-HFP and add it to the solvent. Mechanically stir for 2 h at room temperature until all of the PVDF-HFP is dissolved and evenly mixed to obtain a solution. Weigh 0.05 g of titanium dioxide particles with a D50 particle size of 25 nm and 0.05 g of vinyltriethoxysilane and add them to the solution. First, mechanically stir for 1 h at room temperature, and then continuously mechanically stir in a water bath at 65 °C for 4 h to fully couple the polyvinylidene fluoride-hexafluoropropylene copolymer, inorganic nanoparticles, and silane coupling agent. Let it stand for 0.5 h to remove bubbles and obtain a spinning solution.

[0098] Step 3: Place the spinning solution in a syringe. Set the parameter conditions as follows: environmental humidity is 20%, spinning voltage is 22 kV, syringe pushing speed is 0.3 mm / min, receiver rotation speed is 500 rpm / min, and the distance between the spinneret and the receiver is 9 cm. Start electrospinning, and under the action of a high-voltage electrostatic field, the spinning solution is stretched into nanofibers and wound around the receiver to form a gel polymer electrolyte with an average membrane thickness of 19 μm.

[0099] Comparative Example 2

[0100] The difference from Example 3 is only that the silane coupling agent vinyltriethoxysilane was not added in Step 2.

[0101] Comparative Example 3

[0102] The difference from Example 3 is only that the inorganic nanoparticles titanium dioxide particles were not added in Step 2.

[0103] Comparative Example 4

[0104] The difference from Example 1 is only that the polyethylene glycol acrylate in Step 3 was replaced with PVDF-HFP.

[0105] Comparative Example 5

[0106] The difference from Example 1 is only that the PVDF-HFP in Step 2 was replaced with polyethylene glycol acrylate, and the obtained gel polymer electrolyte has cracks and is extremely easy to break and cannot be used as an electrolyte membrane.

[0107] Performance Test

[0108] 1. Use a scanning electron microscope to characterize the microstructure of the gel polymer electrolyte. The SEM characterization results of the core-shell structured gel polymer electrolytes prepared in Examples 1 to 4 are as Figures 1 to 4As shown, in the gel polymer electrolytes prepared in Examples 1-4, the nanofibers with a core-shell structure have a relatively smooth surface, without obvious protrusions, wrinkles or particulate attachments, which helps to reduce the resistance during lithium ion migration, thereby improving the ionic conductivity. Moreover, no obvious agglomeration of nanoparticles can be observed on the surface of the nanofibers, indicating that the nanoparticles dispersed in the core layer are well coated by the shell layer. In addition, the diameter distribution of the nanofibers is relatively narrow, mainly concentrated between 100 nm and 300 nm, and the electrospinning process can better control the fiber diameter, ensuring the consistency of the microstructure in the gel polymer electrolyte. Furthermore, the nanofibers show good continuity, and no obvious fiber breakage is found, which is beneficial to maintaining the integrity of the overall structure of the membrane product.

[0109] 2. Liquid holding rate test: After the gel polymer electrolyte is dried in a blast dryer at 45°C for 2 h and then in a vacuum dryer at 60°C for 12 h in sequence, it is immersed in a 1 mol / L LiPF6 electrolyte solution (where the solvent is a mixture of EC, DMC, and EMC in a mass ratio of 1:1:1) at room temperature until it reaches a constant weight. Then, it is placed on filter paper and blotted until it reaches a constant weight, and the weight of the gel polymer electrolyte after absorbing the electrolyte is recorded as W. According to the formula liquid holding rate N = (W - W0) / W0×100%, the liquid holding rate of the gel polymer electrolyte is calculated. Here, W is the weight of the gel polymer electrolyte after absorbing the electrolyte; W0 is the weight of the gel polymer electrolyte before absorbing the electrolyte. The liquid holding rates of the gel polymer electrolytes prepared in the examples and comparative examples are shown in Table 1.

[0110] 3. Tensile strength test: After the gel polymer electrolyte is dried in a blast dryer at 45°C for 2 h and then in a vacuum dryer at 60°C for 12 h in sequence, it is cut into rectangular specimens of 2 cm×5 cm and symmetrically installed on the fixtures of a universal testing machine. The tensile speed is set to 10 mm / min. After starting the universal testing machine, the specimen gradually elongates under the action of the tensile force, and the force value and displacement data are recorded in real time. The universal testing machine automatically stops when the specimen breaks, and the maximum tensile force value F max . is recorded at this time. According to the formula the tensile strength is calculated, where σ TS is the tensile strength (MPa), F max is the maximum force value (N) when the specimen breaks, b is the width (mm) of the specimen, and d is the thickness (mm) of the specimen. After testing 3 specimens of the same sample under the same conditions, the average value is taken as the tensile strength value of the specimen. The tensile strength results of the gel polymer electrolytes prepared in the examples and comparative examples are shown in Table 1.

[0111] 4. Ionic conductivity test: After the gel polymer electrolyte was dried in a blast dryer at 45 °C for 2 h and then in a vacuum dryer at 60 °C for 12 h in sequence, it was assembled into a stainless steel (SS) / gel polymer electrolyte / stainless steel (SS) blocking battery system. Then, an electrochemical workstation was used to conduct an AC impedance spectroscopy test at an AC amplitude of 5 mV and a frequency range of 10 Hz to 100 kHz. Then, according to the obtained AC impedance spectrum, the impedance value R of the gel polymer electrolyte was determined. Finally, through the formula The ionic conductivity was calculated, where σ is the ionic conductivity, l is the thickness of the electrolyte membrane, and S is the contact area between the electrode and the electrolyte membrane. The ionic conductivities of the gel polymer electrolytes prepared in the examples and comparative examples at room temperature are shown in Table 1.

[0112] 5. Lithium ion transference number test: The lithium ion transference number was tested by the potentiostatic polarization method. The specific steps are as follows:

[0113] After the gel polymer electrolyte was dried in a blast dryer at 45 °C for 2 h and then in a vacuum dryer at 60 °C for 12 h in sequence, it was assembled into a lithium foil / gel polymer electrolyte / lithium foil symmetric battery. First, the electrochemical AC impedance spectroscopy EIS of the symmetric battery was tested by an electrochemical workstation, where the test frequency range was 1 Hz to 100 kHz and the voltage perturbation was 10 mV, and the AC impedance R0 of the symmetric battery in the initial state was obtained. Then, through the I–t module (chronoamperometry) of the electrochemical workstation, the test was started at a constant potential of 10 mV, and the change of the polarization current with time was recorded to obtain the initial current I0 and the steady-state current I s . Finally, the AC impedance test was still carried out under the conditions of a frequency range of 1 Hz to 100 kHz and a voltage perturbation of 10 mV to obtain the impedance R of the polarized battery s . Substitute the above values into the formula to calculate the lithium ion transference number where ΔV is the potential difference of 10 mV in the chronoamperometry. The lithium ion transference numbers of the gel polymer electrolytes prepared in the examples and comparative examples are shown in Table 1.

[0114] 6. Electrochemical performance test:

[0115] Preparation of the negative electrode sheet: Mix according to the mass ratio of silicon-carbon negative electrode material (theoretical specific capacity is 600 mAh / g): conductive carbon black: CMC: SBR of 8:1:0.5:0.5, use deionized water as the solvent to prepare the negative electrode slurry, coat the negative electrode slurry on the copper foil, and the coating areal density is about 1.5 mg / cm 2 . After drying in a blast dryer at 45 °C for 2 h, it was cut into a circular sheet with a diameter of 16 mm, then rolled by a roll press, and then dried in a vacuum at 80 °C for 10 h to obtain the negative electrode sheet.

[0116] Preparation of electrolyte membrane: The gel polymer electrolyte was first dried in a blast dryer at 45 °C for 2 h, then cut into circular membranes with a diameter of 19 mm, and then dried in a vacuum at 60 °C for 12 h. After that, it was soaked in a 1 mol / L LiPF6 electrolyte solution (where the solvent was obtained by mixing EC, DMC, and EMC in a mass ratio of 1:1:1) at room temperature for 8 h until the gel polymer electrolyte membrane reached a constant weight. Then, it was placed on filter paper to blot the residual electrolyte solution on its surface, and the electrolyte membrane was obtained.

[0117] Assembly of coin-type half-cell: Using the negative electrode plate as the negative electrode and the lithium metal sheet as the counter electrode, in a glove box filled with high-purity argon, the negative electrode plate, lithium metal sheet, electrolyte membrane, and gasket were assembled into a CR2032-type coin-type half-cell.

[0118] Charge-discharge cycle test: The assembled CR2032-type coin-type half-cell was placed on the fixture of a battery tester and subjected to 100 charge-discharge cycles at 25 ± 2 °C. Among them, the charge-discharge conditions were as follows: Discharge: from 0.1C to 0.005V; Charge: from 0.1C to 2.0V. The capacity retention rate was calculated through the formula where C0 was the initial charge specific capacity (mAh / g), and C 100 was the charge specific capacity at the 100th cycle (mAh / g). The initial charge specific capacity, initial Coulomb efficiency, and capacity retention rate of the CR2032-type coin-type half-cells assembled with the gel polymer electrolyte membranes prepared in the examples and comparative examples are shown in Table 1.

[0119] Interface compatibility test: The interface compatibility between the gel polymer electrolyte and the electrode material was characterized by testing the interface impedance of the assembled coin-type half-cell. The specific steps were as follows:

[0120] At room temperature, after the assembled CR2032-type coin-type half-cell was left standing for 12 h, it was placed on the fixture of an electrochemical workstation for AC impedance spectroscopy (EIS) test. Among them, the test frequency range was 1 Hz to 100 kHz, and the voltage perturbation was 10 mV. The interface impedance value R was obtained based on the tested AC impedance spectrogram, as shown in Table 1 specifically.

[0121] Table 1 Physical and Electrochemical Properties of Gel Polymer Electrolytes

[0122]

[0123] Note: "-" indicates that the relevant test was not carried out.

[0124] As can be seen from Table 1, the gel polymer electrolyte with a core-shell structure prepared according to Embodiments 1-9 of the present invention has a high liquid retention rate, tensile strength, ionic conductivity, and lithium ion transference number. The lithium ion battery prepared with it has a low interfacial impedance, a high initial charge specific capacity, initial Coulombic efficiency, and charge-discharge cycle capacity retention rate.

[0125] Compared with Embodiment 7 in which less inorganic nanoparticles are used for compounding in the core layer, and Embodiments 3, 5, and 6 in which the weight ratio of poly(vinylidene fluoride-hexafluoropropylene) copolymer to inorganic nanoparticles is (20-240):1, the ionic conductivity, lithium ion transference number, and tensile strength of the gel polymer electrolyte are improved, and the lithium ion battery prepared has a high charge-discharge cycle capacity retention rate and initial Coulombic efficiency.

[0126] Compared with Embodiment 8 in which a higher weight ratio of poly(vinylidene fluoride-hexafluoropropylene) copolymer to polyacrylate polymer is used, Embodiment 3 in which the weight ratio of poly(vinylidene fluoride-hexafluoropropylene) copolymer to polyacrylate polymer is (1-4):1 has a higher ionic conductivity, lithium ion transference number, tensile strength, and interfacial compatibility, and the lithium ion battery prepared has a high charge-discharge cycle capacity retention rate and initial Coulombic efficiency.

[0127] Compared with Embodiment 9, Embodiment 3 uses smaller particle size inorganic nanoparticles for compounding, which improves the ionic conductivity, tensile strength of the gel polymer electrolyte, and the charge-discharge cycle capacity retention rate of the prepared lithium ion battery.

[0128] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A gel polymer electrolyte with a core-shell structure, characterized in that, Comprising: Nanofibers with a core-shell structure, the nanofibers with the core-shell structure comprising a core layer and a shell layer, the core layer comprising a polyvinylidene fluoride-hexafluoropropylene copolymer and inorganic nanoparticles, the polyvinylidene fluoride-hexafluoropropylene copolymer and the inorganic nanoparticles being connected by a silane coupling agent; the shell layer comprising a polyacrylate polymer.

2. The gel polymer electrolyte with a core-shell structure according to claim 1, wherein, The polyacrylate polymer is selected from one or more of polymethyl methacrylate, polyethyl methacrylate, ethylene glycol polyacrylate, poly(trifluoromethyl) methacrylate, poly(trifluoroethyl) methacrylate, poly(trifluoromethyl) methacrylate.

3. The gel polymer electrolyte with a core-shell structure according to claim 1, characterized in that, The inorganic nanoparticles are selected from one or more of nano-silica, titanium dioxide, zirconium dioxide, aluminum trioxide, zinc oxide; and / or, the D50 particle size of the nanoparticles is 10 nm to 100 nm, preferably 10 nm to 30 nm.

4. The gel polymer electrolyte with a core-shell structure according to claim 1, characterized in that, The silane coupling agent is selected from one or more of 1H,1H,2H,2H-perfluorooctyltrimethoxysilane, vinyltriethoxysilane, 1H,1H,2H,2H-perfluorodecyltrimethoxysilane, vinyltrimethoxysilane, (heptadecafluoro-1,1,2,2-tetradecyl)trimethoxysilane, vinyltris(β-methoxyethoxy)silane.

5. The gel polymer electrolyte with a core-shell structure according to any one of claims 1 to 4, characterized in that, The weight ratio of the polyvinylidene fluoride-hexafluoropropylene copolymer to the inorganic nanoparticles is (20 - 240):1; and / or, the weight ratio of the inorganic nanoparticles to the silane coupling agent is (1 - 2):(1 - 7), preferably (1 - 2): (1～2)； The weight ratio of the polyvinylidene fluoride-hexafluoropropylene copolymer to the polyacrylate polymer is (1 - 4):

1.

6. The gel polymer electrolyte with a core-shell structure according to any one of claims 1 to 4, characterized in that, The diameter of the nanofibers with the core-shell structure is 100 nm to 300 nm.

7. A method for preparing the gel polymer electrolyte with a core-shell structure according to any one of claims 1 to 6, characterized in that, Including the following steps: Mix and react the polyvinylidene fluoride-hexafluoropropylene copolymer, inorganic nanoparticles, silane coupling agent and a first solvent to obtain a core layer spinning solution; Mix the polyacrylate polymer and a second solvent to obtain a shell layer spinning solution; Use coaxial electrospinning technology to make the core layer spinning solution and the shell layer spinning solution into the gel polymer electrolyte with the core-shell structure.

8. The preparation method of the gel polymer electrolyte with a core-shell structure according to claim 7, characterized in that, First, stir and mix the polyvinylidene fluoride-hexafluoropropylene copolymer, the inorganic nanoparticles, the silane coupling agent and the first solvent at room temperature, and then heat and react at 45°C to 65°C for 4 h to 5 h. After the reaction is completed, let it stand for 0.5 h to 2 h to obtain the core layer spinning solution; and / or, First, ultrasonically dissolve the polyacrylate polymer in the second solvent, and then stir and mix for 0.5 h to 2 h. After mixing is completed, let it stand for 0.5 h to 2 h to obtain the shell layer spinning solution.

9. The preparation method of the gel polymer electrolyte with a core-shell structure according to claim 7, characterized in that, The first solvent and the second solvent are each independently selected from the mixture of at least one of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone and acetone; and / or; The weight ratio of the polyvinylidene fluoride-hexafluoropropylene copolymer to the first solvent is 1:(4 - 20); and / or; The weight ratio of the polyacrylate polymer to the second solvent is 1:(4 - 20); Preferably, the compositions of the first solvent and the second solvent are the same; More preferably, both the first solvent and the second solvent are obtained by mixing at least one of N,N-dimethylacetamide, N,N-dimethylformamide, and N-methylpyrrolidone with acetone in a volume ratio of (3 to 7):(3 to 7).

10. A lithium-ion battery, characterized in that, A core-shell structured gel polymer electrolyte comprising the core-shell structured gel polymer electrolyte according to any one of claims 1 to 6, or a core-shell structured gel polymer electrolyte prepared by the preparation method of the core-shell structured gel polymer electrolyte according to any one of claims 7 to 9.

Images