Composite solid electrolyte and preparation method and application thereof

Abstract

The present invention relates to a composite solid electrolyte preparation method, which comprises: S1, dissolving a polyether compound, a lithium salt, a nitrile compound and a polyvinylidene fluoride-based polymer in an organic solvent, and S2, stirring for 2-20 h; s3, performing magnetic field of 100-10000 gauss for 1-600 minutes; and S4, performing vacuum drying. Different from the prior art, the technical scheme provides the preparation method of the composite solid electrolyte modified under the action of the magnetic field, the preparation method is simple and easy to implement, and the raw materials are hardly lost. Under the action of magnetic field force, polyvinylidene fluoride forms a beta crystal phase, so that grain refinement is realized, and ion conduction of DMF (Dimethyl Formamide) is optimized. Meanwhile, the crystallinity and the change of the crystal phase can promote the improvement of the blending degree of polymers in the electrolyte, so that the modified composite solid electrolyte under the action of the magnetic field has better mechanical properties and ionic conduction properties.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery material preparation technology, and in particular to a composite solid electrolyte, its preparation method, and its application. Background Technology

[0002] To meet the growing demand for electronic devices and electric vehicles, solid-state lithium batteries have attracted widespread attention due to their excellent safety and potential high energy density. Among various solid electrolytes, polyvinylidene fluoride (PVDF)-based electrolytes have garnered significant interest due to their superior flexibility, wide electrochemical window, and ease of processing. However, PVDF-based electrolytes still face two major challenges in practical applications. The first challenge is that PVDF itself lacks effective lithium-ion coordinating groups, thus lacking intrinsic lithium-ion conductivity. Its ion conduction mainly relies on residual N,N-dimethylformamide (DMF) solvent to achieve complexation with lithium ions, thereby promoting lithium-ion migration and diffusion. However, DMF is unstable under an electric field, easily undergoing side reactions with lithium and initiating severe interfacial decomposition, leading to battery failure. Therefore, how to improve the ionic conductivity and other properties by adjusting the structure of PVDF or improving its interaction with DMF is a crucial problem that urgently needs to be solved for this solid electrolyte system.

[0003] Besides using DMF to enhance the ionic conductivity of PVDF-based solid electrolytes, another approach is to use high-modulus PVDF as an auxiliary material to strengthen the solid electrolyte structure. However, when PVDF is blended with other polymers, it easily forms a semi-crystalline structure during solvent evaporation. This semi-crystalline characteristic leads to phase separation of PVDF, significantly reducing its compatibility with other matrix polymers and ultimately resulting in a decrease in the ionic conductivity of the composite electrolyte. Therefore, whether in single or composite PVDF-based solid electrolyte systems, improving the structure of PVDF to optimize the uniform distribution of the polymer, or regulating PVDF-DMF interactions to enhance ion conduction efficiency, constitutes the core challenge of this system. Summary of the Invention

[0004] To address the aforementioned problems with composite solid electrolytes, this invention provides a method for preparing a composite solid electrolyte modified under a magnetic field. This method produces a composite solid electrolyte with high stability, high ionic conductivity, and high mechanical strength, which can be applied in solid-state lithium batteries.

[0005] The first aspect of this application provides a method for preparing a composite solid electrolyte, the preparation of which includes the following steps:

[0006] S1: Dissolve polyether compounds, lithium salts, nitrile compounds, and polyvinylidene fluoride polymers in an organic solvent to obtain a mixed solution;

[0007] S2: Stir the mixed solution for 2-20 hours to obtain an electrolyte slurry;

[0008] S3: Use a 500-3000 micrometer thick coater to uniformly coat the electrolyte slurry onto the coating substrate, and then apply a magnetic field of 100-10000 Gauss for 1-600 minutes to obtain the modified electrolyte slurry;

[0009] S4: The modified electrolyte slurry is vacuum dried to finally obtain a composite solid electrolyte modified under the action of a magnetic field.

[0010] Unlike existing technologies, the above-mentioned technical solution provides a method for preparing a composite solid electrolyte modified under the influence of a magnetic field. This method is simple and easy to implement, with almost no loss of raw materials. Under the influence of a magnetic field, polyvinylidene fluoride (PVDF) forms a β-crystalline phase, thereby refining the grain size and optimizing the ion conduction of DMF. Simultaneously, this change in crystallinity and crystalline phase also promotes the degree of polymer blending within the electrolyte. Therefore, the composite solid electrolyte modified under the influence of a magnetic field possesses better mechanical and ion conduction properties.

[0011] Furthermore, in step S1, the polyether compound has a mass percentage content of 0-3% in the mixed solution, the lithium salt has a mass percentage content of 4-7% in the mixed solution, the nitrile compound has a mass percentage content of 0-12% in the mixed solution, the polyvinylidene fluoride polymer has a mass percentage content of 0.2-40% in the mixed solution, and the organic solvent has a mass percentage content of 50-90% in the mixed solution.

[0012] Furthermore, in step S1, each component is dissolved separately in an organic solvent before being mixed to prepare a mixed solution. This promotes the dissolution of each component.

[0013] Furthermore, the dissolution process can be carried out using a low-temperature water bath or an oil bath.

[0014] Furthermore, in step S1, the polyether compound includes one or more of polyethylene oxide, polypropylene oxide, polyethylene glycol, polydimethyl ether, and polytetrahydrofuran; the lithium salt includes one or more of lithium bis(fluoromethanesulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxoborate), and lithium perchlorate; and the nitrile compound includes one or more of succinic anionyl, acrylonitrile, benzonitrile, adiponitrile, and malononitrile.

[0015] Furthermore, in step S1, the polyvinylidene fluoride vinyl polymer includes one or more of polyvinylidene fluoride, poly(vinylidene fluoride-co-trifluoropropylene), poly(vinylidene fluoride-co-trifluoroethylene), polyvinylidene fluoride-trifluorochloroethylene copolymer, and polyvinylidene fluoride-tetrafluoroethylene copolymer.

[0016] Furthermore, in step S1, the organic solvent includes one or more of anhydrous acetonitrile, dimethyl sulfoxide, N,N-dimethylformamide, acetone, and dichloromethane.

[0017] Furthermore, steps S1 and S2 are performed in an environment with humidity below 40%.

[0018] Furthermore, in step S3, the coating substrate includes one or more of the following: polytetrafluoroethylene plate, glass plate, copper foil, silicone paper, and aluminum foil.

[0019] Furthermore, in step S4, the vacuum drying temperature is between 40℃ and 80℃. A drying temperature below 80℃ ensures that the polymer does not decompose, thus protecting its physicochemical properties. Considering the temperature conditions for solvent evaporation, the vacuum baking temperature needs to be higher than 20℃.

[0020] Preferably, the vacuum drying temperature is 55-65℃.

[0021] Preferably, in step S4, atmospheric pressure drying is performed before vacuum drying. The purpose of drying at atmospheric pressure first and then vacuum drying is to avoid the problems of uneven electrolyte thickness and easy formation of pores caused by rapid evaporation of solvent under vacuum.

[0022] A second aspect of this application provides a composite solid electrolyte, which is produced using the preparation method described in the first aspect of this application. Further, the polyvinylidene fluoride vinyl polymer accounts for 1%-75% of the mass percentage of the composite solid electrolyte.

[0023] The third aspect of this application provides the application of the composite solid electrolyte described in the second aspect of this application in solid-state lithium batteries.

[0024] The above description of the invention is merely an overview of the technical solution of this application. In order to enable those skilled in the art to better understand the technical solution of this application and to implement it based on the textual description, and to make the above-mentioned objectives and other objectives, features and advantages of this application easier to understand, the following description is provided in conjunction with the specific embodiments and accompanying drawings of this application. Attached Figure Description

[0025] The accompanying drawings are only used to illustrate the principles, implementation methods, applications, features, and effects of specific embodiments of this application and other related content, and should not be considered as limitations on this application.

[0026] In the accompanying drawings of the instruction manual:

[0027] Figure 1 This is a scanning electron microscope image of Embodiment 1 of the present invention.

[0028] Figure 2 This is an X-ray diffraction test result diagram of Embodiment 1 of the present invention.

[0029] Figure 3 This is a graph showing the ion mobility number test results of the sample prepared in Example 1 of the present invention.

[0030] Figure 4 This is a graph showing the ionic conductivity of the sample prepared in Example 1 of this invention at different temperatures.

[0031] Figure 5 This is the X-ray diffraction test result of Embodiment 2 of the present invention.

[0032] Figure 6 This is a graph showing the ionic conductivity of the samples prepared in Example 2 / Comparative Example 2 of the present invention at different temperatures. Detailed Implementation

[0033] To illustrate the possible application scenarios, technical principles, implementable specific solutions, and achievable objectives and effects of this application in detail, the following description, in conjunction with the listed specific embodiments and accompanying drawings, provides a detailed explanation. The embodiments described herein are merely illustrative of the technical solutions of this application and are therefore intended to limit the scope of protection of this application.

[0034] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0035] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0036] In the description of this application, the term "and / or" is used to describe the logical relationship between objects, indicating that three relationships can exist. For example, A and / or B means: A exists, B exists, and A and B exist simultaneously. Additionally, the character " / " in this document generally indicates that the preceding and following objects have an "or" logical relationship.

[0037] In this application, terms such as “first” and “second” are used only to distinguish one entity or operation from another, and do not necessarily require or imply any actual quantity, hierarchy or order relationship between these entities or operations.

[0038] Unless otherwise specified, the use of terms such as “comprising,” “including,” “having,” or other similar expressions in this application is intended to cover non-exclusive inclusion, which does not exclude the presence of additional elements in a process, method, or product that includes the stated elements, such that a process, method, or product that includes a list of elements may include not only those defined elements but also other elements not expressly listed, or elements inherent to such a process, method, or product.

[0039] Similar to the understanding in the Examination Guidelines, in this application, expressions such as "greater than," "less than," and "exceeding" are understood to exclude the stated number; expressions such as "above," "below," and "within" are understood to include the stated number. Furthermore, in the description of the embodiments in this application, "multiple" means two or more (including two), and similar expressions related to "multiple" are also understood in this way, such as "multiple groups" and "multiple times," unless otherwise explicitly specified.

[0040] Example 1

[0041] Electrolyte slurry A was obtained by dissolving 0.2016 g of polyethylene oxide in 2 mL of acetonitrile and stirring continuously for 4 hours at room temperature with humidity below 40%. Electrolyte slurry B was obtained by dissolving 0.6049 g of polyvinylidene fluoride-hexafluoropropylene in 6 mL of acetone and heating in an environment with humidity below 40% for 2 hours using an oil bath at 40°C. Electrolyte slurry C was obtained by mixing slurry A and slurry B in an environment with humidity below 40% and heating in an oil bath at 40°C for 2 hours. Electrolyte slurry D was obtained by weighing 0.4033 g of lithium bis(trifluoromethanesulfonyl)imide and 0.9 g of succinate and heating in an environment with humidity below 40% for 2 hours using an oil bath at 80°C. Electrolyte slurry C and slurry D were then mixed and stirred for 2 hours at room temperature with humidity below 40% to obtain the final electrolyte slurry.

[0042] The polyether compound in the mixed solution has a mass percentage content of 2.4%, the lithium salt has a mass percentage content of 4.8%, the polyvinylidene fluoride vinyl polymer has a mass percentage content of 7.2%, and the nitrile compound has a mass percentage content of 10.7%.

[0043] In an environment with humidity below 40%, the electrolyte slurry was uniformly coated onto a substrate using a 1000-micron-thick doctor blade. A 6000-gauss magnetic field was then applied to the slurry, and the mixture was allowed to stand for 15 minutes. The sample was subsequently dried at 60°C for 0.5 hours, followed by vacuum drying at 60°C for 1.5 hours to obtain the magnetically modified composite solid electrolyte. The solid electrolyte contained 9.6% polyethylene oxide, 19.1% lithium bis(trifluoromethanesulfonyl)imide, 28.7% polyvinylidene fluoride-hexafluoropropylene, and 42.7% succinic anionyl nitrile.

[0044] Figure 1 This is a scanning electron microscope image of Example 1. It shows that the composite solid electrolyte particles of Example 1 are uniformly distributed and have an irregular sphere morphology of about 1-2 μm.

[0045] Figure 2 These are X-ray diffraction images from Example 1. They show that the composite solid electrolyte of Example 1 tends to form β-phase PVDF at room temperature.

[0046] Activation energy test cell preparation:

[0047] A CR2025 coin cell was assembled by stacking stainless steel sheets as the negative and positive electrodes in the following order: stainless steel sheet, solid electrolyte sheet, and stainless steel sheet again. The test AC frequency range was 1Hz to 1MHz, and the constant voltage bias (ΔV) was 5mV. Figure 3 The figures show the ionic conductivity curves of the composite solid electrolyte of Example 1 at different temperatures, indicating that the ionic conductivity of the composite solid electrolyte prepared in Example 1 changes little with temperature and has a low activation energy.

[0048] Figure 3 The results show the ionic conductivity of the stainless steel-to-stainless steel battery assembled in Example 1, tested between 20°C and 80°C. This indicates that the sample prepared in Example 1 exhibits a high ionic conductivity of 1.1 × 10⁻⁶ at 25°C. -3 The ionic conductivity, measured in S / cm, reaches as high as 3.9 × 10⁻⁶ when the temperature is increased to 80 °C. -3 The ionic conductivity was measured in S / cm. The activation energy of the sample was calculated to be 0.222 kJ / mol by linear fitting.

[0049] Ion transport number test cell fabrication:

[0050] A CR2025 coin cell was assembled using lithium metal sheets as both the negative and positive electrodes, stacked sequentially in the order of lithium metal sheets, solid electrolyte sheets, and lithium metal sheets. First, the impedance of the electrolyte was measured using the impedance testing parameters and methods described above for testing activation energy. Second, the inductively coupled plasma (IT) curve of the battery was tested, with a constant voltage bias (ΔV) of 5mV, a test time of 6000 seconds, and an AC frequency range of 1Hz to 1MHz. After the IT curve test, the impedance of the electrolyte was again measured using the same impedance testing parameters and methods described above for testing activation energy.

[0051] Figure 4 This is the ion transport number test curve for Example 1. It shows that at 27°C, the initial current of Example 1 was 37.6 μA, and after 6000 s, it reached a stable current of 24.9 μA. The calculated ion transport number of the composite solid electrolyte was 0.47. A high ion transport number can reduce concentration polarization while maintaining lithium concentration balance at the electrode interface, thereby suppressing lithium dendrite formation and improving battery life.

[0052] Activation energy test cell preparation:

[0053] A CR2025 coin cell was assembled by stacking stainless steel sheets as the negative and positive electrodes in the following order: stainless steel sheet, solid electrolyte sheet, and stainless steel sheet again. The test AC frequency range was 1Hz to 1MHz, and the constant voltage bias (ΔV) was 5mV.

[0054] Figure 4 The figures show the ionic conductivity curves of Example 1 at different temperatures, indicating that the ionic conductivity of the sample prepared in Example 1 changes little with temperature and has a low activation energy.

[0055] Comparative Example 1:

[0056] Electrolyte slurry A was obtained by dissolving 0.2016 g of polyethylene oxide in 2 mL of acetonitrile and stirring continuously for 4 hours at room temperature with humidity below 40%. Electrolyte slurry B was obtained by dissolving 0.6049 g of polyvinylidene fluoride-hexafluoropropylene in 6 mL of acetone and heating in an environment with humidity below 40% for 2 hours using an oil bath at 40°C. Electrolyte slurry C was obtained by mixing slurry A and slurry B in an environment with humidity below 40% and heating in an oil bath at 40°C for 2 hours. Electrolyte slurry D was obtained by weighing 0.4033 g of lithium bis(trifluoromethanesulfonyl)imide and 0.9 g of succinate and heating in an environment with humidity below 40% for 2 hours using an oil bath at 80°C. Electrolyte slurry C and slurry D were then mixed and stirred for 2 hours at room temperature with humidity below 40% to obtain the final electrolyte slurry. The polyether compound in the mixed solution has a mass percentage content of 2.4%, the lithium salt has a mass percentage content of 4.8%, the polyvinylidene fluoride vinyl polymer has a mass percentage content of 7.2%, and the nitrile compound has a mass percentage content of 10.7%.

[0057] In an environment with humidity below 40%, the electrolyte slurry was uniformly coated onto a substrate using a 1000-micron-thick doctor blade. The sample was then dried at 60°C for 0.5 hours, followed by vacuum drying at 60°C for 1.5 hours to obtain the composite solid electrolyte. The solid electrolyte contained 9.6% polyethylene oxide (PEO), 19.1% lithium bis(trifluoromethanesulfonyl)imide (BTMIM), 28.7% polyvinylidene fluoride (PVDF)-hexafluoropropylene (HPP), and 42.7% succinic anionyl nitrile (SNI).

[0058] The battery assembly and testing methods were the same as in Example 1, and the test results of ionic conductivity and ion transport number are shown in Table 1.

[0059] As can be seen from Table 1, compared with Example 1, the ionic conductivity of Comparative Example 1, which was not subjected to a magnetic field, is lower, and the ion transference number is also lower.

[0060] Example 2

[0061] Weigh 1 gram of polyvinylidene fluoride (PVDF) and 0.5 gram of lithium bis(trifluoromethanesulfonyl)imide and dissolve them in 10 mL of DMF. Place the solution at room temperature with humidity below 40%, and heat and stir in a 55°C oil bath for 3 hours to obtain an electrolyte slurry. The mass percentage content of the PVDF polymer in the mixed solution is 9.1%, and the mass percentage content of the lithium salt in the mixed solution is 4.6%.

[0062] In an environment with humidity below 40%, the electrolyte slurry was uniformly coated onto a polytetrafluoroethylene (PTFE) plate using a 1000-micron-thick scraper. The sample was then dried at 55°C for 60 minutes, followed by vacuum drying at 55°C for 4 hours. Throughout the drying process, a 500-gauss magnetic field was maintained, resulting in a magnetically modified composite solid electrolyte. The mass percentage content of vinylidene fluoride-hexafluoropropylene in the solid electrolyte was 69.1%, and the mass percentage content of lithium bis(trifluoromethanesulfonyl)imide was 30.9%.

[0063] The battery assembly and testing methods were the same as in Example 1, and the test results of ionic conductivity and ion transport number are shown in Table 1.

[0064] Comparative Example 2

[0065] Weigh 1 gram of polyvinylidene fluoride (PVDF) and 0.5 gram of lithium bis(trifluoromethanesulfonyl)imide and dissolve them in 10 mL of DMF. Place the solution at room temperature with humidity below 40%, and heat and stir in a 55°C oil bath for 3 hours to obtain an electrolyte slurry. The mass percentage content of the PVDF polymer in the mixed solution is 9.1%, and the mass percentage content of the lithium salt in the mixed solution is 4.6%.

[0066] In an environment with humidity below 40%, the electrolyte slurry was uniformly coated onto a polytetrafluoroethylene (PTFE) plate using a 1000-micron-thick scraper. The sample was then dried at 55°C for 60 minutes, followed by vacuum drying at 60°C for 4 hours to obtain the composite solid electrolyte. The mass percentage content of vinylidene fluoride-hexafluoropropylene in the solid electrolyte was 69.1%, and the mass percentage content of lithium bis(trifluoromethanesulfonyl)imide was 30.9%.

[0067] The battery assembly and testing methods were the same as in Example 1, and the test results of ionic conductivity and ion transport number are shown in Table 1.

[0068] Figure 5 These are X-ray diffraction images from Example 2. The diffraction peaks at 17.5° and 18.5° belong to the (100) and (020) crystal planes of the α phase, respectively, while the diffraction peak at 20.1° corresponds to the (110 / 200) crystal plane of the β phase. These peaks are visible in both electrolytes. The difference between Example 2 and Comparative Example 2 is that the diffraction peaks at 36.1° and 39.2° have higher intensities, corresponding to the (020 / 101) and (111 / 201) crystal planes of the β phase, respectively. The comparative results show that PVDF tends to form the β phase under the influence of a magnetic field. Since β-phase PVDF has stronger polarity and exhibits superior piezoelectric and ferroelectric properties, it plays a positive role in improving the ionic conductivity and other properties of PVDF-based polymer electrolytes.

[0069] Activation energy test cell preparation:

[0070] A CR2025 coin cell was assembled by stacking stainless steel sheets as the negative and positive electrodes in the following order: stainless steel sheet, solid electrolyte sheet, and stainless steel sheet again. The test AC frequency range was 1Hz to 1MHz, and the constant voltage bias (ΔV) was 5mV.

[0071] Figure 6 These are the ionic conductivity results of the assembled stainless steel-to-stainless steel batteries tested between 80°C and 10°C, comparing Example 2 and Comparative Example 2. The results show that the sample prepared in Example 2 exhibits a conductivity of 3.3 × 10⁻⁶ at 25°C. -4 The ionic conductivity (S / cm) is the same as that shown in Comparative Example 2, which exhibits an ionic conductivity of 1.1 × 10⁻⁶. -4 The S / cm ratio shows a significant improvement. Through linear fitting and calculation, the activation energy of Example 2 was found to be 0.25 kJ / mol, while that of Comparative Example 2 was 0.16 kJ / mol. This comparison demonstrates that a magnetic field can effectively improve the ionic conductivity of the PVDF-based polymer solid electrolyte while simultaneously reducing its activation energy.

[0072] Example 3

[0073] Electrolyte slurry A was obtained by dissolving 0.2016 g of polyethylene oxide in 2 mL of acetonitrile and stirring continuously for 4 hours at room temperature with humidity below 40%. Electrolyte slurry B was obtained by dissolving 0.015 g of polyvinylidene fluoride in 6 mL of DMF and heating and stirring in an oil bath at 40°C for 2 hours in an environment with humidity below 40%. Electrolyte slurry C was obtained by mixing slurry A and slurry B in an environment with humidity below 40% and heating and stirring in an oil bath at 40°C for 2 hours. Electrolyte slurry D was obtained by weighing 0.4033 g of lithium bis(trifluoromethanesulfonyl)imide and 0.9 g of succinic anhydride and heating and stirring in an oil bath at 80°C for 2 hours in an environment with humidity below 40%. Electrolyte slurries C and D were mixed and stirred for 2 hours in an environment with humidity below 40% to obtain the final electrolyte slurry. The polyether compound in the mixed solution has a mass percentage content of 2.5%, the lithium salt has a mass percentage content of 5.1%, the polyvinylidene fluoride vinyl polymer has a mass percentage content of 0.2%, and the nitrile compound has a mass percentage content of 11.5%.

[0074] In an environment with humidity below 40%, the electrolyte slurry was uniformly coated onto aluminum foil using a 3000-micron-thick scraper. A magnetic field of 6000 Gauss was then applied to the electrolyte slurry, and the mixture was allowed to stand for 15 minutes. Subsequently, the sample was dried at 60°C for 0.5 hours, followed by vacuum drying at 60°C for 1.5 hours, yielding a composite solid electrolyte modified under magnetic field conditions. The solid electrolyte contained 13.3% polyethylene oxide (PEO), 26.5% lithium bis(trifluoromethanesulfonyl)imide, 1% polyvinylidene fluoride-hexafluoropropylene, and 59.2% succinic anionyl nitrile.

[0075] Example 4

[0076] Electrolyte slurry A was obtained by dissolving 0.2016 g of polyethylene oxide in 2 mL of acetonitrile and stirring continuously for 4 hours at room temperature with humidity below 40%. Electrolyte slurry B was obtained by dissolving 4.5147 g of polyvinylidene fluoride in 6 mL of DMF and heating and stirring in an oil bath at 40°C for 2 hours in an environment with humidity below 40%. Electrolyte slurry C was obtained by mixing slurry A and slurry B in an environment with humidity below 40% and heating and stirring in an oil bath at 40°C for 2 hours. Electrolyte slurry D was obtained by weighing 0.55 g of lithium bis(trifluoromethanesulfonyl)imide and 0.9 g of succinate and heating and stirring in an oil bath at 80°C for 2 hours in an environment with humidity below 40%. Electrolyte slurries C and D were mixed and stirred for 2 hours in an environment with humidity below 40% to obtain the final electrolyte slurry. The polyether compound in the mixed solution has a mass percentage content of 1.6%, the lithium salt has a mass percentage content of 4.4%, the polyvinylidene fluoride vinyl polymer has a mass percentage content of 36.2%, and the nitrile compound has a mass percentage content of 7.2%.

[0077] In an environment with humidity below 40%, the electrolyte slurry was uniformly coated onto aluminum foil using a 500-micron-thick doctor blade. A magnetic field of 6000 Gauss was then applied to the electrolyte slurry, and the mixture was allowed to stand for 15 minutes. Subsequently, the sample was dried at 60°C for 0.5 hours, followed by vacuum drying at 60°C for 1.5 hours, yielding a composite solid electrolyte modified under magnetic field conditions. The mass percentage content of the solid electrolyte was 3.3% for polyethylene oxide, 8.9% for lithium bis(trifluoromethanesulfonyl)imide, 73.2% for polyvinylidene fluoride-hexafluoropropylene, and 14.6% for succinic anionyl nitrile.

[0078] Example 5

[0079] 0.2016 g of polypropylene oxide was dissolved in 2 mL of acetonitrile and stirred continuously for 4 hours at room temperature with humidity below 40% to obtain electrolyte slurry A. 0.6049 g of poly(vinylidene fluoride-co-trifluoroethylene) was weighed into 6 mL of acetone and placed in an environment with humidity below 40%. Electrolyte slurry B was obtained by stirring in a 40°C oil bath for 2 hours. Slurries A and B were mixed in an environment with humidity below 40% and stirred in a 40°C oil bath for 2 hours to obtain electrolyte slurry C. 0.4033 g of lithium bis(trifluoromethanesulfonyl)imide and 0.9 g of succinate were weighed and placed in an environment with humidity below 40%. Electrolyte slurry D was obtained by stirring in an 80°C oil bath for 2 hours. Electrolyte slurries C and D were mixed and stirred for 18 hours in an environment with humidity below 40% to obtain the final electrolyte slurry. The polyether compound in the mixed solution has a mass percentage content of 2.4%, the lithium salt has a mass percentage content of 4.8%, the polyvinylidene fluoride vinyl polymer has a mass percentage content of 7.2%, and the nitrile compound has a mass percentage content of 10.7%.

[0080] In an environment with humidity below 40%, an electrolyte slurry was uniformly coated onto aluminum foil using a 1000-micron-thick scraper. A 1000-gauss magnetic field was then applied to the slurry, and the mixture was allowed to stand for 1.5 hours. Subsequently, the sample was dried at 60°C for 0.5 hours, followed by vacuum drying at 60°C for 1.5 hours, yielding a composite solid electrolyte modified under magnetic field conditions. The solid electrolyte contained 9.6% polyethylene oxide (PEO), 19.1% lithium bis(trifluoromethanesulfonyl)imide (BTMIM), 28.7% polyvinylidene fluoride (PVDF)-hexafluoropropylene (HPP), and 42.7% succinic anionyl nitrile (SNI).

[0081] The battery assembly and testing methods were the same as in Example 1, and the test results of ionic conductivity and ion transport number are shown in Table 1.

[0082] Example 6

[0083] Electrolyte slurry A was obtained by dissolving 0.2016 g of polyethylene oxide in 2 mL of acetonitrile and stirring continuously for 4 hours at room temperature with humidity below 40%. Electrolyte slurry B was obtained by dissolving 0.6049 g of polyvinylidene fluoride in 6 mL of acetone and heating and stirring in a 40°C oil bath for 2 hours in an environment with humidity below 40%. Electrolyte slurry C was obtained by mixing slurry A and slurry B in an environment with humidity below 40% and heating and stirring in a 40°C oil bath for 2 hours. Electrolyte slurry D was obtained by weighing 0.4033 g of lithium bis(trifluoromethanesulfonyl)imide and 0.9 g of benzonitrile and heating and stirring in an 80°C oil bath for 2 hours in an environment with humidity below 40%. Electrolyte slurries C and D were mixed and stirred for 2 hours in an environment with humidity below 40% to obtain the final electrolyte slurry. The polyether compound in the mixed solution has a mass percentage content of 2.4%, the lithium salt has a mass percentage content of 4.8%, the polyvinylidene fluoride vinyl polymer has a mass percentage content of 7.2%, and the nitrile compound has a mass percentage content of 10.7%.

[0084] In an environment with humidity below 40%, an electrolyte slurry was uniformly coated onto aluminum foil using a 2000-micron-thick scraper. A magnetic field of 3000 Gauss was then applied to the slurry, and the mixture was allowed to stand for 0.5 hours. Subsequently, the sample was dried at 60°C for 0.5 hours, followed by vacuum drying at 60°C for 1.5 hours, yielding a composite solid electrolyte modified under magnetic field conditions. The solid electrolyte contained 9.6% polyethylene oxide (PEO), 19.1% lithium bis(trifluoromethanesulfonyl)imide, 28.7% polyvinylidene fluoride-hexafluoropropylene, and 42.7% succinic anionyl nitrile.

[0085] The battery assembly and testing methods were the same as in Example 1, and the test results of ionic conductivity and ion transport number are shown in Table 1.

[0086] Example 7

[0087] Electrolyte slurry A was obtained by dissolving 0.2016 g of polyethylene oxide in 2 mL of acetonitrile and stirring continuously at room temperature with humidity below 40% for 4 hours. Electrolyte slurry B was obtained by dissolving 0.6049 g of polyvinylidene fluoride-hexafluoropropylene in 6 mL of acetone and heating in an environment with humidity below 40% for 2 hours using an oil bath at 40°C. Electrolyte slurry C was obtained by mixing slurry A and slurry B in an environment with humidity below 40% and heating in an oil bath at 40°C for 2 hours. Electrolyte slurry D was obtained by weighing 0.4033 g of lithium dioxoborate and 0.9 g of adiponitrile and heating in an environment with humidity below 40% for 2 hours using an oil bath at 80°C. Electrolyte slurry C and D were mixed and stirred at room temperature with humidity below 40% for 2 hours to obtain the final electrolyte slurry. The polyether compound in the mixed solution has a mass percentage content of 2.4%, the lithium salt has a mass percentage content of 4.8%, the polyvinylidene fluoride vinyl polymer has a mass percentage content of 7.2%, and the nitrile compound has a mass percentage content of 10.7%.

[0088] In an environment with humidity below 40%, the electrolyte slurry was uniformly coated onto aluminum foil using a 1000-micron-thick scraper. A magnetic field of 9000 Gauss was then applied to the electrolyte slurry, and the mixture was allowed to stand for 8 minutes. The sample was subsequently dried at 60°C for 0.5 hours, followed by vacuum drying at 60°C for 1.5 hours, yielding a composite solid electrolyte modified under magnetic field conditions. The solid electrolyte contained 9.6% polyethylene oxide (PEO), 19.1% lithium bis(trifluoromethanesulfonyl)imide, 28.7% polyvinylidene fluoride-hexafluoropropylene, and 42.7% succinic anionyl nitrile.

[0089] The battery assembly and testing methods were the same as in Example 1, and the test results of ionic conductivity and ion transport number are shown in Table 1.

[0090] Experimental results show that:

[0091] The content of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) in the solid electrolyte should be moderate, with an optimal mass percentage of 28.7%. Excessive content will reduce the electrolyte's flexibility and affect its contact with the electrode; insufficient content will lead to insufficient mechanical strength, reduced ionic conductivity, and decreased ion transport number.

[0092] Both magnetic field strength and magnetization time significantly affect electrolyte performance. Within a certain range, electrolyte performance improves with increasing magnetic field strength; however, when the strength reaches approximately 6000 Gauss, the performance improvement approaches saturation, and further increases in strength have little effect. Since the magnetic field primarily acts during the solvent evaporation stage, magnetization must be matched to this stage. After solvent evaporation is complete, extending the magnetization time has virtually no impact on electrolyte performance.

[0093] Table 1. Comparison of electrochemical performance between embodiments and comparative examples of the present invention.

[0094] Ionic conductivity (S / cm) / Temperature (°C) Ion transport number Example 1 <![CDATA[1.1×10 -3 S / cm25℃]]> 0.47 Comparative Example 1 <![CDATA[5.5×10 -4 S / cm25℃]]> 0.34 Example 2 <![CDATA[3.3×10 -4 S / cm25℃]]> 0.25 Comparative Example 2 <![CDATA[1.1×10 -4 S / cm25℃]]> 0.16 Example 3 <![CDATA[3.5×10 -4 S / cm25℃]]> 0.29 Example 4 <![CDATA[2.4×10 -4 S / cm25℃]]> 0.25 Example 5 <![CDATA[7.5×10 -4 S / cm25℃]]> 0.36 Example 6 <![CDATA[6.8×10 -4 S / cm25℃]]> 0.33 Example 7 <![CDATA[8.1×10 -4 S / cm25℃]]> 0.38

[0095] Compared with Comparative Examples 1 and 2, Examples 1 and 2 with applied magnetic fields exhibited higher ionic conductivity and ion transference number, indicating that the magnetic field does indeed affect polyvinylidene fluoride, thereby improving the performance of the electrolyte.

[0096] The performance of Examples 3 and 4 was worse than that of Example 1, indicating that the content of polyvinylidene fluoride (PVDF) affects the performance of solid electrolytes. Both excessively high and low content can lead to performance degradation.

[0097] Examples 5-7 showed worse performance compared to Example 1, indicating that both magnetic field strength and magnetization time affect the performance of solid electrolytes. When the magnetic field strength reaches approximately 6000 Gauss, the performance improvement approaches saturation. Since the magnetic field acts on the electrolyte slurry, the magnetization time is no longer than the solvent evaporation time.

[0098] Finally, it should be noted that although the above embodiments have been described in the text and drawings of this application, this should not limit the scope of patent protection of this application. Any technical solutions that are based on the essential concept of this application and utilize the content described in the text and drawings of this application, resulting in equivalent structural or procedural substitutions or modifications, as well as the direct or indirect application of the technical solutions of the above embodiments to other related technical fields, are all included within the scope of patent protection of this application.

Claims

1. A method for preparing a composite solid electrolyte, characterized in that, The preparation of the composite solid electrolyte includes the following steps: S1: Dissolve polyether compounds, lithium salts, nitrile compounds, and polyvinylidene fluoride polymers in an organic solvent to obtain a mixed solution; S2: Stir the mixed solution for 2-20 hours to obtain an electrolyte slurry; S3: Use a 500-3000 micrometer thick coater to uniformly coat the electrolyte slurry onto the coating substrate, and then apply a magnetic field of 100-10000 Gauss for 1-600 minutes to obtain the modified electrolyte slurry; S4: The modified electrolyte slurry is vacuum dried to finally obtain a composite solid electrolyte modified under the action of a magnetic field.

2. The preparation method according to claim 1, characterized in that, In step S1, the polyether compound has a mass percentage content of 0-3% in the mixed solution, the lithium salt has a mass percentage content of 4-7% in the mixed solution, the nitrile compound has a mass percentage content of 0-12% in the mixed solution, the polyvinylidene fluoride polymer has a mass percentage content of 0.2-40% in the mixed solution, and the organic solvent has a mass percentage content of 50-90% in the mixed solution.

3. The preparation method according to claim 1, characterized in that, In step S1 The polyether compounds include one or more of the following: polyethylene oxide, polypropylene oxide, polyethylene glycol, polydimethyl ether, and polytetrahydrofuran; The lithium salt includes one or more of lithium bis(fluoromethanesulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxoborate), and lithium perchlorate. The nitrile compounds include one or more of butadionitrile, acrylonitrile, benzonitrile, adiponitrile, and malononitrile; The polyvinylidene fluoride vinyl polymer includes one or more of polyvinylidene fluoride, poly(vinylidene fluoride-co-trifluoroethylene), poly(vinylidene fluoride-co-trifluoroethylene), polyvinylidene fluoride-trifluorochloroethylene copolymer, and polyvinylidene fluoride-tetrafluoroethylene copolymer.

4. The preparation method according to claim 1, characterized in that, In step S1, the organic solvent includes one or more of anhydrous acetonitrile, dimethyl sulfoxide, N,N-dimethylformamide, acetone, and dichloromethane.

5. The preparation method according to claim 1, characterized in that, Steps S1 and S2 are performed in an environment with humidity below 40%.

6. The preparation method according to claim 1, characterized in that, In step S3, the coating substrate includes one or more of the following: polytetrafluoroethylene plate, glass plate, copper foil, silicone paper, and aluminum foil.

7. The preparation method according to claim 1, characterized in that, In step S4, the vacuum drying temperature is between 40°C and 80°C.

8. A composite solid electrolyte, characterized in that, The composite solid electrolyte is produced using the preparation method described in any one of claims 1-7.

9. The method for preparing the composite solid electrolyte according to claim 1, characterized in that, The polyvinylidene fluoride vinyl polymer accounts for 1%-75% of the mass percentage of the composite solid electrolyte.

10. The application of the composite solid electrolyte of claim 9 in solid-state lithium batteries.

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