Composite solid electrolyte and preparation method and application thereof

Abstract

The invention belongs to the technical field of electrolyte preparation, and discloses a composite solid electrolyte and a preparation method and application thereof. The preparation method comprises the following steps: mixing para-aramid fiber, alkali and a polar aprotic solvent, and performing staged dispersion to obtain an aramid nanofiber dispersion; sequentially mixing the aramid nanofiber dispersion with a first organic solvent, a second organic solvent, polyvinylidene fluoride and a lithium salt electrolyte to obtain a spinning solution; and carrying out electrostatic spinning on the spinning solution, and carrying out post-treatment to obtain the composite solid electrolyte. According to the invention, PVDF is introduced to carry out surface modification on the aramid nanofibers, so that the process route is optimized, the compatibility between the aramid nanofibers and a polymer matrix is remarkably improved, the mechanical property and thermal stability of the composite membrane are improved, and the aramid composite membrane shows better interfacial compatibility in an all-solid-state polymer electrolyte, so that the performance of the all-solid-state polymer electrolyte is improved. And the cycling stability and the conductivity of the battery are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolyte preparation, and particularly relates to a composite solid electrolyte, a preparation method thereof, and an application thereof. Background Art

[0002] Para-aramid nanofibers have attracted attention due to their high mechanical strength and excellent heat resistance. However, due to their rigid linear macromolecules, they are difficult to dissolve in conventional solvents and it is difficult to form a uniform spinning solution. In addition, aramid nanofibers are prone to fiber breakage or non-uniformity during the electrospinning process, and their compatibility with other polymer matrices is poor, which limits their application effect in solid electrolytes.

[0003] For example, the existing literature (H. Xu, S. Yagi, S. Ashour, L. Du, M. E. Hoque, and L. Tan, “A review on current nanofiber technologies: Electrospinning, centrifugal spinning, and electro-centrifugal spinning”, Macromolecular Materials and Engineering, vol. 308, no. 3, 2023, doi: 10.1002 / mame.202200502.) mainly focuses on the basic principles and applications of the electrospinning process, and does not deeply explore the effects of solution viscoelasticity and shear behavior on fiber formation.

[0004] In the Chinese patent application with the publication number CN109786634A, the electrospinning process mainly improves the performance of the membrane through simple solution preparation and lamination of composite materials, mainly relying on traditional solvent selection and basic ratios to control the viscoelasticity of the solution, without deeply regulating the viscosity change and shear behavior of the solution, and not involving the fine regulation of the shear thinning behavior of the spinning solution.

[0005] Moreover, in the prior art, when preparing aramid membranes, it mainly relies on electrospinning technology to prepare single-material membranes. For example, in the Chinese patent application with the publication number CN110373814A, the electrospinning process is used to optimize the spinning performance of para-aramid nanofibers through a spinning aid, but its solution does not involve polymer composite and surface modification.

[0006] Due to its rigid molecular chain structure, para-aramid has poor compatibility when compounded with other materials (especially polymer matrices), which limits its application in high-performance batteries. For example, in the Chinese patent applications with publication numbers CN115295961A and CN118326706A, although different solvent systems or compounding strategies are mentioned to optimize the material properties, improving the compatibility between the fiber and the polymer electrolyte matrix through surface modification is not involved.

[0007] Currently, the application of aramid nanofiber membranes in battery separators mainly focuses on improving mechanical properties and preventing the penetration of lithium dendrites. For example, in the Chinese patent application with publication number CN115295961A, the main function of the aramid membrane is to serve as a mechanical strengthening material for the battery separator, and the optimization of battery electrolytes is not involved. Summary of the Invention

[0008] The purpose of the present invention is to provide a composite solid electrolyte, its preparation method and application, so as to solve the above problems existing in the prior art.

[0009] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0010] The present invention provides a preparation method of a composite solid electrolyte, comprising the following steps:

[0011] (1) Mix para-aramid fiber, alkali, and polar aprotic solvent, conduct staged dispersion, and centrifuge to obtain an aramid nanofiber dispersion;

[0012] (2) Sequentially mix the aramid nanofiber dispersion with a first organic solvent, a second organic solvent, polyvinylidene fluoride, and a lithium salt electrolyte to obtain a spinning solution;

[0013] (3) Electrospun the spinning solution and perform post-treatment to obtain a composite solid electrolyte.

[0014] Preferably, in the preparation method, in step (1), the alkali includes KOH and / or LiOH;

[0015] The polar aprotic solvent includes dimethyl sulfoxide and / or N-methylpyrrolidone;

[0016] The mass ratio of the alkali to the volume of the polar aprotic solvent is 0.14 - 0.2 g:10 mL;

[0017] The mass ratio of the para-aramid fiber to the alkali in step (1) is 0.14 - 0.2:0.14.

[0018] Preferably, in the preparation method, the staged dispersion in step (1) includes the following steps:

[0019] (1.1)Disperse para-aramid fiber, alkali, and polar aprotic solvent to obtain an aramid nanofiber solution;

[0020] (1.2)Pre-dissolve the aramid nanofiber solution to obtain an intermediate solution;

[0021] (1.3)Perform ultrasonic-assisted dissolution on the intermediate solution;

[0022] Among them, the conditions for the dispersion in step (1.1) include: temperature is 35 - 45 °C, time is 2 - 4 h, and mixing speed is 200 - 400 rpm;

[0023] The conditions for the pre-dissolution in step (1.2) include: temperature is 35 - 45 °C, time is 1.5 - 3 h, and mixing speed is 150 - 250 rpm;

[0024] The conditions for the ultrasonic-assisted dissolution in step (1.3) include: temperature is 70 - 90 °C, ultrasonic frequency is 35 - 45 kHz, ultrasonic power is 50 - 70 W, and time is 3 - 5 h.

[0025] Preferably, in the preparation method, the first organic solvent in step (2) includes one or more of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide;

[0026] The mass ratio of the para-aramid fiber used in the aramid nanofiber dispersion in step (2) to the volume of the first organic solvent is 1.3 g: 3 - 5 mL;

[0027] In step (2), the conditions for mixing after adding the first organic solvent include: temperature is 20 - 25 °C, time is 5 - 15 min, and mixing speed is 200 - 400 rpm.

[0028] Preferably, in the preparation method, the second organic solvent in step (2) includes acetone and / or ethyl acetate;

[0029] The volume ratio of the first organic solvent to the second organic solvent in step (2) is 2:1 - 1:1;

[0030] The second organic solvent in step (2) is added in 2 - 3 times;

[0031] In step (2), the conditions for mixing after adding the second organic solvent in each batch independently include: temperature is 20 - 25 °C, time is 10 - 20 min, and mixing speed is 500 - 700 rpm.

[0032] Preferably, in the preparation method, the polyvinylidene fluoride in step (2) is PVDF-HSV900;

[0033] The mass ratio of the para-aramid fiber used in the aramid nanofiber dispersion described in step (2) to the polyvinylidene fluoride is 1:2 to 1.8:1;

[0034] In step (2), the conditions for mixing after adding polyvinylidene fluoride include: under water bath conditions, the temperature is 50-70 °C, the time is 1.5-2 h, and the mixing rotation speed is 300-500 rpm.

[0035] Preferably, in the preparation method, the lithium salt electrolyte described in step (2) includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium lanthanum zirconium oxide;

[0036] The mass ratio of the lithium salt electrolyte described in step (2) to the polyvinylidene fluoride is 0.4-0.6:1;

[0037] In step (2), the conditions for mixing after adding the lithium salt electrolyte include: the temperature is 20-40 °C, and the time is 12-24 h.

[0038] Preferably, in the preparation method, the conditions for electrospinning described in step (3) include: the voltage is 15-20 kV, the flow rate of the spinning solution is 0.3-1 mL / h, the distance from the nozzle to the collecting plate is 12-15 cm, the temperature is 20-30 °C, and the relative humidity is 40-60%.

[0039] The present invention also provides a composite solid electrolyte.

[0040] The present invention also provides an application of the composite solid electrolyte in a all-solid-state battery.

[0041] Through the above technical solutions, compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) By optimizing the mixing sequence and ratio of aramid nanofibers (ANF) with two organic solvents (such as dimethylformamide DMF and acetone), adopting the method of adding the second organic solvent in stages, and controlling the stirring speed and time to adjust the solution viscosity (the viscosity is controlled at 0.3-0.4 Pa·s), the present invention realizes the precise regulation of the solution viscoelasticity. Through the optimization of the shear thinning behavior, the stability of the solution and the quality of the fibers are significantly improved, the non-uniformity and breakage of the fibers are reduced, and the uniformity and stability of the fibers during the electrospinning process are ensured.

[0043] (2) Due to the presence of benzene ring groups in the molecular main chain of para-aramid fibers, the molecular chains are rigid and the intermolecular entanglement force is weak, making it difficult to spin fibers under the action of an electrostatic field. The electrospinning process adopted in the present invention not only solves the spinning difficulty of para-aramid, but also enhances the intermolecular chain entanglement between fibers through the composite with PVDF-HSV900, improves the tensile properties and crystallinity of the fibers, and ensures the mechanical properties of the membrane. By changing the composition of the solution, especially the composite of PVDF-HSV900 and aramid, the crystalline structure and pore structure of the fibers are optimized, so that the final membrane material has higher mechanical strength and thermal stability.

[0044] (3) The present invention modifies the surface of aramid nanofibers by introducing PVDF. By optimizing the process route, the compatibility between aramid nanofibers and the polyvinylidene fluoride polymer matrix is significantly improved, thereby enhancing the mechanical properties and thermal stability of the composite membrane. This surface modification process enables the aramid composite membrane to exhibit better interfacial compatibility in all-solid polymer electrolytes, thus effectively improving the cycle stability and conductivity of the battery.

[0045] (4) By compounding the surface-functionalized aramid nanofibers with a lithium salt electrolyte, the present invention improves the ionic conductivity of the membrane. In battery applications, it not only effectively prevents the growth of lithium dendrites, but also improves the safety and cycle life of the battery. In addition, the high specific surface area and good pore structure of the membrane also show excellent performance in preventing short-circuit phenomena and improving the overall stability of the battery. Description of the Drawings

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art.

[0047] Figure 1 For the apparent diagrams of the solutions before and after adjusting the mixing order in Comparative Experimental Examples 1-2 and Experimental Example 1, where a) is Comparative Experimental Example 1, b) is Comparative Experimental Example 2, and c) is Experimental Example 1;

[0048] Figure 2 For the apparent diagrams of the solutions obtained in Experimental Examples 2-5, where a) is Experimental Example 2, b) is Experimental Example 3, c) is Experimental Example 4, and d) is Experimental Example 5;

[0049] Figure 3 For the SEM diagrams of the membrane materials of the solid electrolytes obtained in Example 1 and Comparative Example 1, where a), b), and c) are the SEM diagrams of the membrane materials obtained in Comparative Example 1 at magnification ratios of 500 times, 1000 times, and 10000 times respectively, and d), e), and f) are the SEM diagrams of the membrane materials obtained in Example 1 at magnification ratios of 5000 times, 10000 times, and 20000 times respectively;

[0050] Figure 4 Thermal stability test results of the film materials of the solid electrolytes obtained in Example 1 and Comparative Example 1, where a) is Comparative Example 1 and b) is Example 1;

[0051] Figure 5 Stress-strain curve diagrams of the film materials of the solid electrolytes obtained in Example 1 and Comparative Example 1;

[0052] Figure 6 Thermogravimetric analysis curve diagrams of the para-aramid nanofiber membrane prepared by the method of Example 1 and the pure PVDF HSV900 membrane prepared by the method of Comparative Example 1;

[0053] Figure 7 Fourier transform infrared spectra of the para-aramid nanofiber membrane prepared by the method of Example 1 and the pure PVDF HSV900 membrane prepared by the method of Comparative Example 1;

[0054] Figure 8 Appearance diagrams, where (a) is the appearance diagram of the film material of the solid electrolyte obtained in Comparative Example 1, (b) is the appearance diagram of the film material of the solid electrolyte obtained in Example 1, and (c) is the section of the film material of the solid electrolyte obtained in Example 1;

[0055] Figure 9 EIS diagrams of the composite solid electrolyte in the stainless steel symmetric battery obtained in Application Example 1 before and after polarization at room temperature and 60 °C;

[0056] Figure 10 Polarization curve diagram of the stainless steel symmetric battery obtained in Application Example 1. Detailed implementation manners

[0057] The present invention provides a preparation method of a composite solid electrolyte, comprising the following steps:

[0058] (1) Mix para-aramid fibers, an alkali, and a polar aprotic solvent, perform staged dispersion, and centrifuge to obtain an aramid nanofiber dispersion;

[0059] (2) Sequentially mix the aramid nanofiber dispersion with a first organic solvent, a second organic solvent, polyvinylidene fluoride, and a lithium salt electrolyte to obtain a spinning solution;

[0060] (3) Perform electrospinning on the spinning solution and perform post-treatment to obtain a composite solid electrolyte.

[0061] In the present invention, the alkali in step (1) preferably includes KOH and / or LiOH, and more preferably KOH.

[0062] In the present invention, the polar aprotic solvent in step (1) preferably includes dimethyl sulfoxide (DMSO) and / or N-methylpyrrolidone (NMP), and is further preferably dimethyl sulfoxide.

[0063] In the present invention, the mass ratio of the base in step (1) to the volume of the polar aprotic solvent is preferably 0.14 - 0.2 g:10 mL, more preferably 0.14 - 0.16 g:10 mL, and even more preferably 0.14 g:10 mL.

[0064] In the present invention, the mass ratio of the para-aramid fiber in step (1) to the base is preferably 0.14 - 0.2:0.14, more preferably 0.17 - 0.2:0.14, and even more preferably 0.2:0.14.

[0065] In the present invention, in step (1), the method of mixing the para-aramid fiber, the base, and the polar aprotic solvent is preferably: after mixing the base and the polar aprotic solvent, add the para-aramid fiber thereto.

[0066] In the present invention, the step of stagewise dispersion in step (1) preferably includes the following steps:

[0067] (1.1) Disperse the para-aramid fiber, the base, and the polar aprotic solvent to obtain an aramid nanofiber solution;

[0068] (1.2) Pre-dissolve the aramid nanofiber solution to obtain an intermediate solution;

[0069] (1.3) Perform ultrasonic-assisted dissolution on the intermediate solution.

[0070] In the present invention, the conditions for the dispersion in step (1.1) include: the temperature is preferably 35 - 45 °C, more preferably 38 - 42 °C, and even more preferably 40 °C; the time is preferably 2 - 4 h, more preferably 3 - 4 h, and even more preferably 4 h; the mixing rotation speed is preferably 200 - 400 rpm, more preferably 250 - 350 rpm, and even more preferably 300 rpm.

[0071] In the present invention, after the dispersion in step (1.1), centrifugation is preferably further included. The rotation speed of the centrifugation is preferably 4000 - 5000 rpm, more preferably 4000 - 4500 rpm, and even more preferably 4000 rpm; the time of the centrifugation is preferably 5 - 10 min, more preferably 5 - 8 min, and even more preferably 5 min.

[0072] In the present invention, the conditions for pre-dissolution in step (1.2) include: the temperature is preferably 35 - 45°C, more preferably 38 - 42°C, and most preferably 40°C; the time is preferably 1.5 - 3 h, more preferably 1.8 - 2.5 h, and most preferably 2 h; the mixing rotation speed is preferably 150 - 250 rpm, more preferably 180 - 220 rpm, and most preferably 200 rpm.

[0073] In the present invention, the conditions for ultrasonic-assisted dissolution in step (1.3) include: the temperature is preferably 70 - 90°C, more preferably 75 - 85°C, and most preferably 80°C; the ultrasonic frequency is preferably 35 - 45 kHz, more preferably 38 - 42 kHz, and most preferably 40 kHz; the ultrasonic power is preferably 50 - 70 W, more preferably 55 - 65 W, and most preferably 60 W; the time is preferably 3 - 5 h, more preferably 3.5 - 4.5 h, and most preferably 4 h.

[0074] In the present invention, the conditions for centrifugation in step (1) include: the rotation speed is preferably 8000 - 10000 rpm, more preferably 8000 - 9000 rpm, and most preferably 8000 rpm; the time is preferably 10 - 20 min, more preferably 10 - 15 min, and most preferably 10 min.

[0075] In the present invention, the first organic solvent in step (2) preferably includes one or more of dimethylformamide (DMF), dimethylacetamide (DMAC), N-methylpyrrolidone, and dimethyl sulfoxide, more preferably includes dimethylformamide and / or dimethylacetamide, and most preferably is dimethylformamide.

[0076] In the present invention, the mass ratio of the para-aramid fiber used in the aramid nanofiber dispersion in step (2) to the volume of the first organic solvent is preferably 1.3 g: 3 - 5 mL, more preferably 1.3 g: 3.5 - 4.5 mL, and most preferably 1.3 g: 4 mL.

[0077] In the present invention, in step (2), the conditions for mixing after adding the first organic solvent include: the temperature is preferably 20 - 25°C, more preferably 22 - 25°C, and most preferably 25°C; the time is preferably 5 - 15 min, more preferably 8 - 12 min, and most preferably 10 min; the mixing rotation speed is preferably 200 - 400 rpm, more preferably 250 - 350 rpm, and most preferably 300 rpm.

[0078] In the present invention, the second organic solvent in step (2) preferably includes acetone (ACE) and / or ethyl acetate (EAC), and more preferably is acetone.

[0079] In the present invention, the volume ratio of the first organic solvent to the second organic solvent in step (2) is preferably 2:1 to 1:1, more preferably 2:1 to 1.5:1, and even more preferably 2:1.

[0080] In the present invention, the second organic solvent in step (2) is preferably added in 2 to 3 portions, more preferably 3 portions.

[0081] In the present invention, the addition method of the second organic solvent in step (2) is preferably dropwise addition; the dropping rate is preferably 0.1 to 1 mL / min, more preferably 0.3 to 0.7 mL / min, and even more preferably 0.5 mL / min.

[0082] In the present invention, in step (2), the conditions for mixing after each batch addition of the second organic solvent independently include: the temperature is preferably 20 to 25 °C, more preferably 22 to 25 °C, and even more preferably 25 °C; the time is preferably 10 to 20 min, more preferably 12 to 16 min, and even more preferably 15 min; the mixing rotation speed is preferably 500 to 700 rpm, more preferably 550 to 650 rpm, and even more preferably 600 rpm.

[0083] In the present invention, the role of the first organic solvent in step (2) is illustrated by taking DMF as an example. DMF is a polar aprotic solvent, which can increase the solution conductivity and make electrospinning easier to form filaments; adding DMF can easily stably disperse ANF, and it has a high boiling point, which can delay the evaporation rate of the spinning solution and keep the spinning solution uniform.

[0084] In the present invention, the role of the second organic solvent in step (2) is illustrated by taking ACE as an example. ACE has a low boiling point and is easy to volatilize, which can promote fiber curing; it has a low viscosity, which can dilute the high viscosity of DMF, prevent nozzle blockage and optimize the fluidity of the spinning solution; it has a low surface tension, which can improve the jet stability.

[0085] In the present invention, the polyvinylidene fluoride in step (2) is preferably PVDF-HSV900.

[0086] In the present invention, the mass ratio of the para-aramid fiber to the polyvinylidene fluoride in the aramid nanofiber dispersion in step (2) is preferably 1:2 to 1.8:1, more preferably 1.1:1 to 1.5:1, and even more preferably 1.3:0.9.

[0087] In the present invention, in step (2), the conditions for mixing after adding polyvinylidene fluoride include: under a water bath condition; the temperature is preferably 50 - 70 °C, more preferably 55 - 65 °C, and even more preferably 60 °C; the time is preferably 1.5 - 2 h, more preferably 1.8 - 2 h, and even more preferably 2 h; the mixing rotation speed is preferably 300 - 500 rpm, more preferably 300 - 400 rpm, and even more preferably 300 rpm.

[0088] In the present invention, the lithium salt electrolyte in step (2) preferably includes one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium lanthanum zirconium oxide (LLZO), more preferably includes lithium bis(trifluoromethanesulfonyl)imide or lithium bis(fluorosulfonyl)imide, and even more preferably is lithium bis(trifluoromethanesulfonyl)imide.

[0089] In the present invention, the mass ratio of the lithium salt electrolyte to the polyvinylidene fluoride in step (2) is preferably 0.4 - 0.6:1, more preferably 0.45 - 0.55:1, and even more preferably 0.5:1.

[0090] In the present invention, in step (2), the conditions for mixing after adding the lithium salt electrolyte preferably include: the temperature is preferably 20 - 40 °C, more preferably 20 - 30 °C, and even more preferably 25 °C; the time is preferably 12 - 24 h, more preferably 12 - 18 h, and even more preferably 12 h.

[0091] In the present invention, the conditions for electrospinning in step (3) include: the voltage is preferably 15 - 20 kV, more preferably 16 - 19 kV, and even more preferably 18 kV; the flow rate of the spinning solution is preferably 0.3 - 1 mL / h, more preferably 0.4 - 0.8 mL / h, and even more preferably 0.5 mL / h; the distance from the nozzle to the collecting plate is preferably 12 - 15 cm, more preferably 13 - 15 cm, and even more preferably 15 cm; the temperature is preferably 20 - 30 °C, more preferably 20 - 25 °C, and even more preferably 20 °C; the relative humidity is preferably 40 - 60%, more preferably 40 - 50%, and even more preferably 45%.

[0092] In the present invention, the post-treatment in step (3) preferably includes: successively performing drying and annealing.

[0093] In the present invention, the conditions for drying include: the temperature is preferably 50 - 65 °C, more preferably 55 - 60 °C, and even more preferably 60 °C; the time is preferably 6 - 10 h, more preferably 6 - 8 h, and even more preferably 6 h.

[0094] In the present invention, the annealing conditions include: the temperature is preferably 100-130°C, more preferably 110-120°C, and even more preferably 120°C; the time is preferably 1-2 h, more preferably 1.5-2 h, and even more preferably 2 h.

[0095] The present invention also provides a composite solid electrolyte.

[0096] The present invention also provides an application of the composite solid electrolyte in a all-solid-state battery.

[0097] In the present invention, the method for the application is not limited, and a method well-known in the art can be adopted.

[0098] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0099] Example 1

[0100] This example provides a preparation method of a composite solid electrolyte, including the following steps:

[0101] (1) Preparation of ANF dispersion:

[0102] Take 0.14 g of solid KOH powder and 10 mL of DMSO solution and place them in a beaker to prepare a KOH / DMSO solvent system, and set the initial temperature to 40°C; then take 0.2 g of para-aramid short fibers (Taihe New Material Group Co., Ltd., short fibers, spinning grade, length 38 mm, linear density 1.5 D, breaking strength ≥ 16 cN / dtex, breaking elongation 3.5 ± 0.5%, number of curls 7-10 per 25 mm) and slowly add them to the KOH / DMSO solvent system at 300 rpm and react for 4 h. Under the deprotonation of KOH, the micron-sized aramid fibers are peeled into nanofibers to obtain an ANF suspension containing aramid nanofibers, and the ANF solution is obtained by centrifugation (4000 rpm, 5 min);

[0103] Keep stirring at a low speed (200 rpm) for 2 h at 40°C to allow the para-aramid to fully contact with the solvent to obtain an intermediate solution;

[0104] Raise the temperature of the intermediate solution to 80°C, and at the same time introduce an ultrasonic-assisted dissolution technique (ultrasonic frequency 40 kHz, power 60 W), and continue stirring for 4 h; then remove the undissolved impurities by high-speed centrifugation (8000 rpm, 10 min) to separate a pure ANF dispersion;

[0105] (2) Preparation of electrospinning solution:

[0106] Add the ANF dispersion containing 1.3 g of ANF to 4 mL of DMF solvent, and keep stirring at a low speed (300 rpm) at 25 °C for 10 min until the solution changes from yellow to nearly colorless and transparent; then add acetone dropwise in 3 batches at a dropping rate of 0.5 mL / min, and perform high-speed stirring (600 rpm) at 25 °C for 15 min after each addition to gradually stabilize the solution viscosity. The total dropping amount of acetone is 2 mL; add 0.9 g of PVDF-HSV900 (Arkema) to the above-mentioned mixed solution, heat and stir in a water bath at 60 °C (300 rpm) for 2 h; finally, add 0.45 g of LiTFSI salt to the above-mentioned mixed solution and stir at 25 °C for 12 h to fully dissolve the LiTFSI salt to form a uniform spinning solution;

[0107] (3) Electrospinning process and post-treatment:

[0108] Inject the spinning solution into the electrospinning device and set the following parameters: voltage 18 kV, flow rate 0.5 mL / h, distance from the nozzle to the collecting plate 15 cm, control the temperature and humidity of the electrospinning environment (temperature 20 °C, relative humidity 45%) to optimize the solvent evaporation rate; place the collected fiber film in a vacuum drying oven and dry at 60 °C for 6 h to remove the residual solvent; after drying, transfer it to an annealing treatment box at 120 °C for annealing treatment for 2 h to obtain a composite solid electrolyte, denoted as 1.3ANF-PVDF HSV900.

[0109] Experimental Example 1

[0110] Use the ANF dispersion obtained in step (1) of Example 1; add 4 mL of DMF to 1 mL of ANF dispersion and keep stirring at a low speed (300 rpm) at 25 °C for 10 min to obtain a mixed solution.

[0111] Experimental Example 2

[0112] Use the ANF dispersion obtained in step (1) of Example 1; add 4 mL of DMF to the ANF dispersion containing 0.3 g of ANF and keep stirring at a low speed (300 rpm) at 25 °C for 10 min to obtain a mixed solution; add 2 mL of ACE to the mixed solution and perform high-speed stirring (600 rpm) at 25 °C for 15 min, then add 0.9 g of PVDF-HSV900 and heat and stir in a water bath at 60 °C (300 rpm) for 2 h to obtain a uniform solution.

[0113] Experimental Example 3

[0114] Use the ANF dispersion obtained in step (1) of Example 1; add 4 mL of DMF to the ANF dispersion containing 0.5 g of ANF, and keep stirring at a low speed (300 rpm) at 25 °C for 10 min to obtain a mixed solution; add 2 mL of ACE to the mixed solution, stir at a high speed (600 rpm) at 25 °C for 15 min, and then add 0.9 g of PVDF-HSV900, heat and stir in a water bath at 60 °C (300 rpm) for 2 h to obtain a homogeneous solution.

[0115] Experimental Example 4

[0116] Use the ANF dispersion obtained in step (1) of Example 1; add 4 mL of DMF to the ANF dispersion containing 0.8 g of ANF, and keep stirring at a low speed (300 rpm) at 25 °C for 10 min to obtain a mixed solution; add 2 mL of ACE to the mixed solution, stir at a high speed (600 rpm) at 25 °C for 15 min, and then add 0.9 g of PVDF-HSV900, heat and stir in a water bath at 60 °C (300 rpm) for 2 h to obtain a homogeneous solution.

[0117] Experimental Example 5

[0118] Use the ANF dispersion obtained in step (1) of Example 1; add 4 mL of DMF to the ANF dispersion containing 1.0 g of ANF, and keep stirring at a low speed (300 rpm) at 25 °C for 10 min to obtain a mixed solution; add 2 mL of ACE to the mixed solution, stir at a high speed (600 rpm) at 25 °C for 15 min, and then add 0.9 g of PVDF-HSV900, heat and stir in a water bath at 60 °C (300 rpm) for 2 h to obtain a homogeneous solution.

[0119] Comparative Experimental Example 1

[0120] Use the ANF dispersion obtained in step (1) of Example 1; add 1 mL of the ANF dispersion into a mixed system of 4 mL of DMF / 2 mL of acetone.

[0121] Comparative Experimental Example 2

[0122] Use the ANF dispersion obtained in step (1) of Example 1; add 4 mL of DMF to 1 mL of the ANF dispersion without stirring.

[0123] Figure 1 They are the apparent diagrams of the solutions before and after adjusting the mixing order for Comparative Experimental Examples 1-2 and Experimental Example 1. Figure 1 a) in is Comparative Experimental Example 1. It can be found that when the ANF dispersion is added to the DMF / ACE mixed solvent, there is an obvious phenomenon of uneven solution in the spinning solution before the process improvement; Figure 1In b) of [the above], it is Comparative Experiment Example 2. It can be found that when the solution mixing order is to add the ANF dispersion and DMF into the beaker without stirring, the solution will turn light yellow. If acetone and PVDF-HSV900 are added and stirred at this time, the same uneven phenomenon as in Comparative Experiment Example 1 will occur. However, when the ANF dispersion and DMF are added and stirred (Experiment Example 1), the solution will change from light yellow to colorless and transparent ( Figure 1 in c) of [the above]), but there are flocculants; when acetone is added and stirred at this time, and then PVDF-HSV900 is added and stirred (Experiment Examples 2 to 5), a uniform solution will be presented, as Figure 2 shown.

[0124] Comparative Example 1

[0125] This comparative example provides a preparation method of a solid electrolyte based on a PVDF HSV900 membrane, including the following steps:

[0126] (1) Preparation of electrospinning solution:

[0127] Add 0.9 g of PVDF HSV900 into a mixed solution of 4 mL of DMF and 2 mL of acetone, stir magnetically (300 rpm), and heat in a water bath at 60 °C for 2 h; add 0.45 g of LiTFSI salt into the above-mentioned mixed solution, and stir at 25 °C for 12 h to fully dissolve the LiTFSI salt to form a uniform spinning solution;

[0128] (2) Electrospinning process and post-treatment:

[0129] Inject the spinning solution into an electrospinning device, and set the following parameters: voltage 18 kV, flow rate 0.5 mL / h, distance from the nozzle to the collection plate 15 cm, control the temperature and humidity of the electrospinning environment (temperature 20 °C, relative humidity 45%), to optimize the solvent evaporation rate; place the collected film in a vacuum drying oven, dry at 60 °C for 6 h to remove the residual solvent; after drying, transfer it to an annealing treatment box at 120 °C for annealing treatment for 2 h to obtain a solid electrolyte based on a PVDF HSV900 membrane, denoted as PVDF HSV900.

[0130] Figure 3 Figures a), b), and c) in [the following] are scanning electron microscope images (SEM images) of the membrane materials of the solid electrolytes obtained in Example 1 and Comparative Example 1 at different magnification ratios, Figure 3 in which a), b), and c) are SEM images of the membrane material obtained in Comparative Example 1 at magnification ratios of 500 times, 1000 times, and 10000 times respectively, Figure 3 in which d), e), and f) are SEM images of the membrane material obtained in Example 1 at magnification ratios of 5000 times, 10000 times, and 20000 times respectively. From Figure 3It can be seen that at different magnification ratios, the solid electrolyte membrane of pure PVDF-HSV900 obtained in Comparative Example 1 exhibits a relatively flat and smooth surface feature. At low magnification, the surface is uniform; at high magnification, the surface shows a fine granular structure, but overall lacks obvious fibrous features. After adding para-aramid, the surface morphology of the membrane material obtained in Example 1 has changed significantly: observed at low magnification, the surface shows an obvious fiber interweaving network structure, and the aramid nanofibers form a three-dimensional network structure in the PVDF matrix, enhancing the mechanical strength of the membrane; observed at high magnification, it can be clearly seen that the aramid nanofibers are well integrated with the PVDF matrix, the fiber diameters are uniform, the dispersion is good, and no obvious agglomeration phenomenon is seen. This indicates that the aramid nanofibers are effectively dispersed and evenly distributed in the solution.

[0131] Figure 4 Figure 4 shows the test results of the thermal stability of the membrane materials of the solid electrolytes obtained in Example 1 and Comparative Example 1. Figure 4 a) in it is Comparative Example 1. Figure 4 b) in it is Example 1. It can be seen from Figure 4 that after adding para-aramid, the heat resistance can reach 150 °C without shrinkage and deformation, while the solid electrolyte membrane of pure PVDF-HSV900 has obvious curling at 55 °C, indicating that adding para-aramid can prevent shrinkage at high temperatures, significantly improving the thermal stability of PVDF-HSV900, greatly reducing the risk of thermal runaway, and thus improving the safety of the battery.

[0132] Figure 5 Figure 5 is the stress-strain curve obtained by testing the membrane materials of the solid electrolytes obtained in Example 1 and Comparative Example 1 using a universal tensile testing machine. It can be seen from Figure 5 that the membrane material after adding para-aramid shows a greatly improved mechanical strength. It shows that the aramid composite membrane exhibits higher tensile strength and stiffness than the pure PVDF membrane, while maintaining a considerable tensile fracture strain. Therefore, the introduction of aramid nanofibers can achieve an improvement in the "strength-toughness" balance, significantly enhancing the mechanical properties of the composite membrane, and thus effectively reducing the risk of lithium dendrite piercing.

[0133] According to the method of Example 1, the process of adding LiTFSI salt in step (2) was deleted, and thermogravimetric analysis and Fourier transform infrared spectroscopy tests were performed on the obtained para-aramid nanofiber membrane. The results are shown in Figure 6 and Figure 7 respectively.

[0134] According to the method of Comparative Example 1, the process of adding LiTFSI salt in step (1) was deleted, and thermogravimetric analysis and Fourier transform infrared spectroscopy tests were performed on the obtained pure PVDF HSV900 membrane. The results are shown in Figure 6 and Figure 7 respectively.

[0135] Figure 6 Thermogravimetric analysis curves of the para-aramid nanofiber membrane prepared by the method of Example 1 and the pure PVDF HSV900 membrane prepared by the method of Comparative Example 1. From Figure 6 It can be seen that the pure PVDF-HSV900 membrane shows a relatively obvious mass loss in the thermogravimetric curve, especially in the medium and high temperature regions, mainly due to the thermal degradation characteristics of the PVDF matrix. After introducing aramid nanofibers, the introduction of aramid nanofibers enhances the thermal stability of the pure PVDF-HSV900 membrane, resulting in a reduction in mass loss under the same temperature conditions and a decrease in the mass loss rate; due to the high thermal stability of aramid nanofibers, the pure PVDF-HSV900 membrane retains more residual mass at high temperatures, indicating that the introduction of aramid nanofibers not only delays the thermal decomposition of PVDF to a certain extent, but also forms more char residues at high temperatures, enabling the prepared membrane material to retain a higher mass fraction in the high temperature section, thus exhibiting more excellent thermal stability.

[0136] Figure 7 Fourier transform infrared spectra of the para-aramid nanofiber membrane prepared by the method of Example 1 and the pure PVDF HSV900 membrane prepared by the method of Comparative Example 1. From Figure 7 It can be seen that in the para-aramid nanofiber membrane, the amide groups (C=O and N-H) of ANF appear at absorption peaks at 1600 cm -1 and 1700 cm -1 , and the peak position of the C-F bond (850 cm -1 ) of PVDF shifts to the right, indicating that a weak hydrogen bond (C-F···H-N) may be formed between the N-H of ANF and the C-F of PVDF. Enhancement of the β phase: The β phase peak of the pure PVDF-HSV900 membrane at 850 cm -1 is weak, while in the para-aramid nanofiber membrane, the peak position shifts to the right and the intensity increases, indicating that ANF induces the transformation of PVDF molecular chains from the α phase (non-polar) to the β phase (polar), which is beneficial to polarization and fiber formation during the electrospinning process. Weakening of the O-H peak: The O-H peak at 3300 cm -1 in the para-aramid nanofiber membrane weakens, indicating that the hydrophobic benzene ring structure of ANF reduces the water adsorption of PVDF, which is beneficial to the stability of the battery separator in a humid environment.

[0137] Figure 8 In (a) is the appearance diagram of the membrane material of the solid electrolyte obtained in Comparative Example 1; Figure 8 In (b) is the appearance diagram of the membrane material of the solid electrolyte obtained in Example 1; Figure 8 In (c) is the section of the membrane material of the solid electrolyte obtained in Example 1.

[0138] Application Example 1

[0139] The composite solid electrolyte obtained in Example 1 was assembled into a stainless-steel symmetric cell as follows: The composite solid electrolyte was sliced using a slicing machine to obtain wafers with a diameter of 18 mm. The stainless-steel symmetric cell was assembled in a glove box in the packaging order of a negative electrode case, a shrapnel, a stainless-steel gasket, the composite solid electrolyte obtained in Example 1, a stainless-steel gasket, and a positive electrode case to obtain the stainless-steel symmetric cell.

[0140] Figure 9 It is the EIS diagram of the composite solid electrolyte in the stainless-steel symmetric cell obtained in Application Example 1 before and after polarization at room temperature and 60 °C. Figure 9 The results show that the smaller the semicircle in the high-frequency region, the smaller the charge transfer resistance. The slope of the low-frequency straight line is related to the diffusion control process or the interfacial reaction control process, which is usually shown as the Warburg impedance. This indicates that the composite solid electrolyte can maintain a relatively low internal resistance of the battery without significant increase, and the impedance of the battery remains relatively stable during long-term cycling, indicating that it plays a positive role in the cycling stability of the battery and reduces the occurrence of short-circuit situations.

[0141] Figure 10 It is the polarization curve diagram of the stainless-steel symmetric cell obtained in Application Example 1. From Figure 10 the following key features were observed: ① In the negative potential region (-1.0 to 0 V), at negative voltages, the overall current of the curve is at a relatively low level (close to the order of -7 to -8 A in logarithmic coordinates), indicating that the electronic conduction of the solid electrolyte in this interval is extremely small. ② In the interval near 0 V: Some curves show a certain degree of current fluctuation or noise when approaching 0 V, which is related to the interfacial charge accumulation, adsorption / desorption phenomenon, or polarization internal resistance on the surface of the stainless-steel electrode. ③ In the positive potential region (0 to 1.5 V): As the potential increases in the positive direction from 0 V, the curve may first experience a low-current plateau on the logarithmic coordinate and then show a slow or obvious rise at higher potentials. The increase in current is very small, indicating that the composite solid electrolyte is mainly ion-conductive and weakly electron-conductive in this interval and no obvious oxidation decomposition occurs. After a certain positive voltage (such as 1.0 V or 1.2 V), a significant increase in current often indicates that the electrolyte or interfacial material may start to undergo oxidation decomposition or other side reactions near this potential. ④ The overall curve shows a symmetric trend. Since it is a stainless-steel symmetric electrode, the negative potential and the positive potential may exhibit mirror-like or similar polarization characteristics to some extent. If the curve shapes in the negative potential and positive potential directions are relatively symmetric and there are no obvious mutation peaks, it indicates that the composite electrolyte is relatively stable within the scanned voltage range.

[0142] Figure 10The characteristics are derived from the following mechanisms: ① Ion conduction and interfacial polarization: The composite of aramid (ANF) fiber and PVDF-HSV900 matrix helps to form a three-dimensional cross-linked network, which is beneficial to the transport of ions in the electrolyte. The low current maintained in most voltage ranges in the curve indicates that there are few electron conduction channels and relatively limited interfacial side reactions, which is very important for the safety and cycle stability of solid-state batteries. ② Electrochemical stability window: If there is no obvious decomposition peak in the measured potential range (such as -1.0V to +1.5V), it can be preliminarily judged that the composite electrolyte remains stable in this range. Since this test is only carried out between stainless steel electrodes, the obtained stability window is not equivalent to the true stability window when paired with active electrodes such as lithium metal, but can provide a preliminary reference for interfacial stability. ③ Interfacial impedance and polarization degree: The smoothness and current magnitude of the curve at higher potentials can indirectly reflect the interfacial impedance. If the curve rises steeply, it indicates that the polarization intensifies; if it always remains relatively stable, it indicates that the interfacial impedance is stable and the ion transport is smooth.

[0143] Therefore, Figure 10 the following conclusions can be drawn: ① The polarization curve shows the stability and polarization behavior of the aramid-PVDF HSV900 composite solid electrolyte between stainless steel electrodes: The current changes smoothly in the range of -1.0V to +1.5V, lacking sharp decomposition or side reaction peaks, indicating that it has a certain electrochemical stability window and low leakage current characteristics. ② The curve as a whole shows good symmetry and low polarization current, indicating that the ion conduction and interfacial performance of this solid electrolyte system are excellent under the condition of stainless steel symmetric electrodes. ③ No serious interfacial polarization occurs when the stainless steel electrode contacts the electrolyte, so it can be inferred that this composite electrolyte has good interfacial compatibility and small interfacial impedance. At the same time, Figure 10 the polarization curve provides the voltage response during the discharge / charge process of the battery, indicating that the composite solid electrolyte can effectively control the current density without significant increase and prevent the battery from over-discharging, proving that this membrane helps to prevent the growth of lithium dendrites, thereby improving safety and cycle life. Moreover, the composite solid electrolyte of Example 1 can effectively reduce the polarization voltage and improve the charge-discharge efficiency of the battery, proving that this solid electrolyte membrane helps to improve the overall stability of the battery and reduce the risk of short circuit.

[0144] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a composite solid electrolyte, characterized in that: The following steps are involved: (1) mixing para-aramid fiber, alkali, and polar aprotic solvent, dispersing in stages, and centrifuging to obtain an aramid nanofiber dispersion; (2) mixing the aramid nanofiber dispersion with a first organic solvent, a second organic solvent, polyvinylidene fluoride, and a lithium salt electrolyte in sequence to obtain a spinning solution; (3) The spinning solution is subjected to electrostatic spinning and post-processing to obtain a composite solid electrolyte.

2. The preparation method according to claim 1, characterized in that: In step (1), the base includes KOH and / or LiOH; The polar aprotic solvent includes dimethyl sulfoxide and / or N-methylpyrrolidone; The ratio of the mass of the base to the volume of the polar aprotic solvent is 0.14-0.2 g:10 mL; In step (1), the mass ratio of the para-aramid fiber to the alkali is 0.14-0.2:0.

14.

3. The preparation method according to claim 1 or 2, characterized in that: The staged dispersion in step (1) comprises the following steps: (1.1) dispersing para-aramid fibers, alkali, and a polar aprotic solvent to obtain an aramid nanofiber solution; (1.2) pre-dissolving the aramid nanofiber solution to obtain an intermediate solution; (1.3) subjecting the intermediate solution to ultrasound-assisted dissolution; Wherein, the dispersion conditions in step (1.1) include: temperature of 35-45°C, time of 2-4h, mixing speed of 200-400rpm; The pre-dissolution conditions in step (1.2) include: temperature of 35-45° C., time of 1.5-3 h, and mixing speed of 150-250 rpm; The conditions for the ultrasound-assisted dissolution in step (1.3) include: a temperature of 70 to 90° C., an ultrasound frequency of 35 to 45 kHz, an ultrasound power of 50 to 70 W, and a time of 3 to 5 hours.

4. The preparation method according to claim 1, characterized in that: Step (2) the first organic solvent comprises one or more of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide; The ratio of the mass of the para-aramid fiber used in the aramid nanofiber dispersion in step (2) to the volume of the first organic solvent is 1.3 g: 3 to 5 mL; In step (2), the mixing conditions after adding the first organic solvent include: temperature of 20 to 25° C., time of 5 to 15 min, and mixing speed of 200 to 400 rpm.

5. The preparation method according to claim 4, characterized in that: Step (2) the second organic solvent comprises acetone and / or ethyl acetate; Step (2) the volume ratio of the first organic solvent to the second organic solvent is 2:1 to 1:1; Step (2) the second organic solvent is added in 2 to 3 portions; In step (2), the mixing conditions after adding the second organic solvent in each batch independently include: temperature of 20 to 25° C., time of 10 to 20 min, and mixing speed of 500 to 700 rpm.

6. The preparation method according to claim 4, characterized in that: The polyvinylidene fluoride in step (2) is PVDF-HSV900; The mass ratio of the para-aramid fiber used in the aramid nanofiber dispersion in step (2) to the polyvinylidene fluoride is 1:2 to 1.8:1; In step (2), the mixing conditions after adding polyvinylidene fluoride include: in a water bath, the temperature is 50-70° C., the time is 1.5-2 hours, and the mixing speed is 300-500 rpm.

7. The preparation method according to any one of claims 4 to 6, characterized in that: The lithium salt electrolyte in step (2) includes one or more of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium lanthanum zirconium oxide; In step (2), the mass ratio of the lithium salt electrolyte to the polyvinylidene fluoride is 0.4 to 0.6:1; In step (2), the mixing conditions after adding the lithium salt electrolyte include: temperature of 20 to 40° C. and time of 12 to 24 hours.

8. The preparation method according to claim 1, characterized in that: The conditions for the electrospinning in step (3) include: a voltage of 15 to 20 kV, a spinning solution flow rate of 0.3 to 1 mL / h, a distance from the nozzle to the collecting plate of 12 to 15 cm, a temperature of 20 to 30° C., and a relative humidity of 40 to 60%.

9. A composite solid electrolyte obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the composite solid electrolyte according to claim 9 in an all-solid-state battery.

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