A composite solid electrolyte, its preparation method and application

Abstract

This invention belongs to the field of electrolyte preparation technology, and discloses a composite solid electrolyte, its preparation method, and its application. The preparation method of this invention includes the following steps: mixing para-aramid fibers, an alkali, and a polar aprotic solvent, and dispersing them in stages to obtain an aramid nanofiber dispersion; sequentially mixing the aramid nanofiber dispersion with a first organic solvent, a second organic solvent, polyvinylidene fluoride (PVDF), and a lithium salt electrolyte to obtain a spinning solution; electrospinning the spinning solution, and then performing post-treatment to obtain the composite solid electrolyte. This invention introduces PVDF to modify the surface of the aramid nanofibers, optimizes the process route, significantly improves the compatibility between the aramid nanofibers and the polymer matrix, enhances the mechanical properties and thermal stability of the composite membrane, and thus enables the aramid composite membrane to exhibit better interfacial compatibility in all-solid polymer electrolytes, effectively improving the cycle stability and conductivity of the battery.

Description

Technical Field

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

[0002] Para-aramid nanofibers have attracted attention due to their high mechanical strength and excellent heat resistance. However, their rigid linear macromolecules make them difficult to dissolve in conventional solvents, hindering the formation of uniform spinning solutions. Furthermore, aramid nanofibers are prone to fiber breakage or inhomogeneity during electrospinning, and their poor compatibility with other polymer matrices limits their application in solid electrolytes.

[0003] For example, existing literature (H. Xu, S. Yagi, S. Ashour, L. Du, ME 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 electrospinning technology, without exploring in depth the influence of solution viscoelasticity and shear behavior on fiber formation.

[0004] In the Chinese patent application with publication number CN109786634A, the electrospinning process described mainly improves the performance of the membrane through simple solution preparation and composite material stacking. It mainly relies on traditional solvent selection and basic ratio to control the viscoelasticity of the solution, without deeply regulating the viscosity change and shear behavior of the solution, and does not involve fine control of the shear thinning behavior of the spinning solution.

[0005] Furthermore, existing technologies for preparing aramid films primarily rely on electrospinning to fabricate single-material films. For example, in Chinese patent application CN110373814A, the spinning performance of para-aramid nanofibers was optimized using an electrospinning aid, but the proposed method did not involve polymer composites or surface modification.

[0006] Para-aramid fibers, due to their rigid molecular chain structure, exhibit poor compatibility with other materials (especially polymer matrices), limiting their application in high-performance batteries. For example, while Chinese patent applications with publication numbers CN115295961A and CN118326706A mention optimizing material performance through different solvent systems or composite strategies, they do not address improving the compatibility between the fiber and the polymer electrolyte matrix through surface modification.

[0007] Currently, the application of aramid nanofiber membranes in battery separators is mainly focused on improving mechanical properties and preventing lithium dendrite penetration. For example, in Chinese patent application CN115295961A, the main function of the aramid membrane is as a mechanical reinforcing material for the battery separator, without addressing the optimization of the battery electrolyte. Summary of the Invention

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

[0009] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0010] This invention provides a method for preparing a composite solid electrolyte, comprising the following steps:

[0011] (1) Mix para-aramid fibers, alkali, and polar aprotic solvent, disperse in stages, and centrifuge to obtain aramid nanofiber dispersion.

[0012] (2) The aramid nanofiber dispersion is sequentially mixed with a first organic solvent, a second organic solvent, polyvinylidene fluoride, and a lithium salt electrolyte to obtain a spinning solution;

[0013] (3) The spinning solution is electrospun and then post-treated 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 base 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 to 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 fibers, alkali, and polar aprotic solvent to obtain an aramid nanofiber solution;

[0020] (1.2) The aramid nanofiber solution is pre-dissolved to obtain an intermediate solution;

[0021] (1.3) The intermediate solution is dissolved with ultrasonic assistance;

[0022] The dispersion conditions described in step (1.1) include: a temperature of 35–45°C, a time of 2–4 h, and a mixing speed of 200–400 rpm.

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

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

[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] In step (2), the mass ratio of para-aramid fibers used in the aramid nanofiber dispersion to the volume ratio of the first organic solvent is 1.3 g: 3-5 mL.

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

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

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

[0030] Step (2) The second organic solvent is added in 2 to 3 portions;

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

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

[0033] In step (2), the mass ratio of para-aramid fibers to polyvinylidene fluoride used in the aramid nanofiber dispersion is 1:2 to 1.8:1.

[0034] In step (2), the mixing conditions after adding polyvinylidene fluoride include: a water bath with a temperature of 50-70°C, a time of 1.5-2 hours, and a mixing speed of 300-500 rpm.

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

[0036] In step (2), the mass ratio of the lithium salt electrolyte to the polyvinylidene fluoride is 0.4 to 0.6:1.

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

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

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

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

[0041] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) This invention optimizes the mixing sequence and ratio of aramid nanofibers (ANF) with two organic solvents (e.g., dimethylformamide DMF and acetone), adds the second organic solvent in stages, and adjusts the solution viscosity (controlled at 0.3–0.4 Pa·s) by controlling the stirring speed and time, thus achieving precise control of the solution's viscoelasticity. This method significantly improves solution stability and fiber quality through optimization of shear-thinning behavior, reduces fiber inhomogeneity and breakage, and ensures fiber uniformity and stability during spinning.

[0043] (2) Due to the presence of benzene ring groups in the main molecular chain of para-aramid fibers, the molecular chains are rigid, and the intermolecular entanglement is weak, making spinning difficult under the influence of an electrostatic field. The electrospinning process employed in this invention not only solves the spinning difficulty of para-aramid but also enhances the molecular chain entanglement between fibers through composite with PVDF-HSV900, thereby improving the tensile properties and crystallinity of the fibers and ensuring 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, resulting in a final membrane material with higher mechanical strength and thermal stability.

[0044] (3) This invention introduces PVDF to modify the surface of aramid nanofibers and optimizes the process route to significantly improve the compatibility between aramid nanofibers and the polyvinylidene fluoride polymer matrix, 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) This invention improves the ionic conductivity of the membrane by combining surface-functionalized aramid nanofibers with lithium salt electrolyte. In battery applications, this not only effectively prevents the growth of lithium dendrites but also improves battery safety and cycle life. In addition, the membrane's high specific surface area and good pore structure also give it excellent performance in preventing short circuits and improving the overall stability of the battery. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0047] Figure 1 To compare the solution appearance of Experimental Examples 1-2 with that of Experimental Example 1 before and after adjusting the mixing order, where a) is Experimental Example 1, b) is Experimental Example 2, and c) is Experimental Example 1;

[0048] Figure 2 The images show the appearance of the solutions obtained in Experiments 2 to 5, where a) is Experiment 2, b) is Experiment 3, c) is Experiment 4, and d) is Experiment 5.

[0049] Figure 3 The images show SEM images of the solid electrolyte membranes obtained in Example 1 and Comparative Example 1, where a), b), and c) are SEM images of the membrane obtained in Comparative Example 1 at magnifications of 500x, 1000x, and 10000x, respectively, and d), e), and f) are SEM images of the membrane obtained in Example 1 at magnifications of 5000x, 10000x, and 20000x, respectively.

[0050] Figure 4 The results of thermal stability tests on the membrane materials of the solid electrolytes obtained in Example 1 and Comparative Example 1 are shown, where a) is Comparative Example 1 and b) is Example 1.

[0051] Figure 5 The stress-strain curves of the solid electrolyte membrane materials obtained in Example 1 and Comparative Example 1 are shown.

[0052] Figure 6 Thermogravimetric analysis curves of the para-aramid nanofiber membrane prepared according to the method of Example 1 and the pure PVDF HSV900 membrane prepared according to the method of Comparative Example 1 are shown.

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

[0054] Figure 8 The images are morphological images, in which (a) is a morphological image of the solid electrolyte membrane material obtained in Comparative Example 1, (b) is a morphological image of the solid electrolyte membrane material obtained in Example 1, and (c) is a slice of the solid electrolyte membrane material obtained in Example 1.

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

[0056] Figure 10 The polarization curve of the stainless steel symmetrical cell obtained from Example 1 is shown. Detailed Implementation

[0057] This invention provides a method for preparing a composite solid electrolyte, comprising the following steps:

[0058] (1) Mix para-aramid fibers, alkali, and polar aprotic solvent, disperse in stages, and centrifuge to obtain aramid nanofiber dispersion.

[0059] (2) The aramid nanofiber dispersion is sequentially mixed with a first organic solvent, a second organic solvent, polyvinylidene fluoride, and a lithium salt electrolyte to obtain a spinning solution;

[0060] (3) The spinning solution is electrospun and then post-treated to obtain a composite solid electrolyte.

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

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

[0063] In this invention, the mass ratio of the alkali to the volume of the polar aprotic solvent in step (1) 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 this invention, the mass ratio of the para-aramid fiber to the alkali in step (1) is preferably 0.14 to 0.2:0.14, more preferably 0.17 to 0.2:0.14, and even more preferably 0.2:0.14.

[0065] In this invention, the preferred method for mixing para-aramid fibers, alkali, and polar aprotic solvent in step (1) is to mix the alkali and polar aprotic solvent and then add para-aramid fibers to the mixture.

[0066] In this invention, the phased dispersion in step (1) preferably includes the following steps:

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

[0068] (1.2) The aramid nanofiber solution is pre-dissolved to obtain an intermediate solution;

[0069] (1.3) The intermediate solution is dissolved by ultrasonic assistance.

[0070] In this invention, the dispersion conditions 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 2-4h, more preferably 3-4h, and even more preferably 4h; the mixing speed is preferably 200-400rpm, more preferably 250-350rpm, and even more preferably 300rpm.

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

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

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

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

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

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

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

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

[0079] In this 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 this invention, the second organic solvent in step (2) is preferably added in 2 to 3 times, more preferably in 3 times.

[0081] In this invention, the addition of the second organic solvent in step (2) is preferably by dripping; the dripping 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 this invention, the mixing conditions after adding the second organic solvent in each batch in step (2) are independent, including: the temperature is preferably 20-25°C, more preferably 22-25°C, and more preferably 25°C; the time is preferably 10-20 min, more preferably 12-16 min, and more preferably 15 min; the mixing speed is preferably 500-700 rpm, more preferably 550-650 rpm, and more preferably 600 rpm.

[0083] In this invention, the role of the first organic solvent in step (2) is explained using DMF as an example. DMF is a polar aprotic solvent that increases the conductivity of the solution, making electrospinning easier; adding DMF can easily stabilize and disperse ANF, and its high boiling point slows down the evaporation rate of the spinning solution, keeping the spinning solution uniform.

[0084] In this invention, the role of the second organic solvent in step (2) is explained using ACE as an example. ACE has a low boiling point and is easily volatile, which promotes fiber curing; it has low viscosity, which dilutes the high viscosity of DMF, prevents nozzle clogging, and optimizes the flowability of the spinning solution; it has low surface tension, which improves jet stability.

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

[0086] In this invention, the mass ratio of para-aramid fibers to polyvinylidene fluoride used 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 this invention, the mixing conditions after adding polyvinylidene fluoride in step (2) include: under water bath conditions; the temperature is preferably 50-70°C, more preferably 55-65°C, and more preferably 60°C; the time is preferably 1.5-2h, more preferably 1.8-2h, and more preferably 2h; the mixing speed is preferably 300-500rpm, more preferably 300-400rpm, and more preferably 300rpm.

[0088] In this 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 including lithium bis(trifluoromethanesulfonyl)imide or lithium bis(fluorosulfonyl)imide, and more preferably lithium bis(trifluoromethanesulfonyl)imide.

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

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

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

[0092] In this invention, the post-processing in step (3) preferably includes: sequentially drying and annealing.

[0093] In this invention, the drying conditions include: a temperature preferably of 50-65°C, more preferably of 55-60°C, and even more preferably of 60°C; and a time preferably of 6-10 hours, more preferably of 6-8 hours, and even more preferably of 6 hours.

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

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

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

[0097] In this invention, the method of application is not limited, and any method well known in the art can be used.

[0098] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0099] Example 1

[0100] This embodiment provides a method for preparing a composite solid electrolyte, including the following steps:

[0101] (1) Preparation of ANF dispersion:

[0102] Prepare a KOH / DMSO solvent system by placing 0.14g of KOH solid powder and 10mL of DMSO solution in a beaker, setting the initial temperature to 40℃; then take 0.2g of para-aramid staple fiber (Taihe New Material Group Co., Ltd.). Short fibers (spinning grade, length 38 mm, linear density 1.5D, breaking strength ≥16 cN / dtex, breaking elongation 3.5±0.5%, crimp number 7~10 / 25 mm) were slowly added to a KOH / DMSO solvent system at 300 rpm and reacted for 4 h. Under the deprotonation effect of KOH, the micron-sized aramid fibers were exfoliated into nanofibers, resulting in an ANF suspension containing aramid nanofibers. The ANF solution was obtained by centrifugation (4000 rpm, 5 min).

[0103] Pre-dissolve the para-aramid at 40°C with low stirring (200 rpm) for 2 hours to ensure sufficient contact between the para-aramid and the solvent, thus obtaining an intermediate solution.

[0104] The intermediate solution was heated to 80°C, and ultrasonic-assisted dissolution technology (ultrasonic frequency 40kHz, power 60W) was introduced. The mixture was stirred for 4 hours. Undissolved impurities were then removed by high-speed centrifugation (8000rpm, 10min), and the pure ANF dispersion was separated.

[0105] (2) Preparation of electrospinning solution:

[0106] An ANF dispersion containing 1.3 g of ANF was added to 4 mL of DMF solvent and stirred at low speed (300 rpm) for 10 min at 25 °C until the solution changed from yellow to a nearly colorless and transparent state. Then, acetone was added dropwise in three batches at a dropping rate of 0.5 mL / min. After each addition, the solution was stirred at high speed (600 rpm) for 15 min at 25 °C to gradually stabilize the viscosity. The total amount of acetone added was 2 mL. 0.9 g of PVDF-HSV900 (Arkema) was added to the above mixed solution and the mixture was heated and stirred in a water bath at 60 °C (300 rpm) for 2 h. Finally, 0.45 g of LiTFSI salt was added to the above mixed solution and the mixture was stirred at 25 °C for 12 h to fully dissolve the LiTFSI salt and form a homogeneous spinning solution.

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

[0108] The spinning solution was injected into the electrospinning apparatus, and the following parameters were set: voltage 18kV, flow rate 0.5mL / h, distance from nozzle to collection plate 15cm, and the temperature and humidity of the spinning environment were controlled (temperature 20℃, relative humidity 45%) to optimize the solvent evaporation rate. The collected fiber film was placed in a vacuum drying oven and dried at 60℃ for 6h to remove residual solvent. After drying, it was transferred to an annealing chamber at 120℃ for annealing for 2h to obtain the composite solid electrolyte, denoted as 1.3ANF-PVDF HSV900.

[0109] Experimental Example 1

[0110] The ANF dispersion obtained in step (1) of Example 1 was used; 4 mL of DMF was added to 1 mL of LANF dispersion, and the mixture was stirred at a low speed (300 rpm) for 10 min at 25 °C to obtain a mixed solution.

[0111] Experiment Example 2

[0112] The ANF dispersion obtained in step (1) of Example 1 was used; 4 mL of LDMMF was added to the ANF dispersion containing 0.3 g of ANF, and the mixture was stirred at a low speed (300 rpm) for 10 min at 25 °C to obtain a mixed solution; 2 mL of ACE was added to the mixed solution, and the mixture was stirred at a high speed (600 rpm) for 15 min at 25 °C, and then 0.9 g of PVDF-HSV900 was added. The mixture was heated and stirred in a water bath at 60 °C (300 rpm) for 2 h to obtain a homogeneous solution.

[0113] Experimental Example 3

[0114] The ANF dispersion obtained in step (1) of Example 1 was used; 4 mL of LDMMF was added to the ANF dispersion containing 0.5 g of ANF, and the mixture was stirred at low speed (300 rpm) for 10 min at 25 °C to obtain a mixed solution; 2 mL of ACE was added to the mixed solution, and the mixture was stirred at high speed (600 rpm) for 15 min at 25 °C, and then 0.9 g of PVDF-HSV900 was added. The mixture was heated and stirred at 60 °C in a water bath (300 rpm) for 2 h to obtain a homogeneous solution.

[0115] Experiment Example 4

[0116] The ANF dispersion obtained in step (1) of Example 1 was used; 4 mL of LDMMF was added to the ANF dispersion containing 0.8 g of ANF, and the mixture was stirred at a low speed (300 rpm) for 10 min at 25 °C to obtain a mixed solution; 2 mL of ACE was added to the mixed solution, and the mixture was stirred at a high speed (600 rpm) for 15 min at 25 °C, and then 0.9 g of PVDF-HSV900 was added. The mixture was heated and stirred at 60 °C in a water bath (300 rpm) for 2 h to obtain a homogeneous solution.

[0117] Experimental Example 5

[0118] The ANF dispersion obtained in step (1) of Example 1 was used; 4 mL of LDM was added to the ANF dispersion containing 1.0 g of ANF, and the mixture was stirred at a low speed (300 rpm) for 10 min at 25 °C to obtain a mixed solution; 2 mL of ACE was added to the mixed solution, and the mixture was stirred at a high speed (600 rpm) for 15 min at 25 °C, and then 0.9 g of PVDF-HSV900 was added. The mixture was heated and stirred at 60 °C in a water bath (300 rpm) for 2 h to obtain a homogeneous solution.

[0119] Comparative Experiment Example 1

[0120] The ANF dispersion obtained in step (1) of Example 1 was used; 1 mL of the ANF dispersion was added to a mixture of 4 mL of DMF and 2 mL of acetone.

[0121] Comparative Experiment Example 2

[0122] The ANF dispersion obtained in step (1) of Example 1 was used; 4 mL of DMF was added to 1 mL of the ANF dispersion without stirring.

[0123] Figure 1 To compare the solution appearance of Experimental Examples 1-2 with that of Experimental Example 1 before and after adjusting the mixing order. Figure 1 a) in the example is comparative experiment 1. It can be found that when the ANF dispersion is added to the DMF / ACE mixed solvent, the spinning solution before the process improvement has obvious solution inhomogeneity. Figure 1b) in the example is Comparative Experiment 2. It can be observed that when the solution is mixed in the following order: ANF dispersion and DMF are added to the beaker without stirring, the solution turns pale yellow. If acetone and PVDF-HSV900 are added and stirred at this point, the same unevenness observed in Comparative Experiment 1 occurs. However, when ANF dispersion and DMF are added and stirred (Experiment 1), the solution changes from pale yellow to colorless and transparent. Figure 1 c)) but with flocculent matter; at this point, adding acetone and stirring, then adding PVDF-HSV900 and stirring (Experiments 2-5) will result in a homogeneous solution, such as Figure 2 As shown.

[0124] Comparative Example 1

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

[0126] (1) Preparation of electrospinning solution:

[0127] Add 0.9g of PVDF HSV900 to a mixed solution containing 4mL of DMF and 2mL of acetone and stir magnetically (300rpm). Heat in a water bath at 60℃ for 2h. Add 0.45g of LiTFSI salt to the aforementioned mixed solution and stir at 25℃ for 12h to fully dissolve the LiTFSI salt and form a uniform spinning solution.

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

[0129] The spinning solution was injected into the electrospinning apparatus, and the following parameters were set: voltage 18kV, flow rate 0.5mL / h, distance from nozzle to collection plate 15cm, and the temperature and humidity of the spinning environment were controlled (temperature 20℃, relative humidity 45%) to optimize the solvent evaporation rate. The collected film was placed in a vacuum drying oven and dried at 60℃ for 6h to remove residual solvent. After drying, it was transferred to an annealing chamber at 120℃ for annealing for 2h to obtain a solid electrolyte based on PVDF HSV900 membrane, denoted as PVDF HSV900.

[0130] Figure 3 These are scanning electron microscope (SEM) images of the solid electrolyte membranes obtained in Example 1 and Comparative Example 1 at different magnifications. Figure 3 a), b), and c) in the figures are SEM images of the membrane material obtained in Comparative Example 1 at magnifications of 500x, 1000x, and 10000x, respectively. Figure 3 In the figures d), e), and f), the images are SEM images of the membrane material obtained in Example 1 at magnifications of 5000x, 10000x, and 20000x, respectively. Figure 3It can be seen that, at different magnifications, 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 lacks obvious fibrous features overall. However, after adding para-aramid, the surface morphology of the membrane material obtained in Example 1 changed significantly: at low magnification, the surface showed an obvious interwoven fiber network structure, with aramid nanofibers forming a three-dimensional network structure in the PVDF matrix, enhancing the mechanical strength of the membrane; at high magnification, the good integration of aramid nanofibers and the PVDF matrix was clearly visible, with uniform fiber diameter, good dispersion, and no obvious agglomeration. This indicates that the aramid nanofibers were effectively dispersed and uniformly distributed in the solution.

[0131] Figure 4 The results show the thermal stability test results of the solid electrolyte membrane materials obtained in Example 1 and Comparative Example 1. Figure 4 a) in the example is Comparative Example 1. Figure 4 b) in the text refers to Example 1. From Figure 4 It can be seen that the heat resistance of adding para-aramid can reach 150℃ without shrinkage and deformation, while the solid electrolyte membrane of pure PVDF-HSV900 already shows obvious curling at 55℃. This indicates 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 This is a stress-strain curve obtained after testing the solid electrolyte membrane materials of Example 1 and Comparative Example 1 using a universal tensile testing machine. Figure 5 It is evident that the membrane material with added para-aramid exhibits a significant improvement in mechanical strength. This indicates that the aramid composite membrane demonstrates higher tensile strength and stiffness compared to pure PVDF membranes, while maintaining considerable tensile fracture strain. Therefore, the introduction of aramid nanofibers can achieve an improved balance between strength and toughness, significantly enhancing the mechanical properties of the composite membrane and effectively reducing the risk of lithium dendrite puncture.

[0133] Following the method of Example 1, the process of adding LiTFSI salt in step (2) was omitted. The thermogravimetric analysis and Fourier transform infrared spectroscopy were performed on the obtained para-aramid nanofiber membrane, and the results are as follows: Figure 6 , Figure 7 As shown.

[0134] Following the method of Comparative Example 1, the process of adding LiTFSI salt in step (1) was omitted. Thermogravimetric analysis and Fourier transform infrared spectroscopy were performed on the obtained pure PVDF HSV900 film, and the results are as follows: Figure 6 , Figure 7 As shown.

[0135] Figure 6 The thermogravimetric analysis (TGA) curves are shown for the para-aramid nanofiber membrane prepared according to the method of Example 1 and the pure PVDF HSV900 membrane prepared according to the method of Comparative Example 1. Figure 6 It can be seen that the pure PVDF-HSV900 membrane exhibits significant mass loss in the thermogravimetric curve, especially in the medium- and high-temperature range, mainly attributed to the thermal degradation characteristics of the PVDF matrix. The introduction of aramid nanofibers enhances the thermal stability of the pure PVDF-HSV900 membrane, leading to reduced mass loss under the same temperature conditions and lowering 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 some extent but also forms more char residue at high temperatures, allowing the prepared membrane to retain a higher mass fraction in the high-temperature range, thus demonstrating superior thermal stability.

[0136] Figure 7 The Fourier transform infrared spectra are those of the para-aramid nanofiber membrane prepared according to the method of Example 1 and the pure PVDF HSV900 membrane prepared according to the method of Comparative Example 1. Figure 7 It can be seen that in para-aramid nanofiber membranes, the amide groups (C=O and NH) of ANF at 1600 cm⁻¹ -1 and 1700cm -1 An absorption peak appears at 850 cm⁻¹, and the CF bonds of PVDF (850 cm⁻¹) -1 The rightward shift of the peak position indicates that a weak hydrogen bond (CF···HN) may form between the NH group of ANF and the CF group of PVDF. β-phase enhancement: Pure PVDF-HSV900 membrane at 850 cm⁻¹ -1 The β-phase peak is weaker, while the peak position shifts to the right and the intensity increases in the para-aramid nanofiber membrane, indicating that ANF induces the transformation of PVDF molecular chains from the α-phase (nonpolar) to the β-phase (polar), which is beneficial to polarization and fiber formation during electrospinning. The OH peak weakens: at 3300 cm⁻¹ in the para-aramid nanofiber membrane. -1 The weakening of the OH peak indicates that the hydrophobic benzene ring structure of ANF reduces the adsorption of moisture by PVDF, which is beneficial to the stability of the battery separator in a humid environment.

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

[0138] Application Example 1

[0139] The composite solid electrolyte obtained in Example 1 was assembled into a stainless steel symmetrical battery using the following method: The composite solid electrolyte was sliced ​​using a slicer to obtain a circular slice with a diameter of 18 mm. The stainless steel symmetrical battery was assembled in a glove box using the following encapsulation sequence: negative electrode shell, spring, stainless steel gasket, composite solid electrolyte obtained in Example 1, stainless steel gasket, and positive electrode shell.

[0140] Figure 9 The image shows the EIS diagrams of the composite solid electrolyte in the stainless steel symmetric cell obtained in 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 lower the charge transfer impedance. The slope of the low-frequency straight line is related to the diffusion-controlled process or the interface reaction-controlled process, and is usually displayed as Warburg impedance. This indicates that the composite solid electrolyte can maintain a low battery internal resistance without significantly increasing it, and the battery impedance remains relatively stable during long-term cycling, indicating that it plays a positive role in the cycle stability of the battery and reduces the occurrence of short circuits.

[0141] Figure 10 The image shows the polarization curves of the stainless steel symmetrical cell obtained in Example 1. Figure 10 The following key characteristics were observed: ① In the negative potential region (-1.0 to 0 V), the overall current of the curve is at a relatively low level (approximately -7 to -8 A on a logarithmic scale), indicating that the electronic conductivity of the solid electrolyte is extremely low in this range. ② Near 0 V: Some curves show current fluctuations or noise near 0 V, which is related to the accumulation of interfacial charge, adsorption / desorption, or polarization resistance on the stainless steel electrode surface. ③ In the positive potential region (0 to 1.5 V): As the potential increases from 0 V to the positive, the curve may first experience a low current plateau on a logarithmic scale, and then show a slow or significant rise at higher potentials. The current rise is very small, indicating that the composite solid electrolyte is mainly ionicly conductive and extremely weakly electronically conductive in this range, and no significant oxidative decomposition occurs. A significant increase in current after a certain positive voltage (e.g., 1.0 V or 1.2 V) often indicates that the electrolyte or interfacial material may begin to undergo oxidative decomposition or other side reactions near this potential. ④ The curves generally show a symmetrical trend. Due to the use of stainless steel symmetrical electrodes, the negative and positive potentials may exhibit mirror or similar polarization characteristics to some extent. The relatively symmetrical curves in the negative and positive potential directions without obvious abrupt peaks indicate that the composite electrolyte is relatively stable within the scanned voltage range.

[0142] Figure 10The characteristics stem from the following mechanisms: ① Ion conduction and interfacial polarization: The composite of aramid (ANF) fiber and PVDF-HSV900 matrix helps form a three-dimensional cross-linked network, which is beneficial for ion transport in the electrolyte. The low current maintained in most voltage ranges of 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 no obvious decomposition peak appears in the measured potential range (e.g., -1.0V to +1.5V), it can be preliminarily judged that the composite electrolyte is stable in this range. Since this test is only performed 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 it can provide a preliminary reference for interfacial stability. ③ Interfacial impedance and polarization: The smoothness of the curve and the magnitude of the current at higher potentials can indirectly reflect the interfacial impedance. If the curve rises sharply, it indicates that the polarization is intensified; if it remains relatively stable, it indicates that the interfacial impedance is stable and ion transport is smooth.

[0143] therefore, Figure 10 The following conclusions can be drawn: ① The polarization curves demonstrate the stability and polarization behavior of the aramid-PVDF HSV900 composite solid electrolyte between stainless steel electrodes: the current change is stable within the range of -1.0V to +1.5V, lacking severe decomposition or side reaction peaks, indicating that it possesses a certain electrochemical stability window and low leakage current characteristics. ② The curves as a whole exhibit good symmetry and low polarization current, indicating that the solid electrolyte system has excellent ion conduction and interfacial performance under stainless steel symmetrical electrode conditions. ③ No severe interfacial polarization occurred when the stainless steel electrode was in contact with the electrolyte, suggesting that the composite electrolyte has good interfacial compatibility and low interfacial impedance. Meanwhile, Figure 10 The polarization curves provide the voltage response during the battery's discharge / charge process, demonstrating that the composite solid electrolyte can effectively control the current density without significantly increasing it and prevent over-discharge. This proves that the membrane helps prevent lithium dendrite growth, thereby improving safety and cycle life. Furthermore, the composite solid electrolyte of Example 1 effectively reduces polarization voltage and improves battery charge / discharge efficiency, proving that the solid electrolyte membrane helps improve the overall stability of the battery and reduces the risk of short circuits.

[0144] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a composite solid electrolyte, characterized in that, Includes the following steps: (1) Mix para-aramid fibers, alkali, and polar aprotic solvent, disperse in stages, and centrifuge to obtain aramid nanofiber dispersion; (2) The aramid nanofiber dispersion is sequentially mixed with a first organic solvent, a second organic solvent, polyvinylidene fluoride, and a lithium salt electrolyte to obtain a spinning solution; (3) The spinning solution is electrospun and then post-treated to obtain a composite solid electrolyte; In step (1), the alkali includes KOH and / or LiOH; The polar aprotic solvent includes dimethyl sulfoxide and / or N-methylpyrrolidone; Step (1) of phased decentralization includes the following steps: (1.1) Disperse para-aramid fibers, alkali, and polar aprotic solvent to obtain an aramid nanofiber solution; (1.2) The aramid nanofiber solution is pre-dissolved to obtain an intermediate solution; (1.3) The intermediate solution is dissolved using ultrasound-assisted dissolution; The dispersion conditions described in step (1.1) include: a temperature of 35~45 ℃, a time of 2~4 h, and a mixing speed of 200~400 rpm; The pre-dissolution conditions in step (1.2) include: a temperature of 35~45 ℃, a time of 1.5~3 h, and a mixing speed of 150~250 rpm; The conditions for ultrasound-assisted dissolution in step (1.3) include: temperature of 70~90 ℃, ultrasound frequency of 35~45 kHz, ultrasound power of 50~70 W, and time of 3~5 h; Step (2) The first organic solvent includes one or more of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide; In step (2), the mass ratio of para-aramid fibers used in the aramid nanofiber dispersion to the volume ratio of the first organic solvent is 1.3 g: 3~5 mL. In step (2), the mixing conditions after adding the first organic solvent include: temperature of 20~25 ℃, time of 5~15 min, and mixing speed of 200~400 rpm; Step (2) The second organic solvent includes 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 for each batch are independent, including: temperature of 20~25 ℃, time of 10~20 min, and mixing speed of 500~700 rpm.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio 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, characterized in that, The polyvinylidene fluoride mentioned in step (2) is PVDF-HSV900; In step (2), the mass ratio of para-aramid fibers to polyvinylidene fluoride used in the aramid nanofiber dispersion is 1:2 to 1.8:

1. In step (2), the mixing conditions after adding polyvinylidene fluoride include: a water bath with a temperature of 50~70 ℃, a time of 1.5~2 h, and a mixing speed of 300~500 rpm.

4. The preparation method according to claim 1 or 3, characterized in that, The lithium salt electrolyte in step (2) includes one or more of lithium bis(fluorosulfonyl)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 0.4~0.6:1; In step (2), the mixing conditions after adding lithium salt electrolyte include: temperature of 20~40 ℃ and time of 12~24 h.

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

6. A composite solid electrolyte prepared by the preparation method according to any one of claims 1 to 5.

7. The application of the composite solid electrolyte as described in claim 6 in an all-solid-state battery.

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