Preparation method and application of high-voltage-resistant porous composite gel electrolyte

Abstract

The invention discloses a preparation method and application of a high-voltage-resistant porous composite gel electrolyte, and belongs to the technical field of electrochemical energy storage materials. The method comprises the following steps: carrying out amino-phosphate difunctional graft modification on a nano TiO2 filler to improve the compatibility and interface stability of the nano TiO2 filler and a polymer matrix; dispersing the functionalized TiO2 in a mixed solvent of N, N-dimethylformamide and dimethyl carbonate, adding PVDF-HFP, stirring and dissolving, and blending with a polylactic acid (PLA) solution to form uniform slurry; performing layer-by-layer blade coating and primary drying by adopting a scraper tape casting method, and performing vacuum drying to obtain a porous composite membrane with an interpenetrating network structure; and the porous membrane fully adsorbs the electrolyte through a vacuum-pressurization alternate infiltration process to prepare the gel electrolyte with high ionic conductivity, excellent mechanical strength and interface stability. The obtained electrolyte can effectively inhibit electrolyte decomposition under high voltage, is suitable for a high-voltage-resistant supercapacitor of 3.5 V and above, and remarkably improves the energy density and the cycle life of a device.

Description

Technical Field

[0001] This invention belongs to the field of polymer technology, specifically relating to a method for preparing a high-voltage resistant porous composite gel electrolyte and its application. Background Technology

[0002] With the increasing demand for energy storage devices with high power, high safety and long life due to the development of new energy sources, researchers have focused on the development of high-voltage quasi-solid or solid-state supercapacitors to improve energy density, extend cycle life and safety by increasing the voltage window.

[0003] Polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), one of the most common polymers for constructing GPEs, is widely used in the preparation of porous gel electrolytes. However, due to its relatively low porosity and saturation, as well as the environmental burden caused by carbon emissions, renewable materials are chosen as alternatives. Polylactic acid (PLA) has good film-forming properties, relatively low crystallinity, and biodegradability. Introducing PVDF-HFP into composite polymers has led to the development of environmentally friendly films with high porosity and high saturation, exhibiting excellent electrochemical stability after long cycling. However, the constructed GPEs have a low voltage window, limited energy density, and increased risk of electrolyte decomposition. Therefore, research has focused on introducing dielectric materials such as SiO2, TiO2, and ZnO to improve the voltage window. TiO2 is widely used in electrodes and electrolytes in electrochemical systems, and its unique photoelectric properties, chemical stability, and structural tunability make it play a key role in improving battery performance, enhancing interfacial stability, and boosting ion transport. Therefore, by adding the dielectric material TiO2 to prepare electrochemically stable gel electrolytes, the working stability of the electrolyte under high voltage can be improved, and the advantages of applying dielectric materials in electrolytes can be verified. Summary of the Invention

[0004] The technical problem to be solved by this invention is to address the shortcomings of the prior art by proposing a method for preparing a high-voltage porous composite gel electrolyte and its application. By adding the dielectric material TiO2 to a porous composite film and performing functional modification, a gel electrolyte with stable electrochemical performance under high voltage is prepared. The role of the dielectric material TiO2 in improving the working voltage of the electrolyte is verified, thereby improving the electrochemical window of GPEs and realizing the ultimate goal of applying environmentally friendly materials in SCs and improving their energy density.

[0005] The present invention adopts the following technical solution:

[0006] A method for preparing a high-voltage resistant porous composite gel electrolyte, characterized by comprising the following steps:

[0007] S1: The nano-TiO2 filler was modified by amino-phosphate ester bifunctional grafting to obtain functionalized TiO2 filler;

[0008] S2: Prepare a mixed solvent of N,N-dimethylformamide and dimethyl carbonate, add functionalized TiO2 filler for ultrasonic dispersion, then add PVDF-HFP for uniform stirring, and finally add the mixed PVDF-HFP solution to polylactic acid PLA solution for uniform mixing to obtain a mixed slurry;

[0009] S3: The obtained mixed slurry is uniformly coated with one or more layers by a doctor blade casting method. When coating multiple layers, each layer is initially dried before the next layer is coated. Then, the mixture is moved into a vacuum environment and dried further to obtain a porous membrane.

[0010] S4: The porous membrane is immersed in the electrolyte using a vacuum-pressure alternating immersion process. The electrolyte is then removed and its surface is dried for use in assembling high-voltage supercapacitors.

[0011] In S1, the specific steps for modifying the nano-TiO2 filler with amino-phosphate ester-based bifunctional grafting are as follows:

[0012] Take nano-TiO2 powder, add it to anhydrous ethanol solvent, and disperse it by ultrasonication to obtain a uniform 5-8 wt% TiO2 dispersion.

[0013] Add 3-5% (by mass) of 3-aminopropyltriethoxysilane to the above dispersion, place it in a constant temperature water bath at 60℃-80℃ under a nitrogen atmosphere, stir and react, then add 2-3% (by mass) of dimethyl phosphate to the dispersion, and continue stirring and reacting. After the reaction is complete, centrifuge to collect the precipitate, wash the precipitate, and dry it to obtain the functionalized TiO2 filler.

[0014] In S2, the composite slurry preparation process is as follows:

[0015] Preparation of mixed solvent: Measure N,N-dimethylformamide and dimethyl carbonate in a volume ratio of 7-8:2-3, mix them, stir evenly, add 0.3-0.5 wt% of fluoropropylene carbonate, and continue stirring to obtain a stable mixed solvent;

[0016] Ultrasonic dispersion: Add 8-10 wt% TiO2-PN filler to the mixed solvent, disperse ultrasonically, and then mechanically stir to inhibit secondary agglomeration;

[0017] PVDF-HFP dissolution: Add 12-15wt% of PVDF-HFP powder to the above dispersion, with a PVDF to HFP mass ratio of 3-4:3-4. Heat to 60℃-70℃ and mechanically stir until PVDF-HFP is completely dissolved to form a uniform PVDF-HFP / TiO2-PN dispersion.

[0018] PLA solution preparation and compounding: Prepare a PLA solution with a concentration of 8-10 wt% separately; slowly add the PLA solution to the dispersion at 20-30% of the mass of PVDF-HFP, and continue stirring at 60℃-70℃ to obtain a composite slurry without stratification and precipitation.

[0019] In S3, the preparation of the multilayer gradient pore porous membrane includes: substrate pretreatment: a polytetrafluoroethylene (PTFE) vinyl membrane is selected as the supporting substrate and pretreated by plasma to improve the adhesion between the slurry and the substrate;

[0020] Single-layer or multi-layer coating, with a concentration of 22-30% and a thickness of 50μm-150μm.

[0021] After coating, vacuum drying and curing are performed.

[0022] Vacuum degree ≤ -0.095MPa;

[0023] Heat to 40℃ at a rate of 5℃ / min, and hold for 30-60 minutes;

[0024] Heat to 60℃ at a rate of 5℃ / min, and hold for 8-12 hours;

[0025] Post-processing and cutting: After natural cooling to room temperature, the polytetrafluoroethylene film is peeled off to obtain a multilayer gradient pore porous membrane.

[0026] In step S4, the porous membrane is immersed in the electrolyte using a vacuum-pressure alternating immersion process. The specific steps are as follows:

[0027] Use 1.5M[PYR14]+1MMeEt3NBF4 / AN electrolyte and let it stand in an argon atmosphere beforehand to remove trace bubbles;

[0028] Gradient wetting treatment: Place the porous membrane disc into a vacuum pressure impregnation vessel containing 1.5M[PYR14]+1MMeEt3NBF4 / AN electrolyte. First, evacuate to -0.09MPa and maintain for 40-80 minutes to allow air to escape from the membrane pores. Then, introduce argon gas to pressurize to 0.2MPa and maintain for 40-80 minutes to ensure that the electrolyte fully penetrates into each layer of pores.

[0029] The single-layer or multi-layer coating has a concentration of 22-25% and a thickness of 50μm-80μm.

[0030] The single-layer or multi-layer gradient coating has a concentration of 25-28% and a thickness parameter of 100μm-150μm.

[0031] The multi-layer coating has different slurry concentrations and thicknesses in each layer.

[0032] Another technical solution of the present invention is the application of high-voltage quasi-solid-state supercapacitor gel electrolyte in supercapacitors.

[0033] Working mechanism of the present invention:

[0034] Covalent anchoring + multiple interactions: 3-aminopropyltriethoxysilane (KH550) undergoes a hydrolysis-condensation reaction with the hydroxyl groups on the surface of nano-TiO2 to form Si-O-Ti covalent bonds, stabilizing the amino group (-NH2); dimethyl phosphate is activated through hydrogen bonding (with residual hydroxyl and amino groups on the TiO2 surface) and coordination adsorption (phosphate groups adsorbed onto TiO2). 4+ They form a secondary binding layer, which together constructs a bifunctional interface of "amino-phosphate ester".

[0035] Improved interfacial compatibility: The amino group forms hydrogen bonds with the ester groups (-COO-) of the PLA molecular chain and the fluorinated groups (-CF2-, -CF3-) of PVDF-HFP; the phosphate ester groups react with [PYR14] in the electrolyte. + MeEt3N + The coordination effect not only solves the problem of TiO2 filler agglomeration in the polymer matrix, but also builds ion transport bridges and reduces interfacial impedance.

[0036] Concentration-thickness gradient synergy: The multi-layer coating adopts a slurry design of "high concentration (28-30%) on the surface layer + medium concentration (25-28%) in the transition layer + low concentration (22-25%) in the inner layer", combined with a doctor blade gap gradient of "50μm + 100μm + 150μm", so that the porosity after film formation increases in a gradient (surface layer ≤20% → transition layer 30-40% → inner layer 60-70%), forming an ion transport path of "impermeability-transition-high conductivity".

[0037] High-efficiency transmission guarantee: The dense surface structure prevents electrolyte leakage and electrode active material shedding, the transition layer alleviates the ion transmission resistance caused by abrupt changes in pore size, and the porous inner structure maximizes electrolyte storage capacity and ion contact area. The three work together to reduce ion migration energy consumption and improve transmission efficiency.

[0038] Gel network formation: PVDF-HFP and PLA form an interpenetrating polymer network (IPN), with bifunctional modified TiO2-PN serving as physical crosslinking points to enhance network structure stability; immersion in 1.5M [PYR14] +After adding 1MMeEt3NBF4 / AN electrolyte, the polymer network locks the electrolyte through hydrogen bonds and van der Waals forces, forming a leak-free, highly elastic gel state.

[0039] High voltage tolerance mechanism: Phosphate ester groups and BF4 in the electrolyte - The interaction between the electrodes and the electrolyte inhibits the oxidative decomposition of the electrolyte under a high voltage of 4.5V; the multilayer gradient pore structure reduces the direct contact area between the electrodes and the electrolyte, thus reducing the probability of side reactions; the bifunctional groups on the surface of TiO2-PN adsorb trace amounts of moisture and impurities in the electrolyte, further purifying the electrolyte environment and improving high voltage stability.

[0040] Complete removal of air from pores: First, a vacuum is drawn to -0.09 MPa to quickly remove air from the pores inside the multilayer membrane, avoiding the formation of transmission dead zones due to residual air; then, 0.2 MPa argon gas is introduced to pressurize and promote the rapid and uniform penetration of the electrolyte into the gradient channels at each level, especially ensuring sufficient wetting of the high porosity region in the inner layer. Compared with single vacuum wetting, the wetting efficiency is improved by 30%, and the wetting uniformity is significantly optimized.

[0041] The innovative aspects of this invention are as follows:

[0042] Breaking through the limitations of single modification, this method adopts a synergistic modification approach of "covalent grafting (KH550-TiO2) + hydrogen bond-coordination adsorption (dimethyl phosphate-TiO2)", while simultaneously introducing amino and phosphate groups. This approach addresses the three core pain points of filler dispersibility, interfacial compatibility, and ion transport efficiency in one go, resulting in a modification effect far exceeding that of single functional group modification.

[0043] The modification process is precisely matched with the subsequent solvent system (DMF+DMC) and polymer matrix (PVDF-HFP / PLA). The functional groups do not fall off during ultrasonic dispersion, stirring and compounding, multi-layer coating and drying, and continue to play an interfacial regulation role.

[0044] The pioneering layered synergistic coating process precisely constructs a three-level gradient structure of "dense surface layer - transition layer - porous inner layer" through layered initial drying and overall vacuum drying, overcoming the contradiction of traditional single-pore porous membranes that "either leak or have poor conductivity".

[0045] A ternary composite system of PVDF-HFP / PLA / TiO2-PN was constructed. PVDF-HFP provides resistance to electrolyte swelling and porous structure support, PLA enhances mechanical strength and gel elasticity, and TiO2-PN optimizes interfacial performance and ion transport. The three complement each other and break through the performance bottleneck of binary systems.

[0046] Specifically adapted for 1.5M [PYR14] ++1MMeEt3NBF4 / AN electrolyte, through the synergistic effect of bifunctional groups and electrolyte ions, improves ionic conductivity and high voltage stability, solving the industry pain point of poor compatibility between general electrolytes and specific electrolytes.

[0047] The “vacuum-pressure alternating impregnation” process is adopted to precisely match the impregnation requirements of the multi-layer gradient pore structure, ensuring that the electrolyte quickly fills the pores at each level, avoiding the problem of insufficient impregnation in the inner porous areas, while shortening the impregnation time, improving the preparation efficiency, and adapting to large-scale production.

[0048] Compared with the prior art, the present invention has at least the following beneficial effects:

[0049] This invention discloses a method for preparing a gel electrolyte for a high-voltage quasi-solid-state supercapacitor. The porous composite membrane with added TiO2 has a denser surface and more stable structure compared to pure PLA porous membranes, while being more porous than those without TiO2, which facilitates electrolyte wetting. The TiO2-added porous composite membrane also has a wider thickness and a more uniform cross-sectional network structure, which is beneficial for electrolyte dispersion and storage. Compared to pure PLA porous membranes, the TiO2-optimized porous composite membrane has a coarser framework structure, ensuring its structural stability during charge and discharge processes.

[0050] The purpose of using this doctor blade for coating is to ensure the flatness of the film. If it is too thin, it will be uneven, and if it is too thick, it will increase the impedance. Therefore, it is necessary to ensure that the electrolyte can both isolate the two electrodes and store more electrolyte to ensure that ions move quickly between the two electrodes.

[0051] Setting the soaking time ensures that the electrolyte fully absorbs the electrolyte solution. The absorption chart of the liquid electrolyte shows that the absorption volume reaches a stable level after 2 hours.

[0052] This invention features a simple design, a pollution-free and high-temperature-free preparation process, and is safe to use. Compared to pure PLA porous membranes, the TiO2-optimized porous composite membrane has a coarser framework structure, which ensures its structural stability during charge and discharge processes.

[0053] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0054] Figure 1 This is a SEM image of the porous composite membrane of the present invention.

[0055] Figure 2 This is the XRD pattern of the porous composite membrane of the present invention;

[0056] Figure 3 This is a TGA image of the porous composite membrane of the present invention;

[0057] Figure 4 The contact angle of the porous composite membrane of the present invention after the electrolyte is added;

[0058] Figure 5 This is a rate performance diagram of the porous composite membrane GPEs of the present invention at 3.5V;

[0059] Figure 6 The GCD curve of the porous composite membrane of the present invention at 3.5V is shown.

[0060] Figure 7 This is a graph showing the cycling performance of the porous composite membrane of the present invention at 3.5V. Detailed Implementation

[0061] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, 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.

[0062] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0063] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0064] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0065] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0066] In this invention, unless otherwise specified, the numerical range "a~b" represents an abbreviation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "6~22" means that all real numbers between "6~22" have been listed in this document, and "6~22" is just an abbreviation of these numerical combinations.

[0067] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0068] In this invention, the term "and / or" as used herein refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0069] In this invention, unless otherwise stated, the various reactions or operation steps may be performed sequentially or in a particular order. Preferably, the reaction methods described herein are performed sequentially.

[0070] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0071] This invention provides a method for preparing a high-voltage resistant porous composite gel electrolyte, comprising the following steps:

[0072] S1: Amino-phosphate ester-based bifunctional grafting modification of nano-TiO2 filler

[0073] The nano-TiO2 filler was modified by amino-phosphate bifunctional grafting to obtain functionalized TiO2 filler (TiO2-PN).

[0074] Take nano-TiO2 powder (particle size 20-50nm, specific surface area ≥50m²) 2 / g (purity ≥99.8%), added to anhydrous ethanol solvent, placed in an ultrasonic cleaner, and ultrasonically dispersed at 300W power and 40kHz frequency for 15min to obtain a uniform 5-8wt% TiO2 dispersion.

[0075] Add 3-5% (by mass) of 3-aminopropyltriethoxysilane (KH550, amino donor) to the above dispersion, place it in a constant temperature water bath at 60°C under a nitrogen atmosphere, stir and react for 1 hour, then add 2-3% dimethyl phosphate (phosphate ester donor), and continue stirring and reacting for another hour.

[0076] After the reaction was completed, the mixture was transferred to a centrifuge tube and centrifuged at 8000 rpm for 10 min. The precipitate was collected and washed with anhydrous ethanol to remove unreacted KH550 and dimethyl phosphate.

[0077] The washed precipitate was placed in a vacuum drying oven and dried at 80℃ and a vacuum degree ≤ -0.095MPa for 12h to obtain amino-phosphate ester-based bifunctionalized TiO2 filler.

[0078] S2: Preparation of composite slurry

[0079] Preparation of mixed solvent: Measure N,N-dimethylformamide (DMF, purity ≥99.5%) and dimethyl carbonate (DMC, purity ≥99.9%) in a volume ratio of 7:3, pour them into a three-necked flask, stir evenly, add 0.5wt% fluoropropylene carbonate (FPC, cosolvent), and continue stirring for 10 min to obtain a stable mixed solvent;

[0080] TiO2-PN ultrasonic dispersion: Add 8-10 wt% TiO2-PN filler to the mixed solvent, place the three-necked flask in the ultrasonic reactor, and use an intermittent ultrasonic dispersion process (40℃, 400W power, 5 min working / 1 min pause, total duration 45-60 min) to ensure that the particle size of the filler is ≤200 nm. Stir mechanically at 300 rpm for 30 min to inhibit secondary agglomeration.

[0081] PVDF-HFP dissolution: Add 12-15wt% of PVDF-HFP powder to the above dispersion, place the three-necked flask in a 60℃ oil bath, and mechanically stir at 500rpm for 3-4h until PVDF-HFP is completely dissolved to form a uniform PVDF-HFP / TiO2-PN dispersion.

[0082] PLA solution preparation and composite: Prepare PLA solution separately: Take polylactic acid (PLA, purity ≥98%) with a molecular weight of 50,000-100,000, add it to DMF solvent, stir at 40℃ for 30 min until completely dissolved, and obtain a PLA solution with a concentration of 8-10 wt%; slowly add the PLA solution dropwise to PVDF-HFP / TiO2-PN dispersion at 20-30% of the mass of PVDF-HFP, and continue stirring at 60℃ for 1 h to obtain a uniform, transparent composite slurry without stratification and precipitation.

[0083] S3: Preparation of multilayer gradient pore porous membranes

[0084] Substrate pretreatment: Polytetrafluoroethylene (PTFE) base film is selected as the supporting substrate and pretreated with plasma (100W power, 3min time) to improve the adhesion between the slurry and the substrate;

[0085] Single-layer coating: Composite slurry concentration 25-28%, blade gap 100μm, initial drying at room temperature with low-speed forced air for 20 minutes to form a low-porosity layer; or

[0086] Multi-layer gradient coating: Using an adjustable doctor blade casting machine, coating is performed in layers according to the following concentration gradient and thickness parameters:

[0087] First layer (surface layer): Composite slurry concentration 28-30%, scraper gap 50μm, after scraping, it is initially dried for 30 minutes in a room temperature and humidity ≤40%RH environment with low speed air blowing (wind speed 0.5m / s) to form a dense barrier layer;

[0088] Second layer (transition layer): Composite slurry concentration 25-28%, scraper gap 100μm, scraped onto the surface of the first layer, and initially dried at room temperature and low speed for 20 minutes to form a low porosity transition layer.

[0089] Third layer (inner layer): Composite slurry concentration 22-25%, scraper gap 150μm, scraped onto the surface of the transition layer, initially dried at room temperature and low speed for 15min to form a high porosity conductive layer.

[0090] Vacuum drying and curing: The multi-layer coated base film is transferred into a vacuum drying oven and dried using a programmed temperature rise drying process (vacuum degree ≤ -0.095MPa).

[0091] Heat to 40℃ at 5℃ / min and hold for 1 hour (to initially remove solvent);

[0092] Heat to 60℃ at 5℃ / min and hold for 2 hours (to induce gradient pore structure formation).

[0093] Heat to 100℃ at 3℃ / min and hold for 4 hours (to deeply remove residual solvent).

[0094] Post-processing and cutting: After natural cooling to room temperature, the base film is immersed in 40℃ deionized water for 5 minutes, and the PTFE base film is gently peeled off to obtain a multilayer gradient pore porous membrane; it is then cut into circular pieces with a diameter of 14mm (thickness 180-220μm, thickness deviation ≤±5μm). S4: Vacuum-pressure alternating wetting and supercapacitor assembly.

[0095] Use 1.5M [PYR14] + 1MMeEt3NBF4 / AN electrolyte (purity ≥99.9%, moisture content ≤5ppm, measured by Karl Fischer moisture analyzer), and let it stand in an argon atmosphere for 2 hours in advance to remove trace bubbles.

[0096] Gradient wetting treatment: The multilayer gradient pore porous membrane disc was placed in a vacuum pressure impregnation vessel containing 1.5M [PYR14] + 1MMeEt3NBF4 / AN electrolyte. First, the vacuum was evacuated to -0.09MPa and maintained for 1 hour to allow air to be expelled from the membrane pores. Then, argon gas was introduced to pressurize to 0.2MPa and maintained for 1 hour to ensure that the electrolyte fully penetrated into each layer of pores.

[0097] The electrolyte surface is wiped dry for use in assembling high-voltage supercapacitors.

[0098] In this invention, functional TiO2 is added to a porous composite membrane to enhance the electrochemical window of GPEs. The porous composite membrane with added TiO2 is denser and more stable than pure PLA membrane, and has a wider thickness, which is beneficial for electrolyte dispersion and storage. Moreover, it has a coarser framework structure, ensuring greater stability during charge and discharge.

[0099] Through comparative analysis of physicochemical properties and elemental energy dispersive spectroscopy analysis, it can be observed that Ti and O are uniformly distributed on the surface and cross-section of the thin film, such as... Figure 1As shown, the dispersibility of functionalized TiO2 in the polymer was verified. The presence of TiO2 was also confirmed by XRD pattern analysis, such as... Figure 2 As shown.

[0100] Figure 3 The stability of porous composite membranes before and after the addition of functionalized TiO2 was compared. The thermal stability of the composite membranes before and after the addition of functionalized TiO2 was compared and it was found that the addition of functionalized TiO2 can improve the high temperature stability of the polymer to a certain extent.

[0101] By comparing the contact angle differences of porous composite membranes before and after the addition of functionalized TiO2, the changes in pore morphology on the film surface can be determined. TiO2 dielectric material can enhance the affinity of the film for the electrolyte, thus giving the composite membrane better wettability. Contact angle tests were conducted on the electrolyte, such as... Figure 4 As shown, the porous composite membrane with added functionalized TiO2 has a smaller contact angle. At the same time, the addition of functionalized TiO2 can change the surface morphology of the film, increase the pore size to a certain extent, and thus promote the penetration of electrolyte.

[0102] The electrochemical performance of two porous composite electrolytes was compared using a high-voltage electrolyte to verify the high voltage stability of the functionalized TiO2 porous composite electrolyte.

[0103] The performance of the prepared electrolyte in supercapacitors was evaluated by the capacitance retention rate under different current densities, and it was found that... Figure 5 The results show that as the current density increases, the SC specific capacitance of the functionalized TiO2-optimized electrolyte assembly increases slightly, while maintaining good capacitance performance at 8 Ag⁻¹. In contrast, the specific capacitance of the unoptimized electrolyte significantly decreases at 8 Ag⁻¹, making it unsuitable for charge-discharge operation at high current densities. This clearly demonstrates the significant value of functionalized TiO2 in improving the rate performance of electrolytes.

[0104] By comparing the GCD curves of the 1st cycle, the 500th cycle, and the 10000th cycle, as shown... Figure 6 As shown, the SC prepared with the porous composite membrane containing functionalized TiO2 maintains a symmetrical triangular charge-discharge curve even under long-term cycling, while the charge-discharge time of the sample without TiO2 is significantly shortened after 5000 cycles, approaching the charge-discharge time of the 10000th cycle, highlighting its inferior cycle stability. By comparing the long-term cycling performance of the samples before and after optimization, Figure 7 It can be seen that although the electrolyte with added functionalized TiO2 has a larger equivalent series resistance, the electrolyte capacitance retention rate under long cycling is very similar to that of the sample without added TiO2 (both are around 80.0%), indicating the electrochemical stability of functionalized TiO2 under high voltage.

[0105] In summary, this invention successfully prepared a porous PLA / PVDF-HFP composite gel electrolyte for SCs using a solvent-free phase separation method. This effectively solved the environmentally unfriendly characteristics of pure PVDF-HFP membranes and enhanced the stability of PLA membranes in organic electrolyte applications. The high-performance GPEs prepared in this work provide new insights into the practical application of environmentally friendly polymer electrolytes in wearable devices and represent a decisive step forward in the research of replacing petrochemical polymer electrolytes with renewable polymers. The main points are summarized below:

[0106] The porous polymer membrane was modified by introducing PVDF-HFP into the PLA framework. PVDF-HFP acts as a modifier to connect the porous PLA framework, thereby improving the stability of the porous structure and solving the problem of slight solubility of pure PLA membrane in acetonitrile-based electrolyte.

[0107] To achieve stability of porous composite membranes under high operating voltages, functionalized TiO2 was added to optimize the electrochemical performance of the porous composite membrane. The improved porous composite membrane has a uniform pore structure and better electrolyte wettability, while also exhibiting lower self-discharge and leakage current, thus improving the operating stability under high voltages and effectively reducing energy loss.

[0108] The functionalized TiO2-optimized GPE exhibits excellent electrochemical stability under high operating voltage. It not only maintains 100% of the initial specific capacitance under test conditions of 3.5V and 8Ag-1, but also retains 80.0% of the capacitance after 10,000 cycles at 1Ag-1, which fully demonstrates the feasibility of the optimized porous composite membrane for application under high operating voltage.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0110] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0111] Examples 1-4.

[0112] Serial Number Example 1 (Single-layer foundation type) Example 2 (Single-layer conventional type) Example 3 (Single-layer high-modification type) Example 4 (Single-layer high PLA type) I. S1 Dual-Function Modified Material Parameters <![CDATA[Nano-TiO2 powder]]> <![CDATA[Particle size 20 nm, specific surface area 50 m 2 / g, purity 99.8%]]> <![CDATA[Particle size 30 nm, specific surface area 60 m 2 / g, purity 99.8%]]> <![CDATA[Particle size 50nm, specific surface area 80m 2 / g, purity 99.8%]]> <![CDATA[Particle size 40nm, specific surface area 70m 2 / g, purity 99.8%]]> <![CDATA[TiO2 dispersion concentration]]> 5wt% (using anhydrous ethanol as solvent) 6wt% (using anhydrous ethanol as solvent) 8wt% (anhydrous ethanol as solvent) 7wt% (using anhydrous ethanol as solvent) KH550 addition amount <![CDATA[3% by mass of TiO2]]> <![CDATA[4% TiO2 mass]]> <![CDATA[5% TiO2 mass]]> <![CDATA[Mass of TiO2: 4.5%]]> Dimethyl phosphate addition amount <![CDATA[2% TiO2 mass]]> <![CDATA[2.5% TiO2 mass]]> <![CDATA[3% by mass of TiO2]]> <![CDATA[Mass of TiO2: 2.8%]]> Modification reaction conditions Under a nitrogen atmosphere at 60℃, react first with KH550 for 1 hour, then add dimethyl phosphate and react for another hour. Under a nitrogen atmosphere at 60℃, react first with KH550 for 1 hour, then add dimethyl phosphate and react for another hour. Under a nitrogen atmosphere at 60℃, react first with KH550 for 1 hour, then add dimethyl phosphate and react for another hour. Under a nitrogen atmosphere at 60℃, react first with KH550 for 1 hour, then add dimethyl phosphate and react for another hour. Vacuum drying conditions 80℃, -0.095MPa, 12h 80℃, -0.095MPa, 12h 80℃, -0.095MPa, 12h 80℃, -0.095MPa, 12h II. S2 Composite Slurry Material Parameters Mixed solvent ratio (DMF:DMC) Volume ratio 7:3 Volume ratio 7:3 Volume ratio 7:3 Volume ratio 7:3 Cosolvent FPC addition amount 0.5wt% (based on mixed solvent) 0.5wt% (based on mixed solvent) 0.5wt% (based on mixed solvent) 0.5wt% (based on mixed solvent) <![CDATA[TiO2-P-N addition amount]]> 8wt% (based on mixed solvent) 9wt% (based on mixed solvent) 10wt% (based on mixed solvent) 9.5wt% (based on mixed solvent) Ultrasonic dispersion parameters 40℃, 400W, intermittent (5min / 1min), 45min 40℃, 400W, intermittent (5min / 1min), 50min 40℃, 400W, intermittent (5min / 1min), 60min 40℃, 400W, intermittent (5min / 1min), 55min PVDF-HFP addition amount 12wt% (based on mixed solvent), molecular weight 500,000, HFP content 12mol%. 13wt% (based on mixed solvent), molecular weight 600,000, HFP content 13mol%. 15wt% (based on mixed solvent), molecular weight 800,000, HFP content 15mol%. 14wt% (based on mixed solvent), molecular weight 700,000, HFP content 14mol%. PLA solution parameters Molecular weight 50,000, concentration 8 wt% (DMF as solvent), addition amount 20% of PVDF-HFP mass. Molecular weight 70,000, concentration 9 wt% (DMF as solvent), addition amount 25% of PVDF-HFP mass. Molecular weight 80,000, concentration 10 wt% (DMF as solvent), addition amount 25% of PVDF-HFP mass. Molecular weight 100,000, concentration 10 wt% (DMF as solvent), addition amount 30% of PVDF-HFP mass. Final solids content of composite slurry 23wt% 25wt% 28wt% 26wt% III. S3 Single-Layer Film Forming Materials and Process Parameters Substrate pretreatment PTFE base film, plasma 100W, 3min PTFE base film, plasma 100W, 3min PTFE base film, plasma 100W, 3min PTFE base film, plasma 100W, 3min Scraping type Single-layer scraping Single-layer scraping Single-layer scraping Single-layer scraping Single-layer slurry concentration 23wt% 25wt% 28wt% 26wt% scraper gap 100μm 120μm 150μm 130μm Initial conditions Room temperature and humidity ≤40%RH, low-speed blower (0.5m / s), 20min Room temperature and humidity ≤40%RH, low-speed blower (0.5m / s), 20min Room temperature and humidity ≤40%RH, low-speed blower (0.5m / s), 25min Room temperature, humidity ≤40%RH, low-speed blower (0.5m / s), 22min IV. S4 Immersion and Assembly Parameters Electrolyte specifications <![CDATA[1.5M[PYR14] + +1MMeEt3NBF4 / AN, purity 99.9%, moisture ≤5ppm <![CDATA[1.5M[PYR14] + +1MMeEt3NBF4 / AN, purity 99.9%, moisture ≤5ppm <![CDATA[1.5M[PYR14] + +1MMeEt3NBF4 / AN, purity 99.9%, moisture ≤5ppm <![CDATA[1.5M[PYR14] + +1MMeEt3NBF4 / AN, purity 99.9%, moisture ≤5ppm Immersion process conditions Vacuum -0.09MPa (1h) → Pressurized to 0.2MPa (1h) Vacuum -0.09MPa (1h) → Pressurized to 0.2MPa (1h) Vacuum -0.09MPa (1h) → Pressurized to 0.2MPa (1h) Vacuum -0.09MPa (1h) → Pressurized to 0.2MPa (1h)

Claims

1. A method for preparing a high-voltage resistant porous composite gel electrolyte, characterized in that, Includes the following steps: S1: The nano-TiO2 filler was modified by amino-phosphate ester bifunctional grafting to obtain functionalized TiO2 filler; S2: Prepare a mixed solvent of N,N-dimethylformamide and dimethyl carbonate, add functionalized TiO2 filler for ultrasonic dispersion, then add PVDF-HFP for uniform stirring, and finally add the mixed PVDF-HFP solution to polylactic acid PLA solution for uniform mixing to obtain a mixed slurry; S3: The obtained mixed slurry is uniformly coated with one or more layers by a doctor blade casting method. When multiple layers are coated, each layer is initially dried before the next layer is coated. Then the mixture is moved into a vacuum environment and dried further to obtain a porous membrane. S4: The porous membrane is immersed in the electrolyte using a vacuum-pressure alternating immersion process. The electrolyte is then removed and its surface is dried for use in assembling high-voltage supercapacitors.

2. The method for preparing high-voltage resistant porous composite gel electrolyte according to claim 1, characterized in that, In S1, the specific steps for modifying the nano-TiO2 filler with amino-phosphate ester-based bifunctional grafting are as follows: Take nano-TiO2 powder, add it to anhydrous ethanol solvent, and disperse it by ultrasonication to obtain a uniform 5-8 wt% TiO2 dispersion. Add 3-5% (by mass) of 3-aminopropyltriethoxysilane to the above dispersion, place it in a constant temperature water bath at 60℃-80℃ under a nitrogen atmosphere, stir and react, then add 2-3% (by mass) of dimethyl phosphate to the dispersion, and continue stirring and reacting. After the reaction is complete, centrifuge to collect the precipitate, wash the precipitate, and dry it to obtain the functionalized TiO2 filler.

3. The method for preparing high-voltage resistant porous composite gel electrolyte according to claim 1, characterized in that, In S2, the composite slurry preparation process is as follows: Preparation of mixed solvent: Measure N,N-dimethylformamide and dimethyl carbonate in a volume ratio of 7-8:2-3, mix them, stir evenly, add 0.3-0.5 wt% of fluoropropylene carbonate, and continue stirring to obtain a stable mixed solvent; Ultrasonic dispersion: Add 8-10 wt% TiO2-PN filler to the mixed solvent, disperse ultrasonically, and then mechanically stir to inhibit secondary agglomeration; PVDF-HFP dissolution: Add 12-15wt% of PVDF-HFP powder to the above dispersion, with a PVDF to HFP mass ratio of 3-4:3-4. Heat to 60℃-70℃ and mechanically stir until PVDF-HFP is completely dissolved to form a uniform PVDF-HFP / TiO2-PN dispersion. PLA solution preparation and compounding: Prepare a PLA solution with a concentration of 8-10 wt% separately; slowly add the PLA solution to the dispersion at 20-30% of the mass of PVDF-HFP, and continue stirring at 60℃-70℃ to obtain a composite slurry without stratification and precipitation.

4. The method for preparing high-voltage resistant porous composite gel electrolyte according to claim 1, characterized in that, In S3, the preparation of the multilayer gradient pore porous membrane includes: substrate pretreatment: a polytetrafluoroethylene (PTFE) vinyl membrane is selected as the supporting substrate and pretreated by plasma to improve the adhesion between the slurry and the substrate; Single-layer or multi-layer coating, with a concentration of 22-30% and a thickness of 50μm-150μm.

5. The method for preparing high-voltage resistant porous composite gel electrolyte according to claim 1, characterized in that, After coating, vacuum drying and curing are performed. Vacuum degree ≤ -0.095MPa; Heat to 40℃ at a rate of 5℃ / min, and hold for 30-60 minutes; Heat to 60℃ at a rate of 5℃ / min, and hold for 8-12 hours; Post-processing and cutting: After natural cooling to room temperature, the polytetrafluoroethylene film is peeled off to obtain a multilayer gradient pore porous membrane.

6. The method for preparing high-voltage resistant porous composite gel electrolyte according to claim 1, characterized in that, In step S4, the porous membrane is immersed in the electrolyte using a vacuum-pressure alternating immersion process. The specific steps are as follows: Use 1.5M[PYR14]+1MMeEt3NBF4 / AN electrolyte and let it stand in an argon atmosphere beforehand to remove trace bubbles; Gradient wetting treatment: Place the porous membrane disc into a vacuum pressure impregnation vessel containing 1.5M[PYR14]+1MMeEt3NBF4 / AN electrolyte. First, evacuate to -0.09MPa and maintain for 40-80 minutes to allow air to escape from the membrane pores. Then, introduce argon gas to pressurize to 0.2MPa and maintain for 40-80 minutes to ensure that the electrolyte fully penetrates into each layer of pores.

7. The method for preparing high-voltage resistant porous composite gel electrolyte according to claim 4, characterized in that, The single-layer or multi-layer coating has a concentration of 22-25% and a thickness of 50μm-80μm.

8. The method for preparing high-voltage resistant porous composite gel electrolyte according to claim 4, characterized in that, The single-layer or multi-layer gradient coating has a concentration of 25-28% and a thickness parameter of 100μm-150μm.

9. The method for preparing high-voltage resistant porous composite gel electrolyte according to claim 4, characterized in that, The multi-layer coating has different slurry concentrations and thicknesses in each layer.

10. The application of the high-voltage resistant porous composite gel electrolyte prepared by the method described in claim 1 in supercapacitors.

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