A starch-polyiodide composite solid electrolyte membrane and a preparation method thereof

Abstract

The application belongs to the technical field of lithium metal batteries and photoelectrochemical energy storage, and discloses a starch-polyiodide composite solid electrolyte film and a preparation method thereof. The electrolyte film takes a polymer as a matrix, lithium bisfluorosulfonylimide and the like as a lithium salt, and a mixture of soluble branched starch, lithium iodide and iodine as a redox composite filler. Through the synergistic effect of the soft support effect of starch and the iodine-based redox pair, a uniform mixed conductive network is constructed, which can effectively reduce the interface impedance, inhibit the polymer crystallization, and significantly improve the ionic conductivity, lithium ion transference number and mechanical flexibility. The application further provides an integrated flexible photoelectrochemical energy storage battery device. The positive electrode-electrolyte integration is realized through an in-situ coating process, so that the device can still work stably under repeated bending and folding, and has high-efficiency light charging function, thereby providing a high-performance and high-safety solid electrolyte solution for the flexible light charging lithium metal battery.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a starch-polyiodide composite solid electrolyte membrane and its preparation method. Background Technology

[0002] With the rapid rise of emerging fields such as wearable electronics and flexible robots, the market demand for flexible energy storage systems continues to climb, while placing higher demands on the energy density, mechanical flexibility, and safety reliability of energy storage devices. All-solid-state lithium metal batteries, with their significantly higher energy density than traditional liquid lithium-ion batteries and their high safety advantages of no leakage and non-flammability, are widely recognized as the most promising alternative technology in the field of flexible energy storage, becoming a core breakthrough in solving the battery life and safety issues of flexible electronic devices. Solid-state electrolytes, as the core component of all-solid-state lithium metal batteries, directly determine the battery's energy density, cycle stability, and mechanical adaptability. Currently, solid-state electrolytes are mainly divided into two categories: inorganic solid-state electrolytes and polymer solid-state electrolytes. Among them, inorganic solid-state electrolytes based on oxides or sulfides, although possessing high ionic conductivity and a wide electrochemical window, have significant inherent defects—high brittleness, high rigidity, and high grain boundary resistance—making them unable to withstand the repeated bending and folding mechanical deformations required by flexible devices. Furthermore, they require stringent precision in manufacturing processes and high electrode-electrolyte interface contact quality, greatly limiting their large-scale practical application in flexible electronic devices.

[0003] In polymer solid electrolytes, polyvinylidene fluoride (PVDF) and its copolymers (such as PVDF-trifluoroethylene copolymer P(VDF-TrFE)) have become a research hotspot in the field of flexible solid electrolytes due to their high dielectric constant, excellent mechanical strength, and good thermal stability. However, pure polymer solid electrolytes still have many bottlenecks: the ionic conductivity at room temperature is low, which is difficult to meet the requirements of practical applications; the high crystallinity of polymer molecular chains hinders the free migration of lithium ions, further limiting ion transport efficiency; in addition, the interfacial compatibility between the polymer matrix and the lithium metal anode and high-voltage cathode is poor, which easily forms interfacial impedance during battery cycling, leading to increased battery polarization, a significant decrease in cycle life, and seriously affecting the long-term stable operation of the device.

[0004] To address these issues, constructing composite solid electrolytes and introducing functional fillers to reduce polymer crystallinity and build rapid ion transport channels have become mainstream strategies for modifying polymer solid electrolytes. However, traditional modification methods still have significant limitations: while inorganic ceramic fillers can improve ionic conductivity to some extent, they significantly reduce the mechanical flexibility of the film, and the fillers are prone to agglomeration, which in turn disrupts the uniformity of the ion transport network; conventional organic fillers, on the other hand, make it difficult to achieve a synergistic improvement in ionic conductivity and mechanical properties.

[0005] In recent years, the rise of "photovoltaic charging" self-powered technology has injected new vitality into the development of flexible energy storage devices and has also placed higher demands on the multifunctionality of solid electrolytes. They not only need to possess excellent ionic conductivity and mechanical flexibility, but also need to be adaptable to the photoelectrochemical conversion process and even assist in improving photoelectric conversion efficiency. This has become the core key to realizing the integration of self-powered flexible batteries. Therefore, breaking through traditional modification approaches and exploring polymer electrolytes modified with biomass soft fillers or redox media, and developing composite solid electrolyte membranes with high safety, high electrochemical performance, and good mechanical flexibility from a new perspective, has significant theoretical and practical application value for promoting the research and industrialization of next-generation flexible photoelectrochemical energy storage devices. Summary of the Invention

[0006] To overcome the shortcomings of existing solid electrolytes, this invention, based on the design concept of biomass modification and redox enhancement, provides a starch-polyiodide composite solid electrolyte membrane and its preparation method. The aim is to construct a uniform and efficient ion transport network by using soluble amylopectin as a biomass soft scaffold and combining it with the synergistic effect of the iodine / lithium iodide redox pair. This solves the technical problems of low ionic conductivity, high interfacial impedance, and insufficient mechanical flexibility in existing solid electrolytes, ultimately obtaining a composite solid electrolyte membrane with high ionic conductivity, high lithium-ion transference number, and excellent mechanical flexibility to meet the integration requirements of flexible optoelectronic energy storage devices.

[0007] The present invention first provides a starch-polyiodide composite solid electrolyte membrane, comprising a polymer matrix material, a lithium salt, and a redox composite filler.

[0008] The polymer matrix material is selected from one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-TrFE), and poly(vinylidene fluoride-trifluoroethylene) copolymer (P(VDF-TrFE)), preferably poly(vinylidene fluoride-trifluoroethylene) copolymer (P(VDF-TrFE)), wherein the molar ratio of PVDF units to trifluoroethylene units is 80 / 20, and the weight-average molecular weight is approximately 4.5 × 10⁻⁶. 5 g / mol.

[0009] The redox composite filler is a mixture of soluble amylopectin, lithium iodide (LiI), and elemental iodine (I2) in a mass ratio of 1 to 5:5:5.

[0010] As a further preferred option, the lithium salt is lithium bisfluorosulfonylimide (LiFSI).

[0011] As a further preferred embodiment, the mass ratio of the polymer matrix material to the lithium salt is 5:1 to 5, and the mass of the redox composite filler accounts for 5% to 25% of the total mass of the composite solid electrolyte membrane.

[0012] This invention also provides a method for preparing the starch-polyiodide composite solid electrolyte membrane, which is prepared by solution casting. The method includes: adding a polymer matrix material, a lithium salt, and a redox composite filler to a mixed solvent of N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) (volume ratio 1:0.5-2), and stirring at 50-60°C for 5-10 hours until a uniform slurry is formed. The resulting slurry is then coated onto a substrate and vacuum dried at 45-55°C for 12-24 hours to obtain the starch-polyiodide composite solid electrolyte membrane.

[0013] As a further preferred embodiment, the mixed solvent is composed of DMF and DMSO mixed in a volume ratio of 1:1.

[0014] As a further preferred option, the coating is performed using a thin-film coater, and the wet film thickness is controlled to be 100~300 micrometers.

[0015] The present invention further provides a flexible photoelectrochemical energy storage battery device, which is assembled from a photoelectric storage positive electrode (PSC), a negative electrode, a solid electrolyte membrane and a current collector, wherein the solid electrolyte membrane adopts the above-mentioned starch-polyiodide composite solid electrolyte membrane.

[0016] As a further preferred embodiment, the photovoltaic energy storage cathode is prepared from the following components by mass fraction: 60 wt.% lithium iron phosphate (LFP); 10 wt.% titanium dioxide (TiO2); 10 wt.% lead-free perovskite material (Cs3Bi2I9); 10 wt.% carbon nanotubes; and 10 wt.% polyvinylidene fluoride (PVDF). The above components are dispersed in N-methylpyrrolidone, coated onto the surface of the current collector, and vacuum dried at 60°C to obtain the photovoltaic energy storage cathode.

[0017] As a further preferred embodiment, the current collector is an indium tin oxide (ITO) transparent conductive film. The negative electrode is an ultra-thin lithium foil with a thickness of 10-20 micrometers.

[0018] The flexible photoelectrochemical energy storage battery device is assembled as follows: starch-polyiodide composite solid electrolyte slurry is directly coated in situ onto the surface of the photoelectrochemical positive electrode, vacuum dried to form an integrated positive electrode-electrolyte structure, and then bonded to an ultra-thin lithium metal foil negative electrode. The device is then encapsulated with a transparent PET plastic film to obtain the flexible photoelectrochemical energy storage battery device.

[0019] The beneficial technical effects of this invention are reflected in the following aspects: 1. The starch-polyiodide composite solid electrolyte membrane of the present invention introduces an iodine / lithium iodide redox pair into a polymer matrix such as P(VDF-TrFE), and utilizes the shuttle effect of iodine ions to construct a highly efficient mixed conductive network, thereby effectively regulating the dissociation behavior and ion migration mechanism of lithium salts in the electrolyte and significantly reducing the charge transport barrier.

[0020] 2. Under the condition of maintaining high electrochemical stability, this invention introduces soluble amylopectin, a biomass resource with good biocompatibility, rich functional groups and renewable resources, as a network framework. It not only utilizes its abundant polar groups to promote lithium-ion transport, but also effectively makes up for the defects of traditional inorganic fillers that are easy to agglomerate and have high rigidity, thus enhancing the mechanical flexibility of the membrane.

[0021] 3. Compared with traditional pure polymer electrolytes, this synergistic strategy of biomass modification and redox enhancement has shown a highly efficient promoting effect in improving electrolyte / electrode solid-solid interface contact, significantly reducing interfacial impedance and thus accelerating electrochemical kinetic processes, effectively improving ionic conductivity and lithium-ion transference number at room temperature.

[0022] 4. This invention employs integrated in-situ coating and transparent flexible soft-pack battery assembly technology, combined with a starch-polyiodide composite solid electrolyte membrane to assemble a photoelectrochemical energy storage device, which realizes direct capture and storage of light energy (photocharging). Even under repeated bending and folding mechanical deformation, it can still exhibit stable voltage output and excellent cycle stability. Attached Figure Description

[0023] Figure 1 This is a diagram illustrating the mechanism of action of the starch-polyiodide composite solid electrolyte membrane of the present invention. Figure 2 This is a schematic diagram of the structure of the flexible photoelectrochemical energy storage battery of the present invention; Figure 3 This is a scanning electron microscope image of the starch-polyiodide composite solid electrolyte membrane prepared in Example 1 of this invention; Figure 4 The Fourier transform infrared spectrum of the starch-polyiodide composite solid electrolyte membrane prepared in Example 1 of this invention; Figure 5 This is the X-ray diffraction pattern of the starch-polyiodide composite solid electrolyte membrane prepared in Example 1 of this invention; Figure 6 This is a scanning electron microscope image of the integrated positive electrode-electrolyte structure prepared in Example 1 of this invention; Figure 7 This is an Arenius diagram of the ionic conductivity of the solid electrolyte membranes prepared in Examples 1, 1, 2 and 3 of this invention. Figure 8These are stress-strain test curves of the solid electrolyte membranes prepared in Embodiment 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 of the present invention. Figure 9 This is a time-current graph of the ion transport number of the starch-polyiodide composite solid electrolyte membrane prepared in Example 1 of the present invention. Figure 10 This is a time-current graph of the ion transport number of the pure polymer solid polymer electrolyte membrane prepared in Comparative Example 1 of this invention; Figure 11 This is a time-current plot of the ion transport number of the polymer solid electrolyte membrane modified with a single soluble amylopectin prepared in Comparative Example 2 of this invention. Figure 12 This is a time-current plot of the ion transport number of the single iodine-modified polymer solid electrolyte membrane prepared in Comparative Example 3 of this invention. Figure 13 This is a time-voltage curve of the solid electrolyte membrane prepared in Examples 1, 1, 2 and 3 of the present invention.

[0024] Figure 14 This is a constant current charging curve of the starch-polyiodide composite solid electrolyte membrane prepared in Example 1 of the present invention under light / dark conditions.

[0025] Figure 15 This is a constant current charging curve of the pure polymer solid polymer electrolyte membrane prepared in Comparative Example 1 of the present invention under light / dark conditions.

[0026] Figure 16 This is a capacity-voltage curve of the starch-polyiodide composite solid electrolyte membrane prepared in Example 1 of the present invention under light / dark conditions.

[0027] Figure 17 This is a capacity-voltage curve of the pure polymer solid polymer electrolyte membrane prepared in Comparative Example 1 of the present invention under light / dark conditions.

[0028] Figure 18 This is a time-voltage diagram of the flexible photoelectrochemical energy storage battery prepared in Example 1 of the present invention, showing charging under light and discharging under 0.5C darkness conditions.

[0029] Figure 19 This is a performance curve of the flexible photoelectrochemical energy storage battery prepared in Example 1 of the present invention under illumination at a current density of 1C. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, in order to more clearly illustrate the technical solution of the present invention, rather than limiting the scope of protection of the present invention.

[0031] The mechanism of action of the starch-polyiodide composite solid electrolyte membrane in this invention is as follows: Figure 1 As shown. In traditional polyvinylidene fluoride solid polymer electrolytes, highly crystalline regions hinder the dissociation of lithium salts and the chain movement of lithium ions, resulting in low room-temperature ionic conductivity; simultaneously, the high impedance of the solid-solid interface between the electrode and the electrolyte is also a key factor limiting its performance. This invention introduces soluble amylopectin and an iodine-based redox couple for synergistic modification, wherein: soluble amylopectin, as a hydroxyl-rich biomass "soft scaffold," can effectively disrupt the crystallinity of the polymer matrix, providing more amorphous regions to facilitate ion transport; the redox couple formed by lithium iodide and elemental iodine (I2...) - / I3 - This process can construct a uniform mixed conductive network within the electrolyte. This redox medium not only lowers the charge transport barrier but also facilitates rapid charge transfer at the interface under illumination, significantly reducing interfacial impedance. Based on the synergistic mechanism of biomass modification and redox enhancement, the starch / iodine system was designed as a composite filler to simultaneously enhance the electrochemical kinetics and mechanical flexibility of the solid polymer electrolyte.

[0032] The structure of the flexible photoelectrochemical energy storage battery in this invention is as follows: Figure 2 As shown, a transparent indium tin oxide (ITO) conductive film is used as the current collector to ensure light transmittance and flexibility. The main body of the battery consists of a transparent ITO conductive film, a photoelectric storage positive electrode (PSC), a starch-polyiodide composite solid electrolyte membrane, and a negative electrode (ultra-thin lithium metal foil). The photoelectric storage positive electrode contains lithium iron phosphate (LFP), titanium dioxide (TiO2), lead-free perovskite (Cs3Bi2I9), carbon nanotubes, and polyvinylidene fluoride (PVDF), which can realize the integration of light energy capture and electrical energy storage.

[0033] Example 1 This embodiment first prepared a starch-polyiodide composite solid electrolyte membrane, then prepared a photoelectric energy storage cathode, and further assembled an integrated flexible photoelectric chemical energy storage battery device based on it. The specific operation steps are as follows: 1. Mix N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) in a volume ratio of 1:1 to form a mixed solvent. Add 0.3g of lithium bis(fluorosulfonyl)imide (LiFSI) and 0.5g of poly(vinylidene fluoride-trifluoroethylene) copolymer (P(VDF-TrFE)) to the above mixed solvent and stir until completely dissolved.

[0034] 2. Soluble amylopectin, lithium iodide (LiI) and elemental iodine (I2) are weighed and mixed evenly in a mass ratio of 3:5:5 to obtain a redox composite filler.

[0035] 3. Disperse the above-mentioned redox composite filler, with a mass fraction of 15% (accounting for 15% of the total mass of the starch-polyiodide composite solid electrolyte membrane), into the polymer solution prepared in step 1. Stir the mixed solution at 50°C for 6 hours until a uniform, bubble-free brown slurry is formed.

[0036] 4. The above-mentioned mixed slurry is uniformly coated onto a smooth glass plate (for performance testing) or directly coated onto the prepared photovoltaic storage cathode surface (for integrated battery assembly), and then vacuum dried at 55°C for 24 hours to obtain a starch-polyiodide composite solid electrolyte membrane. A scanning electron microscope image of this electrolyte membrane is shown below. Figure 3 The results showed that the composite solid electrolyte membrane had a uniform and dense surface, without obvious pores, cracks, or particle agglomeration. The microstructure was fine and continuously distributed, indicating that the soluble amylopectin and iodine redox pairs were well dispersed in the P(VDF-TrFE) matrix, forming continuous and stable ion transport channels and ensuring excellent mechanical integrity. Fourier transform infrared spectroscopy (FTIR)... Figure 4 In the X-ray diffraction pattern, the characteristic peaks of the polymer's all-trans crystalline phase (TTTT) were relatively weakened, while the characteristic peaks of the polar / amorphous phases, T3GT3G' and TGTG', were significantly enhanced, confirming that soluble amylopectin effectively disrupted the long-range ordered crystalline structure of the polymer, increased the proportion of amorphous regions, and thus promoted lithium-ion transport; Figure 5 In the study, only a broadened diffuse peak was observed at 2θ≈20°, with no obvious sharp crystalline peaks, further indicating that the polymer crystallinity was significantly reduced. Moreover, the soluble amylopectin, iodine-based filler and other components were uniformly distributed in the matrix in a highly dispersed or amorphous state, without introducing agglomeration crystallization defects. The above microstructure and structural characterization results jointly verified the compactness, low crystallinity and uniform component dispersion of the composite electrolyte membrane of the present invention, laying the structural foundation for its high-performance ion transport and excellent mechanical flexibility.

[0037] 5. First, Cs3Bi2I9 perovskite powder was prepared by reacting BiI3 and CsI in DMF / DMSO and then vacuum drying. Subsequently, 60 wt.% LFP, 10 wt.% TiO2, 10 wt.% Cs3Bi2I9, 10 wt.% carbon nanotubes, and 10 wt.% PVDF binder were dispersed in NMP and stirred to form a homogeneous slurry. Using a 150-micron thin film stretching apparatus, the slurry was uniformly coated onto the surface of a clean ITO conductive film and vacuum dried overnight at 60°C to obtain a photoelectric storage cathode (PSC).

[0038] 6. In an argon-filled glove box (water and oxygen content < 0.1 ppm), using an integrated coating process, the electrolyte slurry prepared in step 3 is directly coated onto the surface of the photovoltaic storage cathode prepared in step 5 and dried to form an integrated cathode-electrolyte structure. A scanning electron microscope image of this cathode-electrolyte structure is shown below. Figure 6 The results show that the cathode and the solid electrolyte layer are tightly bonded at the interface with no obvious gaps or delamination. The particles inside the cathode are evenly packed and the pores are moderately distributed. The electrolyte layer is dense, continuous and uniform in thickness, indicating that the in-situ coating process has achieved efficient interfacial contact between the cathode and the electrolyte.

[0039] 7. An ultra-thin lithium metal foil is placed on the surface of the electrolyte layer as the negative electrode. A battery casing with a 5 mm aperture (CR2032 model) is used for encapsulation to obtain a photoelectrochemical energy storage coin cell. A transparent PET plastic film is then used for encapsulation to obtain a flexible photoelectrochemical energy storage pouch cell, where the electrolyte size is 2×2 cm.

[0040] Comparative Example 1 The specific steps for preparing a pure polymer solid electrolyte membrane in this comparative example are as follows: Poly(vinylidene fluoride-trifluoroethylene) copolymer and LiFSI were dissolved in a mixed solvent of DMF and DMSO in a mass ratio of 5:3, and stirred thoroughly until completely dissolved and no bubbles were generated. Then, the resulting slurry was applied to a smooth glass plate, stretched using a film stretcher, and subsequently dried at 55°C for 24 hours to obtain a pure polymer solid electrolyte membrane.

[0041] Comparative Example 2 This comparative example demonstrates the preparation of a polymer solid electrolyte membrane modified with a single soluble amylopectin. The specific operational steps are as follows: Poly(vinylidene fluoride-trifluoroethylene) copolymer and LiFSI were dissolved in a mixed solvent of DMF and DMSO at a mass ratio of 5:3 (1:1 volume ratio). Then, 15% (by mass) of soluble amylopectin was added and stirred thoroughly until completely dissolved and no bubbles were generated. The resulting slurry was then applied to a smooth glass plate, stretched using a film stretcher, and subsequently dried at 55°C for 24 hours to obtain the polymer solid electrolyte membrane modified with a single soluble amylopectin.

[0042] Comparative Example 3 The comparative preparation of a single iodine-based modified polymer solid electrolyte membrane follows these steps: Poly(vinylidene fluoride-trifluoroethylene) copolymer and LiFSI are dissolved in a mixed solvent of DMF and DMSO at a mass ratio of 5:3 (5:3 by mass). Then, 15% (by mass) of LiI and I2 (1:1 by mass) are added, and the mixture is stirred thoroughly until completely dissolved and no bubbles are generated. The resulting slurry is then applied to a smooth glass plate, stretched using a film stretcher, and subsequently dried at 55°C for 24 hours to obtain the single iodine-based modified polymer solid electrolyte membrane.

[0043] The solid electrolyte membranes obtained in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3, as well as the battery device assembled in Example 1, were subjected to the following performance tests. The test results are described in detail below with reference to the accompanying drawings: 1. Ionic conductivity: Assemble a “steel sheet||solid electrolyte membrane||steel sheet” structure and encapsulate it with a battery case (CR2032, KELUD Co., Ltd.). Test the bulk impedance R at different temperatures and calculate the ionic conductivity σ at different temperatures according to the formula σ=L / RS, where L is the thickness of the film, R is the bulk impedance value, and S is the area of ​​the film.

[0044] Test results as follows Figure 7 As shown: The pure polymer solid electrolyte membrane prepared in Comparative Example 1 has an ionic conductivity of 0.1 mS / cm at 25 °C. -1 The solid electrolyte membrane made from a single soluble amylopectin-modified polymer prepared in Comparative Example 2 had an ionic conductivity of 0.3 mS / cm at 25 °C. -1 The solid electrolyte membrane of the single iodine-based modified polymer prepared in Comparative Example 3 had an ionic conductivity of 0.36 mS / cm at 25 °C. -1 The starch-polyiodide composite solid electrolyte membrane prepared in Example 1 has an ionic conductivity of 0.6 mS / cm at 25 °C. -1 .

[0045] 2. Stress-strain test: Prepare the electrolyte membrane into a 3cm×6cm sample, and apply a gradually increasing tensile load using a tensile testing machine to deform it until it breaks. The maximum tensile stress required for the sample to break is the stress yield strength.

[0046] Test results as follows Figure 8As shown: the composite solid electrolyte membrane obtained in Example 1 has a stress yield strength of 2.2 MPa, the pure polymer electrolyte membrane obtained in Comparative Example 1 has a stress yield strength of 0.57 MPa, the single soluble amylopectin-modified polymer solid electrolyte membrane obtained in Comparative Example 2 has a stress yield strength of 1.26 MPa, and the single iodine-modified polymer solid electrolyte membrane obtained in Comparative Example 3 has a stress yield strength of 0.86 MPa. The stress yield strength of Example 1 is 3.85 times that of Comparative Example 1. This result indicates that the soluble amylopectin introduced in this invention can act as a plasticizer, effectively improving the mechanical properties of the solid polymer electrolyte membrane.

[0047] 3. Ion transport number detection: Assemble a symmetrical battery with a "lithium||solid electrolyte membrane|lithium" structure, clamp it on both sides with steel sheets, encapsulate it with a CR2032 battery case, and place it on an electrochemical workstation for testing.

[0048] Test results are as follows Figure 9-12 As shown: the composite solid electrolyte membrane obtained in Example 1 has an ion migration number of 0.64 at 25°C; the pure polymer solid electrolyte membrane obtained in Comparative Example 1 has an ion migration number of 0.23 at 25°C; the single soluble amylopectin-modified polymer solid electrolyte membrane obtained in Comparative Example 2 has an ion migration number of 0.41 at 25°C; and the single iodine-modified polymer solid electrolyte membrane obtained in Comparative Example 3 has an ion migration number of 0.46 at 25°C. This indicates that the composite modification strategy of the present invention can significantly improve lithium ion migration efficiency.

[0049] 4. Cyclic stability test of symmetrical battery: Assemble a symmetrical battery with a "lithium||solid electrolyte membrane|lithium" structure, clamp it with steel plates on both sides, place it on the Xinwei testing software, and perform a cycle test by setting a specific current density.

[0050] Test results are as follows Figure 13 As shown: at 0.2 mA cm -2 At the specified current density, the symmetrical battery assembled in Example 1 could cycle stably for 1051 hours; while the symmetrical battery assembled in Comparative Example 1 experienced a short circuit after 175 hours of cycling, the symmetrical battery assembled in Comparative Example 2 experienced a short circuit after 591 hours of cycling, and the symmetrical battery assembled in Comparative Example 3 experienced a short circuit after 563 hours of cycling. This indicates that the composite solid electrolyte membrane of the present invention has superior interfacial stability.

[0051] 5. Battery photoelectric performance and cycle stability testing: The photoelectrochemical energy storage coin cell and flexible photoelectrochemical energy storage pouch cell assembled in Example 1 were placed on the Xinwei testing software. A xenon lamp light source (light intensity calibrated to 100 mW cm⁻¹) was used. -2Simulated sunlight irradiation was used to conduct photocharging tests, and constant current charge-discharge cycle tests were performed at different rates to evaluate its photoelectric conversion efficiency and long-term cycle stability. The test results are as follows: (1) Characteristics of the photocharging stage: such as Figure 14 As shown, the photoelectrochemical energy storage coin cell assembled in Example 1 exhibited three distinct charging stages under xenon lamp cold light source irradiation: a rapid initial voltage decrease (~0.15 V), a stable photovoltage plateau, and a final voltage rise; as shown... Figure 15 As shown, the photoelectrochemical energy storage coin cell assembled in Comparative Example 1 only exhibits two stages, with a small initial voltage drop (~0.07 V) accompanied by significant voltage fluctuations.

[0052] (2) Performance under alternating light / dark conditions: such as Figure 16 As shown, the photoelectrochemical energy storage coin cell assembled in Example 1 exhibits excellent stability at 2C, with a significant capacity increase of 52.2 mAh g⁻¹. -1 The overpotential decreased to 77 mV; Figure 17 As shown, the photoelectrochemical energy storage coin cell assembled in Comparative Example 1 only increased the capacity by 39.1 mAh g. -1 The overpotential is as high as 239 mV.

[0053] (3) Flexible battery photocharging performance: Under xenon lamp cold light source irradiation, such as Figure 18 As shown, the flexible photoelectrochemical energy storage pouch battery assembled in Example 1 can be charged under light alone without any external current input, and can be stably discharged at 0.5C. Figure 19 As shown, this flexible battery can maintain good long-term cycle stability at a 1C rate.

[0054] In summary, the starch-polyiodide composite solid electrolyte membrane prepared by this invention can simultaneously achieve high electrochemical stability and good mechanical strength. The flexible photoelectrochemical energy storage pouch battery assembled based on this electrolyte membrane exhibits excellent cycle stability, as well as good mechanical flexibility and efficient photoelectric conversion capability, fully meeting the application requirements of flexible photoelectrochemical energy storage devices.

[0055] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A starch-polyiodide composite solid electrolyte membrane, characterized in that: The starch-polyiodide composite solid electrolyte membrane comprises a polymer matrix material, a lithium salt, and a redox composite filler; wherein the redox composite filler is a mixture of soluble amylopectin, lithium iodide, and elemental iodine.

2. The starch-polyiodide composite solid electrolyte membrane according to claim 1, characterized in that: The polymer matrix material is one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, and poly(vinylidene fluoride-trifluoroethylene) copolymer; the lithium salt is lithium difluorosulfonylimide.

3. The starch-polyiodide composite solid electrolyte membrane according to claim 1, characterized in that: The content of the redox composite filler accounts for 5%-25% of the total mass of the composite solid electrolyte membrane.

4. The starch-polyiodide composite solid electrolyte membrane according to claim 1 or 3, characterized in that: In the redox composite filler, the mass ratio of soluble amylopectin, lithium iodide and iodine is 1~5:5:

5.

5. The starch-polyiodide composite solid electrolyte membrane according to claim 1, characterized in that: In the composite solid electrolyte membrane, the mass ratio of the polymer matrix material to the lithium salt is 5:1~5.

6. A method for preparing a starch-polyiodide composite solid electrolyte membrane according to any one of claims 1 to 5, characterized in that: The polymer matrix material, lithium salt, and redox composite filler are added to a mixed solvent of N,N-dimethylformamide and dimethyl sulfoxide, and stirred at 50-60°C for 5-10 hours to form a uniform starch-polyiodide composite solid electrolyte slurry. The obtained slurry is coated onto a substrate and vacuum dried at 45-55°C for 12-24 hours to prepare the starch-polyiodide composite solid electrolyte membrane.

7. The preparation method according to claim 6, characterized in that: The volume ratio of N,N-dimethylformamide to dimethyl sulfoxide in the mixed solvent is 1:0.5-2.

8. A flexible photoelectrochemical energy storage battery device, characterized in that: It is assembled from a positive electrode, a negative electrode, a solid electrolyte membrane, and a current collector, wherein the solid electrolyte membrane is the starch-polyiodide composite solid electrolyte membrane as described in any one of claims 1 to 5.

9. The flexible photoelectrochemical energy storage battery device according to claim 8, characterized in that: The positive electrode for photovoltaic energy storage is prepared by dispersing the positive electrode material in a solvent, coating it onto the surface of the current collector, and then vacuum drying it. The positive electrode material is composed of lithium iron phosphate, titanium dioxide, lead-free perovskite material, carbon nanotubes, and polyvinylidene fluoride. The negative electrode is an ultra-thin lithium metal foil. The current collector is an indium tin oxide transparent conductive film.

10. An assembly method for the flexible photoelectrochemical energy storage battery device according to claim 8 or 9, characterized in that: Starch-polyiodide composite solid electrolyte slurry is directly coated in situ onto the surface of the photoelectric storage positive electrode, vacuum dried to form an integrated positive electrode-electrolyte structure, and then bonded to an ultra-thin lithium metal foil negative electrode. The device is then encapsulated with a transparent PET plastic film to obtain a flexible photoelectric chemical energy storage battery device.

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