Preparation method of semi-solid electrolyte material for ultra-low temperature battery and application thereof

Abstract

This invention relates to a method for preparing a semi-solid electrolyte material for ultra-low temperature batteries and its application. The method involves gelatinizing starch at high temperature, cooling it to room temperature, adding an electrolyte raw material containing acrylic acid monomers and polyvinyl alcohol, and mixing and stirring to obtain a semi-solid electrolyte precursor solution. Under a protective atmosphere, the reaction is heated, and after cooling, the resulting grafted copolymer material is immersed in an alkaline solution to obtain a three-dimensional porous semi-interpenetrating semi-solid electrolyte material. The semi-interpenetrating grafted copolymer semi-solid electrolyte material prepared by this invention has a three-dimensional hierarchical porous structure that is beneficial for improving ion transport kinetics. The semi-interpenetrating semi-solid electrolyte synergistically enhances its mechanical and mass transfer properties. The prepared semi-solid electrolyte material exhibits high ion conductivity and mechanical strength in ultra-low temperature environments, and the assembled zinc-nickel batteries demonstrate excellent cycle performance and rate performance.

Description

Technical Field

[0001] This invention belongs to the field of solid electrolyte technology, specifically relating to a method for preparing a semi-solid electrolyte material for ultra-low temperature batteries and its application. Background Technology

[0002] For extreme low-temperature applications such as polar scientific research and cold-weather energy storage, advanced cryogenic energy storage battery technology has become a key core area of ​​the global energy revolution, placing stringent demands on energy storage devices to break through the -40℃ cryogenic operating limit and achieve ultra-high safety. Currently, lithium-ion batteries dominate the secondary battery market; however, their flammable and explosive organic electrolytes, limited lithium resources, and high costs severely restrict their applicability in extreme energy storage. In contrast, aqueous zinc batteries have advantages such as intrinsically high safety, abundant zinc resources, and low cost, and are expected to become the most promising new energy storage device. However, existing zinc batteries face scientific challenges such as a sharp drop in ion transport efficiency and deterioration of solid-liquid interface stability under cryogenic conditions. Innovative strategies such as electrolyte composition regulation and electrode / electrolyte interface optimization are urgently needed to overcome the technical bottlenecks of zinc dendrite growth suppression and low-temperature kinetic performance improvement, ultimately achieving the construction of a new generation of energy storage systems with both wide temperature range operation and high energy output.

[0003] Currently, mainstream zinc batteries generally adopt liquid electrolyte systems due to their high ionic conductivity and excellent interfacial contact. However, traditional liquid aqueous electrolytes face severe challenges under low-temperature conditions: (1) hydrogen-bonded water molecule crystallization phase transition (>-20℃) triggers electrolyte solidification, leading to the collapse of ion transport channels and a magnitude-wise decrease in bulk conductivity; (2) a surge in electrode / electrolyte interfacial impedance induces intensified polarization of the solid-liquid interface electrochemical reaction; (3) zinc ion solvation causes distortion of the sheath structure, inducing systemic cascading failures such as uncontrolled zinc dendrite growth and hydrogen evolution corrosion. Therefore, it is urgent to achieve a synergistic breakthrough in ion transport channel reconstruction and electrode interface stabilization control through the multi-scale structural designability of semi-solid electrolytes.

[0004] Semi-solid electrolytes are novel electrolyte materials that exist in a solid-liquid hybrid state, retaining the ion conduction function of liquid electrolytes while possessing solid-state properties to enhance battery safety and stability. Their three-dimensional polymer framework effectively suppresses the lattice ordering of water molecules through dynamic hydrogen bond reconstruction, while the directional regulation of the zinc ion solvation sheath by polar functional groups helps to achieve spatial confinement of zinc metal deposition / stripping behavior. Furthermore, the unique advantages of semi-solid electrolytes, such as synergistic solid-liquid mass transfer, wide potential window, and no risk of leakage, provide an effective solution to address thermal runaway in energy storage devices under extreme conditions. However, traditional hydrogel electrolytes undergo a glass transition at ultra-low temperatures, and the volume expansion caused by the solid-liquid phase transition can easily lead to battery structural damage. In addition, existing semi-solid electrolyte systems suffer from a fundamental contradiction in terms of mechano-electrochemical synergistic coupling performance, making it difficult to simultaneously meet the dual requirements of reduced ion conductivity and mechanical performance at ultra-low temperatures. Summary of the Invention

[0005] To address the challenges of hydrogen bond network phase transitions and heterogeneous interface instability in semi-solid electrolyte systems under cryogenic conditions, current research focuses on strategies such as organic-aqueous composite electrolytes, heterogeneous integration of electrolytes and membranes, and electrolyte particle additives. Specifically, organic composite systems improve antifreeze performance through solvation microenvironment reconstruction assisted by polar solvents; membrane composites enhance mechanical support by adding additional membrane materials; and functionalized particle additive systems promote synergistic optimization of mechanical and conductive processes through the construction of multi-scale mass transfer channels.

[0006] However, current technologies are still limited by path dependence of single-dimensional regulation, which can only specifically disrupt the hydrogen bond network of water molecules to lower the freezing point of the system or improve mechanical strength and interface engineering coupling performance. This ignores the problems introduced by these strategies, such as sacrificing the bulk ionic conductivity of organic systems and increasing charge transfer resistance at heterogeneous interfaces. Furthermore, the increased complexity of the preparation process due to the addition of additives and the engineering integration of heterogeneous interfaces increases the cost of large-scale applications.

[0007] This invention provides a semi-interpenetrating graft copolymer semi-solid electrolyte material resistant to ultra-low temperature (-40℃) environments. Compared to traditional liquid electrolytes and ordinary solid electrolyte systems, this material exhibits higher ionic conductivity, better electrode / electrolyte interface stability, and stronger mechanical strength under extreme low-temperature conditions. These characteristics significantly improve the cycle life and rate performance of zinc batteries in ultra-low temperature environments. Through molecular structure design, this invention achieves highly efficient and controllable material preparation processes. The graft copolymerization reaction system used features low raw material costs, mild reaction conditions, and high batch-to-batch product stability, meeting the industrial production needs of ultra-low temperature battery electrolyte materials for new energy equipment in polar scientific research, aerospace, and high-latitude energy storage fields.

[0008] This invention addresses the current demand for cryogenic electrolytes by providing a method for preparing a semi-solid electrolyte material for cryogenic batteries and its application. Specifically, it describes a method for preparing a semi-solid electrolyte material with a three-dimensional porous structure for zinc batteries. The method involves preparing a semi-interpenetrating graft copolymer semi-solid electrolyte material. The three-dimensional hierarchical porous structure is beneficial for improving ion transport dynamics, and the semi-interpenetrating semi-solid electrolyte synergistically enhances its mechanical and mass transfer properties. The prepared semi-solid electrolyte material exhibits high ion conductivity and mechanical strength in cryogenic environments, and the assembled zinc-nickel battery demonstrates excellent cycle performance and rate capability.

[0009] The objective of this invention can be achieved through the following methods: This invention provides a method for preparing a semi-solid electrolyte material for ultra-low temperature batteries, comprising the following steps: S1. Preparation of semi-solid electrolyte precursor First, the starch is gelatinized, then electrolyte raw materials are added, and after mixing and stirring, a semi-solid electrolyte precursor solution is obtained. Electrolyte raw materials include acrylic acid monomers, polyvinyl alcohol (PVA), crosslinking agents, and initiators; S1, Preparation of semi-solid electrolyte materials The obtained semi-solid electrolyte precursor solution was heated and reacted under a protective atmosphere. After cooling, the resulting grafted copolymer material was immersed in an alkaline solution to obtain a three-dimensional porous semi-interpenetrating semi-solid electrolyte material.

[0010] In one embodiment of the present invention, in step S1, the starch is selected from one or more of tapioca starch, corn starch, and potato starch. All starches used are commercially available starches.

[0011] In one embodiment of the present invention, in step S1, the gelatinization process involves mixing starch and water and then heating the mixture for gelatinization. The gelatinization temperature is controlled between 85 and 95°C to ensure complete gelatinization. The high-temperature gelatinization time is controlled between 1 and 3 hours. The mass ratio of starch to water is 1:8 to 12. After high-temperature gelatinization, the mixture is cooled to room temperature (20 to 30°C) before adding electrolyte raw materials.

[0012] In one embodiment of the present invention, in step S1, the acrylic monomer is added in the form of a neutralized acrylic acid solution, which is obtained by adding the acrylic monomer to an aqueous potassium hydroxide solution under ice bath conditions. The mass ratio of acrylic monomer to potassium hydroxide is 10:6-7. The ratio of potassium hydroxide to water in the potassium hydroxide aqueous solution is 6-7 g:15 ml. The degree of neutralization of the neutralized acrylic acid solution is controlled at 60-8%, as excessive neutralization is detrimental to the crosslinking of the polymer network.

[0013] In one embodiment of the present invention, in step S1, the crosslinking agent is N,N'-methylenebisacrylamide.

[0014] In one embodiment of the present invention, in step S1, the initiator is potassium persulfate.

[0015] In one embodiment of the present invention, in step S1, the mass ratio of starch to acrylic monomer is 1:5~30.

[0016] The PVA used in this invention has excellent water storage and water molecule binding capabilities. Through the strong anchoring of the hydrogen bond network, the "free water" inside the electrolyte is converted into highly stable "bound water". This state change greatly lowers the freezing point of water molecules, allowing the semi-solid electrolyte to maintain its flexibility and prevent freezing and cracking even in extremely cold environments (such as -40°C), while maintaining efficient ion conduction. At the same time, it can suppress water evaporation at high temperatures, significantly expanding the industrial application temperature range of the battery.

[0017] In one embodiment of the present invention, in step S1, the mass ratio of starch to polyvinyl alcohol is 1:0.2~4, preferably 1:0.2~3.

[0018] In one embodiment of the present invention, in step S1, the mass ratio of starch to crosslinking agent is 1:0.002~0.04.

[0019] In one embodiment of the present invention, in step S1, the mass ratio of starch to initiator is 1:0.001~0.02.

[0020] In one embodiment of the present invention, in step S1, the mixing and stirring time is controlled between 3 and 6 hours.

[0021] In one embodiment of the present invention, in step S2, the protective gas includes one or more of nitrogen and argon.

[0022] In one embodiment of the present invention, in step S2, the temperature of the heating reaction is controlled between 70 and 90°C; the copolymerization reaction time is controlled between 3 and 9 hours.

[0023] In one embodiment of the present invention, in step S2, the heating reaction is carried out by pouring the precursor solution into a customized mold. The thickness of the customized mold is controlled between 0.1 and 0.5 mm.

[0024] In one embodiment of the present invention, in step S2, the alkaline solution is a potassium hydroxide solution. The concentration of potassium hydroxide is controlled between 6 and 12 mol / L; the soaking time is controlled between 12 and 48 h. Before soaking, the grafted copolymer material is cooled to room temperature (20-30°C). The alkaline solution soaking of this invention is not only a physical process for shaping the material and creating a three-dimensional porous structure, but also a chemical activation process for the electrolyte. During the soaking process, carboxyl groups and alkali metal cations undergo a neutralization reaction to form carboxylates. This rapidly increases the ion concentration within the network, creating an osmotic pressure difference that drives the electrolyte to uniformly penetrate the network, causing the polymer chains to evenly expand and form a continuous, interconnected three-dimensional porous structure. This porous structure serves as both a storage container for the electrolyte and a continuous channel for ion transport, forming the core structural basis for achieving high ionic conductivity in semi-solid electrolytes.

[0025] In one embodiment of the present invention, the ultra-low temperature battery is an ultra-low temperature zinc battery, preferably an ultra-low temperature aqueous zinc battery. The ultra-low temperature range is preferably -10℃ to -40℃.

[0026] The present invention also provides a preparation method described above to obtain a semi-solid electrolyte material for ultra-low temperature batteries.

[0027] This invention uses low-cost commercially available starch, polyacrylic acid (PAA), and polyvinyl alcohol (PVA) as raw materials to innovatively construct a semi-interpenetrating graft copolymer network structure. By precisely controlling parameters such as the polymer monomer ratio, crosslinking agent ratio, and initiator ratio, a three-dimensional network matrix with both rigid support and dynamic flexible segments is formed. Dynamic hydrogen bond networks are formed in situ by the hydroxyl groups of starch molecular chains and the carboxylic acid groups of PAA, promoting the reconstruction of hydrogen bond networks of water molecules at low temperatures.

[0028] This invention introduces a polar carboxylic acid group through molecular engineering to form a weakly solvated sheath layer with zinc ions, which significantly reduces the activation energy of ion migration at extremely low temperatures. It also proposes a unique semi-interpenetrating electrolyte construction strategy. By controlling the monomer ratio and thermodynamic parameters of the polymerization process, multi-level pores are formed inside the electrolyte. Combined with the directional coordination of the PAA carboxylic acid group, this structure can still maintain efficient ion transport characteristics at -40℃.

[0029] This invention achieves a breakthrough in material system with "zero inorganic fillers" and all-organic reinforcement, forming a dual-network structure through the topological entanglement of starch / PAA graft copolymer and PVA chains. The PVA crystalline regions, acting as dense physical cross-linking points, provide a strong and tough skeletal anchoring effect for mechanical reinforcement; while the amorphous regions of PVA, through a rich network of hydrogen bonds, strongly bind water molecules, effectively inhibiting the growth of ice crystals at low temperatures, thus endowing the material with excellent low-temperature resistance to brittleness and flexibility. This synergistic mechanism successfully constructs excellent mechanical properties that combine rigidity and flexibility, as well as wide-temperature-range weather resistance.

[0030] This invention utilizes PAA-Zn 2+The synergistic effect of coordination bonds and starch hydroxyl groups optimizes the deposition path of zinc ions, inducing their uniform deposition on the zinc electrode surface. At the same time, it significantly reduces the electrode / electrolyte interface impedance, achieving dual optimization of dendrite suppression and interface stability, thus contributing to the long-term stable cycling of ultra-low temperature aqueous zinc batteries.

[0031] This invention also provides an application of the semi-solid electrolyte material for ultra-low temperature zinc batteries obtained by the aforementioned preparation method in ultra-low temperature energy storage batteries. The application scenarios include extreme low-temperature applications such as polar scientific research and extreme cold energy storage. The ultra-low temperature energy storage battery refers to a battery used at a temperature not lower than -50°C, preferably not lower than -40°C, and more preferably used at a temperature between -10°C and -40°C.

[0032] Compared with the prior art, the present invention has the following beneficial effects: (1) The three-dimensional semi-interpenetrating graft copolymer network constructed in this invention is prepared based on low-cost starch material. The hydroxyl groups of starch molecular chains and the carboxylic acid groups of polyacrylic acid form a dynamic hydrogen bond network, which helps to significantly reduce the freezing point of the electrolyte. Moreover, the porous structure of the polymer matrix helps ions migrate efficiently. The ion conductivity is still above 100 mS / cm at -40℃, which is 4 times higher than that of traditional solid electrolytes, effectively solving the problem of ion transport lag at extreme low temperatures.

[0033] (2) This invention achieves breakthrough in the "zero inorganic filler" all-organic reinforcement of electrolyte materials. Through the synergistic toughening effect of the rigid skeleton of starch-based double network polymer and PVA crystalline region, the material has high tensile strength (40 kPa), which is 2 times higher than the comparative sample. It can effectively suppress the stress cracking phenomenon of battery system during charging and discharging.

[0034] (3) This invention utilizes dynamic hydrogen bonds in a semi-solid electrolyte system with Zn 2+ The synergistic effect of in-situ coordination enables the formation of a stable passivation layer similar to SEI at the electrode / electrolyte interface, effectively reducing the electrode interface impedance. The assembled zinc battery can stably cycle 200 times at -40℃, breaking through the low-temperature cycle life bottleneck of existing solid-state zinc batteries. Attached Figure Description

[0035] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 An optical photograph of the semi-solid electrolyte prepared in Example 1.

[0036] Figure 2 The images shown are scanning electron micrographs and elemental distribution maps of the semi-solid electrolyte prepared in Example 1, where a is a scanning electron micrograph of the semi-solid electrolyte, b is a carbon elemental distribution map, and c is an oxygen elemental distribution map.

[0037] Figure 3 X-ray diffraction image of the semi-solid electrolyte prepared in Example 1.

[0038] Figure 4 The images shown are X-ray photoelectron spectroscopy (XPS) images of the semi-solid electrolyte prepared in Example 1, where a is the overall spectrum, b is the C 1s fine spectrum, and c is the O 1s fine spectrum.

[0039] Figure 5 Electrochemical impedance spectroscopy (EIS) of the semi-solid electrolytes prepared in Example 1 and Comparative Example 2.

[0040] Figure 6 The mechanical properties of the semi-solid electrolytes prepared in Example 1 and Comparative Example 1 are shown.

[0041] Figure 7 Scanning electron microscopy image of the negative electrode after cycling in a zinc battery assembled using the semi-solid electrolyte prepared in Example 1.

[0042] Figure 8 Scanning electron micrograph of the negative electrode after cycling in a zinc battery assembled using the PVA electrolyte prepared in Comparative Example 2.

[0043] Figure 9 The battery cycle performance of zinc-nickel batteries using the electrolytes prepared in Example 1 and Comparative Examples 1-2 at -40°C was measured. Detailed Implementation

[0044] To better explain the present invention, further explanation will be provided below with reference to embodiments and accompanying drawings. It is worth noting that the embodiments are merely further elaborations on the results of the present invention, and the scope of protection of the present invention is not limited to the scope represented by the embodiments.

[0045] Example 1 The preparation method of the semi-solid electrolyte material for ultra-low temperature zinc batteries in this embodiment includes the following steps: (1) Weigh 1 g of commercially available cassava starch and mix it thoroughly with 10 g of deionized water. Set the gelatinization temperature to 95°C and the gelatinization time to 2 h. After the reaction is complete, obtain the gelatinized aqueous solution material and cool it down to room temperature (25°C). (2) Weigh 6.23 g of potassium hydroxide and dissolve it in 15 mL of deionized water. Weigh 10 g of acrylic acid monomer and add the acrylic acid monomer dropwise to the potassium hydroxide aqueous solution under ice bath conditions. (3) In a nitrogen atmosphere, the gelatinized cassava starch solution obtained in step (1) is mixed evenly with the acrylic acid solution obtained in step (2). Weigh out 1 g of polyvinyl alcohol, 0.015 g of N,N'-methylenebisacrylamide, and 0.0135 g of potassium persulfate, and gradually add them to the mixed solution. Stir thoroughly for 4 h. (4) Pour the precursor solution obtained in step (3) into a 0.5 mm mold, set the temperature to 80℃ and the time to 6 h, and obtain the grafted copolymer film material after the reaction is completed. (5) The film obtained in step (4) is immersed in an alkaline solution containing 8 mol / L potassium hydroxide for 24 h to obtain a semi-interpenetrating semi-solid electrolyte material.

[0046] Example 2 The preparation method of the semi-solid electrolyte material for ultra-low temperature zinc batteries in this embodiment includes the following steps: (1) Weigh 1 g of commercially available cassava starch and mix it thoroughly with 10 g of deionized water. Set the gelatinization temperature to 95°C and the gelatinization time to 2 h. After the reaction is complete, obtain the gelatinized aqueous solution material and cool it down to room temperature (25°C). (2) Weigh 6.23 g of potassium hydroxide and dissolve it in 15 mL of deionized water. Weigh 10 g of acrylic acid monomer and add the acrylic acid monomer dropwise to the potassium hydroxide aqueous solution under ice bath conditions. (3) In a nitrogen atmosphere, the gelatinized cassava starch solution obtained in step (2) is mixed evenly with the acrylic acid solution obtained in step (1). 0.2 g of polyvinyl alcohol, 0.015 g of N,N'-methylenebisacrylamide, and 0.0135 g of potassium persulfate are weighed and added to the mixed solution gradually, and stirred thoroughly for 4 h. (4) Pour the precursor solution obtained in step (3) into a 0.5 mm mold, set the temperature to 80℃ and the time to 6 h, and obtain the grafted copolymer film material after the reaction is completed. (5) The film obtained in step (4) is immersed in an alkaline solution containing 8 mol / L potassium hydroxide for 24 h to obtain a semi-interpenetrating semi-solid electrolyte material.

[0047] Example 3 The preparation method of the semi-solid electrolyte material for ultra-low temperature zinc batteries in this embodiment includes the following steps: (1) Weigh 1 g of commercially available cassava starch and mix it thoroughly with 10 g of deionized water. Set the gelatinization temperature to 95°C and the gelatinization time to 2 h. After the reaction is complete, obtain the gelatinized aqueous solution material and cool it down to room temperature (25°C). (2) Weigh 6.23 g of potassium hydroxide and dissolve it in 15 mL of deionized water. Weigh 10 g of acrylic acid monomer and add the acrylic acid monomer dropwise to the potassium hydroxide aqueous solution under ice bath conditions. (3) In a nitrogen atmosphere, the gelatinized cassava starch solution obtained in step (2) is mixed evenly with the acrylic acid solution obtained in step (1). Weigh out 4 g of polyvinyl alcohol, 0.015 g of N,N'-methylenebisacrylamide and 0.0135 g of potassium persulfate, and gradually add them to the mixed solution. Stir thoroughly for 4 h. (4) Pour the precursor solution obtained in step (3) into a 0.5 mm mold, set the temperature to 80℃ and the time to 6 h, and obtain the grafted copolymer film material after the reaction is completed. (5) The film obtained in step (4) is immersed in an alkaline solution containing 8 mol / L potassium hydroxide for 24 h to obtain a semi-interpenetrating semi-solid electrolyte material.

[0048] Example 4 The preparation method of the semi-solid electrolyte material for ultra-low temperature zinc batteries in this embodiment includes the following steps: (1) Weigh 1 g of commercially available cassava starch and mix it thoroughly with 10 g of deionized water. Set the gelatinization temperature to 95°C and the gelatinization time to 2 h. After the reaction is complete, obtain the gelatinized aqueous solution material and cool it down to room temperature (25°C). (2) Weigh 6.23 g of potassium hydroxide and dissolve it in 15 mL of deionized water. Weigh 5 g of acrylic acid monomer and add the acrylic acid monomer dropwise to the potassium hydroxide aqueous solution under ice bath conditions. (3) In a nitrogen atmosphere, the gelatinized cassava starch solution obtained in step (1) is mixed evenly with the acrylic acid solution obtained in step (2). Weigh out 1 g of polyvinyl alcohol, 0.015 g of N,N'-methylenebisacrylamide, and 0.0135 g of potassium persulfate, and gradually add them to the mixed solution. Stir thoroughly for 4 h. (4) Pour the precursor solution obtained in step (3) into a 0.5 mm mold, set the temperature to 80℃ and the time to 6 h, and obtain the grafted copolymer film material after the reaction is completed. (5) The film obtained in step (4) is immersed in an alkaline solution containing 8 mol / L potassium hydroxide for 24 h to obtain a semi-interpenetrating semi-solid electrolyte material.

[0049] Example 5 The preparation method of the semi-solid electrolyte material for ultra-low temperature zinc batteries in this embodiment includes the following steps: (1) Weigh 1 g of commercially available cassava starch and mix it thoroughly with 10 g of deionized water. Set the gelatinization temperature to 95°C and the gelatinization time to 2 h. After the reaction is complete, obtain the gelatinized aqueous solution material and cool it down to room temperature (25°C). (2) Weigh 6.23 g of potassium hydroxide and dissolve it in 15 mL of deionized water. Weigh 30 g of acrylic acid monomer and add the acrylic acid monomer dropwise to the potassium hydroxide aqueous solution under ice bath conditions. (3) In a nitrogen atmosphere, the gelatinized cassava starch solution obtained in step (1) is mixed evenly with the acrylic acid solution obtained in step (2). Weigh out 3 g of polyvinyl alcohol, 0.04 g of N,N'-methylenebisacrylamide and 0.02 g of potassium persulfate, and gradually add them to the mixed solution. Stir thoroughly for 4 h. (4) Pour the precursor solution obtained in step (3) into a 0.1 mm mold, set the temperature to 80℃ and the time to 6 h, and obtain the grafted copolymer film material after the reaction is completed. (5) The film obtained in step (4) is immersed in an alkaline solution containing 8 mol / L potassium hydroxide for 48 h to obtain a semi-interpenetrating semi-solid electrolyte material.

[0050] Example 6 The preparation method of the semi-solid electrolyte material for ultra-low temperature zinc batteries in this embodiment is basically the same as that in Example 1, except that cassava starch is replaced with corn starch.

[0051] Example 7 The preparation method of the semi-solid electrolyte material for ultra-low temperature zinc batteries in this embodiment is basically the same as that in Example 1, except that the gelatinization temperature is 85°C and the time is 3 hours.

[0052] Comparative Example 1 The preparation method of this comparative electrolyte material includes the following steps: (1) Weigh 1 g of commercially available cassava starch and mix it thoroughly with 10 g of deionized water. Set the gelatinization temperature to 95°C and the gelatinization time to 2 h. After the reaction is complete, obtain the gelatinized aqueous solution material and cool it down to room temperature (25°C). (2) Weigh 6.23 g of potassium hydroxide and dissolve it in 15 mL of deionized water. Weigh 10 g of acrylic acid monomer and add the acrylic acid monomer dropwise to the potassium hydroxide aqueous solution under ice bath conditions. (3) In a nitrogen atmosphere, the gelatinized cassava starch solution obtained in step (1) is mixed evenly with the acrylic acid solution obtained in step (2). 0.015 g of N,N'-methylenebisacrylamide and 0.0135 g of potassium persulfate are weighed and added to the mixed solution gradually, and stirred thoroughly for 4 h. (4) Pour the precursor solution obtained in step (3) into a 0.5 mm mold, set the temperature to 80℃ and the time to 6 h, and obtain the grafted copolymer film material after the reaction is completed. (5) The film obtained in step (4) is immersed in an alkaline solution containing 8 mol / L potassium hydroxide for 24 h to obtain a semi-interpenetrating semi-solid electrolyte material.

[0053] The pure starch-grafted polyacrylic acid network structure is simple and prone to excessive swelling in strongly alkaline electrolytes, leading to a significant decrease in gel strength and even creep and dissociation. This invention introduces linear polyvinyl alcohol (PVA), which spatially interweaves with the starch-grafted network, further forming a semi-interpenetrating network structure. The highly dense hydroxyl groups on the PVA molecular chain establish an extremely dense hydrogen bond network with the carboxyl groups of polyacrylic acid and the hydroxyl groups of starch. This provides the semi-solid electrolyte with excellent mechanical toughness and tensile strength, effectively suppressing the growth and penetration of zinc anode dendrites during long-term cycling in zinc-nickel batteries, thus preventing internal short circuits.

[0054] Comparative Example 2 This comparative example provides a traditional pure polyvinyl alcohol-based alkaline gel polymer electrolyte, the preparation method of which does not include graft copolymerization and in-situ alkalization pore-forming processes. The specific steps are as follows: (1) Weigh 3 g of PVA powder using a precision balance, add it to 24 mL of deionized water, and stir continuously for 1.5 h in a constant temperature water bath at 90℃ with magnetic stirring to fully dissolve it and obtain a uniform PVA aqueous solution. (2) Weigh 3 g of potassium hydroxide and dissolve it completely in 6 mL of deionized water. Under continuous stirring at 90 °C, slowly add the prepared KOH solution dropwise to the PVA solution obtained in step (1); (3) After the solution becomes transparent and viscous, continue stirring for 20 minutes to obtain a uniform and viscous mixture; (4) Pour the above mixture into a square mold with a depth of 0.5 mm, and then place it in a refrigerator at a low temperature for 3 h to perform physical cross-linking, and finally obtain a traditional pure PVA alkaline gel polymer electrolyte membrane.

[0055] Comparative Example 3 The preparation method of this comparative electrolyte material is basically the same as that of Example 1, except that: no acrylic acid monomer was added, and the amount of polyvinyl alcohol used was 11 g.

[0056] Comparative Example 4 The preparation method of the comparative electrolyte material is basically the same as that of Example 1, except that: no alkaline solution soaking treatment was performed.

[0057] Comparative Example 5 The preparation method of the comparative electrolyte material is basically the same as that of Example 1, except that: gelatinized cassava starch solution was not used.

[0058] Comparative Example 6 The preparation method of the comparative electrolyte material is basically the same as that of Example 1, except that polyvinyl alcohol is replaced with sodium alginate.

[0059] The performance of the semi-interpenetrating graft copolymer semi-solid electrolyte materials prepared according to the embodiments and comparative examples of the present invention will be tested below.

[0060] Test method: (1) Electrolyte morphology The prepared semi-solid electrolyte sample was rapidly frozen and fractured in liquid nitrogen to obtain a flat cross-section without deformation or damage. The fractured sample was then freeze-dried in a vacuum freeze dryer to sublimate and remove internal moisture while fully preserving its internal three-dimensional porous structure. After removal, the sample surface and cross-section were sputter-coated with gold, and scanning electron microscopy was used to observe and record the pore morphology, pore size distribution, and polymer network structure characteristics within the material.

[0061] Figures 1-2 It can be seen that the semi-interpenetrating graft copolymer semi-solid electrolyte material prepared in Example 1 is milky white, has a three-dimensional porous structure with uniform element distribution, and the pore size of the polymer matrix is ​​in the range of 20~100 μm. This structure provides sufficient space for ion transport and helps to significantly improve its ion conductivity.

[0062] (2) Electrolyte crystal phase A suitable amount of the semi-solid electrolyte sample after vacuum freeze-drying was pressed into a thin sheet with a smooth surface. The crystallinity of the material was tested using an X-ray diffractometer (XRD, using a Cu Kα radiation source, wavelength λ = 0.15406 nm). The scanning angle range was set to 10°–90°. The positions and relative intensities of the diffraction peaks were analyzed based on the recorded diffraction patterns to evaluate the phase distribution of polyvinyl alcohol crystalline and amorphous regions in the material.

[0063] Figure 3 It can be seen that the crystal structure of the semi-interpenetrating graft copolymer semi-solid electrolyte material matrix prepared in Example 1 is amorphous, which is conducive to efficient ion transport.

[0064] (3) Electrolyte valence bonds The freeze-dried semi-solid electrolyte sample was placed in the ultra-high vacuum chamber of an X-ray photoelectron spectrometer. Al Kα rays (hν = 1486.6 eV) were used as the excitation source to test the surface elemental composition and valence bond state of the sample. After obtaining the full spectrum, high-resolution energy spectra of major elements (such as C 1s, O 1s, etc.) were further acquired. The test data were charge-corrected based on the C 1s characteristic peak of surface contaminant carbon. Subsequently, peak positions were analyzed using peak fitting software to verify the occurrence state of various functional groups (such as -OH, -COOH, etc.) in the polymer system and the occurrence of crosslinking reactions.

[0065] Figure 4 It can be seen that the semi-interpenetrating graft copolymer semi-solid electrolyte matrix prepared in Example 1 is composed of strong hydrophilic groups such as hydroxyl (-OH) and carboxyl (-COOH), indicating that the acrylic monomer and starch monomer have been successfully graft copolymerized to form a polymer network structure.

[0066] (4) Ion conductivity The ion conductivity of semi-solid electrolytes was tested using electrochemical impedance spectroscopy. The thickness of the gel-state semi-solid electrolyte was precisely measured. L and area A The electrolyte was sandwiched between two symmetrical stainless steel blocking electrodes. Impedance testing was performed using an electrochemical workstation at open-circuit potential, with the AC excitation voltage amplitude set to 5–10 mV and the scan frequency range from 100 kHz to 0.01 Hz. The bulk resistance of the electrolyte was read from the intersection of the high-frequency region and the real axis of the obtained Nyquist plot. R b ). Ionic conductivity ( (Unit: S / cm) Calculated using the formula: .

[0067] Figure 5 It can be seen from the figure that the ionic conductivity of the semi-interpenetrating graft copolymer semi-solid electrolyte materials prepared in Example 1 and Comparative Example 2 in low-temperature environment is as follows: The electrolyte prepared in this example has a high ionic conductivity (>120 mS / cm), which is lower than that of traditional PVA-based electrolytes (~40 mS / cm).

[0068] (5) Mechanical properties The tensile properties of the semi-solid electrolyte were tested using a universal testing machine. The semi-solid electrolyte film was cut into dumbbell-shaped specimens using a standard dumbbell-shaped cutter, and the thickness of the test area was recorded using a thickness gauge. The specimens were vertically fixed at both ends in the upper and lower clamps of the testing machine, and a constant tensile rate was set for uniaxial stretching until the specimens fractured. The force-displacement curves during the stretching process were recorded by software, and the tensile strength at break (MPa) and elongation at break (%) were calculated to evaluate the material's mechanical properties.

[0069] Figure 6 The mechanical properties of the semi-solid electrolyte materials prepared in Example 1 and Comparative Example 1 show that the mechanical strength of the prepared semi-interpenetrating polymer electrolyte gradually increases with the increase of PVA addition.

[0070] 5. Cyclic performance The prepared semi-solid electrolyte was used to assemble zinc-nickel batteries using appropriate sizes.

[0071] (1) The zinc anode is made by grinding and mixing 17.65 g of zinc oxide, zinc, bismuth oxide, potassium polyacrylate binder and polyvinyl alcohol (mass ratio of 1:3) with mass fractions of 60%, 10%, 10%, 5% and 15%, respectively, dissolving in isopropanol dispersant, and coating it onto a 10 cm × 7 cm copper-plated tin current collector by slurry coating method, with a thickness of 0.56 mm. (2) The nickel cathode is made by grinding and mixing 16.53 g of nickel hydroxide, cobalt oxide, zinc powder, carboxymethyl cellulose binder and polytetrafluoroethylene (mass ratio of 5:3) with mass fractions of 75%, 0.2%, 0.8%, 15% and 9%, respectively, dissolving in isopropanol dispersant, and coating it onto a 10 cm × 7 cm foam nickel current collector by slurry coating method. The cathode thickness is 0.67 mm.

[0072] (3) Place the semi-solid electrolyte between the zinc negative electrode and the nickel positive electrode to assemble a zinc-nickel full cell.

[0073] The test conditions were: discharge at a current of 0.5C, discharge depth of 20% DoD, charge at a current of 0.2C to 1.9 V, and cut-off current of 0.02C.

[0074] Figures 7-8 The images show scanning electron microscopy (SEM) images of a zinc symmetric battery assembled with the semi-solid electrolyte prepared in Example 1 and a conventional PVA electrolyte after cycling. The zinc electrode after cycling with the PVA electrolyte exhibits a typical dendritic morphology, while the zinc electrode after cycling with the electrolyte of this example exhibits a planar sheet structure.

[0075] Figure 9The figure shows the battery cycle performance of the zinc-nickel battery assembled using the semi-solid electrolyte prepared in Example 1 at a temperature of -40°C. As can be seen from the figure, the electrolyte prepared in this example has excellent ion transport performance and low temperature resistance, and can support the stable cycling of ampere-hour-level zinc-nickel batteries under extreme low temperature conditions.

[0076] The battery cycle performance and ionic conductivity of the electrolytes prepared in the embodiments and comparative examples of the present invention at a temperature of -40°C are shown in Table 1 below.

[0077] Table 1

[0078] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a semi-solid electrolyte material for ultra-low temperature batteries, characterized in that, Includes the following steps: S1. Preparation of semi-solid electrolyte precursor Starch is gelatinized, cooled to room temperature, and then added to electrolyte raw materials. After mixing and stirring, a semi-solid electrolyte precursor solution is obtained. Electrolyte raw materials include acrylic acid monomers, polyvinyl alcohol, crosslinking agents, and initiators; S1, Preparation of semi-solid electrolyte materials The obtained semi-solid electrolyte precursor solution was heated and reacted under a protective atmosphere. After cooling, the resulting grafted copolymer material was immersed in an alkaline solution to obtain a three-dimensional porous semi-interpenetrating semi-solid electrolyte material.

2. The preparation method according to claim 1, characterized in that, In step S1, the starch is selected from one or more of tapioca starch, corn starch, and potato starch.

3. The preparation method according to claim 1, characterized in that, In step S1, the gelatinization process involves mixing starch with water and heating it to gelatinize the starch. The gelatinization temperature is 85~95℃ and the time is 1~3 h.

4. The preparation method according to claim 1, characterized in that, In step S1, the acrylic monomer is added in the form of a neutralized acrylic acid solution, which is obtained by adding the acrylic monomer to an aqueous potassium hydroxide solution in an ice bath environment.

5. The preparation method according to claim 1, characterized in that, In step S1, the crosslinking agent is N,N'-methylenebisacrylamide; The initiator is potassium persulfate.

6. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of starch to acrylic monomer is 1:5~30; The mass ratio of starch to polyvinyl alcohol is 1:0.2~4; The mass ratio of starch to crosslinking agent is 1:0.002~0.04; The mass ratio of starch to initiator is 1:0.001~0.

02.

7. The preparation method according to claim 1, characterized in that, In step S2, the temperature of the heating reaction is 70~90℃, and the time is 3~9 h.

8. The preparation method according to claim 1, characterized in that, In step S2, the alkaline solution is a potassium hydroxide solution; The concentration of potassium hydroxide is 6~12 mol / L; Soaking time is 12-48 hours.

9. A semi-solid electrolyte material for ultra-low temperature batteries obtained by the preparation method as described in claim 1.

10. The application of a semi-solid electrolyte material for ultra-low temperature batteries prepared by the method described in claim 9 in ultra-low temperature zinc batteries, characterized in that, The ultra-low temperature zinc battery refers to a battery used at a temperature not lower than -50°C.

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