Preparation Of Alkaline Gel Polyelectrolytes Via Freeze-thaw Method For Flexible Zinc-air Battery

The rapid global development of information communication and artificial intelligence has inspired extensive research on wearable electronics.More than ever,there is an urgent demand to develop new flexible energy storage systems with portable,efficient,green,and safe.Zinc-air battery is considered the most promising candidates for energy sources in flexible wearable technologies because of their inherent safety,low cost,high theoretical specific capacity(1218 Wh·kg^-1),and high energy density(6136 Wh·L^-1).However,most of the studies in zinc-air battery use alkaline electrolyte solutions,which have safety risks such as leakage and corrosion,making it difficult to realize the flexible value of the battery.In this case,a polymer electrolyte in a gel state between a solid electrolyte and a liquid electrolyte has developed.As the heart of a flexible battery,the gel polyelectrolyte with“soft and tough”mechanical integrity,qualified ion transport,and good electrode adhesion improves the flexibility and application range of the battery.How to balance excellent ionic conductivity and desirable mechanical properties is an attractive and challenging topic for gel polyelectrolytes.Throughout the thesis,the preparation of alkaline gel polymer electrolytes（AGPEs）is the primary research clue,and the polymers PVA and PAM with ion transport functions chose as substrates.Provides targeted strategies and approaches from different perspectives:（1）From the structural design perspective:the double cross-linked structure PVA/N-PAM/KOH-based AGPEs obtained via in-situ free radical polymerization,the freeze-thaw technique to sequentially construct the cross-linked network,and the application of alkaline swelling.Variable-temperature FT-IR was creatively used to verify the hydrogen bond interaction between hydroxyl and carbonyl groups destroyed by high temperature,demonstrating that the gel system contains a rich hydrogen bond network.Benefiting from the synergistic effects of double cross-linking and intermolecular hydrogen bonds/entanglement,the fabricated PVA/N-PAM/KOH electrolyte exhibits optimal ionic conductivity(309.9 m S·cm^-1),and tenacious mechanical properties(0.69 MJ·m^-3)at 8 mol·L^-1 KOH.（2）From the filler optimization perspective:cellulose-reinforced systems with the coexistence of hydrophilic groups and alkali-resistant components,namely PVA/N-PAM/CNF-based AGPEs,were constructed by adding alkali-resistant material cellulose nanofibers（CNF）.The effect of CNF content on the performance of AGPEs investigate.When the CNF mass content is at 25%,the gel polyelectrolytes possessed the highest ionic conductivity(353.36 m S·cm^-1)and tensile toughness(1.67 MJ·m^-3)at room temperature.Even at low temperatures of 0°C and-20°C,there still have available ionic conductivity and mechanical values.（3）Inspired by cellulose reinforcement and multiple cross-linking:paper-based AGPEs systems with multiple cross-linked structures were constructed using cellulosic paper（CP）as a substrate.The experimental data showed that the existence of cellulose crystals could significantly enhance the alkaline resistance and mechanical properties of AGPEs,although they partially hindered the OH^-ion transport.The CP/PVA/N-PAM/KOH-based AGPEs have acceptable ionic conductivity,extremely high dimensional stability,tensile strength（8.20 MPa）,and toughness value(1.00MJ·m^-3),able to withstand extreme states of twisting and knotting without being damaged.The flexible zinc-air batteries with"sandwich"type assembled based on the above three AGPEs give excellent feedback on power density,long-term cycle life,stable energy efficiency,and operating voltage plateau.The battery can still supply energy stably even when bent under stress.In addition,to meet the different scenarios of wearable products,an ultra-thin battery with a thickness of only 1.44 mm has been assembled successfully,demonstrating the potential for practical application as a flexible power source.This thesis could establish a fundamental idea for the future development of cellulose-based AGPEs that can withstand harsh environments and has far-reaching guiding significance for environmental resource conservation,energy storage cost reduction,and the development of flexible low-temperature resistant ultra-thin batteries with strong adaptability.