Recent Advances in Biopolymer-Based Hydrogel Electrolytes for Flexible Supercapacitors

Abstract

Growing concern regarding the impact of fossil fuels has led to demands for the development of green and renewable materials for advanced electrochemical energy storage devices. Biopolymers with unique hierarchical structures and physicochemical properties, serving as an appealing platform for the advancement of sustainable energy, have found widespread application in the gel electrolytes of supercapacitors. In this Review, we outline the structure and characteristics of various biopolymers, discuss the proposed mechanisms and assess the evaluation metrics of gel electrolytes in supercapacitor devices, and further analyze the roles of biopolymer materials in this context. The state-of-the-art electrochemical performance of biopolymer-based hydrogel electrolytes for supercapacitors and their multiple functionalities are summarized, while underscoring the current technical challenges and potential solutions. This Review is intended to offer a thorough overview of recent developments in biopolymer-based hydrogel electrolytes, highlighting research concerning green and sustainable energy storage devices and potential avenues for further development.G iven the rapid progress in fields such as electric vehicles and smart grids, the importance of highly efficient energy storage systems for sustainable energy development and energy security cannot be overstated. Supercapacitors have emerged as promising energy storage candidates, demonstrating obvious advantages such as outstanding lifespan (>100,000 cycles), excellent safety, and a wide temperature operating range (−50 to 200 °C). 1 Compared to conventional lithium-ion batteries, they enable remarkably rapid charging−discharging rates (within seconds to minutes) and superior power density (>10 kW kg −1 ). 2 Flexible supercapacitors, featuring pliable electrodes and electrolytes, are particularly suitable for powering lightweight wearable electronics. However, in practical applications, flexible supercapacitors are more susceptible to various deformations under mechanical strains, especially bending and shearing forces. This limitation has stimulated innovation in electrode, electrolyte, separator, current collector materials, and interface bonding techniques to mitigate mechanical mismatch while preserving the flexible supercapacitors' excellent electrochemical performance. 3

Porous VN nanosheet arrays on MXene carbon fibers for flexible supercapacitors

“…1,2 Because the energy density of the supercapacitor is determined by the specific capacitance and the voltage window, the specific capacitance can be improved by optimizing the composition and structure of the electrode material or constructing an efficient interface. 3–5…”