Biopolymer-based hydrogel electrolytes for advanced energy storage/conversion devices: Properties, applications, and perspectives

With steadily growing environmental problems by synthetic compounds, using eco-friendly biomass-derived biopolymers and other native materials has drawn tremendous attention and extensive interest, to replace traditional petroleum-based materials. Biopolymer-based hydrogels, as emerging and renewable electrolyte materials, have been considered to be competitive candidates for flexible and smart electrochemical energy storage and conversion devices due to the low cost, eco-friendly and degradability. Recently, biopolymer-based hydrogel electrolytes with desirable structure design or functional development have exhibited broad application prospects in diverse energy storage and conversion devices, such as multifunctional supercapacitors, flexible lithium-ion batteries and zinc-ion batteries. Herein, the characterization, synthesis, and performance validation of biopolymer-based hydrogel electrolytes are summarized, analyzed, and discussed. Current progress of electrochemical performance and additional functions (such as self-healing, stretchability, anti-freezing, and etc.) in developing biopolymer-based hydrogel electrolytes for supercapacitors and batteries are comprehensively reviewed. We also present the remaining challenges of using biopolymer-based hydrogel electrolytes for advanced energy storage and conversion devices and propose the underlying approaches to facilitate further development and research.