Recent advancements in utilizing biomass materials for aqueous electrolytes in rechargeable batteries

In spite of the rising demand for rechargeable batteries and competing advancements in the field, aqueous electrolytes still hold advantage over other types of electrolytes because of their inherent safety, ease of fabrication, feasibility, and environmental friendliness. Addressing the leakage issue of liquid aqueous electrolytes, gel polymer aqueous electrolytes are attracting increasing attention. They have ionic conductivities between liquid and solid electrolytes, are mechanically and thermally stable, have high flexibility and corrosion resistance, and can accommodate volume expansion. However, the transition from synthetic polymers to natural polymers is still in the research phase. This review links biomass materials and aqueous electrolytes of rechargeable batteries by summarizing and analyzing the potential of a wide array of natural polymers (e.g., cellulose, alginate, carrageenan, natural gums, etc.) from various sources (plants, animal, algae). The properties, composites, and electrolyte fabrication techniques of each material are discussed, and future perspective is presented. Results show that the most used fabrication technique is solution casting while the highest ionic conductivity demonstrated is 96.89 mS/cm by a cellulose-based electrolyte. Additionally, natural gums show the highest capacity retentions (100 % even after 3300 cycles). By reviewing a wide range of materials and fabrication techniques, we aim to offer valuable insights into the development of innovative energy storage solutions that are sustainable, safe, and feasible.