Cellulose‐Based Hydrogel Polymer Electrolyte Derived from Coir Fiber for High‐Performance Lead‐Acid Batteries

The common method to improve battery performance and safety issues related to electrolyte leakage and evaporation in lead‐acid batteries (LABs) is by electrolyte immobilization. Herein, a hydrogel electrolyte is proposed by immobilizing sulfuric acid within a cellulose‐based hydrogel derived from coir fibers. The hydrogel is prepared using two steps: cellulose purification and hydrogel formation. In the first step, lignin and hemicellulose in coir fibers are removed using mechanical and chemical treatments to produce cellulose pulp. Then, cellulose hydrogel is prepared from the pulp using the dissolution‐coagulation route in an alkali‐urea system. The hydrogel is soaked in sulfuric acid to produce hydrogel electrolyte. The cellulose hydrogel has good mechanical strength, with a tensile strength of about 4.5 MPa and Young's modulus of about 39.02 MPa. The ionic conductivity of the hydrogel electrolyte is ≈0.183 mS cm −1 , approaching that of the sulfuric acid electrolyte used in LABs. Although the discharge capacity of cell using the hydrogel electrolyte is slightly lower than that of free sulfuric acid electrolyte (1907 vs. 2051 mAh g − 1 ), its stability is better. The study offers gel polymer electrolyte derived from agricultural waste coir fibers for use in LABs in an environmentally friendly and sustainable manner.