Lignin as Polymer Electrolyte Precursor for Stable and Sustainable Potassium Batteries

Potassium batteries show interesting peculiarities as large‐scale energy storage systems and, in this scenario, the formulation of polymer electrolytes obtained from sustainable resources or waste‐derived products represents a milestone activity. In this study, a lignin‐based membrane is designed by crosslinking a pre‐oxidized Kraft lignin matrix with an ethoxylated difunctional oligomer, leading to self‐standing membranes that are able to incorporate solvated potassium salts. The in‐depth electrochemical characterization highlights a wide stability window (up to 4 V) and an ionic conductivity exceeding 10(−3) S cm(−1) at ambient temperature. When potassium metal cell prototypes are assembled, the lignin‐based electrolyte attains significant electrochemical performances, with an initial specific capacity of 168 mAh g(−1) at 0.05 A g(−1) and an excellent operation for more than 200 cycles, which is an unprecedented outcome for biosourced systems in potassium batteries.