Zinc salt in “Water‐in‐Polymer Salt Electrolyte” for Zinc‐Lignin Batteries: Electroactivity of the Lignin Cathode

Abstract Zn‐ion batteries are one of the hot candidates for low‐cost and sustainable secondary batteries. The hydrogen evolution and dendritic growth upon zinc deposition are today's challenges for that technology. One of the new strategies to cope with these issues is to use “water‐in‐salt” electrolyte (WISE), that is, super concentrated aqueous electrolytes, to broaden its electrochemical stability window (ESW), suppressing hydrogen evolution reaction (HER), and perturbing the dendritic growth. Herein, this work proposes to use “water‐in‐polymer salt” electrolyte (WIPSE) concept to mitigate the challenges with Zn ion batteries and bring this technology toward one of the cheapest, greenest, and most sustainable electrodes: Lignin‐carbon (L‐C) electrode. Potassium polyacrylate (PAAK) as WISE bears out as better electrolyte for L‐C electrodes in terms of self‐discharge, cyclic stability, and specific capacity compared to conventional electrolyte based on chemically cousin molecule potassium acetate. Zinc bis(trifluoromethanesulfonyl) imide (Zn(TFSI)₂) added into WIPSE shows deposition and dissolution of Zn in Zn//Zn symmetric cell suggesting that Zn²⁺ are moving into the polyanionic network. Furthermore, the added bis (trifluor omethanesul fonyl) imide (TFSI⁻) metal salts trigger a ≈40% enhancement of the capacity of L‐C electrode. These results show a new promising direction toward the development of cost‐effective and sustainable Zn‐lignin batteries.