Flexible Gel Polymer Electrolytes Based on Carboxymethyl Cellulose Blended with Polyvinyl Alcohol or Polyacrylic Acid for Zinc-Air Batteries

Abstract

Flexible zinc-air batteries are based on gel polymer electrolytes (GPE), soft, semi-solid components devoted to liquid electrolyte retention, ion conduction, and mechanical stability. Many synthetic polymers, and their blends, have been used in early works due to the good compromise between ionic conductivity, electrolyte retention, and mechanical resistance. Naturally occurring biopolymers are a great alternative to increase the sustainability of GPE, but present properties are not sufficient. In this work, the blending of carboxymethyl cellulose (CMC) with polyvinyl alcohol (PVA) or polyacrylic acid (PAA) is studied together with synthesis, cross-linking, and liquid electrolyte embedding method. The CMC : PAA (1 : 2) composite, with ex-situ gel embedding of 8 M KOH electrolyte achieved ionic conductivity of 0.231 S cm−1 at room temperature, high liquid electrolyte uptake and retention, providing a 78 % of zinc utilization and 443.19 Wh kg−1 as energy density for assembled primary zinc-air battery. The CMC : PAA and CMC : PVA also showed unexpected self-healing behavior activated by re-wetting with liquid KOH solution and drying.