Water-Soluble, Spin-Cast-Based Crystalline Poly(Methacrylic Acid) Film as a Reversible Li-Ion Battery Anode

Abstract

Poly(methyl methacrylate) (PMMA) polymer anodes are proposed as potential reversible anode materials for lithium-ion batteries (LIBs) owing to their simple thin-film formation process and cost-effectiveness. Nevertheless, challenges such as the use of toxic aprotic solvents and the irreversible consumption of Li ions during the initial cycle need to be addressed to improve their performance. Herein, a water-soluble poly(methacrylic acid) (PMAA) polymer processed using a simple spin-casting method as a reversible LIB anode is presented. Unlike the PMMA anode, the conjugated carbonyl groups of the crystalline PMAA polymer readily form a chain backbone during ex situ thermal annealing, demonstrating a reversible capacity. The mechanism underlying the superior electrochemical characteristics of the PMAA anode is revealed using grazing incidence X-ray diffraction and theoretical calculations. In particular, the highly crystalline cyclic anhydride PMAA polymer induced by thermal annealing shows enhanced interactions between Li ions and C=O groups during operation, resulting in improved electrochemical properties. The resulting crystalline cyclic anhydride PMAA anode achieves a capacity of approximate to 427.7 mAh g(-1) and retains a reversible specific capacity of 156 mAh g(-1) after 500 cycles, indicating that it is a promising polymeric anode for next-generation LIBs.