Pyridinium-Benzoxazole-Based Anode Material for Sustainable All-Organic Polymer-Based Batteries

In search of anode materials for organic batteries, we propose benzoxazole-based redox-active polymers. We report theoretically calculated redox properties of the monomer and polymer based on small polymer chain models using density functional theory (DFT). Subsequently, a straightforward synthesis of poly(4-(benzoxazol-2-yl)-1-(4-vinyl benzyl)pyridinium chloride) (PBO) via radical polymerization is presented. To our knowledge, PBO is the first representative of this class of redox-active polymers applied in batteries, and it has a theoretical specific capacity of 76.8 mA h g^–1 (first redox process). PBO was utilized as an anode and capacity-limiting electrode in an all-organic radical battery using aqueous- and organic-based electrolytes as well as 2,2,6,6-tetramethylpiperidinyl-N-oxy (TEMPO) derivatives as cathodes, providing a cell voltage of 1.3 and 1.4 V in aqueous- and organic-based electrolytes, respectively. The material revealed 99% capacity utilization at 1 C in the first cycle using an organic electrolyte (1 M LiClO₄ in CH₃CN) and more than 75% capacity utilization in an aqueous electrolyte (1 M LiClO₄ in H₂O). In both systems, after rate capability tests (from 0.2 to 50 C), the cells were cycled again at 1 C, where 50% of the initial capacity was retained after 100 cycles. Even though, due to the linearity and the molar mass of PBO, a capacity decay is observed during cycling tests, this study opens a promising class of molecules for the development of anode materials.