On a high-capacity aluminium battery with a two-electron phenothiazine redox polymer as positive electrode

Abstract

With aluminium being the most abundant metal in Earth’s crust, rechargeable Al batteries hold great promise as next-generation energy storage devices. However, to date it has been a challenge to identify suitable host materials for complex aluminium ions as positive electrodes. Here, we present a strategy for such positive electrode materials using an organic redox polymer with two well-defined redox processes. Cross-linked poly(3-vinyl-N-methylphenothiazine) with phenothiazine as two-electron redox centres reversibly inserts [AlCl₄]⁻ ions at potentials of 0.81 and 1.65 V vs. Al|Al³⁺, delivers experimental specific capacities of up to 167 mAh g⁻¹ and surpasses graphite as positive electrode material. The phenothiazine polymer electrodes exhibit superior cyclability of 5,000 cycles at 10 C rate proceeding with 88% capacity retention, and excellent rate capability. This constitutes a major advance in the development or rechargeable Al batteries and will initiate further explorations of organic redox polymers as positive electrode materials, paving the way towards more sustainable energy storage solutions.