Unlocking Full Discharge Capacities of Poly(vinylphenothiazine) as Battery Cathode Material by Decreasing Polymer Mobility Through Cross-Linking

Otteny F, Kolek M, Becking J, Winter M, Bieker P, Esser B

Abstract

Abstract Organic cathode materials are a sustainable alternative to transition metal oxide-based compounds in high voltage rechargeable batteries due to their low toxicity and availability from less-limited resources. Important criteria in their design are a high specific capacity, cycling stability, and rate capability. Furthermore, the cathode should contain a high mass loading of active material and be compatible with different anode materials, allowing for its use in a variety of cell designs. Here, cross-linked poly(3-vinyl-N-methylphenothiazine) as cathode-active material is presented, which shows a remarkable rate capability (up to 10C) and cycling stability at a high and stable potential of 3.55 V versus Li/Li+ and a specific capacity of 112 mAh g−1. Its use in full cells with a high mass loading of 70 wt\% is demonstrated against lithium titanate as intercalation material as well as lithium metal, which both show excellent performance. Through comparison with poly(3-vinyl-N-methylphenothiazine) the study shows that changing the structure of the redox-active polymer through cross-linking can lead to a change in charge/discharge mechanism and cycling behavior of the composite electrode. Poly(3-vinyl-N-methylphenothiazine) in its cross- and non-cross-linked form both show excellent results as cathode-active materials with variable specifications regarding specific capacity, cycling stability, and rate capability.