Smart Polymeric Cathode Material with Intrinsic Overcharge Protection Based on a 2,5‐Di‐ tert ‐butyl‐ 1,4‐dimethoxybenzene Core Structure

Polymer‐based electroactive materials have been studied and applied in energy storage systems as a valid replacement for transition metal oxides. As early as 1999, Hass et al. proposed an interesting concept on the possible incorporation of both charge storage and overcharge protection functionality into a single material. However, there are virtually no examples of polymeric materials that can not only store the charge, but also consume the overcharge current. Herein, a new material based on a cross‐linked polymer ( I ) with 2,5‐di‐ tert ‐butyl‐1,4‐dimethoxybenzene as the core structure is reported. The cyclic voltammogram of the synthesized polymer shows a single oxidation/reduction peak at 3.9–4.0 V. At 1C rate (56 mA/g), polymer I shows stable cycling up to 200 cycles with <10% capacity loss. The redox shuttle mechanism remarkably can be activated when cell voltage is elevated to 4.3 V and the overcharge plateau at 4.2 V (2 nd plateau) is persistent for more than 100 hours. The overcharge protection was due to the release of a chemical redox shuttle species in the electrolyte during the initial charging process. Both DFT calculations and NMR analysis of the aromatic signals in the 1 H‐NMR spectrum of electrolytes from “overcharged” cells provide evidence for this hypothesis.