Stabilizing redox-active organic molecules via grafting to carbon for cathodes in aqueous rechargeable zinc-ion batteries

Organic molecules such as 9,10-phenanthrenequinone have shown promise as active materials for cathodes in aqueous rechargeable zinc-ion batteries. However, organic molecules are commonly prone to inactivation during charge and discharge that can result in substantial capacity fade, limiting their operational lifespan. One technique to stabilize quinone active materials is covalent grafting on a conductive carbon substrate via diazonium salt reactions. Although explored for other battery chemistries (e.g., Li-ion), this study applies the chemical grafting technique to stabilize 9,10-phenanthrenequinone on carbon black for rechargeable zinc-ion battery cathodes. In one example, cathodes with 9,10-phenanthrenequinone grafted to carbon black maintained a discharge capacity of 99 mAh g−1 (67 % capacity retention) after 1000 cycles of accelerated testing (200 mA g−1), a 12 % improvement in capacity retention compared to cathodes consisting of 9,10-phenanthrenequinone simply adsorbed on carbon black. Grafting was found to restrict quinone mobility and inactivation, leading to increased battery capacity retention and operational lifespan. Such an increase in capacity retention highlights how grafting can be a useful quinone stabilization tool, which could be applied to other organic cathode designs. This work not only emphasized the impact that different carbon substrates can have on organic cathode behaviour, but also demonstrated how grafting organic materials to a carbon substrate is a simple modification that improves organic cathode performance in zinc-ion batteries.