Multi-Functionalized Polymers as Organic Cathodes for Sustainable Sodium/Potassium-Ion Batteries

Abstract

In this work, we designed and synthesized three novel polymeric cathode materials based on azo and carbonyl groups for Na-ion and K-ion batteries. The electrochemical performance of the polymer with a naphthalene backbone structure is better than that with benzene and biphenyl structures due to faster kinetics and lower solubility in the electrolyte. It unravels the rational design principle of extending π-conjugation aromatic structures in redox-active polymers to enhance the electrochemical performance. To further optimize the polymeric cathodes, the polymer with a naphthalene backbone structure is mixed with nitrogen-doped graphene to increase the conductivity and mitigate the dissolution. The resulting cathodes deliver high specific capacity, long cycle life, and fast-charging capability. Post-cycling characterizations were employed to study the chemical structure and morphology evolution upon cycling, demonstrating that the active centers (azo and carbonyl groups) in the polymer can undergo reversible redox reactions with Na+/K+ for sustainable alkali-ion batteries.