Nickel-Salen-Type Polymer as Conducting Agent and Binder for Carbon-Free Cathodes in Lithium-Ion Batteries

Systematic physical and electrochemical characterizations revealed unique positive multifunction of a polymeric salen-type nickel(II) complex, poly[Ni(CH₃-salen)], as an additive for conventional cathodes in lithium-ion batteries. Due to its promising electrochemical and mechanical properties, combined with its unique three-dimensional weblike electron-network structure, the redox-active-organometallic polymer can eliminate conductive carbon and replace a significant portion of the poly(vinylidene fluoride) (PVdF) binder that has been used in conventional LiFePO₄ cathodes. By replacing such electrochemically inactive components (i.e., carbon and PVdF), LiFePO₄ cathodes with poly[Ni(CH₃-salen)] deliver improved energy density compared with the conventional LiFePO₄ cathode. Facile electron transfer via large-area contact at polymer/LiFePO₄ interfaces significantly accelerates charge-transfer reactions and consequently improves the rate capability of the cathodes. In addition, unlike PVdF, poly[Ni(CH₃-salen)] retains steady Young's modulus values after immersing in an electrolyte solvent, which enhances the mechanical integrity of the cathodes during the cycling of battery cells and thereby improves their cycle life. The unique multifunction of the poly[Ni(CH₃-salen)] will be of broad interest for its application in next-generation energy-storage devices.