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 (Li-ion) batteries. Due to its promising electrochemical and mechanical properties, combined with its unique three-dimensional (3D) web-like electron-network structure, the redox-active-organometallic polymer can eliminate conductive carbon and replace significant portion of polyvinylidene fluoride (PVdF) binder that have 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 reaction and consequently improves 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 mechanical integrities of the cathodes during cycling 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.