A novel π-conjugated poly(biphenyl diimide) with full utilization of carbonyls as a highly stable organic electrode for Li-ion batteries

Organic carbonyl redox polymers, especially conjugated polyimides with multiple reversible redox centers have attracted considerable attention as electrode materials for organic Li-ion batteries. However, the low utilization of carbonyls hindered their potential applications in energy storage. Herein, a novel π-conjugated polyimide (PBPI) based on biphenyl diimide (BPI) containing two seven-membered imide rings is developed. PBPI is used as an anode material for organic Li-ion batteries, which show high conductivity and insolubility in the electrolyte and enable intercalation of four Li-ions per BPI unit, thus contributing to a reversible capacity of 136 mA h g^-1 at 100 mA g^-1 with coulombic efficiency close to 100%. Moreover, the battery based on PBPI manifested superior high-rate performance (65 mA h g^-1 at 2000 mA g^-1) as well as significant cycling stability (over 1600 cycles at 100 mA g^-1). Remarkably, the full redox-active site (C[double bond, length as m-dash]O) utilization of an aromatic diimide core to achieve its full potential applications is reported for the first time. This work provides a new strategy for developing redox π-conjugated polyimides and accommodation of more alkaline ions for high performance battery systems.