Design and Synthesis of Viologen-based Copolymers for High Performance Li-Dual-Ion Batteries

Dual-ion batteries based on organic electrodes show great potential to break through the bottlenecks existed in conventional LIBs due to their high specific capacity, lifted working voltage, and environmental benignity. Herein, two innovative viologen-based bipolar copolymers poly(viologen-pyrene-4,5,9,10-tetrone dichloride) (PVPTOCl₂) and poly(viologen-anthraquinone dichloride) (PVAQCl₂) were synthesized and applied as high performance cathodes for lithium-dual-ion battery. Bearing the dual-ion storage capability of viologen and carbonyls, as well as the conjugated structure of pyrene-4,5,9,10-tetrone, the synthesized copolymers show remarkable electrochemical performances for LIBs. Compared to PVAQCl₂, PVPTOCl₂ shows superior electrochemical performance with high initial specific capacity (235.0 mAh g⁻¹ at 200 mA g⁻¹), high reversibility (coulombic efficiency up to 99.96 % at 1 A g⁻¹), excellent rate performance (150.3 mAh g⁻¹ at 5 A g⁻¹) and outstanding cycling stability (a reversible capacity of 197.5 mAh g⁻¹ at a current density of 1 A g⁻¹ and a low capacity loss per cycle of 0.11‰ during 3000 cycles). Moreover, the charge storage mechanism was systematically investigated by ex-situ FT-IR, ex-situ XPS and DFT calculations. The results clearly reveal the structure-property relationship of the bipolar-molecules, providing a new platform to develop efficient bipolar materials for dual-ion batteries.