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

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Conventional lithium-ion batteries (LIBs) face limitations in specific capacity and working voltage.
• Organic electrodes offer potential for high specific capacity, lifted working voltage, and environmental benefits.
• Dual-ion batteries (DIBs) are an emerging technology for advanced energy storage.

Purpose of the Study:

• To synthesize and evaluate novel viologen-based bipolar copolymers as high-performance cathodes for DIBs.
• To investigate the electrochemical performance and charge storage mechanism of these copolymers.
• To establish a structure-property relationship for developing efficient bipolar materials for DIBs.

Main Methods:

• Synthesis of poly(viologen-pyrene-4,5,9,10-tetrone dichloride) (PVPTOCl2) and poly(viologen-anthraquinone dichloride) (PVAQCl2).
• Electrochemical performance testing, including specific capacity, coulombic efficiency, rate capability, and cycling stability.
• In-situ/ex-situ characterization using FT-IR and XPS, alongside Density Functional Theory (DFT) calculations to elucidate the charge storage mechanism.

Main Results:

• Both synthesized copolymers exhibited dual-ion storage capabilities from viologen and carbonyl groups.
• PVPTOCl2 demonstrated superior electrochemical performance compared to PVAQCl2, achieving a high initial specific capacity (235.0 mAh g⁻¹ at 200 mA g⁻¹), excellent reversibility (99.96% coulombic efficiency at 1 A g⁻¹), robust rate performance (150.3 mAh g⁻¹ at 5 A g⁻¹), and outstanding cycling stability (197.5 mAh g⁻¹ at 1 A g⁻¹ over 3000 cycles with 0.11‰ capacity loss per cycle).
• Mechanism investigations confirmed the structure-property relationship of the bipolar molecules.

Conclusions:

• Viologen-based bipolar copolymers are promising cathode materials for high-performance dual-ion batteries.
• PVPTOCl2 exhibits exceptional electrochemical properties, highlighting its potential for next-generation energy storage.
• The study provides a new platform and insights for designing efficient bipolar materials for advanced DIBs.