Performance Enhancement of Polymer Electrode Materials for Lithium-Ion Batteries: From a Rigid Homopolymer to Soft Copolymers

Synthesizing redox-active units containing polymers is a promising route for improving the cycling stability of organic electrode materials. However, constructing uniform electrode architectures with good polymer dispersion is a big challenge in the case of polymer electrode materials. In this work, we design and synthesize two anthraquinone-containing copolymers and compare their electrochemical performance with that of the corresponding homopolymer. It is uncovered that the copolymers with soft units in the main chain display increased chain flexibility, thus leading to a slightly increased solubility. Because of this, the soft copolymers are less likely to precipitate during solvent volatilization of electrode preparation and thus can form more uniform electrode architectures. The cyclic voltammogram and electrochemical impedance spectroscopy measurements indicate that copolymer electrodes display decreased polarization and improved kinetics compared with the homopolymer electrode. The copolymers exhibit significantly enhanced cycling stability and improved rate performance. After 100 cycles, both copolymers reveal very high capacity retention of above 98%, while the homopolymer retains only 71% of its highest capacity. Moreover, the copolymer can discharge/charge at 1C for over 2000 cycles with almost no capacity fading, indicating excellent long-term cycling performance. This work further demonstrates the importance of molecular structure and electrode architecture in determining the electrochemical performance of polymer electrode materials.