Influence of alkali metal ions (Li+, Na+, and K+) on the redox thermodynamics and kinetics of organic electrode materials for rechargeable batteries

Organic electrode materials have been widely applied in rechargeable Li, Na, and K batteries. However, one of the key scientific issues—the influence of Li+, Na+, and K+ ions on the redox thermodynamics and kinetics is still unclear. Herein, by using n-type poly(anthraquinonyl sulfide) (PAQS) and polyimide (PI) and p-type polytriphenylamine (PTPAn) as examples, we have systematically and deeply studied this problem though elaborate electrochemical tests and theoretical calculations. By employing three-electrode cells, the thermodynamic potentials of Li, Na, K metal electrodes as well as the PAQS, PI, and PTPAn organic electrodes have been accurately measured. They follow the order of Li+ > Na+ > K+ for PAQS and PI, and keep unchanged for PTPAn. As an application of this discovery, PAQS–PTPAn dual-ion full-cells show the highest output voltage and low-temperature performance with K+ ion. To explain the tendency, universal thermodynamic models have been established and the theoretical calculations reveal that with the increase of ionic radius, the interactions of metal ion with electrolyte solvent and discharged n-type organic (N–) become weaker, which lower down the thermodynamic potential and enhance the redox kinetics. This work provides a significant guidance for the design of high-performance organic batteries.