Figure 4. a) Photographs of P1/SWNT (9:1 w/w)electrodes. b) Charge/discharge curves of the quasi-solid-state cell (specific capacity of P1 is shown).

A poly(ethylene sulfide) backbone is introduced as the main chain of a radical polymer. Anionic ring‐opening polymerization of an episulfide monomer substituted with 2,2,6,6tetramethylpiperidin1oxyl (TEMPO), a robust nitroxide radical, yields the corresponding polythioether. Compared to the traditional poly(ethylene oxide) backbone, the new polymer shows a lower glass transition temperature (−10 °C), and about threefold higher solid‐state ionic conductivity. The polythioether is also shown to improve the charge/discharge properties of a cathode in solid‐state lithium‐ion batteries.

Redox targeting reaction is an emerging idea for boosting the energy density of redox-flow batteries: mobile redox mediators transport electrical charges in the cells, whereas large-density electrode-active materials are fixed in tanks. This study reports 4 V-class organic polymer mediators using thianthrene derivatives as redox units. The higher potentials than conventional organic mediators (up to 3.8 V) enable charging LiMn2O4 as an inorganic cathode offering a large theoretical volumetric capacity of 500 Ah/L. Soluble or nanoparticle polymer design is beneficial for suppressing crossover reactions (ca. 3% after 300 h), simultaneously contributing to mediation reactions. The successful mediation cycles observed by repeated charging/discharging steps indicate the future capability of designing particle-based redox targeting systems with porous separators, benefiting from higher energy density and lower cost.