Thianthrene polymers as 4 V-class organic mediators for redox targeting reaction with LiMn2O4 in flow 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.

TEMPO-Substituted Poly(ethylene sulfide) for Solid-State Electro-Chemical Charge Storage.

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.

Metal-Free, Solid-State, Paperlike Rechargeable Batteries Consisting of Redox-Active Polyethers.

Metal-free and totally organic based batteries were fabricated from functional polyethers. Aliphatic polyethers, in which 2,2,6,6-tetramethylpiperidin-1-oxyl and viologen were introduced with high density, were used as the cathode and anode active materials, respectively. By stacking nanosheets of the polymers and an imidazolium-substituted polyether as the electrolyte, a solid-state cell only 2 µm thick was made. The anion-type rocking-chair cell showed reversible charge/discharge even at a high rate of 5 C without adding any solvents or plasticizers. Although the unsealed cell was measured under ambient conditions, no significant side reactions (including self-discharging and capacity decay) occurred, whereas conventional electrodes are sensitive to air and water in the charged state. The intrinsic plasticity of the polyethers is also compatible with making free-form, 3D-printable batteries.