Radical Polymers for Rechargeable Batteries
Radical polymers are one of the redox polymers and bear robust radical molecules per repeating unit. Some of the radical polymers are characterized by the rapid and reversible one-electron redox ability of the radical sites. A typical example is poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate), which has a very positive redox potential. The combination of the high density of radical redox sites and the amorphous plasticized state coexisting with a small quantity of electrolytes allows for a rapid self-exchange reaction among the sites driven by a steep concentration gradient, which leads to efficient charge transport and storage throughout the polymers. The chemical bistability of the reduced and oxidized species of radical polymers permits an ultimate energy density and durable cyclability during charging and discharging. Lithium-ion and all-organic batteries have thus been fabricated using radical polymers as electrode-active materials. The output voltage of the batteries is constant, corresponding to their redox potential difference, and can be tuned by the molecular design. The batteries provide burst power, which also allows instant full charging in a few seconds. The syntheses of radical polymers and various types of radical polymer batteries are described herein, with their future perspectives.