Novel highly conductive cathode material based on stable-radical organic framework and polymerized nickel complex for electrochemical energy storage devices

Redox polymers bearing stable nitroxyl radical groups, such as poly-TEMPO-methacrylate (PTMA), are attractive candidates for application in power sources of novel kind, which combine the high power output of supercapacitors and high energy of rechargeable batteries. An important advantage of PTMA is the availability and low cost of the starting materials combined with high charging/discharging voltage, fast electron transfer kinetics and good mechanical properties of the polymer. However, low electron conductivity and high solubility in common organic electrolytes hamper the broad application of TEMPO-based compounds as cathode materials. In the present work, we report a simple strategy to overcome these limitations by the use of a practical and polymer-rich electrode based on redox-conducting polymer blends of polymerized nickel complexes with salen-type Schiff bases and PTMA. Electrochemical properties of the material are tested both in thin film systems and in asymmetric supercapacitor prototypes with aqueous electrolyte, which demonstrate high specific capacity (83 mAh g⁻¹ at 1C, 53 mAh g⁻¹ at 5C and 47 mAh g⁻¹ at 10C), high rate capability as well as cycling stability (55% capacity retention after 1000 cycles).