Phenothiazine-based polymer cathode materials with ultrahigh power densities for lithium ion batteries

Lithium ion batteries (LIBs) currently deliver the highest energy density of any known secondary electrochemical energy storage system. However, new cathode materials, which can deliver both high energy and power densities, are needed to improve LIBs. Herein, we report on the synthesis of a new organic-based redox-active material centered about phenothiazine and phenylenediamine units. Improved Coulombic efficiencies and greater capacity retention during cycling are observed through the copolymerization of a phenothiazine-based monomer that yields cross-linked materials. With this as the positive electrode in Li-coin cells, high specific capacities (150 mAh/g) are delivered at very positive operating voltages (2.8−4.3 V vs Li+ /Li), yielding high energy densities. The material has low charge transfer resistance as verified by electrochemical impedance spectroscopy, which contributes in delivering previously unseen power densities in coin cells for organic-based cathodes. Excellent retention of capacity (82%) is observed at ultrafast discharge rates (120 C).