A Rocking-Chair Proton Battery with Conducting Redox Polymer Active Materials and a Protic Ionic Liquid Electrolyte

Rechargeable batteries that use redox-active organic compounds are currently considered as an energy storage technology for the future. Conducting redox polymers (CRPs) are organic materials being both electronically conducting and resilient to dissolution. While insolubility is an advantageous property for active battery materials, it complicates the processing necessary for fabricating electrodes, including electrode formulation and layer formation. Here we employ a post-deposition electro-polymerization (PDP) method, which allows for solution-processing to be used for electrode layer formation. The polymerization conditions are optimized and the underlying mechanism is studied with the final aim to produce high performance CRPs as energy storage materials. We show that quinizarin (Qz) and naphthoquinone (NQ) based CRPs can reach their theoretical capacity thorough optimization of the polymerization conditions. Combining the two CRPs, with the Qz-CRP as cathode and the NQ-CRP as anode, and a protic ionic liquid electrolyte, yields a 0.8 V proton rocking-chair battery. The conducting additive-free all-organic proton battery exhibits a capacity of 62 mAh/g and a capacity retention of 80% after 500 cycles using rapid potentiostatic charging and galvanostatic discharge at 4.5 C.