EQCM Investigation of a Dual-Doped Polymer Electrode for Li-Ion Batteries with Improved Reversible Capacity

Polymer-based materials with the incorporation of redox-active dopants serve as promising electrodes for Li-ion batteries but their use is restricted by the limited doping level and inevitable dissolution behavior of the dopants. Here, we proposed a conjugated polymer-based electrode with an assistant dopant to realize the reversible capacity contribution of a redox-active dopant. By employing phosphate anion (PO) as the assistant dopant to stable the polymer matrix, the reversible capacity was improved by introducing indigo carmine (IC) into the polymer electrode. Based on the real-time monitoring of the electrochemical quartz crystal microbalance toward the mass change, the charge storage behavior of the redox-active dopant IC was observed and the stabilizing effect of the assistant dopant PO was revealed. The modified electrode delivered an increased capacity of 191 mA h g^-1, and the reversible capacity remained 56% higher than that of the PO-undoped electrode after 200 cycles. The dual-doping strategy with the assistant dopant and the redox-active dopant is used to develop advanced polymer-based electrodes for high-capacity and long-cycling batteries.