Mechanism of chloride modification ambipolar polymer electrode materials for high-performance energy storage device

Abstract

Ambipolar conducting polymer electrode materials exhibit a wide voltage window, contributing to fast development of high-energy–density storage devices. The doping levels of p-doped and n-doped in ambipolar conducting polymers determine the electrochemical performance of energy storage devices. However, n-doped materials always face low doping efficiency, caused by difficulty in electron injection and ion migration, thereby affecting specific capacitance and stability. In this study, two ambipolar conductive polymers were developed, in which the n-doped imine group was chlorinated to improve electron injection, and the mechanism of ion migration process was studied by changing the chlorination of different positions relative to the carbonyl group. The influence of chloride modification on n-doped electrochemical energy storage was thoroughly investigated. The results show that chloride modification can lower the lowest unoccupied molecular orbital (LUMO) energy level of the monomer and make electron injection easier. Interestingly, the chloride modification position not only affects the oxidation–reduction of the carbonyl, but also the binding of the carbonyl with lithium ions. If the chloride modification position is too close to the carbonyl, lithium-ion migration in ambipolar conducting polymer will be restricted, although electron injection is beneficial. Based on this design, the developed PEPCl conducting polymer exhibits excellent electrochemical performance, and the mechanism of chlorination modification of ambipolar polymer electrode materials is described.