Realizing the leucoemeraldine-emeraldine-pernigraniline redox reactions in polyaniline cathode materials for aqueous zinc-polymer batteries

Abstract

Polyaniline (PANI) is a promising cathode material for aqueous zinc batteries. However, only half available capacity based on the leucoemeraldine-emeraldine redox reaction can be used. Further oxidation to pernigraniline requires potential exceeding the top voltage limit of aqueous solutions, and the hydrolysis of pernigraniline leads to PANI degradation. Herein, we show that the redox potential of emeraldine-pernigraniline reaction is effectively shifted within electrolyte voltage window by tuning ion activities in electrolyte based on Nernst shift, so that both redox processes of PANI are realized for energy storage in aqueous zinc cells. Meanwhile, the pernigraniline hydrolysis is inhibited with limited water activity in the concentrated electrolyte, and the long-term stability in ensured. The PANI electrode delivers a high capacity of 221 mAh g−1 at 0.2 A g−1 and maintains 118 mAh g−1 at 5 A g−1 in aqueous zinc batteries. An excellent capacity retention of 96.6% is achieved after 1000 cycles with 99.7% coulombic efficiency. The energy storage processes as well as the active dopants on PANI are identified by a series of characterizations. The work demonstrates an effective strategy to realize energy storage with redox couples outside the voltage window of conventional electrolytes.