π-Bridge Spacer Embedded Electron Donor-Acceptor Polymer for Flexible Electrochromic Zn-ion Batteries.

Zinc ion batteries (ZIBs) have drawn much attention as the next-generation energy storage for smart and wearable electronics due to their high theoretical gravimetric/volumetric energy capacities (820 mAh/g, 5855 mAh/cm 3 ), safety from explosive hazards, and cost-effectiveness. However, at the current state, even the state-of-the-art ZIBs lack the energy capacity necessary to facilitate smart functionalities for intelligent electronics. In this work, a "π-bridge spacer"-embedded electron donor-acceptor polymer cathode combined with Zn 2+ ion-conducting gel electrolyte was proposed for a smart and flexible ZIB system to provide high electrochromic-electrochemical performances. The π-bridge spacer endows the polymeric skeleton with improved physical ion accessibility and sensitive charge transfer along the charging-discharging cycles, providing extremely stable cyclability with high specific capacity (110 mAh/g) at very fast rates (8 A/g) and large coloration efficiency (79.8 cm 2 /C) under severe mechanical deformation over a long period (∼ 14 days). These results are markedly outstanding compared to the topological analogue without the π-bridge spacer (80 mAh/g at current density of 8 A/g, 63.0 cm 2 /C). Our design to incorporate a π-bridge spacer realizes notable electrochromism behaviors and high electrochemical performance in ZIBs, which sheds light on the rational development of multifunctional flexible-ZIBs with color visualization properties for widespread usage in powering smart electronics. This article is protected by copyright. All rights reserved.