Regulating the Double-Way Traffic of Cations and Anions in Ambipolar Polymer Cathodes for High-Performing Aluminum Dual-Ion Batteries.

Abstract

The strong Coulombic interactions between Al³⁺ and traditional inorganic crystalline cathodes present a significant obstacle in developing high-performance rechargeable aluminum batteries (RABs) that hold promise for safe and sustainable stationary energy storage. While accommodating chloroaluminate ions (AlCl₄ ^-, AlCl²⁺, etc.) in redox-active organic compounds offers a promising solution for RABs, the issues of dissolution and low ionic/electronic conductivities plague the development of organic cathodes. Herein, electron donors are synthetically connected with acceptors to create crosslinked, bipolar-conjugated polymer cathodes. These cathodes exhibit overlapped redox potential ranges for both donors and acceptors in highly concentrated AlCl₃-based ionic liquid electrolytes. This approach strategically enables on-site doping of the polymer backbones during redox reactions involving both donor and acceptor units, thereby enhancing the electron/ion transfer kinetics within the resultant polymer cathodes. Based on the optimal donor/acceptor combination, the bipolar polymer cathodes can deliver a high specific capacity of 205 mAh g^-1 by leveraging the co-storage of AlCl₄ ^- and AlCl²⁺. The electrodes exhibit excellent rate performance, a stable cycle life of 60 000 cycles, and function efficiently at high mass loadings, i.e., 100 mg cm^-2, and at low temperatures, i.e., -30 °C. The findings exemplify the exploration of high-performing conjugated polymer cathodes for RABs through rational structural design.