Sulfonic-Group-Grafted Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> MXene: A Silver Bullet to Settle the Instability of Polyaniline toward High-Performance Zn-Ion Batteries
Ying Liu, Ziwen Dai, Wang Zhang, Yue Jiang, Jian Peng, Dianlun Wu, Bin Chen, Wei Wei, Xian Chen, Zhenjie Liu, Zhigang Wang, Fei Han, Dahu Ding, Lei Wang, Lina Li, Yingguo Yang, Yang Huang
Abstract
Polyaniline (PANI) is a promising cathode material for Zn-ion batteries (ZIBs) due to its intrinsic conductivity and redox activity; however, the achievements of PANI in high-performance ZIBs are largely hindered by its instability during the repeated charge/discharge. Taking advantage of the high conductivity, flexibility, and grafting ability together, a surface-engineered Ti3C2Tx MXene is designed as a silver bullet to fight against the deprotonation and swelling/shrinking issues occurring in the redox process of PANI, which are the origins of its instability. Specifically, the sulfonic-group-grafted Ti3C2Tx(S-Ti3C2Tx) continuously provides protons to improve the protonation degree of PANI and maintains the polymer backbone at a locally low pH, which effectively inhibits deprotonation and brings high redox activity along with good reversibility. Meanwhile, the conductive and flexible natures of S-Ti3C2Tx assist the fast redox reaction of PANI and concurrently buffer its corresponding swelling/shrinking. Therefore, the S-Ti3C2Tx-enhanced PANI cathode simultaneously achieves a high discharge capacity of 262 mAh g–1 at 0.5 A g–1, a superior rate capability of 160 mAh g–1 at 15 A g–1, and a good cyclability over 5000 cycles with 100% coulombic efficiency. This work enlightens the development of versatile MXene via surface engineering for advanced batteries.