<scp>Jahn‐Teller</scp> Effect Directed Bandgap Tuning of Birnessite for Pseudocapacitive Application
Sheng Zhu, Yuechao Wang, Jinshu Zhang, Jian Sheng, Feng Yang, Meng Wang, Jiangfeng Ni, Hong Jiang, Yan Li
Abstract
Birnessite M x MnO 2 (M = Na + , K + , etc .) has emerged as a promising alternative to the classical MnO 2 material owing to its improved pseudocapacitive performance for energy storage. Understanding their structure–property correlation is essential for the development and application of advanced supercapacitors. Herein, we adopt the crystal field theory and density functional simulation to reveal the structural dependence of the pseudocapacitive property of K x MnO 2 . Attributing to the Jahn–Teller effect of Mn 3+ , the bandgap of K x MnO 2 can be tuned by changing the x value (i.e., the Mn(III)/Mn(IV) ratio). Then, we design a narrow‐bandgap K 0.25 MnO 2 (0.84 eV), which affords a high capacitance of 415 F g −1 at 1 A g −1 and a desirable rate capability of 293 F g −1 at 20 A g −1 . Operando Raman spectroscopy confirms that the Jahn–Teller induced structure evolution of [MnO 6 ] octahedron accounts for the superior pseudocapacitive behavior of K 0.25 MnO 2 . This finding offers theoretical guidance to the design and application of birnessite materials for pseudocapacitors.