Na<sub>0.91</sub>MnO<sub>2</sub> with an Extended Layer Structure and Excellent Pseudocapacitive Behavior as a Cathode Material for Sodium-Ion Batteries
Lijun Wu, Shoujie Guo, Xiangjun Pu, Hongwei Yue, Hao Li, Pinjiang Li, Wei Li, Kun Cai, Wenjie Ding, Longfei Li, Yange Zhang, Wenjun Fa, Changchun Yang, Zhi Zheng, Weiwei He, Yuliang Cao
Abstract
Developing oxide cathode materials with a large layer spacing and high sodium content is a significant goal to develop high-performance sodium-ion batteries (SIBs). In this work, a Na0.91MnO2 hexagonal micron wafer (EL-NMO-O2) is prepared by purposefully loading Na2CO3 on the internal and external surfaces of α-MnO2-HNPs and calcinating it in an oxygen atmosphere, leading to an increased layer spacing of Na0.91MnO2, adjustable O vacancies in Na0.91MnO2 lattice, and enhanced electrochemical activity of sodium ions. The EL-NMO-O2 electrode exhibits a remarkably high initial discharge capacity of 205 mAh g–1, excellent cycling performance (capacity retention of nearly 78% at 0.1 A g–1 after 150 cycles), and an improved pseudocapacitive characteristic. The outstanding electrochemical performance can be attributed to its utmost thin sheets, unique extended layer structure, and tuned O vacancies, which provide sufficiently fast transport channels and storage space for sodium ions and alleviate volume change stress. The stunning pseudocapacitive behavior of the EL-NMO-O2 material effectively improves the electrochemical reaction kinetics. Besides, the simple synthesizing technique and excellent electrochemical performance make EL-NMO-O2 exhibit great potential as a cathode material for rechargeable SIBs.