Na0.91MnO2 with an Extended Layer Structure and Excellent Pseudocapacitive Behavior as a Cathode Material for Sodium-Ion Batteries

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.