Modulation of Redox Chemistry of Na2Mn3O7 by Selective Boron Doping Prompted by Na Vacancies

作者：Wan, Jing; Qiu, Yuegang; Sun, Xueping; Ou, Mingyang; Xu, Jia; Zhang, Xiaoyu; Liu, Yi; Sun, Shixiong^*; Xu, Yue^*; Fang, Chun; Huang, Li; Chu, Paul K.; Han, Jiantao

来源：ACS applied materials & interfaces, 2022.

DOI：10.1021/acsami.2c09719

• sodium-ion batteries
• layered materials
• Na2Mn3O7
• boron doping
• vacancies

The small energy density and chemomechanical degradation of layered manganese oxide limit practical application to sodium-ion batteries (SIBs). Typically, Na2Mn3O7 shows a low redox plateau at 2.1 V versus Na/Na+, and the oxygen redox reaction at a high voltage causes structural collapse. Herein, a Na vacancy-induced boron doping strategy is demonstrated to improve the properties. Boron is incorporated into selective sites in the lattice in the center of the MnO6 octahedral ring at the O-layer. Bonding of boron in the TM layer enhances the electrochemical activity of low-valence Mn, giving rise to two reversible redox peaks at 2.45 and 2.55 V to enhance the average redox voltage. At the same time, the O 2p chemical state becomes weaker around the Fermi level, thus suppressing oxygen overoxidation for the high charge state and strengthening the layered structure during the redox reactions. The reduced Mn-O covalency and small diffusion barrier energy stemming from bonding of boron in the oxygen layer produce excellent rate characteristics. Modulation of the Mn 3d and O 2p orbital in Na2Mn3O7 by Na vacancies leads to selective doping of boron at different sites, and our results reveal that it is an important strategy for studying transition-metal-oxide-layered electrode materials.

• 单位
  华中科技大学; 武汉大学; y