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Open Access Publications from the University of California

Revealing and suppressing surface Mn(II) formation of Na0.44MnO2 electrodes for Na-ion batteries

  • Author(s): Qiao, R
  • Dai, K
  • Mao, J
  • Weng, TC
  • Sokaras, D
  • Nordlund, D
  • Song, X
  • Battaglia, VS
  • Hussain, Z
  • Liu, G
  • Yang, W
  • et al.
Abstract

Understanding and controlling the surface activities of electrode materials is critical for optimizing the battery performance, especially for nanoparticles with high surface area. Na MnO is a promising positive electrode material for large-scale sodium-ion batteries. However, its application in grid-scale energy storage requires improvements in cycling stability at high rate. Here, we performed comprehensive surface-sensitive soft x-ray spectroscopic studies of the Na MnO electrode. We are able to quantitatively determine the Mn evolution upon the potentials and cycle numbers. We reveal the Mn formation on the top 10nm of Na MnO particles when the electrochemical potential is below 2.6V, which does not occur in the bulk. A portion of the surface Mn compounds become electrochemically inactive after extended cycles, contributing to the capacity fading. Based on the spectroscopic discoveries, we demonstrate that cycling Na MnO above 3V could efficiently suppress the Mn formation. formation. 0.44 2 0.44 2 0.44 2 0.44 2 2+ 2+ 2+

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