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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

© 2015. Understanding and controlling the surface activities of electrode materials is critical for optimizing the battery performance, especially for nanoparticles with high surface area. Na0.44MnO2 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 Na0.44MnO2 electrode. We are able to quantitatively determine the Mn evolution upon the potentials and cycle numbers. We reveal the Mn2+ formation on the top 10nm of Na0.44MnO2 particles when the electrochemical potential is below 2.6V, which does not occur in the bulk. A portion of the surface Mn2+ compounds become electrochemically inactive after extended cycles, contributing to the capacity fading. Based on the spectroscopic discoveries, we demonstrate that cycling Na0.44MnO2 above 3V could efficiently suppress the Mn2+ formation. formation.

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