Journal
NANO ENERGY
Volume 16, Issue -, Pages 186-195Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.nanoen.2015.06.024
Keywords
Sodium ion batteries; Soft x-ray absorption spectroscopy; Na0.44MnO2; Surface reactions
Categories
Funding
- Office of Vehicle Technologies of the U.S. Department of Energy, under the Advanced Battery Materials Research (BMR) Program [DE-AC02-05CH11231]
- Office of Vehicle Technologies of the U.S. Department of Energy, under the Applied Battery Research (ABR) Program [DE-AC02-05CH11231]
- Fundamental Research Funds for the Central Universities of China [N110802002]
- National Natural Science Foundation of China [51204038]
- China Scholarship Council [201208210038]
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-765F00515]
- LDRD program at the Lawrence Berkeley National Laboratory
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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 10 nm of Na0.44MnO2 particles when the electrochemical potential is below 2.6 V, 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 3 V could efficiently suppress the Mn2+ formation. (C) 2015 Published by Elsevier Ltd.
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