Journal
JOURNAL OF PHYSICAL CHEMISTRY C
Volume 119, Issue 49, Pages 27228-27233Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpcc.5b07479
Keywords
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Funding
- Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy [DE-AC02-05CH11231]
- LDRD program at the Lawrence Berkeley National Laboratory
- MRSEC Program of the National Science Foundation [DMR-1420073]
- Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under the Advanced Battery Material Research (BMR) Program [DE-AC02-05CH11231]
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The LiNi0.5Mn1.5O4 spinel is an appealing cathode material for next generation rechargeable Li-ion batteries due to its high operating voltage of similar to 4.7 V (vs Li/Li+). Although it is widely believed that the full range of electrochemical cycling involves the redox of Ni(II)/(IV), it has not been experimentally clarified whether Ni(III) exists as the intermediate state or a double-electron transfer takes place. Here, combined with theoretical calculations, we show unambiguous spectroscopic evidence of the Ni(III) state when the LiNi0.5Mn1.5O4 electrode is half charged. This provides a direct verification of single-electron-transfer reactions in LiNi0.5Mn1.5O4 upon cycling, namely, from Ni(II) to then to Ni(IV). Additionally, by virtue of its surface sensitivity, soft Xray absorption spectroscopy also reveals the electrochemically inactive Ni2+ and Mn2+ phases on the electrode surface. Our work provides the long-awaited clarification of the single-electron transfer mechanism in LiNi0.5Mn1.5O4 electrodes. Furthermore, the experimental results serve as a benchmark for further spectroscopic characterizations of Ni-based battery electrodes.
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