期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 139, 期 50, 页码 18358-18364出版社
AMER CHEMICAL SOC
DOI: 10.1021/jacs.7b10460
关键词
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资金
- MRSEC Program of the National Science Foundation [DMR-1420073]
- Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy [DE-AC02-05CH11231]
- National Science Foundation of China [NSFC 51325703]
A sodium-ion battery (SIB) solution is attractive for grid-scale electrical energy storage. Low-cost hexaeyano-metalate is a promising electrode material for SIBs because of its easy synthesis and open framework Most hexacyanometa-late-based SIBs work with aqueous electrolyte, and interstitial water in the material has been found to strongly affect the electrochemical profile, but the mechanism remains elusive. Here we provide a comparative study of the transition-metal redox in hexacyanometalate electrodes with and without interstitial water based on soft X-ray absorption spectroscopy and theoretical calculations. We found distinct transition-metal redox sequences in hydrated and anhydrated NaxMnFe(CN)(6)center dot zH(2)O. The Fe and Mn redox in hydrated electrodes are separated and are at different potentials, leading to two voltage plateaus. On the contrary, mixed Fe and Mn redox in the same potential range is found in the anhydrated system. This work reveals for the first time how transition-metal redox in batteries is strongly affected by interstitial molecules that are seemingly spectators. The results suggest a fundamental mechanism based on three competing factors that determine the transition-metal redox potentials. Because most hexacyanometalate electrodes contain water, this work directly reveals the mechanism of how interstitial molecules could define the electrochemical profile, especially for electrodes based on transition-metal redox with well-defined spin states.
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