Journal
JOURNAL OF PHYSICAL CHEMISTRY C
Volume 118, Issue 38, Pages 21826-21833Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jp506731v
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Funding
- Office of Vehicle Technologies of the U.S. Department of Energy [DE-AC0205CH11231]
- Welch Foundation [F-1254]
- National Natural Science Foundation in China [21273084]
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The effect of the substitution of Co3+ for equal amounts of Mn4+ and Ni2+ in the lithium-rich layered oxide cathode Li[Li0.2Ni0.2-x/2Mn0.6-x/2Cox]O-2 (0 <= x <= 0.24) has been investigated systematically. Electrochemical charge/discharge measurements in lithium-ion cells indicate that the oxygen loss from the lattice during the first charge is a kinetically slow process, but it can be improved by the substitution of Co3+ due to an overlap of the Co3+/4+:t(2g) band with the top of the O2-:2p band and an increase in metal-oxygen covalence. Although the increased oxygen loss with increasing Co3+ substitution leads to a higher reversible capacity, the first cycle discharge voltage decreases slightly due to the higher concentration of Mn3+ ions created during the first discharge. However, both the capacity fade and the voltage decay increase during extended cycling with increasing Co3+ substitution due to an increasing migration of the transition-metal ions to the lithium layer, which is promoted by the higher number of oxide-ion vacancies in the lattice, to form a spinel-like phase.
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