Egg-shell structured LiCoO 2 by Cu 2+ substitution to Li + sites via facile stirring in an aqueous copper( ii ) nitrate solution

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2017, Vol.5 (47), p.24892-24900
• Main Authors: Kim, Jaemin, Kang, Hyunchul, Go, Nakgyu, Jeong, Seonghun, Yim, Taeeun, Jo, Yong Nam, Lee, Kyu Tae, Mun, Junyoung
• Format: Article
• Language: English
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/C7TA07232E

For practical, high-energy lithium ion batteries, we introduce an egg-shell structured LiCoO 2 , enabling a credible performance with a high cut-off potential of 4.4 V, simply prepared by only stirring in 0.5 mM Cu(NO 3 ) 2 aqueous solution at room temperature without costly heat treatment. Through this, a very robust structure in which the Li + ions in the LiCoO 2 structure were substituted with Cu 2+ is selectively synthesized on the surface of active material particles. The egg-shell structured LiCoO 2 presents excellent cyclability and high coulombic efficiency even in a high potential range of 4.4 V ( vs. Li/Li + ) to allow a high specific capacity. Additionally, the surface-modified LiCoO 2 reaches a high capacity at a fast discharge rate of 20C even after a high temperature cycling sequence. The intended surface modification is also carefully investigated by systematic analyses of STEM, SEM and XPS. Finally, the electrochemical performance of a graphite/surface-modified LiCoO 2 full-cell exhibits an excellent capacity retention of nearly 90% over 1000 cycles. It is concluded that the surface modification method in which the LiCoO 2 powder is added to a low-concentration aqueous solution of copper nitrate and stirred at room temperature is effective in improving the cycle life of LiCoO 2 at high potentials.