In this study, we target to find a new composition for a layered mixed metal oxide, which has a high structural stability and a good electrochemical performance. Our strategy is to alter the transition metal composition focusing on the relative amounts of redox active Ni and Co to the inactive Mn, based on highly-stabilized LiNi1/3Co1/3Mn1/3O2. X-ray absorption near-edge structure and X-ray diffraction analyses show that the degree of cation disorder decreases on increasing the ratio of Ni and Co to Mn, by the presence of Ni3+, suggesting that slightly higher Ni and Co contents lead to improved structural stability. Electrochemical studies demonstrate that LiNi0.4Co0.4Mn0.2O2 cathodes exhibit considerable improvements in both the reversible capacity and the rate capabilities at a voltage range of 2.5–4.6 V. In situ XRD measurements reveal that LiNi0.4Co0.4Mn0.2O2 maintains a single-phase and undergoes lesser structural variations compared to controlled compositions during a delithiation process up to 4.6 V, while achieving a high reversible capacity over 200 mAh g−1. As a result, LiNi0.4Co0.4Mn0.2O2 experiences fewer structural degradations during electrochemical cycling, which explains the excellent long-term cycling performance.
Bibliographical noteFunding Information:
The authors gratefully thank Ms. M. K. Cho in the Advanced Analysis Center at the Korea Institute of Science and Technology for contributions to the microstructure characterization using TEM. We also appreciate Ms. H.J. Ryoo and Mr. D.W. Kim for their help on the ICP-OES and BET measurements. We also thank Ms. N. R. Jahng at the Yonsei Center for Research Facilities for particle size analysis. This work was supported by the National Research Foundation of Korea (NRF-2011-C1AAA001-0030538) and KIST Institutional Program (2E27062).
All Science Journal Classification (ASJC) codes
- Renewable Energy, Sustainability and the Environment
- Energy Engineering and Power Technology
- Physical and Theoretical Chemistry
- Electrical and Electronic Engineering