A series of Ni substituted spinel LiNixMn2-xO 4 (0 ≤ x ≤ 0.5) have been synthesized to study the evolution of the local structure and their electrochemical properties. X-ray diffraction showed a few Ni cations moved to the 8a sites in heavily substituted LiNi xMn2-xO4 (x ≥ 0.3). X-ray photoelectron spectroscopy confirmed Ni2+ cations were partially oxidized to Ni3+. The local structures of LiNixMn2-xO 4 were studied by analyzing the F2g(1) and A1g Raman bands. The most compact [Mn(Ni)O6] octahedron with the highest bond energy of Mn(Ni)O was found for LiNi0.2Mn1.8O4, which showed a Mn(Ni)O average bond length of 1.790 Å, and a force constant of 2.966 N cm-1. Electrolyte decomposition during the electrochemical charging processes increased with Ni substitution. The discharge capacities at the 4.1 and 4.7 V plateaus obeyed the linear relationships with respect to the Ni substitution with the slopes of -1.9 and +1.9, which were smaller than the theoretical values of -2 and +2, respectively. The smaller slopes could be attributed to the electrochemical hysteresis and the presence of Ni3+ in the materials.
Bibliographical noteFunding Information:
This work was supported by the Ministry of Information & Communication of Korea [“Support Project of University Information Technology Research Center” supervised by the Korea IT Promotion Agency] and by the ERC program of MOST/KOSEF (Grant No. R11-2002-102-00000-0). One of the authors, Yingjin Wei, acknowledges the partial support from the Key Project (No. 10411) sponsored by the Ministry of Education of China and the special funds for major state basic research project (973) of China under the Grant 2002CB211802.
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)