Evolution of the local structure and electrochemical properties of spinel LiNixMn2-xO4 (0 ≤ x ≤ 0.5)

A series of Ni substituted spinel LiNixMn2-xO4 (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 LiNixMn2-xO4 (x >= 0.3). Xray photoelectron spectroscopy confirmed Ni2+ cations were partially oxidized to Ni3+. The local structures of LiNixMn2-xO4 were studied by analyzing the F-2g((1)) and A(1g) Raman bands. The most compact [Mn(Ni)O-6] 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 angstrom, 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. (c) 2005 Elsevier Ltd. All rights reserved.