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). X-ray photoelectron spectroscopy confirmed Ni2+ cations were partially oxidized to Ni3+. The local structures of LiNixMn2−xO4 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.