High resolution cyclic voltammograms of LiMn_2-x Ni_xO₄ with a microelectrode technique

Lithium-ion insertion/extraction at a single particle (10-30 μm in diam.) of LiMn_2-xNi_xO₄ (x = 0, 0.2, 0.5) was characterized by a microelectrode technique, in which a fine metal filament was manipulated to make electrical contact with the particle placed in 1 M LiClO₄/ PC + EC solution. By using this technique, we can evaluate the correct current-potential behavior of LiMn_2-xNi_xO₄ without any dilution due to an organic binder and a conductive additive. The cyclic voltammetry (CV) was performed for the particles up to a high anodic potential limit of 5.2 V vs. Li/Li⁺. Undoped LiMn₂O₄ shows two current peaks around 4.1 V due to the redox reaction of Mn^3+/4+ in the solid state phase, while the CV of Ni-doped LiMn₂O₄ was strongly deformed, showing new current peaks in a high potential region (∼ 4.7 V) at the expense of the 4.1 V wave. The 4.7 V wave would arise from the redox reaction of Ni^2+/4+. The cyclability of LiMn_2-xNi_xO₄ was evaluated by multi-scan cyclic voltammetry.