Influence of the Lattice Parameter Difference between the Two Cubic Phases Formed in the 4 V Region on the Capacity Fading of Spinel Manganese Oxides

To develop a better understanding of the capacity-fading mechanisms of spinel lithium manganese oxides, the electrochemical properties, degree of manganese dissolution, and crystal chemistry of a number of singly substituted LiMn 2 - y M y O 4 (M = Li, Al, Ti, Co, and Ni and 0 ≤ y ≤ 0.2) and doubly substituted LiMn 2 - y - z M y Li z O 4 (M = Ti, Co, and Ni, 0 ≤ y ≤ 0.1, and 0 ≤ z ≤ 0.1) oxides have been compared with those of LiMn 2 O 4 . The cation-substituted spinel manganese oxides show better electrochemical performances than LiMn 2 O 4 . Especially, the doubly substituted LiMn 1.85 Ni 0.075 Li 0.075 O 4 exhibits excellent cyclability at both ambient and elevated temperatures with a capacity of around 100 mAh/g. It also exhibits remarkable rate capability and excellent capacity retention (>95%) after storage at 60 °C at various depths of discharge (DOD). Although the degree of manganese dissolution does not vary significantly, the spinel manganese oxides show a clear relationship between the percent capacity fade and the lattice parameter difference (Δ a ) between the two cubic phases formed in the 4 V region. A smaller Δ a and the associated negligible volume change (Δ V ) appear to minimize the microstrain, maintain good interparticle contact, and lead to superior electrochemical performances. The excellent cyclability and high rate capability of the LiMn 2 - y - z Ni y Li z O 4 oxides may make them attractive for electric vehicles.