High voltage nickel manganese spinel oxides for Li-ion batteries

High voltage spinel oxides with composition LiMn_2 − xM_xO₄ (M, a transition metal element) have remarkable properties such as high potential, high energy density and high rate capability. We believe that these positive electrode materials could replace the widespread commercial layered nickel cobalt oxides in some applications. The present assessment highlights electrochemical performance of optimized LiNi_0.5Mn_1.5O₄ and substituted counterparts, all having a spinel structure (cubic close-packed oxygen array) similar to the relative LiMn₂O₄. To fully emphasize the benefit from high potential spinel oxides, tests have been performed versus lithium metal, Li₄Ti₅O₁₂ and graphite, using various electrode loadings (0.3-4.5 mAh cm⁻²) and cycling rates (from C/20 to 60C rate). Steady capacity retention (130-140 mAh g⁻¹ for nearly 500 cycles) and flat voltage (4.7 V vs. Li⁺/Li) have been obtained at C/5 rate at room temperature. Effect of cycling at high temperature has been shown to be less critical than for LiMn₂O₄. High voltage spinel oxides still sustain 100 mAh g⁻¹ and over after 400 cycles at 55 °C at 1C rate. Rate capability is also excellent, with only 4% loss of capacity when comparing C/8 and 8C rates (thin electrodes).