Environmentally friendly 5 V cathode based on Fe-doped LiMn1.5Ni0.5O4 spinel for Li-ion batteries

LiNi0.5Mn1.5O4-based materials are considered an interesting choice to be used as positive electrode for Li-ion batteries. Several years ago, it has been shown that doping this material with an amount of Cr allowed an improvement of its electrochemical performances, particularly at high rate capability. Unfortunately, Cr is one of the most toxic elements, especially at the oxidation state + VI. To solve this drawback, we suggest using a little amount of Fe instead of Cr. In this work, we report the synthesis of a spinel structure material which general formula is LiFe2yNi0.5-yMn1.5-yO4 (y ≤ 0.1) through combustion method. Two annealing temperatures were used: one at 800 and the other at 900 °C. The morphological analysis revealed the samples prepared at 800 °C are nanometric, meanwhile the ones annealed at 900 °C showed two distribution of particle size: ∼200 nm and ∼ 600 nm. Regarding the electrochemical properties, at the slow discharge rate (1C), the samples prepared at 900 °C exhibit high capacity during their discharge and better capacity retention. The best electrochemical performances were delivered by the materials with 0.05 and 0.075 of Fe content, their capacities were around 130 mAh/g and their capacity retentions were in the order of 98.6% after 50 cycles. These excellent performances were confirmed by the tests made at high rate capabilities; LiFe0.1Ni0.45Mn1.45O4 (y = 0.5) material delivered a discharge capacity of 102mAh/g at 20C (complete discharge in 3 min) maintaining a capacity retention of 79.7%. These results correspond to 9.56 kW/kg of power density and 482.5 kWh/kg of energy density. To summarize, doping with iron allowed us to prepare environmentally friendly material to be used as a positive electrode for Li-ion batteries with excellent electrochemical performances, especially at high rate capability. This material is a good candidate to be used for applications which demands are high in density and in power densities.