Lithium-rich spinels were obtained with the same structure but different surface area by two different synthesis routes, namely the “once-annealed” and the “twice-annealed” methods. The elevated temperature performance of Li/Li1+x Mn2O4 cell is significantly improved using a spinel cathode with a small surface area: the cell at 50°C lost 5% of the initial capacity over the first 100 cycles based on a spinel cathode with the small surface area of 1.2 m2/g compared to 8% based on a large one of 6.2 m2/g. Also the mechanism responsible for the reaction of LiMn2O4 with LiOH to form lithium-rich spinel has been investigated.