The present paper comprises results of our studies about the influence of the atmosphere and fuel amount on the synthesis and electrochemical performance of LiNi0.5Mn1.5O4 spinel (LNMS). Reaction of mixtures of metal nitrates with and without sucrose (fuel) in Ar and in air flow has been studied by thermal analysis and coupled mass spectrometry (TG/DTA/MS). Products obtained after the thermal study have been identified and characterized by powder X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). Gases evolved along the thermal treatment have been identified by coupled mass spectrometry (MS). From all these results the synthesis reactions have been put forward. When the reaction is conducted in air sub-micrometric LiNi0.5Mn1.5O4 spinel is obtained independently of the amount of sucrose. When the reaction is done in Ar the spinel is only obtained in absence of fuel. The electrochemical performances at 25°C and 55°C of the synthesized LNMSs have been evaluated by galvanostatic cycling. The samples prepared in air furnish high capacity (≈120mAhg−1) and they work at high voltage (≈4.7V). Besides, they exhibit remarkable cycling properties, even at elevated temperature (55°C), with capacity retentions higher than 90% after 50 cycles.