The high voltage spinel LiNi0.5Mn1.5O4−δ films were obtained by pulsed laser deposition. The effects of oxygen deficiency, annealing treatment, and film thickness on microstructure, morphology and electrochemical properties were investigated. We showed that tuning the oxygen pressure and annealing treatment allows modifying the oxygen film stoichiometry. Trying to determine the oxygen stoichiometry in thin films, a series of oxygen-deficient spinel “LiNi0.5Mn1.5O4−δ ” powder samples by quench steps from different temperatures were prepared. It is demonstrated that powders and thin films presenting similar cell parameters, namely related to the oxygen stoichiometry, show similar electrochemical profiles. Meanwhile, the compatibility of electrolyte with substrate and the stability of the target were also investigated.