Flame synthesis of 5 V spinel-LiNi0.5Mn1.5O4 cathode-materials for lithium-ion rechargeable-batteries

The lithium transition metal oxide LiNi0.5Mn1.5O4 with an Fd3¯m space group (SG) structure has shown great potential as a cathode material for 5 V lithium-ion rechargeable-batteries. In this work, a flame-assisted spray technology (FAST) was developed to produce nanostructured LiNi0.5Mn1.5O4 powder in a continuous manner. The as-synthesized powder had a uniform morphology, was spherical in shape and had a nanocrystalline structure, as observed by SEM and TEM. The XRD pattern of the as-synthesized powder matched the spectrum of spinel-LiNi0.5Mn1.5O4. The average grain size was about 16 nm, as calculated by XRD. However, XRD also indicated the impurity Mn2NiO4 in the powder. By varying flame temperature, it was possible to show that the impurity was formed due to the high temperature of the flame. While flame temperature was minimized by lowering the H2/N2 ratio, it was not possible to completely eliminate Mn2NiO4 from the as-synthesized powder. After annealing at 800 °C for 2 h, the impurity was eliminated, and the XRD pattern of the powder indicated a pure-phase spinel structure with an Fd3¯m SG. The electrochemical performance of the flame-synthesized LiNi0.5Mn1.5O4 powder was tested in coin-type test batteries that were charged and discharged at constant current under a 5 V potential. The test cells showed the characteristic voltage plateaus of spinel-LiNi0.5Mn1.5O4 (Fd3¯m SG). The material proved to be electrochemically active as a cathode material for lithium-ion rechargeable-batteries.