High-entropy oxides (HEOs) have been considered revolutionary electrode materials due to their stable crystal structure and robust lithium storage properties. Here, we synthesize a spinel (MgCoNiCuZn)FeO HEO in several seconds. This simple and effective method enhances the preparation efficiency by four orders of magnitude compared to that of the common sintering methods. As an anode material for Li-ion storage, to our knowledge, for the first time, the as-prepared HEO obtained a high reversible capacity of ∼812 mA h g at 50 mA g in the first cycle and an astonishing cycling stability over 650 cycles at 1 A g. Moreover, conversion and alloying reaction kinetics are identified during the lithiation and de-lithiation processes. Another interesting finding is that the spinel structure disappears after lithiation but recovers in the following de-lithiation stage, suggesting a homogeneous conversion reaction for the charge-discharge cycle.