High-entropy oxides (HEOs) have gained significant attention from lithium-ion batteries since they can present cycling stability and possess a high specific capacity. While many studies have focused on discovering new high entropy oxides by changing their components, the influence of the synthesis environment on the structural properties and thus electrochemical behavior remain unresolved. Herein, we studied the effect of the synthesis environment, which is argon and air on the structural and electrochemical properties of (FeMnCrCoZn)(3)O-4 powders. We observed that the synthesis atmosphere affects greatly oxygen vacancy formation. The sample synthesized under an argon atmosphere (HESO-Ar) shows enhanced cycling and rate performances. Our work can open up new opportunities in designing HEO-based anodes and utilizing other HEO-based functional materials by altering and controlling the synthesis environment.