Abstract: Mechanochemical ball milling is a straightforward and efficient technology for material synthesis. However, cold welding significantly hampers both the reaction rate and the powder yield of the ball milling process. This study introduces a novel strategy to mitigate cold welding by utilizing supercritical carbon dioxide (SCCO₂) as a process control agent. The mechanism by which SCCO₂ inhibits cold welding was elucidated: SCCO₂ reduces surface energy and passivates dangling bonds on the newly exposed surfaces generated by ball milling, thereby preventing undesired re-formation. Building on this approach, a groundbreaking SCCO₂-driven ball milling (SDBM) method was developed, enabling the one-step, scalable production of 100 g of binary spinel oxide at room temperature within 8 h. Remarkably, the powder yield increases significantly from 13 % (conventional ball milling) to 98 %. The synthesized spinel oxide exhibits a small particle size, enhanced Mg migration, abundant oxygen vacancies, and high electrochemical performance (385 C/g for MgCo₂O₄). Beyond MgCo₂O₄, various binary and ternary spinel oxides were fabricated using SDBM technology. These results highlight the considerable benefits and the universality of SDBM technology in the fabrication of innovative materials.

Key words: Binary spinel oxide, Ball milling, Process control agent, Cold welding, Supercritical carbon dioxide