Supercritical CO2-driven mechanochemical synthesis for spinel oxides with high electrochemical performance

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.