Supercritical Fluid‐Based Synthesis of Nanomaterials for Energy Storage Applications: A Pathway Toward High‐Entropy Oxides

Supercritical fluid processing has developed into a versatile and environmentally responsible approach for the controlled fabrication of nanomaterials, distinguished by low density, viscosity, high diffusivity, and negligible surface tension. These intrinsic features enhance nucleation, efficient mass transport, and accurate control over particle dimensions, morphology, and compositional uniformity. This review comprehensively examines the fundamental principles of supercritical fluids, encompassing phase behavior, thermophysical characteristics, and the mechanisms governing nanoparticle formation, along with important engineering aspects related to both batch and continuous‐flow reactor configurations. The preparation of metal, metal oxide, and composite nanostructures through supercritical techniques is critically evaluated, emphasizing their benefits compared with traditional solid‐state and solution‐based synthesis routes. Special attention is given to the evolution toward high‐entropy oxides, where supercritical conditions enable homogeneous multication distribution, enhanced phase development, and defect modulation under kinetically advantageous environments. By establishing clear relationships between processing conditions, structural characteristics, and electrochemical performance, this review highlights the promise of SCF‐enabled methodologies as scalable and sustainable pathways for designing advanced multicomponent oxide materials suited for energy storage and catalytic applications.