Interface engineering of powder-based materials is essential for improving the performance and reliability of energy materials used in energy conversion and storage, including batteries, electrocatalysts, and magnetic materials [1, 2]. Interparticle interfaces in powder-based components often govern local charge transport, electric-field localization, secondary phase formation and energy-loss mechanisms ultimately determining energy efficiency and reliability. Therefore, introducing coating layers onto individual particle, which functions as a interfacial layer in bulk materials, has been proposed as a common strategy to control  interfaces in powder-based component. However, conventional powder-surface coating techniques, such as sol–gel processing and ball milling, often suffer from non-uniform coverage and limited capability for precise nanoscale thickness control. Moreover, residual solvents, surface defects, or by-products remained on particle surfaces during process can deteriorate interfacial stability and long-term reliability. Herein, we introduce rotary-reactor powder sputtering as a solvent-free and precisely controllable route for depositing various shell layers on powder-based energy materials. The proposed sputtering system incorporates a rotary reactor that is designed to continuously disperse and reorient powders, enabling uniform plasma exposure over nonplanar particle surfaces and thereby forming conformal interfacial layers with precisely controlled thickness. This approach was applied to deposit a nanoscale Bi₂O₃ interfacial layer on Fe-based alloy powders widely used for energy-conversion applications. Correlative X-ray photoelectron spectroscopy (XPS) and in situ transmission electron microscopy (TEM) analysis were performed to investigate interfacial phase transformations as a function of annealing temperature, revealing a correlation between the interfacial evolution and the efficiency of energy conversion. By uniformly and precisely controlling the interphase, an optimized interfacial layer resulting from a thickness of 40 nm Bi₂O₃ onto Fe-based magnetic powder showed a substantial reduction of 45.6% in power loss and a 2.2-fold increase in magnetic permeability, indicating enhanced energy-storage capability, compared with the uncoated bare powder. In addition, another example of powder surface coating, energy storage materials is also presented focusing on microstructural analysis and reliability. Overall, the precisely controlled coating layer on powder surface significantly enhance performance and reliability in their applications, highlighting rotary-reactor powder sputtering as a practical and scalable route for precision interface engineering.