Ironless stator axial-flux permanent magnet (AFPM) machines provide many attractive electromagnetic performances such as high efficiency in high-frequency mode and strong short-term overload ability, which make them more competitive in flywheel energy storage applications. However, designing high-torque-density AFPM machines, particularly their ironless stators, is with significant challenges and needs great efforts. In this article, a high-strength oil-immersed cooling stator with nonoverlapping concentrated winding is proposed for high-power ironless stator AFPM machine applications. This article explains in detail the design, analysis, and manufacturing process of the proposed oil-immersed cooling stator. With the three-dimensional finite-element analysis (3-D FEA), a 9000-r/m/50-kW 12-slot/10-pole prototype for a flywheel energy storage system is successfully designed and developed using the proposed high-strength oil-immersed cooling ironless stator. The experimental test results demonstrate the effectiveness of the cooling design and mechanical strength.