<p>The rapid acceleration of global electrification has increased demand for sustainable energy storage, making lithium-ion batteries (LIBs) essential for various applications. However, their limited lifespan presents challenges related to resource waste and environmental risks. Unlike traditional metallurgical methods, which extract key metals from spent cathodes, the direct recycling process repairs damaged materials, maximizing their residual value through effective treatments. Despite widespread interest, systematic protocols to guide interdisciplinary researchers in direct recycling studies remain scarce. Using spent LiMn₂O₄ as an example, this protocol outlines a general approach for direct recycling and upcycling of spent LIBs. Initially, the failure condition of the spent cathode is evaluated using X-ray diffraction and inductively coupled plasma analysis to determine appropriate recycling parameters. The resulting recycled products include regenerated LiMn₂O₄ and upcycled next-generation cathode materials, such as high-voltage LiNi_0.5Mn_1.5O₄ and Co-free, Li-rich Li_1.2Ni_0.2Mn_0.6O₂. Subsequently, electron microscopy, spectroscopic techniques and electrochemical performance tests evaluate recycling effectiveness. This protocol incorporates two representative recycling methods to provide readers with a detailed procedural guide. Solid-phase regeneration forms the basis of most direct recycling technologies; thus, it requires minimal adjustments for broad applicability. Joule heating, a more emerging recycling technology, leverages rapid nonequilibrium reactions, substantially reducing processing time and introducing beneficial structural defects and elemental gradient distributions within the material. Compared to metallurgical methods, solid-phase and Joule heating-based protocols reduce recycling time to ~32 h and 5 h, respectively. Overall, this protocol provides a reliable guide for researchers, promoting sustainable LIB recycling and advancing clean energy research.</p>