The transition toward sustainable, high‐energy density lithium‐ion batteries (LIBs) has intensified the search for cobalt‐free cathode materials, driven by the environmental, economic, and ethical limitations associated with cobalt usage. Among these, single‐crystal (SC) cobalt‐free cathodes have emerged as a transformative class of materials, offering superior structural integrity, enhanced thermal stability, and prolonged cycling life. This review critically examines recent advancements in SC cathode architectures across four major material families: Ni‐rich layered oxides, Li‐Mn‐rich compositions, spinel‐type structures, and olivine‐based frameworks. Unlike their polycrystalline analogues, SC cathodes feature continuous crystal lattices without internal grain boundaries, significantly reducing particle fracture, mitigating surface degradation, and suppressing phase instability during high‐voltage cycling. We explore state‐of‐the‐art synthesis techniques including molten salt‐assisted crystallization, hydrothermal growth, and co‐precipitation that enable the fabrication of phase‐pure SC particles with tailored morphology and minimal defect content. Additionally, the role of structural tuning strategies such as elemental doping, surface coatings, and facet orientation control is discussed in detail, with particular emphasis on improving electrochemical reversibility, lithium‐ion diffusion, and interfacial compatibility. Despite notable progress, key challenges persist, including controlling anisotropic lithium transport, preventing oxygen evolution, and ensuring process scalability. Emerging solutions involving entropy stabilization and advanced interface engineering are also discussed as promising pathways forward. By integrating insights across structure, chemistry, and processing, this review provides a comprehensive foundation for the design and deployment of cobalt‐free SC cathodes, offering practical pathways toward safer, longer‐lasting, and more sustainable LIB systems, compatible with both liquid and solid‐state battery technologies.
Alagar et al. (Sun,) studied this question.