Single-crystal high-nickel layered cathodes for lithium-ion batteries: advantages, mechanism, challenges and approaches

The ever-increasing demand of advanced lithium-ion batteries is calling for high-performance cathode materials. Among promising next-generation cathode materials, high-nickel layered oxides with spherical polycrystalline secondary particles exhibit the outstanding advantage of high energy density. However, polycrystals, suffered from the pulverization of particles and the expansion of cracks, show the shortcoming of poor cycling performance. As an efficient solution, the single-crystal route has been underestimated hitherto. Herein, the unique structural degradation mechanism of single crystals is emphasized, and their advantages against polycrystals are comprehensively summarized in terms of electrochemical, thermal, and mechanical properties. Furthermore, we point out the practical challenges of single-crystal materials toward practical applications and raise hopeful strategies for overcoming such issues. Based on the aforementioned characteristics and approaches, future directions are outlooked as well.