<i>In Situ</i> Mitigation of Calcination-Introduced Surface Damage of Single-Crystal Nickel-Rich Cathode Materials

Single-crystal (SC) Ni-rich cathode materials have attracted great attention for Li-ion battery applications due to their outstanding cyclability. However, the high temperature required for synthesizing SC also causes damage to temperature-sensitive Ni-rich cathode materials. Severe surface damage can result, even without notable bulk property degradation. Fortunately, we reveal that the surface damage can be mitigated by applying molten salt as an <i>in situ</i> protection agent to the particle surface during the high-temperature calcination. Detailed morphology evolution and near-surface features captured by <i>in situ</i> and <i>ex situ</i> techniques demonstrate that even a small amount of molten salt can effectively enclose particles during calcination. As a result, a solid-liquid-gas interface is built to replace the solid-gas interface, inhibiting the irreversible loss of lithium and oxygen to the high-temperature environment. Overall, SC particles synthesized with a suitable amount of molten salt addition show fewer surface defects and impurities than those without molten salt, leading to an enhanced electrochemical performance. This study highlights the importance of controlling surface damage in the production of high-performance SC Ni-rich cathode materials.