Insights into the Fast-Charging Capability of Layered Ni-Rich Cathodes in Full-Cell Lithium-Ion Batteries

Extreme fast-charging (XFC) technology poses severe challenges to Li-ion battery systems, yet the primary challenge, lithium plating on graphite, limits our understanding of the fast-charging capability of nickel-rich layered oxide cathode materials. In this work, we specifically focus on the degradation mechanism of Ni-rich cathodes at fast-charging rates, which is achieved by constructing lithium-plating-free full cells. Intriguingly, both single-crystal LiNi0.82Mn0.07Co0.11O2 and polycrystalline LiNi0.83Mn0.05Co0.12O2 (NMC811) exhibit good fast-charging capability, and when charged at a fast rate of 4C, the increase in polarization is successfully suppressed compared to 1C charging. Analyzing single-crystal NMC811 allows us to unravel the intrinsic mechanism by avoiding intergranular cracking in polycrystalline materials, and the operando synchrotron X-ray diffraction results reveal that 1C charging results in a marginally higher depth of delithiation, which is accompanied by drastic nanostructure change, resulting in a more degraded surface and intragranular cracking. These insights are pivotal for understanding the intrinsic fast-charging capacity of Ni-rich NMCs and refining fast-charging protocols.