Surface reconstruction and chemical evolution of stoichiometric layered cathode materials for lithium-ion batteries

The present study sheds light on the long-standing challenges associated with high-voltage operation of LiNi x Mn x Co 1−2x O 2 cathode materials for lithium-ion batteries. Using correlated ensemble-averaged high-throughput X-ray absorption spectroscopy and spatially resolved electron microscopy and spectroscopy, here we report structural reconstruction (formation of a surface reduced layer, to transition) and chemical evolution (formation of a surface reaction layer) at the surface of LiNi x Mn x Co 1−2x O 2 particles. These are primarily responsible for the prevailing capacity fading and impedance buildup under high-voltage cycling conditions, as well as the first-cycle coulombic inefficiency. It was found that the surface reconstruction exhibits a strong anisotropic characteristic, which predominantly occurs along lithium diffusion channels. Furthermore, the surface reaction layer is composed of lithium fluoride embedded in a complex organic matrix. This work sets a refined example for the study of surface reconstruction and chemical evolution in battery materials using combined diagnostic tools at complementary length scales. Surfaces of electrodes evolve with charging and discharging cycles, leading to deterioration of battery performance. Here Lin et al . report structural reconstruction and chemical evolution at the surface of a stoichiometric layered cathode material with spectroscopy and microscopy techniques.