Insights into the defect-driven heterogeneous structural evolution of Ni-rich layered cathodes in lithium-ion batteries

Recently, considerable efforts have been made in research and development to improve Ni-rich lithium-ion batteries to meet the demands of vehicles and grid-level large-scale energy storage. The development of next-generation high-performance lithium-ion batteries requires a comprehensive understanding of the underlying electrochemical mechanisms associated with their structural evolution. In this work, advanced operando neutron diffraction and four-dimensional scanning transmission electron microscopy techniques were applied to clarify the structural evolution of electrodes in two distinct full cells with identical LiNi0.8Co0.1Mn0.1O2 cathodes but different anode counterparts. It is found that both cathodes in the two cells exhibit non-intrinsic two-phase-like behavior at the early charge stage, indicating selective Li⁺ extraction from cathodes. But the heterogeneous evolution of cathodes is inhibited with a graphite-silicon blended anode compared to that with a graphite anode due to differences in the delithiation rate. Moreover, it is revealed that the formation of heterogeneous structures is driven by the distribution of defects including Li/Ni disordering and microcracks, which should be inhibited by assembling an appropriate anode to avoid potential threats to cell performance. The present work unveils the origin of inhomogeneity in Ni-rich lithium-ion batteries and highlights the significance of kinetics control in electrodes for batteries with higher capacity and longer life.