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

Abstract

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 LiNi_0.8Co_0.1Mn_0.1O₂ 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.