Real-Time Observation of Chemomechanical Breakdown in a Layered Nickel-Rich Oxide Cathode Realized by In Situ Scanning Electron Microscopy
Xiaopeng Cheng, Yonghe Li, Tianci Cao, Rui Wu, Mingming Wang, Huan Liu, Xianqiang Liu, Junxia Lü, Yuefei Zhang
Abstract
It is well-accepted that massive cracks in Ni-rich cathode secondary particles are the determining factors for long-term performance degradation; however, the corresponding crack generation and the state of dynamic propagation are still unknown. In this work, we utilize in situ scanning electron microscopy to reveal the dynamical morphological evolution of a single LiNi0.8Mn0.1Co0.1O2 secondary particle embedded in a cathode blend during electrochemical cycling. These observations show that very few cracks appear in the particle when cycled at a normal cutoff voltage of 4.1 V, but when the cutoff voltage is increased to 4.7 V as an extreme working condition, several cracks were clearly initially generated in the core region and propagated radially along the grain boundaries, finally reaching the particle’s surface. Impressively, crack propagation follows a repeat “grow–stagnate–grow” phenomenon during charge–discharge cycling. Our direct in situ investigation provides a full map of crack evolution in the cathode under electrochemical cycling during early stages.