In‐situ and Real‐time Monitoring the Chemical and Thermal Evolution of Lithium‐ion Batteries with Single‐crystalline Ni‐rich Layered Oxide Cathode

High‐capacity Ni‐rich layered oxides are promising cathode materials for fabrication of lithium‐ion batteries (LIBs) with high energy density. However, thermal runaway of LIBs with these cathodes leads to great safety concerns. In this study, single crystalline LiNi0.9Co0.05Mn0.05O2 (NCM‐SC) has been prepared and a flexible optical fiber was buried inside the pouch‐type LIBs with NCM‐SC cathode to in‐situ study its real‐time temperature evolution during charge/discharge process. NCM‐SC exhibits an enhanced Li+ ions transportation efficiency and electrode reaction kinetics, which can effectively reduce the generation of polarization heat and mitigate the internal temperature rise of the pouch‐type battery. Meanwhile, solid‐electrolyte interface (SEI) film decomposition and gas accumulation are effectively alleviated, due to the enhanced thermal stability of SEI film formed on NCM‐SC. Moreover, the single crystal architecture can effectively retard layered to spinal and rock‐salt phase transition, mitigate the crack formation and structural collapse. Consequently, NCM‐SC exhibits an excellent electrochemical performance and enhanced thermal stability.