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 LiNiCoMnO (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.