Thermal Behavior of Ni-Rich Layered Oxide Cathode Materials during Cycling of 20 Ah-Scale Li-Ion Batteries

Abstract

Ni-rich layered oxide cathode materials have been extensively investigated as a cathode material for lithium-ion batteries because of their higher reversible capacity and lower cost than lithium cobalt oxide. However, most of them have been examined using lab-scale coin cells, and consequently, there is a limit to fully understanding the failure mode of Ni-rich layered oxides in commercial high energy Li-ion batteries. In this paper, the pouch-type 20 Ah-scale Li-ion full cells are fabricated using Ni-rich layered oxides as a cathode and graphite as an anode. Then, the electrochemical performances and thermal behaviors of Ni-rich layered oxides are compared to investigate their failure mode in large-scale Li-ion cells. The cell skin temperature is measured to observe the thermal behavior of Ni-rich layered oxides. A strong correlation between capacity retention, cell temperature variation, and internal cell impedance is observed in Ni-rich layered oxides. Moreover, an increase in the internal cell impedance during cycling is attributed to interfacial degradation of Ni-rich layered oxides rather than their bulk structural deformation. Therefore, we need to focus on the interfacial stability of Ni-rich layered oxide materials to improve their electrochemical performance for large-scale Li-ion batteries.