Thermal Stability Study of Surface Modified Ni-based Cathode Materials using in situ- XRD, hard and soft X-ray Absorption Spectroscopy during Heating

Abstract

The research and development of hybrid electric vehicle (HEV), plug-in hybrid electric vehicle (PHEV) and electric vehicle (EV) are intensified due to the energy crisis and environmental concerns. Having the highest energy density among all rechargeable batteries, lithium-ion battery is considered as the best candidate among rechargeable batteries for transportation applications. In order to meet the challenging requirements of powering those vehicles, the safety characteristics of lithium-ion battery need to be thoroughly studied and significantly improved. For such studies, the thermal stability is the key issue, especially for using the Ni-based layered cathode materials, which have a merit of high capacity. It was reported that at highly delithiated (i.e., charged) states, the reduction of Ni4+ during heating releases oxygen that can accelerate severe thermal runaway by reacting with the electrolyte and leads to catastrophic failure of the battery. One effective way to improve the thermal stability of Ni-based cathode materials is the surface coating or modifications with thermally stable compounds (e.g., ZrO2, Al2O3, AlF3, etc). However, there is little information available about how the surface modification suppresses the thermal decomposition of charged cathode materials in detail.