A Microscopic Investigation on the Local Degradation and Thermal Stability of Charged Nickel-Based Cathode Materials for Lithium-Ion Batteries
- A Microscopic Investigation on the Local Degradation and Thermal Stability of Charged Nickel-Based Cathode Materials for Lithium-Ion Batteries
- 황수연; 김승민; 정경윤; Eric A. Stach; 장원영
- nickel-based cathode; thermal degradation; electron microscopy; lithium ion batteries
- Issue Date
- 14th International Union of Materials Research Societies-International Conference on Advanced Materials
- Ni-based layer structured cathode materials have been considered as one of the prime candidates for next generation batteries due to their higher energy density, less toxicity, and lower cost compared with those of LiCoO2. Despite these advantages, the thermal instability of Ni-rich materials is the largest hurdle that must be overcome before their widespread usage. Previous studies using x-ray based techniques, such as x-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS), have indicated that the substantial safety issues associated with Ni-rich materials are closely related to the existence of a structural instability. There have been quite a number of studies that have investigated the evolution of the average crystallographic structure of the cathode materials as a function of either temperature or degree of delithiation. However, because the degradation of electrode materials and the initiation of thermal runaway may start very locally within electrode materials, a complementary method is required to elucidate where and how these phenomena start and propagate at the nanoscale. In this presentation, we report the local evolution of the surface structure of LixNi0.8Co0.15Al0.05O2 (NCA) and LixNiyMnzCo1-y-zO2 (NMC) cathode materials of different composition (with y, z = 0.8, 0.1, and 0.6, 0.2, and 0.4, and 0.3) as a function of state of charge depth using transmission electron microscopy (TEM) combined with electron energy loss spectroscopy (EELS). In addition, we take advantage of real-time electron microscopy to directly investigate the process of thermal decomposition that occurs at the surface of charged NCA and NMC cathode materials, after they have been charged to different state of charge (SOC). By heating these materials inside the TEM, we are able to directly characterize near surface changes in both their electronic structure (using electron energy loss spectroscopy) and crystal structure and mo
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