Thermal effects on surface structure of charged Ni-rich cathode materials for Li-ion batteries studied by TEM-EELS

Thermal effects on surface structure of charged Ni-rich cathode materials for Li-ion batteries studied by TEM-EELS
황수연김동현김승민정경윤이정용Eric A. Stach장원영
Thermal effects; surface structure; Ni-rich cathode; TEM-EELS
Issue Date
The 2nd International Conference on Advanced Electromaterials
Lithium ion batteries (LIBs) have been utilized as power sources in a wide range of applications from small mobile devices to the large scale transportation systems including hybrid, plug-in hybrid, and electric vehicle (HEV, PHEV, and EV). Layered transition metal oxides based on LiCoO2 has been in general used as a cathode for LIBs, however, to meet the requirement of EV applications, the batteries need to be improved to have higher energy density, longer cycle life, and in particular, better safety. The Nibased layered cathode materials, LiNi0.8Co0.15Al0.05O2, are promising alternatives with their high discharge capacities ~200mAhg-1. However, LiNi0.8Co0.15Al0.05O2 electrodes have several disadvantages such as drastic capacity fading and impedance rise with cycling in addition to poor thermal stability. In addition, oxygen evolution of the charged Ni-rich cathodes at high temperatures is a serious threat for the safety, leading to catastrophic explosion by reaction with flammable electrolyte. Although various spectroscopic techniques, such as X-ray and neutron diffraction, and X-ray absorption (XAS), have been actively used for better understanding of the problems associated with the thermal instability of charged LiNi0.8Co0.15Al0.05O2, there has been a limit to examine local structural disorder or reorganization at the site of interest (e.g. edge or surface). Here, we investigated both electronic and crystal structures of charged LixNi0.8Co0.15Al0.05O2 cathode at elevated temperatures around 55oC as a function of state of charge (0.1≤ x ≤0.5) by transmission electron microscopy (TEM) coupled with electron energy loss spectroscopy (EELS), namely TEM-EELS. High spatial resolution of TEM provides nanoscale observation of the phase transitions that occur in individual particles, allowing us to distinguish subtle changes in crystal structure at surface from interior region after electrochemical delithiation. In ad
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