\textit{In-Situ }X-ray Absorption Spectroscopy Study of Li[LiMnNi]O2 Cathode Material

The cation/Li substituted Li[LiM]O2 layered material (where M is typically a blend of Mn, Ni and Co) is a promising high-capacity Li-ion battery cathode material due to the fact that it has yielded capacities exceeding 240 mAh/g, and up to 285 mAh/g even after many (50) deep-discharge cycles at useable charge/discharge rates (C/20). In an effort to understand the origin and relevance of the substantial irreversible capacity observed during the first charge cycle at a potential of approximately 4.5 V vs. Li, we have performed an \textit{in-situ }x-ray absorption spectroscopy (XAS) study of the charge compensation mechanism associated with the charge/discharge of Li[LiMnNi]O2 cathode material. XAS at the Ni and Mn K edges were carried out during the first two charge cycles of a layered Li[Li0.17Mn0.58Ni0.25]O2 powder based electrode system using an in-situ cell. The XAS results provide information about the electronic and atomic structure around the metals as a function of state of charge.