Advanced In Situ Diagnostic Techniques for Battery Materials

Xiao-Qing Yang and Kyung-Wan Nam, BNL

The high energy density Li-rich layered materials xLiMO2·(1-x)Li2MnO3 are promising candidate cathode materials for electric energy storage in plug-in hybrid electric vehicles (PHEVs) or electric vehicles (EVs). The relatively low rate capability is one of the major problems need to be resolved for these materials. In order to gain fundamental understanding to the key factors limiting the rate capability, in situ X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) studies of the Li1.2Ni0.15Co0.1Mn0.55O2 cathode material has been carried out. Through these studies direct experimental evidence is obtained showing that Mn sites have a much poorer reaction kinetics both before and after initial “activation” of Li2MnO3, comparing with Ni and Co. These results indicate that the Li2MnO3 might be the key component limiting the rate capability of the Li-rich layered materials, providing valuable guidance in designing various Li-rich layered materials with desired balance of energy densities and rate capabilities for different applications.

EXAFS spectra of Li1.2Ni0.15Co0.1Mn0.55O2 during constant voltage charging at 5V. Ni, Co, Mn reacted simultaneously using time-resolved XAS technique.