The Waterloo Institute for Nanotechnology (WIN) and the Department of Chemical Engineering presents a seminar by Professor Fu-Ming Wang, from the Graduate Institute of Applied Science and Technology and National Taiwan University of Science and Technology, Taipei, Taiwan.
Failure Evaluation of Li-Rich Cathode (Li[NixLi(1-2x)/3Mn(2-x)/3]O2) Materials in Novel in-Situ Electrochemical Mass Studies of Lithium Ion Battery
An overview of main results concerning THz detection related to plasma nonlinearities in nanometer field effect transistors is presented. In particular nonlinearity and dynamic range of these detectors are discussed. We present also results on THz detection by Graphene field effect transistors. As a conclusion, we will show one of the first real world application of the FET THz detectors: a demonstrator of the imager developed for fast postal security imaging.
In the presence of literatures [1-4], high-voltage (> 4.8V; 5V class) Li-rich layer compounds (Li[NixLi(1-2x)/3Mn(2-x)/3]O2) have been reported to the next candidate of cathode materials in order to increase the power and energy density instead of LiCoO2 or LiNixMnyCozO2 conventional materials. These high-voltage Li-rich layer materials dedicate their high reversible capacities more than 270 mAh g-1, which is almost twice as higher as LiCoO2. However, this material suffers dramatically challenge due to the irreversible phase change in the first charge. Several studies had discussed the failure mechanism of this high voltage material; however, those comments are different. Mantia et al.  have demonstrated direct evidence of oxygen evolution from the Li-excess material at high potentials by in situ differential electrochemical mass spectrometry (DEMS) as well as Hy et al.  shown an oxygen activation occurs following electrochemical reaction and forms an irreversible formation of Li2O by surface enhanced Raman spectroscopy (SERS). In Jiang’s result , they are unable to detect any oxygen in their ex situ observation. Their XRD pattern and 6Li MAS NMR spectrum comment O2- loss is accompanied with the electrolyte to form CO2.
In our novel in-situ gas evolution experiment, we showed that there are two reaction mechanisms in the first charge process in Figure 1. In the first reaction mechanism, the CO2 (m/z 44) and CO (m/z 28) generate drastically at the potential of 4.25V. In comparison with cyclic voltammogram (CV) (not shown in here), the potential of 4.25V is indicated to the reaction of Ni3+/Ni4+; therefore, the gas evolution at this stage can be concluded the electrolyte is partially decomposed with the catalyst of Ni3+/Ni4+ and the oxygen evolution is not correlated. Second reaction mechanism starts at 4.65V, the CO2 forms solely in accompanied with oxygen evolution (m/z 32) from cathode material. Above result indicates that the second reaction mechanism is lead by the oxygen evolution and further reacts with electrolyte.
In this research, we establish a novel in-situ observation for evaluating gas evolution and define the reaction mechanisms of high voltage cathode material.
Figure 1 In-situ electrochemical mass
 F. La Mantia, F. Rosciano, N. Tran, P. Novak, J. Appl. Electrochem. 38 (2008) 893
 Sunny Hy, Felix, John Rick, Wei-Nien Su, Bing Joe Hwang, J. Am. Chem. Soc. 136 (2014) 999
 Meng Jiang, Baris Key, Ying S. Meng, and Clare P. Grey, Chem. Mater. 21 (2009) 2733
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