Articles by Qinghao Li in JoVE
Elemental-sensitive Detection of the Chemistry in Batteries through Soft X-ray Absorption Spectroscopy and Resonant Inelastic X-ray Scattering Jinpeng Wu1,2, Shawn Sallis2,3, Ruimin Qiao2, Qinghao Li2,4, Zengqing Zhuo2,5, Kehua Dai2,6, Zixuan Guo2,7, Wanli Yang2 1Geballe Laboratory for Advanced Materials, Stanford University, 2Advanced Light Source, Lawrence Berkeley National Laboratory, 3Department of Materials Science and Engineering, Binghamton University, 4School of Physics, National Key Laboratory of Crystal Materials, Shandong University, 5School of Advanced Materials, Peking University Shenzhen Graduate School, 6School of Metallurgy, Northeastern University, 7Department of Chemical Engineering, University of California-Santa Barbara Here, we present a protocol for typical experiments of soft X-ray absorption spectroscopy (sXAS) and resonant inelastic X-ray scattering (RIXS) with applications in battery material studies.
Other articles by Qinghao Li on PubMed
High-efficiency in Situ Resonant Inelastic X-ray Scattering (iRIXS) Endstation at the Advanced Light Source The Review of Scientific Instruments. | Pubmed ID: 28372380 An endstation with two high-efficiency soft x-ray spectrographs was developed at Beamline 8.0.1 of the Advanced Light Source, Lawrence Berkeley National Laboratory. The endstation is capable of performing soft x-ray absorption spectroscopy, emission spectroscopy, and, in particular, resonant inelastic soft x-ray scattering (RIXS). Two slit-less variable line-spacing grating spectrographs are installed at different detection geometries. The endstation covers the photon energy range from 80 to 1500 eV. For studying transition-metal oxides, the large detection energy window allows a simultaneous collection of x-ray emission spectra with energies ranging from the O K-edge to the Ni L-edge without moving any mechanical components. The record-high efficiency enables the recording of comprehensive two-dimensional RIXS maps with good statistics within a short acquisition time. By virtue of the large energy window and high throughput of the spectrographs, partial fluorescence yield and inverse partial fluorescence yield signals could be obtained for all transition metal L-edges including Mn. Moreover, the different geometries of these two spectrographs (parallel and perpendicular to the horizontal polarization of the beamline) provide contrasts in RIXS features with two different momentum transfers.
Role of Superexchange Interaction on Tuning of Ni/Li Disordering in Layered Li(NiMnCo)O The Journal of Physical Chemistry Letters. | Pubmed ID: 29086570 Ni/Li exchange (disordering) usually happens in layered Li(NiMnCo)O (NMC) materials and affects the performance of the material in lithium-ion batteries. Most of previous studies attributed this phenomenon to the similar size of Ni and Li, which implies that Ni should be more favorable than Ni to be located at Li 3b sites in the Li slab. However, this theory cannot explain why in Ni-rich NMC materials where most Ni cations are Ni, Ni/Li exchange happens even more frequently. Using extensive ab initio calculations combined with experiments, here we report that a superexchange interaction between transition metals plays a dominating role in tuning the Ni/Li disordering in NMC materials. Under this scheme, we also propose a new charge compensation mechanism that describes that after Ni/Li exchange the nearest Co transforms to Co in Ni-rich NMC materials. On the basis of this theory, the existence of Co in the initial Ni-rich NMC samples was predicted for the first time, which was further confirmed by our synchrotron-based soft X-ray absorption spectroscopy.
Coupling Between Oxygen Redox and Cation Migration Explains Unusual Electrochemistry in Lithium-rich Layered Oxides Nature Communications. | Pubmed ID: 29233965 Lithium-rich layered transition metal oxide positive electrodes offer access to anion redox at high potentials, thereby promising high energy densities for lithium-ion batteries. However, anion redox is also associated with several unfavorable electrochemical properties, such as open-circuit voltage hysteresis. Here we reveal that in Li NiCoMnO, these properties arise from a strong coupling between anion redox and cation migration. We combine various X-ray spectroscopic, microscopic, and structural probes to show that partially reversible transition metal migration decreases the potential of the bulk oxygen redox couple by > 1 V, leading to a reordering in the anionic and cationic redox potentials during cycling. First principles calculations show that this is due to the drastic change in the local oxygen coordination environments associated with the transition metal migration. We propose that this mechanism is involved in stabilizing the oxygen redox couple, which we observe spectroscopically to persist for 500 charge/discharge cycles.