Browsing by Author "Sun, Cheng-Jun"

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    In Situ and Operando Investigation of the Dynamic Morphological and Phase Changes of Selenium-doped Germanium Electrode during (De)Lithiation Processes
    (RSC, 2020-01) Li, Tianyi; Lim, Cheolwoong; Cui, Yi; Zhou, Xinwei; Kang, Huixiao; Yan, Bo; Meyerson, Melissa L.; Weeks, Jason A.; Liu, Qi; Guo, Fangmin; Kou, Ronghui; Liu, Yuzi; De Andrade, Vincent; De Carlo, Francesco; Ren, Yang; Sun, Cheng-Jun; Mullins, C. Buddie; Chen, Lei; Fu, Yongzhu; Zhu, Likun; Mechanical and Energy Engineering, School of Engineering and Technology
    To understand the effect of selenium doping on the good cycling performance and rate capability of a Ge0.9Se0.1 electrode, the dynamic morphological and phase changes of the Ge0.9Se0.1 electrode were investigated by synchrotron-based operando transmission X-ray microscopy (TXM) imaging, X-ray diffraction (XRD), and X-ray absorption spectroscopy (XAS). The TXM results show that the Ge0.9Se0.1 particle retains its original shape after a large volume change induced by (de)lithiation and undergoes a more sudden morphological and optical density change than pure Ge. The difference between Ge0.9Se0.1 and Ge is attributed to a super-ionically conductive Li–Se–Ge network formed inside Ge0.9Se0.1 particles, which contributes to fast Li-ion pathways into the particle and nano-structuring of Ge as well as buffering the volume change of Ge. The XRD and XAS results confirm the formation of a Li–Se–Ge network and reveal that the Li–Se–Ge phase forms during the early stages of lithiation and is an inactive phase. The Li–Se–Ge network also can suppress the formation of the crystalline Li15Ge4 phase. These in situ and operando results reveal the effect of the in situ formed, super-ionically conductive, and inactive network on the cycling performance of Li-ion batteries and shed light on the design of high capacity electrode materials.
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    In Situ Construction of an Ultrarobust and Lithiophilic Li-Enriched Li–N Nanoshield for High-Performance Ge-Based Anode Materials
    (ACS, 2020-11) Xiong, Bing-Qing; Zhou, Xinwei; Xu, Gui-Liang; Liu, Xiang; Hu, Youcheng; Liu, Yuzi; Zhu, Likun; Shi, Chen-Guang; Hong, Yu-Hao; Wan, Si-Cheng; Sun, Cheng-Jun; Chen, Shengli; Huang, Ling; Sun, Shi-Gang; Amine, Khalil; Ke, Fu-Sheng; Mechanical and Energy Engineering, School of Engineering and Technology
    Alloy-based materials are promising anodes for rechargeable batteries because of their higher theoretical capacities in comparison to graphite. Unfortunately, the huge volume changes during cycling cause serious structural degradation and undesired parasitic reactions with electrolytes, resulting in fragile solid-electrolyte interphase formation and serious capacity decay. This work proposes to mitigate the volume changes and suppress the interfacial reactivity of Ge anodes without sacrificing the interfacial Li+ transport, through in situ construction of an ultrarobust and lithiophilic Li-enriched Li–N nanoshield, which demonstrated improved chemical, electrochemical, mechanical, and environmental stability. Therefore, it can serve as a versatile interlayer to facilitate Li+ transport and effectively block the attack of electrolyte solvents, thus boosting the long-term cycle stability and fast charging capability of Ge anodes. This work offers an alternative methodology to tune the interfaces of other electrode materials as well by screening for more N-containing compounds that can react with Li+ during battery operation.