N. M. Beaver, S. Aryal, Y. Ding, J. P. Katsoudas, Y. Li, E. V. Timofeeva, C. U. Segre

Illinois Institute of Technology

Molybdenum sulfide (MoS₂) is a potential replacement for graphite anodes in Li-ion batteries. While it is not as conductive as molybdenum dioxide (MoO₂) and has a lower theoretical capacity (670 mAh/g for 4 lithium atoms vs. 840 mAh/g of MoO₂), MoS₂ is less prone to polarization losses^[1], volume expansion during lithiation,^[2] and unlike MoO₂ it does not evolve oxygen when reduced during lithiation. Bulk MoS₂ displays a capacity higher than theoretical at slow charge rates (more than 900 mAh/g in the first discharge), but its capacity drops by more than 200 mAh/g over 50 cycles at 35 mA/g.^[3] Composite^[4] and nanoscale^[2][5]materials show much improved stability and rate performance, but there is still uncertainty over the lithium intercalation mechanism.

To better understand this mechanism, in-situ characterization with element specific X-ray absorption spectroscopy (XAS), specifically X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine-structure spectroscopy (EXAFS) was used in this study. XANES provides information about the oxidation state of the element, whereas EXAFS probes the local environment around the atom of interest, such as near neighbors and interatomic distances. XAS measurements do not require long-range crystalline order, so they yield information that X-ray diffraction (XRD) does not. Although ex situ XAS has been used to characterize MoS₂ materials before,^[1][4] in this presentation for the first time we report the results of in-situ XAS characterization of MoS₂electrodes during charge/discharge cycling.

[1] Sen, Uttam Kumar, Priya Johari, Sohini Basu, Chandrani Nayak, and Sagar Mitra. “An Experimental and Computational Study to Understand the Lithium Storage Mechanism in Molybdenum Disulfide.” Nanoscale 6, no. 17 (August 8, 2014): 10243–54. doi:10.1039/C4NR02480J.

[2] Xiao, Jie, Daiwon Choi, Lelia Cosimbescu, Phillip Koech, Jun Liu, and John P. Lemmon. “Exfoliated MoS₂Nanocomposite as an Anode Material for Lithium Ion Batteries.” Chemistry of Materials 22, no. 16 (August 24, 2010): 4522–24. doi:10.1021/cm101254j.

[3] Fang, Xiangpeng, Chunxiu Hua, Xianwei Guo, Yongsheng Hu, Zhaoxiang Wang, Xueping Gao, Feng Wu, Jiazhao Wang, and Liquan Chen. “Lithium Storage in Commercial MoS₂in Different Potential Ranges.” Electrochimica Acta 81 (October 2012): 155–60. doi:10.1016/j.electacta.2012.07.020.

[4] Koroteev, V.O., L.G. Bulusheva, I.P. Asanov, E.V. Shlyakhova, D.V. Vyalikh, and A.V. Okotrub. “Charge Transfer in the MoS2/Carbon Nanotube Composite.” The Journal of Physical Chemistry C 115, no. 43 (November 3, 2011): 21199–204. doi:10.1021/jp205939e.

[5] Hwang, Haesuk, Hyejung Kim, and Jaephil Cho. “MoS₂ Nanoplates Consisting of Disordered Graphene-like Layers for High Rate Lithium Battery Anode Materials.” Nano Letters 11, no. 11 (November 9, 2011): 4826–30. doi:10.1021/nl202675f.