Synthesis of Different Molybdenum Disulfide Nanostructures and their Applicability in Lithium Ion Batteries with Ionic L
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Synthesis of Different Molybdenum Disulfide Nanostructures and their Applicability in Lithium Ion Batteries with Ionic Liquid Electrolytes Daniel Albrecht1, Hendrik Wulfmeier1, Svetlozar Ivanov2, Andreas Bund2, Holger Fritze1 1 Institute of Energy Research and Physical Technologies, Clausthal University of Technology, Am Stollen 19 b, 38640 Goslar, Germany 2 Department of Electrochemistry and Electroplating, Ilmenau University of Technology, GustavKirchhoff-Straße 6, 98693 Ilmenau, Germany ABSTRACT Molybdenum disulfide (MoS2) nanostructures with three different morphologies are synthesized and tested with respect to their applicability in lithium ion batteries. Thereby, electrolytes based on ionic liquids are used. The electrochemical performance of nanostructures and thin films is compared to evaluate the influence of the morphology. Characterization methods include X-Ray diffraction (XRD), cyclic voltammetry (CV), galvanostatic cycling and thin film calorimetry. The thin film and the nanostructured samples show a reversible capacity of 525 mAh/g and a maximum capacity 225 mAh/g, respectively. INTRODUCTION This work is focused on nanocrystalline and amorphous MoS2 to be applied as anode material for lithium ion batteries. MoS2 nano powder shows several advantages in comparison to the standard anode material graphite. Key features include a high gravimetric capacity (1st cycle: > 1000 mAh/g, 20th cycle: 800 mAh/g [1]), a comparably low volume expansion (6.4% for changes from x = 0 to 0.75 in LixMoS2 [2]) and improved breakdown features. The latter is caused by small cavities in between the nanotubes which form a diffusion barrier for water [3]. Further, the high operating voltage (>1 V) suppresses the formation of the solid electrolyte interface (SEI), which is one main reason of irreversible capacity reduction and increased internal cell resistance. In addition MoS2 is cheap, non-toxic, widely available and shows a great variety of morphologies. Further, the investigations include thin films since miniaturized batteries are attractive for applications in medical devices, mobile consumer electronics or micro sensor applications. One advantage of thin film cells is the option to produce extremely thin batteries especially tailored to the device of interest. Another focus of this work is the interaction of MoS2 with the lithium ion containing ionic liquid (IL) [1M Li+ TFSI-, [BMP][TFSI]]. Those electrolytes enable to work in a wider potential window in comparison to conventional electrolytes such as ethylene carbonate or dimethyl carbonate (EC:DMC) [4]. The compatibility of MoS2 with an IL based electrolyte would enable to develop high voltage cells, if combined with a 5 V cathode material like LiCr0.2Ni0.4Mn1.4O4 [5]. Safety is another reason to use wide range stable ILs, since the commonly used alkyl carbonate based electrolytes can be electrochemically oxidized even below 4 V vs. Li/Li+ [6].
EXPERIMENT Synthesis of molybdenum disulfide powders Nanocrystalline samples of MoS2 were synthesized in acidic media using
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