Hydrothermally Synthesized SnS2 Anode Materials with Selectively Tuned Crystallinity as an Asset for Self-Healing Property and One Step in Situ Solid State Carbonization and Synthesis of C-SnS2
Authors: Bekzhanov Akzhan , Kleitz Freddy , Cupid Damian Marlon 
Published: December 2024

Tin-based chalcogenides such as SnS2 have been investigated as potential anode active materials for Li-ion batteries due to their high theoretical reversible capacities (e.g., 644 mAhg-1 for SnS2). These high capacities are associated with the reversible alloying of Sn with Li after the conversion reaction of SnS2 to Sn and Li2S. In this work, SnS2 was prepared via two approaches: hydrothermal synthesis of SnS2 and one step solid state synthesis of carbon coated SnS2. In the hydrothermal reaction, different molar ratios of tin chloride to thioacetamide were employed to synthesize SnS2 nanocrystals with varying fractions of the crystalline and amorphous states. An increase in molar ratio showed more crystalline SnS2 products with intensified different crystal plane orientations and formation of monolayers on the surface grains. During electrochemical analysis vs Li/Li+, partial reversibility of Sn and Li2S back to SnS2 was observed, leading to a unique self-regeneration property of the electrode. The presence of nano crystals and their level of crystallinity was examined by ex-situ Transmission Electron Microscopy (TEM) and X-ray Diffraction analysis (XRD). Galvanostatic Intermittent Titration (GITT) with in-situ Electrochemical Impedance Spectroscopy (EIS) after each galvanostatic step was used to evaluate the lithium diffusion coefficients (DLi+) to elucidate the lithium intercalation kinetics of SnS2 and its conversion to Sn and Li2S phases up to x ≈ 2.08 moles of lithiation or 300 mAh g-1. The SnS2 anode samples showed good cycling stability across 100 cycles at 0.1 C rate (560 mAh g-1) in half cell testing against Li chip. In full cell mode against NCM 811 cathodes, the cell retained a specific capacity of 160 mAh g-1 at 300th cycle.
Further, we introduce a low cost, scalable solid state heat treatment method to produce SnS2-C materials, where the carbon not only facilitates electron transport, but also assists to mitigate the volume expansion of SnS2 during lithiation and enhance its structural stability. However, due to the phase transformations of SnS2 during heating, SnS2-C materials cannot be synthesized via solid state heat treatments of SnS2 with a carbon source. However, in this work, we show a novel method of producing carbon-coated SnS2 by thermally treating Sn-precursors and S with organic polymers. Using this method, SnS2-C materials were prepared, where the SnS2 crystal structure was retained and no impurity tin-sulfides such as SnS and Sn2S3 were formed. The electrochemical performance of the SnS2-C anode active materials was tested vs Li/Li+ and excellent cycling stability can be reported when compared to non-coated SnS2.
Keywords: SnS2, anodes, composite anodes, carbon coating.

Acknowledgement

This research work is funded by Project “RESTINA”, where the main goal is to deliver “generation 3b cells for battery electric vehicles (BEVs)”. Funding agent
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