Correlation between microstructure, thermodynamic stability, and electric work of tin sulfide active anode materials for Li-ion batteries

Abstract

The precipitation and hydrothermal synthesis methods were utilized to prepare phase pure SnS and SnS2 materials with different degrees of crystallinity, particle sizes, and morphology. The crystallite size, morphology, and phase composition of the as-synthesized materials were determined. The limiting molar enthalpies of solution of sulfur, the as-prepared materials, and that of a commercially available, macro-crystalline SnS2 in tin were established by drop calorimetry and subsequently, the enthalpies of formation were derived. The obtained enthalpies of formation of SnS range from − 48.8 to − 52.8 kJ mol−1 of atoms and for SnS2 from − 50.2–51.0 kJ mol−1 of atoms, which aligns well with existing literature results. For SnS, a trend towards less exothermic enthalpy of formation with decreasing crystallite size was observed. The obtained data of the as-prepared SnS2 materials did not clearly show such a trend and were further compared to that from commercially available, macro-crystalline SnS2. The obtained enthalpy of formation was even less exothermic compared to as-prepared SnS2 materials. After ball-milling of macro-crystalline SnS2 its formation enthalpy was the most exothermic of all SnS2 samples. An explanation of these unexpected results is given based on the energetics of crystallite size versus particle shape and size. Furthermore, the as synthesized and purchased materials were subjected to electrochemical discharge tests, and from the resulting voltage (as a function of x in LixSnS and LixSnS2) curves, the electrochemical work of the lithiation reactions was derived.