Investigation of the Li solubility in the intermediate phase Li17Sn4 relevant to understanding lithiation mechanisms in Sn-based anode materials

摘要

A comprehensive study of the Li-rich phase boundary of the intermediate Li17Sn4 compound is given based on thermochemical and electrochemical investigations. From the results a partial phase diagram showing the homogeneity range of this phase could be constructed. Using these results, the defect mechanism for the compound Li17Sn4 could also be clarified. Galvanostatic coulometry with potential limitation (GCPL) was performed using 2032 coin cell equipment. This allowed for the determination of the amount of Li insertion on special crystallographic sites at 25 degrees C, which is 0.41 +/- 0.04 at.%. The respective Li loss mechanisms (solid electrolyte interface formation, Li plating, Li trapping) are discussed. Irreversible capacity according to Li trapping could be excluded due to the limited voltage window of the experiments. Moreover, differential scanning calorimetry (DSC) was carried out on two individual Tian-Calvet type calorimeters. The Li-rich boundary of the Li17Sn4 compound was determined at 81.31 +/- 0.04 (C-80) and 81.28 +/- 0.05 at.% Li (M-HTC) at 427 degrees C. In addition, the latter results were compared to the change of lattice parameters of alloys with compositions Li17+xSn4. (C) 2017 Elsevier B. V. All rights reserved.