WEB Understanding and modelling the thermodynamics and electrochemistry of tin (IV) sulfide as a novel anode material for lithium ion batteriesTuesday (22.09.2020) 11:50 - 12:05 F: Functional Materials, Surfaces, and Devices 1 Part of:
Due to its theoretical capacity of 960 mAh/g, which is more than double that of graphite (372 mAh/g), as well as its natural abundance, Sn is an interesting anode active material to replace graphite in lithium ion batteries. However, Sn-based anodes suffer from prohibitively large volume expansions because of the formation of brittle LixSn alloys during lithiation (>185 % for full lithiation to Li17Sn4). These volume changes lead to crack formation, loss of electrical contact between particles, pulverization of the electrode during cycling, lithium trapping, and an unstable Solid Electrolyte Interphase (SEI) growth. To overcome these degradation mechanisms, Sn-based chalcogenide compounds such as SnS2 can be used as anode active materials due to formation of an inactive Li2S buffer matrix via a conversion-type reaction during first lithiation.
Although the lithiation of SnS2 has been studied by several groups [1-3], there are still many open questions regarding the structural changes of SnS2 electrodes during lithiation and the amount of lithium which can be intercalated into the layered structure of SnS2. Furthermore, there are no data on the effect of pre-lithiation of SnS2 on the first cycle irreversible capacity losses and coulombic efficiencies during cycling, which would be necessary for the balancing of full cells. To address these open questions, computational thermodynamics was combined with key experiments to 1) understand the electrochemical lithiation of SnS2 and 2) model the phase development of the electrodes during lithiation. Furthermore, these data were used to pre-select compositions of pre-lithiated SnS2 and evaluate their electrochemical performance.
Firstly, galvanostatic intermittent titration technique experiments were combined with structural investigations of electrochemically lithiated SnS2 electrodes (ex-situ XRD and Rietveld analysis) to gain fundamental insights into the lithiation mechanism of SnS2. The quasi-open circuit voltages and structural data were used to develop a thermodynamic model for the LixSnS2 phase and calculate the potential vs. capacity curves and phase diagrams. Based on the experimental and calculated data, SnS2 and selected LixSnS2 compositions, which were prepared via electrochemical pre-lithiation, were cycled using constant current constant voltage mode in order to assess the relationship between initial lithium content of the anode and their coulombic efficiencies.