Stanford R. Ovshinsky Sustainable Energy Fellowship award talk: Structural Evolution of Nickel Thiophosphate Electrode Materials

Transition metal phosphorus trichalcognides have demonstrated to be promising electrodes in secondary Li–ion batteries with relatively high initial gravimetric capacity, and NiPS3 is in class of materials [1]. With C2/m symmetry, layers consist of edge-sharing Ni–S octahedra with a third of the Ni sites substituted with phosphorus dimers. NiPS3 has a theoretical capacity of 865 mAh/g corresponding to 6 mol of Li ions. The dual mechanisms of Li insertion/extraction and conversion are not well understood and is of interest due to the potential for high capacity relative to that of intercalation–based host materials. To better advance our understanding of the chemical and structural changes that contribute to capacity fade and irreversibly trapping Li ions, we employ the pair distribution functions technique and density functional theory to investigate the local structure evolution of the parent layered structure of NiPS3. The intercalation mechanism of Li ions shows decreased capacity fade within an operating voltage window of 1.0 V - 3.5 V vs. Li/Li+, depending on mass loading.
[1] R. Brec, D. M. Schleich, G. Ouvrard, A. Louisy, and J. Rouxel, Inorg. Chem. 18, 1814 (1979).