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DOE OSTI2020

Materials Data on Li2Si2O5 by Materials Project

Li2Si2O5 crystallizes in the orthorhombic Pbcn space group. The structure is three-dimensional. Li1+ is bonded to four O2- atoms to form distorted LiO4 tetrahedra that share corners with four equivalent LiO4 tetrahedra, corners with five equivalent SiO4 tetrahedra, and an edgeedge with one LiO4 tetrahedra. There are a spread of Li–O bond distances ranging from 1.96–2.10 Å. Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with three equivalent SiO4 tetrahedra and corners with five equivalent LiO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.60–1.67 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a trigonal planar geometry to one Li1+ and two equivalent Si4+ atoms. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent Si4+ atoms. In the third O2- site, O2- is bonded to three equivalent Li1+ and one Si4+ atom to form a mixture of distorted corner and edge-sharing OLi3Si tetrahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Li2Si2O5 by Materials Project

Li2Si2O5 crystallizes in the orthorhombic Ccc2 space group. The structure is three-dimensional. Li1+ is bonded to four O2- atoms to form LiO4 tetrahedra that share corners with four equivalent LiO4 tetrahedra, corners with five equivalent SiO4 tetrahedra, and an edgeedge with one LiO4 tetrahedra. There are a spread of Li–O bond distances ranging from 1.97–2.08 Å. Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with three equivalent SiO4 tetrahedra and corners with five equivalent LiO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.60–1.67 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded to three equivalent Li1+ and one Si4+ atom to form a mixture of distorted edge and corner-sharing OLi3Si tetrahedra. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent Si4+ atoms. In the third O2- site, O2- is bonded in a trigonal planar geometry to one Li1+ and two equivalent Si4+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Investigating the Chemical Reactivity of Lithium Silicate Model SEI Layers

Silicon anodes suffer from an unstable solid electrolyte interphase (SEI) layer that contributes to undesirable capacity fade with cycling. A key part to addressing this unstable SEI formation is to examine how certain components of the SEI react with the electrolyte over time. One SEI component that has not been thoroughly studied in the context of the chemical reactivity against the electrolyte is lithiated silicate. Four model silicate thin films with increasing lithium content were deposited by radio frequency (RF) magnetron sputtering to study how the lithiation of the native oxide on a silicon anode affects the chemical stability of the anode surface. SiO2, Li2Si2O5, Li2SiO3, and Li3SiOx films were exposed to 1.2 M LiPF6 in the 3:7 wt% ethylene carbonate/ethyl methyl carbonate (EC/EMC) electrolyte for periods of time that are representative of the amount of time it takes to undergo cell formations. Soaked samples were rinsed, dried, and characterized by a combination of attenuated total reflectance-infrared spectroscopy (ATR-IR), focused ion beam-secondary electron microscopy (FIB-SEM), and X-ray photoelectron spectroscopy (XPS) depth profiling. It was found that the rate of the decrease in film thickness of the silicates exposed to the electrolyte over time increases as a function of the lithium content in the thin film. This reaction involves HF etching and LiPF6 salt degradation leading to silicate loss and fluorination throughout the bulk. Understanding this chemical instability is critical to determining the overall mechanism of SEI degradation over time.

ADVANCED PROPULSION SYSTEMS,ENERGY STORAGE↗