High-Throughput Screening Lithium Alloy Phases and Investigation of Ion Transport for Solid Electrolyte Interphase Layer

Abstract

Solid electrolyte interphase (SEI) layers derived from the side reactions between Li metal anode and electrolyte, have great impacts on the electrochemical performance of lithium batteries. In solid-state batteries, SEI layers are also required as the electrical insulators but an ionic conductors, and the mechanical reinforcements for withstanding volume change and suppressing dendritic growth in Li metal anode. Introducing LiF substrates into SEI layers can significantly reduce the electron tunneling ability from Li anode to SEI layer, meanwhile providing the excellent interfacial mechanical strength. However, LiF has a very high energy barrier for ion diffusion, hindering the rapid lithium ion diffusion from SEI layer to lithium anode. Therefore, it is necessary to introduce lithium alloy phases with higher ionic conductivity into the LiF matrix to provide sufficient ion diffusion channels. By the data mining technology, high-throughput first-principle calculation and ab-initio molecular dynamics simulations, this work performed phase diagram and ion diffusion energy barrier calculations to evaluate the thermodynamic stabilities and lithium diffusion abilities of several lithium alloys. 27 lithium alloys that can be used as Li-ion conducting phases in the LiF-based artificial SEI layers are screened. Meanwhile, the structure-function relationship analysis of lithium alloys uncovers that the crystal structure type of lithium alloys has more significant impacts on lithium ion diffusion than alloy elements, that is, lithium alloy structures with the space group of I $\overline{4}$3d and Fm $\overline{3}$m have very excellent lithium ion transport performance, while the diffusion channels of lithium alloy structures with the space group of Pm $\overline{3}$m and F4 $\overline{3}$m are narrow, leading to the poor lithium ion transport performance. In addition, this work uncovers a physical image of lithium ion transport in artificial SEI interface, that is, lithium ion diffusion in LiF crystal bulk is quite difficult, while the diffusion resistance at LiF grain boundaries and LiF/LiM alloy interfaces is small.

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