Independent regulation of the lithium-ion conductivity of LiF using elemental doping: A first-principles study
Na Yang, Xianqi Xu, Jiaxin Zheng
Abstract
Lithium fluoride (LiF) is an important component of solid electrolyte interphase (SEI), but its low ionic conductivity limits the applications in lithium-ion batteries. In order to obtain high-performance SEI layers, we wanted to improve lithium-ion conductivity of LiF by doping at low concentrations while minimizing damage to electronic conductivity and maintaining high mechanical strength. First-principles calculations were performed to initially screen the main group elements, of which Na, K, Be, Mg, Ca, and Al were found to meet this material design requirement. Further, the effect of these elemental dopings on the properties of the bulk, surface, and interfacial phases was systematically investigated. We demonstrate that monovalent ion doping increases lithium-ion conductivity mainly by lowering the diffusion energy barrier, whereas multivalent ion doping increases lithium-ion conductivity by inducing lithium negatively charged vacancy. Divalent ions (${\mathrm{Be}}^{2+}, {\mathrm{Mg}}^{2+}$, and ${\mathrm{Ca}}^{2+}$) are recommended for doping into lithium fluoride because they increase the lithium-ion conductivity by 18 orders of magnitude with insignificant decreases in electronic conductivity and mechanical strength. Our work provides theoretical guidance and a research paradigm for the preparation of artificial SEI films with excellent properties.