Insight into the mechanism of Li ion diffusion in fluorine-doped Li1.3Al0.3Ti1.7(PO4)3 as an electrolyte for solid lithium metal batteries

NASICON structured Li1.3Al0.3Ti1.7(PO4)3 (LATP) has attracted widespread attention due to its simple preparation and excellent stability towards water and air. However, there are many problems such as high interfacial resistance between electrolyte and electrodes as well as low ionic conductivity of LATP. In this paper, the effect of F doping on Li ion diffusion channel in electrolyte was investigated in detail by density functional theory (DFT) calculation. The results show that F doping can effectively reduce the formation energy of Li vacancy. Meanwhile, it can also reduce the diffusion energy barrier and induce the high-energy Li ions at 36f site to carry out synergistic diffusion via various ways at the same time. Then, the F-doped LATP electrolyte was prepared successfully. Its ionic conductivity is as high as 0.358 mS cm-1 at room temperature. At the same time, the solid -state lithium metal batteries with F-doped LATP electrolyte shows a high capacity of 136.2 mA h g-1 at 0.5C and excellent cyclability for 200 cycles. These results demonstrate that F doping may be an effective way to improve the performance of LATP electrolyte.