Effect of surface modification using various acids on electrodeposition of lithium

Sulface modification of lithium was carried out using the chemical reaction of the native film with acids (HF, H₃PO₄, HI, HCl) dissolved in propylene carbonate (PC). The chemical composition change of the lithium surface was detected using X-ray photoelectron spectroscopy. The electrodeposition of lithium on the as-received lithium or the modified lithium was conducted in PC containing 1.0 mol dm^–3 LiClO₄ or LiPF₆ under galvanostatic conditions. The morphology of electrodeposited lithium particles was observed with scanning electron microscopy. The lithium dendrites were observed when lithium was deposited on the as-received lithium in both electrolytes. Moreover the dendrites were also formed on the lithium surface modified with H₃PO₄, HI, or HCl. On the other hand, spherical lithium particles were produced, when lithium was electrodeposited in PC containing 1.0 mol dm^–3 LiPF₆ on the lithium surface modified with HE However spherical lithium particles were not obtained, when PC containing 1.0 mol dm^–3 LiClO₄ was used as the electrolyte. The lithium surface modified by H₃PO₄, HI, or HCl was covered with a thick film consisting of Li₃PO₄, Li₂CO₃, LiOH, or Li₂O. The lithium surface modified with HF was covered with a thin bilayer structure film consisting of LiF and Li₂O. These results clearly show that the surface film having the thin bilayer structure (LiF and Li₂O) and the use of PC containing 1.0 mol dm^–3 LiPF₆ enhance the suppression of dendrite formation of lithium.