X-RAY PHOTOELECTRON SPECTROSCOPIC ANALYSIS AND SCANNING ELECTRON-MICROSCOPIC OBSERVATION OF THE LITHIUM SURFACE IMMERSED IN NONAQUEOUS SOLVENTS

The lithium surface immersed in various electrolytes for 10 min or 3 days was analyzed by x-ray photoelectron spectroscopy. The lithium surface was covered with the native film which consists of Li2CO3, LiOH, and Li2O. During the immersion of lithium in propylene carbonate or gamma-butyrolactone containing 1.0 mol dm-3 LiBF4 or LiPF6, the native film reacted with the impurities in the electrolyte to form LiF. However the native film remains after the immersion of lithium in electrolyte for 10 min. The surface film of lithium immersed in propylene carbonate or gamma-butyrolactone containing 1.0 mol dm-3 LiPF6 for 3 days was different from those immersed in propylene carbonate or gamma-butyrolactone containing 1.0 mol dm-3 LiBF4. The surface film immersed in electrolyte containing LiPF6 for 3 days has a bilayer structure which consists of LiF and Li2O. This surface film seemed to be dense and thin. In the electrolyte containing LiBF4, the lithium surface was covered with a porous layer of LiF. The morphology of lithium deposited on a lithium surface immersed in electrolyte containing 1.0 mol dm-3 LiPF6 for 3 days was semi-spherical. Typical dendrites were observed on lithium surfaces immersed in electrolyte containing LiBF4 for 3 days. Moreover the lithium dendrite was formed on lithium surface immersed in electrolyte for 10 min. From these results, it can be said that the surface state of lithium is strongly related to the morphology of lithium.