Electrochemical Properties of Natural Graphite Fluorinated by ClF[sub 3] and NF[sub 3] in Propylene Carbonate-Containing Solvent

Abstract

Surface fluorination of natural graphite samples with average particle sizes of 5, 10, and 15 μm (NG5, NG10, and NG15 μm) was performed by ClF3 and NF3 (1× 105 Pa) at 200 and 300°C for 5 min, and charge/discharge behavior of fluorinated samples was investigated in 1 mol/ dm3 LiClO4 -ethylene carbonate (EC)/diethyl carbonate (DEC)/propylene carbonate (PC) (1:1:1 in volume). Mesopores with a diameter of 2 nm were increased by the surface fluorination, while those with diameters of 2.5 and 3 nm were reduced. Surface disorder of natural graphite samples also increased with increasing fluorination temperature and particle size. These surface structure changes by surface fluorination would have reduced the decomposition of PC, leading to an increase in first coulombic efficiencies. The increase in first coulombic efficiencies was larger at a current density of 150 mA/g than 60 mA/g, reaching ca. 10 and 20% for NG10 and NG15 μm fluorinated by ClF3. © 2008 The Electrochemical Society.