Preparation of vein graphite anode materials by eco-friendly mild oxidation, for lithium-ion rechargeable batteries

Abstract

Vein graphite with high purity and crystallinity has been identified as a cost-effective source to produce anode material. High anisotropy of graphite surface and impurities in trace levels cause profound alteration of electrochemical activities in Lithium-ion Rechargeable Batteries (LIBs). Surface modification with strong chemical oxidant such as (NH 4) 2 S 2 O 8 , HNO 3 and HF, which are highly toxic and hazardous is identified as a successful method to modify the graphite as an anode material. Therefore, an eco-friendly approach to modify the vein graphite surface was investigated in this study. Purified needle platy graphite was treated with H 2 O 2 solution at 60°C for 24 hours. FT-IR spectra and Powder X-ray diffraction (PXRD) patterns oxidized graphite indicate the formation of acidic groups or an oxidized layer without affecting the crystallographic structure of graphite due to mild oxidation with H 2 O 2. In addition, Thermogravimetric Analysis (TGA) and Scanning Electron Microscopic (SEM) images provided results suggesting that the oxidation eliminates some reactive structural defects in vein graphite. The electrochemical properties of the graphite electrodes were studied with the assembled CR 2032 coin cells. The charge, discharge study of the assembled cells , carried out at C/5 rate with a cutoff voltage of 0.002-1.5 V at room temperature indicate a considerable improvement in the overall electrochemical performance of the graphite electrode material prepared by mild oxidation using H 2 O 2 as the oxidant. This enhancement of electrochemical performance may results due to the improved graphite surface structure formed by the H 2 O 2 mild oxidation process used in this study. Mild oxidation of vein graphite with H 2 O 2 is ecofriendly and cost-effective method since water is the by-product of the oxidation process carried out at low temperature.