Preparation And Electrochemical Performance Of Carbon Anode Materials For Lithium-Ion Battery

In this thesis, the modification of natural graphite, which had good lithium-storage performance but bad compatibility with electrolyte, was studied. X-ray diffraction (XRD), Scanning electron microscope (SEM), and so on was used to analyze the structure of natural graphite. Natural flake graphite was modified by gas-phase and liquid-phase oxidation to improve its cycle performance. Tap density of natural flake graphite was improved and the ratio of surface area was reduced by phenolic resin coating. The electrochemical performances of as-synthesized composite materials were studied primarily.The electrochemical performances of natural graphite were measured. It was showed that SEI films which formed in the first cycle could inhibit further decomposition of solvent and avoid the exfoliation of graphite flake in the electrolyte during cycling. Therefore, at lower current density natural flake graphite exhibited better electrochemical performance.Natural graphite was oxidized by air and H₂O₂. It showed that lithium-storage sites increased and the particle size became more uniform by air oxidation. These changes made the insertion capacity increase and were beneficial to form stable and uniform SEI film. It was proved that the oxygen content on the surface of the graphite increased after H₂O₂ oxidation treatment. The change of surface structure was beneficial to decrease the consumption of Li-ion when SEI film formed in the initial charge process. Furthermore, this change inhibited the decomposition of solvent and electrolyte and increased the coulombic efficiency in the first cycle. In the current density of 1/10 C, the first irreversible capacity of natural graphite modified by H₂O₂ decreased from 71.2 mAh/g to 45.4 mAh/g. The reversible capacity was kept above 357.5 mAh/g, after 30 discharge cycles, discharge capacity still maintained 90% of its initial capacity. The tap density of natural graphite increased from 0.588 g/cm³ to 0.883 g/cm³ by phenolic resin coating, and the specific of surface area was reduced, from 8.194 m²/g to 8.103 m²/g. Along with increase of heat treatment temperature, carbonization of phenolic resin became complete gradually. As a result, electrochemical properties of electrodes were improved. Natural graphite coated with phenolic resin was oxidized in H₂O₂. It showed that in the current density of 1 C, the first charge/discharge capacity was 382.8 mAh/g and 349.4 mAh/g respectively and the efficiency was 92 %. After 10 discharge cycles, efficiency still maintained 96.2%. In the current density of 1/2 C, after 30 discharge cycles, efficiency still maintained 94 %.