Anode materials for lithium ion batteries by oxidative treatment of common natural graphite

Modification of graphite has recently moved into the focus of the preparation of anode materials for lithium ion batteries. We report on an oxidative treatment by air and concentrated nitric acid solution to improve the electrochemical performance of a common natural graphite. Results from X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), thermogravimmetry (TG) and differential thermal analysis (DTA), high resolution electron microscopy (HREM), and measurements of the reversible electrochemical capacity suggest that the surface structure of natural graphite is changed and a fresh dense layer of oxides is formed. Structural imperfections are removed and the stability of the graphite structure is increased. These changes inhibit electrolyte decomposition, block intercalation of solvated lithium ions and prevent graphene planes from moving along the a-axis direction. In addition, nanochannels and micropores are introduced, and thus, lithium intercalation and deintercalation are favored and more sites are provided for lithium storage. Consequently, reversible capacity and cycling behavior of the modified natural graphite through the oxidation treatments is improved considerably. Since common natural graphite is low in cost, this method is promising for industrial application. (C) 2003 Elsevier Science B.V. All rights reserved.