Synthesis of carbon coated Li₂MnO₃ cathode material with enhanced rate capability for lithium-ion batteries

Layered Li₂MnO₃ mixed with sucrose is heat-treated at low temperature under air atmosphere. A uniform carbon layer is found to be coated on Li₂MnO₃ active material according to the analysis of scanning electron microscopy and transmission electron microscopy. The thin carbon coating is in favor of good electrical contact between the cathode active particles as well as prevents the direct contact between the active material and electrolyte. Based on X-ray diffraction and X-ray photoelectron spectroscopy analyses, the crystal structure of Li₂MnO₃ is not degraded and some Mn⁴⁺ on the surface is reduced to Mn³⁺ during the carbon coating process in air. The galvanostatic charge-discharge results show the carbon coated Li₂MnO₃ exhibits greatly improved discharge capacity and rate capability. The carbon modified Li₂MnO₃ treated for 40 min delivers initial discharge capacity of 280.5 mAh g⁻¹ at 10 mA g⁻¹ and 117.5 mAh g⁻¹ at 400 mA g⁻¹ while the pristine sample only delivers 229.1 and 51.8 mAh g⁻¹ at the same current densities. The significantly improved high rate performance demonstrates this synthesis route is a reliable approach for conductive carbon coating on cathode materials used in lithium ion batteries.