Effect of carbon coating process on the structure and electrochemical performance of LiNi0.5Mn0.5O2 used as cathode in Li-ion batteries

LiNi0.5Mn0.5O2 powder was synthesized by a coprecipitation method. LiOH.H2O and coprecipitated [(Ni0.5Mn0.5)C2O4] precursors were mixed carefully together and then calcined at 900A degrees C. Surface modified cathode materials were obtained by coating LiNi0.5Mn0.5O2 with a thin layer of amorphous carbon using table sugar and starch as carbon source. Both parent and carbon-coated samples have the characteristic layered structure of LiNi0.5Mn0.5O2 as estimated from X-ray diffractometry measurements. Transmission electron microscope showed the presence of C layer around the prepared particles. TGA analysis emphasized and confirmed the presence of C coating around LiNi0.5Mn0.5O2. It is obvious that the carbon coating appears to be beneficial for the electrochemical performance of the LiNi0.5Mn0.5O2. A capacity of about 150 mAh/g is delivered in the voltage range 2.5-4.5 V at current density C/15 for carbon coated LiNi0.5Mn0.5O2 in comparison with about 165 mAh/g obtained for carbon free LiNi0.5Mn0.5O2 at the same current density and voltage window. About 92% and 82% capacity retention was obtained at 50th cycle for coated LiNi0.5Mn0.5O2 using sucrose and starch, respectively; whereas, 75% was retained after only 30th cycle for carbon free LiNi0.5Mn0.5O2. This improvement is mainly attributed to the presence of thin layer of carbon layer that encapsulate the nanoparticles and improve the conductivity and the electrochemical performance of LiNi0.5Mn0.5O2.