Abstract
MnO is an attractive anode material for Lithium ion battery(LIB) because of the low conversion potential, low voltage hysteresis (< 0.8 V), low cost, high capacity(756 mAh/g), environmental friendliness, and the high abundance of Mn. However, MnO will have a large amount of irreversible reaction, including formation of solid electrolyte interphase and aggregation of particles during the initial discharge process, leading to the significant reduction of the performance of LIBs. The use of carbon coating on MnO nanoparticles can not only reduces the formation of solid electrolyte interface and avoids particle aggregation, but can also improve the electrochemical performance of MnO. Under appropriate control, surface coating carbon can disperse MnO particles well, limit the volume change of particles and act as a channel for electrons and ions transportation. In summary, MnO /C composite material gets a lot of attention in recent years. In this study, we use manganese oleate as a precursor for both carbon and manganese element, mixing with low-cost sodium sulfate template. After calcination and washing process, the final product is two-dimensional MnO/ C composite. The influence of calcination atmosphere, calcination temperature and holding time on the morphology of composites was examined, and then lithium ion battery anode material. Calcined under nitrogen atmosphere can get high purity MnO. Higher temperature can get better crystallinity of MnO, but the carbon content has dropped. The carbon content is decrease from 12.9 to 0.9 wt% when temperature increased from 500 C to 800 C. The morphology of the composites changed from the layered structures into three-dimensional stacked structures, resulting in the decrease in reaction area, as the carbon amount decreased. In the presence of MnO crystalline and the carbon content, the optimum calcination temperature is 600 C. The long calcination time decreased carbon content slowly. Comparing to temperature effect, the carbon loss tendency in time effect is not obvious, but calcination for 3h can get the most suitable carbon thinckness. Each material will test in the form of half-cell by charging and discharging test and cyclic voltammetry. The carbon content affecting the electrochemical performance show a volcano type result. When the carbon content is higher than 10 wt%, it will show the capacity decrease, excessive electrolyte decomposition and thicker SEI film. In contrast, less carbon content causing the less barriers between MnO particles and fast capacitance decrease after cycling. Considering the carbon content and MnO particles simultaneously, the optimized carbon content in this study is 11.9 wt%. The discharge capacitance can be up to about 500 mAh/g at 100 mA/g scan rate, and the coulomb efficiency is maintained more than 97%; when the scan rate increased to 1000 mA/g, the discharge capacitance value is about 130 mAh/g, coulomb efficiency is maintained above 96%. The manganese oxide crystal growth will limit the improvement of conductivity for carbon content under calcination process.