Studies On Preparation And Electrochemical Performance Of Rice Starch-based Hard Carbon Anode Materials Of Li-ion Batteries

With significant attention of scientific research workers paid on the green chemistry for energy saving and sustainable development, more and more people are concerned about carbon materials preparation which uses biomass resources as raw materials. As a kind of biomass resources, starch, with advantages such as a wide variety of sources, low cost and richness in carbon is an important kind of raw materials for carbon material preparation. Starch-based carbon is a disordered carbon material（hard carbon）, which has a great potential when used as lithium-ion batteries anode material.In this paper, we researched on the pre-carbonization processes of rice starch firstly. By comparing the pre-carbonization process of the rice starch with ammonium chloride and that of pure rice starch as well as their electrical properties after carbonization, we chose the two-step pre-carbonization preparation process. Secondly, according to the technology roadmap, we analyzed the morphology, structures and the first charge/discharge curves of rice starch-based hard carbon prepared at different temperatures. Combined with important parameters which can decide the application value of Li-ion batteries anode material, the optimum carbonization temperature was finally obtained.In order to improve the electrochemical properties of rice starch-based hard carbon, enzymaticon rice starch was used as raw materials to surface-modify the rice starch-based hard carbon. Compared with pure rice starch-based hard carbon without enzymatic treatment, the electrochemical properties of surface-modified rice starch-based hard carbon was improved. At room temperature, the first discharge capacity and the first coulombic efficiency of the surface-modified rice starch-based hard carbon increased from 482.9 m Ahg^-1/69.7% to 504.6 m Ahg^-1/72.7% of 0.1 C, respectively, and showed a good cycle performance and rate performance at the same time. It can be attributed to the fact that the surface order of rice starch-based hard carbon was raised because of the surface-modification by enzymatic method, which can help form a stable surface structure with SEI film. Electrochemical impedance spectroscopy showed that the decreased charge transfer resistance（Rct） and polarization resistance（Rf） were main factors that improved the electrochemical properties.In addition, we also prepared the composite anode materials with rice starch-based hard carbon to improve the first coulombic efficiency. The composite anode material of MnO/C was synthesized by the hydrothermal method. As it is shown in SEM and XRD, the Mn O on the MnO/C is a kind of amorphous state when the potassium permanganate content is less than 0.15 g. At the 0.1C, the initial efficiency of MnO/C is 68.2%, which is higher than that of normal sample（66.1%）. The other composite anode material of hard carbon/sucrose/graphite was synthesized by preparative liquid phase method. As it is shown in SEM, the graphite is scattered around the hard carbon and they are coated with sucrose. At the 0.1C, the initial efficiency of hard carbon/sucrose/graphite is 77.2%, which is higher than that of the normal sample（75.5%）.