Study On The Preparation And Electrochemical Performance Of Starch-based Hard Carbon Spherules

In view of environmental pollution and unrestrained exploitation of fossil fuel, asalternate precursors of carbon materials, biomass resources have attracted more andmore attention. Starch is green, renewable and can be obtained from various plants.Thus starch is a good biomass candidate for the preparation of kinds of carbonmaterials. Besides, starch granules naturally have spherical morphologies. Therefore,it is possible to use this characteristic to develop a new technology of spherical carbonmaterial. This can promote the research of spherical carbon materials, and widen itspotential application.Among kinds of starches, potato starch granules have relatively perfect sphericalmorphologies. In this work, we firstly prepared novel carbon spherules from potatostarch by stabilization and carbonization processes under inert atmosphere, whichpreserved the original spherical morphologies of potato starch granules. In terms ofmicrostructure, the prepared carbon material was typical of disordered hard carbonwith micropores throughout it. During direct carbonization process, starch granulesswelled and melt together. During stabilization process at200-230℃, starch wasslowly dehydrated and crosslink between starch molecules gradually took place.Because of the crosslink reaction, starch granules avoided swelling and melting in thefollowing carbonization process and the prepared carbon spherules preserved theoriginal spherical morphologies of potato starch granules. In this work, the author alsoconfirmed the mechanism of the crosslink reaction in starch granules duringstabilization. When starch was stabilized in air, weight loss and dehydration of starchwere accelerated compared with that in inert atmosphere. Thus stabilization time wasshortened greatly.The starch based spherical hard carbons was also evaluated as an anodic materialfor Li-ion secondary batteries. As carbonization temperatures increased, reversibleand irreversible specific capacities of prepared spherical hard carbons increased andinitial efficiencies decreased. The material carbonized at700℃, had the highestreversible specific capacity of572.4mAh/g with the lowest initial efficiency of55.94%; the one carbonized at1000℃had the highest reversible specific capacity of355mAh/g below0.5V and the1300℃carbonized material had the highest initial efficiency of80.4%. It was found that the potato starch based spherical hard carbonscarbonized at higher temperatures showed better high-rate discharge performances.Discharge curves of the anodic carbon material carbonized at1300℃, almost did notchange with increasing discharge rates. Discharge specific capacities of this samplehad high preserved percentages with increasing discharge rates. Even at10C, thedischarge specific capacity remained88.7%of that at0.1C. Results also showed thestarch based spherical carbon material possessed good cyclic property, excellent PCbased electrolyte compatibility and showed stable electrochemical property afterlong-time storage in atmosphere.Starting from varied starches, hard carbon spherules with different morphologiesand different particle sizes were prepared. It was found that the structures and elementcontents of the prepared carbons almost did not change with different starches.Electrochemical properties mainly affected by the particle sizes of the hard carbonspherules. Prepared carbon spherules with smaller particle sizes showed highreversible specific capacities and possessed better high-rate discharge performances.Among spherical hard carbon anodic materials prepared from different starches, ricestarch based one had the smallest particle sizes and showed good electrochemicalperformances. Discharged at0.1C the rice starch based anodic material had a specificcapacity of582.3mAh/g and an initial efficiency of78.08%; discharged at10C thisanodic material also preserved a specific capacity of478.2mAh/g.