Palmitic Hemicellulose Extraction And Its Activated Carbon Are Used In Lithium-sulfur Batteries

Nowadays, there are two major problems human society is suffering, which refers to energy shortage and environmental pollution. Waste biomass utilization as one of the candidates for the development of renewable cleaning energy is considered to be promising to solve the problems. Biomass is a renewable resource, urgent need to be explored and used. Moreover, Lithium-sulfur battery has attracted much attention in recent years due to their low cost, eco-friendly and remarkable energy density. This work was based on the application of carbon-based/sulfur composites in Li-S battery and the utilization of waste biomass, the development of an efficient method for hemicelluloses extraction, the use of coconut shell residue without hemicelluloses and oil palm shell for preparing biomass-based activated carbon, and the exploration of the electrochemical performance of Li-S battery with activated carbons/sulfur composite when used as cathode material. This study will provide reference for preparation of low-cost, green, efficient, high performance and mass-produced sulfur cathode materials.Firstly, coconut shell hemicelluloses was extracted by alkaline solution of hydrogen peroxide method, We studied the main effect factors of extraction, among which hydrogen peroxide concentration, magnesium sulfate, pH value, reaction temperature and time were analyzed by an orthogonal experimental design with a further optimization by single-factor experiments. The optimal conditions of experiments are as follows:a pH of12.5,8%peroxide concentration,0.05%hydrogen peroxide concentration,80℃, and4h. Under the optimal conditions, hemicelluloses yield was28%to30%of the total weight of coconut shell. The obtained hemicelluloses were characterized by FT-IR, GPC, TGA and XRD. Furthermore, the coconut shell residue without hemicelluloses and oil palm shells serve as raw materials respectively for the preparation of activated carbon, which is used as sulfur cathode materials in lithium-sulfur battery, and the effect factors including preparation parameters, morphology, specific surface and pore structure of the prepared activated carbon on the performance of Li-S battery were studied。The optimum conditions for the coconut shell residue activated carbon (CSRAC) are as follows:The coconut shell residue was carbonized at550℃for2h at a heating rate of10℃/min in a nitrogen gas atmosphere, and then were preactivated at500℃for1h and activated at700℃for1h under nitrogen atmosphere with KOH as activator. The specific surface area of the obtained porous activated carbon was determined to be2791m2/g. Initial discharge capacity of the lithium sulfur battery with S/CSRAC composites as sulfur cathode is1088mAhg-1while capacity retention is88.2%after100cycles and coulomb efficiency remains about98%.Tracheids of oil palm shell with channel pores through the wall are of hollow spherical structure. The size of tracheids is about20-50μm, and there were no obvious changes after isolation by HNO3-CrO3method, carbonation and activation. The isolated tracheids were not proposed to prepare hollow carbon spheres applied in Li-S battery ever. In this paper, The isolated tracheids were carbonized at400℃for2h with a heating rate of10℃/min in a nitrogen atmosphere, and then were preactivated at400℃for1.5h and activated at800℃for1h under nitrogen atmosphere with KOH/K2CO3(1:1in weight) mixture as activator. The specific surface area of the obtained porous hollow carbon spheres (HPHCMs) with mes/micropores were determined to be1450m2/g. Initial discharge capacity of the Li-S battery with S/HPHCMs composites as sulfur cathode is1105mAhg-1while capacity retention is74.1%after100cycles, which shows more excellent performance compared with the carbonized tracheids/S as sulfur cathode. Both the specific surface area and the pore volume of the two carbon materials decreased drastically since the sulfur was homogeneously loaded. In general, the results indicated that the electrochemical properties of Li-S battery is closely relevant to the structure of the obtain activated carbon.