Preparation Of Porous Carbon Material And Its Application In Lithium Sulfur Battery

Lithium sulfur battely,which is composed of sulfur element as positive pole and lithium as negative pole,is expected to become a new generation of commercial battery due to its ultra-high theoretical specific capacity of 1675 mAh·g-1,low cathode material sulfur and environmental friendliness.In this paper,aiming at the problems in the research of lithium sulfur battery,such as the fast attenuation of battery capacity,the large difference between the actual specific capacity and the theoretical specific capacity,taking the egg white as the raw material,a kind of porous carbon material with O and N polar elements,which has simple technology,high repeatability,large specific surface area and many kinds of apertures was explored.Through the control variable method,research the effects of activator NaHCO3 concentration and precursor drying process on porous carbon pore structure and anode performance of lithium sulfur battery were studied.The best porous carbon preparation process was determined and applied to the membrane modification and anode of lithium sulfur battery.The conclusions are as follows:(1)Using egg white as carbon source,adding activator NaHCO3,stirring for foaming,freezing and drying to get precursor,carbonizing completely at 650 ?,the porous carbon material after carbonization contains polar elements N and O.While the increase of activator concentration,the porosity increases,and the pore diameter becomes larger.When NaHCO3 is 0.2 mol·L-1,the specific surface area,pore volume and average pore diameter of porous carbon cool-C obtained by freeze-drying precursor are 1117.14 m2·g-1,0.60 cm3·g-1 and 2.82 nm respectively.The material is porous carbon material with both micropores and mesopores.(2)The polarization degree of sulfur/carbon composite anode prepared by cool-C0.2 is the smallest under different discharge rate.The specific capacity of the first discharge can reach 1435.28,1104.53,873.55,735.32,652.45 and 556.40 mAh·g-1 at the rate of 0.05C,0.1 C,0.2C,0.5C.1C and 2C,respectively.When the ratio current returns to 0.2C,the specific capacity of recovery rate is 92.24%.In addition,the specific capacity of the first discharge can reach 1031.62 mAh·g-1 at 0.2C.After 200 cycles,the specific capacity retention rate is 61.65%,and the coulomb efficiency is 99.9%.(3)When cool-C was applied to the membrane modification of lithium sulfur battery,the cycle performance and rate performance of the battery were significantly improved.At the current density of 0.2C,the initial discharge capacity of the cell with cool-C modified membrane is as high as 1358.64 mAh·g-1.After 100 cycles at 0.2C,the initial discharge capacity is reduced to 781.93 mAh·g-1.The battery with cool-C modified membrane can still maintain a specific capacity of more than 1000 mAh·g-1 in the first 30 cycles.After the modification of cool-C membrane,the specific discharge capacity of the batteries from 0.05C to 2C was 1647.69,1420.55,1150.46,950.32,823.21 and 703.69 mAh·g-1,respectively.The specific discharge capacity of the button cells assembled by cool-C membrane was 939.13 mAh·g-1,when the high ratio of 2C was returned to 0.2C,and 1014.46 mAh·g-1,while the charge discharge cycle was stable.The discharge capacity of cool-C modified membrane is 25.90%higher than that of unmodified membrane cell at 0.2C stable cycle.