The Application Of Coconut Shell Derived Activated Carbon As Cathode Material In Lithium-Sulfur Batteries

To solve the problems of current commercialized lithium-ion batteries, people have paid more attention to high energy density rechargeable batteries in recent years. Among them, the Li-S battery is an appealing candidate according to the high theoretical specific capacity and energy density, which is five times higher than that of a currently commercialized LiCoO2cathode. In addition, sulfur has the advantages such as price moderate, innocuity, and natural abundance. However, lithium-sulfur batteries suffer from capacity fading during charge/discharge cycling, which impedes the commercialization. To solve these problems, more attention has been given to the tunable design of the host structure and the preparation of the electrode materials. One of the most effective methods has been embedding S into conductive carbon hosts. Therefore, we make use of the Hainan coconut shell to synthesize the high specific surface area activated carbon for preparation of carbon based material. The author discussed the possibility of the application of coconut shell derived activated carbon in lithium-sulfur batteries.High-surface-area activated carbon (HSAAC) was synthesized by carbonizing coconut shells and subsequently activating them with KOH. The as-prepared HSAAC had a mostly microporous structure (with small mesoporous inclusions) and exhibited a high specific surface area of2258.7m2g-1.Sulfur was then loaded into the activated carbon (AC), and this S/HSAAC was used as a cathode for Li-S batteries. These batteries showed an initial discharge capacity of1230mAhg-1at a current density of200mAg-1. The cells showed good cycling performance and retained929mAhg-1after100cycles, due to the strong absorption force of the HSAAC and a high pore volume.In order to find the influence of surface modification of activated carbon on the electrochemical performance of Li-S batteries, the high surface area activated carbon was synthesized by using coconut shell as raw material and KOH as activator, and then modified by ammonia and hydrogen peroxide respectively. The S/C composites was used as cathode for Li-S batteries. The experimental results showed that the content of amidogen was increased after ammonia modification, which improved the initial discharge capacity from1058mAh/g to1333mAh/g, while the carboxyl group brought by hydrogen peroxide treatment made a negative influence on the cell performance.The author obtained different pore structure coconut shell derived activated carbon, which used for lithium-sulfur batteries. The author had study their electrochemical performance and find that:as the microporous in coconut shell derived activated carbon increased, the electrochemical performance of lithium-sulfur batteries also gradually increased. The best one among them delivered an initial discharge capacity of1294mAhg'1at a current density of200mAg-1, which showed good cycling performance and retained809.3mAhg-1after100cycles. So microporous structure increased the specific surface area of coconut derived activated carbon, can effectively alleviate the shuttle phenomenon, has a positive effect on electrochemical performance of lithium-sulfur batteries.