The Application Of Accordion-like Structure Layered Materials 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 LiCoO2 cathode. In addition, sulfur offers additional advantages, such as a low cost and environmental benignity and natural abundance. However, to allow for the practical application of Li-S batteries, e.g. the volume expansion of sulfur during the charge/discharge process, the low electrical conductivity of the electrode, and shuttle effects occurring in lithium polysulfides. These phenomena may result in an active mass loss, a lower coulombic efficiency and capacity fading. To solve these problems, more attention has been given to the carbon composites and two-dimensional graphene of the electrode materials.Therefore, a composite containing accordion-like L-Ti3C2 and sulfur was synthesized.The obtained L-Ti3C2 material were characterized by XRD, SEM, TGA and EDS. We demonstrated that a Li-S battery with the composite used as cathode material discussed the possibility of the application of L-Ti3C2 material.An effective and simple strategy was developed to extract the Al layer from Ti3AlC2 by immersing Ti3AlC2 powders in a 50% HF solution for 6 h followed by ultrasonication in ethanol. The optimal conditions of experiments are as follows:40% HF solution, reaction time 6h, mass of HF solution 15ml and ultrasonication time 20 minutes. There were more layers and thinner layer structure, which was deeply studied as sulfur cathode materials in lithium-sulfur battery.Accordion-like L-Ti3C2 material as raw material, molten S was then loaded into the L-T13C2 material hosts in a sealed vessel and this S/L-Ti3C2 mixture was used as a cathode for Li-S batteries. The as-prepared L-Ti3C2 material had a mostly microporous structure and exhibited a relatively low BET specific surface area of 7.8 m2/g, which decreased to 1.6 m2/g after the sulfur loading. These batteries showed an initial discharge capacity of 1291 mAh/gat a current density of 200 mA/g. The cells showed good cycling performance and retained 970 mAh/g after 100 cycles, due to the strong absorption force of the layers. It is worth noting that the reversible capacity retention and the coulombic efficiency are higher under high-rate conditions because a higher rate leads to a lower retention time of the dissolved polysulfides within the electrolyte per cycle.There is a layer of Fn O/OH groups on the surface of L-Ti3C2, which have a great impact on the electrical conductivity of L-Ti3C2. In order to find the influence of surface modification of activated carbon on the electrochemical performance of Li-S batteries, and then modified by ammonia and acetic acid respectively. The experimental results showed that the content of amidogen was decreased after ammonia modification, which was still low of the initial discharge capacity, while the carboxyl group brought by acetic acid treatment made a negative influence on the cell performance.