The Research On Cathode Materials For Lithium Sulfur Batteries

The lithium sulfur(Li–S) battery is a promising electrochemical system for the next generation high energy density rechargeable batteries having a theoretical energy density of 2600 Wh/kg. Moreover, the elemental sulfur is abundant, low-costly, and environment friendly. In spite of the intrinsic advantages, Li–S batteries currently are confronted with a variety of problems such as low specific capacity and short cycle life. The main factors include the poor electronic conductivity of elemental sulfur(5 × 10-30 S/cm at 25 °C), lithium polysulfides as intermediate generated products during the electrochemical reduction reaction process, the dissolution of polysulfides and so on. Therefore, how to improve the electronic conductivity, and avoid the dissolution of polysulfides of the S cathode is crucial for the development of Li-S battery. In order to solve these problems, coconut shell carbon/sulfur, activated clay@sulfur, and complex film composites were prepared by a simple chemical method. The morphologies, crystalline phases and electrochemical evaluation of samples were measured by SEM, XRD and LAND Cell test system. The main contents and results are summarized as follows:1. A novel sulfur/carbon composite was prepared using coconut shell carbon as raw material for Li–S batteries. The structure of the composite could accommodate the volume expansion of sulfur particles and trap the dissolved polysulfide produced during the electrochemical reaction. Therefore, the composite based cell demonstrates a high initial capacity of 878 mAh/g at a rate of 0.1 C, and excellent cycling stability, in which a reversible capacity of 774 mAh/g was maintained even after 50 cycles.2. The bird’s nest structure of activated clay(AC) with large surface area, porosity and natural formation of the small filter screens are employed to support sulfur for the cathode of lithium-sulfur(Li-S) battery. The sulfur/activated clay(AC/S) composite with 57 wt% sulfur is prepared by high temperature solid state method. As expected, the AC/S composite presents the best electrochemical performance, including the utilization of active sulfur, discharge capacity and cycle stability. A high capacity of 1026.8 mAh/g at the rate of 0.1 C in the first cycle and the reversible capacity remains high at up to 703 mAh/g even after 50 cycles, the AC/S composite exhibited a promising future for industrial scale Li-S batteries.3. A simple method to improve electrochemical performance of Lithium Sulfur(Li-S) batteries by placing complex film as adsorbing interlayer between the sulfur cathode electrode and the separator. The complex film was made of the carbonized non-woven fabrics and Ketjen Black to optimize the porosity, electrolyte uptake and electrical conductity. It was shown that the complex film as adsorbing interlayer, loading up 70 wt.% sulfur of the total electrode mass lead to a high capacity of 1486 mAh/g at a rate of 0.1 C(1 C=1675 mA/g) in the first cycle and the reversible capacity remains high at up to 858 mAh/g even after 100 cycles. The new interlayer provides a simple and effective method for the structure designing of Li-S battery.