Porous AAO-Based Separator For High-performance Li-S Batteries

With the development of society and the improvement of people’s living standard,the battery,as the main energy storage device,also needs to have higher energy density and longer service life to meet people’s needs.As a kind of high energy system,lithium-sulfur battery has a theoretical energy density of 2600 Wh kg^-1,far higher than the current lithium ion battery.It is an important direction for the research and development of the next generation of energy storage battery.However,in order to realize its commercialization,there are still many problems to be solved,such as the low conductivity of sulfur and lithium sulfide,the shuttle of lithium sulfide,and the dendrite of lithium metal cathode.The functional design of the separator can have an important effect on the performance of lithium-sulfur batteries.Anodic aluminum oxide separator（AAO）has high hardness and non-flammability,which can significantly improve the safety of the battery.The dense porous AAO separator provides a channel for the rapid transport of lithium ions in the electrolyte,which helps to reduce the generation of lithium dendrites.Based on improving the safety and cycling performance of lithium-sulfur batteries,this study focuses on improving the safety and cycling performance of lithium-sulfur batteries,and explores the effects of AAO-based new separators and their functional design inhibit the polysulfide shuttle and lithium dendrite growth of lithium-sulfur batteries.The main research contents are as follows:1)Commercial Celgard separator is replaced by anodized aluminum oxide（AAO）membranes with different pore sizes as the separators for lithium-sulfur batteries.In the micropores of AAO membrane,electroosmotic flow can improve the conduction rate of lithium ion in the electrolyte,and promote the uniform deposition of lithium metal.In Li|Li symmetrical battery,AAO with different pore size is used as separator make the symmetrical battery,lithium deposition and stripping have little difference,compared with Celgard assembled Li|Li symmetrical battery,the overpotential is lower.At the same time,its dense pores can reduce the shuttle of polysulfide.At 0.1 C,the battery with AAO separator has a specific capacity of 1334.7 m Ah g^-1.After 100 cycles,the capacity retention rate is 71.8%.At high C rate,lithium-sulfur batteries with AAO separators also have better cycle performance than Celgard,especially at 2 C,AAO batteries can be cycled for 480 times with only 0.105%attenuation per cycle.This work shows that AAO as a separator can improve the conductivity of lithium ions in the electrolyte,suppress the shuttle of lithium polysulfide,and improve the electrochemical performance of lithium-sulfur batteries.2)The composite separator of carbon nanotubes（CNT）and AAO was prepared by vacuum filtration to improve the electrochemical performance of lithium-sulfur batteries.The multi-walled carbon nanotubes were dispersed in deionized water and isopropanol by cell crushing apparatus and then filtered with sand core funnel and vacuum pump to make a composite separator with AAO for lithium-sulfur battery.The AAO porosity in the composite membrane prepared by this method improves the conductivity of lithium ions in the electrolyte,so that the battery performs good rate performance.The lithium-sulfur battery assembled with this separator still has a capacity retention rate of 73.6%after 160 cycles at 0.5 C.This work shows that the composite of AAO and CNT can combine the advantages of the two materials to improve the conduction of lithium ions in the electrolyte,inhibit the shuttle of lithium sulfide,reduce the attenuation of battery capacity,and further improve the electrochemical performance of lithium-sulfur batteries.