Researches Of Carbon Nanotube Fluids Modified Separator For Batteries

Lithium-sulfur（Li-S）battery has become one of the most promising energy storage systems due to its high theoretical energy density（2600 Wh/kg）,which is 3-5times higher than Li-ion battery,low cost and environmental friendliness.However,the commercialization of Li-S battery remains a huge challenge because of the low active material utilization and fast capacity fading,which originate from the shuttle effect of polysulfides and the insulating nature of sulfur.Currently,much progress has been tested to address these challenging issues by employing composite cathodes and novel cell configurations.But these designs always involve complex synthesis or tedious technological processes,which are not suitable for large-scale production.The separator,as a basic component,plays a vital role in the overall performance of the Li-S battery.In this regard,exploring a simple and convenient method to modify the separator is of great significance for their practical applications.In this paper,the carbon nanotube fluid（CNTF）was introduced as a coating material to optimize structure,ensure safety and enhance conductivity.The commercial membrane was modified to improve the battery’s performance.The research results are shown as follows:（1）CNTF was synthesized by ion extraction and CNTF-coated separator was prepared using spin coating.Compared with the blank separator,the CNTF-coated separator presented better wettability with the electrolyte and had an excellent cycling performance.The initial discharge capacity reached 1179 mAh/g at 0.1 C and the capacity retention achieved 64.8%after 50 cycles.These results showed that the net structure created by the molecular chains of CNTF could effectively restrain the diffusion of polysulfides and provide a buffer space for the volume change of the cathode,consequently improving the stability of the electrode structure.（2）The CNTF/ZrO₂ composite separator was prepared by introducing nanometer zirconium dioxide（ZrO₂）on the basis of CNTF.Due to the excellent hydrophilicity of ZrO₂ power and its rich pore structure,the electrolyte could infiltrate the separator immediately and the electrolyte uptake increased to 105%.The results showed that the composite system with the ratio of CNTF:ZrO₂=2:1 had the best overall performance with an initial reversible capacity of 1008 mAh/g at 0.1 C.The capacity degradation was only 0.42%per cycle for 50 cycles.The high temperature characteristic of ZrO₂ enhanced the thermal stability of the composite system significantly,ensuring a better safety performance.（3）By replacing ZrO₂ with acetylene black（ACET）,we prepared the CNTF/ACET composite separator.Under the same test conditions,the initial capacity was 982 mAh/g,and the reversible capacity was up to 1173 mAh/g after activation.Compared with the initial value,the retention was 99.4%after 50 cycles.In addition,the composite system also exhibited a high capacity release and cycle stability in the high current density,possessing a certain practical value.The three-dimensional network architecture of CNTF and the unique"dendritic"structure of ACET in the coating could accommodate a large amount of polysulfides.Meanwhile,ACET had good conductivity and provided more active sites for the electrochemical reaction,achieving secondary activation of the polysulfide deposited in the coating and greatly improving the utilization of active material.