Application Of Carbon Fiber As The Interlayer And Composite Cathode Matrix Material Of Lithium-sulfur Batteries

As the potential next generation secondary battery with high energy density,low cost of electrode materials and environmental friendliness,lithium-sulfur batteries can meet the requirements of many new technologies.However,there are still some technical problems that limit its wide application in business,such as poor conductivity of cathode material,volume expansion during charge and discharge,and the "shuttle effect" of the highly soluble lithium polysulfides(LiPSs).In this paper,to overcome these problems,we use commercial T300 carbon fiber plain woven textile,and explore the influence on the performance of lithium-sulfur batteries when it applied as the interlayer and composite cathode matrix material respectively.Carbon fiber,as an important reinforcement material in the preparation of composite materials in various fields in recent years,not only has many excellent properties,but also has mature preparation technology,which can simplify the complicated steps in the preparation of carbon matrix material,controlling the consistency of its performance,and also can reduce the cost of research,making it more accessible to industrialization.The main research contents of our work are as follows:(1)Carbon fiber textile with an areal density of 120 g/m2 was selected in the experiment.The modified carbon fiber interlayer was obtained by calcination for 2 h,and 500? was selected as the optimum calcination temperature.After the calcination treatment,the sizing agent on the surface of the carbon fiber was oxidized and decomposed.And as the increase of oxygen content,the chemisorption to polysulfides was enhanced.Chemical adsorption cooperated with the physical barrier of fiber structure to polysulfides,so that the battery had good cycle stability.At the same time,with the increase of calcination temperature,the degree of decomposition of sizing agent increased,and the internal carbon fiber was gradually exposed.The conductivity of the carbon fiber increased continuously.At 500?,it could reach 94.78 S/cm,further improving the conversion rate of polysulfides and battery capacity during charging and discharging.At 0.2C,the initial discharge capacity can reach 958.3 mAh/g,and it can remain at 550.6 mAh/g after 100 cycles.(2)On the basis of the above research work,the carbon fiber textile with an areal density of 140 g/m2 was used,and the carbon nanotubes coated with polydopamine was electrostatically sprayed on the surface of carbon fiber to modify it in advance.It was then calcined at the optimum temperature and used as a interlayer.After spraying the carbon tube,the oxygen content on the fiber surface increased,and the conductivity further increased to 130.13 S/cm.The interface impedance of the battery was further reduced.At 0.2C rate,the capacity can still be maintained at 667.2 mAh/g after 100 cycles.At a large rate of 1C,the capacity can be stabilized to 508.1 mAh/g after 100 cycles.(3)In the aspect of composite cathode matrix material,calcined carbon fiber textile was used directly as the carrier of sulfur to prepare the carbon fiber/sulfur composite cathode material with high sulfur loading.After the sulfur was loaded,it was coated with poly acrylic acid(PAA).The optimum coating time of PAA selected by the experiment was 30 min,and under the optimal coating time,the battery capacity and stability of the composite cathode material were greatly improved.At 0.2C,the capacity can maintain 493.9 mAh/g after 100 cycles with 3 mg sulfur,which was much higher than the electrode without PAA(86.0 mAh/g).Moreover,its capacity still had 402.7 mAh/g after 100 cycles with 5 mg sulfur,further demonstrating that the coated PAA can effectively improve the electrochemical performance of the lithium-sulfur battery.