Synthesis Of MoS₂ Based Cathode Materials And Its Performance Of Lithium-sulfur Batteries

In recent years,Lithium-Sulfur?Li-S?batteries have been received increasing attention for the promising future due to wide application prospects in electric vehicles,satellites,drones and other energy storage devices.The sulfur cathode possesses a high theoretical specific capacity(1675 mAh g^-1)and energy density(2600 Wh kg^-1),almost ten times and five times higher than the cathode of commercial lithium ion batteries,respectively.In addition,the abundance and non-toxicity of sulfur make Li-S batteries more cost-effective and environmentally friendly.However,the insulating nature of charge and discharge product?S and Li₂S/Li₂S₂?leads to sluggish reaction kinetics and lower actual capacity;the polysulfides generated in the charge/discharge process are easily dissolved in organic electrolyte which induces the loss of active material.These problems seriously restrict the practical application of lithium-sulfur batteries.2D layered transition metal dichalcogenides?TMDCs?consist of stacked 2D S-M-S layers via van der Waals force,have been actively investigated in the area of electrochemical energy storage and conversion due to its unique structure.Among them,the edge sites of molybdenum disulfide?MoS₂?show higher catalytic activity in electrocatalytic reaction,which can promote the conversion of polysulfides and the electrochemical deposition of Li₂S.The strong interactions between the edge sites and the polysulfides anchor the latter effectively.However,the growth characteristics of the layered material limit the number of edge sites.In addition,its semiconductor properties also limit the rapid transfer of electrons.In this paper,we synthesized the edge-rich and metal-phase MoS₂-based materials for solving the above problems,and further studied its application in lithium-sulfur batteries.The main details are listed as follow:?1?The vertically aligned MoS₂ nanosheets with richly exposed edge sites on the carbon cloth were prepared via a one-step hydrothermal method,and subsequently severed as a host material for sulfur.The structure-function relationship between edge active sites and electrochemical performance was discussed briefly.Based on the experiments,thanks to the abundant edge sites of vertically aligned MoS₂nanosheets,high active sulfur nanoparticles with a size of 5-10 nm were anchored on the surface of MoS₂.What is more,it was able to immobilize Li₂S and catalyze it to the charge products.In the meantime,the carbon cloth with higher conductivity was good for the improvement of the rate performance.We used it as cathode material?without conductive agent and binder?,when the current rates increased from 0.1C to 0.2C?0.5C?1C?2C and 3C,the initial discharge specific capacity was 1174,823,721,635,547 and 487 mAh g^-1,respectively.Even cycled at 2C after 800 cycles,the obtained V-MoS₂/CC@S cathode still delivered 579.4 mAh g^-1.This design of the structure-function relationship provided a feasible method for other transition metal dichalcogenides.?2?MoS₂ forms various polymorphisms due to the different stacked modes of the S-Mo-S layer.Among them,the semiconductor 2H phase exists stably in nature,which has already exhibited excellent application in enegy storage system such as secondary batteries and supercapacitors.According to literature,the strong chemical interactions between Co_xS_y and polysulfides are benefit to immobilize the latter at the same time.So we tried to introduce cobalt to improve the conductivity of the host material and the adsorption ability of lithium polysulfides.We used a hydrothermal method to synthesize the Co stabilized 1T phase MoS₂?Co-MoS₂?nanocomposite,the as-prepared Co-MoS₂ had a large specific surface area and pore volume,higher-disorder structure and lower crystallinity.In addition,MoS₂ had a smaller thickness and uniform distribution of size.Benefit to the above advantages,the obtained Co-MoS₂@S cathode could deliver a specific capacity of 556.6 and 374.4mAh g^-1 after 400 cycles at 2C and 5C,respectively.It also exhibited excellent cycling stability at high currents.