| The urgent demand for green and sustainable high specific energy storage system makes lithium sulfur battery with high theoretical capacity,high energy density,low production cost and environment-friendly become one of the ideal energy storage systems,which attracts the attention of researchers at home and abroad.However,in order to promote the large-scale application of lithium sulfur battery,there are still many challenges to be solved,including the extremely poor intrinsic conductivity of sulfur and discharge products,the huge volume expansion of active materials in the cycle process,and the serious shuttle effect of discharge intermediate long-chain lithium polysulfide(LIPSs).The shuttle diffusion of soluble polysulfides in the positive and negative electrodes is the key to affect the electrochemical performance of lithium sulfur battery.The shuttle effect greatly reduces the utilization rate of sulfur and makes the capacity decay very quickly.As a result,lithium sulfur battery shows poor energy storage characteristics and cycle stability,accompanied by serious self-discharge phenomenon.In this paper,Potassium Iodide was used as iodine source to modify the surface of mxene nanosheets with Iodine to enhance the adsorption and catalytic properties of mxene nanosheets for lithium polysulfide and improve the energy storage characteristics of lithium sulfur battery.In addition,L-cysteine was modified on the surface of MXene nanosheets by a simple heating reflux method,and the synergistic effect of the two was used to further optimize the electrochemical energy storage characteristics of MXene based lithium sulfur battery.The MXene nanosheets with high conductivity,strong polarity and good mechanical properties were prepared by chemical etching combined with solvent intercalation.Iodine was modified on the surface of MXene nanosheets by heat treatment.Through the lithium polysulfide diffusion adsorption experiment,combined with the results of material characterization and quantitative calculation,The adsorption and catalysis of I-MXene nanosheets for polysulfides were investigated.The results show that I-MXene nanosheets can anchor the intermediate lithium polysulfide,alleviate its serious shuttle effect,promote the conversion of lithium polysulfide and accelerate the transfer of interface charge.Using I-MXene as the modified layer to modify the separator and its application in Li-S battery system can significantly improve the energy storage characteristics of the battery and effectively improve its electrochemical performance.The first discharge specific capacity at 0.2 C rate can reach 1308.0 m Ah g-1,and the reversible capacity of609.8 m Ah g-1 can still be obtained after 100 cycles at 1 C high current.The enhanced energy storage characteristics are also shown in the high load test above 5 mg cm-2.L-cysteine was modified on the surface of mxene nanosheets by a simple heating reflux method.The MXene-CYSH/S composite was constructed by in-situ sulfur preparation and melt diffusion.The composite was used as the cathode material of lithium sulfur battery.The electrochemical performance of MXene based lithium sulfur battery was enhanced by the synergistic effect of the two materials.The mechanism of MXene-CYSH composite improving the energy storage performance of lithium sulfur battery was discussed.The polar heteroatoms on L-cysteine and the abundant functional groups on MXene surface can enhance the chemical adsorption strength of polysulfides,enhance the catalytic performance of MXene nanosheets for polysulfides,and improve the utilization rate of positive active materials.The specific discharge capacity of the first cycle of lithium sulfur battery with MXene-CYSH/S as electrode is 1051.1 m Ah g-1 at0.2 C rate.After 100 cycles,it still has a reversible capacity of 499.9 m Ah g-1.After 500cycles at 1 C high current,it still has a specific discharge capacity of 340.7 m Ah g-1. |
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