Preparation And Electrochemical Properties Of Molybdenum Disulfide/Carbon Composites For Lithium-ion Batterie

Recently,Lithium ion batteries（LIBs）as a renewable energy,have been widely used in electronic devices and electric vehicle due to their high power density,high energy density and no pollution to the environment.LIBs have relieved the serious energy crisis and the problems of environmental pollution to some degree.M=olybdenum disulfide（MoS₂）has the layered structure similar to graphene and the theoretical capacity（670 m Ah g-1）,higher than that of ordinary graphite electrode（372 m Ah g-1）.In addition,because of its abundant resources and low pollution,MoS₂ has attracted great attention of researchers as a new type of anode material for LIBs.While,the low ionic/electronic conductivity of MoS₂ and the serious volume expansion and mechanism pulverization during the insertion-extraction of Li-ion limit the application as the commercial electrode material.Therefore,the key point of MoS₂ is to improve the cyclic stability and enhance the capacity of electrode materials.In this paper,flower-like MoS₂ nanosheets and MoS₂/C composites were prepared by hydrothermal method to improve the electrochemical performance of MoS₂ as anode materials for LIBs.The results are as follows:（1）The dispersive lamellar MoS₂ was synthetized by one-step hydrothermal method using sodium molybdate and thiourea as molybdenum source and sulfur source,respectively.Then we selected citric acid,Span 20 and polyethylene glycol 4000（PEG 4000）as surfactants,respectively.The effects of surfactants active agents on the morphology,structure and electrochemical properties of MoS₂ were investigated.We found that the best surfactant is PEG 4000.By comparing the content of PEG 4000,the sample has the most regular morphology when adding 0.3 g PEG 4000.The special flower structure increases the contact area between electrode and electrolyte,which accelerates the transfer of lithium ions and improves the capacity of anode materials.（2）We utilized sucrose as carbon source and PEG as surfactant to controllable synthesize flower-like MoS₂/C composites through a one-step hydrothermal procedure.The carbon content has different effects on morphology and electrochemical performance.When the carbon content reached 38%,the MoS₂/C composite showed the highest capacity of 597.7 mA h g-1 after 80 cycles（100 mA g-1）and best cycle stability.The reason for this phenomenon can be attributed to the synergistic effect between amorphous carbon and molybdenum disulfide.（3）We discussed the effects of hydrothermal reaction temperature and reaction time on the morphology and electrochemical properties of MoS₂/C composites.With the increase of reaction temperature and reaction time,the combination of molybdenum disulfide and amorphous carbon is more sufficient,which is beneficial to the formation of regular morphology and the improvement of electrochemical performance.Finally,we found that the optimum reaction temperature is 200℃ and the optimal reaction time is 24 h.