Layered Sulfide Anode Materials For Lithium/Potassium Ion Batteries

On the account of the advantages of stability,reliability and high efficiency,rechargeable battery covers the shortages among other renewable energy storage technologies,being one of the most popular power storage technologies.Benefit by its multiple advantages,lithium ion batteries?LIBs?stands out among all rechargeable battery technologies.With the long-term efforts of scientific researchers,it not only has a rich theoretical research foundation,it has also become increasingly mature in the industrialization of commerce.Despite flaws,lithium ion batteries have shortcomings such as expensive,which prompted researchers to seek potential replacement technology.Therefore,the potassium ion batteries?KIBs?based on it has gradually become an object of study due to its advantages such as large reserves of raw materials and similar chemical properties to lithium,considered as one of the most ideal potential alternative technologies.One of the main ways to improve the performance of lithium/potassium ion battery is the selection of lithium/potassium storage material structure and the electrode active material.In this paper,the performance of lithium/potassium ion battery is improved by selecting appropriate negative active material and modifying its structure.The research is divided into the following three parts:1)In the first part of the work,we selected vanadium disulfide?VS₂?with strong lithium storage capacity as the target anode active material for relevant research after doing a lot of theoretical study work like literature review.Orderly and lacunar stacked VS₂ nanosheets were successfully synthesized by a simple hydrothermal method with the help of polyvinylpyrrolidone?PVP?.It was found that VS₂ showed good cycling stability and rate capability in LIBs(about 450mAh·g^-1 after 100 cycles,300mAh·g^-1 at 1000mA·g^-1).Unfortunately,low capacity was found during dis-charge process of VS₂ due to its low content of S for lithium storage.2)In the second part of the work,in order to improve the specific capacity of the battery,we introduced graphene oxide?GO?to convert VS₂ into vanadium tetrasulfide?VS₄?with higher amount of S and formed VS₄/graphene?rGO?composite material.Although the specific capacity of the obtained material was improved,its stability was insufficient(decayed from about 800mAh·g^-11 to 400mAh·g^-1 after 100 cycles).On the basis of the composite materials research,we introduced the surfactant cetyl trimethyl ammonium bromide?CTAB?for the structure modification.We successfully synthesized the three-dimensional structure of cladding graphene coated neat VS₄nanoparticle composite material,and found its electrochemical performance enhanced in lithium ion batteries(about 750mAh·g^-1 after 50 cycles,400 mAh·g^-1 at2080mA·g^-1).3)In the third part of the work,to broaden its use,molybdenum disulfide?MoS₂?was brought into the the research of KIBs,being the host material of the anodes.With the synergistic effect of GO/glacial acetic acid?HAc?,the ultrathin layered MoS₂/rGO nanocomposite was successfully synthesized by one-step hydrothermal method,and the samples without glacial acetic acid were taken as reference to study the influence of glacial acetic acid in the synthesis of the composite,in which ammonium molybdate(?NH₄?₆Mo₇O₂₄·4H₂O)and thiourea were used as Mo source and S source respectively.On the basis of previous study,the addition amount of thiourea?i.e.,S addition amount?was increased by multiple times,and the composite was able to retain the original structure and have more defects with the help of excessive thiourea,thus exposing more active sites at the edge of the nanosheet.It was found that the composite material with ultrathin and lamellar structure rich in defects got outstanding cycling stability and rate capability(about 350mAh·g^-1 after 100 cycles,280mAh·g^-1 at 5000mA·g^-1).