Preparation Of MoS₂@Wheat Straw Based Carbon Composites And Their Performance As Anode Materials For Lithium Ion Batteries

Energy is the lifeblood of modern society and plays a vital role in the progress of human development.Lithium-ion batteries（LIBs）are widely used in portable electronics and electric vehicles due to their high capacity,high energy density and high operating voltage,making an outstanding contribution to solving problems such as the energy crisis and environmental pollution.Although LIBs have made great technological advances,they still do not meet the needs of high-capacity and high-energy applications associated with the electric vehicle sector.The design/manufacture of high-performance lithium-ion batteries with high energy/power density is still one of the hot topics of research.Ordinary graphite electrodes have a theoretical capacity of only 372 m Ah g^-1,and the microstructure of molybdenum disulfide（MoS₂）is similar to the layered structure of graphene.It is a special"sandwich"structure with a theoretical specific capacity of about 670 m Ah g^-1,making it an ideal material for use as a negative electrode for lithium-ion batteries.However,the low conductivity of MoS₂ itself and the lithium ion will interpenetrate in its structure during operation will cause serious volume problems and structure pulverization,which will adversely affect the cycle stability.This shortcoming limits its use as a commercial electrode material,so it is urgent to improve the MoS₂electrode material.In this paper,MoS₂ and wheat straw biomass carbon composites were prepared by hydrothermal and high temperature carbonisation methods.By using wheat straw biomass carbon as raw material,the electrical conductivity of the composites can be improved to a certain extent and environmental pollution can be reduced.The microstructure of MoS₂ was modified to improve the bulk expansion and low conductivity of molybdenum disulphide,and the microstructure of wheat straw was modified to improve the specific capacity and cycling stability of the composites.The microscopic morphology of the composites was characterized by various means,and their performance as anode materials for lithium-ion batteries was analyzed.Details of the study and conclusions are as follows:1.The MoS₂@WSCC composite was synthesized by a one-step hydrothermal process by extracting wheat straw cellulose（WSCC）as the carbon precursor and selecting cetyltrimethylammonium bromide（CTAB）,polyvinylpyrrolidone（PVP）and sodium dodecylbenzene sulfonate（SDBS）as the surfactants.The morphology,structure and electrochemical properties of MoS₂@WSCC were analysed and summarised with different surfactants,and PVP was finally identified as the best surfactant.In the composite（MoS₂@WSCC-S）formed by PVP induction,MoS₂ was in the form of yarn spheres with uniform particle size.The intercalation of the PVP increases the contact area between the electrode and the electrolyte,thus increasing the transport rate of the lithium ions and thus the reversible capacity.However,the reversible capacity did not achieve the desired desired effect,so we designed flower-like MoS₂ and wheat straw cellulose carbon composites（MoS₂@WSCC-F）by adding HCl and ammonium persulphate for further microscopic modulation.When compared with MoS₂@WSCC-S,the MoS₂@WSCC-F composite exhibited more stable cycling characteristics and better multiplicative performance.After 300 cycles at 1 C(600 m A g^-1),the specific capacity was stable at 1056.3 m Ah g^-1 with a capacity retention rate of 80.4%.This effectively improves the electrical conductivity and mechanical stability of the composite.2.Using wheat straw as a carbon source and ammonium ferrous sulfate hexahydrate as a regulator,wheat straw porous carbon materials were prepared by hydrothermal and high-temperature carbonization treatment.Using the obtained porous carbon as a carbon matrix,a triblock copolymer F127 was selected to control the morphology of MoS₂,and a wheat straw porous carbon and flower-like MoS₂composite（PWSC@MoS₂）was synthesized by hydrothermal method The effects of the amount of structural modifier and the content of porous carbon on the overall electrochemical properties of the composites were investigated.The optimum structural modifier ratio of 1:2 was finally determined and the electrochemical properties of the composite（PWSC@MoS₂-M）were well improved at a medium porous carbon content.The results show that the synergistic PWSC@MoS₂-M composite is able to maintain a charge/discharge specific capacity of 1478.6 m Ah g^-1for 200 cycles at 1 C and still achieves 857.3 m Ah g^-1 at a magnification of 5 C,improved cycling and magnification performance of composite materials...