Preparation Of Stable Metallic Phase MS₂ ?M=Mo?W? Composites And Study On Their Electrochemical Performances

Transition metal sulfide(MS2)materials have been one of the strongest contenders as anode materials of the next generation for LIBs due to their unique layered structure and high theoretical capacity.However,the large volume change of traditional MS2 materials during the process of diacharge-charge limits their application and development.How to improve the conductivity and boost the energy density becomes one of the hottest and most difficult subjects in MS2 anode.In this paper,based on the size effect and composite carbon material with good conductivity,the preparation,electrochemical lithium storage mechanism and electrochemical kinetics process of stable MS2(M=Mo,W)and their composites have been thoroughly investigated,which could serve as a new research route for designing and preparing MS2-based materials and the study of high-performance MS2-based energy storage materials.The concrete research content is as follows:1.A novel method for the preparation of G/MoS2 composite was proposed.GO inserted and exfoliated MoS2 by ultrasonic assisted,and G/MoS2 with different graphene contents were obtained.The electrochemical properties of composite were studied.G/MoS2 composite has shown excellent cyclic and discharge performance as anode of lithium ion batteries(LIBs),and the results of electrochemical kinetic characterization and ex-situ XRD analysis indicated that the embedding and transformation reaction was main stored energy pattern in G/MoS2 composite and pseudocapacitor played an auxiliary role.2.The metallic phase MS2(M?Mo,W)were successfully fabricated by nitrogen element doping in semiconductor MS2,the phase transition from 2H MS2 to 1T MS2 was realized.First,2H MS2 nanosheets were synthesized by hydrothermal,and then 1T MS2 nanosheets were obtained by calcination at ammonia atmosphere,as demonstrated by various structural characterization methods,N atoms incorporated MS2 gave rise to glide of S atom layer,the structure of MS2 from trigonal prismatic coordination to octahedral coordination,and the phase transition from 2H to 1T phase was completed.1T@2H MoS2?CC and 1T@2H WS2?CFC were fabricated by the recombination of 1T@2H MoS2 attached to carbon cloth(CC),and the incorporation of 1T@2H WS2 and carbon fiber cloth(CFC),and the obtained nanocomposite were directly used as free-binder.anode for LIBs,the results of electrochemical measurement indicated that MS2 composite electrodes containing metal phase not only showed a smaller initial discharge loss and a higher reversible capacity than the pure 2H phase electrode,but also further improved the conductivity of the composite material and reduced the internal resistance.The ex-situ XRD and HRTEM results of composites at different cut-off voltages showed that lithium storage mechanism of metallic phase MoS2 was:MoS2 + Li+ + e-?Mo + Li2S.The electrochemical kinetic and capacitive contribution in 1T@2H WS2@CFC electrode were investigated via cyclic voltammetry at different scanning rates,and the test results indicated that the lithium storage mechanism of 1T@2H WS2?CFC electrode is diffusion control as the leading,pseudocapacitor plays a supporting role.These results demonstrated that stable metallic phase MS2 was prepared effectively by nitride doping strategy and the electrochemical properties of composites were improved.3.On the basis of the preparation of metallic phase MS2 materials by nitrogen doping,we proposed a new way to realize phase change of MoS2 by phosphorus doping.Graphene was fabricated by pressurized oxidation method and the composite of MoS2 and graphene were synthesized by hydrothermal process,phosphorus element was introduced into MoS2 by high-energy ball-milling and subsequent thermal treatment under Ar atmosphere,and 1T@2H MoS2@graphene(1T@2H MoS2?G)were obtained.1T@2H MoS2?G electrode exhibited excellent electrochemical properties,and the results of kinetic analysis certified that the diffusion process played a major role and pseudocapacitor played an auxiliary role during the charge-discharge process in 1T@2H MoS2?G electrode.