Preparation Of Carbon-encapsulated Vanadium/Molybdenum Oxide Electrode Material Based On Cyclodextrin Inclusion Compounds

The development of advanced lithium-ion batteries with both high energy density and high power density has become one of the important research goals in the field of electrochemical energy storage.Electrode materials are the basis of lithium-ion batteries,and wanting to obtain lithium-ion batteries with excellent performance depends on the development and application of high-performance positive and negative electrode materials.Carbon composite can improve the conductivity of non-carbon electrode materials and increase the diffusion rate of lithium ions in the process of insertion/extraction.It is one of the effective means to improve the electrochemical performance of materials.However,the conventional carbon composite has the problems of large particle size,easy to fall off,easy to break,etc.,resulting in poor effect.In this paper,starting from the design and synthesis of ?-cyclodextrin inclusion compound,to achieve molecular-level encapsulation,combined with heat treatment technology to prepare carbon-encapsulated transition metal oxide;using a variety of characterization testing methods,the precursor of ?-cyclodextrin inclusion compound The composition,morphology and structure of the bulk and derived carbon-encapsulated transition metal oxides were investigated,and their electrochemical performance was evaluated to study the structure-effect relationship between the composition and structure of the materials and the properties of lithium and sodium storage.For the first time,the inclusion of ?-cyclodextrin inclusion compound was prepared by liquid phase method and freeze-drying technique.The flake V2O3(?)C nanocomposite was obtained by low-temperature pyrolysis and high-temperature carbonization.The effect of calcination temperature on product composition and morphology was studied.Rules,and explored the formation mechanism of nanosheets.The electrochemical properties of the prepared materials were evaluated.Compared with V2O3 and amorphous carbon materials prepared under similar preparation processes,V2O3(?)C nanocomposites showed excellent rate performance and cycle stability when the current density was 0.1,0.2,0.5,1,2,4,8,and 10 A g-1,the specific lithium storage capacities are 1080,893,842,770,694,614,525,and 469 mA h g-1,respectively.The research results show that:from the perspective of molecular structure design,building a carbon-encapsulated nanocomposite structure can effectively improve the lithium ion storage capacity of the material.The versatility of the above carbon encapsulation process was studied,and a sheet-like MoO2(?)C nanocomposite was prepared by a similar process.The carbon encapsulated structure of the material can further alleviate the stress changes during charging and discharging.The electrochemical performance test results show that MoO2(?)C nanocomposite also has excellent lithium ion storage performance.At a current density of 0.2 A g-1,after 20 cycles,its capacity remains at 898 mA h g-1;at a high current density of 1 A g-1,after 500 cycles,its discharge specific capacity can still reach 528 mA h g-1.Using a similar process,flake-shaped VxMoyOz(?)C nanocomposites were prepared.The synergy between vanadium and molybdenum mixed oxides and carbon materials was further enhanced.Compared to V2O3(?)C and MoO2(?)C nanocomposites,carbon-encapsulated mixed metals Oxides exhibit better sodium ion storage capacity.At a current density of 0.1 A g-1,after 100 cycles,the discharge specific capacity of the VxMoyOz(?)C(V:Mo=4:1)material can be maintained at around 245 mA h g-1.