Study On Molybdenum Oxide/Carbon Nanocomposites As Anode Materials For Lithium Ion Batteries

Lithium-ion batteries(LIB)have long been the leader in portable electronics for decades,and the application landscape is continually moving toward large-scale electric vehicles(EVs).When transition metal oxides(TMOs)are used as the electrode material,a large discharge capacity can be provided because of the mechanism of the incorporation/deintercalation of the lithium itself into the conversion reaction or the alloying reaction.Among them,molybdenum oxide has been widely studied as a anode electrode of LIBs in recent years.However,the cycle performance is always compromised by the pulverization shedding caused by the expansion and contraction of the material volume during the(de)lithiation process,resulting in a rapid decay of the capacity of the LIB.Carbon-based anode materials have been known to have excellent cycle stability although their cycle capacity is low.Therefore,the MoO3/C composite nanostructure is designed to maintain high cycle capacity,buffer volume expansion,and improve the overall electronic conductivity of the composite.This work overcomes the shortcomings of molybdenum oxide and helps to obtain higher performance MoOx/C composites for lithium ion battery anodes.In this paper,we combine electrospinning and heat treatment to produce different one-dimensional MoOx/carbon nanofiber composites at different carbonization temperatures and MoO3/with porous structure and so on.The effects of heat treatment at different carbonization temperatures on the morphology of the fibers,as well as the effects of the crystallinity,content and size of the internal particles on the electrochemical lithium storage performance of the lithium ion battery,and the composition of MoO3 in the composite fibers were investigated.Effect of pore size distribution and shape on the electrochemical performance of MoO3/PCNFs composite electrode were researched.1.The simple electrospinning method can obtain MoOx/C composite nanofibers with different carbonization temperatures.With the increasement of carbonization temperature,MoOx crystalline nanoparticles with a size of～2 nm begin to appear uniformly within the CNFs.Moreover,Mo6+is gradually reduced to Mo5+.Mo4+and Mo2+,corresponding to the formation of MoO3,MoO2,and Mo2C inside the CNFs,respectively,which will affect the lithium storage performance to different extents.Among them,MoOx/C-625 with the best performance due to the formation of ultrafine MoO3 nanoparticles during the process has greatly increased the specific surface area,not only shortening the diffusion distance of Li+,but also increasing the power density through capacitive charge storage.It can still maintain a reversible capacity of 604.2 mAh g-1 after 100 cycles with a current density of 0.2A g-1.2.Combine the optimal temperature range with the PMMA thermal degradation temperature,ultrafine MoO3 nanoparticles uniformly embedded in porous carbon nanofibers(PCNFs)anode synthesized by electrospinning are comprehensively investigated.At a carbonization temperature of 750℃,PMMA is decomposed to form a worm-like porous carbon matrix,and ultrafine MoO3 nanoparticles(3-5nm)is uniformly dispersed in carbon nanofibers.0.5-MoO3/PCNFs exhibited the highest reversible capacity and the capacity after circulation was 795.8 mAh g-1.At the same time,the rate performance was much higher than that of the previous step.This work presents a facile and cost-effective approach to synthesis of high-performance electrode materials by nanostructuring and porous design.