Preparation And Electrochemical Performance Investigation Of Low-dimensional Lithium Titanate-based Nanomaterials

As a kind of environmentally friendly energy storage devices,lithium ion batteries?LIBs?have been considered to be one of the most important power sources to meet the increasing demands from portable electronic devices,electrical vehicles?EV?,hybrid electrical vehicles?HEV?and plug-in hybrid electric vehicles?PHEV?.Spinel structure lithium titanate(Li₄Ti₅O₁₂)has a good cycle stability,long service life,high security lithium ion battery anode material.However,the low electrical conductivity and poor lithium ion diffusion coefficient restrict its further application for lithium ion battery.This paper focused on the electrospinning technique and solid phase method for synthesizing ion doping and nitrogen doping carbon coating low dimensional Li₄Ti₅O₁₂ nanomaterials?including sub-microbelts,nanofibers,bamboo nanofibers,nanoparticles?,and the effects of different modification behaviors on their structure and properties were studied in detail.The contents of the paper are as follows:1.One-dimensional Ce³⁺-doped Li₄Ti₅O₁₂(Li₄Ti_5-xCe_xO₁₂,x=0,0.01,0.02,and0.05)submicrobelts with the width of approximately 500 nm and thickness of about200 nm have been synthesized via the facile electrospinning method combined calcination process.The structure and morphology of the as-prepared samples are characterized by XRD,TEM,SEM,EDS mappings,BET,HRTEM and XPS.A series of electrochemical tests show that Ce³⁺-doped Li₄Ti₅O₁₂ electrodes exhibit the brilliant electrochemical performance than undoped counterpart.2.One-dimensional Co²⁺-doped Li₄Ti₅O₁₂ nanofibers with a diameter of approximately 500 nm have been synthesized via electrospinning method combined calcination process.The Co²⁺-doped Li₄Ti₅O₁₂ nanofibers were systematically characterized by XRD,ICP-OES,TEM,SEM,BET,EDS mappings,and XPS.Co²⁺-doped Li₄Ti₅O₁₂ nanofibers exhibit the enlarged lattice volume,reduced particle size and enhanced electrical conductivity.More importantly,Co²⁺-doped Li₄Ti₅O₁₂nanofibers as a lithium ion battery anode electrode performs superior electrochemical performance than undoped Li₄Ti₅O₁₂ electrode.3.One-dimensional bamboo-shaped Li₄Ti_5-xZn_xO₁₂ and Li₄Ti₅Zn_xO₁₂?x=0.05?nanofibers with the diameter of approximately 300 nm have been synthesized via a n electrospinning method.The structure and morphology of the as-prepared materials have been characterized by XRD,TEM,SEM,EDS mappings,BET,ICP-OES and XPS,and the effects of two different kinds of Zn²⁺ions doping behaviors:substitutional doping and interstitial doping on the properties of bamboo-shaped Li₄Ti₅O₁₂ nanofibers have been studied in detail.Fortunately,the introduction of Zn²⁺ions cannot interrupt the original cubic spinel structure and one-dimentional bamboo-shaped nanostructure of Li₄Ti₅O₁₂.The comparative experiments prove that interstitial doping bamboo-shaped Li₄Ti₅O₁₂ nanofibers exhibit the best electrochemicalperformancesthansubstitutionaldopingandundoped bamboo-shaped Li₄Ti₅O₁₂ nanofibers.4.N-doped carbon coating Li₄Ti₅O₁₂ nanocomposites have been synthesized via a one-step solid state method combined calcination process by using chitosan as a noval carbon nitrogen source.The structure and morphology of the as-prepared materials have been characterized by XRD,TG,Raman,TEM,SEM,EDS mappings,BET and XPS.The introduction of chitosan inhibited the agglomeration of Li₄Ti₅O₁₂nanoparticles in the process of high temperature calcination and increased the specific surface area.According to the analysis results of Raman and XPS,the N element doped into the Li₄Ti₅O₁₂ lattice and increased the lattice volume of Li₄Ti₅O₁₂,and the N element in amorphous carbon increases the disorder of carbon.The comparative experiments prove that modified Li₄Ti₅O₁₂ electrode exhibit better electrochemical performances than pure Li₄Ti₅O₁₂ electrode.