Research On The Surface Modification And Electrochemical Performance Of Li₄Ti₅O₁₂ And Sulfur/Expanded Graphite Composites

Lithium-ion batteries have been proven to be a promising power for use in large-scale energy storage and electric vehicles.Titanium-based anode materials,in lithium-ion batteries,face significant challenges during cycling due to their strong affinity to water and propensity to evolve gas.On the other hand,sulfur as the cathode material in Li-S batteries has superior theoretical capacity and high energy density,resulting in consideration as cathode material for promising secondary batteries.However,long-chain polysulfides(Li2Sx,x=4 to 8)are produced by the reduction of sulfur and subsequently dissolve into the electrolyte readily.Additionally,the dissolution of long-chain polysulfides would result in large loss of active materials and the products of Li2S and Li2S2 on the interface of metallic Li will have an enormous influence on the electrical conductivity of cells.To solve these problems,researchers have improved their performance through the use of stencil methods,cladding methods,and so on.In the paper,we demonstrate facile approaches to cover the active sites on the surface of Li4Ti5O12(LTO)and sulfur-expanded graphite(S-EG)for superior electrochemical performance by grafting silane.This thesis mainly included the following contents:(1)We developed a facile approach to cover the active sites on the surface of LTO for water adsorption and catalytic decomposition of solvents by grafting 3-(methacryloyloxy)propyltrimethoxysilane(MPTMS)onto LTO to form a ultrathin protective layer.More Importantly,LTO grafted with MPTMS(LTO@MPTMS)exhibits superior electrochemical performance,relative to the pristine LTO.(2)Sulfur can be embedded into the structural gaps of expanded graphite(EG)by heating treatment.Thus,EG could not only serve as micro-containers for sulfur,but also provide a conductive framework to improve the electrical conductivity of the S-embedded EG(S-EG)cathode in Li-S batteries.(3)To relieve the polysulfide dissolution,herein,we intensively modify the surface of S-EG with 3-cyanpropyl-trichlorosilane(CPS)molecules,which could react with the oxygen-containing groups on the surface of S-EG.It is demonstrated that carboxyl groups modified sulfur-expanded graphite S-(EG-COOH)have superior cycleabilty.