Study On The Modification Of Magneli Titanium Suboxide On Electrode Materials Of Lithium-ion Batteries

Lithium iron phosphate(LiFePO4)and lithium titanate(Li4Ti5012)are the common lithium ion cathode and anode materials.The spinel Li4Ti5O12 is a kind of "zero strain"cathode material,which has the advantages of low cost and cycle stability;LiFePO4 is a safe,environmentally friendly and low cost lithium ion cathode material.However,their low electronic conductivity limits their application in lithium-ion batteries.In order to solve this situation,the high conductivity materials or preparing special structure electrode materials have been used to improve the charge-discharge performance and chemical stability at high rate.Magneli titanium oxide is a general term for a series of non-stoichiometric titanium oxides(Ti-O).The structure of Ti-O is similar with the rutile titanium dioxide,only showing oxygen deficiency at a certain number of layers(structural units).Because of its unique structure,Magneli titanium oxide has better chemical stability,corrosion resistance and conductivity than titanium dioxide.Therefore,it can be developed as a new potential lithium-ion battery material.The main research contents are as follows:(1)Due to the different conductivity of different main TiOx phases obtained by carbothermal reduction at different temperatures,and the influence of holding time on the particle size of the product,the preparation parameters of the main Ti4O7 phase were set as follows:TiO2 was used as the Ti source,and mixing with 3.8 wt.%C,then the mixture was heated to 1075? under Ar atmosphere and kept for 3 h.Ti4O7 with different ratios(3%,5%,7%,9%)was used as a conductive addition to compound with LiFePO4.Metal lithium was used as the counter electrode and assembled into a half-cell for electrochemical performance test.The experimental results show that the addition of TiOx helps to improve the rate and cycle performance of LiFePO4,and when the TiOx is added at 3%,the best comprehensive performance of LiFePO4 can be obtained.At a large rate(10 C),the specific capacity can reach about 40 mAh g-1.(2)Based on the liquid deposition method,a dual modification method of LiFePO4 by Ti4O7 and CNTs was proposed to form a LiFePO4/Ti4O7/CNTs composite.Studies have shown that CNTs and Ti407 can effectively improve the conductivity of LiFePO4.The conductive network composed of CNTs can effectively inhibit the agglomeration and growth of particles,and the conductive particles Ti4O7 distributed in the conductive network can facilitate the transport of lithium ions and electrons.(3)LiFePO4-TiOx/CNTs/rGO,Li4Ti5O12-TiOx/CNTs/rGO flexible composites were prepared by vacuum filtration.Metal lithium was used as the counter electrode and assembled into a half-cell for electrochemical performance test.The experimental results show that the flexible electrode has good rate and cycle performance.The Li4Ti5O12-TiOx/CNTs/rGO flexible electrode is tested at high magnification(30 C)for 100 cycles,maintaining 66 mAh g-1 specific capacity and approximately 99%coulombic efficiency.