Influence Of Wet Modification And A/B Co-doping On Lithium Titanate Structure And Electrochemical Performance

Lithium titanate(Li₄Ti₅O₁₂,LTO)is featured by its“zero strain”characteristic,which can maintain a high stability crystal structure during the Li ion intercalation and deintercalation process.It also has high intercalation potential to avoid lithium being separated out on the surface of anode materials.It is consequently fair to say LTO is an ideal alternative anode material of carbon in lithium ion secondary battery.But low Li ion diffusion coefficient(10^-16-10^-9 cm²·s^-1)and electrical conductivity(<10^-13S·cm^-1)of LTO limit its high rate performance and practical application.This paper comprehensively improved LTO electrochemical properties from four aspects:wet modification synthetic method,uniform dispersion technology,A/B site co-doping structure design and graphene composite.Thus,LTO can get a wide application prospect in high-power battery field.In order to avoid the wide particle size distribution and high content impurities of LTO-1 synthesized by traditional solid state method,wet modification step was introduced.Improved method 1 had in situ amorphous TiO₂·xH₂O coated onto Li₂CO₃ and synthesized decentralized state LTO-2.Improved method 2 used nitric acid to dissolve lithium carbonate,inhibiting the hydrolysis of TBT.It also applied ethylene diamine tetraacetic acid and citric acid as a bi-component chelating agent to stabilize the sol,then synthesized three-dimensional network LTO-3.Comparing with LTO-1,LTO-2 and LTO-3 showed a better first time coulomb efficiency at 0.5 C rate increased from 86.4%to 86.4%and 94.1%,respectively.The first time discharge specific capacity at 40 C rate also gained an increase from 25 mAh g^-1 to 44 mAh g^-1 and 53 mAh g^-1.Ultra-high speed nano-pulverization?USN?was further applied to solve the LTO particle aggregation problem.The continued multiple shear during the pulverizing forced particles separated apart.LTO powders with USN processing did not display obviously sedimentation after the ageing,showing great improvement on particle dispersion.Co-doping by La,Sc,Mg,Ag elements was also done to effectively improve the electrochemical performance of LTO.Li_3.95La_0.05Ti_4.95Sc_0.05O₁₂?LLTSO?,Li_3.95La_0.05Ti_4.95Ag_0.05O₁₂?LLTAO?,Li_3.95Mg_0.05Ti_4.95Ag_0.05O₁₂?LMTAO?,Li_3.95Mg_0.05Ti_4.95Sc_0.05O₁₂?LMTSO?with three-dimensional network structure were simply synthesized by method 2.LLTSO showed a better performance with the first time coulomb efficiency of 99.3%at 0.5 C rate,and first time discharge specific capacity up to 85 mAh g^-1 at 40 C rate.Graphene-coated LTO?LTO-Nano/G,LLTSO/G?were synthesized for further comprehensive improvement on electronic channel and electrochemical performance.LTO-Nano/G and LLTSO/G still retained the original powder structure features.Comparing with original LTO-Nano,LLTSO,lithium ion diffusion coefficient of LTO-Nano/G and LLTSO/G increased by 5 times and 58 times,respectively,and the correspongding capacity at 40 C increased by 16.4%and 18.8%,respectively.The wet activation step was introduced to synthesize LTO powder with high purity and uniform particle size.USN processing effectively broke up the particle aggregation.A/B site co-doping structure design and simple graphene load comprehensively improved the electrochemical performance of LTO.LLTSO/G synthesized by improved preparation method 2 exhibited the best electrochemical performance with the first time coulomb efficiency as high as 99.2%at 0.5 C rate,and an excellent reversible capacity of 101mAh g^-1 at 40 C rate.The result of the cycling performance showed a remarkable capacity retention of 98.5%at 5 C after 400 cycles.