Modification Of Lithium Titanate Anode With Superior Electrochemical Performance

The preparation and modification of anode materials and slurry have attracted much attention in the research of lithium-ion batteries.Spinel Li₄Ti₅O₁₂(LTO)is a typical intercalated anode material with high capacity utilization and good cycling stability,showing a good research and application prospect.However,the low electrical conductivity and lithium ion diffusion coefficient of LTO lead to serious polarization when cycling at high current densities,which limits the electrochemical performance.In this work,starting from the thinking of improving the ionic conductivity and electrical conductivity,LTO anodes modified by Li₂O-2B₂O₃(LBO),Li_1.4Al_0.4Ti_1.6(PO₄)₃(LATP),nitrogen-doped porous carbon(NC),reduced graphene oxide(r GO)and binary conductive additive are prepared,with coating modification as the main strategy,to improve the rate capacity and cycling stability of LTO anode.And the mechanism of the performance improvement is analyzed.The main research work and results are as follows:(1)LBO-LTO anodes with different LBO coating amounts are obtained through a controlled liquid surface modification process combined with sintering under appropriate conditions.The reversible specific capacity of 2 wt%LBO-LTO reaches 172.9 m A h g^-1at 0.1 A g^-1,and still maintains 94.2%after a long-time cycling at 2.0 A g^-1.Instead,the capacity retention of the LTO anode is less than 90%.This indicates that,an appropriate amount of LBO coating can effectively improve the transport rate of lithium ions,reduce the polarization,and improve the capacity retention and cycling stability of LTO anode at high current densities.(2)LATP-LTO anodes with different amounts of LATP coating are obtained by(i) solution method combined with sintering,and(ii)sintering after ultrasonic crushing and mixing.The capacity retention of 2 wt%LATP-LTO is 74.6%after a cycling test at 5.0 A g^-1,while that of the LTO anode is only 30%.The introduction of an appropriate amount of LATP can avoid the direct exposure of LTO to the electrolyte to a certain extent,and reduce the ion diffusion resistance at the interface,thereby increasing the rate capacity and the cycling stability.The electrochemical properties of LATP-modified LTO anode prepared by ultrasonic crushing method are also improved.(3)LTO@NC anodes modified with different amounts of nitrogen-doped porous carbon are prepared by coating LTO with ZIF-8 through a water bath method following by carbonization.The LTO@NC-2 anode(1.62 wt%carbon)shows better rate capacity and cycling performance than both the LTO@NC-1 with less carbon content(0.66 wt%carbon)and the LTO@NC-3 with more carbon content(3.18 wt%carbon).It shows a high specific capacity of 126.2 m A h g^-1 at 10.0 A g^-1.And after a cycling of 1000 cycles at 5.0 A g^-1,the capacity can still maintain 88.7%.The appropriate amount of coating can strengthen the interfacial stability of the electrode material and accelerate the electron conduction,and thus improve the rate and cycling performance of the battery under high current density.(4)LTO@r GO anodes modified with different content of r GO and LTO NPs@r GO anode(r GO coated LTO nanoparticles)are prepared by a combination method of liquid phase mixing,freeze-drying,annealing in the argon atmosphere,and a liquid phase ultrasonic method for crushing LTO particles into ultrafine LTO nanoparticles.The reversible specific capacity of the LTO anode modified with an appropriate amount of r GO(4.39 wt%)is 168.3 m A h g^-1 at 0.1A g^-1,and the capacity retention is 58.4%when the current density is expanded to 10.0 A g^-1,while the reversible specific capacity of the LTO anode is 151.0 m A h g^-1 with a capacity retention of 50.2%.The LTO NPs/r GO anode rich in LTO quantum dots exhibits a specific capacity of 110.4 m A h g^-1 with a capacity retention of 64.0%at 10.0 A g^-1,and the capacity remains 92.2%after 1000cycles at 5.0 A g^-1.The process of ultrasonic crushing combined with freeze-drying and annealing is simple and the sample is of high purity.(5)Exfoliated graphite sheets and acetylene black particles are combined as a binary conductive additive for LTO anode and 2 wt%LBO-LTO anode to construct an optimized conductive network.The capacity retention of the 2 wt%LBO-LTO anode with"7AB+3G"conductive additive added maintains 60.8%after the current density increases from 0.1 to 10.0 A g^-1,which is higher than that with"10AB"conductive additive added(49.9%).The appropriate composition of the binary conductive additive can optimize the electron transport in the electrode,reduce the internal resistance of the battery,so as to improve the rate performance and cycling stability of the LTO anode and the 2 wt%LBO-LTO anode.