Research On Modification Of Lithium Titanate And Its Lithium Storage And Sodium Storage Performance

Energy shortage and environmental pollution are the two major problems through the world nowadays.It is an effective way to solve these two problems by developing renewable energy and developing new energy vehicles,and the energy storage system is the key to realize these two approaches.Lithium ion batteries have been the most popular energy storage system because of their high energy density,long life and environment friendly.However,the shortage of lithium resource will restrict the sustainable development of lithium ion batteries.Sodium resource is rich in the earth's crust,so the sodium ion batteries which are similar to the lithium ion batteries are attracting more and more attention.Spinel lithium titanate oxide(Li₄Ti₅O₁₂,LTO)is currently the anode material of the lithium ion batteries with the high safety performance and long service life,and it can also be used as anode material for sodium ion batteries.However,the conductivity of Li₄Ti₅O₁₂ is poor,which seriously affects its rate capability,so it needs to be modified to meet the requirements.In this paper,we firstly evaluated the structure and electrochemical characteristics of modified lithium titanate prepared by different methods,explored the relationship between structure and properties,and then stud ied the simple and efficient modifying method for preparing high performance lithium titanate anode material.The main results are as follows:1.Six kinds of modified lithium titanate oxide material with bulk doping,surface coating,and size reducing were comprehensive evaluated,including their structural characteristics and electrochemical properties for lithium/sodium storage.The results show that amorphous carbon and carbon nanotubes coated lithium titanate oxide had excellent lithium storage performance,and the nano lithium titanate oxide material had better sodium storage performance.2.Chromium?Cr?-modified lithium titanate oxide with a synergistic effect of bulk doping,surface coating and size reducing was synthesized by a facile sol-gel method.The results show that Cr³⁺ doping in bulk to make some Ti4+ reduced to Ti³⁺,improving the LTO bulk electronic conductivity;Meanwhile,Li₂CrO4 was also formed in situ on the particle surface,improving the surface conductivity of the electrode material.Li₂CrO4 coating and Cr doping inhibited the growth of LTO particles,and the particle size was small.This synergistic modification resulted in excellent electrochemical performance of Li3.9Cr0.3Ti4.8O12,with the capacity of 141 mAh g-1 at 10 C,and over 155 mAh g-1 at 1 C after 1000 cycles.3.The Cr₂O₃ modified Li₄Ti₅O₁₂ was prepared by a solution-based method.The results show the pure Cr₂O₃ coated Li₄Ti₅O₁₂ anode material can be obtained by basic chromium solution modification.The pure Cr₂O₃ works as an adhesive interface to strengthen the connection between Li₄Ti₅O₁₂ particles,providing more electronic conduction channels and reducing the inter-particle resistance.Moreover,Lix Cr₂O₃,formed by the lithiation of Cr₂O₃,can further stabilize Li7 Ti5O12 with high electronic conductivity on the surface of particles.The 1% Cr₂O₃-coated sample exhibited excellent rate performance and low temperature performance,the reversible capacity was 134 mAh g-1 at 10 C.Moreover,its reversible specific capacity was still as high as 118 mAh g-1 at-20 oC.4.Ultrathin Li₄Ti₅O₁₂ nanosheets with ordered microstructures were prepared via a polyether-assisted hydrothermal process,and their sodium storage properties were studied.Pluronic P123,a polyether,can impede the growth of Li₂TiO₃ in the precursor and also facilitate the?Li1.81H0.19?Ti2O5·2H2O precursor to form the LTO nanosheets with the ordered microstructure.Moreover,the addition of P123 can suppress the stacking of LTO nanosheets during calcining of the precursor,and the thickness of the nanosheets can be controlled to be about 4 nm.The ultrathin ordered LTO nanosheets had excellent sodium storage properties,and the reversible capacity of 10 C reached 115 mAh g-1.