Synthesis And Properties Of Li₄Ti₅O₁₂ As Anode Material For Lithium Ion Battery

Spinel lithium titanate is well known as the "zero strain" material,because Li₄Ti₅O₁₂ has prominent safety performance,perfect cycle stability,small volume change and low costs which has great potentials and become one of the new lithium-ion battery cathode materials.The spherical Li₄Ti₅O₁₂ powders are prepared by hydrothermal method assisted with CTAB as structure-directing agent,using LiOH·H₂O and tetrabutyl titanate,as the main raw materials.The process parameters are optimized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,battery testing system and electrochemical workstation.The results show under the condition that hydrothermal temperature is at 170? for 36 h and the calcination reaction is at 600? for 2 h,Li4Ti5012 powders with a diameter of 1?2 ?m can be prepared.After 50 charge-discharge cycles at 0.1 C rate,the discharge capacity of spherical materials decreases from 162.7 mA h g-1 to157.5 mA h g'1,and the capacity retention rate is 96.8%.The hollow spherical Li₄Ti₅O₁₂ powders are prepared by hydrothermal method assisted with NH4HCO3 as structure-directing agent.NH4HCO3 can decompose to form bubbles in the course of heating,leading to the formation of precursor of hollow spherical Li₄Ti₅O₁₂.As the charge-discharge rate increases?from 0.1C to 20C?,the first discharge capacity of hollow spherical materials are 176.4 mA h g-1?164.7 mA h g-1?157.4 mA h g-1?154.2 mA h g-1?141.4 mA h g-1?127.4 mA h g-1 and 112.7 mA h g-1,respectively.And the capacity retention rates in 10 charge-discharge cycles are respectively 98.4%,97.8%,99.7%,97.5%,98.7%,98.0%and 96.2%which maintain high levels.After doping Mg2+ at the basis of hollow spherical Li₄Ti₅O₁₂ prepared by hydrothermal method assisted with NH4HCO3 as structure-directing agent,the Mg-doped Li₄Ti₅O₁₂ shows higher discharge capacity and lower charge transfer impedance compared to pure Li₄Ti₅O₁₂.At 0.1C,the first discharge capacity of Li3.9Mg0.iTi5O12 is 182 mA h g-1.After 10 cycles,the capacity retention rate is 97.8%.The charge transfer impedance of Li4TisO12 and Li3.9Mg0.1Ti5O12 in charge and discharge process is 330.2 ? and 201.1 ?,respectively.The results show the hollow spherical Li₄Ti₅O₁₂ has a better charge and discharge performance and rate performance than spherical Li₄Ti₅O₁₂.Mg-doped Li₄Ti₅O₁₂ shows higher electrochemical performance and lower charge transfer impedance than pure Li₄Ti₅O₁₂.