Preparation And Modification Of Lithium Titanate Cathode Material For Lithium Ion Battery

The existing anode materials system with high energy density has a large volume change in the process of inserting and deintercalating lithium ions,and thus the volume expansion and cycle life of the lithium battery have become a problem that academic and industrial circles have been working on.As a negative electrode material for lithium batteries,Li₄Ti₅O₁₂（LTO）has a small volume change during charge and discharge.This"zero strain"performance makes it have stable cycle capability and long cycle life.However,Li₄Ti₅O₁₂ has poor conductivity and low theoretical specific capacity,which severely limits its performance at high currents.Lithium titanate was prepared by sol-gel method.The conditions of raw material ratio,calcination temperature and holding time were analyzed by XRD and electrochemical tests.The optimal conditions for the synthesis of Li₄Ti₅O₁₂ were as follows:Lithium-titanium molar ratio was 0.84,and the temperature was kept at700°C for 6 hours.The first phase discharge specific capacity of pure phase LTO at1 C was 171.34 mAh/g.In order to improve the reversible capacity of lithium titanate,Fe³⁺,Al³⁺and Cr³⁺doping were used to substate B-site Ti⁴⁺.The effects of ion doping on the structure and electrochemical properties of the electrode were investigated.The results showed that the three doping ions formed a spinel structure with LTO as the skeleton,and the unit cell parameters of the modified samples changed to different degrees.The doping of Cr³⁺had a good inhibitory effect on the agglomeration of Li₄Ti₅O₁₂ particles,and its specific surface area was up to 45.62 m²/g.In terms of electrochemical performance,the introduction of Fe³⁺,Al³⁺and Cr³⁺improved the reversible capacity of the electrode material,and the material doped with Cr³⁺could balance the relationship between the discharge performance and the cycle performance at high rate.Li₄Ti₅O₁₂ material was coated and modified with succinic acid,glucose and stearic acid as carbon sources to improve its electrical conductivity.The test showed that the electrochemical performance of succinic acid as a carbon source coated modified lithium titanate anode material was the best.Adding an appropriate amount of succinic acid（w=0.03）could improve the conductivity of the material and improved its rate performance.The discharge specific capacities of LTO/C composited at 1 C and 10 C were 192.27 mAh/g and 143.33 mAh/g respectively,which was much higher than the discharge capacity of undoped samples.In order to improved the performance of the material under high current,the Li₄Ti₅O₁₂ anode material modified by Cr³⁺/succinic acid was prepared by sol-gel method.The experiment showed that the synergistically modified LTCrO/C anode material not only inhibited the growth of crystal grains,but also increased the specific surface area and shortens the path of Li⁺insertion and removal.It also played a key role in LTO rate-performance.The first discharge specific capacity of LTCrO/C anode materials at 30 C and 60 C ratios was 174.19 mAh/g and 140.12 mAh/g respectively.After 1000 cycles,the reversible capacity still reached 137.86 mAh/g and 99.81mAh/g.Compared with the the pure phase and single method modified Li₄Ti₅O₁₂material,the anode material prepared by and Cr³⁺/succinic acid synergistic modification method exhibited excellent rate performance.