Modification And Electrochemical Properties Of Lithium Titanate Anode Material For Lithium-ion Battery

With the rapid development of science,there is growing demand for electronic devices such as mobile phones and laptops,as well as electric cars and energy storage,powered mainly by lithium-ion batteries.Therefore,the development of lithium-ion batteries with high energy density,long life,high safety,low cost and environmental protection has become a common problem faced by scientists and technicians all over the world.The anode material in lithium-ion battery is considered as the core component to improve the overall performance of the battery,which plays a crucial role.Spinel Li₄Ti₅O₁₂（LTO）is a promising anode material for lithium-ion batteries because of its excellent cycling performance and long life.The material exhibits a very flat discharge and charge curve at a potential of 1.55 V（relative to Li⁺/Li）,which is above the potential range where most electrolytes or solvents are decomposed.The cubic symmetry of the spinel is almost not affected during Li⁺insertion and extraction,and the change of cell volume is less than 1%,which can be regarded as"zero strain"insertion material.However,despite the advantages mentioned above,the further application of LTO anode in lithium-ion batteries is severely limited due to its low lithium-ion diffusion coefficient and intrinsic electronic conductivity.Based on the shortcomings mentioned above,LTO electrode materials with high specific capacity and excellent electrochemical performance were prepared by doping,coating and recombination methods.The research contents mainly include:（1）LTO porous layered anode material modified by Cu²⁺doping was prepared by simple liquid-phase precipitation method,the optimal doping ratio was determined,and the mechanism of Cu²⁺doping modification was analyzed.Among them,0.1Cu²⁺doped LTO anode material showed the best electrochemical performance.At the rate of 1C,the initial charge-discharge ratio capacity reached 244.5/285.1 m Ahg^-1,and the capacity maintained at207.5 m Ahg^-1 after 200 cycles.After 500 cycles at 10C,the capacity of LTO-0.1Cu sample remained at 180.6 m Ahg^-1.In addition,the specific capacities at 1C,2C,5C,10C and 20C are 216.4,206.4,195.1,184.5 and 173.3 m Ahg^-1,respectively.（2）By adding self-made GO,LTO@r GO composite anode material coated with reduced GO（r GO）was prepared,and the lithium insertion behavior of LTO at low potential was analyzed to study the lithium insertion kinetics of LTO@r GO.The coated modified electrode material exhibits high specific capacity and electrochemical performance.The initial charge-discharge capacity is 361.1/445.1 m Ahg^-1 and the initial Coulomb efficiency is 81.1%at 0.2Ag^-1 current density.After 1000 cycles at 1 Ag^-1,the specific capacity is 223.0 m Ahg^-1,and the capacity retention rate is 94.8%.In addition,the specific capacities of LTO@r GO composite at 0.2,0.5,1.0,2.0,5.0 and back to 0.2 Ag^-1 are 376.1,350.1,327.2,297.7,259.9and 369.5 m Ahg^-1,respectively.（3）In this chapter,the composite modification of LTO was firstly carried out by adding Sn O₂ nanoparticles.The results showed that the cycling performance,rate performance and first charge and discharge efficiency were poor by electrochemical characterization.Therefore,in order to further improve the electrochemical properties of the materials,LTO-Sn O₂-r GO ternary composites were prepared.The results show that the cyclic stability and rate performance of the material can be effectively improved by adding r GO coating.The initial charge-discharge capacity at 0.2 Ag^-1 is 548.0/780.1 m Ahg^-1,and the initial Coulomb efficiency is 70.2%.After 200 cycles,the capacity of the electrode remains at 527.1 m Ahg^-1.After 500 cycles at 1 Ag^-1,the specific capacity is 229.1 m Ahg^-1 and the capacity retention rate is 67.8%.At 0.2,0.5,1.0,2.0 and 5.0 Ag^-1 and the current density back to 0.2 Ag^-1,the specific capacities of LTO-Sn O₂-r GO ternary composite are 556.0,490.4,423.5,352.4,301.8 and 535.7 m Ahg^-1,respectively...