Preparation And Modification Of Titanium-bused Oxide Anode Materials

At present,the rapid development of lithium-ion batteries has put forward higher requirements for electrode materials:high energy density,good safety performance,long cycle life and low cost.For anode materials,the development of new anode materials with high capacity,small volume deformation,good rate performance,and long cycle life is the current research hotspot.In this thesis,the"zero strain"material Li₄Ti₅O₁₂ was first modified by Mo⁶⁺doping and carbon coating,in order to the rate capability and cycling stability while expanding the charge and discharge voltage range to 0.1～3.0 V.The research on preparation and carbon-coating of Ti₂Nb₁₀O₂₉ was also investigated to optimize a simple preparation process for preparation of nano-Ti₂Nb₁₀O₂₉/C composite materials with excellent properties.The main research results are as follows:The studies on preparation of Li₄Ti_5-xMo_xO₁₂ materials show that as-prepared materials by the two-step process of“700℃low-temperature treatment+900℃high-temperature calcination”has a smaller grain size and lower charge transfer resistance,and its overall charge and discharge performance is better than that produced by one-step process of“900℃high-temperature calcination”.When the Mo doping amount x is 0.025,as-prepared material shows improved crystallinity,reduced charge transfer resistance,increased Li⁺diffusion rate,and thus improved charge-discharge performance 5%excess of lithium can compensate for the loss of lithium volatilization in the high-temperature synthesis,while the crystal structure of the obtained material is more perfect.Based on the above research results,the preparation conditions of Li₄Mo_xTi_5-xO₁₂materials are optimized as follows:lithium excess 5%,Mo doping amount x is 0.025,calcination at 700℃for 4 h followed by 900℃for12 h.The material prepared under this optimized condition exhibits perfect crystal structure,small charge transfer resistance,high Li⁺diffusion coefficient,and good charge-discharge performance.In the voltage range of 0.1～3.0 V,its reversible capacity at 0.1 C rate is as high as 260.4 m Ah?g^-1,the capacity at 5 C rate reaches 210.6 m Ah?g^-1,and the capacity after 50 cycles at 0.5 C rate remains 99.8%,which indicates that Mo⁶⁺doping can effectively improve the electrochemical performance of Li₄Ti₅O₁₂ materials.The studies on the carbon-coating of Li₄Mo_0.025Ti_4.975O₁₂ material show that carbon-coated material can be prepared by coating Ti O₂ raw material firstly with glucose,and then mixing with other raw materials followed by annealing at high temperature in the air.The coated carbon in the raw material acts as a space-limiting role,reducing the material particle size.The coated material with a glucose content of 5 wt%as carbon source has a small particle size,a high degree of crystallization,a significantly reduced charge transfer resistance,and good charge-discharge performance.In the voltage range of 0.1～3.0 V,its reversible capacity at 0.1 C rate is as high as 280.6 m Ah?g^-1,the capacity at 5 C rate reaches 242.6 m Ah?g^-1,and the capacity after 50 cycles at 0.5C still remains 272.5 m Ah?g^-1,no capacity loss occurs,showing very good structural stability.The studies on preparation and carbon-coating of Ti₂Nb₁₀O₂₉ reveal that by optimizing the calcination temperature,the nano-Ti₂Nb₁₀O₂₉material with perfect grain growth,particle size of 300 nm～500 nm and excellent electrochemical performance can be prepared when the calcination temperature is 1000℃.In the voltage range of 1.0 V～2.5 V,its reversible capacity at 0.1 C rate is as high as 310.2 m Ah?g^-1,the capacity at 5 C rate can reach 260.6 m Ah?g^-1,and the capacity retention after 50 cycles at 0.5 C rate remains 99.8%.Coating the material with glucose on its surface can improve conductivity,reduce charge transfer resistance,and further improve charge and discharge performance.When the amount of glucose is 5 wt%,the carbon-coated material has excellent electrochemical performance.Its reversible capacity at 0.1 C rate is as high as 347.2 m Ah?g^-1,the capacity at 5 C rate can reach 283.5 m Ah?g^-1,and the capacity after 50 cycles at 0.5 C still remains 326.6 m Ah?g^-1 with a capacity retention of 98.5%.