Preparation And Performance Of Lithium Titanate Anode Materials For Lithium-Ion Batteries

The spinel-type lithium-ion battery anode material,lithium titanate(Li₄Ti₅O₁₂),with its"zero strain"structural characteristics of almost constant volume during charging/discharging,can better meet the requirements of modern electronic products for high performance and high capacity batteries.However,because Li₄Ti₅O₁₂ is an insulating material with low electronic conductivity,it observes serious polarization at high rate condition which would result in rapid fading.Therefore it needs to be improved before it is applied to commercial lithium-ion batteries.In this thesis,a series of studies on the preparation of Li₄Ti₅O₁₂ and its electrochemical performance modification have been carried out.The main contents are as follows:The Li₄Ti₅O₁₂ anode material is successfully prepared through sol-gel method using butyl titanate and lithium carbonate as the raw materials.On which basis P⁵⁺-doped Li₄Ti_5-xP_xO₁₂ materials are then prepared.Then the batteries are assembled with Li₄Ti_5-xP_xO₁₂ materials and subjected to constant current charge and discharge test,Cyclic Voltammetry test and AC impedance test.It was found that the Li₄Ti₅O₁₂ anode material synthesized at 850°C shows a higher discharge specific capacity.The P⁵⁺-doped LTO-P2(Li₄Ti_4.8P_0.2O₁₂)sample shows the highest specific discharge capacity and the best cycle stability.At the rate of 1 C,the initial specific discharge capacity reached 132.1 m Ah/g and still maintained at 128.3 m Ah/g after 500 cycles.The Li₄Ti₅O₁₂ anode material is successfully prepared through hydrogen peroxide assisted hydrothermal method using butyl titanate and lithium hydroxide monohydrate as the raw materials.The battery assembled with this Li₄Ti₅O₁₂ anode material has an initial specific discharge capacity of 174.6 m Ah/g at a rate of 1 C,which is almost close to its theoretical specific capacity（175 m Ah/g）.Then,Mg²⁺,Ca²⁺,and Al³⁺are added as doping ions to modify Li₄Ti₅O₁₂ during the preparation process,after which Li_4-xMg_xTi₅O₁₂,Li_4-yCa_yTi₅O₁₂ and Li₄Ti_5-zAl_zO₁₂ materials are assembled into batteries respectively for constant current charge-discharge test,Cyclic Voltammetrytest and AC impedance test.The results show that the electrochemical performance of the three ion-doped Li₄Ti₅O₁₂ materials have had a certain improvement in electrochemical performance.Among them,Al³⁺doping has the best effects on lithium titanate performance.And the LTO-AL10(Li₄Ti_4.5Al_0.5O₁₂)sample with Al³⁺ion doping amount of 10%has the highest initial discharge capacity（217.9 m Ah/g）and lithium ion diffusion coefficient(3.72*10^-13 cm²·S).Li₄Ti₅O₁₂/Si₃N₄ composite anode material has been prepared with Si₃N₄ coating modified Li₄Ti₅O₁₂ for the first time.The effect of different Si₃N₄ content on the performance of Li₄Ti₅O₁₂ anode materials has been studied.The results show that the initial discharge capacity of the LTO-SN2(Li₄Ti₅O₁₂/0.02Si₃N₄)sample with a coating amount of 2%has significantly increased（up to 198.4 m Ah/g）at a rate of 1 C,and the capacity retention rate has reached 89.41%after 200 cycles.