Study On Preparation And Electrochemical Performance Of Modified Li₄Ti₅O₁₂

Lithium ion batteries?LIBs?is widely applied in portable electronics and electromobile due to it possesses the advantages of higher energy density,enabling fast charge and discharge process and excellent cycle performance.While the anode material of LIBs takes a crucial role in electrochemical reaction.Among all of the anode material of LIBs,Li₄Ti₅O₁₂?LTO?possesses some promising advantages,such as the preparation cost is relatively low,the charge/discharge voltages of LTO is around 1.55 V,which avoids the formation of lithium dendrite,hence the safety performance of LIBs can be improved.The most outstanding aspect of LTO is the negligible volume change during Li⁺ions insertion/desertion processes,which is called"zero strain"material,hence compared with other anode material of LIBs,it exhibits excellent cycling performance.Nevertheless,its intrinsic low theoretical capacity(175 mA h g^-1),electronic conductivity(10^-13 S cm^-1),Li⁺ions diffusion coefficient(10^-9-10^-13 cm² s^-1)and the polarization phenomenon is serious at high current density,which restrict its large-scale practical application seriously.In this paper,we directed at the disadvantages of LTO,such as very low electronic conductivity and Li⁺ions diffusion coefficient,two-dimensional Al³⁺-modified Li₄Ti₅O₁₂,two-dimensional Li₄Ti₅O₁₂ nanosheets and hierarchical mesoporous structured Nd³⁺-modified Li₄Ti₅O₁₂ have been synthesized via hydrothermal method or co-precipitation method to improve the disadvantages of Li₄Ti₅O₁₂.The morphology and electrochemical performance of LTO were controlled by adding various amount of doping ions.In the meanwhile,a series of material characterizations combined with electrochemical tests were conducted to study the electrochemical properties of the samples.The details are as follows:1.Two-dimensional Li_4-x/3Ti_5-2x/3Al_xO₁₂?x=0,0.02,0.04,0.06,0.08?nanosheets were prepared via hydrothermal method.The experimental results demonstrate that Al³⁺has doped into the lattice of Li₄Ti₅O₁₂.The effects of different addition amounts of Al?NO₃?₃·9H₂O on the electrochemical properties of the material were discussed in this work.According to the electrochemical characterizations,Li_3.98Ti_4.96Al_0.06O₁₂ shows best electrochemical performance.The initial discharge capacity can reach 163.7 mA h g^-1 of this sample at 1 C,while the initial discharge capacity is only 143.6 mA h g^-1 of the pure Li₄Ti₅O₁₂ at the same current density.The material also present excellent rate performance.The discharge capacity of this sample can achieve 154.7,150.6,147.6 and 145.1 mA h g^-1 at 5 C,10 C,20 C and 30C,while the discharge capacity of pure Li₄Ti₅O₁₂ is only 138.7,130.6,122.7 and118.9 mA h g^-1 at the same current density,respectively.The initial discharge capacity of Li_3.98Ti_4.96Al_0.06O₁₂ can reach 153 mA h g^-1 at 10 C,after 1000 cycles,the discharge capacity of the sample maintains at 131.6 mA h g^-1,the retention of capacity is 86%.While the initial discharge capacity of the pure Li₄Ti₅O₁₂ is only 126.6 mA h g^-1,after1000 cycles,the discharge capacity is only 98.8 mA h g^-1,the retention of capacity is78%.Even when cycled at 40 C,the initial discharge capacity of Li_3.98Ti_4.96Al_0.06O₁₂can achieve 131.8 mA h g^-1,which is higher than the pure Li₄Ti₅O₁₂ significantly(103.3 mA h g^-1).2.Two-dimensional Li₄Ti₅O₁₂2 nanosheets were synthesized via co-precipitation method.The morphology of Li₄Ti₅O₁₂ was controlled by adjusting the addictive amount of anhydrous ethanol.The effects of different addictive amounts of anhydrous ethanol on the electrochemical properties of the synthesized samples were also discussed.The experimental results illustrate that when the volume of the addictive anhydrous ethanol is 15 mL,the prepared sample presents a nanosheets morphology and best electrochemical performance.According to the electrochemical characterizations,the discharge capacity of the two-dimensioanl Li₄Ti₅O₁₂2 nanosheets achieve 147.9,141.2,135.9 and 132.5 mA h g^-1 at 5 C,10 C,20 C and 30 C,while the discharge capacity of the non-two-dimensioanl Li₄Ti₅O₁₂ is only 129,123.6,115.9and 109.1 mA h g^-1,respectively.The initial discharge capacity of the two-dimensioanl Li₄Ti₅O₁₂2 nanosheets can reach 148.2 mA h g^-1 when cycled at 5 C,after 1000 cycles,the discharge capacity of the material retains at 132.2 mA h g^-1,the retention of capacity is 89.2%,while the initial discharge capacity of the non-two-dimensioanl Li₄Ti₅O₁₂2 nanosheets is only 134 mA h g^-1,after 1000cycles,the discharge capacity is only 75.5 mA h g^-1,the retention of capacity is only 56.3%.3.Hierarchical mesoporous structured Li_4-xTi₅Nd_x/3O₁₂?x=0,0.06,0.12,0.18,0.24,0.3?materials have been synthesized via co-precipitation method.The effects of different addition amounts of Nd?NO₃?₃·5H₂O on the electrochemical performance of the samples were discussed in this work.The experimental data demonstrates that partial Nd³⁺has doped into the lattice of Li₄Ti₅O₁₂.Besides,according to the electrochemical teste,Li_3.88Ti₅Nd_0.04O₁₂ shows the most promising electrochemical performance.The initial discharge capacity of the sample can achieve 157.9 mA h g^-1at 1 C,while the initial discharge capacity of the pure Li₄Ti₅O₁₂ is only 143.6 mA h g^-1.In addition,the discharge capacity of Li_3.88Ti₅Nd_0.04O₁₂ is 155,146.7,141.5 and127.8 mA h g^-1 at 2 C,5 C,10 C and 20 C,while the discharge capacity of pure Li₄Ti₅O₁₂ is only 138.6,131.1,123.2 and 117.1 mA h g^-1 at the same current densities,respectively.The initial discharge capacity of Li_3.88Ti₅Nd_0.04O₁₂ is 157.4 mA h g^-1when cycled at 5 C,after 500 cycles,the discharge capacity of the material can maintain at 138.3 mA h g^-1,the retention of capacity is 87.7%,the discharge capacity and retention of capacity are higher than the pure Li₄Ti₅O₁₂ obviously(the initial discharge capacity of pure Li₄Ti₅O₁₂ is 140.4 mA h g^-1,after 500 cycles,the discharge capacity is 102.3 mA h g^-1,the retention of capacity is 72.7%)..