Preparation Of Lithium Zinc Titanate And Its Lithium Storage In Wide Temperature Range

As the electrical vehicles are widely used,the lithium-ion batteries have become more and more important in the field of new energy resources due to their advantages,such as safety,large capacity and long cycle life.Li₂ZnTi₃O₈as an anode for lithium-ion batteries has obtained widespread attention for its good safety and cycling performance.In this paper,the preparation procedures were firstly optimized.Based on the optimized conditions,the effects of various factors on the electrochemical performance of composites for Li₂ZnTi₃O₈ and carbon were investigated.The details are as follows.（1）Li₂ZnTi₃O₈was synthesized by a high temperature solid-state reaction using Li₂CO₃,nano-Zn O and nano-Ti O₂as raw materials.The influences of the calcination temperature and time on the performance of Li₂ZnTi₃O₈were investigated,respectively.The results show that the sample sintered at 700℃for 3 h（LZTO-700-3）has the best electrochemical performance.After 300 and 500 cycles at 0.5 and 1.0 A/g,the capacity retention are 84.7%and 64.1%for Li₂ZnTi₃O₈,respectively.At 0.5,1.0,1.5,2.0,2.5 and 3.0 A/g,the discharge specific capacities are 185.6,179.8,176.5,171.7,163.1 and 156.6 m A·h/g for LZTO-700-3,respectively.（2）Li₂ZnTi₃O₈ anodes coated with N-doped carbon from dopamine hydrochloride were synthesized via a high temperature solid-state method.Part of Ti⁴⁺ions were reduced to Ti³⁺ions during synthesis,achieving the co-modification of coating and doping.The modification method can enhance the lithium diffusion coefficients and reduce the charge-transfer resistance.At 0.5,1.0,1.5,2.0,2.5 and 3.0 A/g,the discharge specific capacities are 244.7,229.4,218.0,207.5,196.8 and 183.9 m A·h/g for Li₂ZnTi₃O₈@C-N-2,respectively.In addition,the sample shows higher specific capacity than un-modified Li₂ZnTi₃O₈ anode material at the low temperature of 0℃.The initial specific capacity is 262.5 m A·h/g at 0.2 A/g,and 241.6 m A·h/g is still obtained at the 300th cycle.Even at 1.0 A/g,147.3m A·h/g is kept at the 300th cycle.（3）Li₂ZnTi₃O₈@C-N composites coated with N-doped carbon was synthesized by a high temperature solid-state route using glucose as a carbon source and dicyandiamide as a nitrogen source.By controlling the proportion of glucose to dicyandiamide,the effects of N doping amount on the properties of the Li₂ZnTi₃O₈@C-N materials were explored,achieving to improve the cycling performance and rate capacity at the same time.Among the composites,Li₂ZnTi₃O₈@C-N-5 shows the best cycling performance and rate capacity at room temperature.The discharge specific capacity was still163.2 m A·h/g after 500 cycles at 1.0 A/g.Compared with un-modified Li₂ZnTi₃O₈,the specific capacities of Li₂ZnTi₃O₈@C-N-5 can improve 39.7,33.3,27.2 and 11.7 m A·h/g at 1.5,2.0,2.5 and 3.0 A/g,respectively.In addition,the sample shows good electrochemical performance at high and low temperatures.At 55℃,the initial coulombic efficiency of Li₂ZnTi₃O₈@C-N-5 is higher than that of the un-modified Li₂ZnTi₃O₈ anode material at 1.0 A/g.After 150 cycles,61.3%is still maintained for the composite.Moreover,Li₂ZnTi₃O₈@C-N has good rate capability and cycling performance at 0℃.At 0.4,0.6,0.8 and 1.0 A/g,the discharge specific capacities are 200.1,185.7,175.5 and 168.9 for Li₂ZnTi₃O₈@C-N-5,respectively.The initial specific capacity is 196.6 m A·h/g at 0.5 A/g,and173.7 m A·h/g is still obtained at the 300th cycle.