锂离子电池TiNb2O7负极材料的嵌脱锂机理、结构设计与可控制备

With the wide application of lithium ion batteries in electric cars and other fields, it is important to find a high power and security anode material for lithium ion batteries. The rate performance of graphite materials used in commercial lithium ion batteries were poor, Li4Ti5O12 has been suggested as a promising alternative to graphite for its excellent high rate properties and cycle stability, however, its low specific capacity leads to low energy density of battery using this material, which limits its application in batteries. Novel anode material TiNb2O7 with a structure ReO3 has excellent rate performance and higher specific capacity, however, there are still many challenges to overcome, such as its poor electronic conductivity and poor cycle stability. Up to now, only few researches were done on , so further studies still need to be done. In this project, the mechanism of diffusion and storage of lithium ions will be revealed through theoretical calculation，combining with structure change of LixTiNb2O7 during the process of electrochemical Li insertion/extraction, the characterization of physical and chemical properties, as well as the study of electrochemical performance. In-situ infrared spectroscopy and mass spectrometry method will also be introduced into the characterization of interface reactions of TiNb2O7 materials, and ex-situ structure analysis method will be used to study the cycle stability. Modification methods for TiNb2O7 material will be proposed. Based on the mechanism of lithium ion transport and storage, we intend to regulate the morphology and structure of TiNb2O7 material in microscale, thereby improving the high-rate charge and discharge properties. This research will provide theoretical and experimental guidance for the study of TiNb2O7, and improve the electrochemical theory of TiNb2O7 materials.

锂离子电池在电动车等领域的应用需要高功率、高安全性的负极材料，然而，常用的石墨材料高功率性能较差，Li4Ti5O12高倍率充放电性能和循环稳定性优异，但是其较低的比容量限制了电池的能量密度，新型的ReO3结构TiNb2O7具有良好的倍率性能和更高的比容量，但是也存在导电性和稳定性差等缺点，目前对其研究还较少。本项目通过理论计算，结合电化学嵌脱锂过程中LixTiNb2O7的结构变化及物理化学性质表征、以及电化学性能研究，揭示锂离子在TiNb2O7中的存储与传输机理；同时引入原位红外光谱和质谱方法表征材料在循环过程中的界面反应，结合非现场的结构分析手段研究其循环稳定性，提出材料的改性方法；以锂离子传输与存储机理为基础，从微尺度调控TiNb2O7材料形貌与结构及改性，提升大倍率充放电性能。上述研究结果将为TiNb2O7负极材料的研发提供理论指导与实验帮助，并完善材料的电化学理论。

TiNb2O7（TNO）材料具备高容量、高安全性、高功率、长循环寿命等优点，有望替代Li4Ti5O12，用作动力锂离子电池的负极材料。.本项目研究了TNO材料的设计、制备和电化学性能。TNO材料属于单斜晶系，层状结构，有利于锂离子的嵌入和脱出。材料导电性差，禁带宽度为2.17 eV，纯相TNO充放电循环时，部分嵌入的锂离子无法脱出，形成死锂，循环性能很差，添加导电材料、改善材料导电性是提升材料性能的必要手段。.锂离子电池负极表面SEI膜限制了锂离子的倍率性能。TNO电极在1-3V之间循环，理论上不生成SEI膜。研究表明，电极表面在嵌锂时也有SEI膜生成，在脱锂时溶解，反复进行，导致电解液持续分解和气体产生。加入电解液添加剂VC可以帮助生成稳定SEI膜，有效抑制电解液的持续分解。.合成了棒状TiNb2O7材料、三维有序多孔（3DOM）Nb2O5和TiNb2O7材料、球形Ti2Nb10O29材料，实现了材料的可控制备。纳米棒直径约为100-300 nm，长度约为300-500 nm; 纳米棒是沿着（003）晶面生长的，典型层间距0.342 nm。3DOM的T-Nb2O5与TiNb2O7材料中，80-120nm大孔提供了电解液的存储位置，大孔之间的5-10nm的连接窗口提供电解液扩散通道，结构骨架上的介孔则为锂离子的存储提供了额外的位置。3DOM结构能够大大提升材料电化学倍率性能，赝电容在充放电容量中占据着绝对的比例。Ti2Nb10O29纳米球呈现了分级多孔结构，增加了电极/电解液的接触面积，缩短了锂离子的扩散距离，有效提升了电化学性能。.自掺杂不影响Ti1-xNb2+xO7材料的结构，Ti0.98Nb2.02O7带隙降为0.768 eV，电子导电性和锂离子扩散系数都最大,具有高可逆容量和倍率性能以及优秀的循环性能。通过DCDA包覆制备包碳掺氮TiNb2O7，0.1C首次充放电，可逆比容量达到268mAh g-1，首次库仑效率为93.5%，循环性能和倍率性能明显提升，1000次循环，可逆容量仅衰减7.7%。材料电阻明显小于空白TiNb2O7材料，锂离子扩散系数是原来的2.6倍。优化了TNO/C中的碳含量，碳包覆可以改善材料的电子导电性，表面碳层对于TNO颗粒表面也有保护作用，抑制界面副反应发生。