基于可控掺杂和精确包覆改性的Na2Li2Ti6O14材料的晶面调控及其储锂过程的电化学原位研究

Na2Li2Ti6O14 with high stability and high safety becomes negative electrode material with great application potential. However, the low electronic conductivity and poor rate performance of this material limit the sufficient application in the field of lithium-ion battery. Starting from the material design link of the project, theoretical models applied to study the transport properties of the carriers and the surface effects of Na2Li2Ti6O14 material are established by using the first-principle calculation, and the effects of surface morphology and facet characteristic on the electrochemical performance of the material are investigated. The doping calculation model and Na2Li2Ti6O14/coating layer material interface theory model are constructed. The influence mechanism of different doping ions and coating layers on the structural stability, conductivity, carrier transport property and electrochemical property of Na2Li2Ti6O14 materials are ascertained, and then a reliable theoretical basis for the design and functional regulation of this material is provided. According to calculation result, Na2Li2Ti6O14 materials with different morphologies are controllably synthesized. By using in situ electrochemical technology, the structure evolution of the materials during the extraction-insertion of lithium ions is revealed, and the electrode process kinetics between the materials and electrolyte at the surface / interface is identified. The lithium storage mechanism is resolved, and then the rate performance of the materials is improved. The rational design and functional synthesis of high-performance Na2Li2Ti6O14 based materials are achieved under the guidance of theory system.

低廉的价格和高安全性使Na2Li2Ti6O14成为极有应用潜力的负极材料，但其电导率低、倍率性能差，限制了它在锂离子电池领域的应用。本项目拟从材料设计环节出发，利用第一性原理计算建立适于研究Na2Li2Ti6O14的载流子输运性能和表面效应的理论模型，研究表面形貌和晶面特性对材料的电化学性能的影响。构建材料的掺杂计算模型及Na2Li2Ti6O14/包覆层材料的界面理论模型，揭示不同掺杂离子及包覆层对Na2Li2Ti6O14的结构稳定性、电导率、载流子输运性质及电化学性能的影响机制，为材料的设计及功能调控提供可靠的理论依据，并根据计算结果可控合成不同形貌的Na2Li2Ti6O14材料。利用电化学原位技术揭示材料嵌脱锂过程中的结构演化，明晰材料与电解液表/界面处的电极过程动力学，揭示其储锂机制，提高材料的倍率性能，实现理论指导下的高性能Na2Li2Ti6O14基材料的理性设计与功能化制备。

低廉的价格和高安全性使Na2Li2Ti6O14成为极有应用潜力的负极材料，但其电导率低、倍率性能差，限制了它在锂离子电池领域的应用。采用第一性原理计算明确了Na2Li2Ti6O14结构稳定性，明晰此类材料在嵌脱锂过程中的结构演变过程。先后合成了Na2Li2Ti6O14纳米片、CeO2包覆的Na2Li2Ti6O14、Na2Li2Ti6O14-Li4Ti5O12微球、Na2Li2Ti6O14@C(生物质碳)微球、Na2Li2Ti6O14@PEDOT微球、Na2Li2Ti6O14@g-C3N4材料、 Na2Li2Ti6O14@C-N纳米纤维、Na2Li2Ti6O14@Li0.33La0.56TiO3复合物、MgF2包覆的Na2Li2Ti6O14纳米材料、Na2Li2Ti6O14@Er2O3纳米棒、金属离子掺杂的Na2Li2Ti6O14等。采用嵌脱锂过程与结构测试平台并联的技术实现对Na2Li2Ti6O14结构变化的原位观察，分析并鉴定不同嵌脱锂阶段样品的物相，构建Na2Li2Ti6O14的物相转变过程与嵌脱锂含量的关系图，判断不同充放电电位下锂的嵌入位置、顺序、输运通道及脱出步骤，再结合第一性原理对锂离子输运通道的理论计算，确定影响锂离子在Na2Li2Ti6O14结构中存储和输运的主要热力学因素，为定量定向改进Na2Li2Ti6O14的性能及其控制合成奠定理论基础。利用XRD、XPS、TEM、SEM、FT-IR等手段表征Na2Li2Ti6O14基材料在嵌/脱锂前后及反应过程中的组成､结构与形貌变化｡利用EIS、CV研究掺杂和表面包覆对锂离子嵌脱动力学的影响；利用电化学in-situ XRD技术研究Na2Li2Ti6O14基材料本征的反应动力学及材料脱嵌锂过程中的结构演化，明晰此类材料的嵌脱锂反应机理。第一性原理计算结果表明当Na2Li2Ti6O14作为锂离子电池负极材料时，其晶格可以容纳约6个锂离子。在放电过程中，当一个锂嵌入晶格时，能量上最有利的位置是8e位。在锂化和去锂化过程中，所有晶格参数的演变反映了准镜像对称性，表明Na2Li2Ti6O14 在充放电过程中的结构转变是准可逆的。稳定的界面可以提供更多位置来储存电解液，然后进行嵌锂/脱出反应，不仅缓解了循环过程中的电化学极化，而且提高了锂离子和电子的转移能力。