磷酸铁锂正极材料中Li+传输机理及材料改性研究

Lithium iron phosphate (LiFePO4), as one of the most promising lithium ion battery cathode materials with environmental benignity and high safety, has become a hotspot of research and development in the world. However, the inherert disadvantages of LiFePO4 cathode material, such as low Li+ diffusion coefficient and poor electronic conductivity, have been limiting its fast development and application. This project aims to solve above mentioned problems by theoretical and technical research. First,the transmission way and mechanism of Li+ in LiFePO4 cathode material are studied and revealed, then to achive high-rate charging and discharging of material by means of appropriate modification. In theory, based on the first principle and molecular dynamics, the theoretical calculation of crystal structure and electronic structure of LiFePO4 is carried out to obtain the minimum transmission energy channel and corresponding theoretical doped state of Li ion, to establish the Li+ transmission model and explore the mechanism of Li+ transmission and influencing factors. In technology, the key modification technologies (like Surface coating, doping, nano-porous particle and so on) are used to prepare the nano-porous LiFePO4 cathode material with high electrochemical properties and realize fast charge and discharge of lithium-ion battery. Also, the effects of particle size and its distribution of materials on its electrochemical properties are analyzed. The basic study of li+ transmission mechanism and modification of LiFePO4 cathode material has important theory significance and application value for improving Li+ diffusion coefficient and electronic conductivity, realizing fast charge and discharge, promoting industrialization process of lithium ion power battery and new energy vehicles, enhancing international competition ability and reducing environmental pollution.

针对当前锂离子电池LiFePO4正极材料所固有的锂离子扩散率慢和电子电导率低两大问题，本项目拟从理论和技术两个层面，研究和揭示LiFePO4正极材料中Li+的传输途径和机理，并通过材料改性以实现磷酸铁锂正极材料的高倍率充放电。理论方面，将基于第一性原理和分子动力学，通过对LiFePO4晶体结构和电子结构的理论计算，获得Li+传输最低能量通道及相应的理论掺杂状态，建立Li+传输模型，探索Li+传输机理及影响因素。技术方面，将通过表面包覆、体相掺杂以及纳米多孔化等手段，制备出电化学性能优异的纳米多孔LiFePO4正极材料，实现其高速充放电性能，并分析颗粒孔径及其分布对材料电化学性能的影响。本项目的研究将对提高LiFePO4正极材料的离子扩散速率和电导率，实现大电流充放电能力，促进锂离子动力电池及新能源汽车产业化进程，降低环境污染都具有重要的理论意义和应用价值。

能源材料是能源开发的基础，但也是能源利用中的瓶颈，所以解决能源问题的关键是能源材料的突破。随着新能源和新能源汽车的快速发展，磷酸铁锂正极材料因其优异的安全和环境友好等性能得到快速发展，但其在商用化过程中也存在两大瓶颈问题：锂离子扩散率慢和电子电导率低。因此本项目从理论和技术两个层面，研究和揭示LiFePO4正极材料中Li+的传输途径和机理，并通过材料改性以实现磷酸铁锂正极材料的高倍率充放电。. 在LiFePO4晶体结构和电子结构第一性原理理论计算的基础上，通过对LiFePO4晶体结构和电子结构的理论计算，获得了各种掺杂状态下LiFePO4晶粒多晶面能量变化情况及晶粒内最低能量通道，建立了掺杂状态下LiFePO4材料中Li+传输模型，掌握了LiFePO4材料Li+传输机理及调控因素。采用表面活性剂为模板剂，通过自组装模板法的方式，制备出了多孔纳米级LiFePO4正极材料，缩短了Li+离子扩散和电子传导距离，并进一步深入研究了模板法制备纳米多孔材料的形成机理；研究了纳米LiFePO4材料粒径大小和孔径分布对材料性能的影响。通过不同制备方法和工艺的优化、颗粒纳米化、离子体相掺杂及表面包覆等改性手段的研究，改善了LiFePO4正极材料离子扩散速率慢、电导率低和一致性不好等问题，提出了磷酸铁锂正极材料新的制备方法，制备出了比容量在160mAh/以上，倍率、循环和其它电化学性能优异，且一致性好的磷酸铁锂正极材料。. 本项目的研究将对提高LiFePO4正极材料的离子扩散速率和电导率，实现大电流充放电能力，促进锂离子动力电池及新能源汽车产业化进程，降低环境污染都具有重要的理论意义和应用价值。