Li2MnSiO4正极材料充放电极化机理与微结构调控研究

Li2MnSiO4 has good thermal stability due to the stability of the Si-O key. As cathode material for lithium-ion batteries, it has high safety, low price, environmental protection, high specific capacity advantages. In recent years, it is becoming a hot topic, and is believed to represent the next generation of safe cathode material. The main obstacles of lithium manganese silicate as cathode material application were the low electronic conductivity, the structure may be not stable during cycle process and serious polarization phenomenon during charge and discharge process. Related research has been reported for the former two questions. This project will focus on the mechanism of polarization phenomenon of lithium manganese silicate and improving method, a series of studies on the link between polarization of lithium manganese silicate during charge and discharge process and microstructure parameter, ionic interactions, poly anionic clusters of association will be done. Accurately analysize the crystal structure of lithium manganese silicate material, diffusion rate of lithium ion in silicate materials by electrochemical method in situ measurement and calculate of diffusion free energy, explore the link between the microstructure and the polarization; control the microstructure of lithium manganese silicate to improve the polarization: change the lattice parameters and anionic polar by doping, change the lithium ion diffusion behavior, improve the degree of polarization of lithium manganese silicate materials in the process of charge and discharge destination and promote the application of lithium manganese silicate materials.

硅酸锰锂因其稳定的Si-O键而具有良好的热稳定性。在作为锂离子电池正极材料时，具有安全性高、价格低廉、绿色环保、比容量高等优点，近年来迅速成为研究热点。目前制约硅酸锰锂正极材料应用的障碍主要是电子电导率低、充放电过程中可能存在结构不稳定以及充放电过程中的严重极化现象。本项目将重点研究硅酸锰锂极化现象产生的机理及改善方法。分析认为，硅酸锰锂的极化与离子扩散行为有重要关联。将系统研究硅酸锰锂微结构参数、离子间作用力、聚阴离子团等因素与离子扩散行为、极化之间的关联。对硅酸锰锂材料的晶体结构进行精细分析，利用电化学方法原位精确测试锂离子在硅酸锰锂材料中的扩散速率并计算扩散自由能，探索微结构对离子扩散、极化程度的影响；探索对硅酸锰锂进行微结构调控来改善极化的方法：通过元素掺杂改变其晶格参数和阴离子极性，改变锂离子扩散行为，达到降低硅酸锰锂材料充放电过程中极化程度的目的。促进硅酸锰锂材料的应用。

作为锂离子电池正极材料，硅酸锰锂因其稳定的Si-O键而具有良好的热稳定性，同时还具有安全性高、价格低廉、绿色环保、比容量高等优点。但电子电导率低、充放电过程中可能存在结构不稳定以及严重极化现象阻碍了它的应用。研究发现：通过离子掺杂和导电物质复合可稳定其晶体结构、改善离子扩散环境和提升电导率、降低极化，有效提高其电化学性能。项目主要研究工作和结果包括：.1、通过溶胶凝胶法制备了Mo、V、Ni掺杂的Li2MnSiO4材料。分析结果表明，Mo、V、Ni元素均成功进入到Li2MnSiO4材料晶格中，三种元素掺杂的最佳比例均为6%。在0.05C下，纯相Li2MnSiO4材料放电比容量为158mAh/g, Li2Mo0.06Mn0.94SiO4，Li2V0.06Mn0.94SiO4和Li2V0.06Ni0.94SiO4放电比容量分别达到207.3mAh/g，259.1mAh/g和222.9mAh/g。循环伏安结果表明：Mo、V、Ni掺杂后的Li2MnSiO4材料极化现象较纯相材料低。从交流阻抗结果可以得到：纯相Li2MnSiO4材料扩散系数为1.64×10-15cm2s-1，Li2Mo0.06Mn0.94SiO4，Li2V0.06Mn0.94SiO4和Li2V0.06Ni0.94SiO4材料离子扩散系数为4.65×10-14cm2s-1，2.97×10-13cm2s-1和4.84×10-15cm2s-1。.2、成功制备出正交晶系P、B掺杂硅酸锰锂电极材料。结果表明，P、B元素掺杂的硅酸锰锂材料晶型结构没有改变。但掺杂后样品颗粒更小、更均匀，且团聚现象减小。P、B元素掺杂的硅酸锰锂材料的充放电比容量更高。从循环伏安结果可以得到：纯相硅酸锰锂样品（3.01×10−11cm2 s−1），P、B元素掺杂的硅酸锰锂材料锂离子扩散系数分别为3.88×10−11cm2s−1、1.14×10-14cm2s-1。.3、以抗坏血酸(VC)、葡萄糖和蔗糖为有机碳源制备了Li2MnSiO4/C材料，合成了ITO复合的Li2MnSiO4材料。分析表明，碳复合、ITO复合并未对Li2MnSiO4材料晶型结构产生影响，但复合后的Li2MnSiO4材料均表现出比纯相材料更高的放电比容量和更好的循环稳定性。