锂离子电池正极材料磷酸铁锂研究进展

电极材料是推进电池技术发展及应用的关键。作为锂离子电池正极材料的LiFePO4表现出优异的电池性能(大容量、优异循环特性),但也有本征低电导率的缺点。具有橄榄石结构的LiFePO4在电池充放电过程发生FePO4与LiFePO4之间的相变,已有实验证明充放电过程中出现固溶体LixFePO4。掺杂是提高材料电导率的常用手段,但LiFePO4的掺杂却一直饱受争议;缺陷化学的研究初步认定通过适当点缺陷的电荷补偿,晶体内引入掺杂元素是可以实现的,并且提出几种缺陷补偿机制。导电相复合可降低电极颗粒间的接触电阻,特别是LiFePO4的碳包覆有效地改善其电化学性能,促进其工业化推广;碳包覆的有效性取决于碳的sp2杂化键的比例及碳含量。由于电极材料形貌影响电池的充放电动力学过程,LiFePO4的颗粒尺寸、形状、表面粗糙度等的控制都成为提高电池性能的重要手段;LiFePO4的薄膜制备及三维构架技术则进一步推动微型电池的应用发展。

Development of LiFePO4 as the Cathode Materials

The cathode material is critical for advancement in battery technology.LiFePO4 with the typify olivine structure shows excellent electrochemical performance besides low electric conductivity.The existence of a temperature-driven solid solution LixFePO4 is confirmed by temperature-controlled XRD pattern results and neutron diffraction data.The debating about doping accumulates the defect chemical studies for LiFePO4,several defect compensation mechanisms have been founded in support of the aliovalent doping.The conductive phase composite enhances the electrical conductivity of LiFePO4,especially carbon surface coating of LiFePO4 particle clear away obstacles of its industrialized application.The morphology of LiFePO4 also affects the electrochemical properties due to adjusting charge/discharge kinetic process.The control of particle size,shape and porosity will adjust the electrode performance,the thin film technique and three dimensional architectures will drive advancement of small cells.