水热法合成LiFePO_4晶体结构的中子衍射研究

Neutron Diffraction Study on Crystal Structure of LiFePO_4 Synthesized by Hydrothermal Method

LiFePO_4具有热稳定性好、原料成本低、环境友好等优点,是重要的锂离子电池电极材料。本文利用水热法合成LiFePO_4,中子衍射和XRD测量结果表明,有5%左右的Fe占Li位。水热法合成的LiFePO_4一般需要热处理后,性能才有所改善。分别在450℃和700℃对样品进行退火,发现Fe占Li位的现象并无明显变化,可见水热样品性能较差并不能简单归因成Fe占Li位阻止了Li离子的传输通道。

LiFePO4 is considered as one of the most important cathod materials for lithium ion batteries, since its good thermal stability, low material cost and better enviromental compatibility. In this paper, LiFePO4 was synthesized by hydrothermal method, with about 5 % Fe atom at lithium site as determined by neutron and X-ray diffraction. In order to attain the capacity approaching the theoretical value, the high temperature annealing is often required. The samples were annealed at 450 ℃ and 700 ℃ respectively, but only little changes took place in the crystallographic structure from Rietveld refinement. This shows that iron disorder is just one of the reasons to lead low capacity for LiFePO4 synthesized by hydrothermal method.