超临界水热制备LiFePO4及煅烧碳包覆改性研究

本文以FeSO_4、H_3PO_4和LiOH为原料,采用超临界水热过程制备了亚微米级LiFePO_4颗粒.在此基础上,为了提升制备的LiFePO_4正极材料的物理和电化学性能,对其进行了后续煅烧碳包覆改性研究.同时,通过XRD、SEM、充放电测试、CV和EIS测试手段,对LiFePO_4正极材料改性前后的结构、形貌和电化学性能进行了表征.结果表明:后续固相煅烧碳包覆改性能够显著改善LiFePO_4的结晶性能,减小颗粒粒径,降低电荷传递阻抗,以及大幅度地提升放电容量和循环性能;以PVP为模板剂、蔗糖为碳源,700℃煅烧1 h得到的LiFePO_4/C颗粒粒径小、分布均一,室温0.2 C倍率的首圈放电比容量为153.1 mAh/g,1 C倍率充放电时,放电比容量可保持在144.2 mAh/g,1 C循环50次,容量保持率达到97.1%.

Supercritical hydrothermal method preparation for LiFePO4 followed by calcination carbon-coating

Pure sub-micro LiFePO4 particles were prepared via supercritical hydrothermal process using FeSO4,H3PO4 and LiOH as raw materials,and as-prepared LiFePO4 was calcined and carbon-coated to further promote its physical and electrochemical properties.The structure,morphology and electrochemical performance of LiFePO4 were characterized by X-ray diffraction (XRD),scanning electron microscope (SEM),charge and discharge test,cyclic voltammetry (CV) and electrochemical impedance spectra (EIS).The results show that calcination and carbon-coating can effectively improve the crystallization property,decrease the particles size,charge the transfer resistance,and enhance the electrochemical performance of LiFePO4.The LiFePO4/C composites with small particle size and uniform structure were obtained with polyvinyl pyrrolidone (PVP) as template and sucrose as carbon source under the conditions of 1 h calcination at 700 ℃.The initial discharge capacity was 153.1 mAh/g and 144.2 mAh/g at 0.2 C and 1 C,respectively.After 50 cycles,97.1％ of the initial discharge capacity was retained at 1 C rate.