LiFe1-xMnxPO4正极材料的磁性研究

The Study on Magnetic Properties of LiFe_(1-x)Mn_xPO_4 Cathode Materials

采用高温固相法制备纯相LiFePO_4、碳包覆的LiFe_(1-x)Mn_xPO_4(x=0.0,0.1,0.3,0.5)5个样品.利用XRD、SEM、VSM、XPS及CT-2001A对材料的结构、形貌、磁性和电化学性能等进行测量.实验结果表明,未掺杂与掺杂的样品均没有明显的杂相,且都是橄榄石结构;在100,200,300 K下,纯相LiFePO_4、碳包覆LiFe_(1-x)Mn_xPO_4(x=0.0,0.1,0.3,0.5)、商业化的正极材料碳包覆磷酸铁锂6个样品都具有弱铁磁性,且磁性强度不同.所有样品都存在三价铁离子,其对应于γ-Fe_2O_3;LiFePO_4的电化学特性与引入的γ-Fe_2O_3杂质有密切的关系;磁测量和XPS谱可以敏感地检测出γ-Fe_2O_3杂质的存在,它们提供了两种检测磷酸铁锂正极材料质量的有效技术.

Pure LiFePO4 and LiFe1-xMnxPO4/C （x = 0. 0,0.1 ,0.3,0. 5 ） were synthesized by a high energy ball milling-promoted solid-state reaction. Their structure, morphology, magnetic properties and rate performance of the materials were measured by XRD, SEM, VSM, XPS and CT-2001 A. The experimental results indicate that, the structures of all the undoped and doped samples are pure olivine. Pure LiFePO4, LiFe-1xMnxPO4/C （x = 0. 0,0. 1,0.3,0.5） and commercialized LiFePO4/C have all weak ferromagnetism at 100, 200, 300 K, but their magnetic moments are different. There exists Fe^3＋ in six samples, which corresponds to γ-Fe2O3. The electrochemical properties of the samples are associated with impure γ-Fe2O3 introduced during preparation. Magnetic and XPS measurements can sensitively probe γ-Fe2O3 impurity which can be used as the effective technique for monitoring quality of LiFePO4 cathode materials.