氟磷酸钒锂正极材料电子结构与离子扩散动力学的第一性原理研究

Firs-principle Calculations on the Electronic Structure and Li Ion Diffusion Kinetic Properties of the LiVPO_4F Cathode Material

采用基于密度泛函理论的第一性原理方法计算了LiVPO_4F正极材料的电子结构和锂离子扩散动力学性质.计算表明LiVPO_4F为低自旋的铁磁态,而当Li离子脱出后,材料转变为反铁磁态.锂离子脱出之后,V—O键的键长趋于均匀,材料晶格的杨-泰勒畸变效应减弱.LiVPO_4F/VPO_4F体系的理论平均插入-脱出电压为4.29 V,与已有实验结论吻合.分子动力学模拟计算表明LiVPO_4F中的锂离子具备良好的扩散能力,并且在电场作用下沿着c轴方向一维扩散.

The electronic structure and lithium diffusion kinetic properties of LiVPO4 F cathode material were studied by first-principle calculations based the density functional theory. LiVPO4 F showed a low spin ferromagnetic state while the de-lithiated VPO4 F showed an antiferromagnetic state. The lengthes of the V—O bonds become uniform after de-lithiation which depresses the Jahn-Teller distortion of the local structure of the material. The theoretical de-lithiation voltage of LiVPO4 F was calculated to be 4. 29 V which is consistent well with the experimental results. Molecular dynamics simulation showed that the Li ions diffuse along the c axis of the material lattice during electrochemical process.