Na-Ti共掺LiFePO_(4)电子结构及弹性性质的第一性原理研究

First-Principles Study on Electronic Structure and Elastic Properties of Na-Ti Co-Doped LiFePO_(4)

本文基于密度泛函理论的第一性原理方法,构建了Na-Ti共掺LiFePO_(4)的模型,并利用CASTEP模块计算了共掺体系的电子结构和弹性性质。计算结果表明,由于引入了杂质原子,共掺体系的晶胞参数略微增加,带隙由0.695 eV降低至0.473 eV,电子跃迁所需能量减小。并且锂离子迁移势垒由0.34 eV降低至0.25 eV,使得共掺后的结构导电性增强。弹性性质计算结果表明,共掺后结构的体积模量、剪切模量以及杨氏模量均有不同程度的下降,而计算的泊松比显示材料掺杂前后均为脆性,但共掺杂后的材料塑性强于未掺杂的材料,并且共掺后晶体的各向异性减弱,提高了LiFePO_(4)的延展性。

In this paper,the model of Na-Ti co-doped LiFePO_(4) was constructed based on the first-principles method of density functional theory,the electronic structure and elastic properties of the co-doped system were calculated using the CASTEP module.The calculated results show that due to the introduction of impurity atoms,the cell parameters of the co-doped system increase slightly,the band gap decreases from 0.695 eV to 0.473 eV,and the energy required for electronic transition decreases.The Li ion migration barrier decreases from 0.34 eV to 0.25 eV,which enhances the conductivity of the co-doped structure.The calculation of elastic properties shows that the bulk modulus,shear modulus and Young’s modulus of the structure after co-doping decrease to varying degrees,while the calculated Poisson ratio shows that materials before and after doping are brittle.However,the plasticity of the co-doped material is stronger than that of the undoped material,and the anisotropy of the co-doped crystal weakens,which improves the ductility of LiFePO_(4).