镍镁掺杂LiFePO4的电子结构

采用基于密度泛函理论的第一性原理研究锂离子电池正极材料LiFePO4掺杂Ni和Mg的电子结构。结果表明:Ni氧化物的电子结构和能量性质受d轨道中电子影响,用于掺杂改性时,结构稳定,带隙降低使电子电导率增加,充放电速率提高;Mg掺杂改性时,当掺杂在Li位时,带隙和总能均降低,同时Li离子的扩散运动也提高,有利于改性,而在Fe位掺杂时,费米面附近Fe-d轨道中电子影响能带,使带隙增加,不利于电子电导,键的布居分析也表明Li—O共价性增强,不利于离子扩散,即不利于改性。因此,通过掺杂可对LiFePO4的微观结构产生影响,从而影响其电化学性能,但这种微观结构主要受d轨道中电子运动对费米面附近能带的影响,而与掺杂离子的化合价和半径无关。

Electronic structure of LiFePO4 doped with Ni and Mg

LiFePO4 doped with Ni and Mg was simulated by using the first-principles.Through the energy band,PDOS and population analysis,it shows that,when the transition metal element Ni is used as dopant,the structure is becomes stable and the band gap reduces when Ni is doped on either Li(M1) or Fe(M2) sites,which results in the increase of the electronic conductivity and the discharge-recharge rate,because the electronic structure and energy properties of the transition metal oxides are greatly affected by the electrons in orbital d.When non-transition metal element Mg is doped at Li-site,both the band gap and total energy decrease,and the lithium ion diffusivity improves.When Mg is doped at Fe-site,the band gap increases because of the influence of electronics in Fe-d orbitals near the Fermi level,which is not beneficial to the electronic conductivity.The covalent interaction between Li and O strengthens through the analysis of population,which is not benefit for the lithium ion diffusivity and modification.So,the electrochemical properties of LiFePO4 are influenced by the changes of microstructure which are affected by dopants.The electrons in orbital d mainly affect the electronic structure near the Fermi level,while has no relative with the chemical valence and atomic radius of dopant.