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铌在铁位掺杂对LiFePO4电子结构和性能的影响

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Abstract:

基于第一原理方法,由广义梯度近似的密度泛函理论计算了Nb在Fe位掺杂的LiFePO4的电子结构,分析了掺杂量对晶胞参数和Fermi能级的影响。Nb掺杂后,晶胞参数a、b、c均呈现增大的趋势,在铌的掺量为0.10时体积从0.2808nm3增至0.2952nm3。体系几何结构发生的变化表明Nb掺杂有利于提高LiFePO4的导电性能。能带结构图中最低空轨道(lowestunoccupiedmolecularorbital,LUMO)与最高占有轨道(highestoccupiedmolecularorbital,HOMO)之间的能隙变窄,从LiFePO4的0.75eV降至LiFe0.90Nb0.10PO4的0.62eV。Nb掺杂对LUMO与HOMO之间的能隙有较大的影响,掺杂体系由Nb的4d5s轨道和Fe的3d4s轨道共同提供电子,掺杂使导电性增强。系统的态密度图中Fermi能级移入导带,Fermi能级附近的价带和导带的峰强度增强。Fermi能随着离子的掺杂量增大而加大,掺杂量的进一步增加,反而下降,LiFe0.95Nb0.05PO4结构具有最大的Fermi能3.871eV。掺杂能明显影响LiFePO4的电子结构,并提高LiFePO4的电化学性能,理论分析与实验结果相符。

References

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