First Principles Studies on the Electronics Structures of (Li0.75Na0.25)(Fe0.75Mn0.25)PO4 Cathode Materials

摘要:

采用第一性原理平面波赝势方法计算研究了在LiFePO4的Li位、Fe位和Fe/Li位共掺杂金属原子对材料的电性能和局部结构稳定性的影响关系。结果表明：Li位掺杂(Li0.75Na0.25)FePO4 比Fe位掺杂Li(Fe0.75Mn0.25)PO4表现出更好的电子电导性，而局部结构稳定性刚好相反。但是Fe/Li位共掺杂对电子电导性和局部结构稳定性具有双重优化作用，这可能是由Na-2p电子与Li-s电子相互作用引起的。同时，根据计算差分电荷密度关系可以发现共掺杂后会有大量其他原子电荷向Li原子周围偏移，从而改善材料的电子电导性能

Abstract:

The effect of the Li-site, Fe-site and co-doping in LiFePO4 on the electronic properties and local structural stability has been calculated by first principle plane-wave pseudopotential method. Our calculation shows that Li-site doped (Li0.75Na0.25)FePO4 exhibit better electronic conductivity than Fe-site doped Li(Fe0.75Mn0.25)PO4 cathode material, the local structural stability is reverse. But the Li-site and Fe-site co-doped (Li0.75Na0.25)(Fe0.75Mn0.25)PO4 possesses double optimization, which is probably ascribed to the interaction between Na-2p electron states and Li-s electron states. Meanwhile, large charges are transferred from the other atoms to lithium atoms in the co-doping LiFePO4 materials based on difference of charge density, this will result in the improvement of intrinsic electronic conductivity