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

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.