Effect of Na-Si co-doping on the performance of LiFePO4

Lithium iron phosphate (LiFePO4) with low electronic and ionic conductivities limits its further development, which can be improved by element doping. Herein, the sample of Na-Si co-doped LiFePO4 are successfully fabricated by the carbothermal reduction method. The species of Li0.97Na0.03FeP0.97Si0.03O4 (LNFS) with controllable particle size is characterized by XRD, SEM and XPS tests. Wherein, the decrease of Li-O bond energy in the lattice leads to the increase of Li+ mobility. Meanwhile, the concentration of oxygen vacancy and the conductivities of the material are enhanced after Na-Si doping. Based on the first-principles calculation, it is confirmed that the electronic conductivity and lithium-ion mobility of LNFS are improved at the aspects of crystal structure, energy band and DOS. Consequently, LNFS can achieve the specific capacity of 92.1 mAh center dot g- 1 at 5 C and excellent rate performance.