Tailoring the sodium doped LiMnPO4/C orthophosphate to nanoscale as a high-performance cathode for lithium ion battery

Abstract

Three-dimensional nanoscale LiMnPO4/C orthophosphate with sodium ion substitution in Li site has successfully synthesized by a facile hydrothermal method, using precipitated Li3−xNaxPO4 hollow microspheres as the sacrificial templates. Meanwhile, Li3PO4 impurity phase is generated. The chemical/physical properties are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), the charge-discharge method, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), and the effects of Li3PO4 on structure and electrochemcial performance have been investigated. In particular, the existence of Li3PO4 and proper sodium ions doping is beneficial to stabilize crystal structure and assemble into three-dimensional porous core-shell structure, aiming to provide abundant channels and active sites for accelerating lithium ion migration rate. Compared with other samples, the Li0.9Na0.1MnPO4/C composite demonstrates the excellent electrochemical performance, which delivers the first specific discharge capacity of 152 mAh/g at 0.05 C with little capacity fading after 200 cycles. The discharge capacity still maintains at 122.3 mAh/g, even at a rate of 10 C. Our experiments indicate that the synergetic effect of sodium doping and the formed three-dimensional porous core-shell structure provide high rate capability and cycle performance.