Electrochemical studies of a high voltage Na4Co3(PO4)2P2O7–MWCNT composite through a selected stable electrolyte

摘要

Cathode materials that operate at high voltages are required to realize the commercialization of high-energy-density sodium-ion batteries. In this study, we prepared different composites of sodium cobalt mixed-phosphate with multiwalled carbon nanotubes (Na _(4) Co _(3) (PO _(4) ) _(2) P _(2) O _(7) –MWCNTs) by the sol–gel synthesis technique. The crystal structure and microstructure were characterized by using PXRD, TGA, Raman spectroscopy, SEM and TEM. The electrochemical properties of the Na _(4) Co _(3) (PO _(4) ) _(2) P _(2) O _(7) –20 wt% MWCNT composite were explored using two different electrolytes. The composite electrode exhibited excellent cyclability and rate capabilities with the electrolyte composed of 1 M sodium hexafluorophosphate in ethylene carbonate:dimethyl carbonate (EC:DMC). The composite electrode delivered stable discharge capacities of 80 mA h g ~(?1) and 78 mA h g ~(?1) at room and elevated (55 °C) temperatures, respectively. The average discharge voltage was around 4.45 V versus Na ~(+) /Na, which corresponded to the Co ~(2+/3+) redox couple. The feasibility of the Na _(4) Co _(3) (PO _(4) ) _(2) P _(2) O _(7) cathode for sodium-ion batteries has been confirmed in real time using a full cell configuration vs. NaTi _(2) (PO _(4) ) _(3) –20 wt% MWCNT, and it delivers an initial discharge capacity of 78 mA h g ~(?1) at 0.2C rate.