Carbon-coated rhombohedral Li3V2(PO4)3 as both cathode and anode materials for lithium-ion batteries: electrochemical performance and lithium storage mechanism

Abstract

We report the electrochemical performance and storage mechanism of a symmetrical lithium-ion battery made of carbon-coated rhombohedral Li₃V₂(PO₄)₃ (r-LVP/C) as both the cathode and anode materials. The electrochemical evaluation of r-LVP/C in lithium half-cells demonstrates reversible lithium extraction/insertion reactions at 3.75 V and average 1.75 V vs. Li⁺/Li. Different storage mechanisms for the two reactions have been identified through ex situ and in situ X-ray diffraction measurements. A two-phase reaction takes place when two Li are extracted from r-LVP/C, while a solid-solution reaction occurs when two Li are inserted into r-LVP/C. In comparison, only one Na ion can be inserted into its sodium counterpart, Na₃V₂(PO₄)₃. Symmetrical batteries presented a high capacity of 120 mA h g⁻¹ with an operating voltage of ∼2.0 V.