A Promising Positive Electrode Material for Na+/Li+ Hybrid-Ionbatteries: Monoclinic-Orthorhombic Na1.1Li2.0V2(PO4)3/C Composite

Abstract

In this paper, we report a new single death-to-fire Na1.1Li2.0V2 (PO4) 3 / C (NLVP / C) compound cathode synthesized from a mono-clinical LVP through a soft ion exchange reaction for use in Na+/Li+ hybrid ion batteries. Thermal studies, High Resolution Synchrotron X-ray diffraction (XRD), and electrochemical data check the room temperature stabilization of the monoclinic-orthorhombic NLVP / C composite phase. In particular, we report application of monoclinic orthorhombic NLVP / C composite as positive materials in Na half-cell. This monoclinic-orthorhombic NLVP/C composite cathode delivered a discharge capacity of 115 mAh g−1 with an average discharge potential of 3.47 V. Corresponding in situ synchrotron XRD patterns recorded during initial electrochemical cycling clearly indicate a series of two-phase transitions and confirm the structural stability of the NLVP/C composite cathode during insertion and extraction of the hybrid ions. In addition, the estimated average working potential and energy density at the initial cycle for the monoclinic orthorhombic NLVP/C composite cathode (3.47 V vs Na/Na+ and 102.5 Wh kg−1, respectively) are higher compared with those of the pyro-synthesized rhombohedral Na3V2(PO4)3 (3.36 V vs Na/Na+ and 88.5 Wh kg−1) cathode. Thus, this study shows the feasibility of using a soft ion-exchange reaction at 150 °C to facilitate the formation of composite phases suitable for rechargeable hybrid-ion battery applications.