Monoclinic-Orthorhombic Na1.1Li2.0V2(PO4)3/C Composite Cathode for Na+/Li+ Hybrid-Ion Batteries

Monoclinic Li3V2(PO4)3 (LVP) has been considered a promising cathode material for lithium-ion batteries for the past decade because of its high average potential (>4.0 V) and specific capacity (197 mAh g–1). In this paper, we report a new monoclinic-orthorhombic Na1.1Li2.0V2(PO4)3/C (NLVP/C) composite cathode synthesized from monoclinic LVP via a soft ion-exchange reaction for use in Na+/Li+ hybrid-ion batteries. High-resolution synchrotron X-ray diffraction (XRD), thermal studies, and electrochemical data confirm room temperature stabilization of the monoclinic-orthorhombic NLVP/C composite phase. Specifically, we report the application of a monoclinic-orthorhombic NLVP/C composite as cathode material in a Na half-cell. The cathode delivered initial discharge capacities of 115 and 145 mAh g–1 at a current density of 7.14 mA g–1 in the 2.5–4 and 2.5–4.6 V vs Na/Na+ potential windows, respectively. In the lower potential window (2.5–4 V), the composite electrode demonstrated a two-step voltage plateau duri...