A novel Mg/Na hybrid battery based on Na2VTi(PO4)3 cathode: Enlightening the Na-intercalation cathodes by a metallic Mg anode and a dual-ion Mg2+/Na+ electrolyte

Na-ion batteries (SIBs) are considered as the most promising candidate for next-generation large-scale electrochemical energy storage. However, the design of such a rocking-chair battery has intrinsic defects. During the first charge process of a SIB, irreversible reduction occurs at the carboneous anode to form solid electrolyte interphase (SEI), which would inevitably consume precious Na resource in the Na-rich cathode and result in a considerable capacity loss. Such an issue has also long existed in LIBs and particularly complicated prelithiation procedures are indispensable in commercial LIB fabrications. In the present study, a novel Mg/Na hybrid battery design is introduced with a Na-intercalation cathode of Na2VTi(PO4)3, a metallic Mg anode and a Mg2+/Na+ dual-ion electrolyte. Such a Mg/Na hybrid battery works perfectly with Na+ intercalation/deintercalation at the Na2VTi(PO4)3 cathode and Mg deposition/dissolution at the Mg anode, providing a high capacity of 168 mAh g−1 and a superior cycleability for 1000 cycles. In contrast, the SIB based on hard carbon anode could hardly cycle due to the large irreversibility at the anode. The present work highlights a novel high-performance and reliable battery design strategy using well-developed Na-storage cathodes, which has high potential in future large-scale energy-storage applications.