Mixed-metal borate FeVBO4 of tunnel structure: Synthesis and electrochemical properties in lithium and sodium ion batteries

Abstract Transition borates exhibit various functions due to their diverse components and structures. Herein, a new mixed-metal borate, FeVBO4 with rhombic and triangular tunnels for ionic transportation, is first synthesized at 800 °C subsequent to a sol-gel routine. The new compound FeVBO4 crystallizes in an orthorhombic space group (Pnma, #62), with cell parameters of a = 9.2367(5) A, b = 3.1772(1) A, and c = 9.3912(6) A. Furthermore, the electrochemical properties of carbon-coated FeVBO4 (FeVBO4/carbon) is evaluated as intercalated anode for rechargeable Li and Na batteries. The Na storage of FeVBO4/carbon via conversion reaction exhibits very low reversible capacity (46 mAh g−1). However, the Li storage of FeVBO4/carbon revealing high capacity is worth to investigate. The Li ions first insert the rhombic tunnels to form the LixFeVBO4 (0