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

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 degrees 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) angstrom, b = 3.1772(1) angstrom, and c = 9.3912(6) angstrom. 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 < x <= 1) solid solution, and then squeeze into the triangular tunnel and activate a conversion reaction accomplished by delivering a high discharge capacity of 621.6 mAh g(-1) (theoretical capacity 737.9 mAh g(-1)) and showing a reversible recharge capacity of 387.3 mAh g(-1). Our study has unlocked the great potential of borate-type anode in rechargeable batteries, and the new compound FeVBO4 with unique structure and mixed metallic elements could be extended to other application area. (C) 2019 Elsevier B.V. All rights reserved.