Synergy of ferric vanadate and MXene for high performance Li- and Na-ion batteries

Ferric vanadate (FeVO4) is a desirable anode candidate for lithium-ion battery (LIB) and sodium-ion battery (SIB) because of its high theoretical capacity, low cost and ease of synthesis. However, its practical application is hindered by its volume expansion during the Li+/Na+ insertion/extraction and low electronic conductivity. Herein, flexible and free-standing FeVO4/Ti3C2Tx (FVO/MX) films have been made via combining FeVO4 nanorods and Ti3C2Tx MXene sheets via a simple method of vacuum assisted filtration. In the composite films, Ti3C2Tx sheets act as host and FeVO4 nanorods are uniformly deposited onto the layers. FeVO4 nanorods are encapsulated by Ti3C2Tx sheets, forming a three-dimensional network sandwich structure. The binder-free FVO/MX films exhibited superior electrochemical performance due to the synergyy between FeVO4 and Ti3C2Tx. Specifically, when FVO/MX electrode was used in a lithium-ion battery, it delivered reversible capacity of 1179 mAh g−1 and 1125 mAh g−1 after 250 cycles at a current density of 0.1 A g−1. Besides, the FVO/MX = 2:1 anode delivered a reversible capacity of 428 mAh g−1 at 5 A g−1 and 69.5% capacity was retained after 2500 cycles. Moreover, the Na-ion storage capacity reaches 129 mAh g−1 at a high current density of 5 A g−1, showing capacity retention of 81.1% after 5000 cycles. The charging and discharging mechanism of the FVO/MX based lithiumion battery was studied by in-situ XRD technique. Owing to high metallic conductivity and 2D morphology of Ti3C2Tx MXene, 3D networks can be constructed by combining other active agents, suggesting that MXene is a promising host material for the next-generation flexible energy storage devices.