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

Ferric vanadate (FeVO 4 ) 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 FeVO 4 /Ti 3 C 2 T x (FVO/MX) films have been made via combining FeVO 4 nanorods and Ti 3 C 2 T x MXene sheets via a simple method of vacuum assisted filtration. In the composite films, Ti 3 C 2 T x sheets act as host and FeVO 4 nanorods are uniformly deposited onto the layers. FeVO 4 nanorods are encapsulated by Ti 3 C 2 T x sheets, forming a three-dimensional network sandwich structure. The binder-free FVO/MX films exhibited superior electrochemical performance due to the synergyy between FeVO 4 and Ti 3 C 2 T x . 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 Ti 3 C 2 T x 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.