Preparation and lithium-storage performance of (Ti1-x,Vx)3C2 MXene solid solutions

Two-dimensional Ti3C2 MXene shows excellent lithium-storage performance as an anode of lithium-ion batteries. The replacement of Ti with V can enhance the lithium-storage performance, but decrease the stability of Ti3C2 MXene. To understand the impact of V replacement, in this study, a series of (Ti1-x,Vx)3C2 (x = 0, 0.1, 0.2…0.6) MXene solid solutions were prepared. The stability and lithium storage performance of the MXene solutions were investigated. The precursors to make (Ti1-x,Vx)3C2 MXene were MAX phase solid solutions of (Ti1-x,Vx)3AlC2, which were made from TiH2, V, Al and C powders at 1400 °C for 2 h under Ar atmosphere. Because of the replacement of > 60 at.% Ti by V destroys the stability of the (Ti1-x,Vx)3AlC2, the MAX solid solutions with x ≤ 0.6 were synthesized in this study. (Ti1-x,Vx)3C2 MXene was made from the corresponding MAX phases by the etching in mixed solutions of NaF + HCl. (Ti1-x,Vx)3C2 MXene (x = 0~0.4) were synthesized at 60 °C for 2 days, and the MXene (x = 0.5~0.6) were synthesized at 70 °C for 6 days. All (Ti1-x,Vx)3C2 solid solutions had better electrochemical performance than pure Ti3C2 MXene. Especially, (Ti0.7,V0.3)3C2 exhibited the best performance. The capacity of (Ti0.7,V0.3)3C2 was 183.5 mAh/g after 100 cycles at a current density of 500 mA/g, which was ~4.3 times of the capacity of the pure Ti3C2 (42.2 mAh/g at 500 mA/g). This is the first report to clarify the effect of V replacement on the stability and lithium performance on (Ti1-x,Vx)3C2 MXene solid solution. This work is critical for the synthesis of novel MXenes and MAX phases. It provides a way to make a MXene that is very close to V3C2 MXene, which is theoretically predicted but cannot be made. This work is vital for the enhancement of MXenes' electrochemical performance.