Mild exfoliation synthesis of two-dimensional layered V2C MXenes for high performance lithium ion batteries†

Abstract

V₂C MXenes have been extensively investigated for their excellent electrochemical performances, as predicted through theoretical calculations. The etching method to obtain V₂C MXenes from a V₂AlC precursor is designed in detail by adjusting etching conditions for extending their energy storage applications. As a result, the well-defined 2D multilayer structure of the V₂C sample is successfully synthesized using a mild etchant of lithium fluoride and hydrochloric acid, compared with other oxidizing fluoride etchants. The existence of Li⁺ in the HCl + LiF etching agent can play a role in the pre-lithiation of V₂C. Moreover, the suitable etching time has a crucial impact on the morphology and cycling properties of the as-prepared V₂C MXenes. We further explore the different lithium storage behaviors of V₂C MXenes to evaluate the advantage of HCl + LiF, relative to other fluoride reagents. The uniform 2D-layered V₂C sample with a high interlayer spacing of 12.13 Å, etched with the HCl + LiF etchant during 72 h (3d), exhibits remarkable electrochemical performance with a high reversible capacity of 446.2 mA h g⁻¹ after 250 cycles at 200 mA g⁻¹ and perfect cycling stability at various rates. This can be attributed to the loose layer structure of the as-prepared V₂C samples with the beneficial ability to accommodate embeddings, equipping them with the advantage of good electrical conductivity, fast lithium ion diffusion and small charge transfer resistance.