Double transition metal MXene (Ti_xTa_4-xC₃) 2D materials as anodes for Li-ion batteries

A bi-metallic titanium-tantalum carbide MXene, Ti_xTa_(4-x)C₃ is successfully prepared via etching of Al atoms from parent Ti_xTa_(4-x)AlC₃ MAX phase for the first time. X-ray diffractometer and Raman spectroscopic analysis proved the crystalline phase evolution from the MAX phase to the lamellar MXene arrangements. Also, the X-ray photoelectron spectroscopy (XPS) study confirmed that the synthesized MXene is free from Al after hydro fluoric acid (HF) etching process as well as partial oxidation of Ti and Ta. Moreover, the FE-SEM and TEM characterizations demonstrate the exfoliation process tailored by the Ti_xTa_(4-x)C₃ MXene after the Al atoms from its corresponding MAX Ti_xTa_(4-x)AlC₃ phase, promoting its structural delamination with an expanded interlayer d-spacing, which can allow an effective reversible Li-ion storage. The lamellar Ti_xTa_(4-x)C₃ MXene demonstrated a reversible specific discharge capacity of 459 mAhg^-1 at an applied C-rate of 0.5 °C with a capacity retention of 97% over 200 cycles. An excellent electrochemical redox performance is attributed to the formation of a stable, promising bi-metallic MXene material, which stores Li-ions on the surface of its layers. Furthermore, the Ti_xTa_(4-x)C₃ MXene anode demonstrate a high rate capability as a result of its good electron and Li-ion transport, suggesting that it is a promising candidate as Li-ion anode material.