Pillared Mo₂TiC₂ MXene for high-power and long-life lithium and sodium-ion batteries

In this work, we apply an amine-assisted silica pillaring method to create the first example of a porous Mo₂TiC₂ MXene with nanoengineered interlayer distances. The pillared Mo₂TiC₂ has a surface area of 202 m² g^-1, which is among the highest reported for any MXene, and has a variable gallery height between 0.7 and 3 nm. The expanded interlayer distance leads to significantly enhanced cycling performance for Li-ion storage, with superior capacity, rate capably and cycling stability in comparison to the non-pillared analogue. The pillared Mo₂TiC₂ achieved a capacity over 1.7 times greater than multilayered MXene at 20 mA g^-1 (≈320 mA h g^-1) and 2.5 times higher at 1 A g^-1 (≈150 mA h g^-1). The fast-charging properties of pillared Mo₂TiC₂ are further demonstrated by outstanding stability even at 1 A g^-1 (under 8 min charge time), retaining 80% of the initial capacity after 500 cycles. Furthermore, we use a combination of spectroscopic techniques (i.e. XPS, NMR and Raman) to show unambiguously that the charge storage mechanism of this MXene occurs by a conversion reaction through the formation of Li₂O. This reaction increases by 2-fold the capacity beyond intercalation, and therefore, its understanding is crucial for further development of this family of materials. In addition, we also investigate for the first time the sodium storage properties of the pillared and non-pillared Mo₂TiC₂.