Silica-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 capacities, rate capabilities and cycling stabilities in comparison to the non-pillared version. The pillared Mo2TiC2 achieved capacities over 1.7 times greater than multilayered MXene at 20 mA g-1 (≈ 320 mAh g-1) and 2.5 times higher at 1 A g-1 (≈ 150 mAh 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 compounds. In addition, we also investigate for the first time the sodium storage properties of the pillared and non-pillared Mo2TiC2.