Mo-MXene-filled gel polymer electrolyte for high-performance quasi-solid-state zinc metal batteries

The production of MXenes from the MAX phase typically requires hydrofluoric acid etching, a process with significant toxicity and severe environmental implications. Given the wide-ranging applications of MXenes, developing a large-scale, environmentally benign chemical etching process is highly desirable. The goal of this study was to establish selective electrochemical aluminum etching (E-etching) from the Mo3AlC2 MAX phase using an innovative 1-ethyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide (EMITFSI) and zinc trifluoromethane sulfonate (Zn(OTF)2) battery electrolyte formulation. The E-etching technique effectively removes the "A" layer from the Mo3AlC2 MAX phase at 60 °C using a TFSI−-based electrolyte. This method demonstrates that the resulting MXene terminal (Tx) contains O and OH groups. Subsequently, the resulting Mo2CTx MXene was embedded into a gel polymer electrolyte (GPE) as an inorganic filler. The Mo2CTx/EMITFSI/Zn(OTF)2/poly(vinylidene fluoride-co-hexafluoropropylene) (PVHF) GPE membrane displayed excellent ionic conductivity, Zn2+ transference number, and galvanostatic Zn plating/stripping compatibility with Zn anodes. Finally, the performance of a zinc-metal battery using a belt-like CaV6O16⋅3H2O cathode was evaluated as a full-cell assembly of CaV6O16⋅3H2O//Mo2CTx/EMITFSI/Zn(OTF)2/PVHF//Zn. This assembly showcased an impressive capacity of 155 mA h g−1, excellent durability (99%), coulombic efficiency approaching 100%, and excellent self-life over 200 h.