Three dimensional Ti3C2 MXene nanoribbon frameworks with uniform potassiophilic sites for the dendrite-free potassium metal anodes

Potassium (K) metal batteries hold great promise as an advanced electrochemical energy storage system because of their high theoretical capacity and cost efficiency. However, the practical application of K metal anodes has been limited by their poor cycling life caused by dendrite growth and large volume changes during the plating/stripping process. Herein, three-dimensional (3D) alkalized Ti3C2 (a-Ti3C2) MXene nanoribbon frameworks were demonstrated as advanced scaffolds for dendrite-free K metal anodes. Benefiting from the 3D interconnected porous structure for sufficient K accommodation, improved surface area for low local current density, preintercalated K in expanded interlayer spacing, and abundant functional groups as potassiophilic nuleation sites for uniform K plating/stripping, the as-formed a-Ti3C2 frameworks successfully suppressed the K dendrites and volume changes at both high capacity and current density. As a result, the a-Ti3C2 based electrodes exhibited an ultrahigh coulombic efficiency of 99.4% at a current density of 3 mA cm-2 with long lifespan up to 300 cycles, and excellent stability for 700 h even at an ultrahigh plating capacity of 10 mA h cm-2. When matched with K2Ti4O9 cathodes, the resulting a-Ti3C2-K//K2Ti4O9 full batteries offered a greatly enhanced rate capacity of 82.9 mA h g-1 at 500 mA g-1 and an excellent cycling stability with high capacity retention (77.7% after 600 cycles) at 200 mA g-1, demonstrative of the great potential of a-Ti3C2 for advanced K-metal batteries.