V2CTX MXene Sphere for Aqueous Ion Storage

Despite the remarkable ion-hosting capability of MXenes, their electrochemical performance is restricted to the ion shuttle barrier stemming from the capacious surface and the sluggish chemical activity of intrinsic transition metal layers. Herein, we construct a vertically aligned array of V2CTX flakes utilizing a carbon sphere template (V2CTX@CS), with the interlayer galleries outward facing the external electrolyte, to shorten the diffusion length and mitigate the ion shuttle barrier. Moreover, we leverage the high sensitivity of V2CTX flakes to the water-oxygen environment, fully activating the masked active sites of transition metal layers in an aqueous environment via continuous electrochemical scanning. Aqueous V2CTX@CS/Zn battery delivers a novel capacity enhancement over 42,000 cycles at 10 A g-1. After activation, the capacity reaches up to 409 mAh g-1V2CTX at 0.5 A g-1 and remains at 122 mAh g-1 V2CTX at 18 A g-1. With a 0.95-V voltage plateau, the energy density of 330.4 Wh kg-1 V2CTX surpasses previous records of aqueous MXene electrodes.