Vertically Aligned Sn4+ Preintercalated Ti2CTX MXene Sphere with Enhanced Zn Ion Transportation and Superior Cycle Lifespan

Abstract

While 2D MXenes have been widely used in energy storage systems, surface barriers induced by restacking of nanosheets and the limited kinetics resulting from insufficient interlayer spacing are two unresolved issues. Here an Sn⁴⁺ preintercalated Ti<inf>2</inf>CT<inf>X</inf> with effectively enlarged interlayer spacing is synthesized. The preintercalated Ti<inf>2</inf>CT<inf>X</inf> is aligned on a carbon sphere to further enhance ion transportation by shortening the ion diffusion path and enhancing the reaction kinetics. As a result, when paired with a Zn anode, 12 500 cycles, which equals 2 800 h cycle time, and 5% capacity fluctuation are obtained, surpassing all reported MXene-based aqueous electrodes. At 0.1 A g^-1, the capacity reaches 138 mAh g^-1, and 92 mAh g^-1 remains even at 5 A g^-1. In addition, the low anti-self-discharge rate of 0.989 mV h^-1 associated with a high capacity retention of 80.5% over 548 h is obtained. Moreover, the fabricated quasi-solid capacitor based on a hydrogel film electrolyte exhibits good mechanical deformation and weather resistance. This work employs both preintercalation and alignment to MXene and achieves enhanced ion diffusion kinetics in an aqueous zinc ion capacitors (ZICs) system, which may be applied to other MXene batteries for enhanced performance.