Ultra-rapid Synthesis of High-entropy MAX Phases and Their Derivative MXenes for Battery Electrodes

Abstract

High-entropy materials hold immense promise for energy storage, owing to their varied compositions and unforeseen physicochemical properties, yet, which poses challenges in synthesis due to tendentious phase separation and extended sintering durations. Herein, an ultra-rapid strategy based on spark plasma sintering (SPS) techniques is proposed to synthesize high-entropy MAX phases within 15 minutes, including a new phase of (Ti_0.2V_0.2Cr_0.2Nb_0.2Mo_0.2)₄AlC₃ and several phases of 413-type TiVNbMoAlC₃, TiVCrMoAlC₃ and (Ti_0.2V_0.2Cr_0.2Nb_0.2Ta_0.2)₄AlC₃, achieving utmost purity level up to 99.54 %. Under high temperature, the overfeed of Al with low melt point (~660 °C) can foster a liquid environment, which remits the immiscibility among starting materials and benefits to diffusion dynamics to some extents. Theoretical calculations are employed to elucidate the thermodynamic preponderance of high-entropy MAX phases in the intricate multi-element systems. Meanwhile, the varied stacking modes among MX slabs in high-entropy MAX phases and the distinct topological transformations to their derivative MXenes can be observed directly at the atomic level. Moreover, four high-entropy MXenes as electrode materials were investigated for rechargeable batteries. Among them, TiVNbMoC₃ electrode demonstrates superior lithium-ion storage capabilities with 725 mAh g⁻¹ after 1000 cycles at 1 A g⁻¹, triggering the edification to the application of high-entropy MXenes for energy domain.