Generic synthesis of high-entropy phosphides for fast and stable Li-ion storage

Abstract

Monophosphides and bi-metallic phosphides have attracted considerable interest for their high-capacity Li-storage capacity, but are currently plagued by the sluggish charge transfer kinetics and large volume changes that hinder their practical applications. Herein, we design a triple-disordered-cation phosphide of GaGeSiP₃ that combines the benefits of the high capacity of Si, high reactivity of P, fast Li ion conduction of Ge, and the self-healing capability of liquid metallic Ga. The GaGeSiP₃ multinary compound features high configurational entropy, with excellent electronic conductivity, rapid Li-ion diffusion, and better resistance to volume change compared to the parent phases of GaGe₂P₃, GaSi₂P₃, Ge, and Si. Crystallographic and spectrographic analyses, electrochemical characterization and theoretical simulations confirm that GaGeSiP₃ undergoes a reversible lithium storage mechanism based on a combination of intercalation and conversion reactions. The GaGeSiP₃ anode delivers a high specific capacity of 1667 mA h g⁻¹ with an initial coulombic efficiency of 90.3% and a low average operating potential of 0.47 V. Moreover, we further create graphite-modified GaGeSiP₃ that combines intercalation and conversion storage to deliver a high rate capacity of 949 mA h g⁻¹ at 20.0 mA cm⁻², and an exceptional cycling stability to retain a capacity of 1121 mA h g⁻¹ after 2000 cycles at 6.0 mA cm⁻². Inspired by this unique feature of high structural entropy, we further synthesized quaternary mixed-cation ZnGaGeSiP₄, CuGaGeSiP₄, and AlGaGeSiP₄; quinary mixed-cation ZnCuGaGeSiP₅, ZnAlGaGeSiP₅, and CuAlGaGeSiP₅; and hexanary mixed-cation ZnCuAlGaGeSiP₆, where the crystalline size was reduced due to the enhanced structural entropy. This work opens up a new synthesis paradigm, which overcomes the thermodynamic immiscibility among different metals and non-metals, for creating an attractive family of high-entropy multinary mixed-cation phosphides as advanced energy storage materials.