Novel Quasi-Liquid K-Na Alloy as a Dendrite-Free Anode for Potassium Metal Batteries

Abstract

Rechargeable potassium metal batteries are promising energy storage devices with potentially high energy density and markedly low cost. However, there are key challenges to eliminate dendrite growth and achieve a stable electrode/electrolyte interface. While liquid potassium-sodium alloy (KNA) has recently been demonstrated to be able to address the dendrite growth issue, it has poor mechanical processability due to its high degree of fluidity, which is difficult to be processed for use in practical potassium batteries. In this presentation, we report a novel “quasi-liquid” KNA comprising only 3.5 wt% Na, which exhibits superior electrochemical performance able to be repeatedly plated and stripped on the copper substrate at 0.5 mA cm-2 up to 220 cycles with a high Coulombic efficiency of above 89%. Moreover, an unusual metastable KNa2 phase is captured during the K-Na plating by in-situ X-ray diffractometry, which may assist in the nucleation of K and Na continually during plating, helping to suppress the formation of dendrites. The “quasi-liquid” KNA-3.5 anode demonstrates markedly enhanced electrochemical performance in a full cell when pairing with Prussian blue analogues or sodium rhodizonate dibasic as the cathode material, compared to the pristine potassium anode. Importantly, unlike the liquid KNA reported before, the “quasi-liquid” KNA-3.5 exhibits good processability and can be readily shaped into sheet electrodes, showing substantial promise as a dendrite-free anode in rechargeable potassium metal batteries.