Abstract
Rechargeable potassium metal batteries are promising energy storage devices with potentially high energy density and markedly low cost. However, eliminating dendrite growth and achieving a stable electrode/electrolyte interface are the key challenges to tackle. Herein, a novel “quasi‐liquid” potassium‐sodium alloy (KNA) anode comprising only 3.5 wt% sodium (KNA‐3.5) is reported, which exhibits outstanding electrochemical performance able to be reversibly cycled at 4 mA cm–2 for 2000 h. Moreover, it is demonstrated that adding a small amount of sodium hexafluorophosphate (NaPF6) into the potassium bis(fluorosulfonyl)imide electrolyte allows for the formation of the “quasi‐liquid” KNA on electrode surface. Comprehensive experimental studies reveal the formation of an unusual metastable KNa2 phase during plating, which is believed to facilitate simultaneous nucleation and suppress the growth of dendrites, thereby improving the electrode's cycle lifetime. The “quasi‐liquid” KNA‐3.5 anode demonstrates markedly enhanced electrochemical performance in a full cell when pairing with Prussian blue analogs 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.
Highlights
Rechargeable potassium metal batteries are promising energy storage devices potentials of alkali metals and their high theoretical energy density that can satwith potentially high energy density and markedly low cost
While previous research works on K-Na alloy (KNA) were concentrated mainly on the liquid state with a typical K:Na composition of 66.3:33.7 (w/w), in this work our focus is placed on the “quasiliquid” state in the K-dominant region of the K-Na equilibrium phase diagram (Figure S1, Supporting Information), that is, the “liquid + βc (Na in K)” phase
According to the above in situ X-ray diffraction (XRD) investigation, we believe that the presence of Na+ ions, whether from the electrolyte or from the stripping process of KNA-3.5, would promote the formation of a “quasi-liquid” KNA layer on the electrode surface, which facilitates the nucleation of K and Na, suppresses the dendrite growth and helps in the formation of a stable solid electrolyte interphase (SEI), thereby boosting the electrochemical performance
Summary
Rechargeable potassium metal batteries are promising energy storage devices potentials of alkali metals and their high theoretical energy density that can satwith potentially high energy density and markedly low cost. Comparing to the pristine solid K metal (Figure 1a), KNA1.8 shows little difference in terms of the appearance and ductility (Figure S2d, Supporting Information).
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