Communication pubs.acs.org/JACS
Reversible Dendrite-Free Potassium Plating and Stripping Electrochemistry for Potassium Secondary Batteries Neng Xiao, William D. McCulloch, and Yiying Wu* Department of Chemistry and Biochemistry, The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210, United States S Supporting Information *
electrolyte.12 Wu Xu et al. discovered that a LiPF6 additive enabled fast charging and stable cycling of lithium metal batteries.13 Yi Cui et al. reported that a traditional NaPF6 salt in diglyme can reversibly plate and strip Na with high Coulombic efficiency.14 More recently, it was demonstrated that a highly concentrated NaFSI-DME electrolyte can enable dendrite-free Na deposition and good compatibility with Na-intercalation cathodes.15−17 To the best of our knowledge, there has not been a reported electrolyte that can passivate the potassium surface and allow long-term reversibility of K metal anodes. With the emergence of potassium-based energy storage technologies, it is crucial to investigate K plating and stripping electrochemistry and determine a desirable electrolyte to passivate the potassium surface. Herein, our work demonstrates for the first time that a longterm and highly reversible plating/stripping of K can be realized by a KFSI-DME electrolyte at room temperature. Without any surface coating or separator modification, the K metal anode was plated and stripped over 200 cycles with high Coulombic efficiency (∼99%). Further characterization confirmed that the uniform SEI is mainly composed of reaction products between the K metal and KFSI salt, along with formate and acetate from DME decomposition. Lastly, the electrochemical window of the KFSI-DME electrolyte can be extended to 5 V (vs K/K+) by tuning its concentration. The electrolyte compatibility with a high-voltage potassium Prussian blue (KPB) cathode is further verified by the high Coulombic efficiency (98%) in the full cell testing. Galvanostatic cycling experiments were performed in order to evaluate the reversibility of K deposition/dissolution processes in various electrolytes. The coin cells were assembled with a K counter electrode, a bare Cu working electrode, and a celgard separator in between. A fixed rate of 0.05 mA/cm2 is used during cycling with a charging cutoff at either 1.0 V (vs K/ K+) or the same discharge depth. The Coulombic efficiency for each cycle is defined by the ratio of K plating capacity to K stripping capacity. Among the different electrolytes tested, the KFSI salt in DME is the only formulation that enabled a reversible K plating and stripping in the long term (Figure 1a). 1 M KPF6-DME, 1 M KTFSI-DME, and 0.8 M KPF6-EC/DEC (water
