Liquid and Polymer Electrolytes for Potassium-Ion Battery

Nonaqueous K-ion batteries have attracted much attention as a potential high-voltage secondary battery owing to the lower standard electrode potential of K+/K than that of Li+/Li.1 Our group has demonstrated a 4 V-class KIB of graphite//K2Mn[Fe(CN)6] (KMnHCF) with 0.7 mol dm-3 KPF6/EC:DEC electrolyte.2 Because of the wide operating potential range, developing nonaqueous electrolytes with higher oxidation stability and the ability to passivate low-potential negative electrodes is one of the major challenges. We will present our recent studies on nonaqueous electrolyte solution, electrolyte additive, and solid polymer electrolyte for KIBs. Based on these results, we provide a design strategy for KIB electrolytes.<br/><br/>KPF6 and KFSA can be used as electrolyte salts because of their sufficient solubility in nonaqueous solvents and their electrochemical stability.3 Highly concentrated KFSA/glyme 4, 5 or KFSA-based ionic liquid (IL)6 electrolytes showed high oxidation stability, good passivation ability toward the Al current collector, and stable solid electrolyte interphase (SEI) formation on the negative electrodes. The KPF6-KFSA binary salt electrolyte allows both Al passivation and suitable SEI formation.7<br/><br/>Electrolyte additives are critical for the long life of K cells. We found that 1,3,2-dioxathiolane 2,2-dioxide (DTD) successfully passivates the K metal surface.8 The DTD addition into nonaqueous electrolytes enables the highly reversible operation of K//KMnHCF cells. Moreover, pretreatment of K metal by a DTD-containing solution enabled the fabrication of 3 V-class all-solid-state K polymer batteries.9<br/><br/>References:<br/>1 T. Hosaka et al, Chem. Rev., 2020, 120, 6358–6466.<br/>2 X. Bie et al., J. Mater. Chem. A, 2017, 5, 4325-4330.<br/>3 T. Hosaka et al., Bull. Chem. Soc. Jpn., 2022, 95, 569-581.<br/>4 T. Hosaka et al., Chem. Commun., 2018, 54, 8387-8390.<br/>5 T. Hosaka et al., J. Mater. Chem. A, 2020, 8, 23766-23771.<br/>6 H. Onuma et al., ACS Energy Lett., 2020, 5, 2849-2857.<br/>7 T. Hosaka et al., ACS Appl. Mater. Interfaces, 2020, 12, 34873-34881.<br/>8 T. Hosaka et al., ACS Energy Lett., 2021, 6, 3643-3649.<br/>9 M. Hamada et al., ACS Energy Lett., 2022, 7, 2244-2246.<br/>&lt;!--![endif]----&gt;