Developing batteries based on Earth abundant elements such as sodium, magnesium or more recently potassium has become a mandatory challenge in the context of renewable energy growth that requires large-scale storage systems for which cost is the dominant factor and lithium supply a possible issue. Due to the beneficial potassium abundance (2.09 wt.% of the Earth’s crust), low standard potential of K+/K,1 weaker K+ Lewis acidity,2 K-ion batteries (KIBs) are expected to greatly favor both the energy and power density compared to NIB. Numerous new materials for KIBs have thus rapidly been proposed3 but their performance evaluation still remains greatly limited by the lack of efficient electrolytes and the high reactivity of K metal in half cells.4 Indeed, the use of KN(SO2F)2 (KFSI) instead of KPF6 have been reported to be beneficial to most of the anode materials5 while detrimental to some cathode materials,6 probably due to the corrosion of Al current collector by KFSI at high potential. In this presentation, the impact of KPF6 and KFSI salts in carbonate- and glyme-based electrolytes is investigated. The reactivity of K metal is first evaluated by its immersion in the different electrolytes. The soluble/gaseous and solid electrolyte degradation species are analyzed using GC/MS and XPS, respectively. A comparison with the reactivity of Li metal in the equivalent Li salts based electrolyte is also performed. Moreover, K//graphite and K//KVPO4F half-cells have also been prepared and stored (no cycling) to investigate interactions between electrodes (i.e. migration of electrolyte degradation species from the K metal to the working electrode) and their impact in solid electrolyte interphases formation and resulting electrochemical performance. References N. Matsuura, K. Umemoto, and Z. Takeuchi, Bull. Chem. Soc. Jpn., 47, 813–817 (1974).M. Okoshi, Y. Yamada, S. Komaba, A. Yamada, and H. Nakai, J. Electrochem. Soc., 164, A54–A60 (2017).K. Kubota, M. Dahbi, T. Hosaka, S. Kumakura, and S. Komaba, Chem. Rec., 18, 1–22 (2018).L. Madec, V. Gabaudan, G. Gachot, L. Stievano, L. Monconduit, and H. Martinez, ACS Appl. Mater. Interfaces, 10, 34116–34122 (2018).N. Xiao, W. D. McCulloch, and Y. Wu, J. Am. Chem. Soc., 139, 9475–9478 (2017).X. Jiang, T. Zhang, L. Yang, G. Li, and J. Y. Lee, ChemElectroChem, 4, 2237–2242 (2017).