Rechargeable potassium (ion) batteries (KIBs) are an emerging energy storage system with many potential advantages over existing battery systems (e.g., Li-ion, Na-ion battery). However, the electrolyte design for KIBs remains challenging because of serious electrolyte decomposition. Particularly, this problem is aggravated when using metal potassium anodes. Herein, we report that the cation-solvent (i.e., K+-solvent) solvation structure which is determined by the electrolyte composition plays a dominant role in the failure of KIBs. We present an analysis of the reaction pathway to understand the behavior of the cation-solvent structure at the surface of metal electrodes (e.g., metal plating or M+-solvent decomposition). The electronegativity change of cation-solvent structure was studied and correlated to the stability of the electrolytes. We find that the electrolyte decomposition can be induced when the K+ -solvent structure accepts one electron from the electrode; however, this process can be suppressed by tuning the electronegativity through varying the solvent chemistry, anions type, and salt concentrations. Our results explain the high stability of existing high-concentration electrolytes, and present a general guideline to design stable electrolytes for KIBs. This approach can pave the way for the realization of high-performance K-ion batteries.