Potassium ion batteries (KIBs) are attracting great attention as an alternative to lithium-ion batteries due to lower cost and better global sustainability of potassium. However, designing electrolytes compatible with the graphite anode and addressing the safety issue of highly active potassium remains challenging. Herein, a new concept of using additives to engineer non-flammable electrolytes for safer KIBs is introduced. It is discovered that the additives, such as the ethylene sulfate (i.e., DTD), can make the electrolyte of 1.0 m potassium bis(fluorosulfonyl) imide in trimethyl phosphate compatible with graphite anode for the first time, without the need of concentrated electrolyte strategies. A new coordination mechanism of additives in the electrolyte is presented. It is shown that the additive can change the K+ solvation structure and then determine the interfacial behaviors of K+-solvent on electrode interface, which are critical to affect the graphite performance (i.e., K+-solvent co-insertion, or K+ (de-)intercalation). Then, an extremely high potassium storage capability is obtained in graphite electrode for potassium (ion) batteries, particularly the presented high-performance graphite|K0.69CrO2 full battery fully demonstrates the practical application of this newly designed electrolyte. This additive-based strategy can offer more opportunities to tune the electrolyte properties and then serve for the more mobile ion battery system.