The development of nonflammable electrolytes can boost energy density and battery safety, especially for layered metal oxide cathodes operating at high voltage. However, most nonflammable electrolytes are designed in a high concentration for compatibility with graphite electrodes and/or less decomposition. Herein, we introduced a solvation structure-mediated model to develop a nonflammable electrolyte based on trimethyl phosphate (TMP) solvent at a normal concentration. This advancement allows the graphite || lithium cobalt oxide full cell to operate at 4.5 V, delivering high energy density and also exhibiting a nonflammable feature. This achievement is realized using previously unreported components, including carbonate solvent, ethylene sulfate (DTD) additives, and conventional LiPF6 salt. We analyzed the molecular behaviors of each electrolyte composition and also uncovered the unreported impact of DTD, highlighting its prerequisite conditions for effectively weakening the Li+-TMP interactions. This bottom-up design strategy offers a fresh perspective on regulating solvation structures and electrolyte formulations.