<p>Aqueous Zn-organic batteries are promising due to the sustainability and tunability of organic cathodes. However, the critical challenge in their practical application lies in dissolution, degradation, and sluggish kinetics, ultimately degrading the cycling stability and rate capability. Herein, we demonstrate a simple effective electrolyte engineering strategy by introducing potassium chloride (KCl) as a co-solute into the ZnCl₂ electrolyte to achieve high-performance Zn batteries utilizing 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) as the cathode. Experimental studies and molecular dynamics simulations reveal that KCl addition not only enhances electrolyte conductivity but also modulates Zn²⁺ solvation environment to form [Zn(H₂O)₂Cl₄]²⁻, significantly improving ion diffusion kinetics. Consequently, the Zn//PTCDA in the ZnCl₂-KCl electrolyte exhibits a remarkable capacity of 124.7&#xa0;mAh g⁻¹ with an average voltage of 0.65&#xa0;V, exceptional rate performance (56% capacity retention at 30&#xa0;A g⁻¹), and prolonged cycling performance (90.9% retention after 10,000 cycles). Experimental and density functional theory mechanistic studies unveil a new reversible Zn²⁺/K⁺ co-storage mechanism in the PTCDA cathode, where K⁺ acts as a charge shield and structural pillar, synergistically decreasing the ion migration energy barrier, enhancing reaction kinetics, and stabilizing the cathode structure. This work elucidates dual-ion storage chemistry and highlights rational electrolyte design for durable, high-power metal–organic batteries.</p>