Electrode material stability is crucial for the development of next-generation ultralong-lifetime batteries. However, current solid- and liquid-state electrode materials face challenges such as rigid atomic structure collapse and uncontrolled species migration, respectively, which contradict the theoretical requirements for ultralong operation lifetimes. Herein, we present a design concept for a soft colloid polyvinylpyrrolidone iodine (PVP-I) electrode, leveraging the inherent water molecule competition effect between (SO4)2- from the electrolyte and PVP-I from the cathode in an aqueous Zn||PVP-I battery. Electrochemical demonstrations measured under various simulated and practical (integrated with photovoltaic solar panel) conditions highlight the potential for an ultralong battery lifetime. The PVP-I colloid exhibits a dynamic response to the electric field during battery operation. More importantly, the water competition effect between (SO4)2- from the electrolyte and water-soluble polymer cathode materials establishes a new electrolyte/cathode interfacial design platform for advancing ultralong-lifetime aqueous batteries.