Rechargeable aqueous zinc-ion batteries present low-cost, safe, and environmentally-friendly battery technology but suffer from the limited choice of cathode materials because of the sluggish kinetics of divalent zinc-ion as- sociated with the high adsorption and migration energy barrier. Herein, a reversible zinc/bismuth selenide mild aqueous system was demonstrated for the first time, where bismuth selenide nanoplate cathode delivers a high specific capacity of 263.2 mA h g − 1 at 0.1 A g − 1 and robust rate capability of 100.6 mA h g − 1 even at 10 A g − 1 with long-term lifespan (82.3% retention after 1000 cycles). Benefiting from the layered structure and nanoplate morphology of the bismuth selenide cathode, surface-dominated ion storage is verified by a quantitative kinetics analysis, particularly at high current rates. Notably, unlike conventional batteries with only the reversible in- tercalation of alkali ions into metal chalcogenides, zinc/bismuth selenide aqueous batteries possess a sequential proton and zinc-ion insertion/extraction process, identified by in situ synchrotron radiation-based X-ray diffrac- tion. Density functional theory analysis approves the low adsorption energy and preferential embedding process of protons, and that can further optimize Zn 2 + adsorption and migration abilities in bismuth selenide nanoplate, which is mainly responsible for the excellent performance.