Ammonium‐ion batteries: NH4+‐rich nickel hexacyanoferrate was successfully synthesized through a facile one‐pot method. It exhibits excellent electrochemical performances as cathode material for ammonium‐ion batteries which can be attributed to reversible redox reaction and durable structure. Abstract Rechargeable aqueous batteries based on ammonium‐ion (NH4+) redox reactions shows great potential for large‐scale energy‐storage due to its plentiful supplies, environmental friendliness, intrinsic security, and sustainability. Prussian blu...