In situBaSO4coating enabled activation-free and ultra-stable δ-MnO2for aqueous Zn-ion batteries

In situ BaSO4 coating, generated in the first discharging of Ba2+ pre-intercalated δ-MnO2, shortens the activation process by inducing fast proton intercalation and stabilizes the MnO2 crystal by suppressing Mn dissolution. The cathode delivers a decent electrochemical performance of 210 mA h g-1 at 1C with a 98% retention after 200 cycles.