A Simple Aqueous Battery with Potential for Scalable Energy Storage Based on MnO 2 Deposition at the Cathode and a Quinoid‐Modified Activated Carbon Anode

Abstract Searching for new materials and battery architecture is highly essential for developing scalable energy storage systems with good reliability, low cost, long cycle life, and high power density. Here, we report the fabrication of a simple and cheap aqueous battery with potential for low‐cost energy storage. In this battery, a quinoid‐modified activated carbon (AC‐AQS) electrode is adopted as the anode and a porous carbon felt is exploited as the current collector in the cathode for reversible MnO 2 deposition (MnO 2 ‐C) from Mn 2+ in the electrolyte. This MnO 2 ‐C/AC‐AQS battery delivers an outstanding power density (4.4 kW kg −1 ), excellent cycling stability (99.9 % of the maximum discharge capacity is maintained after 10 000 cycles), and limited self‐discharging. A maximum energy density of 102.5 Wh kg −1 under the charging capacity of 1.2 mAh cm −2 is achieved. Moreover, owing to the ultrafast redox kinetics of cathode and anode, it can be charged to 0.8 mAh cm −2 within 57.6 s, demonstrating excellent rate capability.