Water-Splitting-Suppressed High-Capacity Bipolar Electrodes Enabled by Topochemical Electron Buffering for Symmetric...

Symmetric aqueous batteries (SABs) that employ bipolar materials as electrodes have attracted tremendous attention due to their intrinsic safety and satisfactory capacity, while they still suffer from water-splitting and thus a narrow voltage window. In this work, we propose a novel topochemical design of introducing an electron buffer (EB) to control the electron stream when working, which efficiently attenuates the electron flow toward the water-splitting reactions at the voltage ends. Careful measurements confirm the sharp reduction of current density applied for water-splitting due to the EB effect. Theoretical calculations for voltage end verify the lower surface electron density of EB-involved electrode than that of EB-excluded electrode, demonstrating the superiority of this EB design in suppressing charge shock for water splitting. Consequently, the charging/discharging plateau of the assembled SABs based on EB increases ∼0.16 V, as well as a high capacity of 80.7 mA h g^-1 achieved, which is superior to reported state-of-the-art aqueous bipolar materials. Moreover, the electrolyte loss of EB-involved SABs reduces to only 24% of that of EB-excluded SABs, validating suppressed water splitting by confining the electron pathway. This work provides a new thought to guide electron stream through introducing a rational buffer layer, aiming at hindering water splitting while maintaining energy storage performance.