Structural Reconstruction Strategy Enables CoFe LDHs for High‐Capacity NH4+ Storage and Application in High‐Energy Density Ammonium‐Ion Hybrid Supercapacitors**

Abstract Exploration of high‐performance aqueous ammonium‐ions hybrid supercapacitor has attracted tremendous research attention recently. Herein, structural reconstructed cobalt‐iron layered double hydroxides (SR‐CoFe LDHs) featuring copious structure defects (i. e., oxygen‐vacancies, M−O bonds, MOO − bonds, coexistence of Co 2+ /Co 3+ and Fe 2+ /Fe 3+ ) are reported as a high‐capacity cathode for NH 4 + storage. The resulting SR‐CoFe LDHs can deliver a reversible capacity of 167.9 mAh g −1 at 0.5 A g −1 , which is 3.3 folds higher than that of pristine CoFe‐LDHs. Ex‐situ experimental results and theoretical studies denote that the presence of structural defects in the CoFe‐LDHs can lower the NH 4 + adsorption energy and induced electron delocalization to enhance the electrical conductivity, rendering the CoFe‐LDHs exhibits excellent performance for NH 4 + storage. As a proof of concept, ammonium‐ion hybrid supercapacitor has been assembled with CoFe‐LDHs as the cathode and hierarchical carbon as the anode, which can deliver a large specific capacitance of 238.3 F g −1 , long cycle stability over 10000 cycles, and high energy density of 66.2 Wh kg −1 within a wide working voltage of 2 V. Overall, this work offers some insights into the design of high capacity cathode for aqueous NH 4 + storage and also illustrates the construction of aqueous hybrid devices with NH 4 + as the charge carrier.