Al‐Doped Nickel Hydroxide Modified via Heterovalent Substitution to Enhance Specific Capacity

As a representative nickel‐based cathode material, layered nickel hydroxide (Ni(OH) 2 ) demonstrates significant potential in electrochemical energy storage devices, such as nickel‐iron batteries and supercapacitors, owing to its high theoretical specific capacity of 289 mAh g −1 . However, constrained by the inherent structural instability in practical systems, Ni(OH) 2 is difficult to demonstrate satisfactory electrochemical performance. In this work, we demonstrate an effective heterovalent doping strategy, successfully substituting aluminum (Al) for nickel (Ni) within the Ni(OH) 2 lattice. Experimental and theoretical calculations reveal that Al can be incorporated into the Ni(OH) 2 lattice by substituting Ni atoms, thereby modifying the internal charge distribution, electrochemical behavior, and structural stability. Consequently, Ni(OH) 2 with an Al doping level of 11% displays the best electrochemical performance. At the current density of 1 A g −1 , it delivers a specific capacity of 276 mAh g −1 . With the current density increasing to 5 A g −1 , the specific capacity can still remain at 201.3 mAh g −1 . This work presents a new approach for significantly enhancing the specific capacity of nickel hydroxide by doping with invariant‐valence elements, and identifies the doping amount as the key factor influencing the specific capacity.