Reconstructing Open‐Pore Structure in NiCo‐LDH/NiCoOOH Composite Films Confined by Two‐Dimensional Graphene Multilayers for Exceptional High‐Mass‐Loading Energy Storage

The development of layered double hydroxides (LDHs) has been hindered by the mismatch between their rate capability and areal capacity at ultrahigh mass loadings. Herein, we address this issue by designing NiCo‐LDH/NiCoOOH composite films with an open‐pore nanosheet structure. These films are fabricated using a ChCl‐urea based deep eutectic solvent (DES) additive‐assisted electrodeposition method followed by electrochemical activation, and confined on each graphene nanolayer of a 2D hierarchical expanded graphene paper (EGP) substrate. This design facilitates rapid charge transport and ion diffusion, enhancing active material utilization. The DES additive induces lower crystallinity and more disordered lattices with vacancies in the composite films, strengthening the synergistic effect with the EGP interface. Consequently, the films achieve high areal capacities of 3.4 mAh cm −2 at 23 mg cm −2 mass loading (84.1% rate capability) and a record 16.6 mAh cm −2 at ultrahigh 100 mg cm −2 mass loading (58.4% rate capability, GP thickness 0.15 mm). We also elucidate the relationship between GP substrate thickness and electrochemical performance. The resulting asymmetric supercapacitor delivers an ultrahigh energy density of 6.4 mWh cm −2 and power density of 64 mW cm −2 . This study provides new insights into constructing high‐mass‐loading energy storage materials through microstructure regulation and interface engineering for practical applications.