N-doped Carbon Nanolayer Modified Nickel Foam: A Novel Substrate for Supercapacitors

Abstract Nickel foam (NF) is the most commonly-used current collector for supercapacitors due to open porous structures, good electrical conductivity, and excellent mechanical toughness. However, its insufficient specific surface area (SSA) and surface trace O affect the nucleation, nanostructures, and mass loadings of active materials, severely limiting the mass- and area-specific energy densities of electrodes. Therefore, it is of vital importance to achieving a higher SSA and preferred chemical composition. This work proposes a novel route to modify the surface with an N-doped carbon nanolayer (about 50 nm thick, ~1 wt% of the NF) and studies its influence on the morphology regulation and capacitive performance of NiCoMn-based carbonate hydroxide (as a case study). The preparation, chemical composition, and microstructure of the nanolayer are studied in depth. The morphology evolution of the carbonate hydroxide refers to shapes (from needles to flakes), flake thicknesses (5.2–18.4 nm), and mass loadings (0.8–6.0 mg cm−2). The optimized nanoflake delivers twice mass-specific capacitance and 4.5-folds area-specific capacitance of the nanoneedle at 1.0 A g−1 in aqueous electrolytes. The reversible capacitance is 1818F g−1 (909C g−1) at 10 A g−1, with 95% retention after 10,000 cycles. The solid-state asymmetric capacitor offers a maximum energy density of 91.22 Wh kg−1 at a power density of 400 W kg−1 that is highly competitive related to reported works.