Regulating Ni³⁺ contents by a cobalt doping strategy in ternary NiCo_3-Al₁-LDH nanoflowers for high-performance charge...

NiAl-LDH and CoAl-LDH as typical two-dimensional layered materials have been widely used as supercapacitor cathodes due to their special composition, morphology and rich electrochemically active centers. However, a clear strategy to enhance their electrochemical performances remains lacking. Here, with NiCo_3-Al₁-LDHs (x = 1, 1.5 and 2, in short: NiCoAl-LDHs) as examples, a Co/Ni ion co-incorporation strategy was used to study the possible effects on their capacitive performance. Our work demonstrated that different cobalt contents in NiCoAl-LDHs show no obvious changes in their crystal structure, morphology, surface area, etc. However, incorporating more cobalt ions into NiCoAl-LDHs will generate more oxygen vacancies, causing more Ni³⁺ ions to appear on the surface, and higher concentrations of Ni³⁺ ions and more oxygen vacancies play active roles in enhancing the capacitive performances. The Ni₁Co₂Al₁-LDH electrode with a Ni³⁺/Ni²⁺ ratio of 1.44 and an oxygen vacancy concentration of 54.83% delivers a high specific capacitance (728 C g^-1 at 1 A g^-1) and excellent capacitance retention (93.18% of initial capacitance at 30 A g^-1 after 10 000 cycles).