Layered double hydroxides (LDHs) hold significant promise for supercapacitors owing to their superior redox properties and customizable structure. Nevertheless, LDHs exhibit an experimental specific capacity lower than the theoretical value due to their undesirable electronic structure and limited electrical conductivity resulting from narrow interlayer spacing. Herein, we prepared Ni₃FeCo₂(SDS)-LDH through Co control and sodium dodecyl sulfate (SDS) intercalation, exhibiting both high capacitance properties and high conductivity. Initially, Ni₃FeCo₂-LDH demonstrated an optimum specific capacitance of 1251 C g⁻¹ (2553 F g⁻¹), and commendable capacitance retention of 68.82% over 5000 cycles at 1 A g⁻¹. The optimized intrinsic electronic structure from Co element control provided more active sites and a stable structure and facilitated a redox reaction in the distributed structure (Fig. 5d and e). On this basis, the as-fabricated electrode using Ni₃FeCo₂(SDS)-LDH exhibits an excellent specific capacitance of 1356 C g⁻¹ (2825 F g⁻¹), which reaches about 2.8 times that of traditional NiCo-LDH, and a capacitance retention of 65.29% after 5000 cycles at 1 A g⁻¹. Additionally, a Ni₃FeCo₂(SDS)-LDH@NF//AC asymmetric supercapacitor could deliver a notable power density of 767.928 W kg⁻¹ at an energy density of 39.015 W h kg⁻¹, and showed a capacity retention of 61.29% after 5000 cycles at 1 A g⁻¹. This phenomenon arose from the expansion of the interlayer spacing, which reduced diffusion resistance, enhanced electron storage capacity, and increased the contact area between LDH and the electrolyte. Furthermore, the enhanced conductivity resulted from the introduction of the sulfur (S) element. Consequently, this study had far-reaching implications for ternary LDHs to improve capacitive performance.

The effects of the grain boundary precipitation on intergranular corrosion behavior were investigated by exfoliation tests and complementary techniques like scanning electron microscope (SEM), optical profilometry (OP), transmission electron microscope together with energy dispersive spectroscopy (TEM-EDS), and atomic force microscope (AFM). The results reveal the influencing mechanism of intergranular corrosion behavior from grain boundary precipitates (GBPs). The potential discrepancy between GBPs and adjacent areas induces corrosion cavity germination along the grain boundary. Furthermore, the increase of both active Mg and Zn content in GBPs improve the potential difference, which aggravates the intergranular corrosion cavity germination. However, the increment of noble Cu content in GBP is beneficial to reduce the potential difference. On the other side, the distribution of the continuous precipitates in the grain boundary region helps the initial corrosion cavities to connect, which improves the growth of intergranular corrosion cracks. Additionally, discontinuous GBPs and precipitation free zone (PFZ) hinder the spread and connection of intergranular corrosion cavities. Therefore, 7050 aluminum alloy forming different grain boundary precipitation characteristics after different aging treatments shows different resistance to intergranular corrosion: peak-aging < under-aging < over-aging.