Al foil coated with CNT–pyrolytic C layer of 300 nm (CNT-C/Al) was obtained by heating Al foil coated with CNTs and polymeric precursors in rolls at 580 °C. In CNT-C/Al, distribution of species containing C and Al in depth and crystal structures of these species were investigated by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results reveal that there are diffusion of Almetal and AlxOy to CNT-C layer and chemical reactions of carbon with AlxOy and Almetal at interface, resulting at Al–O–C and Al–C, respectively, which are clarified to be Al4O4C and Al4C3, respectively. Comparison experiments of CNT-C/Al and CNT-C/Al-control (control sample with Al4C3 undetected) show that interface reactions can improve coating adhesion and promote electrical performances of CNT-C/Al effectively. Aluminum solid electrolytic capacitors using CNT-C/Al display ESRs of 5 ± 0.5 mΩ and capacitances of 460–500 μF, in comparison with 8–50 mΩ and 400–500 μF, respectively, for the control samples. Outstanding long-time stabilities of the capacitors as well as CNT-C/Al are also presented with 94–97% retention of the initial capacitance and less than 15% increase in ESR after 1000 h in accelerated lifetime test at 125 °C.