Acetate ion-intercalated NiCo-LDH with quasi-theoretical capacitance for high energy/power density aqueous supercapacitors

Abstract

Nickel hydroxides are faced with fatal challenges such as low conductivity and structural instability when applied as the positive electrode of supercapacitors, resulting in much lower capacitance than the theoretical value especially at high rates. Herein, we propose an acetate ion-intercalated Ni_0.7Co_0.3-LDH with excellent rate performance and cycling stability via a one-step solvothermal strategy. The cobalt atom can regulate the pore size distribution to stimulate the diffusion of ions and change the heterogeneous electron configuration to enhance the activity of redox sites. Meanwhile, the intercalated acetate anions can act as “pillars” to enlarge the interlayer spacing and are beneficial for the formation of a highly cross-linked architecture, boosting the fast and consecutive transportation of electrolyte ions. Consequently, the Ni_0.7Co_0.3-LDH shows a quasi-theoretical capacitance of 1026 C g⁻¹ at 1 A g⁻¹ and an extraordinary rate performance of 634.5 C g⁻¹ at 50 A g⁻¹. DFT calculations accounting for increased ionization energy, charge differences, and band gap variations systematically verify the mechanism behind the improved electrochemical performance. Moreover, the assembled asymmetric supercapacitor (ASC) delivers a high energy density of 54 W h kg⁻¹ at a power density of 750 W kg⁻¹. The synergetic modification of anions and metal cations in LDH can open a new avenue for the rational design of two-dimensional materials for energy storage and conversion.