Nickel–Cobalt Hydroxides with Tunable Thin-Layer Nanosheets for High-Performance Supercapacitor Electrode

Abstract

Layered double hydroxides as typical supercapacitor electrode materials can exhibit superior energy storage performance if their structures are well regulated. In this work, a simple one-step hydrothermal method is used to prepare diverse nickel–cobalt layered double hydroxides (NiCo-LDHs), in which the different contents of urea are used to regulate the different nanostructures of NiCo-LDHs. The results show that the decrease in urea content can effectively improve the dispersibility, adjust the thickness and optimize the internal pore structures of NiCo-LDHs, thereby enhancing their capacitance performance. When the content of urea is reduced from 0.03 to 0.0075 g under a fixed precursor materials mass ratio of nickel (0.06 g) to cobalt (0.02 g) of 3:1, the prepared sample NiCo-LDH-1 exhibits the thickness of 1.62 nm, and the clear thin-layer nanosheet structures and a large number of surface pores are formed, which is beneficial to the transmission of ions into the electrode material. After being prepared as a supercapacitor electrode, the NiCo-LDH-1 displays an ultra-high specific capacitance of 3982.5 F g−1 under the current density of 1 A g−1 and high capacitance retention above 93.6% after 1000 cycles of charging and discharging at a high current density of 10 A g−1. The excellent electrochemical performance of NiCo-LDH-1 is proved by assembling two-electrode asymmetric supercapacitor with carbon spheres, displaying the specific capacitance of 95 F g−1 at 1 A g−1 with the capacitance retention of 78% over 1000 cycles. The current work offers a facile way to control the nanostructure of NiCo-LDHs, confirms the important affection of urea on enhancing capacitive performance for supercapacitor electrode and provides the high possibility for the development of high-performance supercapacitors.

Non‐Thermal Plasma Assisted Fabrication of Ultrathin NiCoOx Nanosheets for High‐Performance Supercapacitor

“…Figure S8(d) shows the Ragone diagram of the device, which shows that an energy density of 85.9 μWh cm −2 was measured at a power density of 500 μW cm −2 . Compared with the previous work, the performance of our electrode material is better, indicating that the device has a broader application prospect [30–33] …”

“…For Ar-NiCoO x and NiCoO x , pair of distinct peaks associated with the redox reactions of the metal cations appearing around 0.1 and 0.4 V are indicators of their reverse process. [30] Compared to bulk NiCoO x LDHs, Ar-NiCoO x nanosheets demonstrated a smaller oxidation-reduction energy barrier because of fast ion diffusion across the ultrathin and enlarged interlayer spacing resulting from Ar-plasma induced exfoliation of the pristine material. Compared to others, the area from CV curves of NF is negligible indicating the capacitive contribution of NF is quite small.…”

“…Compared with the previous work, the performance of our electrode material is better, indicating that the device has a broader application prospect. [30][31][32][33]…”

“…It is apparent that the integrated area of Ar‐NiCoO x nanosheets and its redox current is higher than pristine NiCoO x and NF, indicative of higher capacitance. For Ar‐NiCoO x and NiCoO x , pair of distinct peaks associated with the redox reactions of the metal cations appearing around 0.1 and 0.4 V are indicators of their reverse process [30] . Compared to bulk NiCoO x LDHs, Ar‐NiCoO x nanosheets demonstrated a smaller oxidation‐reduction energy barrier because of fast ion diffusion across the ultrathin and enlarged interlayer spacing resulting from Ar‐plasma induced exfoliation of the pristine material.…”

Cu-Doped Layered Double Hydroxide Constructs the Performance-Enhanced Supercapacitor Via Band Gap Reduction and Defect Triggering

“…The specific capacities obtained for CuCo-LDH are 433, 407, 374, 352, 341, 325, and 281 C g −1 at 1, 2, 4, 6, 8, 10, and 16 A g −1 , which are superior to that of Co-LDH. When compared with other reported electrode materials, 28,29 our CuCo-LDH is superior (Table S1). Toward optimizing the performance of electrode materials, a series of LDH electrode materials were prepared by regulating the molar ratio of Co and Cu (Figures S12− S16).…”