Hierarchical self-assembly flower-like ammonium nickel phosphate as high-rate performance electrode material for asymmetric supercapacitors with enhanced energy density

Abstract

Ammonium nickel phosphate has a large specific capacitance as an electrode material at low current density, but its capacitance decays fast at high current density, which directly affects the rate performance of supercapacitors. Herein, we demonstrate a facile route for the controllable synthesis of hierarchical self-assembly flower-like ammonium nickel phosphate as a high-rate electrode material for asymmetric supercapacitors, which is an important strategy to enhance the energy density at high power density. The flower-like structures are hierarchically assembled by a mass of rectangular sheets, which can provide fast electron transport and short ion diffusion path, thereby exhibiting excellent electrochemical performance with ultrahigh specific capacitance of 1016 F g at 1.0 A g. More importantly, the NHNiPO · HO materials exhibit outstanding rate performance (800 F g even at large current density of 30 A g) and superior long-term cycle life (83% of capacity retention up to 3000 cycles at 5 A g). Furthermore, the NHNiPO · HO//AC asymmetric supercapacitors are assembled in aqueous KOH electrolyte, and exhibit high energy density (46.2 Wh kg at 160 W kg and 26.7 Wh kg at a large power density of 4000 W kg, respectively). Due to the outstanding electrochemical performance, the all-solid-state asymmetric supercapacitors are successfully constructed using these materials.

One-Step Polyoxometalates-Assisted Synthesis of Manganese Dioxide for Asymmetric Supercapacitors with Enhanced Cycling Lifespan

“…54−56 The excellent specific energy might result from the high SC as well as the large voltage window (2 V), which were the crucial factors to improve the specific energy because of the following formula: E = 0.5 CV 2 . 1,57 The cycle lifespan of the device in neutral Na 2 SO 4 electrolytes at 1 A g −1 showed that S-3//C, S-4//C and S-5//C could keep about 94%, 93% and 90% SC after a 5000 cycle test, demonstrating the outstanding stability of the devices (Figure 5e). Figure 5f shows that the impedance of S-3//C was lower than S-4//C and S-5//C devices, indicating the outstanding electric conductivity of S-3//C asymmetric supercapacitors.…”

“…The PVA-KOH gel electrolytes were fabricated following a previous report. 57 The mass balancing of the electrode materials would be obey the relationship q + = q − . 58…”

Rice Husk‐Based 3D Porous Silicon/Carbon Nanocomposites as Anode for Lithium‐Ion Batteries

“…As shown in Figure f, there are two large arcs in the Nyquist plots for the 3D porous RHs–Si/C nanocomposite before cycling. The high‐frequency arc presented the sum of contact resistance and resistance of the SEI film formed from electrolyte decomposition . The middle and low‐frequency arcs presented the charge transfer resistance.…”

Role of dual redox additivesKI/VOSO4in manganese ammonium phosphate at graphene quantum dots for supercapattery

“…[26][27][28] Since no one, has ever attempted on finding optimal graphene quantum dots (GQD) mass concentration dispersoid for manganese ammonium phosphate (MnAP) host, the present investigation is ventured on it, and enhancing its specific capacitance by using dual redox additives KI/VOSO 4 has also been investigated for the first time toward high-performance SUPAT application. 29…”