Combustion-Synthesized KNiPO₄: A Non-toxic, Robust, Intercalating Battery-Type Pseudocapacitive Electrode for Hybrid Supercapacitors as a Large-Scale Energy Storage Solution

Abstract

Polyanionic-type electrode material made of (PO4) n− polyhedral covalently bonded with Ni–O linkage is envisaged as a novel electrode material for intercalative battery-type hybrid supercapacitors. Highly porous, flake-type KNiPO4 showed robust electrochemical performances as a result of its open framework structure and active participation of the Ni2+/3+ redox couple that results in superior pseudocapacitive intercalating charge storage in the aqueous KOH electrolyte. The KNiPO4 electrode shows the specific charge storage equivalent to 168.5 mAh/g (capacitance of 935 F/g) at 1 A/g current rate in the potential window of 0.65 V in the aqueous 2 M KOH electrolyte. KNiPO4 electrodes exhibit excellent long-term cycle stability at 10 A/g for 5000 cycles with 87% of the initial capacity retention of the electrode and coulombic efficiency (η = t d/t c) equivalent to 95.1% after 5000 cycles. Further, in full cell hybrid supercapacitor (HSC) mode in which porous KNiPO4 acted as the positive electrode and activated carbon (AC) functioned as the negative electrode, in the voltage window of 1.6 V, the highest energy density equivalent to 200 Wh/kg and power density equivalent to ∼819 W/kg were obtained at 1 A/g current rate. At a higher current rate (10 A/g), the hybrid supercapacitor attains a very high power density equivalent to 7981 W/kg with a retention of energy density close to 75 Wh/kg with superior cyclic stability. Coulombic efficiency of the full cell [asymmetric supercapacitor (ASC) mode] has lost only 3.4% with excellent capacity retention (92.3%) of its initial value after 2200 cycles. The robust performance and long cycle life of the electrode in full cells confirm the applicability of the material to power implantable biomedical devices. Further, high power performance coupled with superior cyclic stability coupled with strong electrochemical energy storage properties of the KNiPO4 electrode makes it suitable for bulk, grid-level charge storage applications.

Tailoring the Perovskite Structure to Acquire an Inorganic La2NiCrO6 Double Perovskite as an Efficient Energy Storage Application by Varying Molar Concentrations of Citric Acid

“…In eqs and , k 1 is due to the surface capacitive charge storage and k 2 is the diffusion-controlled charge storage. The values of k 1 and k 2 are calculated from the slope and y -intercept of the i (ν)/(ν) 0.5 vs (ν) 0.5 curve. − The deconvoluted CV curve at 10 mV/s scan rate is shown in Figure c. The deconvoluted CV curves at 5, 15, 20, 25, 30, 35, 40, 45, and 50 mV/s scan rates are shown in Figure S5.…”

NiFe-LDH/MoS2/MXene Nanocomposites as an Electrode Material for Battery-Type Supercapacitors

“…The electrochemical behavior of the optimized NiFe 60 /MM 40 was further studied in detail by recording the effect of the scan rate and current density by CV and GCD techniques. The CV curve at different scan rates (10, 20, 30, 40, 50, 60, 80, and 100 mV s –1 (Figure a) displays prominent redox peaks of Ni 2+ /Ni 3+ and Fe 2+ /Fe 3+ conversion, and it demonstrates interactive redox-facilitated charge storage . As the scan rates are increased, the peak current density is observed to rise correspondingly, exhibiting characteristics of a battery-type supercapacitor.…”

“…The CV curve at different scan rates (10,20,30,40,50,60,80, and 100 mV s −1 (Figure 6a) displays prominent redox peaks of Ni 2+ /Ni 3+ and Fe 2+ /Fe 3+ conversion, and it demonstrates interactive redox-facilitated charge storage. 59 As the scan rates are increased, the peak current density is observed to rise correspondingly, exhibiting characteristics of a battery-type supercapacitor. The oxidation and reduction peaks are found to shift toward higher and lower potentials, respectively; this shift in potentials can be ascribed to the over potential arising from the polarization and interfacial resistance at the electrode−electrolyte interfaces.…”

“…Figure d presents the plot of log (peak current density) vs log (scan rate) for NiFe 60 /MM 40 . From the slope of this plot, the b value is determined to be 0.58, implying a semi-infinite diffusion-controlled process typical of battery-type material in NiFe 60 /MM 40 . Moreover, the capacitive-controlled and diffusion-controlled contributions were quantified through the Dunn’s method by employing the following equation: i false( V false) = i cap + i diff = k 1 ν + k 2 ν 1 / 2 i false( V false) ν 1 / 2 = k 1 ν 1 / 2 + k 2 k 1 and k 2 are the arbitrary constants.…”

“…The Randle equivalent circuit comprising R s , C dl , R CT , and W was fitted with EIS curves using EC-Lab software equipped with Biologic workstation. The elements in the circuit correspond to solution resistance, double-layer capacitance, charge-transfer resistance, and the Warburg diffusive component, respectively. , NiFe 60 /MM 40 exhibited a low R s value of 0.64 Ω, while NiFe-LDH and MM had 1.31 and 0.77 Ω solution resistance, respectively. The charge transfer resistance R CT was observed to be 1.087, 3.673, and 4.914 Ω for NiFe 60 /MM 40 , MM, and NiFe-LDH, respectively.…”