Ni, Co Hydroxide Modified by Partial Substitution of OH^– with Cl^– for Boosting Ultra‐Fast Redox Kinetics up to 500 mV s⁻¹ in Supercapacitors

Abstract

Metal oxides/hydroxides have attracted great attention as battery‐type electrodes for supercapacitors due to their high theoretical capacitance. However, their poor electrical conductivity and ion transport kinetic severely limit their rate performance, hindering the practical application for high power devices. Herein, a simple co‐precipitation method to synthesize partial substitution of OH– with Cl– in Co, Ni layered hydroxide in saturated NaCl solution is reported. The Cl– substitution significantly increases the interlayer H2O content from 5.3% to 10.2% by changing the polarity of the hydroxide layers, leading to ultrafast ion transport through the Grotthuss behavior. Moreover, the Cl– substitution also changes the electron configuration of Ni and Co, enhancing the electrical conductivity and redox activity. Thanks to the robust electrochemical kinetics, the Ni0.85Co0.15(OH)1.77Cl0.23 shows well‐maintained redox peaks at an ultrahigh scan rate up to 500 mV s–1 and an outstanding rate performance (1076.3 C g–1 at 1 A g–1 and 333.6 C g–1 at 100 A g–1), which are among the best in the previously reported Ni(OH)2 based electrodes. Therefore, this simple anion substitution strategy opens up a new concept for achieving ultrahigh rate battery‐type electrodes.

Potentiostatic Reconstruction of Nickel‐Cobalt Hydroxysulfate with Self‐Optimized Structure for Enhancing Energy Storage

“…The high capacitive contribution of NCHS-E indicates that it is less limited by mass transfer and can be attributed to the polycrystalline structure with fully exposed active sites, larger layer spacing, and water molecule transport layer, which can facilitate fast charging/discharging processes. [61] Meanwhile, the presence of lattice sulfate and interlayer K ions of NCHS-E can stabilize the layer framework and improve the capacity and voltage stability. [62,63] In addition, the columnar and needle-like structures of NCHS-E and NCOH-CV maintain a higher contact area with the electrolyte, which helps the electrolyte diffusion and facilitates the proton transfer inside the bulk phase compared to the large scale flower-like structure of NCOH-I.…”

“…In which, the S-site behaves as an electron donor and interacts with corrugated metal-hydroxide layers via SOM, which facilitates the electron transfer between layers. [61] For supercapacitors or alkaline batteries, the energy storage of nickel-cobalt-based materials mainly relies on the deprotonation/protonation process. [7,65,66] The calculated Gibbs free energy change after deprotonation determines the driving force of the charge/discharge process and the electrochemical performance.…”

Graphene Quantum Dots Pinned on Nanosheets‐Assembled NiCo‐LDH Hollow Micro‐Tunnels: Toward High‐Performance Pouch‐Type Supercapacitor via the Regulated Electron Localization

“…where m + /m − , C + /C − , ΔV + /ΔV − are the mass of active materials, specific capacitance, and potential window of cathode and anode electrodes, respectively. The specific capacitance of the hybrid supercapacitor was calculated from Equation (1), where m is the total mass of the active materials on both electrodes. The energy density (E, W h kg −1 ) and the power density (P, W kg −1 ) can be evaluated according to equations as follows:…”

“…Fortunately, the rechargeable supercapacitor by utilizing the non-flammable aqueous electrolyte can easily achieve high safety and, meanwhile, supply a high specific power density (>10 3 W kg −1 ). [1][2][3] However, the energy storage model on a single physical or electrochemical level often engenders low energy density, which is below the energy consumption standards for some electronic products. In this case, hybrid supercapacitors commonly utilize a carbon-based material as one electrode by the physical sorption of ions and a batterytype electrode as the counter electrode via electrochemical conversation, which can release an admirable energy density without compromising the power delivery.…”

Achieving Ultrahigh Energy‐Density Aqueous Supercapacitors via a Novel Acidic Radical Adsorption Capacity‐Activation Mechanism in Ni(SeO3)/Metal Sulfide Heterostructure

“…[ 3 ] Nevertheless, in contrast to pure capacitive behavior, faradic redox reactions usually cause the slow kinetics of charge transport in electrodes, impairing the rate capability and cyclability of AHSCs. [ 4 ] Furthermore, the enhanced energy density of AHSCs is still far lower than that of lithium‐ion batteries. [ 3a ] Therefore, pursuing higher energy density while retaining the intrinsic advantages is still a highly challenging topic of AHSCs.…”