In Situ Construction of Binder-Free Stable Battery-Type Copper Cobaltite and Copper Oxide Composite Electrodes for All-Solid-State Asymmetric Supercapacitors: Cation Concentration and Morphology-Dependent Electrochemical Performance

Abstract

Binder-free electrode materials offer high active material mass loading and usage rate, excellent connectivity between active materials and current collectors, and efficient electron and ion transport inside the electrodes. Herein, we demonstrate a binder-free in situ synthesis of microstructures of CuCo2O4/CuO composites grown on the Ni foam (CCO/NF) by wet chemical methods. Two different morphologies of microspheres (CCO/NF-IPA) and cross-linked microsheets (CCO/NF-DIW) result from solvents of isopropyl alcohol and deionized water, respectively. Using X-ray techniques, the nonstoichiometry of Cu, Co, and O in composites is measured. In the backdrop of the supercapacitor application, even though both electrodes have consistent electrochemical performance, the Co-excess of the CCO/NF-IPA composite has a higher specific capacity (369.6 C g–1 at 1 A g–1) and an extended cyclic performance (98% retention after 5000 cycles) compared to the other. The all-solid-state CCO/NF-IPA//activated carbon (AC) asymmetric supercapacitor (ASC) device with a full operating potential window of 0–1.5 V has exhibited a high specific capacity of 162.6 C g–1 at 1 A g–1. The ASC device retains its initial capacity of 97% over 5000 cycles and renders a notable energy density of 43.7 Wh kg–1 at 752.4 W kg–1 power density.

Engineering cationic vacancies on sphere-like zinc cobaltite microstructuresviaself-assembly of silkworm-like interconnected nanoparticles for battery-type supercapacitors

“…The reversible faradaic reactions of M–O/M–O–OH (M = Co and Zn ions) in association with OH − anions are mainly accountable for a pair of well-defined redox peaks on the CV curves of V Zn -ZCO, indicating the battery-type characteristics. 8,14 The CV curves may also maintain their original shape when the scan rates are increased from 2 to 100 mV s −1 , demonstrating the electrode's greater rate capability. 21 In Fig.…”

“…48 Nevertheless, the demonstrated high-rate capability of the V Zn -ZCO electrode may be responsible for the synergetic role of the surface-regulated and diffusion-regulated processes to the redox reactions and kinetics of the charge storage phenomena. 8…”

“…15,21 In our earlier articles, we covered the concise details of the EIS. 8,21 The R s , R ct , and Z w values were transmitted by the V Zn -ZCO as 0.25 Ω, 1.86 Ω, and 15 Ω s −1/2 , respectively. According to EIS, the V Zn -ZCO have high conductivity, low internal resistance, and quick charge transfer, which may contribute to their good rate capability.…”

“…24 In addition, numerous studies have indicated that altering the micro/nanostructure and morphology of the ZCO electrode materials can significantly enhance their electrochemical performance. 8,17 Consequently, researchers have developed various synthesis methods, including hydro/solvothermal, 8 microwave-assisted, 17 sol–gel, 25 co-precipitation, 18,24 and electrodeposition 26 to produce a wide range of microstructures and morphological modifications, such as nanowires, 27 nanoflakes, 28 nanorods, 29 nanoparticles, 30 microspheres 24 and microflowers. However, there is still considerable scope for improving the morphological structure of ZCO material.…”

Hierarchical MnO2/NiS–MnS with Rich Electro-Microstructural Physiognomies for Highly Efficient All-Solid-State Hybrid Supercapacitors

“…Among the number of energy-storing devices, supercapacitors are truly imperative as they can deliver high power density comparable to that of conventional capacitors and energy density comparable to that of conventional batteries. − The remarkably high cyclic efficiency, quick charging capability, excellent performance durability, and miniature dimension of supercapacitors add to their advantageous integrations in contemporary high-performance electronic architectures. , Based on the electrochemical processes, supercapacitors can store charge by (i) continuous formation and depletion of double layers on the active surface of electrode materials and (ii) potentially induced oscillatory redox reactions occurring in the diffused active sites of the electrode materials. , Essentially, supercapacitors with charge storage processes controlled by the surface double-layer formation and active site-specific redox reactions offer superior energy density without compromising with the deliverable power density . In this regard, hybrid supercapacitor systems with redox-active positive electrodes and double-layer prompting negative electrodes show promising Ragone efficiency (high power and energy density) and have become ominously important in modern-day technologies . Fundamentally, the enhanced energy density of hybrid supercapacitor systems arises due to superior specific capacitance of the integrated redox-active (Faradaic) electrode material and the wide potential window of the device arising due to the assimilated non-Faradaic material, which shows the highest efficiency when operated in a broader potential window. , Further, the deliverable specific capacitance of the Faradaic electrode material in a hybrid supercapacitor can be enhanced by amending the number of redox reactions during the charging and discharging of the device. , In essence, the added number of redox-active metal ions and nonstoichiometric oxidation states of metal ions in the Faradaic electrode materials bring about supplementary redox oscillations and charge transfer during the operation of the device. , Further, intrinsically high conductivity of the electrode materials (Faradaic as well as non-Faradaic) facilitates lowly impeded charge transfer, which decreases the redox overpotential and improves the concerted efficiency of electrochemical processes. , In the overall context, transition multimetal (mostly first row) chalcogenides with chalcogen ion vacancy in the lattice offer rich distribution of redox-active metal ions and nonstoichiometric oxidation states of the corresponding metal ions. , Amongst, Ni and Mn-based oxides are the most efficient class of Faradaic electrode materials as they possess several inherent oxidation states and produce supplementary oxidation states during the redox processes. − In particular, Mn-based oxides produce supplementary oxidation states during the redox processes and are investigated as electrode materials, which can deliver high specific capacitance/capacity and Ragone efficiency.…”