Fabrication of the hollow dodecahedral NiCoZn layered double hydroxide for high-performance flexible asymmetric supercapacitor

Nickel cobaltate/nickel cobalt layered double hydroxide composites as electrodes for asymmetric flexible supercapacitors

The electrochemical performance of electrode materials plays a pivotal role in determining the practical applicability of flexible supercapacitors, and optimization of material morphology has emerged as an effective strategy to augment these properties. This study presents the preparation of nickel cobalt cobaltite (NiCo2O4) nano-arrays exhibiting various morphologies, which serve as a support matrix. This is achieved through hydrothermal and annealing treatments applied to the surface of activated carbon cloth (CC). Subsequently, cobalt-nickel layered double hydroxide (CoNi-LDH) is synthesized onto these nano-arrays via electrochemical deposition, resulting in the formation of CC/NiCo2O4/CoNi-LDH (CC/NCCN) electrode. The constructed asymmetric supercapacitor based on CC/NCCN as the positive electrode demonstrates a 1.7 V voltage window. It achieves 137.88 F g-1 specific capacitance at a 1 A g-1, and 55.35 W h kg-1 energy density at 850.12 W kg-1 power density. In addition, it demonstrates remarkable flexural resistance, exhibiting a capacitance retention of 96.29 % following 500 flexural cycles. Furthermore, the device retains 90.55 % of capacitance while achieving nearly 100 % coulombic efficiency after undergoing 10,000 cycles. This device demonstrates substantial promise for a wide range of future applications, and the findings provide innovative insights for advancing the development of flexible devices.

A low-temperature-tolerant and non-flammable cellulose/HEC/PVA eutectogel for flexible asymmetric supercapacitors

Asymmetric supercapacitors (ASCs), which combine the advantages of electric double-layer capacitors and pseudocapacitors, have attracted more and more research interest. However, the performance of water-based ASCs often faces the challenge of electrolyte freezing at low temperatures. To resolve the problem, a ternary deep eutectic solvent (DES) with an eutectic point of less than -100 °C was first prepared. After the DES was integrated into a polymer matrix composed of microcrystalline cellulose (MCC), hydroxyethyl cellulose (HEC), and poly(vinyl alcohol) (PVA), a flexible and non-flammable eutectogel was fabricated. The optimized eutectogel not only exhibited an ionic conductivity of 23.4 mS cm-1 even at -20 °C, but also displayed a tensile strength value of about 0.37 MPa and an elongation value at break of nearly 600 %. The ASC with a eutectogel demonstrated a high voltage window of 0-1.8 V, an energy density of 15.13 Wh kg-1 at a power density of 87.52 W kg-1, and fantabulous cycling stability with ∼90 % capacitance retention after 5000 cycles. The flexible ASC with such a eutectogel could work well in a wide temperature range from -20 to 60 °C. It is expected that this work could present valuable insights for the development of wide-temperature gel polymer electrolytes in ASC applications.

Hybrid supercapacitors using metal-organic framework derived nickel-sulfur compounds

HYPOTHESIS

Metal-organic frameworks (MOFs) are highly suitable precursors for supercapacitor electrode materials owing to their high porosity and stable backbone structures that offer several advantages for redox reactions and rapid ion transport.

EXPERIMENTS

In this study, a carbon-coated Ni9S8 composite (Ni9S8@C-5) was prepared via sulfuration at 500 ℃ using a spherical Ni-MOF as the sacrificial template.

FINDING

The stable carbon skeleton derived from Ni-MOF and positive structure-activity relationship due to the multinuclear Ni9S8 components resulted in a specific capacity of 278.06 mAh·g-1 at 1 A·g-1. Additionally, the hybrid supercapacitor (HSC) constructed using Ni9S8@C-5 as the positive electrode and the laboratory-prepared coal pitch-based activated carbon (CTP-AC) as the negative electrode achieved an energy density of 69.32 Wh·kg-1 at a power density of 800.06 W·kg-1, and capacity retention of 83.06 % after 5000 cycles of charging and discharging at 5 A·g-1. The Ni-MOF sacrificial template method proposed in this study effectively addresses the challenges associated with structural collapse and agglomeration of Ni9S8 during electrochemical reactions, thus improving its electrochemical performance. Hence, a simple preparation method is demonstrated, with broad application prospects in supercapacitor electrodes.

The Utilization of Metal-Organic Frameworks and Their Derivatives Composite in Supercapacitor Electrodes

Up to now, the mainstream adoption of renewable energy has brought about substantial transformations in the electricity and energy sector. This shift has garnered considerable attention within the scientific community. Supercapacitors, known for their exceptional performance metrics like good charge/discharge capability, strong power density, as well as extended cycle longevity, have gained widespread traction across various sectors, including transportation and aviation. Metal-organic frameworks (MOFs) with unique traits including adaptable structure, highly customizable synthetic methods, and high specific surface area, have emerged as strong candidates for electrode materials. For enhancing the performance, MOFs are commonly compounded with other conducting materials to increase capacitance. This paper provides a detailed analysis of various common preparation strategies and characteristics of MOFs. It summarizes the recent application of MOFs and their derivatives as supercapacitor electrodes alongside other carbon materials, metal compounds, and conductive polymers. Additionally, the challenges encountered by MOFs in the realm of supercapacitor applications are thoroughly discussed. Compared to previous reviews, the content of this paper is more comprehensive, offering readers a deeper understanding of the diverse applications of MOFs. Furthermore, it provides valuable suggestions and guidance for future progress and development in the field of MOFs.