Hierarchical porous nitrogen-doped carbon (HPNC) nanosheets (NS) have been prepared via simultaneous activation and graphitization of biomass-derived natural silk. The as-obtained HPNC-NS show ...favorable features for electrochemical energy storage such as high specific surface area (S BET: 2494 m2/g), high volume of hierarchical pores (2.28 cm3/g), nanosheet structures, rich N-doping (4.7%), and defects. With respect to the multiple synergistic effects of these features, a lithium-ion battery anode and a two-electrode-based supercapacitor have been prepared. A reversible lithium storage capacity of 1865 mA h/g has been reported, which is the highest for N-doped carbon anode materials to the best of our knowledge. The HPNC-NS supercapacitor’s electrode in ionic liquid electrolytes exhibit a capacitance of 242 F/g and energy density of 102 W h/kg (48 W h/L), with high cycling life stability (9% loss after 10 000 cycles). Thus, a high-performance Li-ion battery and supercapacitors were successfully assembled for the same electrode material, which was obtained through a one-step and facile large-scale synthesis route. It is promising for next-generation hybrid energy storage and renewable delivery devices.
Compared with other energy storage devices, supercapacitors have superior qualities, including a long cycling life, fast charge/discharge processes, and a high safety rating. The practical use of ...supercapacitor devices is hindered by their low energy density. Here, we briefly review the factors that influence the energy density of supercapacitors. Furthermore, possible pathways for enhancing the energy density
via
improving capacitance and working voltage are discussed. In particular, we offer our perspective on the most exciting developments regarding high-energy-density supercapacitors, with an emphasis on future trends. We conclude by discussing the various types of supercapacitors and highlight crucial tasks for achieving a high energy density.
Constructing unique mesoporous 2D Si nanostructures to shorten the lithium‐ion diffusion pathway, facilitate interfacial charge transfer, and enlarge the electrode–electrolyte interface offers ...exciting opportunities in future high‐performance lithium‐ion batteries. However, simultaneous realization of 2D and mesoporous structures for Si material is quite difficult due to its non‐van der Waals structure. Here, the coexistence of both mesoporous and 2D ultrathin nanosheets in the Si anodes and considerably high surface area (381.6 m2 g−1) are successfully achieved by a scalable and cost‐efficient method. After being encapsulated with the homogeneous carbon layer, the Si/C nanocomposite anodes achieve outstanding reversible capacity, high cycle stability, and excellent rate capability. In particular, the reversible capacity reaches 1072.2 mA h g−1 at 4 A g−1 even after 500 cycles. The obvious enhancements can be attributed to the synergistic effect between the unique 2D mesoporous nanostructure and carbon capsulation. Furthermore, full‐cell evaluations indicate that the unique Si/C nanostructures have a great potential in the next‐generation lithium‐ion battery. These findings not only greatly improve the electrochemical performances of Si anode, but also shine some light on designing the unique nanomaterials for various energy devices.
Ultrathin mesoporous 2D Si nanosheets with enhanced electrochemical performance are successfully developed by a scalable and low‐cost method. After being encapsulated with the homogeneous carbon layer, the Si/C nanocomposite anodes achieve outstanding lithium‐storage properties with good rate capacity and remarkable cycling stability, which illustrates that the unique nanomaterial is a promising candidate material for the next‐generation lithium‐ion batteries.
High-quality ultrathin two-dimensional nanosheets of α-Ni(OH)2 are synthesized at large scale via microwave-assisted liquid-phase growth under low-temperature atmospheric conditions. After heat ...treatment, non-layered NiO nanosheets are obtained while maintaining their original frame structure. The well-defined and freestanding nanosheets exhibit a micron-sized planar area and ultrathin thickness (<2 nm), suggesting an ultrahigh surface atom ratio with unique surface and electronic structure. The ultrathin 2D nanostructure can make most atoms exposed outside with high activity thus facilitate the surface-dependent electrochemical reaction processes. The ultrathin α-Ni(OH)2 and NiO nanosheets exhibit enhanced supercapacitor performances. Particularly, the α-Ni(OH)2 nanosheets exhibit a maximum specific capacitance of 4172.5 F g(-1) at a current density of 1 A g(-1). Even at higher rate of 16 A g(-1), the specific capacitance is still maintained at 2680 F g(-1) with 98.5% retention after 2000 cycles. Even more important, we develop a facile and scalable method to produce high-quality ultrathin transition metal hydroxide and oxide nanosheets and make a possibility in commercial applications.
We report a simple microwave-assisted method to fabricate high-quality two-dimensional (2D) ultrathin NiCo2O4 nanosheets with a geometrically graphene-like architecture. The unique large-area ...nanostructures represent an ultrahigh surface atomic ratio with almost all active elements exposed outside for surface-dependent electrochemical reaction processes. Experimental results reveal that the as-synthesized ultrathin NiCo2O4 nanosheets show excellent electrochemical performances for lithium storage application. The ultrathin NiCo2O4 nanosheets could deliver a high first discharge capacity (1287.1mAhg−1) with initial Coulombic efficiency of 80.0% at 200mAg−1 current density. The reversible lithium storage capacity still retains at 804.8mAhg−1 in the 100th cycle, suggesting a good cycling stability. The excellent electrochemical properties of the as-synthesized NiCo2O4 nanosheets could be ascribed to the unique ultrathin 2D architecture, which could offer large exposed active surface with more lithium-insertion channels and significantly reduce lithium ion diffusion distance. The cost-efficient synthesis and excellent lithium storage properties make the 2D NiCo2O4 nanosheets as a promising anode material for high-performance lithium ion batteries.
Rechargeable magnesium batteries (rMBs) have been recognized as one of most promising next-generation energy storage devices with high energy and power density. However, the development of rMBs has ...been hampered by the lack of usable cathode materials with high capacity and cycling stability. Herein, we report an ultra-rapid, cost-effective, and scalable synthesis of ultrathin CuS hierarchical nanosheets by a one-step microwave-assisted preparation. Benefiting from the exceptional structural configuration, when used as the cathode material for rMBs at room temperature, the CuS hierarchical nanosheets deliver a high reversible discharge capacity of 300 mA h g–1 at 20 mA g–1, remarkable rate capability (256.5 mA h g–1 at 50 mA g–1 and 237.5 mA h g–1 at 100 mA g–1), and excellent cycling stability (135 mA h g–1 at 200 mA g–1 over 200 cycles). To date, the obtained excellent electrochemical performances are superior to most results ever reported for cathode materials of rMBs.
The development of green and clean synthetic techniques to overcome energy requirements have motivated the researchers for the utilization of sustainable biomass. Driven by this desire we choose rice ...as starting materials source. After the explosion effect, the precursor is converted into puffed rice with a honeycomb-like structures composed of thin sheets. These honeycomb-like macrostructures, effectively prevent the cross-linking tendency towards the adjacent nanosheets during activation process. Furthermore, tuneable micro/mesoporous structures with ultrahigh specific surface areas (SBET) are successfully designed by KOH activation. The highest SBET of 3326 m2 g−1 with optimized proportion of small-mesopores is achieved at 850 °C. The rice-derived porous N-doped carbon nanosheets (NCS-850) are used as the active electrode materials for supercapacitors. It exhibites high specific capacitance specifically of 218 F g−1 at 80 A g−1 in 6 M KOH and a high-energy density of 104 Wh kg−1 (53 Wh L−1) in the ionic liquid electrolytes. These are the highest values among the reported biomass-derived carbon materials for the best of our knowledge. The present work demonstrates that the combination of “puffing effect” and common chemical activation can turn natural products such as rice into functional products with prospective applications in high-performance energy storage devices.
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•Rice derived, tunable micro/mesopores structures of carbon nanosheets.•Honeycomb-like architecture is induced by ‘puffing effect’.•The “puffing effect” avoiding organic solution usage, leading to green route.•Ultrahigh SBET of 3326 m2 g−1 with optimized mesopores.•Highest supercapacitors performance of 104 Wh kg−1 or 53 Wh L−1.
PVdF/SiO2 composite nonwoven membranes exhibiting high safety (thermal stability), high ionic conductivity and excellent electrochemical performances are firstly prepared by electrospinning ...poly(vinylidene fluoride) (PVdF) homopolymer and silicon dioxide (SiO2) sol synchronously for the separators of lithium-ion batteries (LIBs). Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and hot oven tests show that the PVdF/SiO2 composite nonwoven membranes are thermally stable at a high temperature of 400 °C while the commercial Celgard 2400 PP membrane exhibits great shrinkage at 130 °C, indicating a superior thermal stability of PVdF/SiO2 composite nonwoven membranes than that of Celgard membrane. Moreover, the composite membrane exhibits fairly high ionic conductivity (7.47 × 10−3 S cm−1) that significantly improves the performance of LIBs. The PVdF/SiO2 composite membranes are also evaluated to have higher level of porosity (75−85%) and electrolyte uptake (571−646 wt%), lower interfacial resistance compared to the Celgard separator. The lithium-ion cell (using LiFePO4 cathode) assembled with the composite membrane exhibits more stable cycle performance, higher discharge capacity (159 mAh g−1) and excellent capacity retention which proves that they are promising candidates for separators of high performance rechargeable LIBs.
•PVdF/SiO2 composite membranes are first prepared by electrospinning.•Inorganic silicon dioxide sol is added into blended spinning solution directly.•Composite membranes have excellent thermal dimensional stability over a wide range of temperatures.•Composite membranes have superior ionic conductivities.•The electrode electrolyte interfacial resistance is low, indicating good membrane-electrode affinity.
Constructing the heterojunctions or designing the novel nanostructures are thought as effective methods to improve photocatalytic activities of semiconductors. Herein, a one-step green route was ...developed to fabricate bismuth oxyiodide/activated carbon (BiOI/C) composite. The prepared BiOI/C exhibit obviously red shifts and increased absorption range of visible light. The presence of Bi-C bonds confirms the heterojunction, on account of which the BiOI nanosheets tightly grew on the surface of carbon and subsequently provided the hierarchical structure, sufficient interfacial interaction and high specific surface area. Significantly, the sufficient interracial interaction is beneficial to the detachment of electrons (e
)-holes (h
) pairs and the Bi-C bonds work like a bridge to rapidly transmit the e
from BiOI to carbon. What's more, the hierarchical structure of BiOI/C efficiently shortened the diffusion pathways of pollutants and the high S
provided more exposed reaction sites. Benefiting from multiple synergistic effects, the as-prepared BiOI/C exhibited enhanced photocatalytic activities in degrading Rhodamine B (RhB) solution under visible light irradiation. The degradation rate of optimized BiOI/C reaches up to 95% in 120 min, and the efficiency is 3.36 times higher than pure BiOI. This study provides a promising strategy that activated carbon can be utilized in highly-efficiency photocatalysts.
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