Homologous Hierarchical Porous Hollow Carbon Spheres Anode and Bowls Cathode Enabling High-Energy Sodium-Ion Hybrid Capacitors

NiS Nanosheets Decorated on Hollow Carbon Spheres from Liquefied Wood for Supercapacitors

Carbon-based supercapacitors with high performance have a wide foreground among various energy storage devices. In this work, wood-based hollow carbon spheres (WHCS) were prepared from liquefied wood through the processes of emulsification, curing, carbonization, and activation. Then, the hydrodeposition method was used to introduce nickel sulfide (NiS) to the surface of the microspheres, obtaining NiS/WHCS as the supercapacitor electrode. The results show that NiS/WHCS microspheres exhibited a core-shell structure and flower-like morphology with a specific surface (307.55 m² g^-1) and a large total pore volume (0.14 cm³ g^-1). Also, the capacitance could be up to 1533.6 F g^-1 at a current density of 1 A g^-1. In addition, after 1000 charge/discharge cycles, the specific capacitance remained at 72.8% at the initial current density of 5 A g^-1. Hence, NiS/WHCS with excellent durability and high specific capacitance is a potential candidate for electrode materials.

Homologous Nitrogen-Doped Hierarchical Carbon Architectures Enabling Compatible Anode and Cathode for Potassium-Ion Hybrid Capacitors

Potassium-ion hybrid capacitors (PIHCs) have been considered as an emerging device to render grid-scale energy storage. Nevertheless, the sluggish kinetics at the anode side and limited capacity output at the cathode side remain daunting challenges for the overall performances of PIHCs. Herein, an exquisite "homologous strategy" to devise multi-dimensional N-doped carbon nanopolyhedron@nanosheet anode and activated N-doped hierarchical carbon cathode targeting high-performance PIHCs is reported. The anode material harnessing a dual-carbon structure and the cathode candidate affording a high specific surface area (2651 m² g^-1 ) act in concert with a concentrated ether-based electrolyte, resulting in an excellent half cell performance. The related storage mechanism is systematically revealed by in situ electrokinetic characterizations. More encouragingly, the thus-derived PIHC full cell demonstrates a favorable energy output (157 Wh kg^-1 ), showing distinct advantages over the state-of-the-art PIHC counterparts.

Reasonable Construction of Hollow Carbon Spheres with an Adjustable Shell Surface for Supercapacitors

Hollow carbon spheres (HCS) manifest specific merit in achieving large interior void space, high permeability, wide contactable area, and strong stacking ability with negligible aggregation and have attracted attention due to their high supercapacitor activity. As the key factor affecting supercapacitor performance, the surface chemical properties, shell thickness, roughness, and pore volumes of HCS are the focus of research in this field. Herein, the surface chemical properties and structures of HCS are simultaneously adjusted by a feasible and simple process of in situ activation during assembly of resin and potassium chloride (KCl). This strategy involves KCl participating in resin polymerization and the superior performance of potassium species on activating carbon. The surface N/O content, thickness, defects, and roughness degree of HCS can be controlled by adjusting the dosage of KCl. Electrochemical tests show that optimized HCS has suitable roughness, high surface area, and abundant surface N/O functional groups, which endow it with excellent electrochemical capacitance properties, showing its high potential in supercapacitors.

Respective Roles of Inner and Outer Carbon in Boosting the K+ Storage Performance of Dual-Carbon-Confined ZnSe

Potassium-ion batteries (PIBs) have been considered as potential alternatives for lithium-ion batteries since there is a demand for better anode with superior energy, excellent rate capability, and long cyclability. The high-capacity zinc selenide (ZnSe) anode, which combines the merits of conversion and alloying reactions, is promising for PIBs but suffers from poor cyclability and low electronic conductivity. To effectively boost electrochemical performance of ZnSe, a "dual-carbon-confined" structure is constructed, in which an inner N-doped microporous carbon (NMC)-coated ZnSe wrapped by outer-rGO (ZnSe@i-NMC@o-rGO) is synthesized. Combining finite element simulation, dynamic analysis, and density functional theory calculations, the respective roles of inner- and outer-carbon in boosting performance are revealed. The inner-NMC increased the reactivity of ZnSe with K⁺ and alleviated the volume expansion of ZnSe, while outer-rGO further stabilized the structure and promoted the reaction kinetics. Benefiting from the synergistic effect of dual-carbon, ZnSe@i-NMC@o-rGO exhibited a high specific capacity 233.4 mAh g^-1 after 1500 cycles at 2.0 A g^-1 . Coupled with activated carbon, a potassium-ion hybrid capacitor displayed a high energy density of 176.6 Wh kg^-1 at 1800 W kg^-1 and a superior capacity retention of 82.51% at 2.0 A g^-1 after 11000 cycles.

Recent Progress on Asymmetric Carbon- and Silica-Based Nanomaterials: From Synthetic Strategies to Their Applications

HIGHLIGHTS

The synthetic strategies and fundamental mechanisms of various asymmetric carbon- and silica-based nanomaterials were systematically summarized. The advantages of asymmetric structure on their related applications were clarified by some representative applications of asymmetric carbon- and silica-based nanomaterials. The future development prospects and challenges of asymmetric carbon- and silica-based nanomaterials were proposed.

ABSTRACT

Carbon- and silica-based nanomaterials possess a set of merits including large surface area, good structural stability, diversified morphology, adjustable structure, and biocompatibility. These outstanding features make them widely applied in different fields. However, limited by the surface free energy effect, the current studies mainly focus on the symmetric structures, such as nanospheres, nanoflowers, nanowires, nanosheets, and core–shell structured composites. By comparison, the asymmetric structure with ingenious adjustability not only exhibits a larger effective surface area accompanied with more active sites, but also enables each component to work independently or corporately to harness their own merits, thus showing the unusual performances in some specific applications. The current review mainly focuses on the recent progress of design principles and synthesis methods of asymmetric carbon- and silica-based nanomaterials, and their applications in energy storage, catalysis, and biomedicine. Particularly, we provide some deep insights into their unique advantages in related fields from the perspective of materials’ structure–performance relationship. Furthermore, the challenges and development prospects on the synthesis and applications of asymmetric carbon- and silica-based nanomaterials are also presented and highlighted. [Image: see text]

Synthesis of V-notched half-open polymer microspheres via facile solvent-tuned self-assembly

Polymer microspheres with a special V-notched half-open architecture were synthesized in a mixed solvent of water/ethanol (1 : 1 v/v) at room temperature.

Comparative Study on Supercapacitive Performances of Hierarchically Nanoporous Carbon Materials With Morphologies From Submicrosphere to Hexagonal Microprism

Hierarchically nanoporous carbon materials (HNCMs) with well-defined morphology and excellent electrochemical properties are promising in fabrication of energy storage devices. In this work, we made a comparative study on the supercapacitive performances of HNCMs with different morphologies. To this end, four types of HNCMs with well-defined morphologies including submicrospheres (HNCMs-S), hexagonal nanoplates (HNCMs-N), dumbbell-like particles (HNCMs-D), and hexagonal microprisms (HNCMs-P) were successfully synthesized by dual-template strategy. The relationship of structural-electrochemical property was revealed by comparing the electrochemical performances of these HNCMs-based electrodes using a three-electrode system. The results demonstrated that the HNCMs-S-based electrode exhibited the highest specific capacitance of 233.8 F g-1 at the current density of 1 A g-1 due to the large surface area and well-defined hierarchically nanoporous structure. Moreover, the as-prepared HNCMs were further fabricated into symmetrical supercapacitor devices (HNCMs-X//HNCMs-X) using KOH as the electrolyte and their supercapacitive performances were checked. Notably, the assembled HNCMs-S//HNCMs-S symmetric supercapacitors displayed superior supercapacitive performances including high specific capacitance of 55.5 F g-1 at 0.5 A g-1, good rate capability (retained 71.9% even at 20 A g-1), high energy density of 7.7 Wh kg-1 at a power density of 250 W kg-1, and excellent cycle stability after 10,000 cycles at 1 A g-1. These results further revealed the promising prospects of the prepared HNCMs-S for high-performance energy storage devices.

Recent progress in sodium/potassium hybrid capacitors

Metal ion hybrid capacitors (MIHCs) have been recognized as one of the most promising power sources owing to their combined merits of high energy density in batteries and high power output in supercapacitors. The kinetics mismatch between the capacitor-type cathode and battery-type anode yet must be well addressed before implementing their practical feasibility. Here, we overview the recent progress in sodium and potassium ion hybrid capacitors (SIHCs and PIHCs) and discuss the major challenges and give an outlook on the future directions in this field. The fundamental knowledge and the history will be firstly introduced, and special emphasis is then laid on the development of a variety of electrode materials in recent years. The prospects of future research of MIHCs are finally proposed towards their practical applications. We wish that this feature article can not only educate newcomers starting their reasearch in this field, but also inspire experieced researchers to contribute to the development of high-performance MIHC devices.

Cucurbit[6]uril-Derived Sub-4 nm Pores-Dominated Hierarchical Porous Carbon for Supercapacitors: Operating Voltage Expansion and Pore Size Matching

The intrinsic properties of carbon-based material and the voltage window of electrolyte are the two key barriers to restrict the energy density of carbon-based supercapacitors (SCs). Herein, a cucurbit[6]uril-derived nitrogen-doped hierarchical porous carbon (CBCx) with unique pore structure characteristics is synthesized and successfully applied to construct SCs based on different electrolyte systems. Owing to narrow pore size distribution (0.5-4 nm), colossal ion-accessible pore volume, prominent supermesopore volume, and reasonable heteroatom configuration, the CBCx-based SCs demonstrate excellent electrochemical performances with high operating voltages in two distinct systems. The optimal SCs can output a maximum energy/power density of 18 Wh kg^-1 (11.1 Wh L^-1 )/20 kW kg^-1 (12.3 kW L^-1 ) with an operating voltage of 1.2 V in potassium hydroxide aqueous electrolyte, as well as an ultralong cycle life of up to 50 000 cycles (0.046% decay per 100 cycles). Furthermore, the optimal SCs deliver an exceptionally high energy/power density of 95 Wh kg^-1 (58.4 Wh L^-1 )/70 kW kg^-1 (43 kW L^-1 ) with an ultrahigh operating voltage of 3.5 V in 1-ethyl-3-methylimidazolium tetrafluoroborate electrolyte. This work opens up a new application field for cucurbit[6]uril and provides an alternative avenue for optimizing the performances of carbon-based materials for SCs.

Sodium-ion capacitors: Materials, Mechanism, and Challenges

Sodium-ion capacitors (SICs), designed to attain high energy density, rapid energy delivery, and long lifespan, have attracted much attention because of their comparable performance to lithium-ion capacitors (LICs), alongside abundant sodium resources. Conventional SIC design is based on battery-like anodes and capacitive cathodes, in which the battery-like anode materials involve various reactions, such as insertion, alloying, and conversion reactions, and the capacitive cathode materials usually depend on activated carbon (AC). However, researchers have attempted to construct SICs based on battery-like cathodes and capacitive anodes or a combination of both in recent years. In this Minireview, charge storage mechanisms and material design strategies for SICs are summarized, with a focus on the battery-like anode materials from both inorganic and organic sources. Additionally, the challenges in the fabrication of SICs and future research directions are discussed.

Controllable synthesis of aluminum doped peony-like α-Ni(OH)2 with ultrahigh rate capability for asymmetric supercapacitors

Ion substitution and micromorphology control are two efficient strategies to ameliorate the electrochemical performance of supercapacitors electrode materials. Here, Al3+ doped α-Ni(OH)2 with peony-like morphology and porous structure has been successfully synthesized through a facile one-pot hydrothermal process. The Al3+ doped α-Ni(OH)2 electrode shows an ultrahigh specific capacitance of 1750 F g-1 at 1 A g-1, and an outstanding electrochemical stability of 72% after running 2000 cycles. In addition, the Al3+ doped α-Ni(OH)2 electrode demonstrates an excellent rate capability (92% retention at 10 A g-1). Furthermore, by using this unique Al3+ doped α-Ni(OH)2 as the positive electrode and a hierarchical porous carbon (HPC) as the negative electrode, the assembled asymmetric supercapacitor can demonstrate a high energy/power density (49.6 W h kg-1 and 14 kW kg-1). This work proves that synthesizing an Al3+ doped structure is an effective means to improve the electrochemical properties of α-Ni(OH)2. This scheme could be extended to other transition metal hydroxides to enhance their electrochemical performance.