Zn-ion Hybrid Supercapacitors Research Articles

Significant performance enhancement of Zn-ion hybrid supercapacitors based on microwave-assisted pyrolyzed active carbon via synergistic effect of NaHCO3 activation and CNT networks

Zinc-ion hybrid supercapacitors (ZIHSCs) represents a promising technological approach for large-scale energy storage with the combined advantages of supercapacitors and zinc-ion batteries. Unfortunately, it is still challengeable to quickly fabricate low-cost, high-performance carbonaceous cathode materials at relatively low temperature. To address such issues, herein, taking waste Eucommia ulmoides Oliver (EUO) wood as an example, we present a novel microwave-assisted carbonization (MWC) approach at relatively low temperature to quickly prepare active carbon, and we present a synergistic strategy to significantly enhance the electrochemical performance by introducing sodium bicarbonate activation (SA) and constructing conductive carbon nanotubes (CNT) networks. The MWC-SA@CNT hybrid exhibits outstanding specific capacitance of 344.2 F/g at 0.2 A/g within three-electrode system, much better than conventional high-temperature pyrolyzed AC, MWC carbon, and MWC-SA carbon. The superior performance of MWC-SA@CNT can be attributed to the synergistic effect of its large specific surface area of 1102.7 m2/g, high mesoporous percentage of 53.5%, and rich –OH and CO groups due to microwave-assisted carbonization and sodium bicarbonate activation, and rich electron transport paths due to the presence of CNT networks. Furthermore, ZIHSCs assembled by MWC-SA@CNT cathode could delivers impressive performance with excellent capacity (194.37 mA h/g at current density of 1 A/g), energy density (142.30 Wh/kg), and durability (capacitance retention rate of 97.65% after 5000 cycles). This work offers a rapid and low-temperature method for preparing wood-based active carbon with rich nanopores and strong conductivity to improve performance of Zinc ion storage.

Boosting the performance of Zn ion hybrid supercapacitors by regulating the chemically and physically active sites of graphene films.

Reduced graphene oxide (RGO) is an ideal material as an electrode used in the electrochemical energy storage field. However, the serious aggregation of graphene sheets and fewer chemically active sites limit it from exhibiting higher performance. Herein, we introduce a facile solvothermal reaction method to simultaneously regulate the functional groups on RGO, balance the aggregation and connection of graphene sheets, and dope the nitrogen element in a graphene network. The obtained electrode (RGO-N(DMF)) has a high content of carbonyl and nitrogen functional groups, and shows a fluffy structure as well as good electron conductivity, exhibiting both high chemically and physically actives sites. Benefiting from these advantages, RGO-N(DMF) shows a high specific capacity of 135 mA h g-1 at 0.2 A g-1 and favorable rate performance of maintaining 53% capacity at 50 A g-1, which are both higher than those of the normal hydrothermally obtained RGO electrodes. More interestingly, RGO-N(DMF) can maintain the high electrochemical performance at a high mass loading of 5.1 mg cm-2. In addition, when the RGO-N(DMF) electrode is used in the flexible Zn-ion hybrid supercapacitor (ZHS), the capacity retention remains at 100% after 500-time bending, showing excellent mechanical flexibility. This study not only provides an effective strategy for constructing carbon-based cathode materials with excellent properties, but also provides prospects and enlightenment for the practical application of aqueous ZHSs.

Chitin and Cellulose as Constituents of Efficient, Sustainable, and Flexible Zinc-Ion Hybrid Supercapacitors

A zinc-ion hybrid supercapacitor (ZIHS) is a prospective energy storage device featuring cost-effectiveness, operational safety, environmental friendliness, high-power performance, and satisfied energy density.1 The sustainability of this ZIHS technology is even improved by introducing biopolymer constituents into the cell construction.2 Herein, efficient, sustainable, and flexible ZIHSs employing polysaccharide (chitin- or cellulose-based) components are developed.3 Using green ionic liquid solvents, biopolymer-bound, activated carbon-based cathode materials and hydrogel biopolymer electrolytes containing conductive zinc salts are obtained. According to systematical characterization results, the prepared materials possess favorable functional properties. Biopolymer binders provide homogeneity and integrity within the electrode network and high adhesion to the surface of the current collector. Depending on the type of zinc salt, hydrogel biopolymer electrolytes display high ionic conductivity (up to 46 mS cm−1), expanded electrochemical stability window (up to ca. 2.8 V), and zinc dendrites growth suppression. Biopolymer components assembled with zinc foil electrodes operate efficiently in both coin and pouch ZIHS cell configurations, providing satisfactory energy (45–50 Wh kg−1) and high power (10–20 kW kg−1) density combined with excellent cycle stability. Moreover, these ZIHS pouch-type devices exhibit superior durability and flexibility, withstanding mechanical stress up to 150° bending states with at least 90% of capacitance retention. It suggests a prospect for their application in wearable electronics.4 References(1) Wang, Y.; Sun, S.; Wu, X.; Liang, H.; Zhang, W. Status and Opportunities of Zinc Ion Hybrid Capacitors: Focus on Carbon Materials, Current Collectors, and Separators. Nano-Micro Lett. 2023, 15 (1), 78.(2) Kasprzak, D.; Mayorga-Martinez, C. C.; Pumera, M. Sustainable and Flexible Energy Storage Devices : A Review. Energy & Fuels 2023, 37, 74–97.(3) Kasprzak, D.; Liu, J. Chitin and Cellulose as Constituents of Efficient, Sustainable, and Flexible Zinc-Ion Hybrid Supercapacitors. Sustain. Mater. Technol. 2023, 38, e00726.(4) Dubal, D. P.; Chodankar, N. R.; Kim, D. H.; Gomez-Romero, P. Towards Flexible Solid-State Supercapacitors for Smart and Wearable Electronics. Chem. Soc. Rev. 2018, 47 (6), 2065–2129. Figure 1. Graphical abstract of the research on biopolymer-based Zn-ion hybrid supercapacitors. Figure 1

Biomass nanostructure: Cattail leaves derived-porous carbon with high electrochemical performance for Zn-ion hybrid supercapacitors

Biomass-derived porous carbon possesses several advantageous characteristics, such as low cost, inherent properties, and a controllable structure, making it an ideal electrode material for Zn-ion hybrid supercapacitors (ZIHSs). In this investigation, we used cattail leaves (CLs) as the carbon source and employed carbonization and activation techniques to fabricate porous carbon. We aimed to explore the correlation between the morphology, oxygen content, and defects in porous carbon derived from CLs under varying K2CO3 ratios. Remarkably, when the K2CO3/carbon ratio was adjusted to 2:1, the resulting porous carbon from CLs exhibited outstanding electrochemical performance in ZIHSs. These ZIHSs, functioning in an aqueous electrolyte, displayed impressive rate capability, achieving 158.3 mAh g−1 at 0.1 A g−1 and 60.2 mAh g−1 at 20 A g−1, along with a high energy density of 119.5 Wh kg−1. Furthermore, they exhibited exceptional long-term durability with nearly 100 % coulombic efficiency over 10,000 cycles. Additionally, a quasi-solid-state ZIHSs device demonstrated satisfactory specific capacity (148.54 mAh g−1 at 0.1 A g−1) and maintained stability under various orientations. The abundant, renewable, and cost-efficient biomass-derived carbon obtained in this study serves as a valuable guide for the development of portable energy storage devices that are both low in cost and high in performance, thereby contributing to sustainable energy solutions.

Regulating the inner Helmholtz plane with an electrophilic cation additive enabled stacked stratiform growth for highly reversible Zn anodes

Achieving consecutive flattening and dendrite-free deposition for the zinc anodes is essential to avoid internal short circuits or premature failure in the Zn-ion hybrid supercapacitor (ZHSC), which largely depends on the crystal growth during the electrocrystallization process. Herein, the tetrapropyl ammonium bromide additive was employed to reconstruct the inner Helmholtz plane (IHP) structure for manipulating the Zn deposition behavior and stabilizing the interfacial electrochemistry. Joint experimental and theoretical results show that electrophilic quaternary ammonium cations (TPA+) provoke the linkage effect after the specifical adsorption at IHP of the Zn electrode, which includes the molecular/ion distribution regulation, electrostatic shielding effect, crystallographic optimization, and solid electrolyte interphase (SEI) layer formation. The adsorbed TPA+ cations at IHP expel SO42− anions, bringing a reconfiguration of the ion/molecule distribution, which leads to a relatively uniform Zn2+ions distribution at electrode/electrolyte interface and a sluggish electroreduction reaction kinetics. Meanwhile, the electrostatic shielding effect regulates the crystallographic energetic preference of Zn deposits and induces the stratiform Zn growth and dominant Zn (002) texture. Concomitantly, the partial interfacial adsorbed TPA+ cations were electrochemically reduced to form the inorganic-organic hybrid SEI layer to further enhance the corrosion resistance and stability of the Zn electrode. Consequently, TPA+ cations mediated electrolyte enables Zn||Zn cells to exhibit a reversible plating/stripping performance for more than 2800 h. Additionally, a long-term cycling life can be obtained in the Zn||activated carbon ZHSC with this electrolyte. The electrolyte mediation strategy to realize the complementary interface effect and crystalline optimization provides promising feasibility on highly reversible Zn anodes.

Insight into the influence of part in cattails on electrochemical performance of the porous carbon for Zn-ion storage

Recently, biomass-derived porous carbon has gained popularity as a cathode material for Zn-ion hybrid supercapacitor (ZIHSs) due to its unique structure and heteroatoms. However, the understanding of how biomass part affects resulting carbon structure and ZIHSs performance is limited. This study utilizes cattail leaves (CLs), cattail wools (CWs), and cattail stems (CSs) as carbon sources, with each impacting carbon microstructure, morphology, specific surface area (SSA), and oxygen content. CLs-based porous carbon (CLPC) exhibits a distinct hollow tube structure with thinner walls, high oxygen content, and a large SSA, which are crucial for enhanced electrochemical performance. The aqueous Zn//CLPC ZIHSs demonstrate remarkable energy density (190 Wh kg−1), specific capacity (253 mAh/g at 0.1 A/g), and cycle life (91% capacity retention over 10,000 cycles at 10 A/g). Electrochemical processes are studied through various techniques, shedding light on the relationship between cattail parts, carbon structure, and ZIHSs performance, aiding in more efficient biomass utilization.

Biomass-Derived Carbon Materials for Advanced Metal-Ion Hybrid Supercapacitors: A Step Towards More Sustainable Energy

Modern research has made the search for high-performance, sustainable, and efficient energy storage technologies a main focus, especially in light of the growing environmental and energy-demanding issues. This review paper focuses on the pivotal role of biomass-derived carbon (BDC) materials in the development of high-performance metal-ion hybrid supercapacitors (MIHSCs), specifically targeting sodium (Na)-, potassium (K)-, aluminium (Al)-, and zinc (Zn)-ion-based systems. Due to their widespread availability, renewable nature, and exceptional physicochemical properties, BDC materials are ideal for supercapacitor electrodes, which perfectly balance environmental sustainability and technological advancement. This paper delves into the synthesis, functionalization, and structural engineering of advanced biomass-based carbon materials, highlighting the strategies to enhance their electrochemical performance. It elaborates on the unique characteristics of these carbons, such as high specific surface area, tuneable porosity, and heteroatom doping, which are pivotal in achieving superior capacitance, energy density, and cycling stability in Na-, K-, Al-, and Zn-ion hybrid supercapacitors. Furthermore, the compatibility of BDCs with metal-ion electrolytes and their role in facilitating ion transport and charge storage mechanisms are critically analysed. Novelty arises from a comprehensive comparison of these carbon materials across metal-ion systems, unveiling the synergistic effects of BDCs’ structural attributes on the performance of each supercapacitor type. This review also casts light on the current challenges, such as scalability, cost-effectiveness, and performance consistency, offering insightful perspectives for future research. This review underscores the transformative potential of BDC materials in MIHSCs and paves the way for next-generation energy storage technologies that are both high-performing and ecologically friendly. It calls for continued innovation and interdisciplinary collaboration to explore these sustainable materials, thereby contributing to advancing green energy technologies.

Sub-nanopores enabling optimized ion storage performance of carbon cathodes for Zn-ion hybrid supercapacitors

Aqueous Zn-ion hybrid supercapacitors (ZHSs) are attracting significant attention as a promising electrochemical energy storage system. However, carbon cathodes of ZHSs exhibit unsatisfactory ion storage performance due to the large size of hydrated Zn-ions (e.g., [Zn(H2O)6]2+), which encumbers compact ion arrangement and rapid ion transport at the carbon-electrolyte interfaces. Herein, a porous carbon material (HMFC) with abundant sub-nanopores is synthesized to optimize the ion storage performance of the carbon cathode in ZHSs, in which the sub-nanopores effectively promote the dehydration of hydrated Zn-ions and thus optimize the ion storage performance of the carbon cathode in ZHSs. A novel strategy is proposed to study the dehydration behaviors of hydrated Zn-ions in carbon cathodes, including quantitatively determining the desolvation activation energy of hydrated Zn-ions and in-situ monitoring active water content at the carbon-electrolyte interface. The sub-nanopores-induced desolvation effect is verified, and its coupling with large specific surface area and hierarchically porous structure endows the HMFC cathode with improved electrochemical performance, including a 53 % capacity increase compared to the carbon cathode counterpart without sub-nanopores, fast charge/discharge ability that can output 46.0 Wh/kg energy within only 4.4 s, and 98.2 % capacity retention over 20,000 charge/discharge cycles. This work provides new insights into the rational design of porous carbon cathode materials toward high-performance ZHSs.

Cation-driven self-assembly of core–shell covalent organic frameworks@Ti3CN MXene nanospheres for high-performance aqueous zinc-ion hybrid supercapacitors

Rechargeable aqueous Zn-ion hybrid supercapacitors (ZISCs) with the superiorities of high theoretical capacity, low redox potential and aqueous electrolytes with superior ionic conductivity (∼1 S cm−1) are promising energy storage systems. However, a primary concern persists due to the absence of cathode materials with both high energy densities and satisfactory cycling stability for robust ZISCs. In this study, we design a spherical core–shell covalent organic frameworks@Ti3CN MXene (CM-P) cathode via a cation-driven electrostatic self-assembly strategy. The CM-P with the constructed heterostructures shows both well-organized pore channels and excellent intrinsic conductivity, facilitating fast accessibility to intrinsic redox-active sites (such as C = O and N), and promoting effective ion diffusion characterized by low energy barriers. Consequently, the CM-P cathodes demonstrate excellent electrochemical performance, featuring an ultrahigh specific capacity of 260 mAh/g at 0.1 A, a high-rate capability with 68 % retention at 1 A/g, and long-term cycling stability. First-principle calculations elucidate that the enhanced charge-storage mechanism relies on the heterostructures of CM-P, accelerating ion adsorption/diffusion and electron transfer. Furthermore, the assembled CM-P//Zn ZISCs devices show a high energy density of 217.1 Wh kg−1 along with power density of 22.3 kW kg−1. This work provides an innovative approach to design COFs-based heterostructures for advanced ZISCs.

Enhancing the supercapacitive performance of a carbon-based electrode through a balanced strategy for porous structure, graphitization degree and N,B co-doping

Regarding carbon-based electrodes, simultaneously establishing a well-defined meso-porous architecture, introducing abundant hetero-atoms and improving the graphitization degree can effectively enhance their capacitive performance. However, it remains a significant challenge to achieve a good balance between defects and graphitization degree. In this study, the porous structure and composition of carbon materials are co-optimised through a ‘dual-function’ strategy. Briefly, K3Fe(C2O4)3 and H3BO3 were hybridised with a gelatin aqueous solution to form a homogeneous composite hydrogel, followed by lyophilisation and carbonisation. Owing to the dual functionality of raw materials, the graphitization, activation and hetero-atom doping processes can occur simultaneously during a one-step high-temperature treatment. The resultant carbon material exhibits a high graphitization degree (ID/IG = 0.9 ± 0.1), high hetero-atom content (N: 9.0 ± 0.3 at.%, B: 6.9 ± 0.5 at.%) and a large specific area (1754 ± 58 m2/g). The as-prepared electrode demonstrates a superior capacitance of 383 ± 1F g−1 at 1 A/g. Interestingly, the cyclic voltammetry (CV) curves exhibit a distinctive pair of broad redox peaks, which is uncommon in KOH electrolyte. Experiment data and density functional theory (DFT) simulation verify that N-5, B co-doping enhances the activity of the faradic reaction of carbon electrodes in KOH electrolyte. Furthermore, the fabricated Zn-ion hybrid supercapacitor (ZHSC) based on this carbon electrode delivers a high-energy density of 140.7 W h kg−1 at a power density of 840 W kg−1.

Heteroatom Doping in Pollutant Diesel Soot-Derived Nanocarbon for Enhanced Zn-Ion Storage Performance.

Herein, we have isolated onion-like nanocarbon (ONC) from the exhaust soot of diesel engines and further doped it with nitrogen (N) and sulfur (S) to fabricate N,S-co-doped ONC (N-S-ONC). To explore its application feasibility, we have assembled an aqueous Zn-ion hybrid supercapacitor (ZIHSC) with a N-S-ONC cathode, which attains high specific capacitance with good rate capability. In-depth analyses suggest that the mechanism of charge storage in the ONC is governed by both capacitive-controlled and diffusion-controlled processes, with the capacitive processes leading at all sweep rates. The ZIHSC demonstrated a good energy density of 50 Wh/kg, a maximum power density of 3.6 kW/kg, and an impressive cycle life with 73% capacitance retention after 50,000 charge-discharge cycles. The study suggests the potential possibly for the long-term application of BC derived nanocarbon in electrochemical energy storage systems (EESSs).

High-performance Zn-ion hybrid supercapacitors based on biomass-derived hierarchical porous carbon through template-activated bifunctional induced and ice-crystal assisted strategy

As a highly desirable cathode material for Zn ion hybrid supercapacitors (ZHSCs), biomass-derived carbon precursor shrinks and collapses at elevated temperatures resulting in an impeded internal morphology, which severely hampers ion storage and transport. Herein, a unique porous carbon with multi-level pore structures is produced by a one-step carbonization-activation process. The Gelatin with rich functional groups is employed as the gel-state biomass precursor and the ZnCl2 acted as both a template and an activator. Furthermore, the growth of ice crystals during freeze-drying prevents the carbon framework from collapsing and self-polymerizing of ZnCl2, endowing the prepared porous carbon with a high specific surface area (1336 m2/g) and inheritance of biomass precursor heteroatoms (including N and O). Therefore, at 0.5 A/g, the prepared material displays a desirable specific capacitance of 337.6 F/g in 6 M KOH. In particular, the assembled ZHSC simultaneously shows excellent cycling performance (after 10000 cycles, the specific capacitance increases to 95.6% at 10 A/g) and high energy and power density (120.1 Wh/kg at 450 W/kg). This work provides important insights for the facile preparation of electrode materials for high-performance ZHSCs.

Dilute Aqueous-Aprotic Electrolyte Towards Robust Zn-Ion Hybrid Supercapacitor with High Operation Voltage and Long Lifespan

HighlightsA novel aqueous/aprotic electrolyte with low salt concentration (i.e., 0.5 m Zn(CF3SO3)2+1 m LiTFSI) demonstrated an expanded electrochemical window, which can simultaneously stabilize Zn metal anode and increase the operation voltage of Zn-ion hybrid supercapacitors.The coordination shell of the electrolyte induced by acetonitrile and LiTFSI can not only suppress the Zn corrosion and hydrogen evolution reaction but also promote the cathodic stability and ion migration, which is depicted by the density functional theory simulations together with experimental characterizations.The Zn-ion hybrid supercapacitor based on the developed electrolyte can operate within 0–2.2 V in a wide temperature range with an ultra-long lifespan (> 120,000 cycles).

Synergistic effects of defects and surface engineering in Ni-Co metal oxides to improve the high performance of Zn-ion hybrid supercapacitors

NiCo2O4 (NCO) is an auspicious pseudocapacitor material for high energy density zinc-ion hybrid supercapacitors (ZHSCs), but its low intrinsic conductivity and significant volume expansion seriously hinder its electrochemical performance. Here, we develop a nitrogen (N) doped and oxygen-vacancy-rich (Ov) NiCo oxide nanolines grown in-situ on the carbon cloth (CC) named N-Ov-NCO@CC. The morphology and structure of N-Ov-NCO@CC were characterized by XRD, XPS, EPR, SEM and TEM. It can be clearly observed that N-Ov-NCO@CC nanowires are composed of many tiny nanoparticles, and this unique structure provides abundant gaps at the microscopic scale, providing ample sites for the attachment of electrolyte ions. Due to N-functionalization, synergistic effects of doping, defect and surface engineering are realized. As a result, N-Ov-NCO@CC exhibits significantly enhanced electrochemical performance. The N-Ov-NCO@CC single electrode exhibits a high capacitance of 993.0 F/g (496.5C/g) at 1 A/g and excellent cycle stability with a capacitance retention rate of 98 % after 5000 cycles. In addition, the assembled N-Ov-NCO@CC//Zn-ZHSC operates stably in the voltage range of 1.2–2.0 V. A high specific capacitance of 484.4 F/g is available at current densities of 1 A/g. In addition, it still has a high cycle life with a capacitance retention rate of 97.1 % after 10,000 cycles and a high specific energy/power (50.3 Wh/kg at 300.2 W/kg). Density function theory (DFT) verification shows that N-Ov-NCO has higher conductivity than Ov-NCO and pristine NCO, which is conducive to improving electrochemical performance. This work provides a new idea for developing stable electrode materials for new ZHSCs.

Multifunctional Polyoxometalates-Based Ionohydrogels toward Flexible Electronics.

Multifunctional flexible electronics present tremendous opportunities in the rapidly evolving digital age. One potential avenue to realize this goal is the integration of polyoxometalates (POMs) and ionic liquid-based gels (ILGs), but the challenge of macrophase separation due to poor compatibility, especially caused by repulsion between like-charged units, poses a significant hurdle. Herein, the possibilities of producing diverse and homogenous POMs-containing ionohydrogels by nanoconfining POMs and ionic liquids (ILs) within an elastomer-like polyzwitterionic hydrogel using a simple one-step random copolymerization method, are expanded vastly. The incorporation of polyzwitterions provides a nanoconfined microenvironment and effectively modulates excessive electrostatic interactions in POMs/ILs/H2O blending system, facilitating a phase transition from macrophase separation to a submillimeter scale worm-like microphase-separation system. Moreover, combining POMs-reinforced ionohydrogels with a developed integrated self-powered sensing system utilizing strain sensors and Zn-ion hybrid supercapacitors has enabled efficient energy storage and detection of external strain changes with high precision. This work not only provides guidelines for manipulating morphology within phase-separation gelation systems, but also paves the way for developing versatile POMs-based ionohydrogels for state-of-the-art smart flexible electronics.

Polymer-mediated vacancy defects of graphene sheets as high-performance cathode materials for aqueous zinc-ion hybrid supercapacitors

The electrochemical behavior of graphene sheets in energy storage system is closely related to its electronic structures. Specifically, structural vacancy defects can expose more active sites and enhance the electrochemical performance. However, it is still a challenging problem to realize valid defect regulation on improving the reaction kinetics of electrode materials. Herein, vacancy-defective graphene sheets were constructed through the thermal mediated method via intercalation of polyacrylonitrile nanofibers. The vacancy defects were generated from the NH3 gas resulting from polymer decomposition at gradient carbonization temperature. The obtained composites of the graphene sheets and carbon nanofibers demonstrate that the vacancy defects benefit to charge transport, allowing more electrons to pass through the interlayered structure, and enhance the adsorption capacitance during the reversible electrochemical process. In addition, the as-assembled Zn ion hybrid supercapacitors exhibit a high energy density of 129.9 Wh kg−1 and outstanding cyclic stability (99.8 % after 10,000 cycling). The confined polymer-mediated thermal modification strategy can afford abundant vacancy defective sites and exhibit promising outlook for constructing high-performance graphene-based electrode materials for Zn ion hybrid supercapacitors.

Fallen autumn leaves – The source of highly porous carbon for Zn-ion hybrid supercapacitors

Over the years, many sophisticated synthetic two-dimensional (2D) carbon materials have become increasingly popular for supercapacitors, e.g. zinc-ion hybrid supercapacitors (ZHSC) due to their ordered structure and high energy density. Additionally, ZHSC is a very demanding device, where finding efficient materials is challenging and the energy storage mechanism remains unclear. Biomass-derived carbon materials exhibit many drawbacks due to their impurities and defective structure, low stability and poor capacitance. In this study, a ZHSC was assembled via carbonization and activation of leaves collected from city streets and utilized as a cathode material. The AC650_Zn-foil presented a high specific capacitance of 95 F·g−1 and a high energy density of 86 W·h·kg−1 at 210 W·kg−1. Furthermore, a superior power density of 40,960 W·kg−1 at 33 W·h·g−1 was presented compared to other investigated materials. In addition, we identified the processes that occurred in the following device, which demonstrated a mechanism that determines the migration of Zn ions, as well as the chemical reactions involved in Zn ions.

Layered S-Bridged Covalent Triazine Frameworks via a Bifunctional Template-Catalytic Strategy Enabling High-Performance Zinc-Ion Hybrid Supercapacitors.

Exploring covalent triazine frameworks (CTFs) with high capacitative activity is highly desirable and challenging. Herein, the S-rich CTFs cathode is pioneeringly introduced in Zn-ion hybrid supercapacitors (ZSC), achieving outstanding capacity and energy density, and satisfactory anti-freezing flexibility. Specifically, the S-bridged CTFs are synthesized by a bifunctional template-catalytic strategy, where ZnCl2 serves as both the catalyst/solvent and in situ template to construct triazine frameworks with interconnected pores and layered gaps. The resultant CTFs (CTFS-750) are employed as a reasonable pattern-like system to more deeply scrutinize the synergistic effect of S-bridged triazine and layered porous architecture for polymer-based cathodes in Zn-ion storage. The experimental results indicate that the adsorption barriers of Zn-ions on CTFS-750 are effectively weakened, and accessible Zn2+-absorption sites provided by the C─S─C and C═N bonds have been confirmed via DFT calculations. Consequently, the CTFS-750 cathode-assembled ZSC displays an ultra-high capacity of 211.6 mAh g-1 at 1.0 A g-1, an outstanding energy density of 202.7Wh kg-1, and attractive cycling performance. Moreover, the resulting flexible ZSC device shows superior capacity, good adaptability, and satisfactory anti-freezing behavior. This approach sheds new light on constructing advanced polymer-based cathodes at the atom level and paves the way for fabricating high-performance ZSC and beyond.

Molten salt-assisted fabrication of hierarchical porous carbon derived from lignite for Zn-ion hybrid supercapacitors

Zn-ion hybrid supercapacitors (ZIHCs) are considered as the most potential energy storage device. Herein, a hierarchical porous carbon was prepared by molten salt-assisted one-pot activation strategy. The molten salt synthesized lignite-derived porous carbon (MLPC) has high specific surface area (3035 m2 g−1) and unique architecture with dual majority pores of size in 1–3 nm. The assembled ZIHC delivers a high specific capacitance of 570.6 F g−1 at 0.1 A g−1 and a remarkable energy density of 82.8 W h kg−1 at a power density of 16 kW kg−1. The cell achieves good long-term cycling stability with 82.2 % capacity retention at 2 A g−1 after 5000 cycles. This study provides a facile approach to utilize lignite to fabricate superior carbon cathode for high-performance aqueous ZIHCs.

Enabling Wasted A4 Papers as a Promising Carbon Source to Construct Partially Graphitic Hierarchical Porous Carbon for High-Performance Aqueous Zn-Ion Storage.

Considering the superiorities of abundance, easy collection, low cost, and nearly constant composition, the wasted A4 papers are deemed as a recyclable and scalable carbon source to fabricate functional carbon materials for Zn-ion hybrid supercapacitors (ZIHSCs), which integrate the supercapacitors' high-power output and batteries' high energy density. Herein, the wasted A4 papers are efficiently converted into an advanced carbon material owning a hierarchical porous structure with a high surface area and interconnected multiscale channels, a graphitic structure, and a good level of N/O codoping. By taking advantage of these features, an express electron/ion transfer pathway, a large accessible surface interface, and a robust architecture are achieved for swift kinetics, numerous active sites, and excellent steadiness to afford a charming Zn2+ storage capability for the aqueous coin-type ZIHSC device (a high capacity of 244 mAh g-1 at 0.1 A g-1 with a capacity conservation of 116.4 mAh g-1 even amplifying the current density by 200 times, a supreme energy density of 190.4 Wh kg-1, a supreme power output of 18 kW kg-1, and an eminent durability of 93.8% over 10,000 cycles at 10 A g-1). Excitingly, the quasi-solid ZIHSC device also bespeaks an enjoyable capacity of 211.7 mAh g-1, a high energy density of 159.3 Wh kg-1, good mechanical flexibility, and a low self-discharge rate. This work puts forward a simple and scalable strategy to enable the wasted A4 paper as a competitive carbon source to construct advanced cathode material for Zn2+ storage.