The investigation of mechanism for electrochemical cycling process has become ever more important in supercapacitor electrode material for achieving higher stability and electrochemical performance. ...Herein, an electrochemical cycling effect has been demonstrated basing on the comprehensive study on the morphological and electronic evolution, which provides an insight into the capacity fluctuation mechanism in a typical MnO2-based supercapacitor. The results reveal that the significant changes of morphologies and chemical valence state of MnO2 take place accompanying with the intercalation of electrolyte ions (i.e. Na+) during the electrochemical cycling process. A structural reconstruction model is established to unravel the origin of microscopic changes of MnO2@carbon nanotubes (MnO2@CNTs) composites electrode and their relationships with the capacity at different electrochemical stages. It was found that the morphological and structural evolution of the electrode should be attributed to the dissolution-redeposition process of MnO2, which governed by the cation distribution near the interface between electrode and electrolyte. The ion intercalation-deintercalation process is evidenced by the oxidation state variations of Mn with the Na+ intercalation amount. Therefore, the capacity performance of MnO2@CNTs was strongly correlated with its structural and chemical states. This work will open up new perspectives for the capacity performance improvement of MnO2-based electrode materials.
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•An obvious electrochemical cycling effect was demonstrated in MnO2.•A structural reconstruction model was established.•It gives a significant insight into the energy storage mechanism of MnO2.
Aqueous zincIodine batteries are considered as a promising energy storage system due to their high energy/power density, and safety. However, polyiodide shuttling leads to severe active mass loss, ...which results in lower Coulombic efficiency and limits the cyclic life. Herein, a novel structure‐limiting strategy to pre‐embed iodide ions into Prussian blue (PBI) is proposed. The DFT calculations and electrochemical characterization reveal that the formation of FerrumIodine bond reduces the electrochemical reaction energy barrier of subsequent iodide‐ions at the pre‐embedding sites, improves the I− oxidation reaction kinetic process, and suppresses the polyiodide self‐shuttle. The PBI//Zn batteries exhibit a low Tafel slope (155 mV dec−1). Moreover, UV–vis spectroscopy confirms that the proposed strategy suppresses the polyiodide self‐shuttle. As a result, the PBI//Zn battery achieves high iodide utilization and Coulomb efficiency (242 mAh g−1 at 0.2 A g−1, CEs ≈ 100%), as well as high multiplicity performance of 197.2 mAh g−1 even at 10 A g−1(82% of initial capacity). The PBI//Zn battery also renders excellent cyclic stability with a capacity retention of 94% at 4 A g−1 after 1500 cycles. The device exhibits a high energy density of 142 W h kg−1 at a power density of 5538 W kg−1.
A novel structure‐limiting strategy to pre‐embed iodide ions into Prussian blue (PB), targeting to enhance the electrochemical performance of PB‐based zincIodine batteries is proposed. The theoretical calculations and electrochemical mechanism studies reveal that the formation of FeI bond reduces the reaction barrier and suppresses the polyiodide self‐shuttle, leading to the highest capacity of 242 mAh g−1.
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•A physical spatial-confining strategy enhances the performance of Fe2O3 electrode.•Physical separation induced by decorating Al2O3 benefits for the rate performance.•The resultant ...Fe2O3-based anode shows an excellent capacitance of 2371F g−1.•The capacitance of resultant Fe2O3-based anode retains 95.38% after 5000 cycles.•The novel-designed ASC device delivers an energy density as high as 174 W h kg−1.
Developing an anode with outstanding electrochemical properties remains a significant challenge in building high-performance asymmetric supercapacitor devices. The promising Fe2O3-based anode shows exceptional theoretical electrochemical performance but limited by its undesired practical energy density and long-term cycling stability. Herein, we propose a physical spatial-confining strategy to enhance the electrochemical performance of the Fe2O3-based electrode with tunable surface pseudocapacitance using redox electrolyte Na2SO3. By introducing Al2O3 nanograins on the surface of Fe2O3, electrolyte Na+ can diffuse through the surface-anchored Al2O3 nanograin but SO32- was physically blocked due to the Na+ ions fast diffusion nature of Al2O3 during the electrochemical operations. And a positive charge center by Na+ was formed on the side of Fe2O3, which attracts SO32- securing a stable bridge between the dissociative SO32- groups and electrode. Such a physically constrained structure ensures the fast dual-ion-involved redox reactions, leading to a significant electrochemical performance (including capacitance performance and long-term cycling stability). The Al2O3/Fe2O3-based anode delivers a high capacitance of 2371F g−1 at 5 mV s−1 with a capacitance retention of 1277F g−1 even at 200 mV s−1, which also shows superior cycling stability of 95.38% after 5000 cycles. A novel dual-electrolyte Al2O3/Fe2O3@CNTs/Na2SO3//MnO2@CNTs/Na2SO4 asymmetric supercapacitor device with a potential window of 0–2.2 V was configured, which shows the remarkable performance of energy density of 174 W h kg−1 at a power density of 4492 W kg−1.
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•A versatile recipe was proposed to obtain lattice oxygen vacancies in MnO2.•MnO2 with lattice oxygen vacancies shows enhanced elctrochemical perfromance.•The resultant LOV-MnO2 based ...cathode shows an excellent capacitance of 445.1 F g−1.•LOV-MnO2 based cathode renders capacitance retention of 96.6% after 10000-cycles.
Defect engineering has been considered as an efficient strategy to enhance the electrochemical performance of transition metal oxides based energy storage devices. However, the electrochemical activity and stability were greatly determined by the defect located crystal and external environments, which dominate the electrochemical properties of its based electrode. Thus, regulating a defect engineering recipe becomes a vital and direct route to advance the performance of the electrode materials. Herein, a versatile recipe combining the mild H-plasma and O-plasma was demonstrated for prototypical birnessite-MnO2 to achieve the robust lattice oxygen vacancies in birnessite-MnO2 (LOV-MnO2), targeting to boost its electrochemical energy storage performance. Theoretical calculation reveals the facilitated ion intercalation and diffusion kinetics due to the lower energy barrier in the LOV-MnO2. The LOV-MnO2 demonstrates an exceptional electrochemical performance with a specific capacitance as high as 445.1 F g−1 (at the current density of 1 A g−1), and the diffusion-controlled capacitance contribution reaches unprecedented ~70% (at a scan rate of 5 mV s−1). Besides, the configured symmetrical supercapacitor device LOV-MnO2//LOV-MnO2 delivers remarkable performance with an energy density of 92.3 Wh kg−1 at a power density of 1100.3 W kg−1 with a widen working voltage of 2.2 V. An outstanding cyclic life of 92.2% capacitance retention was also achieved after 10,000 charge–discharge cycles. Such superior electrochemical performance suggests that the proposed defect engineering recipes here will aid in the future development of advanced electrode materials for electrochemical energy storage devices.
Conductive 2D conjugated metal−organic frameworks (c‐MOFs) are attractive electrode materials due to their high intrinsic electrical conductivities, large specific surface area, and abundant ...unsaturated bonds/functional groups. However, the 2D c‐MOFs reported so far have limited charge storage capacity during electrochemical charging and discharging, and the energy density is still unsatisfactory. In this work, a strategy of selective center charge density to expand the traditional electrode materials to the electrode−electrolyte coupled system with the prototypical of 2D Co‐catecholate (Co‐CAT) is proposed. Electrochemical mechanism studies and density functional theory calculations reveal that dual redox sites are achieved with the quinone groups (CAT) and metal‐ion linkages (Co−O) serving as the active sites of pseudocapacitive cation (Na+) and redox electrolyte species (SO32−). The resultant electrode delivers an exceptionally high capacity of 1160 F g−1 at 1 A g−1 and a special self‐discharge rate (86.8% after 48 h). Moreover, the packaged asymmetric device exhibits a state‐of‐the‐art energy density of 158 W h kg−1 at the power density of 2000 W kg−1 and an excellent self‐discharge rate of 80.6% after 48 h. This success will provide a new perspective for the performance enhancement for the 2D‐MOF‐based energy storage devices.
A strategy of selective center charge density to expand the traditional electrode materials to the electrode−electrolyte coupled system with prototypical of 2D Co‐catecholate is proposed. The lower electron cloud density of the metal‐ion center in the Z‐axis provides the ability to attract a group of electron donors, leading to exceptionally high pseudocapacitance and energy density.
•Low-crystalline birnessite-MnO2 nanograins architecture enhances the ion diffusion kinetics and electrochemical activity significantly.•The MnO2 features high electrochemical performance of 1154 ...mF/cm2, excellent rate retention of 69 %, and almost 100% cycle stability.•The asymmetric supercapacitor device with a wide operation voltage of 2.3 V delivers a maximum areal energy density of 0.36 mWh/cm2.•In-situ Raman was utilized to explain the ion intercalation/deintercalation in low-crystalline birnessite-MnO2 nanograins.
Crystallized transition metal oxides were widely used as the electrode materials for the electrochemical energy storage devices. However, their electrochemical performance including the capacitance and rate capability was greatly hindered due to ion penetrating long distances into the bulk regimes during the electrochemical process. Herein, low-crystalline birnessite-MnO2 nanograins are obtained, which can enhance the ion diffusion kinetics and electrochemical activity significantly due to the structural disorder and defects. The resultant electrode features a superior electrochemical performance with an areal capacitance up to 1154 mF/cm2 at 2 mA/cm2 and rate retention of 69 % when the current density increasing 10 times to 20 mA/cm2 with a commercial standard mass loading about 4.58 mg/cm2. And the cycle stability measurement shows no attenuation after 10000-cycle charge/discharge operation. Moreover, assembled asymmetric supercapacitor device (wide operation voltage of 2.3 V) delivers a maximum areal energy density of 0.36 mWh/cm2 with the areal power density of 5.57 mW/cm2. The electrochemical behavior studies and in-situ Raman reveal that the structural disorder in the low-crystalline nanograins greatly facilitate the reversible ion intercalation/deintercalation process during the electrochemical cycling process. Our results will provide an instructive route for the formulation of the design principle for the high-performance of transition metal oxides electrode material.
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In aqueous zinc-based batteries, the reaction by-product Zn4SO4(OH)6·xH2O is commonly observed when cycling vanadium-based and manganese-based cathodes. This by-product obstructs ion ...transport paths, resulting in enhanced electrochemical impedance. In this work, we report a hybrid aqueous battery based on a Na0.44MnO2 cathode and a metallic zinc foil anode. The surfactant sodium lauryl sulfate is added to the electrolyte as a modifier, and the performance before and after modification is compared. The results show that sodium lauryl sulfate can generate an artificial passivation film on the electrode surface. This passivation film reduces the generation of Zn4SO4(OH)6·xH2O and inhibits the dissolution of Na0.44MnO2 in the electrolyte. Therefore, the reaction kinetics and cycle stability of the battery are significantly enhanced. A battery with this electrolyte additive delivers an initial discharge capacity of 235 mA h g−1 at a current density of 0.1 A g -1. At the same time, the battery has excellent rate performance. Under the high-rate condition of 1 A g−1, the battery still maintains a capacity retention rate of 93% after 1500 cycles. Finally, the functional mechanism of by-product inhibition by the electrolyte additive is discussed.
Mn-based aqueous electrochemical energy storage devices (AEESDs) are promising candidates for sustainable and flexible energy applications due to their environmental benignity, high theoretical ...capacity and versatile architecture. One of the effective strategies to boost their electrochemical performance is to introduce Mn2+ ions into the electrolyte, which can trigger a reversible solid/liquid reaction process of Mn2+/MnO2 deposition/dissolution with a high capacity and an ideal electrochemical kinetics. However, the complex energy storage mechanism that involves the Mn2+/MnO2 deposition/dissolution and the intrinsic insertion/extraction of proton and metal ions remains elusive and poses a great challenge for the rational design of Mn-based AEESDs. Moreover, the insufficient dissolution of MnO2 can lead to the deterioration of performance, which hinders their practical applications. To address these issues, we systematically investigate the Mn2+ ions added Mn-based AEESDs by employing a novel quasi-steady electrochemical measurement technique, and establish a kinetic evolution model to elucidate the solid/liquid reaction at different interface conditions. Furthermore, a full cell is assembled and measured to explore the real electrochemical process of Mn-based electrode with additive Mn2+ ions, which is influenced by the potential windows and charge-discharge rate. This study may provide new insights for the development of advanced AEESDs.
•The kinetics evolution model has been established by using MPSM, which visually illustrates the kinetics of Mn-based AEESDs.•The dissolution of MnO2 is insufficient due to low concentration of protons and leading to lower coulombic efficiency.•The insertion/extraction of metal cations will be eliminated as the wide potential window and fast electrochemical process.
Micro-supercapacitors (MSCs) have emerged as one of the most promising power supply candidates to meet the ever-increasing requirement for various miniaturization application scenarios due to the ...merits of high power density, long life span, superior rate capabilities and ease of maintenance and integration. However, wide applications of MSCs were greatly hindered due to the poor energy density. In this regard, designing and constructing three-dimensional (3D) architecture electrodes have been considered an effective strategy to improve the energy density of MSCs, which secures enhanced electrochemical active sites and facilitates ions kinetics for efficient charge storage capability. Herein, high-performing MSCs have been achieved with a graphene-based electrode of a rational 3D micro/nano-interconnected scaffold, in which the robust 3D architecture can be effectively regulated by controlling the amount of carbon nanotubes (CNTs). Electrochemical mechanism and theoretical simulation results reveal that enhanced electrolyte ion accessible sites and facilitated ion kinetics can be ensured since the homogeneous electric streamlines distribution in the 3D micro/nano-interconnected scaffold. As expected, the resultant MSCs possess an outstanding electrochemical performance with an areal capacitance as high as 53.49 mF cm−2 under the pack of gel-based electrolytes, delivering a power density of 25 mW cm−2 and an energy density of 8.82 μWh cm−2. Moreover, the MSCs show superior long-term stability with 99% retention after 20 000 cycles, which is beyond most reported 3D graphene-based MSCs. The 3D micro/nano-interconnected scaffold electrodes might provide a method to enhance the electrochemical performance of micro-scale power sources for the applications of micro-devices.
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The mild electrolyte working environment of rechargeable aqueous Zn-ion batteries (AZIBs) features its promising characteristic and potential application for large-scale energy ...storage system. However, the poor cycling stability significantly hinders the broad application of AZIBs due to the complex electrochemical conversion reactions during charge-discharge process. Herein, we propose a strategy to improve the electrochemical performance of AZIB by enhancing the successive electrochemical conversion reactions. With a rational design of electrode, an even homogeneous electric field can be achieved in the cathode side, resulting to significantly enhanced efficiency of successive electrochemical conversion reactions. Charge storage mechanism studies reveal that the reversibility behaviors of byproducts alkaline zinc sulfate (ZHS) can dramatically determine the H+/Zn2+ de/intercalation process, and a high reversibility characteristic ensures the facilitated electrochemical kinetics. As expected, the resultant AZIB possesses outstanding electrochemical performance with a high specific capacity of 425.08 mAh⋅g−1 at 0.1 A⋅g−1, an excellent rate capacity of about 60% (246.6 mAh⋅g−1 at 1 A⋅g−1) and superior cycling stability of 93.7% after 3000 cycles (at 3 A⋅g−1). This effective strategy and thinking proposed here may open a new avenue for the development of high-performing AZIBs.
