MnO2 Mass Research Articles

Hydrothermally decorating MnO2 onto NiCo layered double hydroxide nanosheets for electrochemical energy storage

In research out of the sustainable electrochemical energy storage material, NiCo-LDH/MnO2 composite has been prepared via simple hydrothermal method. The experimental characterizations of XRD, SEM/TEM and XPS have been utilized to explore the structure and morphology of prepared composite. The needle-like MnO2 was found adhered to NiCo-LDH sheet. The composite's electrochemical properties were evaluated through cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. It has been realized that the MnO2 dosage not only changes the composite's microstructure but also affects its electrochemical properties. The best specific capacitance (2602 F g−1 at a current density of 1 A g−1) was achieved for the composite sample with 38% MnO2 (mass), which is almost two times high from the same composite in previous reports. With the sample, the assembled asymmetric supercapacitor exhibits a remarkable energy density of 19.56 Wh.Kg−1 at 800.29 W Kg−1. It could be attributed to the synergetic effects of two components as well as their good interfacial coupling. The good electrochemical activity makes our synthesized composite feasible to be applied as electrode material and provides valuable insights for the development of smart capacitors utilizing NiCo-LDH.

A facile in‐situ fabrication of black polyimide films with ultrahigh electrical properties

AbstractConsidering the ongoing evolution of flexible printed circuit boards and the importance of safeguarding the intellectual property of circuit designs, there exists an imperative demand for the development of a black film exhibiting exceptional electrical properties and remarkable light‐shielding capabilities. Consequently, this work employs a straightforward strategy to enhance the opacity of polyimide films by incorporating carbon black (CB) and manganese dioxide (MnO2) as black fillers using an in situ doping method. Rigorous tests are conducted, analyzing properties such as dielectric constant, dielectric loss, breakdown field strength, current density, and ferroelectric energy storage. The optimal ratio of CB to MnO2 (mass fraction) is determined as 1:5, with a total powder doping amount of 6 wt%, providing the best ratio relative to the matrix resin. This ratio ensures an optimal powder dispersion state, resulting in an outstanding breakdown field of 147.4 kV/mm and ultralow dielectric constants, measuring less than 3.78 at 103 Hz. This composite film is anticipated to find applications as a cutting‐edge material for electronic devices and the semiconductor industry.

Fabrication of a 3D structure MnO2 electrode with high MnO2 mass loading as the cathode for high-performance aqueous zinc-ion batteries

Benefiting from the remarkable advantages (eco-friendly, cost-effective, and high safety) of rechargeable aqueous zinc-ion batteries (AZIBs), AZIBs are regarded as viable alternatives to traditional Lithium-ion batteries (LIBs). However, in prevailing research, the excellent electrochemical performance usually achieved by ultra-low active material loadings (e.g., <1 mg/cm²), which is far from the active material mass loading of commercial electrodes in practical (≥10 mg/cm²). Balancing superior properties with high mass loading has posed a challenge. To surmount this, an innovative method combined ultrasonic processing, freeze-drying, and 3D printing technologies is used to engineer a high MnO2 mass loading cathode for AZIBs (3D cathode). Notably, the grid structure of 3D cathode substantially augmenting the surface area for redox reactions during charge/discharge processes, which greatly enhanced the pseudo-capacitance process of cathode. Additionally, the uniform and stable microstructure exhibited the dual capability of expediting ion/electron transfer and sustaining the structural integrity throughout charge/discharge cycles. Consequently, the 3D cathode demonstrated superior comprehensive electrochemical properties at the MnO2 high mass loading of 10 mg/cm2 (138.7 mAh/g at 1 A/g, 87.4 mAh/g after 500 cycles, 82 % energy efficiency) and 15 mg/cm2 (113.3 mAh/g at 1 A/g, 56.3 mAh/g after 400 cycles, 81 % energy efficiency).

Aligned Dipoles Induced Electric-Field Promoting Zinc-Ion De-Solvation toward Highly Stable Dendrite-Free Zinc-Metal Batteries.

Water-induced parasitic reactions and uncontrolled dendritic Zn growth are long-lasting tricky problems that severely hinder the development of aqueous zinc-metal batteries. Those notorious issues are closely related to electrolyte configuration and zinc-ion transport behavior. Herein, through constructing aligned dipoles induced electric-field on Zn surface, both the solvation structure and transport behavior of zinc-ions are fundamentally changed. The vertically ordered zinc-ion migration trajectory and gradually concentrated zinc-ion achieved inside the polarized electric-field remarkably eliminate water related side-reactions and Zn dendrites. Zn-metal under the polarized electric-field demonstrated significantly improve reversibility and a dendrite-free surface with strong (002) Zn deposition texturing. Zn||Zn symmetric cell delivers greatly prolonged lifespan up to 1400h (17 times longer than that of the cell based on bare Zn) while the Zn||Cu half-cell demonstrate ultrahigh 99.9% coulombic efficiency. NH4 V4 O10 ||Zn half-cell delivered exceptional-high 132mAhg-1 capacity after ultralong 2000 cycles (≈100% capacity retention). In addition, MnO2 ||Zn pouch-cell under aligned dipoles induced electric-field maintains 87.9% capacity retention after 150 cycles under practical condition of high MnO2 mass loading (≈10mg cm-2 ) and limited N/P ratio. It is considered that this new strategy can also be implemented to other metallic batteries and spur the development of batteries with long-lifespan and high-energy-density.

Wet Spinning of Graphene Oxide Fibers with Different MnO2 Additives.

We present the fabrication of graphene oxide (GO) and manganese dioxide (MnO2) composite fibers via wet spinning processes, which entails the effects of MnO2 micromorphology and mass loading on the extrudability of GO/MnO2 spinning dope and on the properties of resulted composite fibers. Various sizes of rod and sea-urchin shaped MnO2 microparticles have been synthesized via hydrothermal reactions with different oxidants and hydrothermal conditions. Both the microparticle morphology and mass loading significantly affect the extrudability of the GO/MnO2 mixture. In addition, the orientation of MnO2 microparticles within the fibers is largely affected by their microscopic surface areas. The composite fibers have been made electrically conductive via chemical or thermal treatments and then applied as fiber cathodes in Zn-ion battery prototypes. Thermal annealing under an argon atmosphere turns out to be an appropriate method to avoid MnO2 dissolution and leaching, which have been observed in the chemical treatments. These rGO/MnO2 fiber cathodes have been assembled into prototype Zn-ion batteries with Zn wire as the anode and xanthan-gum gel containing ZnSO4 and MnSO4 salts as the electrolyte. The resulted electrochemical output depends on the annealing temperature and MnO2 distribution within the fiber cathodes, while the best performer shows stable cycling stability at a maximum capacity of ca. 80 mA h/g.

Flexible Ammonium-Ion Pouch Cells Based on a Tunneled Manganese Dioxide Cathode.

Aqueous ammonium-ion (NH4+) batteries are becoming the competitive energy storage candidate on account of their safety, affordability, sustainability, and intrinsically peculiar properties. Herein, an aqueous NH4+-ion pouch cell is investigated based on a tunneled manganese dioxide (α-MnO2) cathode and a 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) anode. The MnO2 electrode possesses a high specific capacity of ∼190 mA h g-1 at 0.1 A g-1 and displays excellent long cycling performance after 50,000 cycles in 1 M (NH4)2SO4, which outperforms the most reported ammonium-ion host materials. Besides, a solid-solution behavior is revealed about the migration of NH4+ in the tunnel-like α-MnO2. The battery displays a splendid rate capacity of 83.2 mA h g-1 even at 10 A g-1. It also exhibits a high energy density of ∼78 W h kg-1 as well as a high power density of ∼8212 W kg-1 (based on the mass of MnO2). What is more, the flexible MnO2//PTCDA pouch cell based on the hydrogel electrolyte shows excellent flexibility and good electrochemical properties. The topochemistry results of MnO2//PTCDA point to the potential practicability of ammonium-ion energy storage.

More from Less but Precise: Industry-relevant Pseudocapacitance by Atomically-precise Mass-loading MnO2 within Multifunctional MXene Aerogel

Ever-increasing mass loading of transition metal oxides (TMOs) yields high pseudocapacitance in laboratory electrochemical capacitors. However, their performance based on whole electrode mass is still far from industry standards. Highly-promising solution based on loading TMOs into 3D porous electrodes causes a yet unresolved challenge to find ways to achieve ultimate energy storage by atomically precisely loading less active material. Inspired by single-atom catalysis, we propose a new “more from less but precise” concept of homogeneously dispersing a common MnO2 TMO via atomic sites to maximize atom redox reaction efficiency for industry-relevant pseudocapacitance. The concept is materialized by multifunctional MXene aerogel with super-hydrophilicity and surface functional groups, which provides 3D atomic nucleation sites to homogeneously load in-situ-formed, covalently-bonded MnO2 nanosheets. The gravimetric capacitance of MnO2 is largely enhanced, yielding superior pseudocapacitance of >400 F/g at > 5 mg/cm2 that is typically achieved at 10 times lower loadings. Outstanding electrode areal capacitance is achieved using 2–3 times less MnO2 mass, demonstrating industry-relevant pseudocapacitance almost twice higher than in state-of-the-art devices. MnO2/MXene//MXene asymmetric supercapacitor shows practically-high energy (~50.1 Wh/kg) and power (~10.0 kW/kg) densities, among the best MnO2 pseudocapacitors. Capacitive-mechanism-controlled redox reactions, rarely achievable in diffusion-controlled porous pseudocapacitive electrodes, are revealed.

α-MnO2 nanotube@δ-MnO2 nanoflake hierarchical structure on three-dimensional graphene foam as a lightweight and free-standing supercapacitor electrode

Three-dimensional graphene foam (3D GF) is one of the promising candidates due to its fascinating characteristics. In the paper, we reported a simple hydrothermal method to fabricate hierarchical α-MnO2 nanotube@δ-MnO2 nanoflake on GF (GF@MNT@MNF) as a lightweight and free-standing electrode of supercapacitor. The 3D GF could serve as an ideal supporter to grow MnO2 active material, and MnO2 mass percentage affects significantly on the electrochemical properties of the composite electrode. When the mass percentage of MnO2 is 60%, a maximum specific capacitance of 202 F·g−1 with respect to the entire electrode and 336 F·g−1 relative to active material is achieved. The GF@MNT@MNF electrode presents a remarkable cyclic stability (maintaining about 97% of original capacitance over 5000 cycles). The excellent electrochemical performance of the GF@MNT@MNF electrode is resulted from the combination of the lightweight, flexible, conductive GFs and MnO2 hierarchical structure with large contacting interface and proper space distribution. Furthermore, an asymmetric supercapacitor based on GF@MNT@MNF composites was assembled, which showed a great energy density of 23.2 Wh·kg−1 under a power density of 119.9 W·kg −1 in wide potential range of 0–1.8 V. The research may provide a method for lightweight, free-standing and high-performance electrode material for efficient and convenient energy storage device.

Improvement in Charge Storage Capability By Synergetic Effect between RuO2 Nanosheets and MnO2 Particles

MnO2 shows fast redox behavior (Mn(Ⅲ)/Mn(Ⅳ)) and has a large overpotential for oxygen evolution reaction, hence has been used as an active material for aqueous electrochemical capacitors. MnO2 electrodes generally consists of MnO2 powder, conductive carbon and polymeric binders. However, conductivity additives and polymer binders are electrochemically non-active or poorly active for energy storage. The reduction in the amount of such additives and polymeric binder will lead to the improvement in the energy and power density. Conductive nanosheets such as MXene has been recently studied as an active binder, acting as a redox active conductive additive.1 Unfortunately, MXene has poor stability in aqueous electrolyte at high potentials due to irreversible oxidation and is not sufficient for use with MnO2 positive electrodes.2 In this work, RuO2 nanosheets with high electronic conductivity and specific capacitance is studied as an active and stable binder. 3 RuO2 nanosheets4 and MnO2 particles5 were synthesized according to literature. The MnO2-RuO2 nanosheet composite electrodes (MnO2(100-x)-RuO2(x); x=100, 80, 60, 50, 30, 20, 10, 0, x indicates the molar ratio of RuO2 ) were prepared by dropping dispersions of composite ink on a mirror-polished glassy carbon electrode. Electrochemical characterization was conducted by cyclic voltammetry using a three-electrode cell consisting of Pt mesh as a counter electrode and a Ag/AgCl (KCl sat.) reference electrode. 1.0 M Li2SO4 (25°C) was used as the electrolyte.The morphologies of MnO2(50)-RuO2(50) and MnO2(80)-RuO2(20) were analyzed by SEM-EDX. The SEM images show the presence both of particles and nanosheets. The EDX mappings show a homogeneous distribution of ruthenium atoms, and the distribution of manganese atoms agrees with the location of the particles. Figure 1 show the specific capacitance of MnO2(100-x)-RuO2(x) as a function of RuO2 nanosheet additive at scan rates of 2 and 50 mV s-1. The specific capacitance of the MnO2 particle and the RuO2 nanosheet at 2 mV s-1 were 144 and 233 F (g-material)-1, respectively. By adding 20 mol% RuO2 nanosheet to the MnO2 particle, the specific capacitance increased 188 F (g-material)-1, which was 1.3 times higher than pure MnO2 particle. While the specific capacitance of MnO2 was 23 F (g-material)-1 at 50 mV s-1, by adding 20 mol% RuO2 nanosheet, the specific capacitance increased to 155 F (g-material)-1. This is ~6.5 times higher than pure MnO2. It should be noted that the specific capacitance of MnO2 can easily be improved by adding only 20 mol% RuO2 nanosheets. To clarify the reason of the improved specific capacitance, the specific capacitances per mass of MnO2 or RuO2 were calculated. Based on the results, it is concluded that RuO2 nanosheet acts as a conductive additive for MnO2 while MnO2 acts as a spacer to suppress re-stacking of RuO2 nanosheets, thereby affording high utilization of both MnO2 and RuO2 nanosheets.This work was supported in part by a JST program on Open Innovation Platform with Enterprise Institute and Academia (OPERA JPMJOP 1843) and ISHIFUKU Metal Industry Co. Ltd. Yu, L. Hu, B. Anasori, Y. T. Liu, Q. Zhu, P. Zhang, Y. Gogotsi and B. Xu, ACS Energy Lett., 3, 1597 (2018).R. Lukatskaya, O. Mashtalir, C. E. Ren, Y. Dall’Agnese, P. Rozier, P. L. Taberna, M. Naguib, P. Simon, M. W. Barsoum and Y. Gogotsi, Science, 341, 1502 (2013). Saito, Y. Sato, D. Takimoto, S. Hedeshima and W. Sugimoto, Electrochem. In pressFukuda, T. Saida, J. Sato, M. Yonezawa, Y. Takasu and W. Sugimoto, Inorg. Chem., 49, 4391 (2010).Devaraj and N. Munichandraiah, J. Phys. Chem. C, 112, 4406 (2008). Figure 1

Scalable In Situ Reactive Assembly of Polypyrrole‐Coated MnO2 Nanowire and Carbon Nanotube Composite as Freestanding Cathodes for High Performance Aqueous Zn‐Ion Batteries

AbstractFlexible aqueous zinc‐ion batteries are attracting increasing interest owing to high theoretical capacity, low cost and high safety, however, it is highly challenging to design and fabricate suitable cathodes with superior Zn2+ storage as well as high flexibility. Herein, a free‐standing flexible film composed of carbon nanotubes and polypyrrole (PPy)‐coated MnO2 nanowires is prepared via a facile in situ reactive self‐assembly and following vacuum filtration. The unique hierarchically porous 3D architecture of uniformly dispersed MnO2 nanowires with PPy coating in highly electrically conductive and interconnected CNTs networks not only improve the reaction kinetics and structural stability of the electrodes during repeated cycling, but also provides abundant sites for Zn2+ and H+ adsorption, giving rise to additional pseudocapacitive charge storage. When the free‐standing flexible film is used as a freestanding cathode for an aqueous zinc ion battery, the electrode shows a good storage capacity of H+ and Zn2+ ions and a superior durability with a good capacity retention rate of 87.4 % after 1000 times at 1 A/g. And the energy density of the flexible device is about 341.6 Wh/kg (based on the mass of MnO2).The results provide a feasible strategy of constructing high‐performance cathodes for flexible aqueous zinc‐ion batteries.

Construction of MnO2/micro-nano Ni-filled Ni foam for high-performance supercapacitors application

The MnO2/Micro-nano Ni-filled Ni foam (MNFNF) hybrids were systematically studied as supercapacitor electrodes. Micro-nano Ni-filled Ni foam (MNFNF) was prepared via a facile NiC2O4·2H2O coating process on foam, followed by sintering treatment, and then employed as substrate for electrodeposition of MnO2. The morphology of the MNFNF substrate exhibited an obviously second-porous structure, deriving from dehydration, decarboxylation, and the lattice contraction occurred in the sintering treatment process of NiC2O4·2H2O. The structure of pores was irregular with 0.05~2 μm in diameter, and the pore walls were composed of nanoparticles with 200~500 nm in diameter. Such porous MNFNF not only provided a conductive network to enhance the charge transport and mass transfer in the electrochemical process but also achieved a large MnO2 mass loading capacity. Electrochemical test showed the MnO2/MNFNF electrode exhibited a mass specific capacitance (SC) of 723.7 F g−1 and an areal specific capacitance of 1.16 F cm−2 at a current rate of 0.25 A g−1. The asymmetric supercapacitor device based on the MnO2/MNFNF electrode and active carbon electrode could supply an energy density of 24.5 Wh kg−1 at the maximum power density of 4.4 kW kg−1. Meanwhile, the supercapacitor device also exhibited a good cycling stability along with 93.2% specific capacitance retained after 5000 cycles. These results demonstrated that the MnO2/MNFNF electrode could be one of the potential electrode material for energy storage applications.

Electrodeposition of Metal Oxides on Spray-Coated Nanostructured Carbon Framework As High Performance Electrode Materials for Asymmetric Pseudocapacitors

Combining transition metal oxides and nanostructured hierarchical carbon materials is considered as one of the best strategy to achieve high performance supercapacitors electrodes [1]. Here is reported a novel way to increase energy densities while maintaining high power densities exploiting pseudocapacitance and nanostructuration of electrode materials.In the first part of this study, carbon nanotubes/graphene/manganese dioxide nanostructured films were designed as pseudocapacitors electrodes (Fig. A). While MnO2 is a well-known pseudocapacitive cathode material and will increase energy densities [2], nanostructured carbon materials provide high electronic conductivity and specific surface. The challenge is to assemble these three materials (CNTs/G/MnO2) into a nanostructured electrode with controlled homogeneity, morphology, and composition. First, carbon nanotubes and graphene foils are associated in a specific multi-layered organization onto a current collector by dynamic spray gun deposition. It creates a controlled porous network in the electrodes. This deposition method used for nanostructuration of thin films generates homogeneous mats with tunable thickness. This structuration of the carbon nanomaterials is reproducible, easily scalable and low-cost considering that it is compatible with large surfaces. The CNTs/G multilayered structure provides a good accessibility with an appropriate porosity for ion insertion (pores of 2 to 6 nm), a high specific surface area (~360 m2/g), and an electrically conductive network (~3600 S/m), all necessary to confer high power densities. Our approach consists in synthesizing MnO2 by anodic electrodeposition directly onto the conductive nanostructured carbon framework. Electrodeposition is very versatile [3] and simply. The morphology of the manganese dioxide (shape, particles size, and mass loading) can be controlled and the electrochemical performances can be tuned by adjusting the deposition conditions. The MnO2 nanoparticles are deposited through the thickness (seen in cross section Figure A) of the carbon mat with controlled sizes ranging from 50 to 200 nm.Materials are characterized by SEM, XPS, microporosity analysis and electrochemistry. Results demonstrate that the capacitance can reach up to 220 F/g for binder free electrodes with a MnO2 mass loading of 55%. The pseudocapacitive oxide insures a faradaic contribution that enhances the specific capacitance by a factor 5 compared to the carbon nanomaterials structure only. The electrodes present an outstanding stability of 96% over 3 000 cycles in aqueous electrolytes (Na2SO4 1M). Then an asymmetric system with activated carbon as the negative electrode is developed to demonstrate the energy density increase compared to a symmetric system with activated carbon as electrodes. When adding MnO2 to the cathode the exploitable potential window can be widen up to 1.4V and the energy density increases from 1 Wh/kg to 6 Wh/kg for a power density of 0.7 kW/kg. Stability of 85% in capacitance was demonstrated for 20 000 cycles on this system.The second part of the contribution is devoted to molybdenum oxide (MoO3) that has been recently introduced as an appropriate anode material for pseudocapacitors in view of its low cost nature and high electrochemical activity [4,5]. It has been reported to be suitable in terms of potential window as a negative counterpart to manganese oxide in asymmetric pseudocapacitors [6]. This study focuses on the development of a carbon nanotubes/molybdenum oxide composite by spray-coating and cathodic electrodeposition (Fig. B). The growth of this specific metal oxide is quite complex with several possible intermediaries presenting different oxidation states depending on the environment [7]. Studies on the impact of the chemical and electrochemical conditions on the morphology, crystallinity, and homogeneity of the oxide layer are performed and thermal treatments aiming to enhance these parameters and stabilize the electrochemical performances are explored. Solubility of the deposited MoOx has been found to be a major issue in aqueous electrolytes and in that regard tests have been performed in organic electrolytes with lithium salts to insure stability of the final system. First results obtained for a simple binary MoOx-CNTs electrode already present a good maximum specific capacitance of 110 F/g. [1] National Science Review, 4, 1 (2017) 71–90 [2] Prog. Mater. Sci. 74 (2015) 51-124. [3] Ceram. Int. 44 (2018) 10863-10870. [4] Chem. Commun., 2011, 47, 10058–10060 5] Materials Letters 66 (2012) 102–105 [6] Adv. Funct. Mater. 2013, 23, 5074–5083 [7] Analytica Chimica Acta 496 (2003) 39–51 Figure 1

Constructing a Super-Saturated Electrolyte Front Surface for Stable Rechargeable Aqueous Zinc Batteries.

Rechargeable aqueous zinc batteries (RAZB) have been re-evaluated because of the superiority in addressing safety and cost concerns. Nonetheless, the limited lifespan arising from dendritic electrodeposition of metallic Zn hinders their further development. Herein, a metal-organic framework (MOF) was constructed as front surface layer to maintain a super-saturated electrolyte layer on the Zn anode. Raman spectroscopy indicated that the highly coordinated ion complexes migrating through the MOF channels were different from the solvation structure in bulk electrolyte. Benefiting from the unique super-saturated front surface, symmetric Zn cells survived up to 3000 hours at 0.5 mA cm-2 , near 55-times that of bare Zn anodes. Moreover, aqueous MnO2 -Zn batteries delivered a reversible capacity of 180.3 mAh g-1 and maintained a high capacity retention of 88.9 % after 600 cycles with MnO2 mass loading up to 4.2 mg cm-2 .

Constructing a Super‐Saturated Electrolyte Front Surface for Stable Rechargeable Aqueous Zinc Batteries

AbstractRechargeable aqueous zinc batteries (RAZB) have been re‐evaluated because of the superiority in addressing safety and cost concerns. Nonetheless, the limited lifespan arising from dendritic electrodeposition of metallic Zn hinders their further development. Herein, a metal–organic framework (MOF) was constructed as front surface layer to maintain a super‐saturated electrolyte layer on the Zn anode. Raman spectroscopy indicated that the highly coordinated ion complexes migrating through the MOF channels were different from the solvation structure in bulk electrolyte. Benefiting from the unique super‐saturated front surface, symmetric Zn cells survived up to 3000 hours at 0.5 mA cm−2, near 55‐times that of bare Zn anodes. Moreover, aqueous MnO2–Zn batteries delivered a reversible capacity of 180.3 mAh g−1and maintained a high capacity retention of 88.9 % after 600 cycles with MnO2mass loading up to 4.2 mg cm−2.

Salt-concentrated acetate electrolytes for a high voltage aqueous Zn/MnO2 battery

Aqueous rechargeable Zn/MnO2 batteries are attractive due to their low-cost, high safety and use of non-toxic materials. In term of electrolyte materials, it is anticipated that an aqueous electrolyte with a wider electrochemical window will improve the stability and energy density. In this work, we investigated salt-concentrated electrolytes based on relatively inexpensive acetate salts. An electrochemical window of 3.4 ​V was achieved in salt-concentrated 1 ​m Zn(OAc)2+31 ​m KOAc electrolyte. Its total ionic conductivity is 2.96 ​× ​10-2 ​S ​cm-1 while the ionic conductivity of Zn2+ ions is 7.80 ​× ​10-3 ​S ​cm-1, estimated by a current interrupt method. This electrolyte is regarded as a mild alkaline environment with a pH value of 9.76, causing the different storage mechanism for anode with Zn2+ ions and, cathode with OH- ions as the charge carriers respectively. A Zn/MnO2 battery was assembled using 1 ​m Zn(OAc)2+31 ​m KOAc electrolyte, self-supported α-MnO2-TiN/TiO2 cathode and Zn foil anode. The Zn/MnO2 battery can be charged to 2.0 ​V versus Zn/Zn2+ and delivers discharge capacity and energy density of 304.6 ​mAh·g-1 (calculated on the mass of MnO2) or 0.32 mAh·cm-2 (calculated on the area of electrode) and, 368.5 ​Wh·kg-1 (calculated on the mass of MnO2) or 232.7 Wh·kg-1 (calculated on the total active mass of electrodes and electrolyte) in the first cycle under a current density of 100 mA·g-1 (~ C/3, based on the mass of MnO2) or 0.1 mA·cm-2 (based on the area of electrode). During cycling, the coulombic efficiency can be maintained around 99% and reached 99.9% during the 14-340th cycles. After the cycling tests, almost no dendrites were observed on the Zn foil anode attributing to the super-high salt concentration in that acetate-based electrolyte, which will benefit the stability of aqueous Zn/MnO2 batteries.

Bi-Cation Electrolyte for a 1.7 V Aqueous Zn Ion Battery.

Rechargeable aqueous zinc-ion batteries (ZIBs) are receiving increased attention because of their high safety and low cost. However, their practical application is plagued by their low energy density as a result of low output voltage and a narrow voltage window of aqueous electrolytes. Here, we explored a ZIB with a wider potential window using bication (1 M Al(CF3SO3)3/1 M Zn(CF3SO3)2) as the electrolyte and α-MnO2 as the cathode, obtaining a discharge voltage of 1.7 V, ∼0.3 V higher than the value reported earlier. The resultant cell delivers a record high energy density of 448 W h kg-1 (based on MnO2 mass) and retains 100% capacity over 1000 cycles. The ion-storage mechanism and the role of Al3+ in enlarging the output voltage were elucidated. This research indicates the important role of using bications in improving the electrochemical performance of aqueous ZIBs, opening a new way to increase the energy density of aqueous energy storage devices.

CNT/High Mass Loading MnO2/Graphene-Grafted Carbon Cloth Electrodes for High-Energy Asymmetric Supercapacitors

HighlightsCNT/MnO2/graphene-grafted carbon cloth electrode is designed and achieves high MnO2 mass loading (9.1 mg cm−2).The electrode with favorable electronic/ionic conductivity delivers a large areal capacitance and rate capability.The assembled asymmetric supercapacitor yields a large energy density of 10.18 mWh cm−3.

Development of a New 3D Hybrid Nanostructured Carbon/MnO2 Framework By Automated Spray Coating and Electrodeposition As High Performance Electrode Material for Supercapacitor Applications

Nano-engineering of electrode through a versatile spray coating and subsequent electrochemical controlled modifications with metal oxide have been explorated toward a specific design of electroactive material targeting an increase energy densities in supercapacitors while maintaining high power densities. Exploiting pseudocapacitance and nanostructuration by combining transition metal oxides and nanostructured carbon materials in one electrode is considered as one of the best ways to achieve these performances. In this study, carbon nanotubes/graphene/manganese dioxide nanostructured films were designed as supercapacitors electrodes. MnO2 is a well-known pseudocapacitive material used to increase the energy density allowing quite good cyclability of thousand cycles. The selected carbon nanomaterials generate high conductivity and their association is an efficient way to insure large surface area to maintain a high power density. The challenge is to assemble these materials into a nanostructured electrode with controlled homogeneity, morphology, and composition. Our approach consists in synthesizing MnO2 by anodic electrodeposition directly onto the conductive nanostructured carbon framework. The association of carbon nanotubes and graphene in a specific multi-layered organization by spray aim at creating a porosity controlled network in the electrodes with highly accessible and electroactive surface. The carbon nanomaterials were deposited onto a current collector by dynamic automated spray gun deposition, an easily scalable, reproducible and industrially suitable method used for nanostructuration of thin films. Materials were characterized by SEM, XPS, microporosity analysis; their electrochemical behavior has been evaluated by cyclic voltammetry and impedance spectroscopy and their performances and cyclability by galvanostatic charge/discharge experiments. Results demonstrate that the capacitance can reach up to 190 F/g (110 F/cm3) for binder free electrodes thanks to a control of the MnO2 morphology, particle size and mass loading.

MnO2 based sandwich structure electrode for supercapacitor with large voltage window and high mass loading

The need for developing energy storage devices with high energy and power densities has motivated tremendous effort in the research of supercapacitors. Major challenges still exist in improving the working voltage window and specific capacitance of the devices. Here, we report a systematic effort in achieving remarkable supercapacitor performance. Firstly, a flexible CNT film/double side carbon tape/CNT film@MnO2 (CDC@MnO2) positive electrode with a large voltage window of 0–1.2 V was fabricated via a facial one-step water bath process. The large interfacial area created by the CDC sandwich structure enabled a high MnO2 mass loading up to 6.6 mg cm−2, resulting in a high area capacitance of 1.1 F cm−2 at a current density of 1 mA cm−2. Secondly, inspired by the superior electrochemical performance of the CDC@MnO2 positive electrode, a CDC@Fe2O3 film with area capacitance up to 339.1 mF cm−2 was fabricated as the negative electrode. Thirdly, a flexible asymmetric supercapacitor was successfully assembled which possesses a large voltage window of 0–2.1 V, a high volume capacitance of 6.8 F cm−3, and a high energy density of 4.1 mWh cm−3 at the power density of 22.3 mW cm−3.

Sputtered manganese oxide thin film on carbon nanotubes sheet as a flexible and binder-free electrode for supercapacitors

In this work, flexible carbon nanotubes (CNTs)/manganese oxide (MnO2) composite electrode was fabricated by direct deposition of MnO2 nanoparticles on CNTs sheet by RF magnetron sputtering. The surface morphology and microstructure of the CNTs and CNTs/MnO2 composite electrodes were characterized by X-ray diffraction (XRD), scanning electron microscope-energy dispersive spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. It was found that 1-μm thick MnO2 film covered the surface of CNTs sheet with MnO2 mass loading of 0.125 mg/cm2. CNTs/MnO2 composite was tested as electrode materials for supercapacitors in sulfate media (1-M H2SO4 and Na2SO4) by cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD). The results obtained showed that CNTs/MnO2 composite electrode displayed good electrochemical performance in 1-M Na2SO4, while the chemical stability of MnO2 film was highly affected due its dissolution in acidic medium. A specific capacitance of 940 F/g was retained (with a capacitance retention of about 80%) after 3000 GCD cycles. CNTs/MnO2 all-solid symmetric supercapacitor using PVA/H3PO4 gel electrolyte exhibited an initial specific capacitance 80 F/g and decreased by 25% after 3000 cycles.