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Assembling asymmetric supercapacitors (SCs) combined with ionic liquid (IL) electrolytes is a very efficient strategy to enhance the energy density of SCs. However, the poor cycle stability of pseudocapacitive metal oxides in ILs seriously affects the performance of this class of asymmetric SCs. Improving the structural stability of metal oxides during the charge/discharge process is one of the greatest challenges at present. Herein, RuO2 nano-dots/reduced graphene oxide (RGO) composites are firstly prepared, and an IL-based asymmetric SC is built using the component-optimized composite (20 wt% RuO2/RGO) as the cathode and activated polyaniline-derived carbon nanorods (denoted as APDC) as the anode. It exhibits a high energy density of 108 W h kg−1, but shows poor cycling stability. In order to solve this problem, an ultrathin carbon layer originating from glucose is employed to encapsulate RuO2 nano-dots anchoring on RGO, forming a core/shell structure of RuO2@C. With the protection of the carbon shell, the as-made RuO2@C/RGO//APDC asymmetric SC exhibits superior long-term stability with 98.5% capacitance retention after 100 000 cycles in the IL electrolyte, as well as a high energy density of 103 W h kg−1 with a potential window of 3.8 V. Furthermore, this protection mechanism of the carbon layer is analyzed by electrochemical quartz crystal microbalance experiments. [ABSTRACT FROM AUTHOR]

Although flexible all-solid-state supercapacitors (f-SSCs) have been receiving much attention as promising flexible energy storage devices, most of them cannot operate at high temperatures due to the volatility or flammability of currently used aqueous and organic electrolytes. Here, we report an ionic liquid (IL) gel-based asymmetric supercapacitor having excellent heat-resistant performance and flexibility. To this end, low-cost γ-FeOOH is firstly electrodeposited on carbon cloth, and its pseudocapacitive behavior in a typical IL is investigated through an electrochemical quartz crystal microbalance (EQCM) for the first time. The results show that the pseudocapacitance mainly originates from a diffusion-controlled insertion process of the cations. By taking advantage of the prominent pseudocapacitance of γ-FeOOH, as well as excellent characteristics of IL gel electrolytes (thermostability, non-flammability, chemical inertness and wide potential), an advanced high-temperature f-SSC is fabricated by using γ-FeOOH as the anode and porous N-doped activated carbon as the cathode. The f-SSC exhibits outstanding electrochemical performance at elevated temperatures, and can achieve a maximum volumetric energy density of 1.44 mW h cm−3 (based on the whole device volume) at 200 °C. Moreover, it is able to maintain a stable energy-storage ability during the bending process even at 180 °C, providing the highest reported temperature for flexibility tests in f-SSCs to date. [ABSTRACT FROM AUTHOR]

Rutile TiO2 embedded in carbon submicron-tablets (TiO2/C) with a “blueberry muffin” morphology was fabricated via a two-step pyrolysis from a metal–organic framework precursor. Such a unique structure of the TiO2/C submicron-tablets provides the ideal anode characteristics (high reversible capacity, superior rate capability and excellent long-term cycling stability) for fast rechargeable lithium ion batteries. [ABSTRACT FROM AUTHOR]

Lithium-oxygen (Li-O2) batteries are receiving intense interest because of their high energy density. A new tubular δ-MnO2 material prepared by a simple hydrothermal synthesis is an efficient electrocatalyst for Li-O2 batteries. The synthesized δ-MnO2 exhibits a unique tubular structure, in which the porous walls are composed of highly dispersed ultrathin δ-MnO2 nanosheets. Such a unique structure and its intrinsic catalytic activity provide the right electrocatalyst characteristics for high-performance Li-O2 batteries. As a consequence, suppressed overpotentials-especially the oxygen evolution reaction overpotential-superior rate capability, and desirable cycle life are achieved with these submicron δ-MnO2 tubes as the electrocatalyst. Remarkably, the discharge product Li2O2 of the Li-O2 battery exhibits a uniform nanosheet-like morphology, which indicates the critical role of the δ-MnO2 in the electrochemical process, and a mechanism is proposed to analyze the catalysis of δ-MnO2. [ABSTRACT FROM AUTHOR]

Pseudocapacitance is commonly associated with surface or near-surface reversible redox reactions, as observed with transition metal oxides in alkaline aqueous electrolytes. Here, we demonstrate that pseudocapacitive behavior of Fe2O3 can occur in a 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) ionic liquid (IL), and it is closely related to the chemical state variation between Fe3+ and Fe2+ on the surface of a Fe2O3 electrode during the charging/discharging process. By taking advantage of such pseudocapacitance, we prepared a promising electrode material, i.e., graphene nanosheet-supported Fe2O3 nanoparticles (denoted as Fe2O3@GNS), and then built high-performance asymmetric supercapacitors (ASs) using Fe2O3@GNS as the battery-type electrode material, commercial activated carbon (AC)/or activated polyaniline-derived carbon nanorods (denoted as APDC) as the capacitor-type electrode material, and EMIMBF4 IL as the electrolyte. The as-made ASs are able to work reversibly in a full operation voltage region of 0-4 V and exhibit very high energy density. Especially, the AS of Fe2O3@GNS//APDC achieves an extremely high energy density of 177 W h kg-1 and shows a superior combination of high energy and power density (the energy density still remains 62.4 W h kg-1 even at a high power density of 8 kW kg-1). [ABSTRACT FROM AUTHOR]

Balloon-borne or ground-based high resolution long range observation has extensive applications in border monitoring and area surveillance. Performance of long-distance oblique or horizontal imaging systems is closely related to the atmospheric transmittance of the observing spectral band. Compared with visible and near infrared, the shortwave infrared (SWIR) band benefits from less scattering effects, which enables it to provide better quality images under harsh atmospheric conditions. We present a signal-to-noise ratio (SNR) model including atmospheric influences. Based on the model, image SNR was calculated in the spectral range of 0.4 µm to 2.5 µm. In order to validate the imaging performance model of SWIR, a multi-band camera was designed and spectral imaging experiments were conducted. The results clearly demonstrated the advantage of SWIR imaging. The experiments show that the contrast and SNR of SWIR images reduced insignificantly for long distances and under low visibility conditions. This advantage makes SWIR multiband cameras suitable for long-distance remote sensing and for observing through haze. [ABSTRACT FROM AUTHOR]

Owing to their unique nanosize effect and surface effect, pseudocapacitive quantum dots (QDs) hold considerable potential for high‐efficiency supercapacitors (SCs). However, their pseudocapacitive behavior is exploited in aqueous electrolytes with narrow potential windows, thereby leading to a low energy density of the SCs. Here, a film electrode based on dual‐confined FeOOH QDs (FQDs) with superior pseudocapacitive behavior in a high‐voltage ionic liquid (IL) electrolyte is put forward. In such a film electrode, FQDs are steadily dual‐confined in a 2D heterogeneous nanospace supported by graphite carbon nitride (g‐C3N4) and Ti‐MXene (Ti3C2). Probing of potential‐driven ion accumulation elucidates that strong adsorption occurs between the IL cation and the electrode surface with abundant active sites, providing sufficient redox reaction of FQDs in the film electrode. Furthermore, porous g‐C3N4 and conductive Ti3C2 act as ion‐accessible channels and charge‐transfer pathways, respectively, endowing the FQDs‐based film electrode with favorable electrochemical kinetics in the IL electrolyte. A high‐voltage flexible SC (FSC) based on an ionogel electrolyte is fabricated, exhibiting a high energy density (77.12 mWh cm−3), a high power density, a remarkable rate capability, and long‐term durability. Such an FSC can also be charged by harvesting sustainable energy and can effectively power various wearable and portable electronics. [ABSTRACT FROM AUTHOR]

[Display omitted] • DFT results prove that Mo 2 N, Mo 3 N 2 and MoN are typically pseudocapacitive materials. • Pseudocapacitance difference is mainly caused by the work function change. • Hexagonal MoN features the best rate performance due to the smallest effective mass. • Minimal work function change of cubic Mo 2 N leads to the highest pseudocapacitance. Molybdenum nitride-based materials have been extensively investigated as pseudocapacitive materials due to their superior metallic conductivity and thermal stability. Nevertheless, few studies have focused on the origin of pseudocapacitance (C redox) differences for charged molybdenum nitride electrodes with different crystal structures. Herein, taking cubic Mo 2 N (NaCl-type), Mo 3 N 2 (CsCl-type) and hexagonal MoN (AlB 2 -type) as the research targets, we have systematically investigated the differences in rate performance and capacitance of these three materials by experimental methods and density functional theory (DFT) calculations to obtain the origin of C redox differences among them. DFT calculations prove that the proportions of C redox are 86.45%, 85.32% and 84.57% for Mo 2 N, Mo 3 N 2 and MoN and thus the Mo 2 N features the most obvious pseudocapacitive behavior. Furthermore, the rigid band approximation (RBA) method reveals that the differences of work function change (Δ W F) are the root cause of C redox differences for these three kinds of charged materials. The highest electrochemical capacitance retention, highest conductivity, and fastest K+ ion mobility indicate that the MoN possesses the best rate performance among these three materials. Additionally, the most intact nanowire morphology and smallest Δ W F of Mo 2 N enable it to possess the highest electrochemical capacitance and theoretical total capacitance (C total). The above findings will shed light on examining capacitance in a charged environment while screening the next-generation high-performance pseudocapacitive materials under various crystal structures. [ABSTRACT FROM AUTHOR]

[Display omitted] • PILs with huge cation enabled the observation of independent ions during charge. • CV and EQCM were employed to in-situ monitor energy storage behavior. • Anions that freely flow into and out of pores contributed to provide capacity. • Polycations PVBIm+ merely participated in ions transport and charge balance. • Interaction between charged particles determined ions adsorption/desorption. A fundamental understanding of the charge storage mechanism of electrochemical double-layer capacitors (EDLCs) requires an in-depth storage behavior investigation of independent ions (individual cations or anions) on the electrode surface. The direct in-situ observation for energy storage behavior of individual ions under realistic conditions remains challenge. Herein, in-situ monitoring the energy storage behavior of independent ions is realized with assistance of polymeric ionic liquids skillfully. Triangle cyclic voltammogram (CV) curves indicate that polymeric imidazole cations PVBIm+ with huge size cannot enter the active carbon pores upon charging, whereas only free anions can. The CV and electrochemical quartz crystal microbalance (EQCM) simultaneously detect ion adsorption/desorption during charging. It's proposed that ion adsorption/desorption is governed by electrostatic attraction and repulsion of charged particles. PVBIm+ are adsorbed on the electrode surface due to ion adsorption mechanism during the negative polarization and have a small capacity contribution. Free anions contribute capacitance, their number entering the pore is determined by the interaction between polycaions and anions. Moreover, PVBIm(0.1)+ with higher polymerization degree may promote desorption of polycations and prevent further adsorption of anions at higher potential in positive polarization. This work not only observes the charging behavior of independent ions, but also reveals the relevant charging mechanism through EQCM, paving the way for panorama of EDLC. [ABSTRACT FROM AUTHOR]

• A polymeric ionic liquid is synsthesized and served as an electrolyte additive. • PVEIm.TFSI can improve the electrochemical stability of EMIm.TFSI/PC based electrolytes. • The operational voltage of EDLC with PIL additive increases from 2.8 V to 3.2 V. • Equivalent circle model and bode plots demonstrate changes in interface behaviors. • PIL additive reduces each element of impedance and improves the ions diffusion. Improving the energy density of electrochemical double layer capacitors (EDLC) is an important but challenging research topic. Electrolytes with wide operating potential windows are key materials for current EDLC technology. In this work, an ether branch polymeric imidazole ionic liquid (PVEIm.TFSI) is synsthesized and served as an electrolyte additive in common electrolyte to optimize the working potential ranges of carbon-based EDLC. The addition of PVEIm.TFSI can improve the electrochemical stability of electrolytes and effectively adjust the upper limit potential (P U), lower limit potential (P L). Under the optimal addition ratio of 10%, the operational voltage of EDLC increases from 2.8 V to 3.2 V, which lead to an approximately 41.5% energy density increase compared with EDLC without additive. Cycling stabibity of EDLC containing 10% PVEIm.TFSI is significantly enhanced under both 3.0 V and 3.2 V. Furthermore, an equivalent circuit model and Bode plots are proposed from the electrochemical impedance spectroscopy (EIS) measurements. Both simulated and measured date dedicate that PVEIm.TFSI reduces each element of resistance, which result in more ions movement and smaller energy barrier for the diffusion processes, thereby improving the electrochemical performance of cells. [Display omitted] [ABSTRACT FROM AUTHOR]

Aqueous zinc ion batteries (AZIBs) have attracted much attention due to their safety, reliability, low cost, simple operation and environmental friendliness. However, the stability and safety of AZIBs are seriously affected by uncontrolled hazardous zinc dendrite growth and adverse side reactions of the zinc anode. To address these problems, we present a strategy of adding polydopamine (PDA) modified h-BN (h-BN@PDA) additive into 1 M ZnSO 4 electrolyte to inhibit Zn dendrites and construct safe batteries. The h-BN@PDA additive endows a dendrite-free electrodeposition behavior by regulating the concentration gradient of Zn2+, redistributing the uneven Zn2+ flux, and covering the formation sites of dendrites. This is mainly attributed to the combined action of redistribution of Zn2+ by h-BN and the immobilization of electrolyte anions by the catechol functional groups of PDA. Consequently, the Zn||Zn cell with h-BN@PDA additive can be cycled for more than 1700h at 0.5 mA cm−2 with a small plating/stripping overpotential of around 0.03 mV, and more than 1000h even at 1 mA cm−2. Additionally, the Zn||ZnSO 4 +h-BN@PDA||V 2 O 5 battery can render excellent stability for 1500 cycles at 10 A g−1. These results open up an opportunity for h-BN@PDA and other solid electrolyte additives in the design of advanced and durable AZIBs. [Display omitted] • The functional molecule h-BN could be chemically modified with dopamine. • The h-BN@PDA additive endowed a dendrite-free electrodeposition behavior. • The battery with h-BN@PDA additive revealed excellent electrochemical performance. • Provide insights for other functional suspension electrolytes to stabilize Zn anode. [ABSTRACT FROM AUTHOR]

Lithium titanate is a promising anode material for lithium-ion batteries, but its specific capacity and rate performance are low, which restricts its further development. In this paper, by modifying with anchoring carbon particles on the surface, the electrochemical energy storage performance of lithium titanate has been improved at a deeper voltage (0.01–3 V vs. Li+/ Li). The experimental results show that the modified lithium titanate has significant improvement in specific capacity, rate and cycle stability (305.7 mAh g−1 at 0.1 A g−1, 157 mAh g−1 at 5 A g−1, and 245.3 mAh g−1 at 0.1 A g−1 after 800 cycles). Further research found that the improvement of lithium titanate performance is mainly related to a multi-step restore of Ti4+ below 0.6 V, but not to the electrochemical redox of Ti4+/Ti3+ at 1.55 V. This work provided an effective way to promote the comprehensive electrochemical performance of LTO-based materials. Unlabelled Image • Nitrogen-doped carbon nanoparticles • Modified lithium titanate by non-full coverage carbon coating • Effectively improving the rate performance of lithium titanate as Li- battery anode [ABSTRACT FROM AUTHOR]

Perovskite-based aqueous supercapacitors have important development prospects due to their advantages of high energy density, low cost, environmental benignity. Here, bimetallic Ni-Mn and trimetallic Ni-Co-Mn perovskite fluorides are prepared via facile solvothermal method and characterized as positive electrode materials for supercapacitors. The structure, composition, chemical states and the electrochemical properties of these samples are investigated in detail. Three electrode measurements indicate that the electrochemical properties of the perovskite fluorides KNiF 3 depend on the nature and amount of dopants. Partial doping of Ni by Mn increases the rate capability but decreases the specific capacity, while Co and Mn co-doping improve both the rate capability and specific capacity of perovskite fluoride KNiF 3 . The K-Ni-Co-Mn-F (Ni/Co/Mn = 12:2:1) sample exhibits the maximum specific capacity of 211 mAh g -1 , low internal resistance and a high rate capability (82% capacity retention from 1 to 16 A g -1 ). Furthermore, the AC//K-Ni-Co-Mn-F (Ni/Co/Mn = 12:2:1) asymmetric supercapacitor delivers a maximum energy density of 50.2 Wh kg -1 . These results prove that Co and Mn co-doped KNiF 3 can be a promising material for supercapacitor., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Large Li 2 O 2 aggregations can produce high-capacity of lithium oxygen (Li-O 2 ) batteries, but the larger ones usually lead to less-efficient contact between Li 2 O 2 and electrode materials. Herein, a hierarchical cathode architecture based on different discharge characteristics of α-MnO 2 and Co 3 O 4 is constructed, which can enable the embedded growth of large Li 2 O 2 aggregations to solve this problem. Through experimental observations and first-principle calculations, it is found that α-MnO 2 nanorod tends to form uniform Li 2 O 2 particles due to its preferential Li + adsorption and similar LiO 2 adsorption energies of different crystal faces, whereas Co 3 O 4 nanosheet tends to simultaneously generate Li 2 O 2 film and Li 2 O 2 nanosheets due to its preferential O 2 adsorption and different LiO 2 adsorption energies of varied crystal faces. Thus, the composite cathode architecture in which Co 3 O 4 nanosheets are grown on α-MnO 2 nanorods can exhibit extraordinary synergetic effects, i.e., α-MnO 2 nanorods provide the initial nucleation sites for Li 2 O 2 deposition while Co 3 O 4 nanosheets provide dissolved LiO 2 to promote the subsequent growth of Li 2 O 2 . Consequently, the composite cathode achieves the embedded growth of large Li 2 O 2 aggregations and thus exhibits significantly improved specific capacity, rate capability, and cyclic stability compared with the single metal oxide electrode.

In this work, MnCoNiO x (denoted as MCNO) nanocrystals (with a size of less than 30 nm) finely encapsulated in double-carbon (DC, including reduced graphene oxide and amorphous carbon derived by polymer) composite nanofibers (MCNO@DC) were successfully synthesized via an electrospinning method followed by a sintering treatment. The as-obtained MCNO@DC nanofibers present superior sodium storage performance and retain an especially high specific capacity of 230 mAh g -1 with a large capacity retention of about 96% at 0.1 A g -1 after 500 cycles and a specific capacity of 107 mAh g -1 with capacity retention of about 89% at 1 A g -1 after 6500 cycles. The outstanding cycle characteristic is mainly due to the tiny MCNO nanoparticles, which shorten the ion migration distance, and the three-dimensional DC framework, which remarkably promotes the electronic transfer and efficiently limits the volume expansion during the progress of insertion and extraction of Na + ions. Moreover, nitrogen doped in carbon is able to improve the electrochemical capability as well. Finally, kinetic analysis of the redox reactions is used to verify the pseudocapacitive mechanism in charge storage and the feasibility of using MCNO@DC composite nanofibers as an anode for sodium-ion batteries with the above-mentioned behavior.