Wide Operating Voltage Window Research Articles

One-step rapid prototyping of recyclable ultrathin CNF/MWCNT/Fe-based spinel oxide asymmetric interdigital nanopaper electrodes for high performance flexible supercapacitors

Flexible asymmetric supercapacitors (FASCs) are potential energy storage devices for wearable electronics, considering that these have a wide operating voltage window, high specific capacity, and high energy density. However, achieving high energy density through the optimization of structure and electrode remains a challenge. Herein, two electrode inks with exceptional homogeneity nature and stability are prepared by using in-situ grown Fe-based spinel oxide (MFe2O4 = Fe3O4/MnFe2O4) on multi-walled carbon nanotubes (MWCNT) combined with eco-friendly and renewable cellulose nanofiber (CNF). Meanwhile, ultrathin flexible asymmetric interdigital nanopaper electrodes (NFT@MnFe and NFT@Fe) with customized patterns are fabricated through a one-step mask-assisted vacuum filtration strategy by using the obtained electrode inks. The planar interdigital FASC device based on the NFT@MnFe cathode and the NFT@Fe anode has excellent area specific capacity (309.8 mF cm−2), energy density (110.2 μW h cm−2), and power density (0.47 mW cm−2). The FASC maintain over 95 % of the original capacity after 5000 charge/discharge cycles. Noteworthy, a stacked interdigital FASC can be achieved with an energy density of up to 273.8 μW h cm−2 at 0.47 mW cm−2 power density, combining the structural benefits of planar interdigital and sandwich-type devices.

Mullite Mineral-Derived Robust Solid Electrolyte Enables Polyiodide Shuttle-Free Zinc-Iodine Batteries.

Zinc dendrite, active iodine dissolution, and polyiodide shuttle caused by the strong interaction between liquid electrolyte and solid electrode are the chief culprits for the capacity attenuation of aqueous zinc-iodine batteries (ZIBs). Herein, mullite is adopted as raw material to prepare Zn-based solid-state electrolyte (Zn-ML) for ZIBs through zinc ion exchange strategy. Owing to the merits of low electronic conductivity, low zinc diffusion energy barrier, and strong polyiodide adsorption capability, Zn-ML electrolyte can effectively isolate the redox reactions of zinc anode and AC@I2 cathode, guide the reversible zinc deposition behavior, and inhibit the active iodine dissolution as well as polyiodide shuttle during cycling process. As expected, wide operating voltage window of 2.7V (vs Zn2+/Zn), high Zn2+ transference number of 0.51, and low activation energy barrier of 29.7kJ mol-1 can be achieved for the solid-state Zn//Zn cells. Meanwhile, high reversible capacity of 127.4 and 107.6 mAh g-1 can be maintained at 0.5 and 1 A g-1 after 3000 and 2100 cycles for the solid-state Zn//AC@I2 batteries, corresponding to high-capacity retention ratio of 85.2% and 80.7%, respectively. This study will inspire the development of mineral-derived solid electrolyte, and facilitate its application in Zn-based secondary batteries.

Three-Dimensional Vanadium and Nitrogen Dual-Doped Ti3C2 Film with Ultra-High Specific Capacitance and High Volumetric Energy Density for Zinc-Ion Hybrid Capacitors.

Zinc-ion hybrid capacitors (ZICs) can achieve high energy and power density, ultralong cycle life, and a wide operating voltage window, and they are widely used in wearable devices, portable electronics devices, and other energy storage fields. The design of advanced ZICs with high specific capacity and energy density remains a challenge. In this work, a novel kind of V, N dual-doped Ti3C2 film with a three-dimensional (3D) porous structure (3D V-, N-Ti3C2) based on Zn-ion pre-intercalation can be fabricated via a simple synthetic process. The stable 3D structure and heteroatom doping provide abundant ion transport channels and numerous surface active sites. The prepared 3D V-, N-Ti3C2 film can deliver unexpectedly high specific capacitance of 855 F g-1 (309 mAh g-1) and demonstrates 95.26% capacitance retention after 5000 charge/discharge cycles. In addition, the energy storage mechanism of 3D V-, N-Ti3C2 electrodes is the chemical adsorption of H+/Zn2+, which is confirmed by ex situ XRD and ex situ XPS. ZIC full cells with a competitive energy density (103 Wh kg-1) consist of a 3D V-, N-Ti3C2 cathode and a zinc foil anode. The impressive results provide a feasible strategy for developing high-performance MXene-based energy storage devices in various energy-related fields.

Synthesis and application of NiLa-layered double hydroxides on nickel-coated carbon nanotubes with Co-ZIF-67 composite in supercapacitors

Owing to the global climate emergency, there is considerable interest in new energy generation and storage solutions. Supercapacitors have many desirable properties of particular interest for energy storage. However, they have low energy densities, which must be improved. Materials based on zeolite imidazole skeletons (ZIFs) have uniform pores, large specific surface areas, and simple structures. Moreover, Co-ZIF-67 has high electrical conductivity, which makes it a promising candidate for energy storage applications. In this study, a Co-ZIF-67 precursor with a regular cubic structure is synthesized. This precursor is combined with Ni-coated carbon nanotubes (Ni-CNTs) and NiLa-layered double hydroxides (NiLa-LDHs). Thus, by controlling the hydrothermal reaction time, an electrode material with a nanosheet structure is applied to the CNTs. Electrochemical analysis shows that the resulting Co-ZIF-67/Ni-CNT@NiLa-LDH composite has a specific capacitance of 1710 F g−1 at a current density of 1 A g−1. The composite is combined with activated carbon (AC) to produce a Co-ZIF-67/Ni-CNT@NiLa-LDH//AC asymmetric supercapacitor, which exhibits outstanding capacitive performance (150.1 F g−1 at a current density of 1 A g−1), a wide operating voltage window (1.7 V), and outstanding stability.

1D Layered LiVO3 Nanorods Synthesized by Ultrasonic‐Assisted Chemical Route for Supercapacitor Applications

Herein, 1D layered lithium vanadate (LiVO3) nanorods are successfully synthesized using a facile ultrasonic‐assisted chemical route using V2O5 as the starting material. The as‐prepared LiVO3 nanorods are characterized by X‐ray diffraction, X‐ray photoelectron spectroscopy, and field emission scanning electron microscopy techniques. The reaction and growth mechanism of LiVO3 nanorods formation are provided. The synthesized LiVO3 nanorods are used as electrode material for supercapacitor applications and exhibit a high specific capacitance of 426.2 F g−1 at 0.5 A g−1. Additionally, the LiVO3 // AC asymmetric coin cell supercapacitor device fabricated with LiVO3 as the cathode shows an excellent energy density of 25.4 Wh kg−1 at a power density of 228.5 Wkg−1 along with superior cyclic stability of ≈80% after 5000 cycles and wide operating voltage window of 1.6 V. Density functional theory studies show that the decrease in the bandgap of the LiVO3 is one of the intrinsic reasons that the conductivity and capacitive charge storage performance are greatly improved over V2O5. This design of a 1D layered LiVO3 nanorods presented in this work will provide a path to discover high performing electrode materials for supercapacitor applications.

Decoupling the Trade‐Off Between the Photosignal and Photonoise in Upconversion Devices Through a Solution‐Processed Nickel Oxide Interconnecting Layer

AbstractNear‐infrared (NIR) to visible upconversion devices (UCDs) provide a viable and cost‐effective way for NIR visualization and pixel‐less imaging techniques. An excellent electrical connection between the NIR detection unit and the visible emission unit in the UCD is one of the prerequisites for achieving efficient upconversion performance. In this study, a low temperature‐ and solution‐processed nickel oxide (NiOx) interconnecting layer (ICL) with high hole mobility and favorable energy levels is demonstrated to decouple the trade‐off between photosignal and photonoise in the UCDs. The use of such a NiOx ICL suppresses intrinsic visible emission in the dark (photonoise) but enhances visible light output under NIR illumination (photosignal) by triggering an efficient charge injection in the UCDs. As a result, a hybrid UCD monolithically integrating an organic NIR photodetector and a visible quantum dot light‐emitting diode via the NiOx ICL achieves excellent performance, exhibiting an ultralow turn‐on voltage as low as 1.6 V, a high luminance close to 6.3 × 103 cd m−2, a wide operation voltage window up to 7.4 V, and a high contrast ratio reaching 5 × 104. The resulting UCD is also used for imaging demonstrations showing clear visible images of the NIR targets, which paves the way for practical applications.

Exceptionally flexible and stable quasi-solid-state supercapacitors via salt-in-polyampholytes electrolyte with non-freezable properties

Hydrogel electrolytes have been intensively studied for a decade, due to their outstanding intrinsic physical properties, such as good flexibility, high stretchability, and high ionic conductivity. However, due to their low mechanical strength (<103 Pa) and poor ionic conductivity (<1 mS/cm) at low temperatures, many researchers have been focusing on improving these issues. Thus, in our study, we prepared salt-in-polyampholytes (SIPAs) that have two different counterions (Li+ and Cl-) in an aqueous medium via facile one-step UV radical polymerization. Polyampholyte (PA) improves the toughness and elongation by inducing strong ionic interactions between opposite charges in the polymer chains, but also exhibits excellent recovery ability under periodically changing strain and strong adhesion with electrodes. Furthermore, the incorporation of LiCl salt into our PA results in SIPA with high ionic conductivity at 25 °C (134 mS/cm) and even at sub-zero temperatures (15 mS/cm). Consequently, the non-freezable SIPA-based quasi-solid-state supercapacitor (QSS), assembled with activated carbon electrodes, exhibits a wide operating voltage window as high as 2.0 V, a high specific capacitance of 241 F/g, and high energy (34 Wh/kg) and power (598 W/kg) densities, along with excellent cycling stability, retaining 91 % of the initial capacitance even after 20,000 cycles at 1 A/g. Besides, the QSS electrochemical performance remains unaffected under bending and rolling deformations at a low temperature, demonstrating excellent mechanical, thermal, and electrochemical stability of our system. This work provides an effective strategy for designing energy storage devices that are both foldable and reliable, making them suitable for use in extreme environments.

One-step fabrication of N/O self-doped porous carbon derived from 2-MeIM for high-performance supercapacitor electrode

Doping engineering is a high-efficiency strategy to introduce heteroatom species and modify the surface electronic structures of porous carbon materials. However, the conventional doping strategies for porous carbons usually involve with either complicated fabrication processes or difficulty in quality control. Herein, nitrogen‑oxygen self-doped porous carbons (NOPCs) with adjustable structure are prepared by a facile one-step process of direct carbonization/activation the mixture of 2-methylimidazole (2-MeIM) and KOH. The as-prepared NOPCs possess hierarchical porous structure with interconnected micro-/meso-/macropores, high specific surface area (2900 m2 g−1), large pore volume (1.2 cm3 g−1) and high N,O heteroatoms level (26.8 at.% in total), which exhibit ultra-high specific capacitance of 424.2 F g−1 at 1.0 A g−1 in a three-electrode system in 2 M KOH electrolyte and 173.4 F g−1 at 1.0 A g−1 in a two-electrode system in EMIMBF4 ionic liquid electrolyte. Impressively, the symmetric supercapacitor based on NOPC exhibits a wide operating voltage window up to 3 V, a high energy density of 56.4 Wh kg−1 at a power density of 373.6 W kg−1, excellent rate performance with the retention of ~76.2 % from 1.0 to 100 A g−1, and splendid cycling stability with only 0.0011 % capacity fading per cycle within 10,000 loops. Consequently, the one-step carbonization/activation strategy with commercial-available 2-MeIM as raw material is promising for mass production of high performance NOPC materials.

Laser writing of graphene‑tin hybrid composite-based supercapacitor for battery-like performance

Supercapacitor (SC) with a wide operation voltage window in an aqueous electrolyte is a critical key for boosting energy, overcoming safety and fabrication cost obstacles. Thus, tin dioxide/graphene (SGO) was synthesized using one-pot method for easy and hybrid metal oxide decoration on graphene sheet. Laser writing (LW) technique was employed to enhance SGO active material's electrochemical performance through high-power laser irradiation of two different optical ranges 355 and 1046 nm. Photothermal laser processing achieved ternary Sn-SnO2-RGO composition of specific capacitance to ~872 and 385 F/g at 5 mV/s and 1 A/g, respectively. Nanosecond laser pulses induced extensive SGO exfoliation and redistribution of reduced tin metal on graphene sheets' edges. Laser-processed SGO SCs offer a battery-like energy density of 173 Wh/Kg at 1 A/g coupled with high power of 283 kW/Kg at 80 A/g. Interestingly, the retention at a high current of 80 A/g is nearly >99.6 %, which suggests a strong coupling between tin metal/tin dioxide and graphene 3D conductive networking. LW impact on capacitive performance was deliberately guarded by photothermal and photochemical interactions. SGO-based SCs binder-free electrodes were conducted to Raman spectroscopy, X-ray diffraction, different electron imaging, elemental analysis and extensive electrochemical characterization.

Electrochemical performance of SrMoO4 as electrode material for energy storage systems

In this work, strontium molybdenum oxide (SrMoO4) is reported as electrode material for supercapacitors (SCs). The physico-chemical properties of SrMoO4 were investigated and tested for capacity performance by employing cyclic voltammetry (CV), chronopotentiometry (CP), and electrochemical impedance spectroscopy (EIS). SrMoO4 showed significant specific capacity of 384 C g−1 at 5 mVs−1 with good cyclic stability and capacity retention of 91.1% upto 3000 GCD cycles at current density 1 Ag−1. Also, the as-fabricated SrMoO4 showed the coulombic efficiency and energy efficiency of 81.2% and 82.6% respectively over 5000 GCD cycles. The substantial by active surface area and increased abundance of reactive sites, revealed by the morphological analysis contributed for the higher specific capacity. The lowest values of Rs and Rct exhibited by SrMoO4 such as 2.21 Ω and 1.31 Ω, respectively predicted the faster reaction kinetics. Furthermore, symmetric supercapacitor device (SSD) was also assembled and it exhibited a wide operating voltage window of 1.6 V, with an energy density of 67.3 Wh kg−1 at a power density of 3150 Wkg−1. The pseudocapacitive performance of SrMoO4 was attributed to its unique structure, which enabled fast ion /electron transport and low solution resistance. The electrochemical results demonstrated that SrMoO4 could be utilized as electro-active material for SCs.

Construction of high-performance solid-state asymmetric supercapacitor based on Ti3C2Tx MXene/CuS positive electrode and Fe2O3@rGO negative electrode

The reasonable and logical construction of electrode materials along with greater electrochemical features and solid architectural design is an effective strategy for boosting the electrochemical performance of supercapacitors. In this paper, Ti3C2Tx MXene/CuS composites have been synthesized using an electrostatic attraction connection of negatively charged 2D few-layered Ti3C2Tx MXene sheets with positively charged CuS nanoparticles and are investigated as an asymmetric supercapacitor active material. The addition of MXene enhances the conductivity and specific surface area of the MXene/CuS electrode compared to their individual components. The as-prepared MXene/CuS electrode exhibits a high specific capacity (1541.6C g−1 (2569.3 F g−1)) at 1 A g−1 and an excellent cycle performance with 93.5 % capacity retention after 10,000 cycles. Furthermore, Fe2O3 nanoparticles/reduced graphene oxide (rGO) nanosheets (Fe2O3@rGO) composite electrode is also produced. The designed Fe2O3@rGO negative electrode with a wide operation voltage window of 1.1 V can deliver a capacity of 255.6C g−1 at 1 A g−1. Ultimately, the MXene/CuS//Fe2O3@rGO device displays energy density of 74.1 Wh kg−1 and power density of 849.8 W kg−1. In addition, the ASC shows excellent cycling stability of 91.3 % capacity retention after 10,000 cycles.

Exploring potassium trifluoroacetate as a novel electrolyte for enhancing energy density of biomass-derived carbon-based supercapacitors and improving electrolyte-electrode adaptability

Improving the energy density by expanding the operating voltage of electrolytes and enhancing the charge storage capacity of electrode materials is crucial for the development of supercapacitors. This work proposes a potassium trifluoroacetate (CF3COOK, CFK) electrolyte for improving the energy density of supercapacitors without sacrificing the high power density and long-cycle performance while developing honeycomb-like interconnected hierarchical porous carbons (HIHPCs) with controlled pore size distribution, large specific surface area (3028 m2 g−1), interconnected pore structure, and high electrical conductivity (2.01 S cm−1) from waste biomass to match the proposed CFK electrolyte for harvesting high charge storage capability. The prepared HIHPCs exhibit excellent electrochemical performance in the proposed CFK electrolyte, achieving a high specific capacitance of up to 409 F g−1 over a wide operating voltage window of −1.0 to 0.9 V, with high coulomb efficiency, low internal resistance, good rate capability, and perfect electrochemical stability. Symmetric supercapacitors constructed using the obtained HIHPCs and the proposed CFK electrolyte can operate stably at 1.9 V and deliver high specific energy of 24.8 Wh kg−1 at 237.8 W kg−1 with good cycling stability. The effectiveness of the proposed CFK electrolyte as an ideal electrolyte with extended electrochemical stability windows to significantly improve the energy density of aqueous supercapacitors was verified. This work presents a promising approach for developing high-performance aqueous supercapacitors with potential applications in renewable energy systems.

Achieving high area capacitance of Ti3C2Tx//MnO2 flexible aqueous zinc-ion hybrid microsupercapacitors with wide operating voltage window

Aqueous zinc-ion hybrid supercapacitors (AZIHSs) are extensively studied as a new kind of electrochemical energy storage devices that combine advantages of capacitors and batteries. It is highly desirable to develop AZIHSs with flexibility and miniaturization with the fast development of portable and wearable electronic devices. Herein, flexible aqueous zinc-ion hybrid microsupercapacitors (FAZIHMs) based on Ti3C2Tx anode and MnO2 cathode are constructed, which can successfully operate under 2.0 V voltage window and deliver a high area capacitance up to 252.8 mF/cm2 at 1 mV/s. The Ti3C2Tx//MnO2 FAZIHMs still maintain above 70.8 % capacitance retention with 94.5 % coulombic efficiency after 5000 successive cycles at 11.5 mA/cm2. Furthermore, favorable electrochemical performances are achieved under a series of mechanical bending levels with bending angles ranging from 0° to 90° for the Ti3C2Tx//MnO2 FAZIHMs. A LED and an electronic thermometer can be switched on simultaneously by the two above Ti3C2Tx//MnO2 FAZIHMs in series connection after being fully charged. This study of the FAZIHMs built upon Ti3C2Tx anode and MnO2 cathode with a high area capacitance and a wide operating voltage window aims at opening up a new way to exploit next-generation flexible and miniature electrochemical energy storage devices.

The Morphology-Controllable Synthesis of Ni–Co–O Nanosheets on a 3D Porous Ni Template as a Binder-Free Electrode for a Solid-State Symmetric Supercapacitor

In this work, a porous Ni template (Ni–Co–O@3D Ni) with Ni–Co oxide nanosheets (Ni–Co–O)@3D was synthesized by incorporating Ni–Co oxide nanosheets within a 3D porous Ni template as a binder-free electrode for a supercapacitor. The 3D Ni template was synthesized with hydrogen bubble templates that possessed different applied voltages that marked differences in terms of physicochemical properties, as well as factors that affect the subsequent growth of Ni–Co–O nanosheets. Then, Ni and Co metal ion sources were introduced to produce the morphology adjustment of Ni–Co–O@3D Ni with a multiple hierarchical architecture with a hydrothermal process. Field emission scanning electron microscopy (FESEM), X-ray absorption spectroscopy (XAS), and an electrochemical analysis were employed to investigate the morphological, structural, and electrochemical characteristics. FESEM and XAS results evidenced that Ni–Co–O@3D Ni consists of a 3D, well-designed hierarchical interconnected network, and the local electronic structure change has a great influence on the capacitive performance. The electrochemical results of Ni–Co–O@3D Ni displayed an excellent electrochemical performance due to the synergistic effect of Ni and Co on Ni–Co–O@3D Ni, which possessed multiple oxidation states to enable various reversible Faradaic redox reactions. Remarkably, the solid-state symmetric supercapacitor fabricated with Ni–Co–O@3D Ni exhibited excellent capacitive behaviour at a wide operating voltage window and cycling performance. Also, the as-assembled solid-state symmetric supercapacitor (two devices in series) can successfully illuminate a desired parallel pattern consisting of 36 red LED lights, demonstrating its practical application as a supercapacitor.

Flexible Electro‐Optical Perovskite/Electrolyte Synaptic Transistor to Emulate Photoelectric‐Synergistic Neural Learning Rules and Reflex‐Arc Behavior

AbstractThe design and fabrication of a flexible electric‐optical perovskite/electrolyte synaptic transistor are demonstrated for the first time, which emulates important neuromorphic functions under dual‐mode modulation. Benefiting from the bipolar charge transport properties of light‐harvesting perovskite and the high specific capacitance and mechanically robust multi‐ion electrolyte, the device exhibits bidirectional plasticity, better reliability, retaining &gt;70% of the initial current level after 2500 flex per flat laps, and a very wide operating voltage window from 0.04 to 10 V, and responsive to ultralow stimuli down to tens of millivolt level with femtojoule‐level energy consumption. The synergistic high response under dual‐mode modulation enables the device to emulate complex neural learning rules and achieve neuromorphic applications, including classical conditioning and spatiotemporal learning, and image recognition tasks with higher accuracy of 81%. Moreover, an enhanced artificial reflex‐arc behavior is emulated by employing the flexible electro‐optical artificial synapses that serve as key information‐receiving‐processing units to manipulate the actions of electrochemical artificial muscles to a larger extent. These properties show great potential in soft neurorobotic systems and prostheses.

Microwave-Assisted Rational Designed CNT-Mn3 O4 /CoWO4 Hybrid Nanocomposites for High Performance Battery-Supercapacitor Hybrid Device.

Extensive research interest in hybrid battery-supercapacitor (BSH) devices have led to the development of cathode materials with excellent comprehensive electrochemical properties. In this work, carbon nanotube (CNT)-Mn3 O4 /CoWO4 triple-segment hybrid electrode is synthesized by using a two-step microwave-assisted hydrothermal route. Systematic physical characterization revealed that, with the assistance of microwave, granular Mn3 O4 and spheroid-like CoWO4 with preferred orientation, and oxygen vacancies are stacked or arranged on CNTs skeletons to construct a rational designed hybrid nanocomposite with abundant heterointerfaces and interfacial chemical bonds. Electrochemical evaluations show that the synergistic cooperation in CNT-Mn3 O4 /CoWO4 resulted in an ultra-high specific capacity (1907.5Cg-1 /529.8mAhg-1 at 1Ag-1 ), a wide operating voltage window (1.15V), the satisfactory rate capability (capacity maintained at 1016.5Cg-1 /282.3mAhg-1 at 15Ag-1 ), and excellent cycling stability (117.2% initial capacity retention after 13000 cycles at 15Ag-1 ). In addition, the assembled CNT-Mn3 O4 /CoWO4 //N doped porous carbon (NC) BSH device delivered a stable working voltage of 2.05V and superior energy density of 67.5Whkg-1 at power density of 1025Wkg-1 , as well as excellent stability (92.2% capacity retained at 5Ag-1 for 12600 cycles). This work provides a new and feasible tactic to develop high-performance transition metal oxide-based cathodes for advanced BSH devices.

Rational design of hierarchically nanostructured NiTe@CoxSy composites for hybrid supercapacitors with impressive rate capability and robust cycling durableness

The hierarchically nanostructured NiTe@CoxSy composites are constructed on a foamed nickel substrate by a two-step electrode preparation process. Structural characterization shows the dense growing of CoxSy nanosheets around NiTe nanorods forms a hierarchical nanostructure which possesses synergetic effects from both compositional and structural complementarity, more pathways for ion/electrolyte transport, richer redox active sites, and better conductivity. Thanks to the rational design of this hierarchical structure, NiTe@CoxSy delivers a high areal capacitance of 7.7F cm−2 at 3 mA cm−2 and achieves the improved capacitance retention of 97.9% after 10,000 cycles. Of particular importance is the successful fabrication of NiTe@CoxSy//activated carbon hybrid supercapacitors. This hybrid device has a wide operating voltage window, high areal energy density of 0.48 mWh cm−2 at 2.55 mW cm−2, impressive rate capability of 62.3% even after a 20-fold increase of the current density, and a 115.1% of initial capacitance retention after 15,000 cycles. Meanwhile, two tandem such hybrid devices can easily drive a pair of mini fans or light up a heart-like pattern assembled by 10 red LEDs. These experimental results not only demonstrate that the hierarchically nanostructured NiTe@CoxSy composites can serve as a prospective candidate electrode; but also develop a novel strategy about how to achieve high-performance stockpile equipment by rationale designing a desirable nanostructures.

High-performance flexible all-solid-state asymmetric supercapacitors based on binder-free MXene/cellulose nanofiber anode and carbon cloth/polyaniline cathode

The search for wearable electronics has been attracted great efforts, and there is an ever-growing demand for all-solid-state flexible energy storage devices. However, it is a challenge to obtain both positive and negative electrodes with excellent mechanical strength and match positive and negative charges to achieve high energy densities and operate voltages to satisfy practical application requirements. Here, flexible MXene (Ti3C2Tx)/cellulose nanofiber (CNF) composite film negative electrodes (MCNF) were fabricated with a vacuum filtration method, as well as positive electrodes (CP) by combining polyaniline (PANI) with carbon cloth (CC) using an in-situ polymerization method. Both positive and negative free-standing electrodes exhibited excellent electrochemical behavior and bendable/foldable flexibility. As a result, the all-pseudocapacitance asymmetric device of MCNF//CP assembled with charge-matched between anode and cathode achieves an extended voltage window of 1.5 V, high energy density of 30.6 Wh·kg−1 (1211 W·kg−1), and 86% capacitance retention after 5000 cycles, and the device maintains excellent bendability, simultaneously. This work will pave the way for the development of all-pseudocapacitive asymmetric supercapacitors (ASC) with simultaneously preeminent mechanical properties, high energy density, and wide operating voltage window.

Understanding the origin of the wide voltage window of microporous carbon electrodes with oxygen-containing defects by modulating surface chemistry

Benefiting from the specific microporous carbon/electrolyte interface with O-containing defect, the interfacial water molecules in Na+ solvation shell lose HER activity. Thus, the EDL structure has wide operating voltage window.

Na-Rich Layered Transition Metal Oxides with Core/Shell Structures for Improved Performance of Sodium-Ion Batteries

While P2-type layered transition metal oxides are regarded as potential cathode candidates for sodium-ion batteries because of the high theoretical capacity and a wide operating voltage window, they still suffer from low capacity and sluggish sodium-ion kinetics. Here, we report a Na0.67Mn0.66Co0.17Ni0.17O2 cathode material with a core/shell structure. P2-Na0.67Mn0.66Co0.17Ni0.17O2 has exhibited excellent discharge specific capacity (266 mAh g–1 at 0.1 C and 89 mAh g–1 at 5 C) and ultralong cycle stability, which are among the best state-of-the-art values for Na-based Na-ion batteries. The superior stability results from core/shell structures composed of nanosheets, and the space between the core and shell effectively relieves the volume expansion caused by the deintercalation of sodium ions. Transition metal doping effectively improves the structural distortion caused by the Jahn–Teller effect and provides high sodium mobility, creating higher specific capacity. These findings provide new ideas for the design and development of high-performance sodium-ion battery cathode materials.