Operating Voltage Window Research Articles

Electrodeposited poly(phenylene oxide) suppresses anodic parasitic processes in carbon-based supercapacitor electrodes operating in an aqueous electrolyte

Aqueous electrolytes, when compared to organic electrolytes, are safer, cheaper and usually enable a higher capacitance and lower internal resistance. However, their narrow operational voltage window (ca. 1.2 V) limits the device's energy density and, as such, their current commercial use is limited. Poly(phenylene oxide) was electrodeposited on the surface of activated carbon electrodes and has been shown to decrease the anodic parasitic current. The impact on the cathodic parasitic current was minimal. Comparison of the polarisation curves obtained in 1 M Na2SO4 (aq) for coated and uncoated electrodes between 0.5 V and 1.1 V vs Ag|AgCl demonstrated a >66% decrease in the exchange current density of anodic processes (from 10.1 μA/cm2 to 3.4 μA/cm2). Assuming supercapacitor degradation is proportional to the parasitic faradaic current, this change in the anodic parameters enables a 31% increase in the upper positive potential when a maximum parasitic current density of 29 μA/cm2 is considered acceptable. When these coated electrodes were mounted as symmetrical coin cells and operated at an increased voltage window of 1.5 V (up from 1.2 V), gains in energy and power densities were from 2.2 Wh/kg to 4.6 Wh/kg and 159 W/kg to 465 W/kg, respectively.

Low‐Temperature and High‐Voltage‐Tolerant Zinc‐Ion Hybrid Supercapacitor Based on a Hydrogel Electrolyte

AbstractFor flexible supercapacitors, adequate flexibility, a wide voltage window, and the ability to operate under ultralow temperatures remain a great challenge. In this study, a high‐performance solid hydrogel (referred to as the PAM‐SA‐Ca2+ hydrogel) with a tensile length reaching 2013.5 % and strong low‐temperature tolerance was constructed. This ensured its stable structure at levels as low as −75 °C . When it was used as the electrolyte in a flexible zinc‐ion hybrid supercapacitor (ZHS), it could provide a wide operating voltage window of 0–2.2 V for ZHSs. Benefiting from these advantages, the ZHS device not only delivered a high specific energy (202.3 W ⋅ h ⋅ kg−1), specific power (1048 W ⋅ kg−1) and excellent cycling stability with capacity retention of 85.82 % after 11000 cycles, but it could also drive a timer at the ultralow‐ temperature of −75 °C, emphasizing its great application potential as an advanced flexible electronic device.

Symmetric supercapacitor devices based on pristine g-C3N4 mesoporous nanosheets with exceptional stability and wide operating voltage window

We report a facile low-cost thermal polymerization method of urea to produce 2D carbon nitride nanosheets (GCN) as confirmed via a plethora of morphological and structural characterization techniques. The GCN electrodes showed excellent electrochemical performance with a very wide operating voltage window upon their use as positive and negative poles in supercapacitor devices. The GCN exhibited high specific capacitance as positive and negative electrodes in 0.5 M H2SO4. The symmetric supercapacitor (GCN//GCN) device possesses a wide operating voltage window of 2 V, with an ultrahigh energy density of 19.33 Wh/kg and superior stability over 21,000 charge/discharge cycles. The device was assembled on graphite sheet and not on Ni foam to avoid the raised caveats on the contribution of the redox-active Ni foam to the measured capacities. These unique properties can be ascribed to the high nitrogen doping level (exceeding 12%), revealing the potential of pristine GCN as promising candidates for further investigation and development in energy conversion and storage applications.

Exploring the chemistry of “Organic/water-in-salt” electrolyte in graphene-polypyrrole based high-voltage (2.4V) microsupercapacitor

Aqueous electrolytes are facing substantial barriers for their all-around use in electrochemical energy storage applications due to their limited operating voltage window. To overcome this issue, “Water-in-salt” electrolyte is known to be the best finding to deal with the electrochemical stability window (ESW). The present work demonstrates the fabrication of laser-irradiated graphene (LIG)-polypyrrole (PPy) hybrid material with enhanced effective surface area, electrical and electrochemical properties, which was further used to build a symmetrical metal-free microsupercapacitor (MSC) with greater electrochemical performances. The attractive feature of this work is the incorporation of a pseudocapacitive material (i.e., PPy) in LIG to increase the electrochemical storage capacity of the device in “Acetonitrile/water-in-salt” electrolyte (AWIS) accompanying higher ESW up to 2.4 V. Moreover, the changes in the electrolyte solvation structure with salt concentration and different solvent mixture ratios were studied via Raman analysis in support with 1H NMR measurements. The resulting symmetrical metal-free LIG-PPyAWIS MSC yields high specific capacitance of 124 mF cm−2, the energy density of 99.2 μWh cm−2 and a power density of 47.75 mW cm−2, shows significant progress among other graphene based MSCs. The designed LIG-PPy module attains a large voltage of 20 V by integrating only nine devices in series combination which provides the future scope of the material in high voltage energy applications.

2.4 V ultrahigh-voltage aqueous MXene-based asymmetric micro-supercapacitors with high volumetric energy density toward a self-sufficient integrated microsystem

Two-dimensional MXenes are key high-capacitance electrode materials for micro-supercapacitors (MSCs) catering to integrated microsystems. However, the narrow electrochemical voltage windows of conventional aqueous electrolytes (≤ 1.23 V) and symmetric MXene MSCs (typically ≤ 0.6 V) substantially limit their output voltage and energy density. Highly concentrated aqueous electrolytes exhibit lower water molecule activity, which inhibits water splitting and consequently widens the operating voltage window. Herein, we report ultrahigh-voltage aqueous planar asymmetric MSCs (AMSCs) based on a highly concentrated LiCl-gel quasi-solid-state electrolyte with MXene (Ti3C2Tx) as the negative electrode and MnO2 nanosheets as the positive electrode (MXene//MnO2-AMSCs). The MXene//MnO2-AMSCs exhibit a high voltage of up to 2.4 V, attaining an ultrahigh volumetric energy density of 53 mWh cm−3. Furthermore, the in-plane geometry and the quasi-solid-state electrolyte enabled excellent mechanical flexibility and performance uniformity in the serially/parallel connected packs of our AMSCs. Notably, the MXene//MnO2-AMSC-based integrated microsystem, in conjunction with solar cells and consumer electronics, could efficiently realize simultaneous energy harvesting, storage, and conversion. The findings of this study provide insights for constructing high-voltage aqueous MXene-based AMSCs as safe and self-sufficient micropower sources in smart integrated microsystems.

High-Energy-Density Asymmetric Supercapacitor Based on Free-Standing Ti3C2TX@NiO-Reduced Graphene Oxide Heterostructured Anode and Defective Reduced Graphene Oxide Hydrogel Cathode.

The rational design of an asymmetric supercapacitor (ASC) with an expanded operating voltage window has been recognized as a promising strategy to maximize the energy density of the device. Nevertheless, it remains challenging to have electrode materials that feature good electrical conductivity and high specific capacitance. Herein, a 3D layered Ti3C2TX@NiO-reduced graphene oxide (RGO) heterostructured hydrogel was successfully synthesized by uniform deposition of NiO nanoflowers onto Ti3C2TX nanosheets, and the heterostructure was assembled into a 3D porous hydrogel through a hydrothermal GO-gelation process at low temperatures. The resultant Ti3C2TX@NiO-RGO heterostructured hydrogel exhibited an ultrahigh specific capacitance of 979 F g-1 at 0.5 A g-1, in comparison to that of Ti3C2TX@NiO (623 F g-1) and Ti3C2TX (112 F g-1). Separately, a defective RGO (DRGO) hydrogel was found to exhibit a drastic increase in specific capacitance, compared to untreated RGO (261 vs 178 F g-1 at 0.5 A g-1), owing to abundant mesopores. These two materials were then used as free-standing anode and cathode to construct an ASC, which displayed a large operating voltage (1.8 V), a high energy density (79.02 Wh kg-1 at 450 W kg-1 and 45.68 Wh kg-1 at 9000 W kg-1), and remarkable cycling stability (retention of 95.6% of the capacitance after 10,000 cycles at 10 A g-1). This work highlights the unique potential of Ti3C2TX-based heterostructured hydrogels as viable electrode materials for ASCs.

Novel preparation of attapulgite-reduced graphene oxide hydrogel composite and its application in flexible solid-state supercapacitors

After graphite oxide assisted the liquid phase shear exfoliation of attapulgite, the good dissociation and dispersion of attapulgite rod crystals are realized. Due to the spatial hindrance effect of attapulgite, which prevents the stacking of RGO sheets, the attapulgite-reduced graphene oxide three-dimensional porous hydrogel with abundant pore structure enables rapid transfer of electrolyte ions and exhibits good electrochemical performance and rate performance. The assembled flexible solid-state supercapacitor has a high operating voltage window and good flexibility and cycle stability. At a current density of 0.1 mA cm−2, it has an area specific capacitance of 127.33 mF cm−2. A series of solid-state supercapacitors can be used as the power supply for LED lights.

Mechanistic Elucidation of Electronically Conductive PEDOT:PSS Tailored Binder for a Potassium‐Ion Battery Graphite Anode: Electrochemical, Mechanical, and Thermal Safety Aspects

AbstractPotassium‐ion batteries (KIBs) are considered more appropriate for grid‐scale storage than lithium‐ion batteries (LIBs) due to similar operating chemistry, abundant precursors, and compatibility with low‐cost graphite anodes. However, a larger ion reduces rate capabilities and exacerbates capacity fading from volumetric expansion. Herein, conductive polymer, poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), is substituted for standard insulating polyvinylidene fluoride (PVDF). Half‐cells using carbon black (CB) in continuously conductive PEDOT:PSS/CB binder outperforms PVDF/CB by mitigating electrically isolated “dead” graphite, improving 100 cycle capacity retention at C/10 from 63 to 80%. Enhanced electrical contact with PEDOT:PSS/CB also reduces ion impedance and improves rate capabilities. Without CB however, PEDOT:PSS binder performs poorly in electrochemical studies despite promising ex situ electronic conductivity. This discrepancy is mechanistically elucidated through identification of redox activity between PEDOT:PSS and K+ which results in high impedances in the anode operating voltage window. Additionally, the impact of conducting binder on mechanical properties and thermal safety of the anode is investigated. Brittleness and poor wettability of PEDOT:PSS are identified as issues, but greater stability against reactive KC8 reduces overall heat generation. Binder substitution offers a promising means of mitigating issues with current KIB anodes regardless of active material, and the work herein addresses issues towards further improvement.

Co-MOF@MXene-carbon nanofiber-based freestanding electrodes for a flexible and wearable quasi-solid-state supercapacitor

Freestanding and flexible electrodes are crucial for advancing flexible and wearable energy storage devices (FW-ESD). However, the significant trade-off between mechanical flexibility and electrochemical performance of electrodes limits the development of high-performance FW-ESD. Therefore, flexible and freestanding multi-component hybrid electrodes with improved electrochemical properties are in high demand. This work reports a rational design of cobalt-metal organic framework (Co-MOF) structures on a highly flexible and electroconductive MXene-carbon nanofiber mat (MX-CNF). Further, the Co-MOF@MX-CNF was used as a starting material to derive capacitive-type Co-PC@MX-CNF and battery-type MnO2@Co3O4-PC@MX-CNF functional multi-component electrodes for a high-performance flexible wearable hybrid supercapacitor (FW-HSC). Owing to their high specific surface area (SSA), wettability, conductivity, and abundant active sites, Co-PC@MX-CNF and MnO2@Co3O4-PC@MX-CNF exhibited a specific capacitance of 426.7 F g−1 and a specific capacity of 475.4 mAh g−1 at 1 A g−1, respectively, with excellent mechanical flexibility. Moreover, the two electrodes were used to fabricate an FW-HSC with an operating voltage window of 1.5 V, delivering an energy density of 72.5 Wh kg−1 at a power density of 832.4 W kg−1 with long-term stability (90.36 % capacitance retention). Furthermore, a series connection of two identical FW-HSC devices could power a digital clock and light up a green LED, demonstrating its potential as a power source for various wearable devices.

Influence of charging protocols on the charging capability and aging of lithium-ion cells with silicon-containing anodes

Silicon with a high gravimetric capacity of 3579 mAh g−1 of the pure material becomes increasingly common in the anode of lithium-ion batteries to increase energy density on the full cell level. However, silicon changes its volume excessively during (de-)lithiation making it prone to aging. In commercial cells, it is typically applied either as SiOx or nano-Si in small quantities in a composite anode together with graphite. A different operation voltage window of silicon, varying quantities of silicon in the anode but also different technologies of the applied silicon materials, however, result in different aging behavior of the full cell—even if silicon content and capacities are similar on the data sheet. In this study, two commercial cylindrical cells in the 18650 format with differing silicon technologies are thus compared with a focus on their charging behavior and degradation mechanisms. One way to increase cycling stability with respect to the different silicon cell chemistries is the adaption of the charging protocols. Voltage limits as well as current have therefore been varied in this study using five different charging protocols. Their influence on the charging times and aging behavior is analyzed in great depth: dilatometer investigations of the anodes and their lithiation behavior, differential voltage investigations as well as a detailed post-mortem analysis including ICP-OES, SEM and EDX have identified silicon expansion at low full cell voltages as root aging mechanism in both cells.

Role of the voltage window on the capacity retention of P2-Na2/3[Fe1/2Mn1/2]O2 cathode material for rechargeable sodium-ion batteries

P2-Na2/3[Fe1/2Mn1/2]O2 layered oxide is a promising high energy density cathode material for sodium-ion batteries. However, one of its drawbacks is the poor long-term stability in the operating voltage window of 1.5–4.25 V vs Na+/Na that prevents its commercialization. In this work, additional light is shed on the origin of capacity fading, which has been analyzed using a combination of experimental techniques and theoretical methods. Electrochemical impedance spectroscopy has been performed on P2-Na2/3[Fe1/2Mn1/2]O2 half-cells operating in two different working voltage windows, one allowing and one preventing the high voltage phase transition occurring in P2-Na2/3[Fe1/2Mn1/2]O2 above 4.0 V vs Na+/Na; so as to unveil the transport properties at different states of charge and correlate them with the existing phases in P2-Na2/3[Fe1/2Mn1/2]O2. Supporting X-ray photoelectron spectroscopy experiments to elucidate the surface properties along with theoretical calculations have concluded that the formed electrode-electrolyte interphase is very thin and stable, mainly composed by inorganic species, and reveal that the structural phase transition at high voltage from P2- to “Z”/OP4-oxygen stacking is associated with a drastic increased in the bulk electronic resistance of P2-Na2/3[Fe1/2Mn1/2]O2 electrodes which is one of the causes of the observed capacity fading.

Interfacial Engineered Vanadium Oxide Nanoheterostructures Synchronizing High-Energy and Long-Term Potassium-Ion Storage.

Potassium ion hybrid capacitors (KICs) have drawn tremendous attention for large-scale energy storage applications because of their high energy and power densities and the abundance of potassium sources. However, achieving KICs with high capacity and long lifespan remains challenging because the large size of potassium ions causes sluggish kinetics and fast structural pulverization of electrodes. Here, we report a composite anode of VO2–V2O5 nanoheterostructures captured by a 3D N-doped carbon network (VO2–V2O5/NC) that exhibits a reversible capacity of 252 mAh g–1 at 1 A g–1 over 1600 cycles and a rate performance with 108 mAh g–1 at 10 A g–1. Quantitative kinetics analyses demonstrate that such great rate capability and cyclability are enabled by the capacitive-dominated potassium storage mechanism in the interfacial engineered VO2–V2O5 nanoheterostructures. The further fabricated full KIC cell consisting of a VO2–V2O5/NC anode and an active carbon cathode delivers a high operating voltage window of 4.0 V and energy and power densities up to 154 Wh kg–1 and 10 000 W kg–1, respectively, surpassing most state-of-the-art KICs.

Achieving Wide Operating Voltage Windows in Non-Carrier Injection Micro-LEDs for Enhancing Luminance Robustness

Since the luminance of Micro-LEDs is highly dependent on the injected current density, inevitable voltage fluctuations will lead to luminance fluctuations and weak luminance robustness. In this work, Micro-LED chips working in non-electrical contact and non-carrier injection (NEC and NCI) mode is proposed, which is totally different from the current-injected mode. The luminance of NEC and NCI Micro-LEDs first increases with the increase of the voltage, and the saturation luminance can be obtained during a relatively large voltage range, which is defined as an operating voltage window. Then the luminance decreases when the voltage is further increased. It is demonstrated that the operating voltage windows can enhance luminance robustness. Finally, the insulating layer that is crucial for the operating voltage windows is optimized. And the working mechanisms related to the existence of operating voltage windows are discussed.

Understanding the Relationship between the Dynamic Process of Interfacial Water Molecule and Operating Voltage Window in Graphene-Based Supercapacitors and Geometrical Origin of the Wide Voltage Window in Nitrogen-Doped Graphene

Understanding the Relationship between the Dynamic Process of Interfacial Water Molecule and Operating Voltage Window in Graphene-Based Supercapacitors and Geometrical Origin of the Wide Voltage Window in Nitrogen-Doped Graphene

Flexible in-plane zinc-ion hybrid capacitors with synergistic electrochemical behaviors for self-powered energy systems

Flexible in-plane zinc-ion hybrid micro-capacitors (ZIHCs) are built up with matchable device capacitance, operating voltage window and life span for advanced self-powered energy systems.

On-chip high ion sensitivity electrochromic nanophotonic light modulator.

Since the discovery of electrochromism, the prospect of employing various electrochromic materials for smart window glass, variable reflectivity mirrors, and large-area displays has been the main drive for such an intriguing phenomenon. However, with advances in nanofabrication and the emergence of improved electrochromic materials offering reversible large changes in dielectric properties upon electrically induced redox reactions, the application strategies are starting to encompass the field of nanophotonics and nanoplasmonics. Herein, a novel strategy is proposed and demonstrated for offering both ultrahigh light modulation depth and high sensitivity ion detection in a single nanophotonic waveguiding platform. By using WO3 to ionically-drive dynamic light control via modulating the refractive index and the losses within the waveguide at ±1.5 V, ultrahigh optical modulation depth of 106, rapid response speed of <0.56 s, long cyclic life, and very sensitive Na+ ion detection ability in 1 mM-1 M concentration, are achieved within a volume of a few μm3. It is envisioned that our introduction of such a multifunctional electrochromic nanophotonic waveguide platform will stimulate and promote further efforts toward fundamental research on technologically promising on-chip integrated next-generation nanophotonic and nanoplasmonic devices for various niche applications.

Development of Co0.5Ho0.5Fe2O4/graphene hybrid nanocomposites electrodes for all-solid-state printable micro-supercapacitor on flexible substrates

Herein, we report the synthesis of Co0.5Ho0.5Fe2O4/graphene hybrid nanocomposite electrodes for all-solid-state printable supercapacitor on flexible substrate using a one-step laser scribe approach. The structure, morphology, oxidation state, and elemental composition characteristics were studied using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), selected area of electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDS), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) measurements. The results revealed that the laser scribe can not only used to print the films on the flexible substrate but also has high capability to convert the graphene oxide and the cobalt, holmium and iron salts to Co0.5Ho0.5Fe2O4/graphene hybrid nanocomposite during printing this suspension on a flexible substrate. The cyclic voltammetry and the galvanostatic charge/discharge measurements revealed that the decoration of the surface of graphene with Co0.5Ho0.5Fe2O4 nanocrystals increases the operational voltage window to 1.5 V. The combination of the developed polyethylene glycol/silica/lithium triflates (48:37:15) ionic gel with the Co0.5Ho0.5Fe2O4/graphene hybrid electrodes exhibits a capacitance of 590 F.g−1 (204 mF.cm−2). Furthermore, the printed supercapacitor on the flexible substrate exhibited an energy density of 161.3 Whkg−1 and a maximum power density of 211kWkg−1. The developed Co0.5Ho0.5Fe2O4/LSG hybrid nanocomposite supercapacitor showed outstanding capacitive performance under harsh mechanical conditions.

Highly Ordered Micropores Activated Carbon from Long Fiber Biomass for High Energy Density Supercapacitors

AbstractThe electrochemical performance of carbon based supercapacitors not only depends on the specific surface area and conductivity, but also the structure of materials. In order to construct the carbon materials with effective structure, the long fibrous plant‐saussurea involucrata stalk was chosen as the new style carbon source. Highly ordered micropores activated carbon (HOMAC) materials have been successfully obtained via KOH chemical activation method. The synthesized HOMAC exhibits high specific surface area of 2692 m2 g−1 and pore volume of 1.14 cm3 g−1. The assembled HOMAC‐based electrode can deliver a high specific capacitance of 379 F g−1 at 2 mV s−1 in 1 M H2SO4 aqueous electrolyte, and show excellent cyclic stability (the capacitance retention ∼95 %) over 10000 cycles at a current density of 1 A g−1, which authenticates excellent charge storage capacity of electrode material. Moreover, the operation voltage window can be expanded to 0–1.8 V in 1 M Na2SO4 electrolyte for the 2‐electrode system. The symmetric supercapacitor can deliver a high energy density of 33.91 Wh kg−1 at power density of 180.03 W kg−1. These high performances can be ascribed to the high surface area and ordered microporous structures obtained using KOH as activator. We further discussed the relationship between fibrous plants and electrochemical performances of the final activated carbon materials. This present work can provide beneficial guidance for the preparation of high performance activated carbon electrodes from a biomass‐based carbon source. Comparing with two different biomass materials, it can be found that the ionic diffusion coefficient of saussurea involucrata is 5.074×10−13 m2 s−1, which is 2.5 times of cotton stalk (1.547×10−13 m2 s−1). This phenomenon indicates the different ion transmission rate in different pore structures.

BCN‐Assisted Built‐In Electric Field in Heterostructure: An Innovative Path for Broadening the Voltage Window of Aqueous Supercapacitor

AbstractThe relatively low operating voltage window is the main factor limiting the energy density of aqueous energy storage devices. The delicate design of heterostructured electrode materials can efficiently increase the intrinsic electrochemical performance through synergistic effects. For the first time, to broaden the voltage window of aqueous supercapacitors the synergistic effect between boroncarbonitrides (BCN) and built‐in electric field existing in heterostructures is designed to utilize. Based on this design concept, MnO/MnS@BCN electrode materials are synthesized, in which the synergistic effect can effectively strengthen the storage of electrolyte ions on the electrode surface, thus inhibiting the electrolysis of H2O and eventually broadening the voltage window of aqueous supercapacitor. In MnO/MnS@BCN‐based symmetrical supercapacitors, the voltage window of the device is extended from 1.2 V (single‐component) to 2 V, with the energy density enhanced to 75.0 W h kg−1. The strategy blazes an efficient and convenient path to broaden the intrinsic voltage window of transition metal oxide supercapacitors.

Progress in solid-state high voltage lithium-ion battery electrolytes

• Five major class of electrolytes for high voltage batteries reviewed. • Future trends and opportunities on solid Li-ion cells analyzed. • Operating voltage window and Li+ conductivity of key materials are compared and summarized. Developing high specific energy Lithium-ion (Li-ion) batteries is of vital importance to boost the production of efficient electric vehicles able to meet the customers’ expectation related to the electric range of the vehicle. One possible pathway to high specific energy is to increase the operating voltage of the Li-ion cell. Cathode materials enabling operation above 4.2 V are available. The stability of the positive electrode-electrolyte interface is still the main bottleneck to develop high voltage cells. Moreover, important research efforts are devoted to the substitution of graphite anodes with Li metal: this would improve the energy density of the cell dramatically. The use of metallic lithium is prevented by the dendrite growth during charge, with consequent safety problems. To suppress the formation of dendrites solid-state electrolytes are considered the most promising approach. For these reasons the present review summarizes the most recent research efforts in the field of high voltage solid-state electrolytes for high energy density Li-ion cells.