Ion Storage Electrode Research Articles

N/O-functionalized ultrathin carbon nanosheets for zinc-ion hybrid capacitors

2D carbon materials have outstanding electrical properties and rich anchoring sites, and can be used as zinc ion storage electrodes. However, it remains a formidable challenge to fabricate these materials with tunable composition by a simple synthesis strategy. Herein, folic acid-derived N/O-functionalized ultrathin carbon nanosheets are synthesized via the activation effect of nano-ZnO template. The as-fabricated FACN-800 exhibits extremely thin thickness (∼1.6 nm), hierarchically porous structure and rich N/O heteroatoms (14.9 at.% of N and 8.4 at.% of O), which is conducive to accelerate ion transport and provide additional active sites for Zn-ion storage. Thus, the optimized FACN-800 based aqueous zinc-ion hybrid capacitor delivers excellent zinc-ion storage capabilities with high specific capacity (163.6 mAh g−1 at 0.1 A g−1), admirable energy density (130.8 Wh kg−1) and ultralong cycle stability (90.3 % capacity retention over 40,000 cycles) and FACN-800 has a specific surface area of 554.3 m2 g−1. Moreover, a series of ex-situ measurements and DFT theoretical calculations further elucidate the electrochemical mechanism between zinc ion storage and N/O dopants.

Ionic-storage capacitance enhanced by a self-assembled CoO-Nafion nanocoating on single-walled carbon nanotubes

We introduce a novel approach for enhancing ion-storage capabilities through the self-assembled formation of ternary nanowires, consisting of a CoO-and-Nafion nanocomposite encasing metallic single-walled carbon nanotubes (SWNTs). These nanowires highlight the indispensable role of the conductor-semimetallic SWNT-CoO heterojunction in expediting the redox reaction kinetics of the CoO while the Nafion component facilitates the transport of hydroxide ions. Consequently, supercapacitors comprising the ternary nanowires deliver the specific capacitance of calculated 18.84 mF cm−2, five times higher than those obtained at the counterpart devices that lack Nafion and/or CoO. This self-assembly method precisely organizes functional components within the nanowires, aligning with electrochemical principles to optimize charge transfer and minimize concentration gradients for improved electrochemical polarization. Our function-enhanced ternary nanowires, together with their straightforward synthetic process, promise an alternative opportunity for formulating high-performance ion-storage electrodes and thus pave the way for their application in next-generation supercapacitor technologies.

Electropolymerization of an EDOT-Quinoxaline Monomer for Green Electrochromic Thin Films and Devices.

In this study, we present a 5,8-bis(3,4-ethylenedioxythiophene)quinoxaline monomer with two 4-(octyloxy)phenyl side chains (EDOTPQ) that can be electropolymerized on ITO glass in standard electrolytes containing lithium salts and propylene carbonate as solvent. The electrochemically deposited PEDOTPQ layers show very good adhesion and homogeneity on ITO. The green-colored polymer thin films exhibit promising electrochromic (EC) properties and are interesting for applications such as adaptive camouflage, as well as smart displays, labels, and sensors. Novel organic-inorganic (hybrid) EC cell configurations were realized with Prussian blue (PB) or titanium-vanadium oxide (TiVOx) as ion storage electrodes, showing a highly reversible and fast color change from green to light yellow.

High-vacancy-type titanium oxycarbide for large-capacity lithium-ion storage

Electrochemical processes involving the ion insertion/desertion are usually accompanied by composition variation and structural evolution of electrode materials. Here we propose a meaningful lattice regulation by inserting lithium ions to unlock an active crystalline plane from which high energy storage performance can be obtained. A rock-salt titanium oxycarbide featuring 12% titanium vacancies (Ti0.88□0.12C0.63O0.37) in high active (011) crystalline plane bears excellent electrochemical activity that enables additional reversible lithium insertion, providing a high initial specific capacity of 390 mAh g−1 at 0.05 A g−1. EPR, XAS, PDF and TEM measurements confirm abundant titanium vacancies, electrochemical studies combined with computational calculations demonstrate high activity of (011) crystalline plane as domain channels for lithium-ion insertion, and ex-situ XRD investigations disclose structural evolution during lithium-ion insertion/desertion. Notably, the repeated lithium-ion insertion/desertion promotes new exposure of (011) crystalline planes, leading to a capacity “negative fading” from the initial 120 to 325 mAh g−1 after 1100 cycles at 0.5 A g−1. The study presents the inner relationship between material microstructural transformation and electrochemical properties, providing a new perspective for mechanism re-understanding and structure development of ion-storage electrode materials.

Polyxylylviologen Chloride as an Organic Electrode Material for Efficient Reversible Chloride-Ion Storage

Organic molecules such as viologens with a nitrogen redox center show promise as efficient anion storage materials in rechargeable batteries. However, the high solubility of viologens in liquid electrolytes limits their wide electrochemical application. Herein, an insoluble polymerized polyxylylviologen chloride (PXVCl2) is first developed as a chloride ion storage electrode in chloride ion batteries. The as-prepared PXVCl2 electrode exhibits a competitive discharge capacity of 140 mA h g–1 (86% of the theoretical discharge capacity) compared to that of the previously reported organic conducting polymer electrodes. The incorporation of graphene in the PXVCl2 material achieves significant improvements in reaction reversibility and rate capability of the PXVCl2 electrode. Importantly, the nitrogen redox reactions based on chloride ion transfer of the PXVCl2 electrode are demonstrated.

Mixed metal oxides as optically-passive ion storage layers in electrochromic devices based on metallopolymers

Electrochromic devices (ECDs) based on iron metallopolymers (Fe-MEPE) and different oxide-based ion storage electrodes on fluorine-doped tin oxide (FTO)-coated glass as transparent, conductive substrates are investigated in detail. Titanium-manganese oxide (TMO) thin film electrodes deposited by reactive magnetron co-sputtering on FTO glass were compared to commercially available titanium-vanadium oxide (TiVOx) for use as optically-passive ion storage layers. The ECDs with Fe-MEPE combined with TiVOx (coloration efficiency η = 2 cm2 C−1 at 584 nm) and Ti-rich TMO (η = −4 cm2 C−1) are blue-purple in the dark state at 0 V and become highly transmissive when 1.5 V is applied with a visible light transmittance (τv) change from 28% to 69% and 21% to 57% in 3 s and 13 s, respectively. The ECDs show fast responses and high reversibility over more than 100 cycles. The combination of Fe-MEPE and Mn-rich TMO (η = −24 cm2 C−1) leads to a dark brown ECD, which can be brightened at 2.5 V (τv: 4% ↔17%, 9 s for decoloring).

Chloride ion storage performance of polyaniline/graphene nanocomposite in aqueous sodium chloride solution

The use of anion storage materials has played an important role in the development of electrochemical energy storage systems and water desalination. Herein, the graphene-supported polyaniline (PANI/GN) nanomaterial is developed as a new chloride ion storage electrode in aqueous sodium chloride solution. The as-prepared PANI/GN electrode exhibits highly reversible electrochemical stability in both a three-electrode system and a full desalination battery using a sodium ion storage electrode. Competitive electrochemical properties with a reversible capacity of 126 mA h g−1, a coulombic efficiency of more than 95 % and a high rate capability are achieved for the PANI/GN electrode compared to the previously reported electrodes of metals, antimony oxychloride, and polypyrrole. The anionic chloride species instead of covalent chloride species in the as-prepared PANI/GN is demonstrated to be electrochemically active.

Layered ferric vanadate nanosheets as a high-rate NH4+ storage electrode

ABSTRACT Aqueous rechargeable batteries hold the potential for the application in large-scale energy storage system due to low cost, environmentally friendliness, and high safety. In the past several decades, tremendous research efforts have been devoted to the batteries with metal ions as charge carriers. However, little attention is paid to the non-metal charge carriers, such as ammonium ions. In this work, layered iron vanadate nanosheets are first introduced as ammonium ion storage electrode. In comparison with the Na+ and K+ storage performance, iron vanadate nanosheets show a much improved pseudocapacitance behavior with NH4+ as charge carriers. In this way, at the high current density of 5 A/g, the FVO nanosheets in aqueous (NH4)2SO4 electrolyte display the highest specific capacity of 72.5 mAh/g for 500 cycles, compared with the FVO nanosheets in Na2SO4 (64.7 mAh/g) and K2SO4 (17.3 mAh/g). The difference is attributed to the dirctional H-bondings between the intercalated NH4+ ions and the host iron vanadate nanosheets. This work provides a new direction to expand aqueous batteries with ammonium ion as charger carriers.

Quasi-Solid-State Electrochromic Cells with Energy Storage Properties Made with Inkjet Printing.

In common commercially available electrochromic glass panes, the active materials such as WO3 and NiOx films are typically deposited by either physical vapor or sputtering under vacuum. In the present studies, we report on the inkjet printing method to deposit both electrochromic and ion storage electrode layers under ambient conditions. An ion storage layer based on cerium modified TiO2 and electrochromic nanocrystalline WO3 were both prepared under the wet method and deposited as inks on conductive substrates. Both compounds possess porous morphology facilitating high ion diffusion during electrochemical processes. In particular, the ion storage layer was evaluated in terms of porosity, charge capacity and ion diffusion coefficient. A scaled up 90 cm2 electrochromic device with quasi-solid-state electrolyte was made with the aforementioned materials and evaluated in terms of optical modulation in the visible region, cyclic voltammetry and color efficiency. High contrast between 13.2% and 71.6% for tinted and bleached states measured at 550 nm was monitored under low bias at +2.5 volt and −0.3 volts respectively. Moreover, the calculated energy density equal to 1.95 × 10−3 mWh cm−2 and the high areal capacitance of 156.19 mF cm−2 of the device could combine the electrochromic behavior of the cell with energy storage capability so as to be a promising candidate for future applications into smart buildings.

Chloride ion-doped polyaniline/carbon nanotube nanocomposite materials as new cathodes for chloride ion battery

Finding and optimizing the appropriate cathode materials in the electrolyte are critical to the development of chloride ion batteries. Herein, chloride ion-doped polyaniline/carbon nanotubes (PANI/CNTs) composite materials, which were prepared by an in situ chemical oxidative polymerization method using FeCl3·6H2O as the oxidant, have been developed as new cathodes for chloride ion battery. The PANI/CNTs cathode showed reversible electrochemical energy storage through redox reactions of nitrogen species and chloride ion transfer, as confirmed by the results of the electrochemical testing and X-ray photoelectron spectroscopy. The structural configuration of PANI by the incorporation of conductive CNT carrier contributed to significant improvement in the electrochemical properties. More than 80 mAh g−1 stable capacity and a high Coulombic efficiency of about 99% were delivered. This work offers a promising strategy for designing chloride ion storage electrode and novel electrochemical systems.

Standing pillar arrays of C-coated hollow SnO2 mesoscale tubules for a highly stable lithium ion storage electrode

This work reports the direct growth of hollow one-dimensional nanostructure arrays on conducting substrates for use as efficient electrodes in Li-ion batteries. The C-coated hollow SnO2 pillar array structures can be prepared by template-directed synthesis, selective wet etching, and a carbonization route. The well-oriented ZnO nanorod arrays, which are grown on titanium substrates, are used as a sacrificial template for the deposition of SnO2 layers through a simple hydrothermal process. The ZnO portions are selectively removed by wet etching, producing hollow SnO2 arrays that are consecutively covered with carbon layers via the carbonization of glucose. The lithium storage performance of the synthesized C-coated hollow SnO2 pillar array structures is demonstrated by applying them directly to a working electrode without additive materials. The standing pillar array electrode, consisting of C-coated hollow SnO2, exhibits an excellent discharge capacity of ca. 1251.9 mA h g−1 on the first cycle, and it also shows promising cyclability, rate capability, and coulombic efficiency, indicating that C-coated hollow SnO2 arrays fabricated on the current collector can be powerful candidates for a highly stable lithium storage electrode platform.

Model for the Particle Size, Overpotential, and Strain Dependence of Phase Transition Pathways in Storage Electrodes: Application to Nanoscale Olivines

In the drive toward improved electrical energy storage for applications ranging from wireless devices to electric vehicles to grid stabilization, nanoscale materials are of growing interest as ion storage electrodes. Nanoscale olivines based on LiMPO4 (M = Fe, Mn, Co, Ni) are one class of compounds for which recent experimental developments reveal very different phase transition and solid-solubility behavior compared to larger particles. The olivines may be an exemplar for generalized behavior for which metastable crystalline or amorphous phases are produced under the large driving forces incurred during electrochemical reactions. Here we use a diffuse-interface thermodynamic model to assess the conditions under which amorphous phase transitions may occur in nanoscale LiMPO4 particles. There are three central conclusions. First, assuming as with similar solids that the amorphous phase has the lower surface energy, it is found that an initially crystalline phase may undergo amorphization during cycling when the particle size is below a critical value. Second, the effect of applied electrical overpotentials on the phase stability is evaluated for the first time, and is found to strongly influence the phase transition pathways of small particles. Third, the tendency to amorphize is significantly affected by the magnitude of the misfit strain between the lithiated and delithiated crystalline phases. It is shown that there exists a critical misfit strain above which the preferred transformation pathway is amorphization, regardless of the particle size. We use these results to interpret experimentally observed behavior of olivines, including data that up to now have been unexplained.

Electrochromic smart windows

A solid state electrochromic smart window has the configuration glass/TC/EC/IC/IS/TC/glass, where TC is a transparent conductor, EC is an electrochromic coating, IC is an H + or Li + ion conductor and IS is an H + or Li + ion storage layer. Application of a small voltage at the TC electrodes changes optical transmission of the device in a persistent reversible manner. Porous and slightly crystallized sol-gel coatings of TiO 2-CeO 2 composition have the required properties for ion storage counter electrodes. Layers 150 nm thick have 80% optical transmission in the visible range, do not color after H + and Li + insertion and show good electro-chemical stability. These layers have been used as H + or Li + ion storage electrodes, where EC was WO 3. The protonic IC was a cellulose polyacetate polymer and the lithium IC was PEO-LiN(SO 2CF 3). Electro-chemical and optical performances of the cells are reported.

Sol-Gel Coatings for Electrochromic Devices

ABSTRACTAll solid state electrochromic smart windows with the configuration glass/ITO/WO3/electrolyte/TiO2-CeO2/ITO/glass have been realized. These devices have potential applications in architectural and automotive fields to regulate the transmission and reflection of the radiant energy. The ion storage electrode TiO2–CeO2 have been realized by sol-gel process and its electrochemical properties are studied as a function of various parameters (thickness, heat treatment, etc.). The electrochemical and optical performances of two cells are reported.