Ionic Conductivity Studies Research Articles

Ionic Conductivity Studies on Proton Conducting Solid Biopolymer Electrolyte based on 2-Hydroxyethyl Cellulose (2HEC) Doped with Ammonium Chloride (NH4CL)

Solution casting techniques have been used to create a solid biopolymer electrolyte (SBEs) based on 2-hydroxyethyl cellulose (2HEC) doped with varying amounts of ammonium chloride (NH4Cl) to investigate the potential of NH4Cl in enhancing the ionic conductivity of SBE. Electrical impedance spectroscopy (EIS) was used to measure the impedance of the electrolytes between 50 Hz and 1 MHz in frequency. At room temperature, ionic conductivity was at its highest for 16% weight percent of NH4Cl which was 1.74 x 10-3 Scm-1. The temperature dependence data of 2HEC-NH4Cl SBEs abides Arrhenius behaviour. Complex electrical modulus and complex permittivity were used to assess the dielectric data for the sample at various temperatures.

Lithium ionic conductivity and structural studies of NASICON structured Li0.4Sr0.3Zr0.5Ti1.5(PO4)3

Stable solid electrolytes have been the subject of intense research due to the growing demand for energy storage and portable energy sources in rechargeable Li-ion batteries. Sodium (NA) super (S) ionic (I) conductor (CON) abbreviated as NASICON are suitable for use as solid electrolytes due to their excellent ionic conductivity and chemical stability. We have reported the effect of partial doping of Sr at Li and Zr4+ at Ti4+ position on the structure and ionic conductivity of composition Li0.4Sr0.3Ti2(PO4)3 (LSTP). The composition with formula Li0.4Sr0.3Ti2−xZrx(PO4)3 (x = 0.0, 0.5, 2.0) were prepared by solid state reaction method. The phase and crystal structure were examined using X-ray diffraction (XRD) patterns. The compositions were in rhombohedral phase with the space group R 3¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\overline{3}$$\\end{document} c. The doping of Zr4+ in LSTP causes the peaks in the XRD spectra for doped composition (x = 0.5, 2.0) to move towards lower angle. The displacement of the XRD peaks towards lower angle side show the expansion in the lattice of the Zr doped compositions Li0.4Sr0.3Ti1.5Zr0.5(PO4)3 and Li0.4Sr0.3Zr2(PO4)3. The presence of stretching and bending modes of PO4 groups in the prepared compositions was identified by FTIR spectra. The enhanced bulk conductivity of 4.32 × 10–5 S/cm for Zr doped composition Li0.4Sr0.3Ti1.5Zr0.5(PO4)3 and 3.20 × 10–5 S/cm for composition Li0.4Sr0.3Zr2(PO4)3 is observed at 25 °C. The modulus peaks in the Zr doped composition Li0.4Sr0.3Ti1.5Zr0.5(PO4)3 is displaced towards higher frequencies at 450 °C, indicating the presence of the thermally produced dielectric relaxation phenomenon and charge carrier hopping. The cole cole plot consisting of one semicircle in case of Li0.4Sr0.3Ti1.5Zr0.5(PO4)3 discusses the contribution of bulk and grain boundary resistances and is fitted by equivalent circuit consisting of CPE and R element joined in parallel.

Systematic study of ionic conduction in silver iodide/mesoporous alumina composites 2: effects of silver bromide doping.

In our preceding paper (Y. Fukui et al., Phys. Chem. Chem. Phys., 2023, 25, 25594-25602), we reported a systematic study of the Ag+-ion conducting behaviour of silver iodide (AgI)-loaded mesoporous aluminas (MPAs) with different pore diameters and AgI-loading ratios. By optimising the control parameters, the Ag+-ion conductivity has reached 7.2 × 10-4 S cm-1 at room temperature, which is more than three orders of magnitude higher than that of bulk AgI. In the present study, the effect of silver bromide (AgBr)-doping in the AgI/MPA composites on Ag+-ion conductivity is systematically investigated for the first time, using variable-temperature powder X-ray diffraction, differential scanning calorimetry, and electrochemical impedance spectroscopy measurements. The AgBr-doped AgI/MPA composites, AgI-AgBr/MPA, formed a homogeneous β/γ-AgI-structured solid solution (β/γ-AgIss) for the composites with AgBr ≤ 10 mol%, above which the composites underwent a phase separation into β/γ-AgIss and face-centred cubic AgBr solid solutions (AgBrss). The onset temperature of the exothermic peaks attributed to the transition from α-AgI-structured solid-solution phase to β/γ-AgIss or AgBrss decreased with increasing the AgBr-doping ratio. The room-temperature ionic conductivity of the AgI-AgBr/MPA composites exhibited a volcano-type dependence on the AgBr-doping ratio with the highest value (1.6 × 10-3 S cm-1) when the AgBr content was 10 mol%. This value is more than twice as high as that of the highest conducting AgI/MPA found in our previous study.

Exploration of Variable Solvent Directed Self-Healable Supramolecular M(II)-Metallogels (M = Co, Ni, Zn) of Azelaic Acid: Investigating Temperature-Dependent Ion Conductivity and Antibacterial Efficiency.

Molecular self-assembly assisted self-healing supramolecular metallogels of azelaic acid with cobalt(II)-, nickel(II)-, and zinc(II)-based metal acetate salts were successfully fabricated. Individually, N,N'-dimethylformamide and dimethyl sulfoxide were immobilized within these distinctly synthesized soft-scaffolds of metallogels to attain their semisolid viscoelastic nature. Rheological experiments such as amplitude sweep, frequency sweep, and thixotropic measurements were executed for these metallogels to ratify their gel features. The different extents of supramolecular interactions operating within these solvent-directed metallogels were clearly reflected in terms of their distinct morphological patterns as investigated through field emission scanning electron microscopy. Comparative infrared (IR) spectral properties of metallogels along with individual metal salts and azelaic acid were analyzed. These experimental data clearly depict the significant shifting of Fourier transform (FT)-IR peaks of xerogel samples of different metallogels from the gel-forming precursors. The networks present within the soft-scaffold are evidently illustrated by the electrospray ionization-mass experimental data. The temperature-dependent ionic conductivity studies with these solvent-directed versatile metallogel systems were investigated through impedance spectroscopy. The temperature-dependent impedance spectroscopic studies clearly demonstrate that the ion-transportation within the gel matrix depends not only on the types of cations but also on the dielectric properties of the immobilized solvents. The antipathogenic effect of these metallogel systems has also been explored by testing their effectiveness against human pathogenic Gram-negative bacteria Klebsiella pneumoniae (MTCC 109) and Vibrio parahemolyticus, and Gram-positive bacteria like Bacillus cereus (MTCC 1272). These gel soft-scaffolds show no significant cytotoxicity against both the human neuroblastoma cell line-SH-SY5Y and the human embryonic kidney cell line-HEK 293.

Graphene-Doped Hydrogels Promoting Ionic Conductivity in Gel-Valve-Regulated Lead Acid Batteries.

In this study, the impact of graphene-doped poly(vinyl alcohol) hydrogels on gel-valve-regulated lead acid batteries was examined. The gel formulations were made by adding various amounts of graphene into the gel system comprising poly(vinyl alcohol) and sulfuric acid. Gel formulations were subjected to an ionic conductivity study and Fourier transform infrared spectroscopy (FTIR) to understand ionic mobility and material interaction, respectively. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP) were utilized to find the optimized amount of graphene in gel formulations. Galvanostatic charge-discharge (GCD) techniques were employed on a battery comprising an optimized gel electrolyte. The battery exhibited a discharge capacity of 12.82 mAh at a current density of 15 mA cm-2. After 500 prolonged cycles, the battery displayed a discharge capacity of 87% at 25 mA cm-2 current density, indicating that graphene-doped hydrogels can be a promising gel electrolyte for lead acid batteries.

On the Influence of Counter-Ion Nature on Properties of Perfluorosulfonic Acid Membranes with Long and Short Side Chain

In this work, the study of water uptake, ionic conductivity, and Donnan potential in systems with perfluorosulfonic acid membranes in H+, Li+, Na+, and K+ forms and solutions of inorganic electrolytes is presented. The properties of the commercial Aquivion E87-05S and Nafion 212 membranes, as well as the membranes prepared from the dispersions of Nafion 212 in the solvents of different nature (N,N-dimethylformamide, 1‑methyl-2-pyrrolidone, isopropyl alcohol–water mixtures in volume ratio of 80–20) were investigated. The influence of the number of functional groups, the length of the side chains of the polymer macromolecules, and the polymer morphology in the membranes on their equilibrium and transport properties depending on the counter-ion nature was revealed. The effect of the relaxation and electrophoretic factors on the alkali metal ion transfer through the system of pores and channels of the perfluorosulfonic acid membranes was discussed. The slope of the concentration dependencies of the Donnan potential for all highly hydrated membranes in the H+ form was close to the Nernstian one, while the selectivity to the alkali metal ions increased for the membranes with the highest ion-exchange capacity or the lowest amount of sorbed water and diffusion permeability due to the exclusion of the co-ions from the membrane phase.

Permselectivity and Ionic Conductivity Study of Na+ and Br- Ions in Graphene Oxide-Based Membranes for Redox Flow Batteries.

Permselectivity of a membrane is central for the development of electrochemical energy storage devices with two redox couples, such as redox flow batteries (RFBs). In RFBs, Br3-/Br- couple is often used as a catholyte which can cross over to the anolyte, limiting the battery's lifetime. Naturally, the development of permselective membranes is essential to the success of RFBs since state-of-the-art perfluorosulfonic acid (PFSA) is too costly. This study investigates membranes of graphene oxide (GO), polyvinylpyrrolidone (PVP), and imidazole (Im) as binder and linker, respectively. The GO membranes are compared to a standard PFSA membrane in terms of ionic conductivity (Na+) and permselectivity (exclusion of Br-). The ionic conduction is evaluated from electrochemical impedance spectroscopy and the permselectivity from two-compartment diffusion cells in a four-electrode system. Our findings suggest that the GO membranes reach conductivity and permselectivity comparable with standard PFSA membranes.

The study of ionic conductivity of the Li10GeP2S12 type Solid State Electrolyte by an extrapolation method and a deep-learning method

An extrapolation method is usually applied when Ab initio molecular dynamics (AIMD) is applied to studying ionic conductivity in solid-state electrolytes in lithium-ion batteries. As the ions move slowly in solid-state electrolytes, the first-principles method typically involves computationally intensive calculations, and it can take significant time to obtain accurate results. First-principles method is too expensive for the time scale required at room temperature. The classical molecular dynamics method is typically applied to systems containing thousands of atoms and can simulate the system’s behavior over nanoseconds. During the simulation, the positions and velocities of the atoms are updated at discrete time intervals, allowing the system’s behavior to be studied over time. However, its accuracy depends on the empirical force-field libraries. Limited by the computational resource, the previous studies applied the extrapolation method to obtain the room temperature ionic conductivity, which was not accurate because the linear relationship in the Arrhenius equation was not valid in a wide range of temperatures. Deepmd-Kit is a tool that integrates these two different computational approaches. The extrapolation and Deepmd methods were applied to the materials Li10GeP2S12, Li10SiP2S12, Li10GePS12Cl, and Li10SiPS12Cl, respectively. Both methods showed that the lithium ions favor the c direction when diffusing in the LGPS-type solid-state electrolytes. The ionic conductivity is more accurate with the dependent method compared with experiments.

Evaluation of Conducting Properties of Biopolymer Electrolyte K-Carrageenan with The Effect of Three Different Ammonium Salts

In the present work kappa-carrageenan (KC) with different ammonium salts NH4Cl, NH4Br, and NH4I membrane were successfully synthesized by the solution casting technique. The prepared eco-friendly membrane is subjected to ionic conductivity study, XRD study, transference number studies, and then it’s compared. The ionic conductivity value for KC with 200 mg NH4Cl is 1.81× 10-4 S/cm, KC with 300 mg NH4Br is 2.80× 10-3 S/cm, KC with 400 mg NH4I is 5.88× 10-5 S/cm. Among all the three, combinations the KC with 300 mg NH4Br gives high ionic conductivity. From the X-Ray Diffraction pattern, KC-NH4Cl incorporation greatly enriched the amorphous region. All the three membranes transference numbers are very close to unity. Among all the three combinations, KC with 300 mg NH4Br is the best combination for the application of fuel cell battery.

A systematic ab initio study of vacancy formation energy, diffusivity, and ionic conductivity of Ln2NiO4+δ (Ln=La, Nd, Pr)

This study systematically investigates the vacancy formation energy, diffusivity, and ionic conductivity of the Ln2NiO4+δ (Ln = La, Nd, Pr, and δ = 0.125) compound using the ab initio approach. Specifically, the impact of thermal expansion on the oxygen transport properties is considered, using a combination of quasi-harmonic approximation (QHA) and a linear regression model to study and reproduce the temperature-dependent properties of Ln2NiO4+δ. Overall, the predictions are in excellent agreement with previous theoretical studies in the literature. It is confirmed that the ionic transport properties of the Ln2NiO4+δ are not dominated by oxygen vacancy diffusion due to the high vacancy formation energy. Additionally, the interstitialcy mechanism, which involves interstitial O2- hopping parallel to the a-b plane with the rocksalt layer, is determined to be the more favorable diffusion path. Meanwhile, the predicted energy barrier, diffusion coefficient, and ionic conductivity of Ln2NiO4+δ show reasonable agreement with experimental data, with Pr2NiO4+δ exhibiting the lowest activation energy barrier (ΔEb = 0.722 eV) and the highest thermal expansion, diffusivity, and ionic conductivity. Overall, this study presents an efficient and computationally facile tool for predicting ionic transport properties in materials where thermal expansion is the main driving force for temperature-dependent properties.

An insight into lithium-ion transport in germanium-doped lithium titanate anode through NMR spectroscopy and post-carbonization for anode applications in lithium-ion battery

Adapting toward lithium titanate as a negative electrode for lithium-ion batteries led to the safest and long-lasting battery technology, especially for electric vehicle applications. However, the poor conductivity and lithium-ion diffusion of lithium titanate have to be addressed for widespread usage in next-generation E-mobility. The lithium-ion motion inside lithium titanate and germanium-doped lithium titanate was investigated through pulsed-field gradient nuclear magnetic resonance spectroscopy and temperature-dependent ionic conductivity studies. The superior charge carrier mobility of germanium enhanced the lithium-ion diffusion in lithium titanate significantly to 1.48 × 10−8 cm2 s−1 in Li4Ge0.1Ti4.9O12 at 500 °C. While germanium improves the ionic diffusion, an ex situ carbon coating was adapted over the sample for electronic conductivity enhancement. Samples with two different carbon contents (5 and 10 wt. %) were examined for electrochemical analysis. Significant improvements in battery performance were observed on carbon-coated germanium-doped lithium titanate. The carbon-coated sample gave superior initial performance (191 and 178 mAh g−1 for 10 and 5 wt. % carbon at 0.1C) than the pristine lithium titanate and preserved the exceptional capacity retention over a thousand cycles at 1C rate.

Ionic liquid incorporated SPEEK/Chitosan solid polymer electrolytes: ionic conductivity and dielectric study

Ionic liquid incorporated SPEEK/Chitosan solid polymer electrolytes: ionic conductivity and dielectric study

Systematic study of ionic conduction in silver iodide/mesoporous alumina composites 1: effects of pore size and filling level.

A systematic study of Ag+-ion conducting behavior in Ag+-loaded porous materials was conducted over the entire sub-10 nm region for the first time. The effects of the pore diameter of mesoporous aluminas (MPAs) and the amount of silver iodide (AgI) loaded into MPAs were investigated using N2 gas adsorption/desorption, powder X-ray diffraction, differential scanning calorimetry, and electrochemical impedance spectroscopy measurements. Confinement of AgI in the mesoporous space lowers the phase transition temperature between the β/γ- and α-phases relative to that of bulk AgI. The AgI-loading into the MPAs with smaller pores led to a more significant decrease in the transition temperature, possibly because the smaller AgI nanoparticles in the pores must have a higher surface energy to stabilize the high-temperature phase. The room-temperature ionic conductivity exhibits a volcano-type dependence on the pore diameter with the highest value when AgI was loaded into MPA with a pore diameter of 7.1 nm (7.2 × 10-4 S cm-1 at room temperature). Concerning the 7.1 nm-MPA, the room-temperature ionic conductivity was the highest for the nearly fully occupied composite, which is more than three orders of magnitude higher than that of the bulk AgI. The present study reveals that the Ag+-ion conductivity in AgI/MPA composites can be controlled by optimizing the pore diameter of MPA and the AgI-loading ratio.

Electrical properties of zinc sulfide and silver sulfide as binary salts in gel polymer electrolytes for quantum Dot-Sensitized solar cells

Gel polymer electrolytes (GPEs) with methyl cellulose (MC) polymer host have been prepared by solution casting. Succinonitrile (SN) is the plasticizer. ZnS and Ag2S are the sulfide salts added. The ZnS:Ag2S weight ratio has been varied. The crystallinity of MC:SN:co-ZnS-Ag2S:S has been investigated using X-ray Diffraction (XRD). The use of two cations from two different salts has decreased crystallinity of the GPEs and the. The MC:SN:(ZnS:Ag2S = 80:20):S GPE exhibited the lowest degree of crystallinity of 21.18 %. Ionic conductivity and dielectric studies have been studied using electrochemical impedance spectroscopy (EIS). MC:SN:(ZnS:Ag2S = 80:20):S electrolyte demonstrated the highest ionic conductivity at room temperature. The value is 6.93 × 10-2S.cm−1. The activation energy is 0.23 eV. The cell FTO/ZnOFe2O4/CdS/MC:SN:(ZnS:Ag2S = 80:20):S/GPE/Pt/FTO has been assembled and characterized. The efficiency obtained is 0.58 % with short current density (Jsc) of 2.15 mA.cm−2, open circuit voltage (Voc) of 0.48 V and fill factor (FF) of 0.56.

Ionic conductivity and dielectric studies on PVP/PEO/(NH4)2Ce(NO3)6 based solid polymer-blend electrolytes

Ionic conductivity and dielectric studies on PVP/PEO/(NH4)2Ce(NO3)6 based solid polymer-blend electrolytes

Development of solid polymer electrolytes based on poly (ethylene oxide) complexed with 2-trifluoromethyl-4, 5-dicyanoimidazole lithium salt and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid for Li-ion batteries

Ion conducting solid polymer electrolyte films based on polymer poly (ethylene oxide) (PEO) complexed with 2-trifluoromethyl-4, 5-dicyanoimidazole lithium salt and ionic liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide are synthesized using anhydrous acetonitrile as solvent. Prepared electrolyte films are characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), complex impedance spectroscopy and cyclic voltammetry techniques. Incorporation of IL into the PEO20-LiTDI polymer electrolyte changes different physicochemical properties of these materials. By characterizations, particularly XRD, DSC and ionic conductivity studies, the synthesized SPEs showed decreased crystallinity, melting points and increased ionic conductivity by the introduction of ionic liquid. The 40 wt% of IL doped polymer electrolyte showed an ionic conductivity of the order of 1.78 × 10−4 S/cm at 60°C with better thermal stability. The optimum conducting composition showed very good electrochemical stability window at ambient temperature. These results suggested that the IL-doped polymer electrolyte would be a potential separator in Li-ion batteries.

Conductivity Studies in Poly Methyl Methacrylate Based Solid Polymer Electrolytes Complexed with Different Chloride Salts

Ionic conducting polymers are of considerable interest recently, as they have wide range of applications including electrical storage devices. The present study is aimed at designing and characterizing one such ion conducting polymer complexed with various ionic salts. Here, solid polymer electrolyte films consisting of Poly methyl methacrylate (PMMA) complexed with various chloride salts (X) (X= KCl, NaCl, MgCl2) have been prepared by the solvent casting technique. Fourier transform infrared spectroscopy (FTIR) confirmed the formation of polymer-ion complex. The ionic conductivity studies have also been carried out using AC impedance spectroscopy technique. Interestingly, the maximum value of conductivity (8.268 X 10-8 S/cm) has been observed for PMMA/NaCl complex at ambient temperature.

Study of novel synthesized Gum-Arabic-Ammonium thiocyanate based polymer electrolyte for testing electrical properties and electrochemical sensing

The novel Gum Arabic-Ammonium Thiocyanate-based solid polymer electrolyte was synthesized using the solvent casting technique, which involved mixing Gum Arabic (GA) with ammonium thiocyanate (NH4SCN) in the presence of water. The different concentrations of NH4SCN admixture with the GA synthesized have been characterized by X-ray Diffraction (XRD), Fourier Transform Infrared (FT-IR), dielectric, and ionic conductivity studies. The structural behavior (amorphous or semi crystalline, vibrational shifts), dielectric constant & dielectric loss behavior, relaxation time, and ionic conductivity response of various NH4SCN concentrations admixture on the GA have shown significant variation and the results are presented in detail. To make the batteries have a better ionic conductivity, the synthesized GA-NH4SCN sample, two cathode materials (MnO2(Cell I) and PbO2 + V2O5(Cell II)), and one anode material (Zn/ZnSO4·7H2O) have been taken for examining the open circuit voltage and discharge characteristics at different resistances as a function of time, and their results were discussed in detail.

Novel electrospun separator‐electrolyte based on PVA‐K2CO3‐SiO2‐cellulose nanofiber for application in flexible energy storage devices

AbstractElectrospun fiber membrane as a separator‐electrolyte have been prepared in this study using electrospinning process from cellulose acetate, PVA, K2CO3, and SiO2 with different concentrations. Five different concentration were prepared (14–22 wt%) using mixture of dimethyl sulfoxide and acetone in a fixed ratio of 2:3. The prepared electrospun membranes were characterized and shown to exhibit good and well‐structured morphology formed by interlaying of fibers, where the thinnest and finest fibers were achieved at 20 wt% polymer concentration, resulting in average diameters of 480 ± 80 nm. The prepared membranes were activated with plasticized gel polymer electrolyte where its electrochemical properties/performance was evaluated. Based on the good porous nature of the fiber, the membrane with 20 wt% concentration exhibited good electrolyte uptake of 450.75% that is higher than the commercially prepared separator. Similarly, the membranes displayed good electrolyte retention (R) ability of 8.8. The ionic conductivity studies revealed that, the conductivity of the electrospun membranes increased with increasing polymer concentration up to 20 wt% where an optimum ionic conductivity of 3.73 × 10−3 and 7.54 × 10−3 Scm−1 at ambient temperature and 373.15 K, respectively, have been achieved. The oxidation stability of the prepared membrane in this study showed a good electrochemical stability of up to 4.8 V that is higher than that of the commercially prepared membrane and other reported electrolytes.

Study of ionic conduction, dielectric relaxation, optical and electrochemical properties of AgPO3/graphene glasses for magnesium battery applications

Developing suitable cathode material for alkali ion batteries is the most significant challenge facing commercialization. The effect of graphene nanoplatelets (GNP) on the physical and optical properties of AgPO3 glass is demonstrated. For the first time, AgPO3/Graphene glasses have been synthesized by melt-quenching method to assess the physical and the electrochemical performance as a cathode for a Magnesium ion battery. The complex impedance method determines bulk conductivity; the bulk conductivity increases with increasing temperature and graphene content. AgPO3_2 wt%GNP (sample 2) shows the optimum stoichiometric ratio with linear conductivity-temperature growth up to fast-ionic conductivity ∼ 1.79×10−2 (ohm. cm)−1 at 150 °C. The study of frequency dependence of both dielectric constant and dielectric loss have been explained based on ion hopping beside the ionic polarization mechanism. Optical properties such as the refractive index, optical energy gap, molar refractivity, molecular polarizability, dispersion, and oscillator energy of AgPO3 glass with different graphene nanoplatelets are investigated. The data reveal the lowest energy gap for the glass sample (AgPO3/2 wt%GNP). On the contrary, the values of refractive index, dispersion energy, molar refractivity and molecular polarizability are the highest for (AgPO3_2%wt%GNP) sample. The coin cell has been fabricated with the cell configuration Mg//electrolyte//AgPO3 and Mg//electrolyte//AgPO3_2 w%GNP. The cell with AgPO3_2 wt% GNP electrode has a high initial discharge capacity of ∼187 mAh/g compared with AgPO3 electrodes of ∼100 mAh/g.