Conductivity of Nafion-117 membranes intercalated by polar aprotonic solvents

The Nafion-117 membranes in the Li⁺ form with pore-intercalated aprotonic organic solvents were prepared. The prepared materials were characterized by IR, impedance, and ⁷Li NMR spectroscopy. The solvent uptake of the membranes is shown to be controlled by the composition of organic solvents and their mixtures as well as by the conditions of the preliminary treatment of the initial membranes. For the Nafion-117 membrane, the degree of solvation can be improved by the preliminary treatment with alcohols, especially by the thermal treatment in methanol. Conductivity of the membranes is shown to increase with increasing content of the sorbed solvents. The best conductivity at 25 °C (2.5 × 10^?3 and 1.6 × 10^?3 S cm^?1) was attained for the electrolytes based on the Nafion-117 membrane in lithium form with sorbed ethylene carbonate-propylene carbonate and ethylene carbonate-dimethoxyethane mixtures, respectively.     

Novel cross-linked membrane for direct methanol fuel cell application: sulfonated poly(ether ether nitrile)s

In order to reduce water uptake, swelling ratio, and methanol permeability in sulfonated proton exchange membranes (PEM), novel-sulfonated aromatic poly(ether ether nitrile)s-bearing pendant propenyl groups had been synthesized by direct copolymerization method. All the results showed that the propenyl groups were suitable cross-linkable groups, and that this method was an effective way to overcome the drawbacks of sulfonated polymers at high ion exchange capacity (IEC) values. By cross-linking, the water uptake, swelling ratio, and methanol diffusion could be restricted owing to the formation of compact network structure. For example, CSPEN-60 membranes showed the proton conductivity of 0.072 S cm^?1 at 80 °C, while the swelling ratios and water uptake (17.9 and 60.7 %) were much lower than that of the SPEN-60 membrane (60.8 and 295.2 %). Meanwhile, a 1.1 × 10^?7 cm² s^?1 of methanol diffusion was obtained which was much lower than that of Nafion 117 (14.1 × 10^?7 cm² s^?1). Although the proton conductivity of the CSPEN-60 membranes is lower than that of the SPEN-60 membrane, the selectivity is much higher. The CSPEN-60 membrane exhibited the highest selectivity among the tested membranes, about 5.8 times higher compared with that of Nafion117.     

Irradiation effects of 12 eV oxygen ions on polyimide and fluorinated ethylene propylene

Polyimide (PI) and Fluorinated Ethylene Propylene (FEP) samples (15 mm×15 mm×50 μm ) were exposed to atomic oxygen ions of average energy ～12 eV and flux ～5×10¹³ ions cm ^?2 s ^?1, produced in the Electron Cyclotron Resonance (ECR) plasma. The energy and the flux of the oxygen ions at different positions in the plasma were measured by a retarding field analyzer. The fluence of the oxygen ions was varied from sample to sample in the range of ～5×10¹⁶ to 2×10¹⁷ ions cm ^?2 by changing the irradiation period. The pre- and the post-irradiated samples were characterized by the weight loss, Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), and Fourier Transform Infrared (FTIR) techniques. The weight of the PI and FEP samples decreased with increasing the ion fluence. However, the erosion yield for the PI is found to be higher, by almost a factor five, when compared with that of FEP. On the surface region of irradiated samples, the concentrations of the carbon, fluorine, and oxygen and their corresponding chemical bonds have changed appreciably. Moreover, blisters and nanoglobules were also observed even at a fluence of ～10¹⁷ ions cm ^?2. This oxygen ion fluence is almost two orders of magnitude lower than that of the 5 eV atomic oxygen, which a satellite encounters in the space, at the low Earth orbit, during its mission period of about 7 years.     

Lithium ion conductivity and dielectric properties of P(VdCl-co-AN-co-MMA)-LiCl-EC triblock co-polymer electrolytes

Lithium ion conducting polymer electrolytes based on triblock polymer P(VdCl-co-AN-co-MMA)–LiCl were prepared using a solution casting technique. XRD studies show that the amorphous nature of the polymer electrolyte has been increased due to the addition of LiCl. The maximum amorphous nature has been observed for 40 m% P(VdCl-co-AN-co-MMA)/60 m% LiCl samples. The FTIR study of the lithium ion conducting polymer membrane confirms the complex formation between the polymer P(VdCl-co-AN-co-MMA) and LiCl. The lithium ion conductivity is found to be 1.6 × 10^?5 Scm^?1 for the 40 m% P(VdCl-co-AN-co-MMA)/60 m% LiCl sample at room temperature. This value is found to be greater than that of pure polymer whose conductivity is found to be 1.5 × 10^?8 Scm^?1. To improve ionic conductivity, ethylene carbonate has been added as a plasticizer to the 40 m% P(VdCl-co-AN-co-MMA)/60 m% LiCl sample. When we add 0.6 m% of ethylene carbonate, it has been observed that the lithium ion conductivity has increased to 1.3 × 10^?3 Scm ^?1 . This value is two orders of magnitude greater than the 40 m% P(VdCl-co-AN-co-MMA)/60 m% LiCl sample. It is also observed from XRD patterns of 40 m% P(VdCl-co-AN-co-MMA)/60 m % LiCl/0.6 m % EC that the amorphous nature has been increased further. A dielectric study has been performed for the above membranes.     

Synthesis and characterisation of the Fe(II–III) hydroxy-formate green rust

A new methodology was envisioned in order to prepare green rust compounds build on organic anions that could intervene in microbiologically influenced corrosion processes of iron and steel. The formate ion was chosen as an example. The formation of rust was simulated by the oxidation of aqueous suspensions of Fe(OH)₂ precipitated from Fe(II) lactate and sodium hydroxide, in the presence of sodium formate to promote the formation of the corresponding green rust. The evolution of the precipitate with time was followed by transmission Mössbauer spectroscopy at 15 K. It was observed that the initial hydroxide was transformed into a new GR compound. Its spectrum is composed of three quadrupole doublets, D ₁ (δ?=?1.28 mm s^?1, Δ?=?2.75 mm s^?1) and D ₂ (δ?=?1.28 mm s^?1, Δ?=?2.48 mm s^?1) that correspond to Fe(II) and D ₃ (δ?=?0.49 mm s^?1, Δ?=?0.37 mm s^?1) that corresponds to Fe(III). The relative area of D ₃, close to the proportion of Fe(III) in the GR, was found at 28.5?±?1.5% (～2/7). Raman spectroscopy confirmed that the intermediate compound was a Fe(II–III) hydroxy-formate, GR(HCOO^?).     

Influence of the carboxylic acid groups on the structure and properties of sulfonated poly(arylene ether nitrile) copolymer

A series of novel sulfonated poly(arylene ether nitrile) (SPEN) containing carboxylic acid group was successfully synthesized by direct aromatic nucleophilic substitution polycondensation of 2,6-difluorobenzonitrile (DFBN), potassium 2,5-dihydroxybenzenesulfonate (SHQ), phenolphthalin (PPL), and 4,4′-biphenol (BP). The expected chemical structure of copolymers was confirmed by using FTIR and ¹H NMR. To balance the performance for PEM applications, the proportion of four different components were controlled. The influences of the carboxylic acid groups on the structure and properties of SPEN, including thermal and mechanical properties, oxidative stability, water uptake, swelling, proton conductivity, and methanol permeability, were investigated in detail. The results revealed that SPEN membranes containing nitrile and carboxylic acid groups could lead low water absorption, swelling, and methanol penetration. In such a way, efficient proton transport channels were constructed by the formation of the hydrogen bonds. The proton conductivity of SPEN with high sulfonation degree (DS >?0.6) was higher than 0.05 S/cm and increased with increasing temperature. Especially, the conductivity of SPEN-0.6 and SPEN-0.7 reached up to 0.157 and 0.267 S/cm at 80 °C, respectively. Meanwhile, SPEN membranes exhibit low methanol permeability (0.13 ×?10^-6– 0.52 ×?10^-6 cm²·s^?1). Consequently, the highest selectivity of SPEN-0.6 reaches 2.02 ×?10⁵ S·cm^?3·s, which is about 4.5 times higher than that of Nafion 117 (0.45 ×?10⁵ S·cm^?3·s). All the data prove that this series of membranes exhibits excellent comprehensive performance and might have potential applications in direct methanol fuel cells.     

Preparation and comparative structural properties of porous SnO2 microrods and submicrorods

A facile two-step approach has been used for the synthesis of porous SnO₂ rods: the initial room-temperature precipitation of precursor SnC₂O₄ and its subsequent thermal decomposition at 550 °C. Both the as-obtained porous SnO₂ microrods (length ～10.0?±?3.5 μm, diameter ～1.1?±?0.4 μm) and submicrorods (length ～5.8?±?1.9 μm, diameter ～0.4?±?0.1 μm) are the crystalline mixtures of major tetragonal and minor orthorhombic crystal phases, showing a tetragonal fraction of 84.7 and 87.0 %, respectively. When applied as a lithium-ion battery anode, the porous submicrorods (specific surface area ～13.6 m² g^?1) can deliver an initial discharge capacity of 1,730.7 mAh g^?1 with a high coulombic efficiency of 61.6 % and show the 50th discharge capacity of 662.8 mAh g^?1 at 160 mA g^?1 within a narrow potential range of 10.0 mV to 2.0 V. Similarly, even the anode of porous microrods (specific surface area ～11.8 m² g^?1) can still exhibit an initial discharge capacity of 1,661.1 mAh g^?1 at 160 mA g^?1 with a coulombic efficiency of 60.9 %. Regardless of the polymorphic nature, the acquired porosity may only alleviate the huge volume change of anodes for the first cycle; thus, the structural parameters of average size and specific surface area can be feasibly associated with the enhanced lithium storage capability. Anyway, these indicate a facile oxalate precursor method for the controlling synthesis and high performance of rodlike SnO₂ for lithium-ion batteries.     

50 MeV Li3+ ion irradiation effect on structural, electrical, and dielectric properties of PVA-based nanocomposite polymer electrolytes

Nanocomposite polymer electrolyte thin films of polyvinyl alcohol (PVA)-orthophosphoric acid (H₃PO₄)-Al₂O₃ have been prepared by solution cast technique. Films are irradiated with 50 MeV Li³⁺ ions having four different fluences viz. 5?×?10¹⁰, 1?×?10¹¹, 5?×?10¹¹, and 1?×?10¹² ions/cm². The effect of irradiation on polymeric samples has been studied and characterized. X-ray diffraction spectra reveal that percent degree of crystallinity of samples decrease with ion fluences. Glass transition and melting temperatures have been also decreased as observed in differential scanning calorimetry. A possible complexation/interaction has been shown by Fourier transform infrared spectroscopy. Temperature-dependent ionic conductivity shows an Arrhenius behavior before and after glass transition temperature. It is observed that ionic conductivity increases with ion fluences and after a critical fluence, it starts to decrease. Maximum ionic conductivity of ～2.3?×?10^?5 S/cm owing to minimum activation energy of ～0.012 eV has been observed for irradiated electrolyte sample at fluence of 5?×?10¹¹ ions/cm². The dielectric constant and dielectric loss also increase with ion fluences while they decrease with frequency. Transference number of ions shows that the samples are of purely ionic in nature before and after ion irradiation.     

Preparation and characterization of zirconium sulfophenyl phosphate-doped sulfonated poly(phthalazinone ether sulfone) composite proton exchange membrane

Polymer composite membranes based on sulfonated poly(phthalazinone ether sulfone) (SPPES) and zirconium sulfophenyl phosphate (ZrSPP) were prepared. Three ZrSPP concentrations were used: 10, 20, and 30 wt%. The membranes were characterized by infrared spectroscopy (IR), X-ray diffraction spectroscopy, thermal gravimetric analysis, and scanning electron microscopy (SEM). The IR results indicated the formation of intense hydrogen bonds between ZrSPP and SPPES molecules. The SEM micrographs showed that ZrSPP well dispersed with SPPES and form a lattice structure. The proton conductivity of the SPPES (degree of sulfonation (DS) 64 %)/ZrSPP (10 wt%) composite membrane reached 0.39 S/cm at 120 °C 100 % relative humidity and that of the 30 wt% of SPPES (DS 16.1 %)/ZrSPP composite membrane reached 0.18 S/cm at 150 °C. The methanol permeabilities of the SPPES/ZrSPP composite membranes were in the range of 2.1?×?10^?8 to 0.13?×?10^?8?cm²/s, much lower than that of Nafion®117 (10^?6?cm²/s). The composite membranes exhibited good thermal stabilities, proton conductivities, and good methanol resistance properties.     

MgAl2SiO6-incorporated poly(ethylene oxide)-based electrolytes for all-solid-state lithium batteries

Poly(ethylene oxide) (PEO)-based composite polymer electrolytes (CPEs), comprising various concentrations of lithium hexafluorophosphate and magnesium aluminium silicate, were prepared by hot-press technique. The membranes were characterised by scanning electron microscopy, tensile and thermal analyses. It has been demonstrated that the incorporation of the ceramic filler in the polymeric matrix has significantly enhanced the ionic conductivity, thermal stability and mechanical integrity of the membrane. It also improved the interfacial properties with lithium electrode. Finally, an all-solid-state lithium cell composed of Li/CPE/LiFePO₄ has been assembled and its cycling performance was analysed at 70 °C. The cell delivered a discharge capacity of 115 mAh g^?1 at 1 °C rate and is found to be higher than previous reports.     

Fabrication of highly selective PVA-g-GO/SPVA membranes via cross-linking method for direct methanol fuel cells

Organic/inorganic composite membranes were prepared using sulfonated poly(vinyl alcohol) (SPVA), mixed and cross-linked with different amounts of poly(vinyl alcohol)-grafted graphene oxide (PVA-g-GO). The introduction of PVA-g-GO to the membranes not only reduced the methanol permeability but also positively affected the mechanical properties: Increasing the PVA-g-GO content increased the blocking effect of GO. The PVA-g-GO/SPVA membranes were cross-linked with glutaraldehyde, resulting in the formation of cross-linking chains within the matrix, as well as between the matrix and the filler. Therefore, the microstructure of the PVA-g-GO/SPVA cross-linking membrane was different from that of the existing membranes. This structure also reduced the methanol permeability. The composite membranes exhibited proton conductivities ranging from 0.0141 to 0.0319 S/cm at 60 °C, and low methanol permeability ranging from 3.13?×?10^?7 to 1.53?×?10^?7 cm² s^?1 at 25 °C.     

Solid-Phase Extraction Using Polymer-Based Cartridge Modified with 2-(2-benzothiazolylazo)-3-hydroxyphenol for Preconcentration of Uranium(VI) Ions from Water and Real Samples

ABSTRACT

A highly sensitive, selective, and rapid method for the determination of ng mL^?1 level of U(VI) based on the rapid reaction of U(VI) with 2-(2-benzothiazolylazo)-3-hydroxyphenol (BTAHP) and the solid-phase extraction of the colored complex with a reversed-phase polymer-based C18 cartridge was developed. The BTAHP reacted with U(VI) to form a violet complex of molar ratio 2:1 [BTAHP to U(VI)] in the presence of 4.0 M of phosphoric acid solution and Triton X-114 medium. This complex was enriched by the solid-phase extraction with a polymer-based C18 cartridge. The enrichment factor of 200 was achieved. The molar absorptivity of the complex is 2.73 × 10⁶ L mol^?1 cm^?1 at 639 nm in the measured solution. The system obeys Beer's law in the range of 2.0–125 ng mL^?1, whereas the optimum concentration range obtained from Ringbom plot was 8.0–115 ng mL^?1. The relative standard deviation for 10-replicates sample of 100 ng mL^?1 level is 1.05%. The detection and quantification limits are 0.6 and 1.98 ng mL^?1 in the original sample. This method was applied to the determination of uranium(VI) in sea, tap, and waste waters, ore standard reference material, soil and sediment samples with good results comparing to the graphite furnace atomic absorption spectroscopy (GFAAS) method.     

Hard carbon derived from corn straw piths as anode materials for sodium ion batteries

Hard carbon is considered as the most promising anode material for practical sodium ion batteries. Herein, we report biomass-derived hard carbon made from corn straw piths through a simple carbonization process. X-ray diffraction patterns and Raman spectra elucidated highly disordered structures, and high-resolution transmission electron microscopy confirmed that the hard carbons have many local ordered structures containing turbostratic nanodomains and more nanovoids surround the turbostratic nanodomains. The electrochemical performances of the hard carbons were systematically investigated in sodium ion batteries. By optimizing the carbonization temperature, the sample carbonized at 1400 °C (HC1400) exhibited high reversible capacity of 310 mAh g^?1 and good cycling stability; the capacity can still retain 274 mAh g^?1 after 100 cycles. More importantly, HC1400 can deliver reversible capacity of 206 mAh g^?1 with 79% retention rate after 700 cycles measured at a current density of 200 mA g^?1, which is much better than those in most previous reports. This study provides a way to develop inexpensive, renewable, and recyclable materials from biomasses towards next-generation energy storage applications.     

Influence of the annealing technique on the properties of Li ion-conductive Li1.3Al0.3Ti1.7(PO4)3 films

Li_1.3Al_0.3Ti_1.7(PO₄)₃ films were comparatively prepared by rapid thermal annealing (RTA) and conventional furnace annealing(CFA). The phase identification and surface morphology of the prepared films were characterized by X-ray diffraction and scanning electron microscopy. The electrochemical window, ionic conductivity, activation energy, and electronic conductivity were conducted by cyclic voltammetry, electrochemical impedance spectroscopy, and four-probe technique. The results show that the films prepared by RTA and CFA are homogenous and crack-free. The film prepared by RTA shows smaller grains and is denser than the one prepared by CFA. The electrochemical windows of the two films are beyond 2.4 V. The ionic conductivities of the films prepared by RTA and CFA are 2.7?×?10^?6 S cm^?1 and 1.4?×?10^?6 S cm^?1, respectively. The activation energy of the film prepared by RTA is 0.431 eV, which is slightly smaller than the one prepared by CFA. The electronic conductivity of the two films is about 10^?10 S cm^?1.     

Preparation and properties of crosslinked hybrid proton exchange membrane based on sulfonated poly (arylene ether nitrile) with improved selectivity for fuel cell application

Novel sulfonated poly (arylene ether nitrile) with pendant carboxylic group copolymers have been prepared as proton exchange membranes which were applied in direct methanol fuel cells (DMFCs). Compared with others, this work shows two main advantages: the crosslinked method is uncomplicated and the membranes were prepared via the hydroquinonesulfonic acid potassium salt (SHQ) as crosslinker mingled in sulfonated poly (arylene ether nitrile) (SPEN) to avoid the decrease of proton conductivity. The obtained crosslinked membranes exhibited improved dimensional stability; larger tensile strength than that of pure SPEN; and good thermal, mechanical properties. Furthermore, after crosslinking, the membranes had low methanol permeability values (0.78–3.4 × 10^?7 cm² s^?1) and displayed good proton conductivities in the range of 0.0328–0.0385 S·cm^?1 at room temperature. The sample of SPEN-SHQ-5 % showed highest selectivity value of 4.205 × 10⁵ S·s cm^?3, which was 11.9 times higher than that of Nafion 117. All of these results indicated that these membranes would be the potential candidates as proton exchange membranes (PEMs) in DMFCs.     

Electrochemical characterization of ionic liquid based gel polymer electrolyte for lithium battery application

High molecular weight polymer poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP), ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIMFSI), and salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-based free-standing and conducting ionic liquid-based gel polymer electrolytes (ILGPE) have been prepared by solution cast method. Thermal, electrical, and electrochemical properties of 80 wt% IL containing gel polymer electrolyte (GPE) are investigated by thermogravimetric (TGA), impedance spectroscopy, linear sweep voltammetry (LSV), and cyclic voltammetry (CV). The 80 wt% IL containing GPE shows good thermal stability (~?200 °C), ionic conductivity (6.42?×?10^?4 S cm^?1), lithium ion conductivity (1.40?×?10^?4 S cm^?1 at 30 °C), and wide electrochemical stability window (~?4.10 V versus Li/Li⁺ at 30 °C). Furthermore, the surface of LiFePO₄ cathode material was modified by graphene oxide, with smooth and uniform coating layer, as confirmed by scanning electron microscopy (SEM), and with element content, as confirmed by energy dispersive X-ray (EDX) spectrum. The graphene oxide-coated LiFePO₄ cathode shows improved electrochemical performance with a good charge-discharge capacity and cyclic stability up to 50 cycles at 1C rate, as compared with the without coated LiFePO₄. At 30 °C, the discharge capacity reaches a maximum value of 104.50 and 95.0 mAh g^?1 for graphene oxide-coated LiFePO₄ and without coated LiFePO₄ at 1C rate respectively. These results indicated improved electrochemical performance of pristine LiFePO₄ cathode after coating with graphene oxide.     

Tribological characterization of TiCN coatings deposited by two crossed laser ablation plasma beams

The simultaneous laser ablation of two targets (graphite and titanium) in an Ar-N₂ gas mixture was carried out to deposit thin films of the ternary compound TiCN at room temperature. The base conditions used to produce the TiN without carbon were taken from our previous studies. The experimental conditions for the ablation of the carbon target were varied so that the carbon content in the films could be changed depending on the carbon ion energy. The control of the experimental conditions was carried out using a Langmuir planar probe which permitted the determination of the mean kinetic ion energy. The maximum hardness value of 35 GPa, was obtained with a carbon ion energy of about 250 eV, which corresponds to a film with 5 at% carbon content. In order to perform tribological and scratch tests, two types of substrate were used: nitrided AISI 316 stainless steel and AISI 316 stainless steel previously coated with a thin titanium layer (～50 nm). Values of the wear rate in the range of 1.39×10^?6 to 7.45×10^?5 mm³?N^?1?m^?1, friction coefficient from 0.21 to 0.28 and adhesion from scratch test measurements up to 80 N for final critical load, were obtained.     

Highly Sensitive Fluorescence Optode Based on Polymer Inclusion Membranes for Determination of Al(III) Ions

This paper reports the use of a polymer inclusion membranes (PIMs) for direct determination of Al(III) ions in natural water by using a fluorescence based optode. The best composition of the PIMs consisted of 60 wt.% (m/m) poly (vinyl chloride) (PVC) as the base polymer, 20 wt.% (m/m) triton X-100 as an extractant, 20 wt.% (m/m) dioctyl phthalate (DOP) as plasticizer and morin as the reagent, was used in this study. The inclusion of triton X-100 was used for enhancing the sorption of Al(III) ions from liquid phase into the membrane phase, thus increasing the optode fluorescence intensity. The optimized optode was characterized by a linear calibration curve in the range from 7.41?×?10^?7 to 1.00?×?10^?4 molL^?1 of Al(III), with a detection limit of 5.19?×?10^?7 molL^?1. The response of the optode was 4 min and reproducible results were obtained for eight different membranes demonstrated good membrane stability. The optode was applied to the determination of Al(III) in natural water samples. The result obtained is comparable to atomic absorption spectrometry method.     

Ionic conductivity and interfacial resistance of electrospun poly(acrylonitrile)/poly(methyl methacrylate) fibrous membrane-based polymer electrolytes for lithium ion batteries

Electrospun poly(acrylonitrile) fibrous membrane (PAN-EFM) is prepared and enhanced by adding poly(methyl methacrylate)(PMMA) and subsequently minimizing the average diameter of the PAN/PMMA blend fibers. Electrospinning of the 50/50 wt% PAN/PMMA solution is carried out with the aim of the simultaneous presence of both polymers on the fiber surface. Their presence in exterior surface is confirmed using the Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) technique next to the leaching of PMMA with acetone. The process parameters are optimized in four stable modes with the average diameter decreasing from 445 to 150 nm. Mechanical strength of the membrane is measured and reported. Comparing the sample electrochemical properties of the EFMs reveals that the addition of PMMA increases ionic conductivity from 1.02 to 3.31 mS cm^?1 and reduces interfacial resistance from ~1000 to ~400?Ω. It is also demonstrated that the ~300-nm reduction in average diameter of the blend fibers increases ionic conductivity from 3.31 to 5.81 mS cm^?1 and reduces interfacial resistance from ~400 to ~200?Ω.     

New-type low-cost cathode materials for Li-ion batteries: Mikasaite-type Fe2(SO4)3

In the present work, a new-type low-cost lithium ion battery cathode material, the Mikasaite-type iron sulfate, has been studied. It can be prepared by heating the water-containing iron sulfate raw chemicals in air atmosphere. The experimental results have shown that the oxidation and the reduction peaks are 3.92 and 3.37 V in the cyclic voltammogram, respectively, when the scanning rate is 0.05 mV s^?1. The galvanostatic measurements have explored that the voltage plateau during charging is slightly less than 3.70 V and the discharge voltage plateau is 3.40 V for the first cycle and 3.50 V for the following cycles at 0.1 C rate. The discharge capacity in the first cycle can reach 116 mAh g^?1, about 87 % of the theoretical capacity (134 mAh g^?1). It is believed that the product in the fully discharged state is Li₂Fe₂(SO₄)₃. However, the insertion reaction is reversible only for the second lithium ion. During cycling, the reversible capacity remains about 60 mAh g^?1. Further capacity fade is not found in the 20 discharge–charge cycles. The electrochemical impedance measurements have shown that there are two compressed semicircles in the Nyquist plots and a Warburg impedance in the low-frequency domain. The high-frequency semicircle is related with the electrode’s structural factor and the intermediate-frequency semicircle corresponds to the charge-transfer process.