Charge-discharge Measurements Research Articles

Tracing the impact of CO2 on the electrochemical and charge–discharge behavior for Al–Mg alloy in KOH and LiOH electrolytes for battery applications

For the first time, it has been found that the electrochemical performance of the Al–Mg alloy as an anode in alkaline batteries has been markedly enhanced in the presence of CO2 and LiOH as an electrolyte. This work compares the electrochemical performance of an Al–Mg alloy used as an anode in Al-air batteries in KOH and LiOH solutions, both with and without CO2. Potentiodynamic polarization (Tafel), charging-discharging (galvanostatic) experiments, and electrochemical impedance spectroscopy (EIS) are used. X-ray diffraction spectroscopy (XRD) and a scanning electron microscope (SEM) outfitted with an energetic-dispersive X-ray spectroscope (EDX) were utilized for the investigation of the products on the corroded surface of the electrode. Findings revealed that the examined electrode’s density of corrosion current (icorr.) density in pure LiOH is significantly lower than in pure KOH (1 M). Nevertheless, in the two CO2-containing solutions investigated, icorr. significantly decreased. The corrosion rate of the examined alloy in the two studied basic solutions with and without CO2 drops in the following order: KOH > LiOH > KOH + CO2 > LiOH + CO2. The obtained results from galvanostatic charge–discharge measurements showed excellent performance of the battery in both LiOH and KOH containing CO2. The electrochemical findings and the XRD, SEM, and EDX results illustrations are in good accordance.

Influence of Electrolyte Concentration on the Electrochemical Behavior of Copper Hexacyanoferrate as an Active Material for Zinc-Ion Batteries

This study investigates the impact of electrolyte concentration on the electrochemical behavior of copper hexacyanoferrate (CuHCF), a promising active material for aqueous zinc-ion battery electrodes. Cyclic voltammetry, charge-discharge measurements, and X-ray diffraction analysis were employed to assess the electrochemical reactions and structural integrity of the CuHCF electrode under varying electrolyte concentrations. The results revealed a significant influence of electrolyte concentration on the electrochemical performance of the CuHCF electrode. Specifically, the charge-discharge capacity exhibited an initial increase as the electrolyte concentration increased from 1.0 to 2.0 mol dm‒3, followed by a subsequent decrease. This decrease in capacity was attributed to the occurrence of an electrode/electrolyte interfacial reaction in the low-potential region of 0.0–0.3 V, coupled with structural changes in the CuHCF active material. Notably, these findings underscore the strong correlation between the electrochemical performance of the CuHCF electrode and the hydration structure of zinc ions, as well as the pH of the electrolyte solution. Thus, optimizing the electrolyte composition holds significant potential for enhancing the performance of aqueous zinc-ion batteries employing CuHCF electrodes.

Variation of electrochemical performance of Li2ZrCl6 halide solid electrolyte with Mn substitution for all-solid-state batteries

All-solid-state batteries (ASSLBs) have gained attention as a next-generation battery technology. Halide solid electrolytes may be a candidate material for next-generation batteries due to their high stability in combination with cathode-active materials and good deformability. However, the halide solid electrolyte exhibits low ionic conductivity compared to other solid electrolytes, such as oxide and sulfide solid electrolytes. In this study, in order to improve the ionic conductivity, a strategy is presented to increase the ionic conductivity by changing the Li + concentration and metal charge by doping Mn2+ in the trigonal Li2ZrCl6. Mn-doped Li2ZrCl6 is synthesized by high-energy ball-milling. Structural analysis is conducted by powder X-ray diffraction, 7Li-Nuclear magnetic resonance, Raman spectroscopy and X-ray photoelectron spectroscopy. Electrochemical performance is evaluated using electrochemical impedance spectroscopy, cyclic voltammetry and galvanostatic charge-discharge measurement. Each value of ionic conductivity in the bare and optimized compositions is 0.4 mS cm−1 and 0.8 mS cm−1, respectively. The activation energy of Li2ZrCl6 and 5 mol% Mn doped Li2ZrCl6 is 0.342 and 0.326 eV. Galvanostatic charge-discharge is conducted to confirm cycling performance. The initial discharge capacity for Li2ZrCl6 and 5 mol% Mn-doped Li2ZrCl6 are 171.6 and 185.6 mAh g−1, respectively.

Impact of Li-ions and CO2 on the electrochemical efficiency of Al and Al-4%Sn in KOH electrolyte for alkaline batteries application

This study investigates the electrochemical behavior of aluminum (Al) and aluminum‑tin (Al-Sn) alloy as anodes in aluminum-air (Al-air) batteries in a potassium hydroxide (KOH) electrolyte with varying concentrations of lithium hydroxide (LiOH), in both the presence and absence of carbon dioxide gas (CO2). Experimental techniques such as potentiodynamic polarization (Tafel behavior), galvanostatic charging-discharging processes, and electrochemical impedance spectroscopy (EIS) were employed. Characterization techniques including X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) were utilized to analyze the surface products of each electrode. The findings indicate a significant decrease in the corrosion current density (icorr.) for both two electrodes with increasing LiOH concentration, however, Al-Sn exhibits lower values than those of commercial Al. Moreover, the presence of Li-ions revealed an interesting phenomenon of Al, where icorr. gradually decreased with temperature rise. Also, in the presence of CO2, icorr. significantly decreased for both two electrodes, particularly Al-Sn, indicating complete repression of the corrosion process on the surface. The corrosion rate of the studied electrodes in basic solutions, with and without CO2, follows the order: KOH > KOH + LiOH > KOH + LiOH + CO2. Galvanostatic charge-discharge measurements demonstrated higher capacity, improved electrochemical performance, and excellent charge-discharge behavior in the presence of LiOH. The electrochemical findings align well with the results from XRD, SEM, and EDX analysis.

The effect of B – site cation on the supercapacitive properties of LaBO3 (B = Cr, Mn, Fe and Co) porous perovskites

Perovskite oxides have attracted great attention as favorable electrode materials for supercapacitors due to their sole structure, intrinsic oxygen vacancy and compositional flexibility. However, a facile synthetic route which is simple and economical is a challenging issue related to the synthesis of such complex functional oxides. We present a facile and ultrafast way to synthesize LaBO3 (B = Cr, Mn, Fe and Co) perovskite nanocrystallites using glycine-nitrate autocombustion followed by annealing. The structure, phase purity, thermal stability, morphology and surface features of thus synthesized perovskite oxides were analyzed by X-ray diffraction, Fourier transform infrared spectroscopy, Field emission scanning electron microscopy, High resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and Brunauer-Emmet-Teller measurements. The role of B – site cation on the electrochemical performance has been investigated by cyclic voltammetry, galvanostatic charge discharge measurements and electrochemical impedance spectroscopy. Electrochemical measurements showed that, among the synthesized materials, LaBO3 nanoparticles with smallest transition metal cation at its B – site, that is LaCoO3 delivered highest value of specific capacitance (750 F/g) and the value of specific capacitance decreases in the order LaCoO3 ˃ LaMnO3 ˃ LaCrO3 ˃ LaFeO3. Therefore, B – site transition metal cation holds the key to regulate perovskite's properties which are essential prerequisites for supercapacitors. An asymmetric device fabricated using LaCoO3 and activated carbon as the positive and negative electrode respectively acted in broad potential window (1.7 V) and delivered an energy density of 22.2 Wh/kg at a power density of 997.7 W/kg and two supercapacitors connected in series could power a red light emitting diode efficiently.

Harnessing the potential of NiMn2O4 nanoparticle: a next-generation supercapacitor electrode material

This research addresses the pressing demand to enhance energy density and power in energy storage devices, including batteries, fuel cells, and supercapacitors. Here, NiMn2O4 is synthesized using the urea combustion method. Characterization techniques, including powder x-ray diffraction, field emission scanning electron microscopy, and BET analysis, are employed to investigate its properties. The diffraction peaks showed that NMO had a face-centered tetragonal structure, and the Scherrer equation was used to figure out the average crystallite size (t) as 8.73 nm. Its electrochemical behavior is extensively evaluated through cyclic voltammetry and galvanic charge–discharge measurements. The findings indicate that the fabricated NiMn2O4 electrodes exhibited remarkable specific capacitance and exceptional cycling stability, retaining 97% of their initial performance over 10000 cycles. The specific capacitance of the electrode from GCD was obtained 80 F g−1 at a current density of 0.25 A g–1. This study highlights the potential of NiMn2O4 as an electrode material for high-performance electrochemical supercapacitors, offering a viable solution for advancing energy storage technologies.

The electrochemical performances of high surface area mesocellular anatase TiO2 foam anode for lithium–ion battery

Porous anatase TiO2 with mesocellular foam structure (MCF−TiO2) was facilely prepared through hard-templating using mesocellular foam carbon (MCF−C), which had been prepared through hard-templating using mesocellular silica foam (MCF). During the dual hard-templating processes, the MCF−TiO2 well preserved the original three-dimensional (3D) mesocellular nanostructure of MCF. The wall of MCF−TiO2 was composed of very tiny anatase TiO2 nanocrystals (NCs). The TiO2 NCs were of less than 20 nm dimension. The surface area of MCF−TiO2 was 144 m2 g−1, and the MCF−TiO2 also contained large void spaces. The high surface area 3D nanostructured anatase MCF−TiO2 with large void spaces was ideal for Li+ transport and charge transfer reactions when MCF−TiO2 was applied to the anode material of the lithium–ion battery (LIB). Galvanostatic charge–discharge measurement and cyclic voltammetry confirmed that the MCF−TiO2 was an efficient anode material. The specific capacity after 50 cycles at a current rate of 0.1C reached 187 mAh g−1; it also showed stable recycling performances due to the robust high surface area 3D nanostructure.

High‐Strength Self‐Healable Supercapacitor Based on Supramolecular Polymer Hydrogel with Upper Critical Solubility Temperature

AbstractHere, poly(N‐acryloylglycinamide‐co‐vinyltriazole) p(NAGA‐co‐VTZ) supramolecular polymer hydrogel doped with carbonized and activated polypyrrole nanotubes as a high‐strength self‐healable material is presented for supercapacitors. Initially, the p(NAGA‐co‐VTZ) hydrogel films are synthesized by photopolymerization of N‐acryloylglycinamide and 1‐vinyl‐1,2,4‐triazole without the use of any cross‐linkers. The hydrogels demonstrated remarkable self‐healing ability via hydrogen bonding at temperatures above upper critical solubility temperature, excellent mechanical properties (0.86 MPa), large stretchability (1300%) and cut resistance. Subsequently, carbonized and ethanol/KOH‐activated polypyrrole nanotubes (acNTs) are prepared as the active material for electrochemical double‐layer capacitors (EDLC). Then, a symmetric self‐healable supercapacitor employing p(NAGA‐co‐VTZ) hydrogel, acNTs and aqueous 3 m KCl solution is assembled. Cyclic voltammetry and galvanostatic charge–discharge measurements show that the prepared device gives a specific capacitance of 282.62 F g−1 at 0.2 A g−1 and a high areal capacitance of 316.86 mF cm−2 at a scan rate of 10 mV s−1. Importantly, the supercapacitor operates over a wide voltage window (0–1.2 V) and provides excellent cyclic performance with capacitance retention of 97% after 10 000 cycles and 94% after self‐healing. In summary, the developed self‐healable supercapacitor exhibits considerable potential as a high‐performance energy storage device.

One-Pot Facile Synthesis of a Cluster of ZnS Low-Dimensional Nanoparticles for High-Performance Supercapacitor Electrodes.

To maximize the use of ZnS low-dimensional nanoparticles as high-performance supercapacitor electrodes, this work describes a simple one-pot synthesis method for producing a cluster of these particles. The ZnS nanoparticles fabricated in this work exhibit a cluster with unique low-dimensional (0D, 1D, and 2D) characteristics. Structural, morphological, and electrochemical investigations are all part of the thorough characterization of the produced materials. An X-ray diffraction pattern of clustered ZnS nanoparticles reflects the phase formation with highly stable cubic blende sphalerite polymorph. The confirmation of nanoparticle cluster formation featuring multiple low-dimensional nanostructures was achieved through field emission scanning electron microscopy (FE-SEM), while the internal structure was assessed using transmission electron microscopy (TEM). Systematically assessing the ZnS nanoparticles' electrochemical performance reveals their prospective qualities as supercapacitor electrode materials. The electrode assembled with this material on Ni foam demonstrates elevated specific capacitance (areal capacitance) values, reaching 716.8 F.g⁻1 (2150.4 mF.cm-2) at a current density of 3 mA.cm⁻2. Moreover, it reflects 69.1% capacitance retention with a four times increase in current density, i.e., 495.5 F.g-1 (1486.56 mF.cm-2) capacitance was archived at 12 mA.cm-2 with 100% Coulombic efficiency. Furthermore, the electrode exhibits prolonged cycling capability with 77.7% capacitance retention, as evidenced by its charge-discharge measurements sustained over 15,000 cycles at a current density of 25 mA cm⁻2.

Electrochemical capacitance and hydrogen adsorption behavior of activated carbon derived from cattail fiber

AbstractIn this paper, we have reported the synthesis of activated carbon (AC) from biomass cattail fiber through hydrothermal carbonization, followed by chemical activation, and its electrochemical capacitance and hydrogen storage properties. The AC exhibits a Brunauer‐Emmett‐Teller (BET) surface area (SBET) of 1597.5 m2g−1, determined from the low‐pressure N2 adsorption isotherm at 77 K using a BET‐multipoint plot. The AC sample shows a reversible hydrogen adsorption capacity of 0.25 wt.% H2 (1.25 mmol H2 g−1) at 293 K and 74 atm. The capacitance performance of AC was investigated with various conductive additives such as carbon nanotubes (CNTs), carbon black (CB), and reduced graphene‐oxide (rGO). From galvanostatic charge discharge (GCD) and cyclic voltammetry (CV) measurements, the as‐derived AC with polymer binder exhibits a specific capacitance (Cs) of 245.2 F g−1 at 0.2 A g−1 and 158.1 F g−1 at 5 mV s−1. Among the investigated conductive additives, AC with CNTs in KOH electrolyte exhibit highest Cs of 326 F g−1 at 0.2 A g−1 and 173 F g−1 at 5 mV s−1. Furthermore, the symmetrical two‐electrode device fabricated using AC with CNTs (as a conductive additive) in 1 M aq. Na2SO4 electrolyte shows a Cs of 97.2 F g−1 at 0.1 A g−1. The energy and power densities of the two‐electrode device were observed to be 28 kW kg−1 and 2.64 Wh kg−1, respectively.

Pistachio Waste-Derived Activated Carbon Materials for Sustainable Energy Storage: Supercapacitor Applications

This study explores the potential of utilizing pistachio waste which is of low-cost and eco-friendly precursor for the synthesis of activated carbon for supercapacitor applications. Pistachio shells, a common agricultural waste product, were subjected to a controlled pyrolysis process followed by the activation to produce activated carbon materials. The resulting activated carbon was characterized by using various analytical techniques, including scanning electron microscopy (SEM), Raman spectroscopy, X-ray Photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electrochemical testing. The electrochemical performance of the pistachio waste-derived activated carbon was evaluated through cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) measurements. The pistachio waste-derived activated carbon exhibits excellent capacitive behaviour, with a high specific capacitance and good cycling stability. The use of agricultural waste-derived activated carbon not only addresses the environmental concerns but also contributes to the development of green energy storage solutions.

Exploring the potential of polyaniline-calcium titanate (PANI-CaTiO3) nanocomposites in supercapacitors: Synthesis and electrochemical investigation

This work presents the simple approach for the synthesis of CaTiO3 incorporated polyaniline nanocomposites (PANI- CaTiO3) by facile in-situ oxidative polymerization route, to be used as electrode materials for supercapacitors (SCs). The developed samples were evaluated using several analytical methods viz. X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, field emission scanning electron microscopy (FESEM), and Brunauer-Emmett-Teller analysis (BET). The electrochemical performance of the prepared nanocomposites for energy storage application was evaluated by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) in 3 M of KOH as an electrolyte. In comparison to pristine PANI, which demonstrated a specific capacitance of 257 Fg−1, and pure CaTiO3, which exhibited a specific capacitance of 142 Fg−1, the results of cyclic voltammetry (CV) for PANI-35 % CaTiO3 nanocomposites revealed a higher specific capacitance of 966 Fg−1 at 10 mV/s sweep rate. The highest energy density and power density for the PANI-35 % CaTiO3 nanocomposites were shown by galvanostatic charge-discharge (GCD) measurements to be 58.14 Whkg−1 and 3.2 kWkg−1, respectively, at a higher specific capacitance value of 984.21 Fg−1 at 6.86 Ag−1 current density. Additionally, the straight line in low frequency Nyquist plots was linked to the low electrolyte diffusion (Warburg) resistance within the electrode and ions diffusion into the electrode surface, confirming the CV results. Moreover, this study proposes an innovative research concept for the fabrication of electrode materials specifically designed for supercapacitors.

An eco-friendly polycaprolactone/graphite composite as a robust freestanding electrode platform for supercapacitive energy storage.

We present the successful development and characterization of a novel eco-friendly polycaprolactone-graphite (PCLGr) composite as a freestanding platform, serving as a bulk conducting chip electrode for supercapacitor applications. Notably, this is the first report of using this biodegradable polymer for making such a self-standing conductive platform. Traditional polymer and carbon-based electrodes often rely on insulating supports or non-eco-friendly materials, which we have addressed in our work. Direct deposition of the redox material, polyaniline (PANI), onto the electrode via the galvanostatic method has been achieved. The specific capacitance of PANI demonstrates comparability to previous studies utilizing conventional current collectors. Notably, the electrode exhibits exceptional stability in highly acidic environments. Comprehensive characterization utilizing bulk conductivity measurements, XRD, TGA, DSC, SEM, and stress-strain analyses shows advanced properties of the electrode. It complements the evaluation of PANI's supercapacitive performance through cyclic voltammetry, charge-discharge measurements, and impedance spectroscopy. We achieved a specific capacitance of ≈162 F g-1 at 0.5 A g-1. This innovative electrode presents a promising alternative to conventional counterparts across various electrochemical applications.

Carbon-doped titanium dioxide (TiO2) as Li-ion battery electrode: Synthesis, characterization, and performance

Development of lithium-ion batteries (Li-ion batteries) with high safety and solidity features has become a main challenge of researchers when practical implementations for large-scale energy storage systems are prioritized. In this work, we introduce a useful and efficient strategy to manufacture a long-standing and high-rate carbon-doped TiO2 (C-TiO2) as an anode material. Titanium (TiO2) and C-TiO2 were successfully prepared through hydrothermal method in order to improve the electrical performance of Li-battery. The structure and thermal properties were investigated by XRD, Raman and TGA; whereas the electrical properties were evaluated by Glvanostatic discharge–charge measurements. The density function theory (DFT) results revealed that TiO2 doped with carbon atoms causes considerable stress inside the crystal lattice of TiO2, and to avoid or minimize this stress the lattice of TiO2 underwent relaxation and then optimized. The performance of the prepared electrodes in Li-battery was analyzed by 100 cycles at different calcination temperatures of 400 and 450 °C. The results also showed the charge capacities of 400 and 500 mAhg−1 at 100 mAg−1.

Development of Novel High Capacity Fluoride Ion Battery Cathode Utilizing Anion Redox of Sulfur

All-solid-state fluoride-ion batteries (FIBs), which are based on the shuttling of fluoride ions, have been considered as one of the promising alternates for next-generation energy storage devices because of high theoretical energy density and safety. Benefiting from the multi-covalent fluorination process, metal/metal fluorides (M/MFx) have been firstly utilized as electrode materials for FIBs with high theoretical energy densities.[1] However, M/MFx systems suffer from exceptionable volume expansion upon fluorination process due to the close-packed metal atoms, which would cause blockage of the F- diffusion pathway, resulting in devastating damage to the electrode-electrolyte interfaces. To solve these problems, cathode materials that utilize topotactic fluoride ion intercalation reactions, similar to the electrode materials applied in lithium-ion secondary batteries, are being developed.[2] Cathode materials that utilize topotactic intercalation of fluoride ions are often composed of heavier elements than the cathodes of lithium-ion batteries that use the same type of reaction mechanism, and effective anion redox is required if capacity is to be increased beyond that of lithium-ion secondary batteries.In this research, we investigated Sr2F2Fe2OS2 (SFFOS) compound with a layered structure as a novel cathode material for all-solid-state FIBs, and evaluated its electrochemical properties and elucidated the charge compensation mechanism using anion redox of sulfur.SFFOS was synthesized by a solid-state reaction under vacuum environment using SrF2, SrO, Fe, and S.[3] SFFOS/La0.9Ba0.1F2.9/vapor grown carbon fiber (VGCF) was used as the composite cathode, La0.9Ba0.1F2.9 as the electrolyte and Pb/PbF2/ La0.9Ba0.1F2.9/VGCF as the composite anode to construct the electrochemical cell. Charge-discharge measurements were carried out in the cut-off voltage range of -1.5 to 1.5 V at 140°C. Ex-situ X-ray Diffraction (XRD), X-ray absorption spectroscopy (XAS) measurements of Fe K-edge, S K-edge, O K-edge and F K-edge were carried out under different state of charge during the 1st and the 2nd cycle.SFFOS showed reversible intercalation/de-intercalation of fluoride ions and a capacity of ~6.1 fluoride ions per unit cell (403 mAh g-1). The charge compensation mechanism was revealed for SFFOS by XAS measurements, where S redox contributed to the whole voltage range from -1.5 V to 1.5 V vs. Pb/PbF2, and Fe+2/+3 redox contributed from the middle SOC. The S-S dimers were formed upon charging, which was similar to the trapped O2 molecules observed in lithium-excess metal oxide during charge process[4]. Not only can the F- anions insert around Fe to form Fe-F bonds, but the excess F- anions can also occupy the Sr-S interstitial layers in the original lattice. Compared to the Fe-based layered oxide Sr3Fe2O5, the Fe-based oxysulfide SFFOS showed a lower average voltage but a higher specific capacity. We believe that this study could provide a new understanding of sulfur-based charge compensation and electrochemical fluorination reactions. Reference s : [1] D. Zhang, K. Yamamoto, Y. Uchimoto et al., J. Mater. Chem. A, 2021, 9, 406–412.[2] Y. Wang, K. Yamamoto, Y. Uchimoto, et al., Chem. Mater., 2022, 34, 609–616.[3] Kabbour H, Janod E, Corraze B, et al ., J. Am. Chem. Soc., 2008, 130(26): 8261-8270.[4] R. A. House, P. G. Bruce, et al., Nat. Energy 2020, 5, 777–785. Figure 1

Intercalation Reaction Mechanism of Fluoride-Ions in (Ca, Sr)FeO2 Cathodes with Infinite Layer Structure for All-Solid-State Fluoride-Ion Batteries

Fluoride ion batteries, which use fluoride ions as carriers, are attracting attention as the next generation of storage batteries because of their theoretical high energy density. Conventional research has focused on metal/metal fluorides such as Cu/CuF2 as cathode materials.[1] However, these cathodes have disadvantages of the power density and cyclability due to the rapid decrease in electronic conductivity and large volume change during fluorination and defluorination. To solve these problems, cathode materials that utilize topotactic fluoride ion intercalation reactions, similar to electrode materials applied in lithium-ion secondary batteries, are being developed[2]. However, these materials have the disadvantage of relatively small capacity, compared to metal/metal fluorides.In this study, we focused on SrFeO2and Ca-doped SrFeO2 cathodes with infinite layer structure as new high-capacity intercalation cathodes, and evaluated its electrochemical properties and clarified the charge compensation mechanism.Ca1-xSrxFeO2 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) was synthesized by a low-temperature reduction method using CaH2. Ca1-xSrxFeO2/La0.9Ba0.1F2.9/vapor grown carbon fiber (VGCF) was used as the composite cathode, La0.9Ba0.1F2.9 as the electrolyte and Pb/PbF2/ La0.9Ba0.1F2.9/VGCF as the composite anode to construct the electrochemical cell of the piezoelectric material. Charge-discharge measurements were carried out in the cut-off voltage range of -1.5 to 3.0 V at 140°C. X-ray absorption spectroscopy (XAS) measurements of Fe K-edge, O K-edge, and F K-edge and resonant inelastic X-ray scattering (RIXS) measurements of O K-edge were performed on the samples after charging and discharging.All the Ca1-xSrxFeO2 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) cathode showed voltage plateaus around -0.5 V and 1.5 V during charging, and the maximum discharge capacity (580 mAh g-1) was obtained when x = 0.8, and the cathodes could be repeatedly charged and discharged. XAS of the Fe K-edge revealed that Fe compensated for the charge in the flat potential region around -0.5 V. XAS and RIXS measurements of the O K-edge revealed that the charge compensation was carried out by the formation of O2 molecules (oxidation of oxide ions), as which is observed in lithium-excess metal oxide on charge process[4], in the voltage plateau around 1.5 V. Using inexpensive Ca and Fe, we succeeded in developing an intercalation cathode material that significantly exceeds the capacity of conventional lithium-ion battery cathodes.

Electrochemical Analysis of Charge Overpotentials in Non-Aqueous Lithium and Sodium Oxygen Batteries

Aprotic metal-oxygen batteries, especially Li-O2 and Na-O2 batteries, could afford theoretical specific energies of more than 500 Wh/kg. However, while not compromising on rechargeability, the practical realization of the theoretically possible high specific energies has been elusive. A better understanding of the differences and similarities between Li–O2 and Na–O2 battery systems in terms of charge-discharge mechanisms and parasitic chemistry will be meaningful in solving these challenges. Here, we explore the differences between the two systems using a combination of galvanostatic charge-discharge measurements, Differential Electrochemical Mass spectrometry (DEMS), and Potentiostatic Electrochemical Impedance Spectroscopy (PEIS) analysis. The discharge profiles of these battery chemistries are similar in terms of overpotential and have been widely studied. But the origins of the differences in charge overpotentials are not clear. Using in-situ pressure decay measurements during discharge, we calculated the number of electrons/oxygen (e-/O2) to be 2.02 and 1.01 for Li-O2 and Na-O2 cells, respectively. Further, DEMS analysis during charge has shown that the ideal 2 e-/O2 is attained only during the initial phases of charging for Li-O2 cells. However, for Na-O2, the ideal 1 e-/O2 is achieved during a signification portion of the galvanostatic charge step. We corroborate these findings with PEIS and distribution of relaxation times (DRT) analysis to develop a mechanistic view of the processes that lead to poor coulombic and oxygen evolution efficiencies in metal-oxygen cells. Based on DRT analysis, we identify a lower time constant process that is common to both Li-O2 and Na-O2 cells. Interestingly, we observed that voltage polarization is preceded by the observation of this lower time constant peak. In the case of Li-O2 cells, this lower time constant process was observed at the end of discharge and throughout the recharge process, while for the Na-O2 cells, this was only observed after about 70% of recharge. We discuss the possible origins of this low time-constant process and its implications for recharging metal-oxygen batteries. We will also discuss the role of singlet oxygen, if any, in the recharge efficiencies of these two aprotic metal-oxygen batteries. Our results imply that the identification of the origins of this lower time constant process and possible suppression of this process will be key for rechargeable metal-oxygen batteries.

Efficient Sodium-Ion Storage Using MoS2@rGO Nanocomposite Anode: Exploring Na-Ion Diffusion in Metallic Phase

Sodium-ion batteries (SIBs) are gaining attention as a better and more economical option than lithium-ion batteries, owing to the abundance and low cost of sodium in comparison to lithium. The anode component of rechargeable batteries plays a vital role in obtaining superior energy and power density. Consequently, the investigation of novel materials for SIBs with enhanced performance is imperative. Transition metal chalcogenides (TMDs) are found to be promising contenders for this purpose, particularly MoS2 due to their two-dimensional open framework, structural tunability, and high theoretical specific capacity as an anode material in sodium ion storage. In this regard, we conducted a facile strategy to synthesize MoS2 and aluminium-doped MoS2 incorporated into reduced graphene oxide (rGO) using the hydrothermal method. The structural and morphological properties of the samples have been explored through X-ray diffraction (XRD), Raman spectroscopy, field-emission scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) measurements which revealed that the addition of aluminium increased the interlayer spacing of the (002) plane of MoS2 nanosheets and stabilized it in metallic 1T phase. The enhanced interlayer distance and improved conductivity of the electrode material displayed a significantly higher initial discharge specific capacity of around 750 mAhg−1 which is stabilized around 380 mAhg−1 at the current rate of 50 mAg−1 after 10 cycles as investigated through galvanostatic charge-discharge measurement. The long cycling test for 200 cycles revealed the capacity retention of ~65% and ~55 % at the current density of 100 and 300 mAg-1, respectively. The kinetic behavior of the Na-ion is studied employing cyclic voltammetry (CV), galvanostatic intermittent titration technique (GITT), and electrochemical impedance spectroscopy (EIS), and the diffusion coefficient of Na-ion in the bulk of the electrode was found to be in the range of 10-10 to 10-12 cm2s-1. Additionally, in-situ EIS analysis demonstrates the electrode's electrochemical kinetics at different charge-discharge states by showing variations in charge transfer resistance. Ex-situ XRD and X-ray photoemission spectroscopy (XPS) demonstrated the coexistence of 1T and 2H phases, and field-emission SEM validated the stable morphology after cycling. Keywords: Sodium-ion batteries, Transition metal chalcogenides (TMDs), Anode material, MoS2

Reductive Treatment of δ-MnO2 with Sodium Borohydride: Method for Increasing the Electrode Material Capacitance

The effect of reductive treatment on the phase composition, morphology, and electrochemical parameters of δ-MnO2 produced by the hydrothermal method from KMnO4 at a temperature of 160°C in the presence of HNO3 was studied. δ-MnO2 processing with 3 M NaBH4 aqueous solution leads to partial reduction of Mn(IV) to Mn(III) and Mn(II). The electrochemical characteristics of the obtained electrode materials were examined by cyclic voltammetry, galvanostatic charge–discharge measurements, and impedance spectroscopy. Reductive treatment increases the specific capacitance of δ-MnO2 in 1 M Na2SO4 up to 204 F g–1 at a current density of 0.1 A g–1, and also reduces diffusion limitations during cycling due to an increase in the specific surface area. The loss of specific capacitance after 2000 charge–discharge cycles does not exceed 2.6%, which confirms the high electrochemical stability of the obtained electrode materials.

Preparation of Zn–Al–Gd-hydrotalcite and performance in zinc-nickel batteries

In this study, Zn–Al-Gd layered double hydroxides (LDHs) were synthesized via a hydrothermal method and investigated as possible negative electrode materials for zinc-nickel batteries. X-ray diffraction analysis and scanning electron microscopy images showed that the as-prepared samples were well crystallized with a hexagonal structure. The electrochemical performance was investigated for Zn–Al-LDHs and Zn–Al-Gd-LDHs with different Zn/Al/Gd molar ratios by cyclic voltammetry, Tafel polarization, electrochemical impedance spectroscopy, galvanostatic charge–discharge measurement, and cycle charge–discharge analysis. The initial discharge capacity reached 416.7 mAh g−1 for the Zn–Al-LDHs electrode and the discharge capacity decreased to 347.3 mAh g−1 after 150 cycles, with a cycle retention rate of 83.34 %. Compared with Zn–Al-LDHs, Zn–Al-Gd-LDHs with different Zn/Al/Gd molar ratios had higher discharge capacities and more stable cycling performance, especially the sample with Zn/Al/Gd = 3:0.8:0.2 (molar ratio). After 150 cycles, the retention rate for the sample with Zn/Al/Gd = 3:0.8:0.2 (molar ratio) was 88.73 %. Zn–Al-Gd-LDHs with a high rate capability can meet the needs of high-storage applications.