Galvanostatic Charge-discharge Profiles Research Articles

Effect of fluoride (CoF2) based electrode material for high energy and power density asymmetric flexible supercapacitors

Herein, an asymmetric supercapacitor (ASC) device was assembled by employing the pristine CoF2 as active positive electrode material and activated carbon (AC) as negative electrode material. The CoF2 electrode exhibited an outstanding electrochemical behavior with enhanced specific capacitance (Cs) of 872 F/g at 1 A/g current density in three electrode configurations. The reversible Faradaic redox reactions in CoF2 instigate the formation of cobalt-oxyfluorides and generating the mixed valence state of Co (Co2+ and Co3+) which improves its electrical conductivity and electrochemical behaviors. Furthermore, the room temperature paramagnetic nature of CoF2 increases the gradient force of ions which could possibly increase the redox reactions at the electrolyte/electrode interface. The constructed asymmetric device structure of CoF2//AC revealed a quasi-rectangular shaped cyclic voltametric curve and symmetrical semi-triangular shaped galvanostatic charge-discharge profiles, respectively, which affirms the combined electric double layer capacitance and pseudocapacitive nature by its hybrid assembly. Hence, the constructed CoF2//AC ASC demonstrated a remarkable specific capacitance of 141 F/g, energy density of 44.06 Wh.Kg−1, and power density of 422.97 W.Kg−1 at 1 A/g with the high cell voltage of 1.5 V. The CoF2//AC ASC device retained c.a. 92 % of its initial capacitance and attained over 96 % of Coulombic efficiency after 2000 cycles of charge-discharge profiles at 1 A/g, which suggests the high electrochemical stability. This admirable electrochemical performance and the origin towards the magneto-capacitance of CoF2 could pave a new way to explore next generation high-performance supercapacitors.

Clarifying the Limitations of Copper Hexacyanoferrate in Rechargeable Aqueous Zinc-Ion Batteries Via in Situ X-Ray Techniques

Copper hexacyanoferrate (CuHCF) is a compound belonging to the Prussian Blue Analogue (PBA) family, known for its open structure with cubic symmetry and large cavities capable of accommodating various cations, such as alkali-metal ions and divalent cations, making it an interesting candidate for ion-insertion batteries.CuHCF has been increasingly attracting attention for innovative approaches in rechargeable aqueous batteries which represent an emerging alternative technology for realizing sustainable and efficient stationary storage of intermittent electricity produced via renewable sources1.CuHCF stands out as an environmentally friendly cathode material in rechargeable aqueous Zn-ion batteries (ZIBs), enabling the realization of cost-effective and safe cells that support elevated charge/discharge rates and thus provide high power delivery2, 3. Relying only on abundant, inexpensive and non-toxic materials, combined with non-flammable and mildly acidic electrolytes, Zn/CuHCF cells are an attractive electrochemical system for addressing the challenges of developing energy storage devices for power grids due to their quick response and contained fabrication costs, although their energy density is intrinsically limited4 (< 100 Wh·kg-1).CuHCF displays one of the highest operating potentials (≈1.7 V vs. Zn2+/Zn) among cathode materials in aqueous ZIBs2, 3 and a modest capacity of ≈60 mAhg-1. Yet, what sets CuHCF apart is its ability to undergo ion insertion/de-insertion with negligible structural variations or volume changes5, making these electrodes apt for extensive cycling under heavy-duty conditions without risking induced mechanical or electrical damages causing early cell failure.However, a series of obstacles are present along the way of Zn/CuHCF cell development. Aside from issues on the Zinc side (e.g. uncontrolled Zn deposition/stripping), notoriously challenging in terms of interface stabilization6 and effective utilization4, significant limitations arise from the CuHCF ageing mechanisms during cycling. Such mechanisms have remained elusive so far, mostly due to the complexity of this compound and a simultaneous interaction of various species in the electrochemical processes. To date, there have been only speculative attempts to explain the capacity fading in CuHCF and, consequently, only a few scenarios have been suggested for it. Possible phase segregation and formation of spurious, non-stoichiometric Zn-rich phases (e.g. ZnxCu1-xHCF) have been argued7-9, while also signs of Cu dissolution were previously detected10, yet thought to be minimal and not affecting the CuHCF performances.Here, we will shed light on the limitations of CuHCF during cycling in ZIBs and explore its ageing mechanism by conducting a thorough study employing X-ray techniques11. Our investigation reveals that CuHCF is less stable than previously assumed, and that its debated Cu dissolution is linked to the ageing process11, forming Cu vacancies that can accept Zn2+. This Cu dissolution also results in a gradual activation of the Fe3+/Fe2+ couple, which has unambiguously been assigned to the appearance of a plateau on charge at ≈1.8 V vs. Zn2+/Zn (Figure 1). This is believed as the main contributor to the subsequent capacity loss. These insights into the CuHCF ageing in ZIBs may help in devising strategies to mitigate this critical aspect and improve battery performances in terms of stability and cycle life. Figure 1. (a) Scheme of an aqueous Zn/CuHCF cell. (b) Galvanostatic charge-discharge profiles of a Zn/CuHCF cell between 1.00 and 2.15 V at 0.6 mAcm-2. Note the emergence of a sloping plateau around 1.8 V and a slight capacity loss after 200 cycles. Acknowledgements M.V. acknowledges the funding by the ÅForsk Foundation, the support by the Swedish Electromobility Centre, the Swedish Energy Agency and StandUp for Energy. References C. D. Wessells, R. A. Huggins and Y. Cui, Nature communications, 2011, 2, 1-5.R. Trócoli and F. La Mantia, ChemSusChem, 2015, 8, 481-485. Z. Jia, B. Wang and Y. Wang, Materials Chemistry and Physics, 2015, 149, 601-606.G. Zampardi and F. La Mantia, Nature communications, 2022, 13, 687. V. Renman, D. O. Ojwang, M. Valvo, C. P. Gómez, T. Gustafsson and G. Svensson, Journal of Power Sources, 2017, 369, 146-153. Z. Cao, P. Zhuang, X. Zhang, M. Ye, J. Shen and P. M. Ajayan, Advanced Energy Materials, 2020, 10, 2001599.G. Kasiri, R. Trócoli, A. B. Hashemi and F. La Mantia, Electrochimica Acta, 2016, 222, 74-83. R. Trócoli, G. Kasiri and F. La Mantia, Journal of Power Sources, 2018, 400, 167-171. G. Kasiri, J. Glenneberg, A. B. Hashemi, R. Kun and F. La Mantia, Energy Storage Materials, 2019, 19, 360-369. J. Lim, G. Kasiri, R. Sahu, K. Schweinar, K. Hengge, D. Raabe, F. La Mantia and C. Scheu, Chemistry–A European Journal, 2020, 26, 4917-4922. M. Görlin, D. O. Ojwang, M.-T. Lee, V. Renman, C.-W. Tai and M. Valvo, ACS Applied Materials & Interfaces, 2021, 13, 59962-59974. Figure 1

Alleviating Manganese – Vanadium Redox Flow Batteries for Energy Storage and Subsequent Hydrogen Generation

Dual-circuit redox flow batteries (RFBs) consist of two discharging modes which has the potential to store energy beyond the capacity of the electrolytes in the form of hydrogen generation [1-3]. Inspired from the recent exploratory study by Reynard and Girault et al., this work focuses on utilizing Mn3+/Mn2+ (RFB catholyte ~ 1.51 V vs. SHE) in conjunction with V3+/V2+ (RFB anolyte ~ −0.26 V vs. SHE) as indirect redox mediators to drive mediated electrolysis of water in spatially separated external catalytic reactors [3]. The advantage of an additional layer to existing RFB is that a fully charged battery could potentially be chemically discharged particularly when green electricity is available in abundance to provide a secondary resource for energy such as hydrogen gas or other value-added commodity chemicals. However, Mn3+ is prone to rapid chemical disproportionation yielding Mn4+ which precipitates as MnO2(s) particles in acidic media, responsible for severe capacity fade during cycling. Studies in the literature suggest that oxygen scavenging additives such as V5+ is possibly the best defense mechanism to prevent MnO2 formation [4].In this study, the electrochemical behavior of Mn3+/Mn2+ couple in the favorable presence of V5+ is elucidated using cyclic voltammetry and ionic speciation diagrams. The voltammograms obtained under systematically varied conditions provide direct experimental evidence for competing redox reactions at the electrode surface. Nonetheless, the response measured from a macroelectrode mainly describes the quasi reversibility of the redox couple and gives little insight on electrode-electrolyte interface phenomenon. To obtain a more detailed picture of the diffusion layer, we employ carbon disk ultramicroelectrode (UME) for in-depth qualitative analysis. We anticipate that any deviation from the sigmoidal shape is an indication of a growing diffusion layer due to MnO2 passivation on the surface of electrode. Lastly, galvanostatic charge discharge profiles are obtained for Mn-V based redox flow battery with an aim to reveal the optimum state of charge because there exists a trade-off between the extent of Mn disproportionation within RFB during energy storage mode and volume of hydrogen gas produced during secondary mode. The knowledge obtained throughout the study will provide a fundamental understanding required for the rational design and development of aqueous electrochemical flow systems using Mn as the redox active species. Peljo, P., et al., All-vanadium dual circuit redox flow battery for renewable hydrogen generation and desulfurisation. Green Chemistry, 2016. 18(6): p. 1785-1797. Piwek, J., et al., Vanadium-oxygen cell for positive electrolyte discharge in dual-circuit vanadium redox flow battery. Journal of Power Sources, 2019. 439: p. 227075. Reynard, D. and H. Girault, Combined hydrogen production and electricity storage using a vanadium-manganese redox dual-flow battery. Cell Reports Physical Science, 2021: p. 100556. Reynard, D., et al., Vanadium-Manganese Redox Flow Battery: Study of MnIII Disproportionation in the Presence of Other Metallic Ions. Chemistry - A European Journal, 2020. 26.

Characterization of alginate hydrogel electrolytes for use in symmetric supercapacitor based on polypyrrole-modified electrodes

The use of biopolymers for the preparation of gel polymer electrolytes (GPEs) to construct high-performance energy storage devices contributes to the development of new sustainable materials. Herein, an alginate-based gel electrolyte was used in the construction of a supercapacitor, to aim for an environmentally friendly device. Alginate was crosslinked with calcium ions (ALG-Ca2+) resulting in gels with good mechanical properties and ionic conductivity, suitable for their use as electrolyte and separator for a symmetric supercapacitor, assembled in a coin cell architecture and using polypyrrole as the electrode. The device presented a specific cell capacitance of 39.5 F g-1 at 0.2 A g − 1, and durability of 70.9% after 2000 galvanostatic charge-discharge (GCD) cycles. Based on these properties, three devices were connected in series and demonstrated to be able to light up a 3.0 V LED. The influence of temperature on supercapacitor performance was verified by varying the temperature from 10 to 60 °C and evaluating the characteristic cyclic voltammograms and GCD profiles. The devices were able to operate in the temperature range of 10 to 60 °C, with no loss of their capacity properties.

Diverse carbonous nanocomposites of Ce2Y2O7 for boosting hydrogen storage capacity; Synthesis, characterization and electrochemical studies

Carbon based materials due to high conductivity can provide the best conditions for energy storage through electrochemical process. Especially, nanosized carbon materials with active sites can participate in the hydrogen storage process along with metal oxide compounds. This work focuses on the hydrogen storage ability of sol-gel synthesized Ce2Y2O7 nanoribbons as active materials. Effect of carbonous materials with different structures such as GO, N-GQDs and g-C3N4 were compared on the hydrogen storage capacity of Ce2Y2O7 nanoribbons. The provided carbonous nanocomposites were characterized using different methods in terms of identification of phase purity, shape and porosity. The galvanostatic charge-discharge profiles for all samples performed for achieving ideal capacitance. The results illustrate the maximum discharge capacity of 656, 686 and 757 mAhg−1 for nanocomposites of GO/Ce2Y2O7, N-GQDs/Ce2Y2O7 and g-C3N4/Ce2Y2O7, respectively while the pristine Ce2Y2O7 nanoribbons have discharge capacity of 643 mAhg−1 after 15 cycles.

A new cadmium oxide (CdO) and copper selenide (CuSe) nanocomposite: An energy-efficient electrode for wide-voltage hybrid supercapacitors

In this paper, cadmium oxide (CdO) was effectively developed on copper selenide (CuSe) nanoparticles via the wet-chemical method for the first time to explore their electrochemical properties for hybrid supercapacitors (HSC). The XRD Raman analysis proves the successful formation of the CdO, CuSe, and CdO-CuSe nanocomposite. The morphological results exposed that CdO and CuSe are composed of irregular particles-like morphology. Cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) analysis demonstrated the battery-type behavior of the electrode materials, with prominent redox peaks and voltage plateau in the GCD profile with good reversibility. Interestingly, it was observed that the freshly prepared CdO-CuSe electrode displays a relatively higher capacity (386 C/g) compared to CdO and CuSe electrodes (175 and 216 C/g). Furthermore, we built a CdO-CuSe//AC HSC, which expanded the voltage limit to 1.8 V. It delivered a high energy and power densities of 51 Wh kg−1 and retained 16 Wh kg−1 when power density reached its maximum value of 6488 W kg−1. More importantly, a stable cycling performance (94.8%) was attained after 9000 cycles at the highest current rate of 15 A g−1, which can be attributed to the high conductivity, which offers more active sites for electrolyte ions on the electrode surface.

Synthesis of Molybdenum Sulfide/Tellurium Hetero-Composite by a Simple One-Pot Hydrothermal Technique for High-Performance Supercapacitor Electrode Material.

It is necessary to investigate effective energy storage devices that can fulfill the requirements of short-term and long-term durable energy outputs. Here, we report a simple one-pot hydrothermal technique through which to fabricate the MoS2/Te nanocomposite to be used as an effective electrode material for high-performance supercapacitors. Comprehensive characterization of the as-fabricated nanomaterial was performed using FESEM, HRTEM, XRD, FTIR, XPS, etc., as well as electrochemical characterizations. The electrochemical characterization of the as-fabricated nanocomposite electrode material showed a high specific capacitance of 402.53 F g−1 from a galvanostatic charge-discharge (GCD) profile conducted at 1 A g−1 current density. The electrode material also showed significant rate performance with high cyclic stability reaching up to 92.30% under 4000 cycles of galvanostatic charge-discharge profile at a current density of 10 A g−1. The highly encouraging results obtained using this simple synthetic approach demonstrate that the hetero-structured nanocomposite of MoS2/Te electrode material could serve as a promising composite to use in effective supercapacitors or energy storage devices.

Capacitive properties of novel Sb-doped Co3O4 electrode material synthesized by hydrothermal method

We are reporting here a novel antimony doped cobalt oxide based electrode material for supercapacitor application to overcome the current scenario of energy crises by offering excellent capacitive abilities. A facile hydrothermal route was employed to produce this antimony doped cobalt oxide material by varying content value of antimony in the range of 2–6 at. %. The X-ray diffraction results have successfully explored the cubic crystal structure along with phase composition of these as obtained Sb doped Co3O4 materials. The development of sub-micron sized structures-based material was explored by obtaining scanning electron microscopic images. The energy dispersive X-ray spectroscopy results have shown the highly pure nature of as obtained material. Cyclic voltammogram results have exhibited that among the SbCo-0, SbCo-2, SbCo-4 and SbCo-6 materials, SbCo-4 has exhibited higher specific capacitance value i.e 894.15 F/g than remaining, which was obtained by scanning the material at the scan rate of 5 mV/s. More significantly, Galvanostatic charge-discharge profiles obtained at different scan rates ranging from 1 to 10 A/g, for SbCo-4 material has shown even good capacitance retention i.e 75.70% at higher sweep rate, equal to 10 A/g. On the basis of electrochemical impedance spectroscopic analysis, it is concluded that this material has also shown excellent conductive properties. Furthermore, after performing 3000 galvanostatic charge-discharge cycles, it is concluded that this material can possessed an excellent cycling stability equal to 82.02%. All these excellent capacitive properties shown by this material have suggested that it can be proved as a potential applicant in the field of energy storage devices.

Preparation and high-performance lithium storage of intimately coupled MnO2 nanosheets@carbon nanotube-in-nanotube

MnO2 nanosheets@carbon nanotube-in-nanotube is rationally constructed through carbonization of tannic acid-treated zeolitic imidazolate framework-8 string of carbon nanotubes and subsequent chemical reaction of KMnO4 and carbon. The ultrathin MnO2 nanosheets are intimately coupled on the surface of carbon nanotube-in-nanotube. The composite shows large specific surface area (126.6 m2 g−1) and pore volume (0.4 cm3 g−1). Comparative studies of cyclic voltammetry curves and galvanostatic charge-discharge profiles indicate that for MnO2 nanosheets@carbon nanotube-in-nanotube, electrochemical activities and charge-discharge capabilities of MnO2 and carbon are both significantly improved. The cycling measurements reveal that the composite shows much higher reversible capacity and cycling stability than pure MnO2, carbon nanotubes, carbon nanotube-in-nanotube and MnO2 nanosheets@carbon nanotubes. The superior Li storage performance is attributed to synergistic effect of MnO2 nanosheets and carbon nanotube-in-nanotube. The ultrathin nanosheet structure of MnO2 and the unique nanotube-in-nanotube structure of carbon remarkably shorten diffusion paths of Li ions, facilitate transport of electrolyte ions, promote contact between electrode material/electrolyte, improve structural stability of the composite, increase electronic conductivity of MnO2, enhance reaction kinetics.

Development of Catalyst with Optimum Calcination Temperature for the Application of Zinc-Air Battery

Zinc-air batteries (ZABs) have been considered as the next-generation electrochemical energy-storage devices due to the high theoretical energy density. It has a theoretical specific energy density of 1086 W h kg−1, which is 2.5 times higher than that of Li-ion battery [1]. Moreover, the appropriate operating voltage of ZAB is ca. 1.65 V, which is not too high to induce the decomposition of water in electrolyte. However, the actual voltage drop may occur (less than 1.40 V) depending on the applied current density. Takeguchi et al. [2] reported that the origin of this drop is mainly due to the high overpotential. As a result of increased overpotential, the performance of charge/discharge reaction and stability decrease. In order to improve the kinetics reaction and stability of oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), non-precious metals as electrocatalysts need to be used more efficiently. Perovskite oxides are one such promising family of multifunctional materials, which possess catalytic activity toward the OER/ORR, especially LaSrFeCoO is considered as cost-effective catalyst for application in rechargeable ZABs [2]. However, its electrocatalytic activities and stability remain poorly understood. Herein, we prepared LaSr3Fe1.5Co1.5O10-δ (LSFCO) catalyst using different calcination temperatures due to investigate the effects of catalytic performance. The effects of calcination temperature on structural properties and its catalytic performance were investigated using different characterization methods, such as SEM, EDX, XRD, charge-discharge and so on.For preparation of LSFCO perovskite oxide as cathode catalyst, complex polymerization synthesis method was used. High-purity La(NO3)3 × 6H2O (99%), Sr(NO3)2 (98%), Fe(NO3)3 × 9H2O (99%), Co(NO3)2 × 6H2O (98%), C6H8O7 (99%), and distilled water were used as stirring materials. The mixture was kept in the oil bath at 120 ºC with the constant stirring at 300 rpm till the gels were completed. Then, the gels were dried at 200 ºC for 1 h. Finally, the LSFCO powders were obtained 1200, 1300, 1350, and 1400 ºC for 2 h each. Besides, electrolyte solution was prepared by mixing of 26.4 g of KOH (85%), 3.0 g of ZnO (99%) and approximately 100 mL of distilled water.Fig. 1 shows the XRD patterns of LSFCO perovskite catalysts synthesized with different calcination temperatures ranging from 1200-1400 ºC. As shown in Fig.1, almost similar diffraction peaks are observed for all of the samples. All of the samples exhibit the obvious peaks, and no other unknown impurity peak was detected. It can be ascribed to the well-crystallized perovskite structure. To elucidate the temperature effects on the surface morphology of as-prepared LSFCO perovskite catalysts, SEM observation was performed. Fig. 2 shows the SEM image of LSFCO. As shown in Fig (a)-(d), the average grain size of LSFCO increases with increasing calcination temperature level. The estimated size of the particles are ca. 1.5 µm, 5.0 µm, 7.0 µm, and 12 µm for the LSFCO perovskite catalysts obtained at 1200 ºC, 1300 ºC, 1350 ºC and 1400 ºC, respectively. The chemical composition of the as-prepared catalyst is examined by EDX, which is consistent with the reported literatures. Fig. 3 shows the galvanostatic charge-discharge profiles of ZABs prepared with LSFCO perovskite oxide as cathode catalyst and polished zinc foil as an anode at 1.0 mA/cm2 under O2. As shown in Fig. 3, the LSFCO perovskite oxide catalysts prepared at calcination temperatures of 1300 ºC, 1350 ºC and 1400 ºC exhibit the charge-discharge voltage gaps of ca. 1.50, 1.70 and 1.50 V, respectively. Low charge-discharge voltage gaps, i.e. the low overvoltage of the device can be attributed to its efficient bifunctional O2 activation. On the other hand, the higher energy efficiency of ca. 27.2% was achieved in the case of LSFCO perovskite oxide catalyst prepared at 1300 ºC, while it is 11.8% and 22.3% in the case of 1350 ºC and 1400 ºC, respectively. Therefore, it can be concluded that the LSFCO catalyst prepared at 1300 ºC is the most promising bifunctional catalyst for both OER and ORR because of its overall superior catalytic activity, high energy efficiency and stability compared with LSFCO catalysts prepared at 1350 ºC and 1400 ºC, respectively. Finally, this approach with simple synthetic route is highly suitable for commercialization of ZABs operated in an ambient air environment.Acknowledgement:The authors would like to thank the Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, Japan for financial support of this work.

Structural and Electrochemical Properties of the High Ni Content Spinel LiNiMnO4

This work presents a contribution to the study of a new Ni-rich spinel cathode material, LiNiMnO4, for Li-ion batteries operating in the 5-V region. The LiNiMnO4 compound was synthesized by a sol-gel method assisted by ethylene diamine tetra-acetic acid (EDTA) as a chelator. Structural analyses carried out by Rietveld refinements and Raman spectroscopy, selected area electron diffraction (SAED) and X-ray photoelectron (XPS) spectroscopy reveal that the product is a composite (LNM@NMO), including non-stoichiometric LiNiMnO4-δ spinel and a secondary Ni6MnO8 cubic phase. Cyclic voltammetry and galvanostatic charge-discharge profiles show similar features to those of LiNi0.5Mn1.5O4 bare. A comparison of the electrochemical performances of 4-V spinel LiMn2O4 and 5-V spinel LiNi0.5Mn1.5O4 with those of LNM@NMO composite demonstrates the long-term cycling stability of this new Ni-rich spinel cathode. Due to the presence of the secondary phase, the LNM@NMO electrode exhibits an initial specific capacity as low as 57 mAh g−1 but shows an excellent electrochemical stability at 1C rate for 1000 cycles with a capacity decay of 2.7 × 10−3 mAh g−1 per cycle.

CNTs embedded in layered Zn-doped Co3O4 nano-architectures as an efficient hybrid anode material for SIBs

Advantageous utilization of sodium-ion batteries (SIBs) requires superior performance, enriched with cost-effective anode materials, having excellent storage capability, high conductivity, and structural stability. Hybrid structures based on inorganic metal oxides and organic nano-carbons are evolving as satisfactory electrode materials for the next-generation SIBs owing to their exceptional properties. In this study, Co2.98Zn0.02O4/CNTs hybrid is synthesized using a facile hydrothermal followed by a solvothermal route. As prepared hybrid has been utilized as an anode in a Na half cell and the results are compared with Co2.98Zn0.02O4 and bare Co3O4 anodes. Galvanostatic charge-discharge profiles revealed a high reversible capacity of 721 mAh g−1 for the electrode containing carbon nanotubes (CNTs) i.e. Co2.98Zn0.02O4/CNTs exhibiting remarkable coulombic efficiency of 99% as compared to the other two electrodes. The hybrid anode showed improved capacity retention (289 mAh g−1) after 100 cycles as computed from the cyclic test which is much higher than bare Co3O4. The rate capability test of Co2.98Zn0.02O4/CNTs showed that specific capacity retained as high as 138 mAh g−1@10 C which is an outstanding rate performance, whereas bare Co3O4 couldn’t perform even after 0.5 C. Sodium insertion/extraction is also improved for Co2.98Zn0.02O4/CNTs, as revealed by electrochemical impedance and diffusion coefficient. From these findings, it is inferred that carbon-based Zn-doped Co3O4 hybrid electrode materials can be a superior combination for high-performance and fast charging future SIBs.

Enhanced electrochemical properties of silver-coated zirconia nanoparticles for supercapacitor application

ABSTRACT Silver-coated ZrO2 and individual ZrO2 nanoparticles have been synthesized using the simple reduction and co-precipitation methods, respectively. The synthesized products were examined using the X-ray diffraction, energy-dispersive X-ray and UV–visible spectroscopy, which confirmed the successful synthesis of materials. Scanning electron microscopy and transmission electron microscopy revealed the round-shaped nanoparticles of both materials. The cyclic voltammograms revealed the well-defined redox peaks and recommended the pseudocapacitive nature of the electrodes. The silver-coated zirconia showed higher specific capacitance of 792 F/g at 10 mV/s as compared to individual zirconia (10.22 F/g). Silver-coated ZrO2 also showed good power density of 274.5 W/kg at current density of 5 mA/cm2 through the galvanostatic charge discharge profile. Hence, the results suggest that silver-coated ZrO2 showed improved electrochemical performance as compared individual ZrO2 due to higher electrical conductivity and specific surface area. Hence, silvercoated ZrO2 nanoparticles can be employed as an electrode material for supercapacitor applications.

Improving Kinetic in Redox Conversion By Adopting Cosse Catalytic Material in Li-S Battery

The increasing demand of the energy sources and devices are facilitating the needs of the development in the energy storage systems. Lithium-sulfur (Li-S) battery is considered as one of the most promising energy storage systems because of its high theoretical energy density (2600 Wh kg-1), natural abundance leading to low cost, and their environmental friendliness. However, there are some obstacles to be solved in order to use the Li-S battery practically as follows. First, the sulfur and finally reduced product (Li2S) have a low conductivity, impeding the rate of reactions, and hence limiting total utilization the active sulfur. Second, the shuttling of the polysulfide intermediates (Li2Sx, 4 ≤ x ≤ 8) (Shuttle effect) leads to the low Coulombic efficiency and fast degradation of both electrodes of Li metal and Sulfur. Particularly, the transformation from liquid to solid state occurs unevenly on the surface of sulfur, leading to the aggregation, and hence a large overpotential [1]. To overcome such the problems, some researchers have adopted various methods to prevent the shuttling of the polysulfides. Though many effective structures of the carbon and heteroatom doped carbons have been presented, it is not enough to perfectly hold the polysulfides because of the low polarity of the carbon. Recently, metal sulfides have been reported for their strong affinity with the polysulfides. However, to enhance the kinetics in the Li-S battery, it is not only important to have a high interaction between polysulfides, but should have interfacial advantages to provides nucleation sites of Li2S2/Li2S, that can prevent aggregation during growth and increase electrical conductivity for fast redox reaction between polysulfide chain and solid products.In the context, we developed the cobalt sulfide selenide, CoSSe with high catalytic activity for redox conversion of sulfur. The material is formed on the porous carbon framework, which was also synthesized in this work, with as the large active surface.The as-prepared CoSSe particles show the average size of about 200 nm (Figure 1a). For those composite with the carbon (Figure 1b), it shows that the carbon has CoSSe particles on the surface and comprises the many pores with an average diameter of ~1µ, that can infiltrate the sulfur inside. The XRD results demonstrates that the CoSSe the CoS2 and CoSe2 are both in the pyrite group (Figure 1bTo verify the catalytic effects of the CoSSe/C, the chemical adsorption ability of CoSSe was tested by UV-vis spectroscopy (Figure 2a). The supernatant containing CoSSe clearly shows reduction in 340 nm and 420 nm, which are from the Li2S6, confirming the CoSSe has high binding capability of liquid-phase polysulfides [3]. Enhanced in the liquid-liquid phase kinetics of redox reactions was probed by the symmetric cells with Li2S6 containing electrolyte, which CoSSe/C exhibited a higher current density than that of Ketjenblack (KB) showing catalytic capability (Figure 2b). Galvanostatic charge-discharge profiles show the actual improvement in the Li-S cell when using CoSSe/C with sulfur infiltrated (CoSSe/C@S) (Figure 3). It shows that the CoSSe/C@S exhibits a higher initial capacity (1487 mAh g-1 vs. 1320 mAh g-1) and also has a lower polarization between charge and discharge plateau (0.16 V vs. 0.18 V) than C@S. Also, Figure 3c-d shows that the CoSSe/C@S has an overpotential of 0.021 V for the initiate charging, while C@S has 0.066 V, demonstrating that CoSSe facilitates the redox conversion in solid to liquid phase. From these results, it is concluded that the fabricated CoSSe with a pyrite structure has more effective properties in enhancing the redox reaction of polysulfide intermediates.

Electrochemical performance of Li2MnSiO4/C lithium-ion cathode materials with low-level doping of Ru in the Mn site

Lithium manganese orthosilicate (Li2MnSiO4, LMS), a prospective high-voltage lithium-ion battery cathode material, exhibits poor cycling performance due to structural instabilities during charge and discharge. To alleviate cathode degradation and understand the effects of transition metal dopants on the material properties, Mn was partially substituted by Ru between 0.5 and 3 mol% in carbon-coated LMS (LMS/C) cathode. Undoped LMS/C had orthorhombic LMS structure in the Pmn21 space group. While Ru doping of 0.5 and 1 mol% yielded phase-pure orthorhombic Pmn21 phase, Ru doping of 3 mol% yielded an additional orthorhombic Pmnb phase. The galvanostatic charge-discharge profiles showed a slight improvement in first discharge capacity for 0.5 mol% Ru-doped LMS/C compared to undoped LMS/C, but the discharge capacity decreased with higher doping levels. The capacity retention, however, improved with increasing doping level. In situ XRD results showed that Ru-doped LMS/C was able to retain a higher level of crystallinity than undoped LMS/C during the first charge. By the end of the first charge, in situ XANES of LMS/C revealed that Mn2+ in [MnO4] was partially oxidized to Mn3+ in [MnO6] ligand upon first charging, which coincided with a reduction in crystallinity of LMS/C. As shown by in situ XANES, Ru doping decreased the extent of oxidation of Mn2+ to Mn3+ upon charging. The results revealed that Ru doping of LMS/C between 0.5 and 3 mol% in the Mn site could help maintain Li2MnSiO4 crystallinity during the initial charging step.

Alternately Dipping Method to Prepare Graphene Fiber Electrodes for Ultra-high-Capacitance Fiber Supercapacitors.

SummaryFlexible fiber supercapacitors are promising candidate for power supply of wearable electronics. Fabrication of high-performance fibers is in progress yet challenging. The currently available graphene fibers made from wet-spinning or electro-deposition technologies are far away from practical applications due to their unsatisfactory capacitance. Here we report a facile alternately dipping (AD) method to coat graphene on wire-like substrates. The excellent mechanical properties of the substrate with greatly diverse choices can be carried over to the fiber supercapacitors. Under such guideline, the graphene fiber with a titanium core made by our AD method (AD:Ti@RGO) shows an ultra-high specific capacitance of up to 1,722.1 mF cm−2, which is ∼1,000 times that of wet-spinning- and electro-deposition-fabricated neat graphene fibers and presents the highest specific capacitance to date. With excellent mechanical properties and striking electrochemical performances, the AD:Ti@RGO-based supercapacitors light the path to the next-generation technologies for wearable devices.

NiF2 as an efficient electrode material with high window potential of 1.8 V for high energy and power density asymmetric supercapacitor

We investigated NiF 2 as an energy storage material in asymmetric supercapacitor together with activated carbon (AC) as the counter electrode. Cyclic voltammetry and galvanostatic charge-discharge profile are carried out to investigate the oxidation-reduction process and capacitive behavior of the NiF 2 sample. The interfacial electron transport properties of the sample are also explored using Nyquist plots in two and three electrodes configurations of electrochemical impedance spectroscopy. A very high specific capacitance of 751 F/g is achieved at 1 A/g current density in three electrode system. Further, the asymmetric supercapacitor device based on NiF 2 //AC structure reveals high capacitance of 175 F/g at 1 A/g in the high window potential of 1.8 V. The fabricated device retained 93% of its initial capacitance after 1000 cycles at 3 A/g current density affirms high electrochemical stability of the device. Ragone plot depicts high energy density of 79.65 Wh/kg with power density of 1727.35 W/kg for 1.8 V window potential at 1 A/g current density. High electrochemical stability of NiF 2 sample endures the tetragonal phase even after electrochemical measurement which can be more useful in recycling the electrode material for future recycled supercapacitor devices. • Pristine NiF 2 was employed for the fabrication of asymmetric supercapacitor device. • NiF 2 //AC device presented high C s of 175 F/g@1 A/g with high window potential of 1.8 V. • Ragone plot depicts high E D = 79.65 Wh/kg and P D = 1727.35 W/kg for 1.8 V@1A/g. • After electrochemical measurement, NiF 2 can be recyclable for further device fabrication.

Charge redistribution and electrode history impact galvanostatic charging/discharging and associated figures of merit

This work highlights, for the first time, the important impact of charge redistribution (CR) on the results of galvanostatic charge/discharge (GCD) experiments, as demonstrated with pseudocapacitive manganese oxide films and a transmission line circuit. CR causes the GCD protocol (single- vs. multiple-currents) and electrode history to significantly influence the profile shape and associated figures of merit. Systems that have undergone previous GCD cycling display much shorter charging profiles as CR has already somewhat charged the bulk material in the previous cycles. CR in early GCD cycles can also introduce curvature in the GCD profile. Because of these CR effects, we calculate a full range of the typical GCD-derived figures of merit (capacitance, capacity, energy, coulombic- and energy-efficiencies and Ragone plots) to identify those most strongly impacted by CR and those which are impervious. Generally, the charging data show significant CR-induced variations; the discharging profiles are relatively unaffected by CR. With multiple cycles, the data from the different experimental protocols coalesce. Clearly, researchers must consider CR when designing GCD protocols and evaluating data. Additionally, literature comparisons between GCD data are not possible without an exact description of the experimental protocol and cycle number used to calculate the figures of merit.

Promoting Transport Kinetics in Li-Ion Battery with Aligned Porous Electrode Architectures.

Developing scalable energy storage systems with high energy and power densities is essential to meeting the ever-growing portable electronics and electric vehicle markets, which calls for development of thick electrode designs to improve the active material loading and greatly enhance the overall energy density. However, rate capabilities in lithium-ion batteries usually fall off rapidly with increasing electrode thickness due to hindered ionic transport kinetics, which is especially the issue for conversion-based electroactive materials. To alleviate the transport constrains, rational design of three-dimensional porous electrodes with aligned channels is critically needed. Herein, magnetite (Fe3O4) with high theoretical capacity is employed as a model material, and with the assistance of micrometer-sized graphine oxide (GO) sheets, aligned Fe3O4/GO (AGF) electrodes with well-defined ionic transport channels are formed through a facile ice-templating method. The as-fabricated AGF electrodes exhibit excellent rate capacity compared with conventional slurry-casted electrodes with an areal capacity of ∼3.6 mAh·cm-2 under 10 mA·cm-2. Furthermore, clear evidence provided by galvanostatic charge-discharge profiles, cyclic voltammetry, and symmetric cell electrochemical impedance spectroscopy confirms the facile ionic transport kinetics in this proposed design.

A Square Channel Vanadium Phosphite Framework As Cathode for Li- and Na- Ion Batteries

The need for high-performance cathode materials for lithium and sodium-ion batteries has been the main driving force to explore new materials through innovative solid state chemistry. Polyanion-based cathode materials are shown to be promising cathode materials for both Na- and Li-ion batteries. Recently, we have expanded the family of polyanion-based cathodes by introducing phosphite-based (HPO3 2–) materials as viable cathode for Li-ion batteries, for example, LiFe(HPO3)2 and Li3Fe2(HPO3)2Cl.1, 2 In an effort to double the capacity we intended to replace Fe with V in these structures as V is known to display facile V+2/V+3 and V3+/V4+ couples. In this presentation, we will discuss the synthesis of LiV(HPO3)2, iso-structural to the reported iron compound, LiFe(HPO3)2 and their electrochemical properties with respect to lithium and sodium-ion batteries. The synthesized V compound display facile electrochemical properties with an average voltage of 4.0 V vs Li+/Li and 3.8 V vs Na+/Na in Li- and Na–ion batteries, respectively, when cycled between 4.5 to 1.5 V. The galvanostatic charge-discharge profile indicates that LiV(HPO3)2 can be cycled between V(HPO3)2 and Li2V(HPO3)2. Besides synthesis and electrochemistry, the presentation would also include spectroscopic and magnetic characterizations, details of structural characterization as a function of oxidation and reduction and some insights into the mechanism of alkali-metal insertion chemistry.