Electrodes For Energy Storage Systems Research Articles

Approaches to Electrolyte Solvent Selection for Poly-Anthraquinone Sulfide Organic Electrode Material.

Organic materials such as polyanthraquinone sulfide (PAQS) are receiving increased attention as electrodes for energy storage systems owing to their good environmental compatibility, high rate capability, and large charge-storage capacity. However, one of their limitations is the solubility in organic solvents typically composing the electrolytes. Here, the solubility of PAQS was tested in 17 different solvents using UV/Vis spectroscopy. The results show that PAQS exhibits a very wide range of solubility according to the nature of the solvent and the obtained trend agrees well with the predictions from Hansen solubility analysis. Furthermore, the transport properties (conductivity, σ, and viscosity, η) of selected electrolytes composed of non-solubilising solvents with 1 m LiTFSI are compared and discussed in the temperature range from -40 °C to 80 °C. In the second part of this study, the electrochemical characterization of PAQS as electrode material in selected pure or mixture of solvents with 1 m LiTFSI as salt was made in half-cells by a galvanostatic method. In a methylglutaronitrile (2MeGLN)-based electrolyte that exhibits low solubility of PAQS, it appears that the capacity fade is intricately linked to the large irreversibility of the second step of the redox process. Although the standard cyclic carbonate solvents mixture (ethylene carbonate and propylene carbonate) led to rapid capacity fade in the initial 10-15 cycles owing to their high solubilising ability. Finally, it is shown that a pure linear alkylcarbonate (dimethyl carbonate) or binary mixture of ether-based (dioxolane/dimethoxy ethane) electrolyte is much more compatible for enhanced capacity retention in PAQS with more than 120 mAh g-1 for 1000 cycles at 4 C.

Fabrication of high-performance metal ion doped iron oxide electrode for supercapacitor applications through a novel platform

We provide a novel electrodeposition platform of undoped and Eu3+ doped iron oxide nanoparticles (Eu-IONPs) from an additive-free electrolyte containing Fe(NO3)3, FeCl2 and EuCl3. The prepared IONPs were analyzed using x-ray diffraction, field emission electron microscopy and energy-dispersive x-ray techniques, and the obtained data showed successful electrosynthesis of magnetite nanoparticles (size ≈ 10 nm) doped with about 10 wt% Eu3+ ions. The Eu-IONPs were used as supercapacitor electrode materials, and characterized by cyclic voltammetry and galvanostatic charge–discharge measurements. The as-synthesized Eu-IONPs exhibit remarkable pseudocapacitive activities including high specific capacitances of 212.5 and 153.2 F g−1 at 0.5 and 2 A g−1, respectively, and excellent cycling stabilities of 93.9% and 86.5% after 2000 discharging cycles. Furthermore, vibrational sample magnetometer data confirmed better superparamagnetic performance of Eu-IONPs (Ms = 72.8 emu g−1, Mr = 0.24 emu g−1 and HCi = 3.48 G) as compared with pure IONPs (Ms = 51.92 emu g−1, Mr = 0.95 emu g−1 and HCi = 14.62 G) due to exhibiting lower Mr and HCi values. This novel synthetic platform of metal ion doped iron oxide is potentially a convenient way to fabricate high-performance iron oxide electrodes for energy storage systems.

Solvothermal Synthesis of Nickel–Aluminum Layered Double Hydroxide Nanosheet Arrays on Nickel Foam as Binder-Free Electrodes for Supercapacitors

Well-defined nickel–aluminum layered double hydroxide (NiAl LDH) nanosheet arrays grown on conductive nickel foam (NF) have been prepared using a facile solvothermal method and further investigated as a binder-free electrode for high-performance supercapacitors. The NiAl LDH nanosheet arrays are grown uniformly on the skeleton of the NF with a high density. Vertically-aligned nanosheets are interconnected with each other, forming highly porous wall-like structure. The NF supported NiAl LDH nanosheet arrays provide rapid electron and ion pathway, large electroactive surface area, and great structural stability. This binder-free electrode exhibits a specific capacitance of 784.1 F g−1 at 1 A g−1 and 459.6 F g−1 at 10 A g−1, respectively. Furthermore, it displays great cycling performance with 70.2% capacitance retention after 5000 cycles. The results demonstrate that the NF supported NiAl LDH nanosheet arrays can be a promising binder-free electrode for energy storage systems.

Core/shell nanorods of MnO2/carbon embedded with Ag nanoparticles as high-performance electrode materials for supercapacitors

Core/shell nanorods of MnO2/carbon embedded with Ag nanoparticles (MCA) were successfully fabricated via a facile and effective hydrothermal and reduction method in situ. Typically, a MCA-1.5 sample (1.5g·L−1 glucose reactant) exhibited the highest specific capacitance of 628F·g−1 at the current density of 1A·g−1 in three-electrode systems. Particularly, a fabricated asymmetric supercapacitor, using MCA-1.5 and active carbon as the positive and negative electrodes, respectively, delivered a maximum energy density of 48.3W·h·kg−1 at power density of 851.7W·kg−1 and exhibited a superior, long cycle life, showing∼98.5% specific capacitance retention after 2000 cycles. The practical energy-storage applicability of this device was demonstrated by the operation of an LED bulb when a duo of two such devices was charged. These results indicated that synthesized ternary nanocomposites have potential applications as supercapacitor electrodes in energy storage systems.

Impact of Solvent Co-Intercalation in Cathodes: A Study on Mg-Xerogel V2O5

The electrochemical performance of several known Li- and Na-ion cathode materials can be influenced by the presence of specific solvents, such as water, either in the electrolyte or the electrodes. Indeed co-intercalation of solvent molecules, along with the redox active ions, is an approach to potentially impact the voltage and mobility with which cation species intercalate into electrodes in energy storage systems. While Multi-valent (MV) ion intercalation batteries that replace the Li+ with a MV cation, such as Mg2+, provide a pragmatic approach to improve upon the energy densities of current cutting-edge Li-ion batteries, several cathode hosts suffer from sluggish MV ion mobility within the cathode structure. One of the approaches that has been deployed to mitigate poor MV ion migration so far, specifically in layered oxide cathodes such as Xerogel-V2O5, is to introduce solvent molecules (water) in the structure that electrostatically shield the high positive charge density around MV ions and lower the local structural distortions. However, the role of water during the process of Mg2+ (or MV) intercalation is not well known yet, specifically if the structural water in the cathode “shuttles” along with the Mg2+ ion or stays in the structure during Mg-cycling. In this study, we use first-principles calculations combined with the framework of grand potential phase diagrams to gain insight into the thermodynamics of Mg-water co-intercalation into Xerogel-V2O5. Based on our calculations, we find that Mg-water shuttling depends heavily on the water concentration of the electrolyte, ranging from full co-intercalation in wet to none in superdry electrolytes. Also, the Mg insertion voltages depend on the activity of water in the electrolyte in regimes where water shuttles with the Mg2+, leading to important consequences in the design of electrodes and electrolytes. We believe that this study can be further extended to other complex solvent-electrode pairs to develop a general understanding of the phenomenon of solvent co-intercalation.

Titanium Phosphite Ti2(HPO3)3, a New Negative Electrode Material for Lithium Ion Batteries

Research in the area of solids open-framework metal phosphates, has been experiencing considerable growth over the past two decades. Since 1980s, a series of transition metal phosphates with three-dimensional structure have been investigated. More recently, it has been revealed that the phosphite group, could also be of great interest, because of its tendency to form new solids open framework structure. In the literature, mixed-phosphite metal compounds have been widely synthesized with a variety of cations going from alkali metals to group IIIA of the periodic table. Some rare earth based phosphites have been also isolated. However, to the best of our knowledge, no compound with titanium and phosphite group has been reported. This compound has an interesting structure allowing it to be used as insertion material for electrodes of Li-ion batteries, while only phosphates and phosphides compounds have been used as electrode materials. Recently, two inorganic phosphite materials were tested as electrodes for energy storage systems and have shown very small specific capacities toward lithium insertion [1,2]. Besides, both works dealt with the use of phosphite based-compound as positive electrode. In this study, we are presenting a new titanium phosphite compound used as negative electrode material for lithium ion batteries. Ti2(HPO3)3 has been prepared under hydrothermal conditions and autogenous pressure. The structure of titanium phosphite with the determined crystallographic formula Ti2(HPO3)3 was solved in hexagonal system in centrosymmetric P63/m space group from single crystal diffraction data. The structure was solved by the direct method using, refined by full matrix least square.It has a three dimensional structure with tunnels along a- and b-axes (see figure). This is exactly what interests us to test it as an insertion electrode material. This compound displays a high thermal stability limit showed by TGA analysis. Structural and chemical characterization have been realized by XRD, IR and Raman spectroscopies respectively. Electrochemical analyses were done by galvanostatic cycling and cyclic voltammetry. On the initial discharge of cell, the Ti2(HPO3)3 electrode delivers a capacity of 740 mAh/g. In the aim of enhancing the electrochemical performances, Ti2(HPO3)3/graphene composite was also prepared via hydrothermal route. Results of both compounds will be presented and compared in this present publication. [1] U. Chung, J.L. Mesa, J.L. Pizarro, I. de Meatza, M. Bengoechea, J. Rodríguez Fernandez, M. I. Arriortua, and T. Rojo, J. Chem. Mater. 23 (2011) 4317-4330. [2] H. Yaghoobnejad Asl, K. Ghosh, M. P. Vidal Meza, A. Choudhurya, J. The Royal Society of Chemistry. (2013), 00, 1-3. Figure 1

Suspensions of carbon nanofibers in organic medium: rheo-electrical properties.

The nonaqueous suspensions of carbon nanofibers (CNFs) in 1 M lithium bis(trifluoromethanesulfonaimide) in propylene carbonate electrolyte reveal unique structural evolution and shear-induced transition due to the high aspect ratio. The rheo-electrical behavior elucidates a microstructural transition from entangled-to-aggregated networks above a distinct percolation threshold. Under shear flow, both networks show a three-regime flow curve and an inverted-bell-like conductivity curve as a consequence of shear-induced alignment (entangled network) and shear-induced breaking up (aggregated network). The different particle morphology of carbon nanofibers (anisometric) and carbon black (CB; isometric) causes different aggregation mechanisms (aggregate vs. particulate) and then varied microstructure for their suspensions in the same electrolyte. This fact explains the higher rigidity and lower electric conductivity of CNFs than CB suspensions. Interestingly, the suspension of hybrid carbons at the optimum mixing ratio merges the advantages of both carbons to operate efficiently as precursors in the formulation of electrodes for energy storage systems.

High energy density supercapacitors using macroporous kitchen sponges

Macroporous, low-cost and recyclable kitchen sponges are explored as effective electrode platforms for supercapacitor devices. A simple and scalable process has been developed to fabricate MnO2–carbon nanotube (CNT)–sponge supercapacitor electrodes using ordinary kitchen sponges. Two organic electrolytes (1 M of tetraethylammonium tetrafluoroborate (Et4NBF4) in propylene carbonate (PC), 1 M of LiClO4 in PC) are utilized with the sponge-based electrodes to improve the energy density of the symmetrical supercapacitors. Compared to aqueous electrolyte (1 M of Na2SO4 in H2O), the energy density of supercapacitors tripled in Et4NBF4 electrolyte, and further increased by six times in LiClO4 electrolyte. The long-term cycling performance in different electrolytes was examined and the morphology changes of the electrode materials were also studied. The good electrochemical performance in both aqueous and organic electrolytes indicates that the MnO2–CNT–sponge is a promising low-cost electrode for energy storage systems.

Electrochemical behaviour of tin borophosphate negative electrodes for energy storage systems

Tin borophosphate compounds doped with antimony, Sn 2BP 1− x Sb x O 6 ( x = 0–0.3), have been prepared and studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transmission infrared spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) and galvanostatic measurements. XRD patterns of all the samples were indexed to the tetragonal system. The EIS showed that the conductivities are enhanced by antimony doping. It was observed that the Warburg impedance coefficient ( σ w) was 1163.265 Ω cm 2 s −0.5 for the Sn 2BP 0.9Sb 0.1O 6 ( x = 0.1) sample, and this was the lowest value compared to those of the other samples. Sn 2BP 0.9Sb 0.1O 6 ( x = 0.1) showed the highest specific discharge capacity of 1050 mAh g −1 among all the samples and a reversible capacity of 540 mAh g −1 at the 150th cycle.