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A novel cyclic sulfonium cation-based ionic liquid (IL) with an ether-group appendage and the bis{(trifluoromethyl)sulfonyl}imide anion was synthesised and developed for electrochemical double layer capacitor (EDLC) testing. The synthesis and chemical-physical characterisation of the ether-group containing IL is reported in parallel with a similarly sized alkyl-functionalised sulfonium IL. Results of the chemical-physical measurements demonstrate how important transport properties, i.e. viscosity and conductivity, can be promoted through the introduction of the ether-functionality without impeding thermal, chemical or electrochemical stability of the IL. Although the apparent transport properties are improved relative to the alkyl-functionalised analogue, the ether-functionalised sulfonium cation-based IL exhibits moderately high viscosity, and poorer conductivity, when compared to traditional EDLC electrolytes based on organic solvents (propylene carbonate and acetonitrile). Electrochemical testing of the ether-functionalised sulfonium IL was conducted using activated carbon composite electrodes to inspect the performance of the IL as a solvent-free electrolyte for EDLC application. Good cycling stability was achieved over the studied range and the performance was comparable to other solvent-free, IL-based EDLC systems. Nevertheless, limitations of the attainable performance are primarily the result of sluggish transport properties and a restricted operative voltage of the IL, thus highlighting key aspects of this field which require further attention.
Mixtures of Li2O/Li3N and Na2O/Li3N have been investigated for hydrogen storage. When Li3N is doped with ca. 5mol% Li2O and annealed, both binary compounds exist as separate phases as evident from powder X-ray diffraction. Li2O acts as a spectator in the hydrogen storage reactions and there is no evidence of enhanced Li+ or H+ mobility. Na2O (5mol%) interacts more strongly with Li3N, leading to the generation of an unidentified phase, which also appears to play no part in the hydrogen storage reactions of the composite system. We conclude that addition of these levels of Li2O or Na2O to Li3N followed by annealing does not improve the hydrogen storage properties of Li3N.
A hybrid aqueous rechargeable battery with Na3V2(PO4)3 as cathode and metal Zn as anode has been proposed. Na3V2(PO4)3 is co-incorporated by carbon and reduced graphene oxide. The battery delivers a capacity of 92 mAh g−1 at a current density of 50 mA g−1 with a high and flat operating voltage of 1.42 V. It exhibits a capacity of 60 mAh g−1 at a high current density of 2000 mA g−1, indicative of excellent rate capability. Such inexpensive and safe battery shows an energy density as high as 112 Wh kg−1, demonstrating that it is potential for future application in large-scale energy storage.
Hybrid-electric vehicles require lithium-battery electrolytes that form stable, low impedance passivation layers to protect the electrodes, while allowing rapid lithium-ion transport under high current charge/discharge pulses. In this article, we describe data acquired on cells containing LiNi0.8Co0.15Al0.05O2-based positive electrodes, graphite-based negative electrodes, and electrolytes with lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiBOB) and lithium difluoro(oxalato) borate (LiF2OB) salts. The impedance data were collected in cells containing a Li–Sn reference electrode to determine effect of electrolyte composition and testing temperature on individual electrode impedance. The full cell impedance data showed the following trend: LiBOB>LiBF4 >LiF2OB>LiPF6. The negative electrode impedance showed a trend similar to that of the full cell; this electrode was the main contributor to impedance in the LiBOB and LiBF4 cells. The positive electrode impedance values for the LiBF4, LiF2OB, and LiPF6 cells were comparable; the values were somewhat higher for the LiBOB cell. Cycling and impedance data were also obtained for cells containing additions of LiBF4, LiBOB, LiF2OB, and vinylene carbonate (VC) to the EC:EMC (3:7 by wt.)+1.2M LiPF6 electrolyte. Our data indicate that the composition and morphology of the graphite SEI formed during the first lithiation cycle is an important determinant of the negative electrode impedance, and hence full cell impedance.
Abstracts A conductive polyaniline-wrapping hollow sulfur composite used as a cathode material for lithium/sulfur batteries was successfully fabricated by a facile and controllable chemical reaction with MCM-41 template. The polyaniline-wrapping hollow sulfur composite had a good reversible capacity of 506.3 mAh g−1 at the 150th cycle, reflecting the low loss of sulfur and polysulfide encapsulated by polyaniline during the charge and discharge cycles. The results of SEM and EIS show that the polyaniline-wrapping hollow sulfur composite presented many good electron-conducting paths for the rechargeability of lithium/sulfur battery. XRD and TG-DSC results revealed the formation of fine sulfur particles encapsulated by polyaniline and sulfur distributed on the polyaniline surface because of low sulfur melting temperature, which was the key reason for the activation.
In this work, three dimensional self-supported Co3O4@Ni3S2 nanowire arrays on nickel foam substrates are prepared by a multi-step method. The as-synthesized product harvests the advantages of the high electrical conductivity of the Co3O4 nanowire arrays, large surface area provided by the Ni3S2 nanosheets, and the efficient ion diffusion pathway offered by the self-supported structure. The sample is subsequently used as the electrode material for supercapacitors, at a current density of 2 mA cm−2 a charge storage capability of 2.41C cm−2 (5.5 F cm−2) was achieved. When the sample is charged and discharged at 50 mA cm−2 for 10000 cycles, a stable capacity of 0.86C cm−2 (1.5 F cm−2) can still be maintained at the end of the test. Such a performance is better than those values reported in the literature obtained with similar systems even at a lower current density. We also assemble an asymmetric supercapacitor by pairing the Co3O4@Ni3S2 nanoarrays with activated carbon, and it shows good cyclability over 10000 cycles. The device yields energy densities of 65 and 32.3 Wh kg−1 at power densities of 361 and 9090 W kg−1, respectively. Furthermore, it is able to light up 12 red light-emitting diodes, showing promising potential for practical applications.
Phenolic resin-derived activated carbon (AC) cloths are used as electrodes for large-scale electric double-layer capacitors or supercapacitors. To increase the energy and power density of the supercapacitor, the contact resistance between the carbon cloth and the aluminium foil current collector is reduced by modifying the Al current collectors. Different modified Al current collectors, including Toyal-Carbo®(surface-modified Al), DAG® (deflocculated Acheson™ graphite) coating and poly(3,4-ethylenedioxythiophene) (PEDOT) coating, have been tested and compared. The use of modified Al current collectors are shown to greatly reduce the contact resistance between the AC cloth and the Al foil. Another solution investigated in this study is to coat AC cloth with graphene through electrophoretic deposition (EPD). The graphene coated AC cloth is shown increased the capacitance and greatly reduced internal resistance.
Graphene-based nanocomposites have been synthesized and tested as electrode materials for high power lithium-ion batteries. In the synthesis of such nanocomposites, graphene is generally introduced by either thermally or chemically reduced graphite oxide (GO), which has poorer electric conductivity and crystallinity than mechanically exfoliated graphene. Here, we prepare few-layer graphene sheet (FLGS) with high electric conductivity, by sonicating expanded graphite in DMF solvent, and develop a simple one-pot hydrothermal method to fabricate monodispersed and ultrasmall Co3O4 nanocubes (about 4 nm in size) on the FLGS. This composite, consisting of homogeneously assembled and high crystalline Co3O4 nanocubes on the FLGS, has shown higher capacity and much better cycling stability than counterparts synthesized using GO as a precursor. The products in different synthesis stages have been characterized by TEM, FTIR and XPS to investigate the nanocube growth mechanism. We find that Co(OH)2 initially grew homogeneously on the graphene surface, then gradually oxidized to form Co3O4 nanoparticle seeds, and finally converted to Co3O4 nanocubes with caboxylated anion as surfactant. This work explores the mechanism of nanocrystal growth and its impact on electrochemical properties to provide further insights into the development of nanostructured electrode materials for high power energy storage.
Intraluminal suture middle cerebral artery occlusion (MCAO) model is the most frequently used model for ischemic stroke. However, the success rate of this model is variable among different research studies. This study aimed to investigate the effect of postischemic temperature on the success rate. A total of 100 C57BL/6 mice were randomized into two groups: control group (n =50), body temperature was allowed to self-regulate after MCAO; temperature-controlled group (n =50), mice were kept warm in an incubator for 12h after MCAO. The body temperature of animals was measured before, during, and for 12h after MCAO. Neurological deficits and infarct volumes were measured at 24h after MCAO. There was significant difference (P <0.05) of the body temperature between the two groups from 0.5h to 3.5h post ischemia. Moreover, there was obvious difference between the success rates of the two groups (control group: 52%, temperature-controlled group: 84%, P <0.05). In the successful models, infarct volume was significantly (P <0.05) higher in temperature-controlled group (53.44%±9.83%, n =42) than control group (45.63%±10.24%, n =26). There was significant difference of the modified neurological severity scores (P <0.05), left adhesive tests (P <0.05) between the two groups. Our data demonstrated that postischemic warming contributed to the success of mouse MCAO model.
Porous, hollow, glass microspheres (PHGMs) can be used to increase porosity in lead acid battery electrodes to improve the battery's power and energy performance at higher discharge rates. As reported in this paper, the PHGM additives did improve electrolyte storage and porosity in the electrodes. However, the nonconductive PHGMs do reduce the critical volume fraction (CVF) of the electrodes as predicted from conductivity models. The increase in electrode performance due to increased porosity may therefore be partially offset by the drop in capacity due to a lower critical volume fraction. Empirical equations are developed that relate the CFV and porosity of an electrode to the amount, size, and porosity of the additives in that electrode. The porosity estimates made from the empirical equations compare favorably with the experimental data from plates fabricated with these additives. The performance of electrodes with additives is estimated from computer models using the electrode's CVF and porosity as provided by the equations. Tests were performed on plates having volume loadings of PHGMs from 11% to 44% of total solids in positive electrodes to determine their effect on active material utilizations. The results from these discharge tests are reported and compared with theoretical models.
Electrolytic hydrogen production faces technological challenges to improve its efficiency, economic value and potential for global integration. In conventional water electrolysis, the water oxidation and reduction reactions are coupled in both time and space, as they occur simultaneously at an anode and a cathode in the same cell. This introduces challenges, such as product separation, and sets strict constraints on material selection and process conditions. Here, we decouple these reactions by dividing the process into two steps: an electrochemical step that reduces water at the cathode and oxidizes the anode, followed by a spontaneous chemical step that is driven faster at higher temperature, which reduces the anode back to its initial state by oxidizing water. This enables overall water splitting at average cell voltages of 1.44–1.60 V with nominal current densities of 10–200 mA cm−2 in a membrane-free, two-electrode cell. This allows us to produce hydrogen at low voltages in a simple, cyclic process with high efficiency, robustness, safety and scale-up potential.
Lithium-deficient Li Y Mn2O4 spinels (LD-Li Y Mn2O4) with nominal composition (0.9≤ Y <1) have been synthesized by melt impregnation from Mn2O3 and LiNO3 at temperatures ranging from 700°C to 850°C. X-ray diffraction data show that LD-Li Y Mn2O4 spinels are obtained as single phases in the range Y =0.975–1 at 700°C and 750°C. Morphological characterization by transmission electron microscopy shows that the particle size of LD-Li Y Mn2O4 spinels increases on decreasing the Li-content. The influence of the Li-content and the synthesis temperature on the thermal and electrochemical behaviours has been systematically studied. Thermal analysis studies indicate that the temperature of the first thermal effect in the differential thermal analysis (DTA)/thermogravimetric (TG) curves, T C1, linearly increases on decreasing the Li-content. The electrochemical properties of LD-Li Y Mn2O4 spinels, determined by galvanostatic cycling, notably change with the synthesis conditions. So, the first discharge capacity, Q disch., at C rate increases on rising the Li-content and the synthesis temperature. The sample Li0.975Mn2O4 synthesized at 700°C has a Q disch. =123mAhg−1 and a capacity retention of 99.77% per cycle. This LD-Li Y Mn2O4 sample had the best electrochemical characteristics of the series.
The cycle life of zinc anode in alkaline medium was enhanced by tetraphenylporphyrin (TPP) as modifier through a facile co-precipitation method. The as-prepared electrode material before and after charge/discharge test were characterized by scanning electron microscopy (SEM) to investigate the effect of TPP on the zinc dendrite growth. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and polarization measurement were utilized to examine the electrochemical performances of TPP-modified ZnO as anode material. TPP-modified ZnO possess higher discharge voltage, higher cycle stability and lower corrosion current, but larger charge-transfer resistance in comparison with bare ZnO.
In this communication, we disclose a proof-of-concept lithium/sulfur liquid battery that has exceptionally high capacity density. In such a battery, the cathode consists of a highly porous carbon cloth (CC) as the cathode current collector and a porous sulfur paper as the source of active material. In the first discharge, sulfur is reduced on the CC surface into high order lithium polysulfide (PS), which dissolves into liquid electrolyte and serves as the catholyte of the so-called “Li/S liquid battery”. By adopting a LiNO3-contained electrolyte to protect Li anode, the Li/S liquid cell is shown to cycle reversibly between 1.7 V and 2.8 V with an initial capacity of 778 mAh g−1 S, corresponding to a capacity density of 10.1 mAh cm−2 CC, which could be the highest capacity density among the rechargeable Li/S batteries reported ever. This work reveals that the high capacity density Li/S batteries can be made through a “Li/S liquid cell” by employing a highly porous carbon electrode to accommodate the insoluble sulfur reduction products (Li2S2/Li2S) with appropriate protection of the Li anode.
In the present work, novel gel-based composite polymer electrolytes for lithium batteries were prepared by introducing a hierarchical mesoporous silica network to the poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP)-based gel electrolytes. As compared with the PVDF-HFP-based gel electrolytes with/without conventional nano-sized silica fillers, the novel electrolytes have shown more homogeneous microstructure, higher ionic conductivity and better mechanical stability, which could be caused by the strong silica network and the effective interactions among the polymer, the liquid electrolytes and the silica. Moreover, the cell with this kind of electrolytes could achieve a discharge capacity as much as 150mAhg−1 at room temperature (LiCoO2 as the cathode active material), with high Coulomb efficiency.
V2O3/C composites were synthesized by oxygen corrosive and carbon coating process by the one-pot hydrothermal method. The uniform carbon coating and bridged pores significantly improved its electrochemical performance. It delivers more than two times the capacity of V2O3 and an impressive capacity of 283 mAh g−1 @ 25 A g−1.
Layered mixed transition metal oxides of the type LiMO2 (M=Ni, Co, Mn), known as stoichiometric NCM for equal amounts of transition metals, have been proposed as positive electrode materials for lithium-ion batteries. If overlithiated, these compounds can be written as xLi2MnO3·(1–x)LiMO2, are referred to as high-energy NCM and show higher specific charges and improved cycling stabilities. For the first time, the Raman spectroscopic changes occurring in stoichiometric and high-energy NCM upon electrochemical cycling under identical conditions are compared. The former was synthesised via the sol-gel method while the latter was obtained commercially. The compounds were characterised by scanning electron microscopy and X-ray diffraction. Ex situ Raman measurements of NCMs with increasing overlithiation revealed a shift of the A1g band towards the Ag band of Li2MnO3, whereas no such shift was observed after electrochemical cycling, thus lending support to the Li2MnO3 domain model and the irreversibility of Li2MnO3 activation, respectively. Finally, in situ Raman spectra of stoichiometric and high-energy NCM exhibited the emergence of a new reversible band at ∼545cm−1, which was stable over a larger potential range in the latter compound.
Parallel-connected lithium-ion cells are extensively applied in electric vehicles to satisfy the capacity and power capability. However, unavoidable cell-to-cell parameter variations lead to inhomogeneous current and state-of-charge distributions, causing early degradation of the cells. Therefore, knowledge of correlations of the parameter variations on current and state-of-charge distributions is crucial for improving these inhomogeneities. In order to clearly analyze the correlations, this paper provides a simplified analytical circuit model consisting of a resistance and a capacitance in series, and the capacitance is a function of capacity and open circuit voltage slope. Using the two parallel-connected cells analytical model, the current and state-of-charge distributions are theoretically investigated by varying cell parameters. For a large number of parallel-connected cells with Gaussian distributed parameters, a Laplace transform-based approximate analytical model is proposed based on the simplified analytical circuit model and validated by the simulation. Then the model is utilized to deduce mathematical correlations of the standard deviation and mean value of the cell parameters on maximum differences of current rate and state-of-charge. Results verify that decreasing the deviation of the product of cell resistance and capacity can effectively reduce the inhomogeneities, which is helpful for optimal screening approach for parallel-connected new and retired batteries.
Cd doped porous Co3O4 nanosheets were successfully synthesized via a facile chemical coprecipitation method without using of surfactant or template. The samples were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption/desorption isotherms (BET) and X-ray photoelectron spectrum (XPS) for their composition, structure/morphology, and BET surface area, respectively. The nanosheets consisting of nanoparticles prepared here are porous in nature, with average pore sizes of approximately 50nm or smaller. The electrochemical properties of the Cd doped porous Co3O4 nanosheets were investigated by cyclic voltammetry (CV), galvanostatic charge–discharge, electrochemical impedance spectroscopy (EIS) in 6mol/L KOH solution. The 5% Cd doped porous Co3O4 nanosheets electrode shows the maximum specific capacitance as high as 737F/g at the current density of 1A/g, which is 69% higher than that of the undoped porous Co3O4 nanosheets electrode. Furthermore, it has good specific capacitance retention of ca. 96% after 1000 continuous charge–discharge cycles. It shows a better cyclic stability than undoped porous Co3O4 nanosheets electrode, indicating that the Cd doped porous Co3O4 nanosheets is a promising electroactive material for supercapacitor.
Due to their high specific capacities beyond 250 mA h g−1, lithium-rich oxides have been considered as promising cathodes for the next generation power batteries, bridging the capacity gap between traditional layered-oxide based lithium-ion batteries and future lithium metal batteries such as lithium sulfur and lithium air batteries. However, the practical application of Li-rich oxides has been hindered by formidable challenges. To address these challenges, the understanding of their electrochemical behaviors becomes critical and is expected to offer effective guidance for both materials and cell development. This review aims to provide fundamental insights into the reaction mechanisms, electrochemical challenges and modification strategies of lithium-rich oxides. We first summarize the research history, the pristine structures, and the classification of lithium-rich oxides. Then we review the critical reaction mechanisms that are closely related to their electrochemical features and performances, such as lattice oxygen oxidation, oxygen vacancy formation, transition-metal migration, layered to spinel transitions, ‘two-phase mechanism’, and lattice evolution. These discussions are coupled with state-of-the-art characterization techniques. As a comparison, the anionic redox reactions of layered sodium transition metal oxides are also discussed. Finally, after a brief overview of the correlation among the aforementioned mechanisms, we provide perspectives on the rational design of lithium-rich oxides with high energy densities and long-term cycling stability.
When surrounded by the heterogeneous networks environment, mobile terminals are often expected to select an optimal network quickly from the detected alternatives to ensure the required or better quality of service. How to reduce the probability of ping-pong effect of the process as much as possible is one of the most prominent challenges. From the two viewpoints of attribute weight and utility value, a flexible hybrid multiple attribute decision making heterogeneous network selection algorithm consisting of FAHP, standard deviation, and GRA is proposed. In this algorithm, comprehensive evaluation value of each candidate network is calculated by integrating attribute weight and utility value. Only the network whose comprehensive evaluation value is larger than that of current network and is at least the preassigned threshold will be chosen as the target network and start the handover process. Otherwise the terminal will remain on the current network. Simulation results show that among the four traffic classes this algorithm can quickly select the most suitable network and significantly reduce the number of vertical handovers and the number of ping-pong effects, compared with other four existing baseline algorithms.