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Volume expansion and “dead Li” accumulation in the Li anode forbid the development of practical pouch-cell type Li metal batteries (pLMBs). Thus, development of highly reversible and long-life Li metal anodes is of great importance in this area. Herein, a facile thermally initiated conversion method is proposed to fabricate a Li/graphene composite anode (Li@G) by a heating induced local reaction among Li powder, graphene and PVDF. Using simple mixing–coating–drying–heating procedures, a large-area Li@G anode can be prepared in a roll-to-roll way with a film casting machine. The detailed morphology and functions of the LiC6 skeleton in this composite anode on alleviating “dead Li” accumulation are confirmed. Failure analysis and morphology characterization demonstrate the improvement in reducing cell resistance and concentration polarization by using this novel Li anode. As a result, a 0.55 A h pLMB (Li@G/NCM811) strictly following practical conditions can cycle stably 140 times due to the improved reversibility of Li stripping/plating. Moreover, a 2.6 A h pLMB (Li@G/NCM811) delivers a high energy density of 356 W h kg−1 (based on the whole cell) with a high capacity retention of 70% for 100 cycles. The scalable preparation method of the advanced Li@G anode presented in this paper makes promising progress in design and fabrication of Li composite anodes for practical pLMBs.

With the development of new classes of high-speed vessels like LCAC, which are expected to ingest high amounts of salt particulates, it is of vital importance to develop a new class of filtration media which can meet this requirement. A microfibrous filter media embedded with nanofibers was thus developed using a nanofiber flocked suspension with a microfibrous support created using traditional wet-lay papermaking methods. While the pressure drop is normally used as the conventional parameter to predict service-life of the filter media, it does not give a proper indication of filter service life. Therefore, a novel thermal impedance technique was applied in this work to characterize the filtration media using thermal parameters via a heat pulse excitation signal. The transient response for the phase lag of temperature was observed because heat transfer occurs during the air flow across the filtration media. The related thermal parameters were obtained through a thermal equivalent circuit model and a nonlinear least-squares fitting algorithm. The thermal impedance method can be used as a filter media diagnostic tool to obtain useful parameters which can be utilized to regenerate filter media and assist to define the operational lifetime of the filter. This can help protect the power systems and reduce the maintenance, operation, and replacement costs. The improved air quality that can be obtained using this advanced filtration technology will enable enhanced protection of engine turbines and other onboard air-breathing systems.

Placing metallic Li inside 3D porous scaffold is effective to improve its reversibility. However, in most cases, excessive Li jeopardizes energy density of cells, and causes deterioration of electrochemical performances, due to uncontrollable thermal infusion process. Herein, by analyzing parameters that influence capillary pressure acting on molten Li using Young-Laplace equation, a novel strategy to control Li content in 3D scaffolds by regulating pore size and surface lithiophilicity of scaffolds is proposed. Especially, choosing lightweight 3D graphene with tunable surface lithiophilicity as the scaffold can generate appropriate capillary pressure to achieve ultralow areal mass loading (1.8 mg cm−2) of Li. The as-prepared Li anode possesses comparable weight with thinnest commercial Li foil, but exhibits improved reversibility to sustain 700 h of stable stripping/plating at 3.0 mAh cm−2. Moreover, the relationship between areal Li loading and lithiophilicity of graphene scaffold is established. Thus, the areal loadings of Li can be tuned in a wide range from 1.8 mg cm−2 to over 9.0 mg cm−2, making this novel anode applicable to pair with a variety of high areal loading (∼10 mg cm−2) cathodes, including lithium iron phosphate, Li-rich layered oxide and sulfur, showing great application potentials in practical Li metal batteries.

Metallic lithium anode has attracted immense attention for high energy density rechargeable batteries. However, the infinity volume change and safety issues caused by the uncontrollable growth of lithium dendrites during long-term cycling hinder its practical applications. Herein, we explore an effective strategy to solve these problems by building a secondary conductive graphene network inside the macropores of copper foam as a three-dimensional host to fabricate metallic lithium (CuFG@Li) anode. The graphene network, nested in the Cu foam, can further split the large pores of Cu foam to form micron-sized cages. After the molten lithium being infused inside the host, this graphene conductive network can be used as a deposition matrix for lithium metal in the pores and minimize the local size of lithium metal to enhance the reversibility of plating/stripping of lithium and maintain the constant volume of anode during the long cycles. The CuFG@Li anode displays stable cycling for more than 1300 h at a current density of 1 mA/cm2, and exhibits high Coulombic efficiency of 98% over 200 cycles at 1 mA/cm2, which is much better than bare Li foil anode. The CuFG@Li/LiFePO4 full cell is also fabricated and displays excellent rate performance. This strategy presents a general approach to suppress the growth of lithium dendrites and regulate the volume changes for long-lifespan lithium metal batteries.

A FeF2/PVDF protective layer modified metallic lithium anode was prepared by coating a hybrid layer of ferrous fluoride (FeF2) and polyvinylidene fluoride (PVDF) on the surface of the lithium foil. The morphology of the electrode before and after cycling was characterized by scanning electron microscopy (SEM). The electrochemical properties of the modified metallic lithium anode were analyzed by the galvanostatic charge/discharge, electrochemical impedance spectroscopy (EIS) and rete test. Compared with the traditional lithium foil anode, the metallic lithium anode with protective layer has no lithium dendrite and “dead lithium” on the surface after cycling. Therefore, it shows good cyclic stability, and the voltage hysteresis between charge and discharge keeps steady at 20 mV after galvanostatic (1 mA/cm2) charge/discharge cycling for 360 h. A full battery using modified metallic lithium anode and lithium iron phosphate cathode into also exhibits excellent rate performance, whose discharge specific capacity can still reach 110 mAh/g at the current density of 3 C.

A novel thermal management structure has been developed for Lithium-ion (Li-ion) battery packs operated at extremely high power rates. This structure integrates copper microfibrous media (MFM) with high thermal conductivity (60–65 W m−1K−1) and porosity (70–90 vol%), active cooling structures (i.e. metal cooling tubes), and passive cooling material (i.e. phase change material (PCM)). In this structure the PCM is embedded in the MFM (MFM-PCM). MFM drastically improves interfacial heat transfer and efficiently conducts heat between Li-ion cells, cooling tubes, and PCM. PCM embedded in MFM regulates the cell surface temperature, capping it near the PCM's melting point. It stores the excessive heat generated by the cells under peak use and releases it to the cooling tubes during off-peak use. The MFM-PCM pack enables mid-form Li-ion cells using lithium iron phosphate cathodes to perform at their maximum allowed discharge rates (15C) for individual cells and maintains cell surface temperature below 48 °C, which is much lower than the threshold of 60 °C. As a result, no derating is necessary for safe pack operations. A COMSOL 2D thermal model estimates that the thermal conductivity of MFM-PCM is 58 W m−1K−1; this is close to the measured value. The model predicts that the pack can protect cells from catastrophic cascading failure if one cell experiences thermal runaway and releases up to 130% of its full electric energy (440 kJ) into the pack in 1 s.

Construction of 3D electrode structures has emerged as an effective way to stabilize Li metal anodes. However, a 3D porous structure with relatively large surface area will enlarge the contact area between the electrolyte and Li, resulting in a low coulombic efficiency and capacity decay due to electrolyte decomposition at the 3D interface, especially under high areal capacity conditions. Herein, an ultrathin and conformal lithium-ion conductive coating, composed of a PEO/LiTFSI-based solid polymer electrolyte with graphene oxide as a functional filler to enhance the ionic conductivity, is proposed as a protective layer to address the abovementioned issues for 3D Li metal anodes. This coating layer can be applied to various 3D current collectors, such as Ni foam and carbon fiber cloth, and is effective in suppressing electrolyte decomposition and guiding uniform deposition of Li beneath it. As a result, the irreversible capacity loss of the protected 3D Li anode reduces to one-sixth that of the uncoated anode, and an average coulombic efficiency of 98.9% and stable cycling for over 800 h can be achieved at the high areal capacity of 10 mA h cm−2. This study establishes a general approach of surface modification to depress the irreversible reactions on the surface of practical 3D metallic Li anodes.

Practical application of metallic Li anode in Li-ion batteries has been restricted because of dendrite growth of Li which induces poor stability and safety issues. Despite various hosts for Li having been developed to address these issues, it is still a challenge to achieve highly reversible and stable stripping/plating behavior of Li, especially at high-rate conditions. Herein, we propose a simple method of incorporating Li in commercial carbon fiber cloth (CFC) to realize high-rate and stable metallic Li anodes by confining stripping/plating of Li in microchannels of ZnO-decorated CFC (CFC/ZnO) and dissipating high current densities through conductive carbon fiber networks. The symmetrical cell using this novel anode can run stably for over 1800 h (900 cycles) under 1 mA cm–2 and even 320 h (800 cycles) at 5 mA cm–2, which has rarely been achieved previously through structural evolution of Li-metal anode. When it is paired with commercial activated carbon, the as-made Li-ion capacitor coin cell can deli...

The cost of Ni–MH and Li-ion battery packs is cut considerably for applications in HEV and pHEV onboard energy storage. The operational lifetime of these battery packs is still a cost concern for end users and limits long distance applications. The battery storage devices currently dominate onboard energy storage fields via slow electrochemical reactions. The battery pack experiences an extra burden when absorbing bursts of energy or releasing the required energy to facilitate quick acceleration. The dynamic operation under thermal and mechanical stresses especially during severe weather conditions has adverse effects on the battery operating life due to chemical compounds and electrode materials degradation. To overcome these limitations, an ultracapacitor can quickly polarize electrolyte solutions and accumulate energy via rapid electrostatic charges at the electrode–electrolyte interface. The ultracapacitor combines advantages including long cycle life and high power density of a conventional capacitor with enhanced energy storage capability due to high electrode surface area and low internal resistance. A hybrid ultracapacitor can be designed by using both a double-layer capacitor electrode and a battery electrode. This hybrid structure increases energy conservation and capacitance. It is also recognized as an asymmetric ultracapacitor. A power module consisting of 10 asymmetric ultracapacitors with 300 F at an operating window from 4.0 V to 14.5 V was tested for studying of these unique features. These 10 electrochemical capacitors were connected in series and performed electrical characterizations including Ragone plots, self-discharge, features at high current loads, working voltage, and related energy storage performance. The ultracapacitor module was then operated together with a Pb–acid battery as a hybrid power device. Performance of the hybrid power system was characterized by using an adjusted cold cranking and a modified hybrid pulse power profile. The irreplaceable structures on energy storage and power delivery serve as a potential to further reduce the cyclic burden and thermal stress in advanced battery packs for onboard energy storage applications.

The needs for onboard energy storage are practically dependent on the Ni-MH and Li-ion battery packs, because these two power-assisting systems have features of proper energy density, longer cycle lifetime, quick charge acceptance, and proper operating windows for both voltage and temperature. In particular, the Ni-MH power system has a proper tolerance mechanism for overcharge and overdischarge, a lower cost for battery pack maintenance, and a slightly longer cycle lifetime profile. We studied the self-discharge characteristics, state-of-health, state-of-charge, and energy efficiencies at various charge input levels. The end-of-voltages during charge and discharge were evaluated for the Ni-MH storage batteries. The impedance measurements and data analysis have also been conducted for equivalent circuit simulations. The performance deterioration and capacity decay are fundamentally analyzed and discussed in details, including electrode side-reactions, structure degradations, separator weakening, and level changes of electrolyte saturation in the battery. Further battery quality enhancement through cycle duration improvement for onboard energy storage potentially provides more suitable power and energy delivery in order to obtain higher efficiency, save more fuels, and reduce CO2, SO2, and NOx emissions.

A temperature above 100 °C is always desired for proton exchange membrane (PEM) fuel cell operation. It not only improves kinetic and mass transport processes, but also facilitates thermal and water management in fuel cell systems. Increased carbon monoxide (CO) tolerance at higher operating temperature also simplifies the pretreatment of fuel supplement. The novel phosphoric acid (PA) doped polybenzimidazole (PBI) membranes achieve PEM fuel cell operations above 100 °C. The performance of a commercial high temperature (HT) PEM fuel cell stack module is studied by measuring its impedance under various current loads when the operating temperature is set at 160 °C. The contributions of kinetic and mass transport processes to stack impedance are analyzed qualitatively and quantitatively by equivalent circuit (EC) simulation. The performance of a traditional PEM fuel cell stack module operated is also studied by impedance measurement and EC simulation. The operating temperature is self-stabilized between 40 °C and 65 °C. An enhancement of the HT-PEM fuel cell stack in polarization impedance is evaluated by comparing to the traditional PEM fuel cell stack. The impedance study on two commercial fuel cell stacks reveals the real situation of current fuel cell development.

The Ni–MH batteries were tested for battery energy storage characteristics, including the effects of battery charge or discharge at different rates. The battery energy efficiency and capacity retention were evaluated through measuring the charge/discharge capacities and energies during full and partial state-of-charge (SoC) operations. Energy efficiency results were obtained at various charge input levels and different charge and discharge rates. The inefficient charging process started to take place at ca. 90% state-of-recharge (SoR) when charged at no more than 0.2 C rate. For the NiMH-B2 battery after an approximately full charge (∼100% SoC at 120% SoR and a 0.2 C charge/discharge rate), the capacity retention was obtained as 83% after 360 h of storage, and 70% after 1519 h of storage. The energy efficiency was decreased from 74.0% to 50% after 1519 h of storage time. The Coulomb efficiency was initially 83.34%, and was reduced to 57.95% after 1519 h of storage. The battery has relatively higher energy efficiency at approximately 50% SoC. The energy efficiency was calculated to be more than 92% when the NiMH-C3 battery was charged to 30–70% SoC then discharged to 0% SoC at a 0.2 C charge/discharge rate. In consideration of energy efficiency, charge acceptance, capacity retention rate, and power output needs, as well as Nelson’s analysis on HEV power requirements, the Ni–MH battery is appropriate to work at ca. 50 ± 10% SoC with an operating limitation of 50 ± 20% SoC. This work is potentially beneficial for determination of the current SoC level during the battery pack being operated for energy storage applications.

In this work, impedance measurement was performed on a high temperature PEM fuel cell stack module consisting of 65 planar single cells. Pure hydrogen and ambient air were supplied into the stack. The impedance data of the stack were collected under varying loads at 160ºC. However, temperature variations and gradient existed over the whole stack during the measurement. The impedance measurement was then repeated under the same operating conditions to collect the second set of data. An unexpected increase of cell impedance was observed. An EC diagram was derived to simulate the impedance data of the stack module. The electronic auxiliaries and temperature profiles of the stack module were analyzed to study their effects on stack impedance.

A high temperature PEM fuel cell stack, consisting of 65 planar single cells, was operated in a commercial power module with pure hydrogen and ambient air. AC impedance tests were conducted on the stack module after it reached a steady operating status. The equivalent circuit diagram with three time constants was derived to simulate the measured impedance data. The impedance measurement and simulation were performed to the stack module at different operation settings of stack temperature and load current in order to validate the derived equivalent circuit diagram. In this way, the kinetic and mass transfer processes occurring inside the stack were mechanistically discriminated and identified.

Three main types of battery chemistries in consideration for vehicle applications are Pb–acid, nickel–metal hydride, and lithium-ion batteries. Lead–acid batteries are widely used in traditional automotive applications for many years. Higher voltage, high-rate discharge capability, good specific energy, lower temperature performance, lower thermal management requirement, and low-cost in both manufacturing and recycling are the advantages of the rechargeable battery. Disadvantages of the lead–acid battery are: weight concerns of lead metal (lower energy density and lower power density) and limited cycle-life (especially in deep-cycle duties). If two major disadvantages have been significantly changed to a proper state to compete with other battery chemistries, the Pb–acid battery is still a good candidate in considering of cost/performance ratio. The lead–acid battery is always a good power source for fast starting of cold vehicles, for recharging from either a stop-start braking system, or for a charge from the engine itself, which consumes battery energy or stores electricity back into chemical energy. The main reasons for reexamining this battery chemistry are cost-savings and life-cycling considerations upon advances in electrode structure design and enhancement of capacitance behavior inside the battery pack. Several Pb–acid batteries were evaluated and tested through a unique method, i.e., the electrochemical impedance method at different loads, in order to characterize and further understand the improved electrode processes and mechanisms in performance enhancement. The impedance data at loads were collected from these lead–acid batteries at load for further analysis. Battery electrode behaviors are evaluated through impedance data simulation using a proper equivalent circuit model. A defective battery and a failed Pb–acid battery were used in non-destructive analysis. The recent Pb–acid battery advancement in structures and designs and its potential application are also discussed for power reserve in energy-efficient vehicles and sustainable electricity storage.

Ingestion and accumulation of sea salt and other impurities is a major challenge for high speed vessels, turbine engines, and other air breathing systems. The performance and reliability of filters are anticipated to be improved significantly after the rate of performance degradation is reduced via enhanced filtration media and well-designed filtration approaches. This study proposes to apply anionic surfactant to disperse the nanofibers thoroughly and employ cationic surfactant to flocculate the dispersed nanofibers into numerous small groups of nanofiber flocs. Using the wet-lay procedure in the lab, the novel porous microfiber media was then fabricated with small groups of nanofiber flocs together with activated carbon and polyester fibers. The unique nanofiber filter media was then evaluated for filtration performance using face velocity, pressure drop, and filtration efficiency parameters. Due to nanoflocced fiber inclusion, an anomalous region in the filtration efficiency versus pressure drop regime was observed where wall slip occurring at the nanostructured surface provided an unusually high level of filtration efficiency near the most penetrating particle size (MPPS) region of 0.1-0.4 μm with a concomitant reduction in the normally encountered levels of pressure drop. This anomalous increase in the filtration efficiency versus pressure drop is a novel phenomenon and it is highly beneficial to aerosol filtration. The enhanced filtration reveals that the quality factor near the MPPS region increases significantly due to the inclusion of nanofiber flocs. The unique porous filtration media is expected to increase the dirt holding capacity and prolong the lifecycle of the turbine air filter systems.

The PEFC stack in a commercial power system was operated with room air and pure hydrogen. After the system reached a steady temperature, an ac impedance test was conducted on the fuel cell power system. The impedance data were real-time response generated by the ac sinusoidal excitation. Data for a single PEM stack and PEM stacks operating in parallel and series were collected with or without an embedded system controller board and electronic devices. The equivalent circuit model with three time constants and the non-linear least square fitting program (NLLS) were applied for fitting the stack impedance spectrum. The Levenberg–Marquardt algorithm utilized in the NLLS fitting process automatically adjusted the parameter values of the physical elements in the model to find the best fit result. From the preliminary results, data interpretation and the equivalent circuit model identified the physical elements, the related electrochemical processes, and the phenomenon inside the fuel cells or stacks. Losses from ohmic conduction, anode activation, cathode activation, and mass transfer were separated and analyzed. Further PSpice simulation curves using these equivalent circuit elements demonstrate good agreement with the pulse testing data measured from the PEFC power system.

Impedance measurement was conducted at the entire cell level for studying of the Ni-MH rechargeable batteries. An improved equivalent circuit model considering diffusion process is proposed for simulation of battery impedance data at different charge input levels. The cell capacity decay was diagnosed by analyzing the ohmic resistance, activation resistance, and mass transfer resistance of the Ni-MH cells with degraded capacity. The capacity deterioration of this type, Ni-MH cell, is considered in relation to the change of activation resistance of the nickel positive electrodes. Based on the report and surface analysis obtained from the energy dispersive X-ray spectroscopy, the composition formula of metal-hydride electrodes can be closely documented as the AB5 type alloy and the “A” elements are recognized as lanthanum (La) and cerium (Ce). The capacity decay of the Ni-MH cell is potentially initiated due to starved electrolyte for the electrochemical reaction of active materials inside the Ni-MH battery, and the discharge product of Ni(OH)2 at low state-of-charge level is anticipated to have more impeding effects on electrode kinetic process for higher power output and efficient energy delivery.

Proton exchange membrane (PEM) fuel cells experience performance degradation, such as reduction in efficiency and life, as a result of poisoning of platinum catalysts by airborne contaminants. Research on these contaminant effects suggests that the best possible solution to allowing fuel cells to operate in contaminated environments is by filtration of the harmful contaminants from the cathode air. A cathode air filter design methodology was created that connects properties of cathode air stream, filter design options, and filter footprint, to a set of adsorptive filter parameters that must be optimized to efficiently operate the fuel cell. Filter optimization requires a study of the trade off between two causal factors of power loss: first, a reduction in power production due to poisoning of the platinum catalyst by chemical contaminants and second, an increase in power requirements to operate the air compressor with a larger pressure drop from additional contaminant filtration. The design methodology was successfully applied to a 1.2 kW fuel cell using a programmable algorithm and predictions were made about the relationships between inlet concentration, breakthrough time, filter design, pressure drop, and compressor power requirements.

This paper presents a method for collecting ac impedance data from a commercial PEFC power system at operational loads. The PEM fuel cell stack in the power system, including 47 MEAs, was operated using room air and pure hydrogen (>99.99%). For a stack test in the power system, the power source for the embedded controller board was simultaneously switched from the fuel cell stack to a similar external power source after the system reached a steady temperature. The PEM fuel cells in the stack were tested by collecting the ac impedance data at different current levels. By using ac impedance, a single fuel cell, a group of fuel cells, and a complete stack were then tested without the embedded control devices for ohmic, activation, and mass transport losses. The ohmic resistance for each cell component in the stack was obtained as 117 mΩ cm 2 at operational loads from 2.5 A to 35 A. The membrane thickness was further estimated as ca. 51–89 μm. Resistances from ohmic conduction, anode/cathode activation, and mass transport were measured and discussed using the Nyquist plots from the ac impedance spectra.

The Hg/HgO electrode is usually utilized as a reference electrode in alkaline solution such as for development of an alkaline hydrogen electrode. The reference electrode provides a suitable reference point but is available from few commercial vendors and suffers from inadequate documentation on potential in varying electrolytes. A new numerical method uses activity, activity coefficients, and a few correlated empirical equations to determine the potential values in both dilute and concentrated sodium hydroxide solutions at temperatures of 0–90 °C and at concentrations of 0.100–12.8 mol k g H 2 O − 1 . The computed potentials of the Hg/HgO electrodes versus a normal hydrogen electrode (NHE) at 25 °C and 1 atm are 0.1634 V for 0.100m, 0.1077 V for 1.00m, and 0.0976 V for 1.45m NaOH solutions. The Hg/HgO reduction potential further changes to −0.0751 V versus NHE and hydrogen evolution potential changes to −0.9916 V versus NHE in a solution of 30.0 wt.% NaOH at 80 °C. The calculated values are compared with the measured data at 25 and 75 °C. The experimental data agree well with the numerical values computed from the theoretical and empirical equations.

A manual purge line was added into the exterior fuel exhaust stream of a Ballard PEM stack in a Nexa™ power module. With the addition of manual exhaust purge, high levels of inert gases were intentionally added to the anode feed without changing normal operational procedures. A new method of determining the critical minimum flow rate in the anode exhaust stream was given by an anode mass balance. This type of operation makes dual use of membranes in the MEAs as both gas purifiers and as solid electrolytes. The PEM stack was successfully operated with up to ca. 7% nitrogen or carbon dioxide in the absence of a palladium-based hydrogen separator at ca. 200 W power level. Nitrogen in the anode stream was concentrated from 7.5% to 91.6%. The system maintained a fuel efficiency of 99% at a manual purge rate of 2.22 ml s−1 and no auto purge. The fuel cell stack efficiency was 64% and the stack output efficiency was 75%. The overall system efficiency was 39%. After troublesome CO and H2S poisons were removed, a hydrocarbon reformate containing high levels of CO2 and H2O was further used in the Nexa™ stack. The size and complexity of the fuel processing system may be reduced at a specified power level by using this operational method.

The Nexa™ power module is evaluated at membrane-electrode-assembly (MEA) and stack levels. The I–V Curves of the Nexa™ PEM fuel cell system is measured using periodic current interruption to maintain isothermal stack temperature. The uniformity analysis is mainly performed on the load of 800 W for all MEAs in 10 individual Nexa™ stacks. Statistical data show that the MEA voltage without an external load averages 224 mV higher than that with a load of 800 W. The MEA voltage difference is especially pronounced around the two cells at the air compressor side. The average difference is 8.8% and the highest difference is 13.1% between the minimum MEA voltage in the stack and the mean value. This voltage difference reveals a possibility to increase the product power capability and cut the cost per kilowatts by improving the weak performance electrodes or MEAs in the stack.

Thin composite cathodes for air reduction were manufactured using microfibre-based papermaking technology. The electrodes have a thin structural design, less than 0.15 mm in thickness. Composite cathode materials for oxygen reduction applications were fabricated by entrapping carbon particles in a sinter-locked network of 2–8 μm diameter metal fibres. The thin structure not only results in electrodes that are 30–75% thinner than those commercially available, but also offers an opportunity for custom-built air cathodes optimized for high-rate pulse applications. Using a thin composite structure for the air cathode in a zinc–air battery that is part of a zinc–air/capacitor hybrid is likely to increase the pulse capability of the hybrid power system. The thin cathode structure provides a better, more efficient three-phase reaction zone. In a half-cell test, the ultrathin air cathode generated more than 1.0 V vs Zn/ZnO for a current of 200 mA cm−2. Half-cell, full-cell and pulse-power tests revealed that thin composite cathodes have a better rate and pulse performance than the air cathodes commonly used.

Thin microfibrous substrates were built using a low cost, high speed, wet lay papermaking process with nickel and copper microfibers. High quality microfiber sheets with designed thickness and void volumes were fabricated at the Center for Microfibrous Materials Manufacturing at Auburn University. Products include thin microfibrous nickel and copper substrates with or without suitable expanded metal meshes, either sandwiched inside or on the backside. An improved method for fabrication of zinc electrodes was accomplished by electro-depositing active zinc material on 6 and/or 9 μm diameter microfibrous copper substrates. These zinc electrodes with various additives were examined for shape change and tested for performance. A new structure of electrode design was employed using an accordion-fold cell. By using five individual segments sintered onto an expanded metal mesh, an accordion-fold cell (670 mAh rated capacity) was assembled and had 98.0% coulomb efficiency, 88.6% energy efficiency at 72% depth-of-discharge (DOD) and 73.2% state-of-recharge (SOR) in the 79th cycle. A Ni–Zn cell consisting of one thick nickel and one thick zinc electrode was tested for rate performance in comparison with the 670 mAh accordion-fold cell. The accordion-fold cell (1279 mAh rated capacity) was scaled-up and tested for 835 cycles at 38% DOD at a 0.3 C charge and discharge rates, and continuously operated at 38% DOD until the 1050th cycle was finished at 0.16 C charge/discharge rates. A 7115 mAh accordion-fold demonstration cell was tested at 0.28 C charge and discharge rates for 608 cycles and still had a 4.7 Ah capacity at a 0.08 C discharge rate.

The use of microfibrous nickel substrates is advantageous for increasing the surface area available for the deposition of active material and reducing the substrate weight and consequently, yields a higher specific capacity for nickel hydroxide electrodes. Porous, microfiber-based nickel substrates were produced by sintering a composite preform. The preforms, consisting of nickel fibers with diameters as small as 2 μm and cellulose fibers, were formed using a papermaking process. The fabricated nickel electrodes that included a supporting nickel mesh in the substrate tested in a 26% KOH half-cell delivered a specific capacity of more than 250 mAh/g of the electrode weight (i.e. fibrous substrate, nickel mesh, and active material) at a 1.0 C discharge rate. An Auburn electrode without a nickel mesh tested in the same half-cell attained a higher specific capacity of 268 mAh/g at a 1.37 C discharge rate. The substrates used in these electrodes had porosities of 95–97%, and greatly improved the specific capacity of the nickel electrode. With the use of the microfibrous electrode, improved specific energies of nickel-based cell and battery designs are possible. When assembled in a nickel–hydrogen (Ni–H 2 ) boilerplate cell, the specific capacity of nearly 230 mAh/g was observed for the nickel electrode at a 0.5 C rate during the 127th cycle test. The results of high specific capacity and quick rise in utilization of microfibrous nickel hydroxide electrodes make these electrodes good candidates for significantly improving the energy density and performance of nickel–hydrogen cells.

This paper focuses on investigation of gas recombination in a positive-limited-sealed Ni–MHx cell. The positive electrodes were prepared by electrochemical impregnation of fibrous nickel plaques. The metal hydride negative electrodes were made by pasting the mixture of rare-earth hydrogen storage alloy powders, conducting and binding agents on foamed nickel substrates. The measurement of the positive capacity at different charge times was used to estimate the partial current for oxygen evolution at the same time. The effects of charge rate, electrolyte saturation level and initial state of charge of the positive electrodes on the recombination were investigated in sealed Ni–MHx cells. By determining the differential capacity of nickel hydroxide electrodes, an improved mathematical model was used to evaluate the gas recombination parameters during charge, overcharge, rest and discharge of the positive-limited-sealed Ni–MHx cell. The gas recombination during rest, discharge and overdischarge was also examined. The oxygen recombination on the nickel hydroxide electrodes can be neglected due to the consumption of water when the nickel hydroxide electrodes were discharged. The longer overdischarge produced an increase in cell pressure for the sealed Ni–MHx cell at an electrolyte unsaturated level and the evolving gas can be recombined by a following recharge operation. © 1997 SCI.

Metal hydride electrodes with copper-encapsulated alloys and non-coated alloys were fabricated using suitable conductive and binding agents. The charge-discharge characteristics of three kinds of hydride electrodes were comparatively investigated. The encapsulated alloy electrode is remarkably superior to the non-coated LaNi5-based one, discharging at a high rate and exhibiting a smaller capacity decay at the stage of cycle tests. The hydride alloy quality of hydride electrodes can be effectively determined by measuring rate capability. The results of vented cell experiments confirm that the capacity decay of non-coated alloy electrodes in sealed cells is not due to the oxidation of oxygen from the nickel hydroxide positive electrodes. The relationship between the equilibrium potential of hydride electrode and the equilibrium hydrogen pressure has been deduced by a succinct thermodynamic method, without consideration of the unknown activity of water and fugacity coefficient of hydrogen.

The combustion of fossil fuels predominates in the commercial implementation of energy conversion and power generation. However, it brings severe problems to the environment due to inevitably incomplete combustion. Meanwhile, the price of fossil fuels keeps increasing due to the depletion of natural resources. The growing concerns of global warming, as well as the reducing availability of fossil fuels, require replacements of gasoline and diesel fuels, such as Fischer-Tropsch synthetic fuels [1-3], biofuels [4, 5], and hydrogen fuel [6, 7]. The thermal conversion efficiency of a traditional automobile engine is between 17% and 23% [8], limited by the intrinsic characteristics of Carnot cycle. Energy storage and conversion systems with low/zero emissions, high efficiency, and great durability are required by the development of sustainable energy and power economy.

The flexible plaque of porous nickel is crucially important for the cycle life of nickel/cadmium, nickel/hydrogen and nickel/metal hydride batteries. The use of hollow fiber can increase the flexibility of porous plaque. The sintered porous plaque containing hollow nickel fiber is fabricated by a traditional. slurry-scraping technology. The pore-creating agent and the pore-strengthening additive are applied to increase the plaque porosity and optimize the pore structure. Nickel hydroxide is used as a pore-strengthening agent and it also assists the gasification of organic pore-creating agent to some extent. The plaque porosity reaches more than 88% when using thinner skeleton and large amount of hollow fiber.

Nickel composite electrodes (NCE) with various additives are prepared by a chemical impregnation method from nitrate solutions on sintered porous plaques. The electrochemical properties, such as utilization of active material, swelling and the discharge potential of the nickel oxide electrode (NOE) are determined mainly through the composition of the active material and the characteristics of nickel plaques. Most additives (Mg, Ca, Sr, Ba, Zn, Cd, Co, Li and Al hydroxide) exert effects on the discharge potential and swelling of the NOE. Chemical co-precipitation with the addition of calcium, zinc, magnesium and barium hydroxide increases the discharge potential by more than 20 mV, but that with zinc hydroxide results in an obvious decrease of active-material utilization and that with calcium and magnesium hydroxide produces a larger increase of electrode thickness. The effects of anion additives are also examined. Less than 1% mol of NiS in the active material increases the discharge potential, Cadmium, cobalt and zinc hydroxide are excellent additives for preventing swelling of the NCE. Slow voltammetry (0.2 mV s(-1)) in 6 M KOH is applied to characterize the oxygen-evolving potential of the NCE. The difference between the oxygen-evolution potential and the potential of the oxidation peak for the NCE with additives of calcium, lithium, barium and aluminium hydroxide is at least + 60 mV.

This paper focuses on investigation of gas recombination in a positive-limited-sealed Ni–MHx cell. The positive electrodes were prepared by electrochemical impregnation of fibrous nickel plaques. The metal hydride negative electrodes were made by pasting the mixture of rare-earth hydrogen storage alloy powders, conducting and binding agents on foamed nickel substrates. The measurement of the positive capacity at different charge times was used to estimate the partial current for oxygen evolution at the same time. The effects of charge rate, electrolyte saturation level and initial state of charge of the positive electrodes on the recombination were investigated in sealed Ni–MHx cells. By determining the differential capacity of nickel hydroxide electrodes, an improved mathematical model was used to evaluate the gas recombination parameters during charge, overcharge, rest and discharge of the positive-limited-sealed Ni–MHx cell. The gas recombination during rest, discharge and overdischarge was also examined. The oxygen recombination on the nickel hydroxide electrodes can be neglected due to the consumption of water when the nickel hydroxide electrodes were discharged. The longer overdischarge produced an increase in cell pressure for the sealed Ni–MHx cell at an electrolyte unsaturated level and the evolving gas can be recombined by a following recharge operation. © 1997 SCI.