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Review Article

J. Electrochem. En. Conv. Stor.. 2019;16(4):040801-040801-12. doi:10.1115/1.4042987.

Lithium-ion (Li-ion) battery pack is vital for storage of energy produced from different sources and has been extensively used for various applications such as electric vehicles (EVs), watches, cookers, etc. For an efficient real-time monitoring and fault diagnosis of battery operated systems, it is important to have a quantified information on the state-of-health (SoH) of batteries. This paper conducts comprehensive literature studies on advancement, challenges, concerns, and futuristic aspects of models and methods for SoH estimation of batteries. Based on the studies, the methods and models for SoH estimation have been summarized systematically with their advantages and disadvantages in tabular format. The prime emphasis of this review was attributed toward the development of a hybridized method which computes SoH of batteries accurately in real-time and takes self-discharge into its account. At the end, the summary of research findings and the future directions of research such as nondestructive tests (NDT) for real-time estimation of battery SoH, finding residual SoH for the recycled batteries from battery packs, integration of mechanical aspects of battery with temperature, easy assembling–dissembling of battery packs, and hybridization of battery packs with photovoltaic and super capacitor are discussed.

Commentary by Dr. Valentin Fuster

Research Papers

J. Electrochem. En. Conv. Stor.. 2019;16(4):041001-041001-9. doi:10.1115/1.4042923.

The chlor-alkali industry produces significant amounts of hydrogen as by-product which can potentially feed a polymeric electrolyte membrane (PEM) fuel cell (FC) unit, whose electricity and heat production can cover part of the chemical plant consumptions yielding remarkable energy and emission savings. This work presents the modeling, development, and experimental results of a large-scale (2 MW) PEM fuel cell power plant installed at the premises of a chlor-alkali industry. It is first discussed an overview of project’s membrane-electrode assembly and fuel cell development for long life stationary applications, focusing on the design-for-manufacture process and related high-volume manufacturing routes. The work then discusses the modeling of the power plant, including a specific lumped model predicting FC stack behavior as a function of inlet stream conditions and power set point, according to regressed polarization curves. Cells’ performance decay versus lifetime reflects long-term stack test data, aiming to evidence the impact on overall energy balances and efficiency of the progression of lifetime. Balance of plant is modeled to simulate auxiliary consumptions, pressure drops, and components’ operating conditions. The model allows studying different operational strategies that maintain the power production during lifetime, minimizing efficiency losses, as well as to investigate the optimized operating setpoint of the plant at full load and during part-load operation. The last section of the paper discusses the experimental results, through a complete analysis of the plant performance after startup, including energy and mass balances and allowing to validate the model. Cumulated indicators over the first two years of operations regarding energy production, hydrogen consumption, and efficiency are also discussed.

Commentary by Dr. Valentin Fuster
J. Electrochem. En. Conv. Stor.. 2019;16(4):041002-041002-8. doi:10.1115/1.4042922.

Electric vehicles have become a trend in recent years, and the lithium-ion battery pack provides them with high power and energy. The battery thermal system with air cooling was always used to prevent the high temperature of the battery pack to avoid cycle life reduction and safety issues of lithium-ion batteries. This work employed an easily applied optimization method to design a more efficient battery pack with lower temperature and more uniform temperature distribution. The proposed method consisted of four steps: the air-cooling system design, computational fluid dynamics code setups, selection of surrogate models, and optimization of the battery pack. The investigated battery pack contained eight prismatic cells, and the cells were discharged under normal driving conditions. It was shown that the optimized design performs a lower maximum temperature of 2.7 K reduction and a smaller temperature standard deviation of 0.3 K reduction than the original design. This methodology can also be implemented in industries where the battery pack contains more battery cells.

Commentary by Dr. Valentin Fuster
J. Electrochem. En. Conv. Stor.. 2019;16(4):041003-041003-7. doi:10.1115/1.4042986.

Multilayer nickel–copper coatings consisting of layers of nickel–copper alloy and a mixture of metals with hydroxides were obtained by electrodeposition from polyligand pyrophosphate–ammonia electrolyte by the two-pulse potentiostatic method. A comparison between two different electrodes with the same real surface area is presented. The equality of the surface area of electrodes deposited from the electrolyte containing different copper and nickel ions’ concentration ratio was achieved by deposition of different numbers of layers. It is shown that the increase in the copper content in electrolyte leads to an increase in the copper ions’ content in the coating and the electrode surface develops more intensively. Freshly deposited coatings have approximately the same catalytic activity in the glucose oxidation reaction in the alkaline solution. But a multilayer coating with a higher copper content is more corrosion resistant and more stable in long-term electrolysis.

Commentary by Dr. Valentin Fuster
J. Electrochem. En. Conv. Stor.. 2019;16(4):041004-041004-11. doi:10.1115/1.4042985.

The ejectors used for the fuel cell recirculation are more reliable and low cost in maintenance than high-temperature blowers. In this paper, an anode and cathode recirculation scheme, equipped with ejectors, was designed in a solid oxide fuel cell-gas turbine (SOFC-GT) hybrid system. The ejector model, SOFC model, and other component models and the validation were conducted to investigate the performance of the hybrid system with anode and cathode ejectors. The geometric parameters of the ejectors were designed to perform the anode and cathode recirculation loops according to the design conditions of the hybrid system with a blower-based recirculation loop. The cathode ejector geometries are much larger than the anode ejector. In addition, the sensitivity analysis of the primary fluid for the standalone anode and cathode ejectors is investigated. The results show that the ejector can recirculate more secondary fluid by reducing the ejector outlet pressure. Then, the anode and cathode ejectors were integrated into the SOFC-GT hybrid system. A blower gets involved downstream, and the compressor is necessary to avoid high expensive cost of redesigning compressor. The off-design and dynamic performance were characterized after integrating the anode and cathode ejectors into the hybrid system. The dynamic and off-design performances show that the designed ejectors are effectively integrated into the anode and cathode recirculation loops to replace the blower-based recirculation loops. The safety range of relative fuel flow rate is 0.62–1.22 in the fixed rotational speed strategy, and it is 0.53–1.1 in the variable rotational speed strategy. The variable rotational speed strategy can ensure higher system efficiency, which is more than 61% at a part-load condition.

Commentary by Dr. Valentin Fuster
J. Electrochem. En. Conv. Stor.. 2019;16(4):041005-041005-11. doi:10.1115/1.4043156.

In this paper, an economical and simple procedure was adopted for the fabrication of chemically crosslinked polyvinyl alcohol (PVA)-based KOH-doped alkaline membrane for the use in an alkaline direct ethanol fuel cell (ADEFC). The membrane parameters, namely, water uptake, KOH uptake, and ionic conductivity were systematically evaluated. The ionic conductivity of the synthesized membrane was in the order of 9 × 10−3 S/cm. The performance of the synthesized alkaline membrane is evaluated in a single ADEFC. Commercial Pt–Ru (30 wt %: 15 wt %)/C and Pt (40 wt %)/high surface area carbon (CHSA) from Alfa Aesar, Haverhill, MA, were used for anode and cathode, respectively. The performance of the membrane was further evaluated in a single cell using different grades of membranes containing different glutaraldehyde (GA) concentration, anode and cathode electrocatalyst loading, ethanol concentration, and KOH concentration. The maximum open circuit voltage (OCV) of 0.73 V was obtained at a temperature of 35 °C for anode feed containing 2 M ethanol and 1 M KOH for the membrane crosslinked with 2.5 wt % glutaraldehyde doped with 6 M KOH. The maximum power density of 4.15 mW/cm2 at a current density of 20.69 mA/cm2 was obtained for the same condition. The optimum electrocatalyst loading was 1 mg/cm2 of Pt-Ru/C at the anode and 1 mg/cm2 of Pt/CHSA at the cathode. The performance of KOH-doped chemically crosslinked PVA membrane was comparable with the published literature.

Commentary by Dr. Valentin Fuster
J. Electrochem. En. Conv. Stor.. 2019;16(4):041006-041006-7. doi:10.1115/1.4043155.

In this study, the phase separation phenomenon and diffusion-induced stresses in lithium iron phosphate (LiFePO4) particles under a potentiostatic discharging process have been simulated using the phase field method. The realistic particles reconstructed from synchrotron nano X-ray tomography along with idealized spherical and ellipsoid shaped particles were studied. The results show that stress and diffusion process in particles are strongly influenced by particle shapes, especially at the initial lithiation stage. Stresses in the realistic particles are higher than that in the idealized spherical ones by at least 30%. The diffusion-induced hydrostatic stress has a strong relationship with lithium ion concentration. The hydrostatic stresses and first principal stresses tend to shift from lower values to higher values as the particle takes in more lithium ions. Additionally, the diffusion-induced stresses are related to the maximum concentration difference in the particle. High concentration difference will cause high stresses. In ellipsoid particles, the stress levels increase with the aspect ratios. The model provides a design tool to optimize the performance of cathode materials with phase separation phenomena.

Commentary by Dr. Valentin Fuster
J. Electrochem. En. Conv. Stor.. 2019;16(4):041007-041007-7. doi:10.1115/1.4043229.

Li−O2 batteries with carbon electrodes made from three commercial carbons and carbon made from waste tea leaves are investigated in this study. The waste tea leaves are recycled from household tea leaves and activated using KOH. The carbon materials have various specific surface areas, and porous structures are characterized by the N2 adsorption/desorption. Vulcan XC 72 carbon shows a higher specific surface area (264.1 m2/g) than the acetylene black (76.5 m2/g) and Super P (60.9 m2/g). The activated tea leaves have an extremely high specific surface area of 2868.4 m2/g. First, we find that the commercial carbons achieve similar discharge capacities of ∼2.50 Ah/g at 0.5 mA/cm2. The micropores in carbon materials result in a high specific surface area but cannot help to achieve higher discharge capacity because it cannot accommodate the solid discharge product (Li2O2). Mixing the acetylene black and the Vulcan XC 72 improves the discharge capacity due to the optimized porous structure. The discharge capacity increases by 42% (from 2.73 ± 0.46 to 3.88 ± 0.22 Ah/g) at 0.5 mA/cm2 when the mass fraction of Vulcan XC 72 changes from 0 to 0.3. Second, the electrode made from activated tea leaves is demonstrated for the first time in Li−O2 batteries. Mixtures of activated tea leaves and acetylene black confirm that mixtures of carbon material with different specific surface areas can increase the discharge capacity. Moreover, carbon made from recycled tea leaves can reduce the cost of the electrode, making electrodes more economically achievable. This study practically enhances the discharge capacity of Li−O2 batteries using mixed carbons and provides a method for fabricating carbon electrodes with lower cost and better environmental friendliness.

Commentary by Dr. Valentin Fuster
J. Electrochem. En. Conv. Stor.. 2019;16(4):041008-041008-14. doi:10.1115/1.4043340.

This study investigates the dynamic behavior of a solid oxide steam electrolyzer (SOSE) system without an external heat source that uses transient photovoltaic (PV) generated power as an input to produce compressed (to 3 MPa) renewable hydrogen to be injected directly into the natural gas network. A cathode-supported crossflow planar solid oxide electrolysis (SOE) cell is modeled in a quasi-three-dimensional thermo-electrochemical model that spatially and temporally simulates the performance of a unit cell operating dynamically. The stack is composed of 2500 unit cells that are assumed to be assembled into identically operating stacks, creating a 300 kW electrolyzer stack module. For the designed 300 kW SOSE stack (thermoneutral voltage achieved at design steady-state conditions), powered by the dynamic 0–450 kW output of PV systems, thermal management and balancing of all heat supply and cooling demands is required based upon the operating voltage to enable efficient operation and prevent degradation of the SOSE stacks. Dynamic system simulation results show that the SOSE system is capable of following the dynamic PV generated power for a sunny day (maximum PV generated power) and a cloudy day (highly dynamic PV generated power) while the SOSE stack temperature gradient is always maintained below a maximum set point along the stack for both days. The system efficiency based upon lower heating value of the generated hydrogen is between 0–75% and 0–78% with daily hydrogen production of 94 kg and 55 kg for sunny and cloudy days, respectively.

Commentary by Dr. Valentin Fuster

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