Accepted Manuscripts

Divya Chalise, Krishna Shah, Ravi Prasher and Ankur Jain
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4038258
Thermal management of Li-ion battery packs is a critical technological challenge that directly impacts safety and performance. Removal of heat generated in individual Li-ion cells into the ambient is a considerably complicated problem involving multiple heat transfer modes. This paper develops an iterative analytical technique to model conjugate heat transfer in coolant-based thermal management of a Li-ion battery pack. Solutions for the governing energy conservation equations for thermal conduction and convection are derived and coupled with each other in an iterative fashion to determine the final temperature distribution. The analytical model is used to investigate the dependence of the temperature field on various geometrical and material parameters. The model shows that the coolant flowrate required for effective cooling can be reduced significant by improving the thermal conductivity of individual Li-ion cells. Further, the analytical model helps understand key thermal-electrochemical trade-offs in the design of thermal management for Li-ion battery packs, such as the trade-off between temperature rise and energy storage density in the battery pack.
Ryan Longchamps, Zachary K. Van Zandt, Hassina Bilheux, Indu Dhiman, Louis J. Santodonato, Yevgenia Ulyanova, Sameer Singhal and George Nelson
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4038244
Enzymatic electrochemical cells are a candidate for providing “green” solutions to a plethora of low-power, long-lifetime applications. A prototype three-electrode biobattery configuration of an enzymatic electrochemical cell has been designed and fabricated for neutron imaging and electrochemical testing to characterize cell performance. The working electrode was catalyzed by a polymer ink-based biocatalyst with carbon felt serving as the supporting material. Results of both ex situ and in operando neutron imaging are presented as methods for relating fuel distribution, the distribution of the enzymes, and cell electrochemical performance. Neutron radiography was also performed on fuel solutions of varied concentration to calibrate fuel solution thickness and allow for transient mapping of the fuel distribution. The calibration data proved useful in mapping the thickness of fuel solution during transient radiography. When refueled after electrochemical testing and neutron imaging, the cell surpassed its original performance, indicating that exposure to the neutron beam had not detrimentally affected enzyme activity. In operando mapping of the fuel solution suggests that increased wetting of the catalyst region increases cell performance. The relation of this performance increase to active region wetting is further supported by fuel distributions observed via the ex situ tomography. While useful in mapping aggregate solution wetting, the calibration data did not support reliable mapping of detailed glucose concentration in the working electrode. The results presented further demonstrate potential for the application of neutron imaging for the study of enzymatic electrochemical cells, particularly with respect to mapping distribution of aqueous fuel solutions.
TOPICS: Neutrons, Imaging, Glucose, Electrochemical cells, Fuels, Wetting, Electrodes, Electrochemical analysis, Calibration, Transients (Dynamics), Enzymes, Catalysts, Inks, Neutron beams, Neutron radiography, Polymers, Engineering prototypes, Carbon
Corey T. Love, Christopher Buesser, Michelle D. Johannes and Karen E. Swider-Lyons
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4038075
This paper for inclusion in the special issue provides a brief synopsis of battery safety research efforts at the Naval Research Laboratory (NRL) and presents the viewpoint that lithium-ion battery safety research is a worthy and necessary pursuit for academic and applied researchers. The number of lithium-ion battery research efforts worldwide has plateaued while publications associated with safety aspect of lithium-ion batteries is on a rapid incline. The safety challenge creates a unique research opportunity to not only understand basic phenomena but apply that knowledge directly to enable the safe implementation of existing fielded system through advanced controls and prognostics. As the number of lithium-ion battery safety research contributions climbs, no doubt significant advancements will come in the area of modeling across multiple time and length scales. Additionally, the utility of in-situ and in-operando techniques, several performed by NRL and collaborators, will feed the data necessary to validate these models. Lithium-ion battery innovations are not tied to performance metrics alone anymore. Safety research will unlock the full potential of lithium-ion batteries. There is much work to be done.
TOPICS: Lithium-ion batteries, Safety, Modeling, Batteries
Marta Hatzell and Kelsey Hatzell
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4037907
There is a growing interest in minimizing the energy and cost associated with desalination. To do this, various new desalination systems and approaches are being explored. One growing area of interest revolves around electrochemical separations for deionization. Electrochemical separations primarily consists of technologies which either intercalate or electroadorb species of interest from a bulk mixture. This can be conducted through polarizing a battery electrode, or more commonly a capacitive electrode. One example is the technology capacitive deionization (CDI). CDI is being investigated as a means to augment the current state of the art, and as a stand alone brackish water treatment technology. Despite the potential of this technology, there is still much that is not known regarding the energetics and efficiency of both the desalination and brine formation process. Here, blue refrigeration is a term used to broadly describe desalination cycles and processes. The analogy aims to compare the energetics associated with a desalination cycle to the energetics well studied in thermal refrigeration cycles. This perspective aims to evaluate some of the emerging energetic issues associated with CDI, and how new system architectures may play a role in achieving more ideal energy and desalination performance.
TOPICS: Refrigeration, Water, Energetics, Electrodes, Cycles, System architecture, Batteries, Refrigeration cycles, Water treatment
Alexander Headley, Martha Gross and Dongmei Chen
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4037772
Membrane electrolyte assembly aging is a major concern for deployed proton exchange membrane fuel cell stacks. Studies have shown that working conditions, such as the operating temperature, humidity, and open circuit voltage, have a major effect on degradation rates and also vary significantly from cell to cell. Individual cell health estimations would be very beneficial to maintenance and control schemes. Ideally, estimations would occur in response to the applied load to avoid service interruptions. To this end, this paper presents the use of an Extended Kalman Filter (EKF) to estimate the effective membrane surface area (EMSA) of each cell using cell voltage measurements taken during operation. The EKF method has a low computational cost, and can be applied in real time to estimate the EMSA of each cell in the stack. This yields quantifiable data regarding cell degradation. The EKF algorithm was applied to experimental data taken on a 23-cell stack. The load profiles for the experiments were based on the FTP-75 and HWFET standard drive cycle tests to test the ability of the algorithm to perform in realistic load scenarios. To confirm the results of the EKF method, low performing cells and an additional "healthy" cell were selected for SEM analysis. The images taken of the cells confirm that the EKF accurately identified problematic cells in the stack. The results of this study could be used to formulate online sate of health estimators for each cell in the stack that can operate during normal operation.
TOPICS: Manufacturing, Electrolytes, Membranes, Proton exchange membrane fuel cells, Stress, Algorithms, Circuits, Cycles, Operating temperature, Kalman filters, Maintenance

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