Engineering topics

Kuppan, Saravanan

Publications and source records attributed to Kuppan, Saravanan.

8 records

DOE OSTI2021

Carbon Corrosion in Polymer Electrolyte Fuel Cells: A Complex Interplay between Morphological Changes and Electrochemical Performance

Due to the high gravimetric energy density of hydrogen, the focus of implementation of polymer electrolyte fuel cells (PEFCs) has shifted from light duty passenger vehicles to heavy duty vehicles such as buses, trucks, locomotives and marine vessels. A mechanistic understanding of degradation is therefore necessary to improve durability and efficiency. During start-up and shut-down (SUSD) of PEFC systems, the catalyst (Pt nanoparticles embedded on carbon support) undergoes local potentials ~ 1 - 1.5 V caused by a combination of fuel (H 2 ) starvation, mixed fuel region and cell reversal. This leads to a series of degradation phenomenon including reduction in cathode catalyst layer (cCL) thickness and porosity, loss in electrochemical surface area (ECSA), ionomer degradation and loss in electrical contact, therefore resulting in severe performance loss. The convoluted relationship between these individual degradation mechanisms, their chronology and their effects on electrochemical performance are yet unresolved. Here, the complex interplay between morphological changes due to carbon corrosion and its effects on the electrochemical performance were analyzed using a combination of detailed electrochemical characterization, spectroscopy, and electron microscopy techniques.

25 ENERGY STORAGE↗

DOE OSTI2021

Location-Dependent Cobalt Deposition in Smartphone Cells upon Long-Term Fast-Charging Visualized by Synchrotron X-ray Fluorescence

In this work, we investigate the transition-metal dissolution of the layered cathode material LiCoO 2 upon repeated fast-charging of three smartphone batteries from different manufacturers using synchrotron micro X-ray fluorescence (μ-XRF). Using this spatially resolved technique, dissolution of Co and subsequent location-dependent deposition on the anode are observed. μ-XRF mapping of selected parts of the anode electrode sheets, such as electrode folds and edges of the jelly roll, reveals the difference in the way Co is deposited on specific regions of the anode electrode. While some folds show no depositions, edges of the anode show gradually accumulating Co depositions. Furthermore, careful quantification of the dissolved Co reveals that the capacity loss scales with the amount of deposited Co on the anode, that is, total Co loss from within the cathode. Soft X-ray absorption spectroscopy of the Co depositions on the anode shows that Co is mainly deposited in a reduced 2 + state. While optimization of the fast-charging protocol mitigates Li plating on the anode, no significant difference in the amount of deposited Co can be observed between an optimized and a nonoptimized fast-charging algorithm.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Probing Heterogeneous Degradation of Catalyst in PEM Fuel Cells under Realistic Automotive Conditions with Multi-Modal Techniques

The heterogeneity of polymer electrolyte fuel cell catalyst degradation is studied under varied relative humidity and types of feed gas. Accelerated stress tests (ASTs) are performed on four membrane electrode assemblies (MEAs) under wet and dry conditions in an air or nitrogen environment for 30 000 square voltage cycles. The largest electrochemically active area loss is observed for MEA under wet conditions in a nitrogen gas environment AST due to constant upper potential limit of 0.95 V and significant water content. The mean Pt particle size is larger for the ASTs under wet conditions compared to dry conditions, and the Pt particle size under land is generally larger than under the channel. Observations from ASTs in both conditions and gas environments indicate that water content promotes Pt particle size growth. ASTs under wet conditions and an air environment show the largest difference in Pt particle size growth for inlet versus outlet and channel versus land, which can be attributed to larger water content at outlet and under land compared to inlet and under channel. From X-ray fluorescence experiments Pt particle size increase is a local phenomenon as Pt loading remains relatively uniform across the MEA.

25 ENERGY STORAGE↗

DOE OSTI2021

Performance and lifetime of intercalative water deionization cells for mono- and divalent ion removal

We report intercalative deionization (IDI) uses two cation intercalation electrodes separated by an anion exchange membrane in a symmetric cell design that has the potential to deliver electrochemically desalinated water in an energy- and water-efficient way. Here, we define and measure metrics to describe the performance and lifetime of IDI cells and compare them for NaCl and CaCl 2 feed solutions. With 20 mM NaCl, NiHCF/AEM/NiHCF flow cells achieve 10 mM average concentration change at a productivity of 20 l/h/m 2 and 5 mM average concentration change at 130 l/h/m 2 . In both cases the cells are operated at a 3C current rate and consume ~30 Wh/m 3 of energy. With 10 mM CaCl 2 , the specific capacity and salt removal of IDI flow cells is ~4 times lower. NiHCF/NiHCF beaker cells with CaCl 2 electrolyte suffer from strong capacity fade, while the same cells with NaCl electrolyte achieve 500 cycles without any capacity fade. Our post-mortem analysis using X-ray diffraction, secondary electron microscopy, energy dispersive X-ray spectroscopy, synchrotron-based X-ray absorption spectroscopy and micro X-ray fluorescence mapping reveals that NiHCF dissolves upon repeated intercalation with Ca 2+ , releasing residual K + , Ni 2+ and Fe(CN) 6 3 , which precipitates as a crystalline decomposition product on the electrodes. This side reaction deprives the active material NiHCF of charge compensating Fe, and thus accounts for the observed capacity fade.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

A Study of Model-Based Protective Fast-Charging and Associated Degradation in Commercial Smartphone Cells: Insights on Cathode Degradation as a Result of Lithium Depositions on the Anode

The ever expanding mobile consumer electronic market has accelerated the need for safe and efficient fast-charging approaches that improve the overall speed of battery charging without hastened deterioration of the battery performance. Herein, the impact of a resource inexpensive, physics-based, electrochemically optimized fast-charging algorithm (charging time < 2 h) for mobile devices is investigated. A critical difference in the amount and morphology of lithium deposits on the anode for cells fast-charged without an optimized algorithm is observed and found to be the main cause of capacity decay. Furthermore, an in-depth study of the LiCoO 2 cathode regions opposite to pronounced lithium deposits on the anode reveals a “mirroring” phenomenon, i.e., a frozen monoclinic phase, and inactivity to relithiation. In operando hard X-ray absorption spectroscopy reveals that degraded spots on harvested cathodes seem to be activated again and participate in the intercalation process when lithiated at low rates from lithium foil counter electrodes. On the other hand, tests at higher C-rates, closer to the actual fast-charging rate, reveal only negligible oxidation state changes and therefore poor performance.

25 ENERGY STORAGE↗

DOE OSTI2020

Mapping of Heterogeneous Catalyst Degradation in Polymer Electrolyte Fuel Cells

Pt catalysts in polymer electrolyte fuel cells degrade heterogeneously as the catalyst particles are exposed to local variations throughout the catalyst layer during operation. State-of-the-art analytical techniques for studying degradation of Pt catalysts do not possess fine spatial resolution to elucidate such non-uniform degradation behavior at a large electrode level. A new methodology is developed to spatially resolve and quantify the heterogeneous Pt catalyst degradation over a large area (several cm ) of aged MEAs based on synchrotron X-ray microdiffraction. PEFC single cells are aged using voltage cycling as an accelerated stress test and the degradation heterogeneity at a micrometer length scale is visualized by mapping Pt catalyst particle size after voltage cycling. It is demonstrated in detail that the Pt catalyst particle size growth is non-uniform and follows the flow field geometry. The Pt particle size growth is greater in the area under the flow field land, while it is minimal in the area under the flow field channel. Additional non-uniformity is observed with the Pt particle size increasing more rapidly at the air outlet area than the Pt particle size at the inlet area.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Removal of Na + and Ca2 + with Prussian blue analogue electrodes for brackish water desalination

Desalination of brackish water sources is critical to addressing the growing global freshwater demand. One promising approach is electrically driven desalination using intercalation electrodes. While intercalation electrodes have been widely researched for energy storage applications, only a small subset of those materials is suitable for desalination. In this work, we report the synthesis, characterization, and in-device testing of three Prussian blue analogue intercalation compounds: copper, manganese, and zinc hexacyanoferrate with formulas K x M[Fe(CN) 6 ] z ·nH 2 O (M = Cu, Mn, Zn). The desalination performance for each of these materials against carbon electrodes is reported for Na + intercalation and for Ca 2+ intercalation using 1000 ppm NaCl and 1000 ppm CaCl 2 feed solutions, respectively. While the copper and manganese analogs showed promising performance for Na + and Ca 2+ intercalation, the zinc compound was unstable and underwent rapid dissolution. Manganese hexacyanoferrate showed the best desalination performance in terms of salt removal capacities and salt removal rates with NaCl while copper hexacyanoferrate performed the best with CaCl 2 . The manganese analog proved to be the most stable intercalation material, retaining 83% and 72% of its salt removal capacity after 280 cycles in NaCl and CaCl 2 feed solutions respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

Effect of Liquid Electrolyte Soaking on the Interfacial Resistance of Li 7 La 3 Zr 2 O 1 2 for All-Solid-State Lithium Batteries

In this work, the impact of liquid electrolyte soaking on the interfacial resistance between the garnet-structured Li 7 La 3 Zr 2 O 12 (LLZO) solid electrolyte and metallic lithium has been studied. Lithium carbonate (Li 2 CO 3 ) formed by inadvertent exposure of LLZO to ambient conditions is generally known to increase interfacial impedance and decrease lithium wettability. Soaking LLZO powders and pellets in the electrolyte containing lithium tetrafluoroborate (LiBF 4 ) shows a significantly reduced interfacial resistance and improved contact between lithium and LLZO. Raman spectroscopy, X-ray diffraction, and soft X-ray absorption spectroscopy reveal how Li 2 CO 3 is continuously removed with increasing soaking time. On-line mass spectrometry and free energy calculations show how LiBF 4 reacts with surface carbonate to form carbon dioxide. Using a very simple and scalable process that does not involve heat-treatment and expensive coating techniques, we show that the Li–LLZO interfacial resistance can be reduced by an order of magnitude.

25 ENERGY STORAGE↗