Analytical Electrochemical Impedance Modeling of Li-Air Batteries under D.C. Discharge

The performance of Li-air batteries with carbon nanotube and carbon nanofiber cathodes has been investigated using galvanostatic discharges at different current densities and scanning electron microscopy of the cathode electrode surfaces. It was found that the discharge capacity of the cathode electrode was mainly limited by the combination of oxygen diffusion and electrical resistance of the discharge product on the electrode surface. In addition, it was found that the specific capacity of Li-air batteries depends significantly on the discharge rates at the beginning and end of the discharge process: batteries that are being discharged at higher rates at the beginning and lower rates at the end show an approximately 10% higher specific capacity than batteries that are discharged with lower discharge rate at the beginning and higher discharge rate at the end. A novel mathematical model for the discharge of Li-air batteries with carbon nanotube and carbon nanofiber cathodes is also developed to describe the effects of the finite conductivity of the deposit layer in cathode. The model takes into consideration the fiber size distribution and the nonuniform deposition of the discharge product on fibers of different sizes and at different locations. The simulation results are in good agreement with the experimental findings and indicate that, although the effect of the deposit layer is to slightly decrease the power density of Li-air batteries, it can increase the total specific capacity of the battery. Li-air batteries have received significant interest in the past several years due to their high theoretical specific energy that could make long-range electric vehicles widely affordable.1-4 Li-air batteries using organic electrolyte are usually composed of a Li-metal anode, a separator, and a porous carbon cathode filled with organic electrolyte. During discharge, external air is allowed to penetrate the pores of the cathode and diffuse through the electrolyte, reacting with the Li ions to form solid lithium peroxide:The theoretical capacity of a Li-air battery is limited by the volume of pore space available in the cathode for the formation of Li 2 O 2 . Accordingly, the theoretical specific energy of Li-air batteries using organic electrolyte is estimated up to 3,000 Wh/kg, which is approximately one order of magnitude higher than that of Li-ion batteries. Albertus et al. 10 have also studied the capacity limitations of Li/oxygen batteries using experiments and modeling.Although Li-air batteries have an extremely high theoretical specific energy, the practical capacity and specific energy start to fall off at current densities over 0.1 mA/cm 2 or in batteries with thick cathodes. Previous studies suggest that this performance limitation is related to the electrochemical processes in the cathode. During discharge, the solid discharge product deposits on the air side of the cathode due to the higher O 2 concentration on this side, limiting the access of O 2 inside the cathode and eventually causing the "sudden death"...

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“…The low-frequency spectrum is due to the combined reaction-diffusion process of the oxygen in the cathode, as recently explained in Ref. 25.…”

Section: Resultsmentioning

confidence: 61%

Combined Effects of Oxygen Diffusion and Electronic Resistance in Li-Air Batteries with Carbon Nanofiber Cathodes

Chen

Bevara

Andrei

et al. 2014

J. Electrochem. Soc.

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“…Obviously, a single approach cannot account for the complex physics that govern processes at these disparate length scales. Therefore, modeling efforts in Li-air batteries have included first-principles calculations, classical molecular simulations, thermodynamic models for cell components, physics-based models for cell performance [9][10][11], and equivalent electric circuit models [12]. For instance, issues regarding reaction kinetics, catalysis, and species transport are best addressed with atomistic simulations, while overall cell characteristics can be obtained from physics-based continuum-scale models that account for potential gradients across the cell and reaction kinetics at individual electrodes.…”

Section: Introductionmentioning

confidence: 99%

A Review of Lithium-Air Battery Modeling Studies

et al. 2017

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Li-air batteries have attracted interest as energy storage devices due to their high energy and power density. Li-air batteries are expected to revolutionize the automobile industry (for use in electric and hybrid vehicles) and electrochemical energy storage systems by surpassing the energy capacities of conventional Li-ion batteries. However, the practical implementation of Li-air batteries is still hindered by many challenges, such as low cyclic performance and high charging voltage, resulting from oxygen transport limitations, electrolyte degradation, and the formation of irreversible reduction products. Therefore, various methodologies have been attempted to mitigate the issues causing performance degradation of Li-air batteries. Among myriad studies, theoretical and numerical modeling are powerful tools for describing and investigating the chemical reactions, reactive ion transportation, and electrical performance of batteries. Herein, we review the various multi-physics/scale models used to provide mechanistic insights into processes in Li-air batteries and relate these to overall battery performance. First, continuum-based models describing ion transport, pore blocking phenomena, and reduction product precipitation are presented. Next, atomistic modeling-based studies that provide an understanding of the reaction mechanisms in oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), as well as ion-ion interactions in the electrolyte, are described.

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“…(A) Discharge-charge curves of cell with Pd 21 Cu 79 /C catalyst (current density: 0.12mA/cm 2 ) (B) Nyquist plots as a function of state of charge (SOC) or depth of discharge (DOD) (pristine; D1: 0.10 discharge; D2: 0.66 discharge; D3: 0.91 discharge; C1: 100% Charge; 2 nd D1: second cycle 0.28 discharge) for a cell with catalyst Pd 21 Cu 79 /C.As a qualitative assessment of the charge transfer and interfacial properties, the data were analyzed using an ideal equivalent circuit with a series combination of resistor in the electrolyte (R Ω ) and a parallel combination of double-layer capacitance (C dl ) with impedance (Z F ). The impedance Z F could be simplified as charge transfer resistance (R t ) under certain conditions[48]. It is important to note that there is no well-developed impedance model for the operating battery cell due to the double layer complications on the counter electrode, since most models are for the three electrodes system.…”

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confidence: 99%

Synergistic catalytic properties of bifunctional nanoalloy catalysts in rechargeable lithium-oxygen battery

Kang

Shan

et al. 2016

Journal of Power Sources

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The understanding of factors influencing the performance of catalysts in the air cathode of a rechargeable lithium-oxygen battery, including overpotentials for oxygen reduction/evolution and discharge capacity, is essential for exploration of its ultimate application. This report describes new findings of an investigation of PdCu nanoalloys as cathode catalysts. Alloying Pd with oxophilic base metals such as Cu leads to reduction of the overpotentials and increase of the discharge capacity. The nanoalloy structures depend on the bimetallic composition, with an atomic ration near 50:50 featuring mixed bcc and fcc structures. The discharge potential exhibits a maximum while the charge potential display a minimum in the range of 20~50% Cu, closer to 25%, both of which correspond to a maximum reduction of the discharge-charge overpotentials. The discharge capacity displays a gradual increase with Cu%. This type of catalytic synergy is believed to be associated with a combination of ensemble and ligand effects. In particular, the activation of oxygen on Pd sites and oxygen oxophilicity at the alloyed Cu sites in the catalyst may have played an important role in effectively activating oxygen and maneuvering surface superoxide/peroxide species. These findings have implications to the design of multifunctional cathode catalysts in rechargeable lithium-oxygen batteries.

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Analytical Electrochemical Impedance Modeling of Li-Air Batteries under D.C. Discharge

Cited by 22 publications

References 37 publications

Combined Effects of Oxygen Diffusion and Electronic Resistance in Li-Air Batteries with Carbon Nanofiber Cathodes

Combined Effects of Oxygen Diffusion and Electronic Resistance in Li-Air Batteries with Carbon Nanofiber Cathodes

A Review of Lithium-Air Battery Modeling Studies

Synergistic catalytic properties of bifunctional nanoalloy catalysts in rechargeable lithium-oxygen battery

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