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Results for “Porous Electrodes”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Topology optimization for the design of porous electrodes

Porous electrodes are an integral part of many electrochemical devices since they have high porosity to maximize electrochemical transport and high surface area to maximize activity. Traditional porous electrode materials are typically homogeneous, stochastic collections of small-scale particles and offer few opportunities to engineer higher performance. Fortunately, recent breakthroughs in advanced and additive manufacturing are yielding new methods to structure and pattern porous electrodes across length scales. These architected electrodes are emerging as a promising new technology to continue to drive improvement; however, it is still unclear which structures to employ and few tools are available to guide their design. Here we address this gap by applying topology optimization to the design of porous electrodes. We demonstrate our framework on two applications: a porous electrode driving a steady Faradaic reaction and a transiently operated electrode in a supercapacitor. We present computationally designed electrodes that minimize energy losses in a half-cell. For low-conductivity materials, the optimization algorithm creates electrode designs with a hierarchy of length scales. Further, the designed electrodes are found to outperform undesigned, homogeneous electrodes. Finally, we present three-dimensional porous electrode designs. We thus establish a topology optimization framework for designing porous electrodes.

25 ENERGY STORAGE↗
NASA NTRS1987

Effect of structure on current and potential distributions in porous electrode

Porous electrodes generally contain constricted macropores and localized micropores. The effects of the macropore constrictions on the resistance of a capillary were studied and an analytical model was developed for predicting the current distribution in a constricted macropore which directly includes constriction effects and does not require an empirical tortuosity parameter. The current and concentration distributions in localized micropores were also investigated and it was shown that the microporous area is fully accessible to charge and mass transfer processes. From these analyses it was concluded that the micropores primarily affect the kinetics of the interfacial processes by contributing to the interfacial area, while the macropores impose ohmic and mass transport limitations through the volume of the porous electrode.

Lanzi, Oscar↗
DOE OSTI2018

Scaffold-free 3D porous electrode and method of making a scaffold-free 3D porous electrode

A scaffold-free 3D porous electrode comprises a network of interconnected pores, where each pore is surrounded by a multilayer film including a first layer of electrochemically active material, one or more monolayers of graphene on the first layer of electrochemically active material, and a second layer of electrochemically active material on the one or more monolayers of graphene. A method of making a scaffold-free 3D porous electrode includes depositing one or more monolayers of graphene onto a porous scaffold to form a graphene coating on the porous scaffold, and depositing a first layer of an electrochemically active material onto the graphene coating. The porous scaffold is removed to expose an underside of the graphene coating, and a second layer of the electrochemically active material is deposited onto the underside of the graphene coating, thereby forming the scaffold-free 3D porous electrode.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Lithium vanadium oxide (Li 1.1 V 3 O 8 ) thick porous electrodes with high rate capacity: utilization and evolution upon extended cycling elucidated via operando energy dispersive X-ray diffraction and continuum simulation

The phase distribution of lithiated LVO in thick (~500 μm) porous electrodes (TPEs) designed to facilitate both ion and electron transport was determined using synchrotron-based operando energy dispersive X-ray diffraction (EDXRD). Probing 3 positions in the TPE while cycling at a 1C rate revealed a homogeneous phase transition across the thickness of the electrode at the 1st and 95th cycles. Additionally, continuum modelling indicated uniform lithiation across the TPE in agreement with the EDXRD results and ascribed decreasing accessible active material to be the cause of loss in delivered capacity between the 1st and 95th cycles. The model was supported by the observation of significant particle fracture by SEM consistent with loss of electrical contact. Overall, the combination of operando EDXRD, continuum modeling, and ex situ measurements enabled a deeper understanding of lithium vanadium oxide transport properties under high rate extended cycling within a thick highly porous electrode architecture.

25 ENERGY STORAGE↗
NASA NTRS1990

The impedance of a tubular electrode - A model for a porous electrode

A cylindrical tube is used as the basis for a two-dimensional mathematical model to calculate the impedance of a flooded porous electrode. The model incorporates charge-transfer, mass-transfer, and ohmic resistances to obtain the axial and radial dependencies of the concentration and potential profiles. A linearized Butler-Volmer kinetic expression for a simple redox reaction O + e yielding R is used, in conjuction with analytical expressions for the surface concentration and overpotential, to compute the open-circuit impedance. The results of the two-dimensional model, which omits double-layer charging, are compared with the results of a more standardly applied one-dimensional model in which radial variations are neglected, with and without double-layer charging. The simpler-to-apply one-dimensional model is found to be satisfactory when mass-transfer and ohmic resistances are small with respect to charge-transfer resistance. The omission of double-layer charging does not introduce error into the two-dimensional model in the frequency range in which capacitive-like effects are caused by mass-transfer limitations.

Viner, Andrew S.↗
NASA NTRS1991

Modelling of nickel-cadmium batteries using porous electrode theory

A porous electrode modeling technique is discussed which is considered a viable means for quantitatively predicting Ni-Cd cell performance. The authors describe the integration of the cell model into a battery model useful in the design and operation of aerospace applications. Test data from a sealed boilerplate cell are presented for constant current charge and discharge conditions. Performance predictions for similar cases have been performed, and a comparison to the boilerplate data is made. Areas for further development are also noted.

Timmerman, Paul J.↗
DOE OSTI2016

Improvement of the electrochromic response of a low-temperature sintered dye-modified porous electrode using low-resistivity indium tin oxide nanoparticles

An indium tin oxide (ITO) nanoparticle-based porous electrode sintered at low temperatures was investigated as a transparent electrode for electrochromic displays (ECDs). The electrochromic (EC) response of the dye-modified ITO porous electrode sintered at 150 °C, which exhibited a generally low resistivity, was markedly superior to that of a conventional dye-modified TiO{sub 2} porous electrode sintered at the same temperature. Moreover, the EC characteristics of the dye-modified ITO porous electrode sintered at 150 °C were better than those of the high-temperature (450 °C) sintered conventional dye-modified TiO{sub 2} porous electrode. These improvements in the EC characteristics of the dye-modified ITO porous electrode are attributed to its lower resistivity than that of the TiO{sub 2} porous electrodes. In addition to its sufficiently low resistivity attained under the sintering conditions required for flexible ECD applications, the ITO porous film had superior visible-light transparency and dye adsorption capabilities. We conclude that the process temperature, resistivity, optical transmittance, and dye adsorption capability of the ITO porous electrode make it a promising transparent porous electrode for flexible ECD applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

One- and Two-Equation Models to Simulate Ion Transport in Charged Porous Electrodes

Energy storage in porous capacitor materials, capacitive deionization (CDI) for water desalination, capacitive energy generation, geophysical applications, and removal of heavy ions from wastewater streams are some examples of processes where understanding of ionic transport processes in charged porous media is very important. In this work, one- and two-equation models are derived to simulate ionic transport processes in heterogeneous porous media comprising two different pore sizes. It is based on a theory for capacitive charging by ideally polarizable porous electrodes without Faradaic reactions or specific adsorption of ions. A two-step volume averaging technique is used to derive the averaged transport equations for multi-ionic systems without any further assumptions, such as thin electrical double layers or Donnan equilibrium. A comparison between both models is presented. The effective transport parameters for isotropic porous media are calculated by solving the corresponding closure problems. An approximate analytical procedure is proposed to solve the closure problems. Numerical and theoretical calculations show that the approximate analytical procedure yields adequate solutions. Lastly, a theoretical analysis shows that the value of interphase pseudo-transport coefficients determines which model to use.

25 ENERGY STORAGE↗
DOE OSTI2021

Quantifying Uncertainty in Tortuosity Estimates for Porous Electrodes

Measuring tortuosity in porous electrodes is important for understanding rate capability and optimizing design. Here, we describe an approach to determine electrode tortuosities and quantify the associated uncertainties by fitting a P2D model to discharge profiles from a standard rate capability test. A dimensionless current is identified as a design-of-experiment parameter that can be used to identify experiments that return confident estimates of tortuosity, even when other model parameters are not known with certainty. This approach is applied to analysis of L i x V 3 O 8 (LVO) electrodes and L i x N i 0.33 M n 0.33 C o 0.33 O 2 (NMC) electrodes. The details of the assumptions made in these measurements and their impact on the reported uncertainties are discussed. We also perform an uncertainty analysis on the standard method for quantifying tortuosity in the literature: electrochemical impedance spectroscopy collected under blocking electrolyte conditions. We find that confident estimates can be obtained using this approach even when uncertainties in equivalent circuit model parameters are considered.

25 ENERGY STORAGE↗
DOE OSTI2021

Computational design of microarchitected porous electrodes for redox flow batteries

Porous electrodes are used as the core reactive component across electrochemical technologies. In flowing systems, controlling the fluid distribution, species transport, and reactive environment is critical to attaining high performance. However, conventional electrode materials like felts and papers provide few opportunities for precise engineering of the electrode and its microstructure. To address these limitations, architected electrodes composed of unit cells with spatially varying geometry determined via computational optimization are proposed. Resolved simulation is employed to develop a homogenized description of the constituent unit cells. These effective properties serve as inputs to a continuum model for the electrode when used in the negative half-cell of a vanadium redox flow battery. Porosity distributions minimizing power loss are then determined via computational design optimization to generate architected porosity electrodes. The architected electrodes are compared to bulk, uniform porosity electrodes and found to lead to increased power efficiency across operating flow rates and currents. The design methodology is further used to generate a scaled-up electrode with comparable power efficiency to the bench-scale systems. Finally, the variable porosity architecture and computational design methodology presented here thus offers a novel pathway for automatically generating spatially engineered electrode structures with improved power performance.

25 ENERGY STORAGE↗
DOE OSTI2019

Atomic layer deposition in porous electrodes: A pore-scale modeling study

Coating porous electrodes of Li-ion batteries with functional materials by atomic layer deposition (ALD) can enhance their capacity stability. Because of the complex microstructure of the porous electrodes, predicting the required exposure time of the precursors for achieving a desired coating and the coating characteristics for a given exposure time remains difficult. Here, a three-dimensional (3D) pore-scale lattice Boltzmann model is developed to investigate the reactive transport processes during the ALD of reconstructed electrodes and to assess the accuracy of one-dimensional (1D) mean-field models. The effects of the hierarchical structure of pores and their connectivity on the coating process of ALD are investigated and the detailed coating characteristics in the electrodes are resolved. Electrodes with smaller pore sizes requires a longer exposure time to achieve full coating. At the same depth within an electrode, the smaller pores are coated more slowly than the wider pores (especially at high Damkohler numbers) and the coating speed of well-connected pores are faster than that of poorly connected pores. Furthermore, simulations also reveal that the 1D mean-field model can capture the average coating characteristics reasonably well when pores in the electrodes are well connected but may perform poorly if the pores are poorly connected.

25 ENERGY STORAGE↗
DOE OSTI2017

Modeling Battery Performance Due to Intercalation Driven Volume Change in Porous Electrodes

Simulations are presented that result from incorporating dimensional and porosity changes in porous electrodes caused by volume changes in the active material during intercalation into a detailed lithium-ion battery model. Porosity and dimensional changes in an electrode can significantly affect the resistance of the battery during cycling, which in turn alters the reaction distributions in the porous electrodes. In addition, volume changes generate stresses in the electrode which can lead to premature failure of the battery. Material conservation equations are coupled with the mechanical properties of porous electrodes to link dimensional and porosity changes to stresses and the resulting resistances that occur during the intercalation processes. Through the use of porous rock mechanics, porosity and strain gradients can be predicted based on state of discharge and discharge rate. Several different battery casings and discharge rates are examined and operating curves are predicted.

25 ENERGY STORAGE↗