Utilizing Pore Network Modeling for Performance Analysis of Multi-Layer Electrodes in Vanadium Redox Flow Batteries

Abstract

Vanadium redox flow batteries (VRFBs) are promising energy storage devices. The microstructure of the porous electrode affects the performance of VRFBs. Therefore, identifying optimized electrode structures is an active research area. However, designing optimal microstructures requires studying varieties of structural parameters and design cases using a modeling tool with low computational cost. In this study, a pore network modeling (PNM) framework was developed to study the effects of multi-layer electrodes on VRFB electrode performance. In contrast to previous experimental works that were focused on multi-layer structure of the same material, this study explored the effect of using different microstructures in each layer. Using an image generation algorithm, fibrous materials were generated from which pore networks were extracted. The developed PNM included a modification by adding throat nodes in the geometry to accommodate a velocity dependent mass transfer coefficient. The results showed that putting a highly permeable layer near the membrane provides an alternative preferential path for fluid to distribute and supply those regions with reactive species, resulting in 57% increase in limiting current density in contrast to the opposite order. However, selection of the desired structures must be based on a trade-off between the current/power density and pressure drop.

A versatile optimization framework for porous electrode design

“…The idealization of the void space allows a simplification of the model equations while retaining microstructural information, 23 thereby capturing the electrochemical performance in realistic electrode structures. 21,22,27,28 The PNM was developed for single-electrolyte flow cell designs in discharge mode with the co-flow operation of the anodic and cathodic half-cells and thus optimizes the electrode in only one half-cell, assuming perfect electrode wetting. The required computational time for the reference system on a single Intel® Core™ i7-8700K CPU was ∼48 hours for 1000 generations based on 50 individuals and 10 parent networks (∼2 seconds per network), which can be significantly reduced when using multiple computing cores.…”

Understanding the Role of Electrode Thickness on Redox Flow Cell Performance**

“…However, when an additional third layer is added, the increase in ohmic resistance counteracts the decrease in the activation and mass transfer overpotentials, and the overall electrochemical performance is no longer improved. We envision that modifying the throughplane microstructure of electrodes (i. e., gradients in porosity, pore size and morphology through new synthesis techniques and materials [13,60,94] ) shall enhance the electrolyte transport towards the membrane interface, increasing the reactant supply. Thereby, alleviating ohmic resistances and pressure losses in IDFF configurations, improving the electrolyte distribution and enabling the use of thicker electrodes with a high surface area.…”

“…A few groups have investigated the role of the electrode thickness on the flow cell performance. [53,54,[57][58][59][60] Aaron et al varied the electrode thickness in each separate half-cell by stacking multiple SGL 10AA carbon paper electrodes (1, 2 or 3 layers) using a serpentine flow field at a constant flow rate of 20 mL min À 1 . They demonstrated a performance gain in allvanadium RFBs by stacking electrodes, with an enhanced performance for two electrode layers.…”

Micrometer Scale X-ray CT-Informed Optimization of Heterogeneous Pore Distribution in Double Layered Thick LiNCM 811 Cathode

“…This paper aims to address several challenges observed in this field and provide a concrete method to improve the spatial energy density of cathodes at different rates. [1][2][3][4][5][6][7] Pore structure engineering is particularly vital for high-rate cycling, which induces variations in lithiation states along the thickness direction of the cathode due to the large amount of ion transport disparity and consequently, high localized lattice stress. 1,[8][9][10][11] This phenomenon is of particular importance in high energy density materials where volumetric ion concentration is high.…”

“…Based on this reconstruction, a pore network model is created to simplify the structure further and provide a comparable summary of pore space characteristics, such as dimension, tortuosity, and porosity of each region, in a reduced amount of time. 5,[24][25][26] The cathodes were tested in half cells with lithium metal as anodes to evaluate their performances under different conditions. We opted not to use full cells to isolate the effect of cathode design and avoid possible variations introduced by the inclusion of graphite anodes.…”