Expanding the Cell Design Space: Modeling the Impact of Electrolyte Convection on the Performance of Intercalation Batteries
Authors: Gao Weiran , Drake Javit , Brushett Fikile R. 
Published: July 2021

Ubiquitous in portable electronics and emergent in transportation and grid applications, lithium (Li)-ion batteries represent the state-of-the-art in energy storage technology due to their energy density, roundtrip efficiency, and cycle life.1,2 While the past decade has seen a steady decline in battery price and concomitant increase in energy density due to a combination of materials development, manufacturing advances, and market scale,3,4 current Li-ion batteries are still unable to meet the often incongruous requirements of emerging applications.5,6 Most current research efforts focus on advancement of new material sets with improved property profiles,7–9 but decidedly fewer efforts contemplate re-engineering the cell format to support the heat and mass transfer conditions necessary for higher-performing energy storage devices. To this end, one potentially promising approach is the convection battery (Figure 1a), in which electrolyte is pumped through the cell to enhance transport properties.10,11 As compared to traditional configurations, this cell format offers improvements in several areas, including (1) electrodes with an increased and controllable ion flux, (2) improved safety and maintenance, (3) simplified manufacturing, and (4) reduced system costs.
Here, we combine mathematical modeling, battery simulation, and dimensional analysis to examine the impact of convection on cell performance over a range of operating conditions as well as electrode and electrolyte properties. Qualitatively, we find that electrolyte flow (1) reduces spatial concentration gradients in the electrolyte (Figure 1c), eliciting enhanced accessed capacity for cells experiencing large electrolyte transport resistance (Figure 1b) and (2) serves as an effective mean of thermal regulation, ensuring battery safety and minimizing degradation. Quantitatively, we derive dimensionless groups to describe observed behaviour and provide further insight into critical previously unanswered questions, such as, when convection is needed, how much is needed, and what is the upper bound of enhancement when convection is used. Ultimately, our results suggest that this platform offers opportunities to expand the technology space of existing and emerging intercalation chemistries, enabling new user applications and revivifying materials previously thought unsuitable due to incompatibility with traditional designs.

Acknowledgements: We gratefully acknowledge funding from the MIT Energy Initiative.

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Figure 1. (a) Simple schematic of the convection battery and (b) fully-validated simulation of cell polarization and accessed capacity as a function of electrolyte flow that (c) prevents depletion in the positive electrode (a limiting conditions for traditional Li-ion batteries).

Figure 1