Elucidating Concentration and Temperature-dependent Energy Limitations of a Novel Fluorinated-organosulfur Catholyte for Li Primary Batteries
Name
Sevilla-asevilla-MS-MechE-2023.pdf
Description
Thesis PDF
Size
3.1 MB
Format
Adobe PDF
Checksum (MD5)
11e9d7ac4acf494a1a511ca08fa392b3
Author(s)
Sevilla, Alejandro R.
Advisor(s)
Gallant, Betar M.
Date Issued
February 2023
Publisher
Massachusetts Institute of Technology
Abstract
Increasing the energy density of Lithium (Li) primary batteries requires exploring novel electrochemical reactions. Herein, the novel Li–carbon cell with a liquid catholyte based on the reactant 4-nitrophenylsfur (NO₂-Ph-SF₅) is studied in detail with emphasis on its energy limitations under practical cell conditions. While it has been demonstrated that the novel cell design can surpass the gravimetric energy density of industry leader Li–carbon monofluoride (Li–CFₓ) (1085 vs ~1000 Wh kg⁻¹) at 50 °C, calculations detailed in this study suggest that greater energy density (~20% greater) may still be possible. The energy shortfall arises from incomplete reduction of the cathode material at high reactant concentrations (4-5 M). Such concentrations are necessary for future practical applications of the cell. This study first investigates the effect of reactant concentration on capacity and energy density, followed by characterization of reaction intermediates and products, including a major product, lithium fluoride (LiF). Despite its electronically insulating nature, LiF was not found to induce carbon surface passivation under the conditions studied. Instead, the energy shortfall is shown to be constrained by the solubility of polysulfide-like intermediates whose electrochemical activity is hindered under concentrated catholyte conditions. Furthermore, the rate capability of the novel cell design is studied in the ~20–50 °C range. It is found that temperatures below 50 °C significantly inhibit energy density obtained at high current densities (> 1 mA cm⁻²), affecting the cell’s power delivery at room temperature. Despite efforts to improve the electrolyte ionic conductivity and transport of reactant species in the catholyte through catholyte engineering (i.e., varying species concentrations and solvent), performance is still limited under these conditions, and further study is required to further elucidate the effect of temperature on the reaction. Nonetheless, this study reveals key design parameters that can inform future iterations of the promising Li–NO₂-Ph-SF₅ primary battery.
MIT Department
Massachusetts Institute of Technology. Department of Mechanical Engineering
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