Date/Time
Date(s) - 27/10/2022
1:30 pm - 2:30 pm

Please join us for a department seminar delivered by PhD Candidate Chris Franko.

Title: Solid-State and Diffusional Nuclear Magnetic Resonance Investigations of Oxidatively Stable Materials for Sodium Batteries

Date: Thursday, October 27, 2022

Time: 1:30-2:30 

Room: ABB 165 

Zoom: Please email chemgrad@mcmaster.ca for Zoom details.

Host: Gillian Goward

Abstract:

Sodium-based battery chemistries have potential for use as competitive energy storage alternatives to Li-ion batteries (LIBs), largely due to the low cost and wide availability of raw sodium materials compared to their lithium counterparts (150 USDt^-1vs 5000 USDt^-1, for Na and Li carbonate respectively).¹ Na-oxygen batteries (NaOBs) are a promising candidate, reaching high theoretical capacities of 1108 Wh kg^-1.² Typically, a sodium metal anode is oxidized upon discharge, and O₂ gas is reduced to form either sodium superoxide (NaO₂) or sodium peroxide (Na₂O₂)in competing oxygen reduction pathways, both of which deposit as crystallites on the carbon cathode. Although theoretical gravimetric capacity in these batteries is high, cell lifetime is hindered by the oxidative instability of both the organic electrolyte at high charging voltages, and the carbon cathode toward NaO₂.³

In this work reduced titanium dioxide (Ti₄O₇) is investigated as a starting material for alternative cathode substrates. Electrically insulatingTiO₂ is reduced via hydrogen gas to produce highly conductive single phase Ti₄O₇. The stability of Ti₄O₇toward NaO₂ is confirmed by solid state ²³Na NMR. NaOB cells are constructed and Ti₄O₇ is used a coating in carbon-based cathodes in an attempt to improve cell stability. It is shown that cell lifetime is increased with increasing Ti₄O₇ doping percent. In order to determine the mechanism of this phenomena, discharged cathodes are examined via solid state ²³Na magic angle spinning (MAS) NMR at a field of 11.7 T and spinning at frequencies of 30 kHz. The triple-quantum MAS(3QMAS) and {¹H}-²³Na dipolar heteronuclear multiple quantum correlation (D-HMQC) experiments are used to identify the electrochemical discharge product slurry. NaO₂ is identified as the main discharge product in Ti₄O₇-coated and pure carbon cells, and is seen to degrade at slower rates in Ti₄O₇-coatedcathodes. To prove that Ti₄O₇ is participating in the electrochemistry of the cell, NaO₂ crystallites are shown to be formed on the Ti₄O₇ surface of the cathode via scanning electron microscopy (SEM). It is believed that the carbon backbone of the substrate is the main oxygen reduction reaction (ORR) active material, and Ti₄O₇acts a stable nucleation point for NaO₂ formed in solution.

1              Slater, M. D., Kim, D., Lee, E. & Johnson, C. S. Sodium-Ion Batteries. Advanced Functional Materials 23, 947-958, doi:10.1002/adfm.201200691(2013).

2              Lutz, L. et al. Role of Electrolyte Anions in the Na–O2 Battery: Implications for NaO2 Solvation and the Stability of the Sodium Solid Electrolyte Interphase in Glyme Ethers. Chemistry of Materials 29,6066-6075, doi:10.1021/acs.chemmater.7b01953 (2017).

3              Reeve, Z. E. et al. Detection of Electrochemical Reaction Products from the Sodium-Oxygen Cell with Solid-State(23)Na NMR Spectroscopy. J Am Chem Soc139, 595-598,doi:10.1021/jacs.6b11333 (2017).