(316g) Controlling Discharge Product Distribution through an Electrode Surface-Mediated Mechanism in Alkali Metal-O2 Battery Cathodes

Aprotic alkali metal-O₂ (M-O­₂; M = Li, Na) batteries have attracted significant attention due to their high specific energies (energy per unit mass).¹ These batteries consist of an alkali metal anode, an alkali metal salt dissolved in an aprotic solvent as the electrolyte, and generally a porous carbon-based cathode. The complexity of the electrochemistry at the battery cathode where solid M_xO₂ species are formed and dissociated has been an obstacle in achieving the desired theoretical capacities to unable their commercialization.¹ Therefore, understanding of the mechanism and factors that govern M_xO₂ product formation at the cathodes remains important toward advancing the battery performance. We have combined well-controlled synthesis, with theoretical calculations, electrochemical studies and detailed characterization, to show that potential-dependent discharge product distribution on oxide cathode electrocatalysts significantly affects the charge overpotentials, consequently the cell performance. We find that, through an electrode surface-mediated discharge mechanism, nanostructured oxides provide a platform to stabilize M-deficient oxide species, consequently lowering overpotential losses associated with their oxidation during charge, leading to enhanced performance.^1-2 Quantum chemical modeling of the solid-solid interface between the oxide and M_xO₂ discharge products suggests that stabilization of the M-deficient products is due to formation of a M-modified oxide surface with enhanced electronic conductivity.² These findings provide a framework for elucidating mechanisms to control discharge product distribution in aprotic alkali metal-O₂ batteries, consequently minimizing charge overpotentials and enhancing cell cyclability.

References

(1) SamiraS, Deshpande S., Greeley J.*, Nikolla, E.*, ACS Energy Letters, 6, 2, 665–674, 2021

(2) Samira,S^‡, Deshpande S^‡, ..., Greeley J.*, Nikolla E*, Chemistry of Materials, 31 (18), 7300-7310, 2019.