NMR Insights into Pore Architecture and Li+ Accessibility for Optimized Energy Density in Li-O2 Batteries.

Abstract

Lithium-oxygen batteries have gained prominence in recent years due to their potential advantages over conventional lithium-ion batteries, including higher energy density, cost-effectiveness and environmental sustainability. To fully exploit these advantages, it is essential to understand the interplay between porous carbon electrode materials and electrolytes in these devices. This study presents a nuclear magnetic resonance investigation of the confined LiTFSI (lithium bis(trifluoromethanesulfonyl)imide) - TEGDME (tetraethylene glycol dimethyl ether) electrolyte within carbonaceous materials with different pore sizes. Three carbon materials (microporous, mesoporous, and hierarchical) were synthesized from the same precursor to ensure equivalent surface chemistry, which was verified by X-ray photoelectron spectroscopy. The dynamics and distribution of solvent and Li ions in the different pores were studied by ${}^1$ H and ${}^7$ Li, 1D and 2D exchange, NMR spectroscopy. It was found that the accessibility of Li ${}^{+}$ within the pores of the carbonaceous material depends not only on their size but also on their size distribution. The knowledge gained from this study can contribute to the design of the appropriate pore size distribution, which could optimize the electrolyte utilization and consequently increase the energy density of lithium-oxygen batteries.