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Probing and Interpreting the Porosity and Tortuosity Evolution of Li-O2 Cathodes on Discharge through a Combined Experimental and Theoretical Approach

Torayev, Amangeldi and Engelke, Simon and Su, Zeliang and Marbella, Lauren E. and De Andrade, Vincent and Demortière, Arnaud and Magusin, Pieter C. M. M. and Merlet, Céline and Franco, Alejandro A. and Grey, Clare P. Probing and Interpreting the Porosity and Tortuosity Evolution of Li-O2 Cathodes on Discharge through a Combined Experimental and Theoretical Approach. (2021) Journal of Physical Chemistry C, 125 (9). 4955-4967. ISSN 1932-7447

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Official URL: https://doi.org/10.1021/acs.jpcc.0c10417

Abstract

Li-O2 batteries offer a high theoretical discharge capacity due to the formation of light discharged species such as Li2O2, which fill the porous positive electrode. However, in practice, it is challenging to reach the theoretical capacity and completely utilize the full electrode pore volume during discharge. With the formation of discharge products, the porous medium evolves, and the porosity and tortuosity factor of the positive electrode are altered through shrinkage and clogging of pores. A pore shrinks as solid discharge products accumulate, the pore clogging when it is filled (or when access is blocked). In this study, we investigate the structural evolution of the positive electrode through a combination of experimental and computational techniques. Pulsed field gradient nuclear magnetic resonance results show that the electrode tortuosity factor changes much faster than suggested by the Bruggeman relation (an equation that empirically links the tortuosity factor to the porosity) and that the electrolyte solvent affects the tortuosity factor evolution. The latter is ascribed to the different abilities of solvents to dissolve reaction intermediates, which leads to different discharge product particle sizes: on discharging using 0.5 M LiTFSI in dimethoxyethane, the tortuosity factor increases much faster than for discharging in 0.5 M LiTFSI in tetraglyme. The correlation between a discharge product size and tortuosity factor is studied using a pore network model, which shows that larger discharge products generate more pore clogging. The Knudsen diffusion effect, where collisions of diffusing molecules with pore walls reduce the effective diffusion coefficients, is investigated using a kinetic Monte Carlo model and is found to have an insignificant impact on the effective diffusion coefficient for molecules in pores with diameters above 5 nm, i.e., most of the pores present in the materials investigated here. As a consequence, pore clogging is thought to be the main origin of tortuosity factor evolution.

Item Type:Article
Audience (journal):International peer-reviewed journal
Uncontrolled Keywords:
Institution:French research institutions > Centre National de la Recherche Scientifique - CNRS (FRANCE)
Other partners > Collège de France (FRANCE)
Other partners > Columbia University (USA)
Other partners > Ecole Nationale Supérieure de Chimie de Paris - ENSCP (FRANCE)
Other partners > Ecole Nationale Supérieure de Chimie de Montpellier - ENSCM (FRANCE)
Université de Toulouse > Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE)
Other partners > Institut polytechnique de Grenoble (FRANCE)
Other partners > Sorbonne Université (FRANCE)
Other partners > Université Grenoble Alpes - UGA (FRANCE)
Other partners > University of Cambridge (UNITED KINGDOM)
Université de Toulouse > Université Toulouse III - Paul Sabatier - UT3 (FRANCE)
Other partners > Université de Nantes (FRANCE)
Other partners > Université de Picardie Jules Verne (FRANCE)
Other partners > ALISTORE-ERI (FRANCE)
Other partners > Université de Pau et des Pays de l'Adour - UPPA (FRANCE)
Other partners > Université de Haute Alsace - UHA (FRANCE)
Other partners > Université de Montpellier (FRANCE)
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Deposited On:23 Mar 2021 08:05

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