Combined Influence of Meso- and Macroporosity of Soft-Hard Templated Carbon Electrodes on the Performance of Li-O2 Cells with Different Configurations.

Mara Olivares-Marín,Dino Tonti,Mohamed Aklalouch

doi:10.3390/nano9060810

Abstract

Li-O2 batteries can offer large discharge capacities, but this depends on the morphology of the discharged Li2O2, which in turn is strongly affected by the nanostructured carbon used as support in the air cathode. However, the relation with the textural parameters is complex. To investigate the combined effect of channels of different sizes, meso-macroporous carbons with similar mesopore volume but different pore size distribution were prepared from the polymerization of resorcinol-formaldehyde (RF) in the presence of surfactants and micro-CaCO3 particles. The carbon materials were used as active materials of air cathodes flooded by ionic liquid-based electrolytes in Li-O2 cells with two different configurations, one with a static electrolyte and the other with a stirred electrolyte, which favor a film-like and large particle deposition, respectively. The presence of large pores enhances the discharge capacity with both mechanisms. Conversely, with respect to the reversible capacity, the trend depends on the cell configuration, with macroporosity favoring better performance with static, but poorer with stirred electrolytes. However, all mesoporous carbons demonstrated larger reversible capacity than a purely macroporous electrode made of carbon black. These results indicate that in addition to pore volume, a proper arrangement of large and small pores is important for discharge capacity, while an extended interface can enhance reversibility in Li–O2 battery cathodes.

Highlights

Many studies based on the impact of porous carbon-based air cathodes architecture on Li-O2 battery performance coincide with the fact that the discharge capacity increases with pore volume especially when pore sizes are within the mesoporous range [1,2,3]
Nimon et al [5] and Kuboki et al [6] noticed that the deposition of solid discharge products occurred within the pore volume rather than on their surface; while the former noticed the filling of pores with radii of up to 10 nm, the latter found that large open volumes such as those of Super P carbon black are suitable for Li-O2 batteries
Some uniform mesopore structures are connected by large pores or voids with various shapes and sizes, which can be attributed to the presence of the spherical CaCO3 templates

Summary

Introduction

Many studies based on the impact of porous carbon-based air cathodes architecture on Li-O2 battery performance coincide with the fact that the discharge capacity increases with pore volume especially when pore sizes are within the mesoporous range [1,2,3]. Instead, when the mechanism changes to solution-phase growth, the same materials are much less effective than structures with high porous volume such as Super P carbon black, able to host large amounts of precipitate [11] This general principle only takes into account the way that the space offered by the electrode can be filled by discharge products of a given morphology. Several authors [22,23] have reported that a network throughout the electrode formed by micron-sized macropores can enhance the O2 transport and, result in high discharge capacity Modeling has confirmed this concept a proper balance between macroporosity and microporosity is required for optimal results [24]. Most of these studies only consider the impact of porosity on the discharge capacity, but not on rechargeability

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Conclusion