AFM as an analysis tool for high-capacity sulfur cathodes for Li–S batteries

Linus Carlé,Brigitta Pascucci,K Andreas Friedrich,Ines Galm,Natalia Cañas,Seniz Sörgel,Renate Hiesgen,Rémi Costa

doi:10.3762/bjnano.4.68

Abstract

In this work, material-sensitive atomic force microscopy (AFM) techniques were used to analyse the cathodes of lithium–sulfur batteries. A comparison of their nanoscale electrical, electrochemical, and morphological properties was performed with samples prepared by either suspension-spraying or doctor-blade coating with different binders. Morphological studies of the cathodes before and after the electrochemical tests were performed by using AFM and scanning electron microscopy (SEM). The cathodes that contained polyvinylidene fluoride (PVDF) and were prepared by spray-coating exhibited a superior stability of the morphology and the electric network associated with the capacity and cycling stability of these batteries. A reduction of the conductive area determined by conductive AFM was found to correlate to the battery capacity loss for all cathodes. X-ray diffraction (XRD) measurements of Li2S exposed to ambient air showed that insulating Li2S hydrolyses to insulating LiOH. This validates the significance of electrical ex-situ AFM analysis after cycling. Conductive tapping mode AFM indicated the existence of large carbon-coated sulfur particles. Based on the analytical findings, the first results of an optimized cathode showed a much improved discharge capacity of 800 mA·g(sulfur)−1 after 43 cycles.

Highlights

Lithium rechargeable batteries with high capacity are a key technology for the widespread implementation of batterypowered cars
We aim to demonstrate that a direct correlation exists between the cycling stability and the properties on the nanometre scale, and that atomic force microscopy (AFM) analysis can disclose the morphology of the carbon–sulfur interface
After 50 cycles, the remaining which combines with Li+ ions to yield high-order lithium polysulfides (Li2Sx, x ≥ 4)

Summary

Introduction

Lithium rechargeable batteries with high capacity are a key technology for the widespread implementation of batterypowered cars. The specific energy of existing lithium batteries needs further improvement to enable acceptable driving ranges of electric vehicles. Besides efficiency and energy density, numerous other requirements have to be fulfilled, which include industrial scalability and the capability for mass-production. In the last few decades, lithium–sulfur batteries have attracted increasing attention due to their high theoretical.

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Conclusion