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

Abstract

SummaryIn 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.

Insight into the Interfacial Process and Mechanism in Lithium–Sulfur Batteries: An In Situ AFM Study

“…Using an in situ AFM probe in the PeakForce QNM mode, quantitative mapping of the elastic modulus are produced and processed typically through the Derjaguin–Muller–Toporov (DMT) model . The individual stiffness of the image areas allows for a distinction of different phases . Topography and mapping of the DMT modulus were measured simultaneously at the time when lamella structure were about to be fully oxidized (Supporting Information, Figure S5).…”

Influence of cycling profile, depth of discharge and temperature on commercial LFP/C cell ageing: post-mortem material analysis of structure, morphology and chemical composition

“…Steinhauer et al used in-situ AFM to follow the SEI evolution during the first cycle on crystalline carbon and observed dynamic surface structures with a potential dependent speed of growth [21]. Hiesgen et al used AFM to analyse the morphology of sulphur cathodes depending on the binder material and observed a decrease of the electronic surface conductivity after ageing, which correlated with the capacity decay [22]. Wu et al analysed aged LiCoO 2 cathode surfaces and observed an increase in grain size and surface roughness and a decrease of the surface potential and material stiffness.…”

Carbon Materials for Lithium Sulfur Batteries—Ten Critical Questions

“…Ex situ investigations of Li–S operation based on liquid chromatography coupled with mass spectrometry, atomic force microscopy, Fourier transform IR spectroscopy, Raman spectroscopy, or X‐ray‐based methods, coupled with scanning electron microscopy, are helpful for a better mechanistic understanding of Li–S cells. However, since the cells are disassembled for the measurements, ex situ studies only identify components and structures present before and after operation and do not investigate reaction pathways or intermediate components with short lifetimes that might react further before the studies are carried out.…”