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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.

Electrochemical reactionshigh theoretical capacity (1675 Ah kg sulfur -1 ) high energy density (2500 Wh kg -1 ) low cost and non-toxicity of sulfur high degradation due to loss of active material electrochemical processes and degradation mechanisms are still not well understood. Solid reactants Dissolved polysulfides intermediates Solid productDischarge Charge Lithium-sulfur battery Materials and methodsIn-situ XRD cell EIS End Voltages (V): 2.8/1.5 Discharge current: 300 A kg sulfur -1 Results Discharge ChargeVariation of the equivalent circuit elements during cycling determined by EIS analysis.• The highest electrolyte resistance, related to the highest concentration of polysulfides is detected at the end of the first discharge and charge plateau (43 % DOD and 56 % DOC).• The impedance contributions associated to the processes in the cell are strongly dependent on the depth of discharge and charge of the cell [2]. Swagelok-cellPotentiostatic: 5 mV amplitude Equidistant intervals of 50 mC Frequency range: 1 MHz to 60 mHz Discharge Charge • At discharge rate of 300 A kg -1 sulfur reduces consecutively during the first discharge to Li 2 S.• The formation of Li 2 S was observed for the first time at a depth of discharge of 60 % in the second discharge plateau at 1.8 V.• During the charge cycle, Li 2 S reacts entirely and sulfur recrystallizes with a different orientated structure and smaller particle size [1].The AFM results confirm the formation of an isolating layer in the cathode, which increases the surface resistance on the cathode, as observed through the analysis of the impedance at low frequencies (R 3 ).