The formation of fractal silica networks from a colloidal initial state was followed in situ by ion conductivity measurements. The underlying effect is a high interfacial lithium ion conductivity arising when silica particles are brought into contact with Li salt-containing liquid electrolytes. The experimental results were modeled using Monte Carlo simulations and tested using confocal fluorescence laser microscopy and ζ-potential measurements.
Modeling and simulation of lithium batteries is becoming of increasing importance both for improving the fundamental understanding of electrochemical processes and for developing battery management systems for practical applications. We present a 1D+1D+1D multi-scale electrochemical and thermal model of a lithium-ion battery with lithium iron phosphate (LiFePO 4 , LFP) positive electrode material. The model uses a hierarchical representation of spatial scales: On the nanoscopic level, diffusive transport takes place in the active material particles. On the microscopic level, multi-component mass and charge transport as well as heat production is described in a single repeat unit (anode, separator, cathode, current collectors). On the macroscopic scale, the model describes heat transport in the radial direction of a cylindrical cell. Molar enthalpies and entropies are incorporated as function of state of charge (SOC) for reliable simulation of heat production. The model is validated using experimentally-determined discharge curves over a wide range of discharge currents.
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.
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