Processing conditions of battery slurries into electrodes are known to affect final battery performance. However, there is a lack of fundamental understanding of how the relationships between ...processing conditions, the slurry microstructure, and the film microstructure affect electrode performance. This study determines the effects of the coating shear rate and drying temperature on battery electrode performance via discharge capacity. We use rheological measurements and energy dispersive X-ray spectroscopy (EDS) to correlate slurry and electrode microstructures to trends in discharge capacity. The radial distribution function is used to quantify differences in the electrode microstructure. More specifically, we show that the correlation between carbon and active material EDS detections to be the most relevant in understanding battery performance. Electrodes with both short- and long-range carbon/active material orders have the highest discharge capacities. This microstructure can be obtained through high shear rates, which induce better carbon dispersion via strong hydrodynamic forces, or through high temperature drying by preventing unwanted time-dependent structural changes after flow cessation. This analysis provides concrete evidence for the importance of both short-range and long-range contacts between the conductive additive and active material on battery performance.
The viscosity and microstructure of Li-ion battery slurries and the performance of the resulting electrodes have been shown to depend on the mixing protocol. This work applies rheology to understand ...the impact of shear during mixing and polymer molecular weight on slurry microstructure and electrode performance. Mixing protocols of different shear intensity are applied to slurries of LiNi0.33Mn0.33Co0.33O2 (NMC), carbon black (CB), and polyvinyldiene difluoride (PVDF) in N-methyl-2-pyrrolidinone (NMP), using both high-molecular-weight (HMW) and low-molecular-weight (LMW) PVDF. Slurries of both polymers are observed to form colloidal gels under high-shear mixing, even though unfavorable interactions between high molecular weight PVDF and CB should prevent this microstructure from forming. Theoretical analysis and experimental results show that increasing shear rate during the polymer and particle mixing steps causes polymer scission to decrease the polymer molecular weight and allow colloidal gelation. In general, electrodes made from high molecular weight PVDF generally show increased rate capability. However, high shear rates lead to increased cell variability, possibly due to the heterogeneities introduced by polymer scission.
Replacing conductive carbon black with commercial carbon-coated iron nanoparticles yields an effective contrast-enhancing agent to differentiate between active material, conductive additive, and ...binder in lithium-ion battery electrodes. Nano-XCT resolved the carbon–binder domain with 126 nm voxel resolution, showing partial coatings around the active material particles and interparticle bridges. In a complementary analysis, SEM/EDS determined individual distributions of conductive additives and binder. Surprisingly, the contrast-enhancing agents showed that the effect of preparation parameters on the heterogeneity of conductive additives was weaker than on the binder. Incorporation of such contrast-enhancing additives can improve understanding of processing–structure–function relationships in a multitude of devices for energy conversion and storage.
Ionic liquid interlayers improve the oxygen reduction reaction (ORR) kinetics on bulk and nanostructured catalysts for both Pt and alloyed-Pt materials. Despite the demonstrated performance ...enhancement at the half-cell and membrane electrode assembly level, the mechanism of the improvement is not fully understood. In this work, we combine single-crystal experiments with microkinetic modeling to uncover the origin of the ORR kinetic improvement on Pt(111) in the presence of ionic liquids and hydrophobic cations. With the incorporation of a modified Frumkin isotherm, our model accurately simulates the disorder–order transition observed in hydroxyl and bisulfate adsorption on Pt(111) under acidic conditions. Voltametric analysis shows that ionic liquids impact solvation to break so-called scaling relations between the adsorption strength of OHad and Oad, but these effects have little impact on ORR activity. Instead, destabilized OHad reduces the overall hydroxyl (spectator) coverage, resulting in higher availability of active sites.
Stable, reproducible, and well-defined reference electrodes are vital for accurate quantification of battery material properties and physical mechanisms. Repeated studies have shown sodium metal to ...be an unreliable reference electrode material in nonaqueous solvents. This work evaluates several alternative reference electrode chemistries including sodium-tin alloy, nickel hexacyanoferrate and carbon. Of the systems tested, non-aqueous silver/silver-ion reference electrodes were shown to yield the most stable and reproducible voltage measurements.
Ionic liquid interlayers improve the oxygen reduction reaction (ORR) kinetics on bulk and nanostructured catalysts for both Pt and alloyed-Pt materials. Despite the demonstrated performance ...enhancement at the half-cell and membrane electrode assembly level, the mechanism of the improvement is not fully understood. In this work, we combine single-crystal experiments with microkinetic modeling to uncover the origin of the ORR kinetic improvement on Pt(111) in the presence of ionic liquids and hydrophobic cations. With the incorporation of a modified Frumkin isotherm, our model accurately simulates the disorder–order transition observed in hydroxyl and bisulfate adsorption on Pt(111) under acidic conditions. Voltametric analysis shows that ionic liquids impact solvation to break so-called scaling relations between the adsorption strength of OHad and Oad, but these effects have little impact on ORR activity. Instead, destabilized OHad reduces the overall hydroxyl (spectator) coverage, resulting in higher availability of active sites.
Falling costs of electricity from renewable and non-renewable sources have motivated interest in electrochemical production of chemicals and fuels. Among commodity chemicals, the production of KA oil ...(cyclohexanol and cyclohexanone) from cyclohexane is attractive as selective alkane oxidation remains a major industrial challenge. Although this reaction has been demonstrated in the literature, its fundamental chemistry remains poorly understood. This review identifies possible pathways for the reaction mechanism, their experimental support, and remaining critical gaps in molecular understanding of electrochemical cyclohexane oxidation to KA oil.
At high operating voltages, metals like Mn, Ni, and Co dissolve from Li-ion cathodes, deposit at the anode, and interfere with the performance of the solid-electrolyte interphase (SEI) to cause ...constant Li loss. The mechanism by which these metals disrupt SEI processes at the anode remains poorly understood. Experiments from Part I of this work demonstrate that Mn, Ni, and Co all affect the electronic properties of the SEI much more than the morphology, and that Mn is the most aggressively disruptive of the three metals. In this work we determine how a proposed electrocatalytic mechanism can explain why Mn contamination is uniquely detrimental to SEI passivation. We develop a microkinetic model of the redox cycling mechanism and apply it to experiments from Part I. The results show that the thermodynamic metal reduction potential does not explain why Mn is the most active of the three metals. Instead, kinetic differences between the three metals are more likely to govern their reactivity in the SEI. Our results emphasize the importance of local coordination environment and proximity to the anode within the SEI for controlling electron transfer and resulting capacity fade.
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