No abstract

Increased thermal conductivity, electronic conductivity, and reversible capacity (i.e., reduced irreversible capacity loss, or ICL) have been demonstrably achievable by compression of anodes into higher volume fraction plates, though excessive compression can impair Li-ion battery performance. In our previous study, we correlated conductivity and compression of these materials. Here, we further investigated the effects of friction and deformability of particles on the compressibility of model carbons of Li-ion anodes. First, we implemented a statistically unbiased technique for generating a range of random particulate systems, from permeable to impermeable arrangements, along with a contact model for randomly arranged triaxial ellipsoidal particles, suitable for implementation in finite element analysis of compression of a random, porous system. We then quantified the relationship between interfacial friction and jamming fraction in spherical to ellipsoidal systems and applied these models to correlate maximum stresses and different frictional coefficients, with morphology (obtained by image analysis) of graphite particles in Li-ion anodes. The simulated results were compared with the experiments, showing that the friction coefficient in the system is close to 0.1 and that the applied pressure above 200kg∕cm2(200MPa) can damage the materials in SL-20 electrodes. We also conclude that use of maximum jamming fractions to assess likely configuration of mixtures is unrealistic, at best, in real manufacturing processes. Particles change both their overall shapes and relative orientations during deformation sufficient to alter the composite properties: indeed, it is alteration of properties that motivates post-processing at all. Thus, consideration of material properties, or their estimation post facto, using inverse techniques, is clearly merited in composites having volume fractions of particles near percolation onset.

No abstract

Remineralization of early enamel lesions was studied in situ using a F chewing gum or a F-releasing device (FRD). Enamel specimens with subsurface lesions were mounted in removable lower appliances in 6 adults. A F-free dentifrice was used for all regimens. Test groups chewed five sticks/day (0.1 mg F/stick), or one FRD (0.5 mg F/day) was mounted in the midline of the appliance. The microhardness was measured after the 21-day intraoral exposure, and in vitro acid resistance testing was performed. Separate specimens were used to measure F content or changes in mineral density. Comparable values for both F gum and FRDs were higher (p > 0.05) than controls for acid resistance testing and percent remineralization. The F content for FRDs exceeded that of both F gum and controls.

No abstract

Several promising Li-ion technologies incorporate micro- and nanoarchitectured carbon networks, typically in the form of whisker/particle blends bonded with thermoplastic binders, in the electrodes. Degradation of these battery electrode materials is currently a persistent problem, with damage presenting as blistering and/or delamination. We are investigating bonding in micro- and nanostructured materials in order to predict onset of this degradation of these stochastic materials. Here, we describe a general methodology in modeling the small junctures in these porous network materials. We have found previously that the joint properties are the controlling feature in a significant class of materials, and suggest that 3D simulations on the bonds may be used in 2D simulations of overall network behavior.