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We evaluated the Coulombic interactions of the lithium cation in the separator membrane of lithium secondary batteries in terms of the morphological factors of the separator membrane and the solvation structure of the lithium cation carriers. The magnitudes of the cation/ membrane and cation/anion interactions increased with the increasing tortuosity and decreasing width of the ion transport pathways comprising the linked-pore spaces in the membrane, which decreased cation mobility. Lithium cations strongly solvated by high-polarity solvents interacted weakly with the membrane and the anion due to the strong shielding by the solvent molecules coordinated to the lithium cation. In particular, we confirmed that the new membranes, which were tailored to have almost linear pathways across the membrane surface, showed no cation/membrane interaction, thereby indicating that the low-tortuosity aligned-pore pathways could be an ideal stressfree pathway for ion transport. Finally, DC resistance measurements of a lithium secondary battery with these membranes established the advantage of the linear pathway separator for enhanced discharge performance of the battery system. These results provide a clear direction for considering the ion migration mechanism in the design of high-power lithium secondary batteries.

Bioabsorbable and functionally graded apatite (fg-HAp) ceramics were designed using bovine bone by the calcination and partial dissolution-precipitation methods. The fg-HAp ceramics that were developed had gradual distributions of the degree of crystallinity and the grain size of single-phase hydroxyapatite from the surface layer of the pore wall to the bulk structure region. Calcination at 1073 K gave a specific surface area of 30 m2 x g-1 and porosities of 60-80%. The pore structure of the fg-HAp was classified into two regions: a macro-pore region (100-600 microm) originating from spongy bone and a micro-pore region (10-160 nm) related to body fluid permeation and blood permeability. By implantation in subcutaneous tissue of rat, it was confirmed that body fluid permeated the bulk region of the fg-HAp ceramics through the micro-pores. The volumetric populations occupied by body fluid were 60% at 4 weeks and 68% at 8 weeks in the ceramics explants, indicating drastic bioabsorption, although the body fluid was found to be immunopositive for an albumin as the main serum protein in blood. On the fg-HAp ceramics developed here, the bioabsorption rate could be controlled by careful selection of the calcination temperature. These ceramics can be applied as new biomimetic ceramics exhibiting surface and bulk degradations and cellular absorption by giant cells.

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