Structural and electrochemical properties of three-dimensionally ordered macroporous tin(IV) oxide films

This paper presents a colloidal-crystal templating technique to prepare three-dimensionally ordered macroporous (3DOM) tin(iv) oxide films for use as lithium ion anodes. In principle, 3DOM architectures are expected to diminish diffusional polarization and yield high rates of charge/discharge due to ion diffusion pathlengths on a nanometer scale and ready electrolyte access to relatively large internal electrode/electrolyte interfacial areas. Uniformly-sized polymer spheres were deposited in a close-packed arrangement on a current collecting substrate. A tin(IV) fluid precursor infiltrated the interstitial space between the spheres and was dried. Subsequent calcination removed the polymer sphere template and formed an inverse opal film composed of nanocrystalline SnO₂. These films were characterized by SEM, XRD, elemental analysis, BET, CV, and galvanostatic cycling. Large structural changes occurred in these samples as a result of the formation of Li_xSn (0 ≤ x ≤ 4.4) alloys during cycling. This swelling could not be suppressed by the inclusion of additives to the precursor solution. Morphological changes were absent after cycling at significantly higher rates, possibly due to ohmic losses that prevented the electrochemical reactions from occurring.