The template method for synthesizing nanostructures involves the synthesis of the desired material within the pores of a nanoporous membrane or other solid. Our work has involved using porous alumina and polymeric filter membranes as the templates. Fibrils or tubules of the desired material are formed within each pore of the template membrane. A number of synthetic methods have been used to synthesize these nanostructures. This paper reviews sol-gel template synthesis: the use of sol-gel chemistry to synthesize semiconductor oxide micro-and nanostructures within the pores of micro-and nanoporous membranes. For example, TiO 2 nanotubules and nanofibers of the anatase form have been synthesized. The high surface area offered by these TiO 2 nanostructures has been used for photodecomposition of salicylic acid in sunlight. Enzyme immobilization by stannous bridges inside the TiO 2 tubes has also been studied. In addition, V 2 O 5 fibrous electrode materials have been prepared by this method and Li intercalation electrochemistry is reported here. Other semiconductor oxides such as MnO 2 , Co 3 O 4 , ZnO, WO 3 , and SiO 2 have also been prepared.

We have prepared nanostructured electrodes of orthohombic V 2 0 5 using the template synthesis method. These electrodes were used to investigate the effects of Li-ion diffusion distance and surface area on V 2 0 5 rate capability. Nanowires of V 2 0 5 were prepared by depositing a precursor into the pores of microporous polycarbonate filtration membranes. This procedure yielded an ensemble of 115 nm diameter, 2 urn long nanowires of V 2 0 5 which protruded from a V 2 0 5 surface layer like the bristles of a brush. The galvanostatic discharge performance of these nanostructured V 2 0 5 electrodes was compared to a thin film electrode of similar V 2 0 5 mass and geometric area. The Li + storage capacity of the thin film electrode was equivalent to that of the nanostructured electrode at low (C/20) discharge rates. However, at a rate of 200C, the nanostructured electrode delivered three times the capacity of the thin film electrode. Above 500C the nanostructured electrode delivered four times the capacity of the thin film control electrode. 12. Subject terms: Nanostructured battery electrodes, V 2 0 5 , Li-ion batteries 17. 18. 19. Unclassified

Nanostructured LiMn 2 O 4 electrodes consisting of LiMn 2 O 4 nanotubules that protrude from a current collector surface like the bristles of a brush were prepared using the template method. The rate capabilities of these nanostructured electrodes were investigated at the 4 V (vs. Li/Li ϩ ) potential plateau in aqueous LiNO 3 electrolyte. Rate capability improved with decreasing wall thickness of the tubules which formed the electrode. This result is in agreement with our prior investigations of template-synthesized electrode materials which showed that rate capabilities improve with decreasing distance for Li ϩ transport in the solid state. The rate capabilities of electrodes prepared from the smallest-wall-thickness tubules are extraordinary; these electrodes can be cycled at C rates as high as 109 C. In addition, these investigations suggest that the poor cycling performance observed in prior studies of this electrode/electrolyte system results from unwanted oxidation of water during the charging process. By controlling the charge rate and the dimensions of the nanotubules making up the template-synthesized cathodes, this unwanted side reaction can be eliminated and good cycle life is observed. These data show that the nanostructured electrodes offer a unique advantage to this particular electrode/electrolyte system.

Template synthesis is a versatile nanomaterial fabrication method used to make monodisperse nanoparticles of a variety of materials including metals, semiconductors, carbons, and polymers. We have used the template method to prepare nanostructured lithium-ion battery electrodes in which nanofibers or nanotubes of the electrode material protrude from an underlying current-collector surface like the bristles of a brush. Nanostructured electrodes of this type composed of carbon, LiMn2O4, V2O5, tin, TiO2, and TiS2 have been prepared. In all cases, the nanostructured electrode showed dramatically improved rate capabilities relative to thin-film control electrodes composed of the same material. The rate capabilities are improved because the distance that Li+ must diffuse in the solid state (the current- and power-limiting step in Li-ion battery electrodes) is significantly smaller in the nanostructured electrode. For example, in a nanofiber-based electrode, the distance that Li+ must diffuse is restricted to the radius of the fiber, which may be as small as 50 nm. Recent developments in template-prepared nanostructured electrodes are reviewed.

Membrane-based template synthesis was used to prepare nanostructured V2O5 electrodes with high Li-insertion rate capabilities and improved volumetric charge capacities. Two methods were used to increase volumetric capacity. The first entailed chemically etching the template membrane prior to template-synthesis of the V2O5 within the pores of the membrane. Chemical etching increased both the pore diameter and porosity of the membrane. Nanostructured electrodes were prepared by depositing an alkoxide V2O5 precursor within the pores of the etched template membranes. The resulting electrodes consisted of V2O5 nanofibrils protruding from a Pt current collector surface like the bristles of a brush. The second approach for increasing volumetric capacity entailed applying additional V2O5 to the nanostructured electrodes prepared from the etched membranes. Results of investigations of the volumetric and geometric rate capabilities and the cycling performance of these electrodes are presented here. © 2001 The Electrochemical Society. All rights reserved.