Titanium silicide nanonet as a new material platform for advanced lithium ion battery applications.

Compared with competing technologies, rechargeable lithium ion batteries offer relative advantages such as high capacity and long cycle lifetime. Remarkable advances in the development of this technology notwithstanding significant performance improvements are still required to meet society's ever-growing electrical energy storage need. In particular, we long for devices with greater capacity, a higher power rate and a longer cycle lifetime. Aimed at solving challenges associated with poor charge transport within electrode materials, we have recently tested a new, nanonet-based material platform. The nanonet, made of TiSi2 (C49), is similar to the more commonly used porous carbon in that it has high surface area and good electrical conductivity. The key uniqueness of the nanonet lies in that its morphology is well-defined, permitting us to design and test various heteronanostructures. In essence, the TiSi2 nanonet can serve as a charge collector and a mechanical support for the construction of electrodes for a wide range of applications. We show that when combined with Si, an anode with superior performance is obtained. Similarly, a high-performance cathode is enabled by the TiSi2-V2O5 combination.

Layered titanium disilicide stabilized by oxide coating for highly reversible lithium insertion and extraction.

The discovery of new materials has played an important role in battery technology development. Among the newly discovered materials, those with layered structures are often of particular interest because many have been found to permit highly repeatable ionic insertion and extraction. Examples include graphite and LiCoO(2) as anode and cathode materials, respectively. Here we report C49 titanium disilicide (TiSi(2)) as a new layered anode material, within which lithium ions can react with the Si-only layers. This result is enabled by the strategy of coating a thin (<5 nm) layer of oxide on the surface of TiSi(2). This coating helped us rule out the possibility that the measured capacity is due to surface reactions. It also stabilizes TiSi(2) to allow for the direct observation of TiSi(2) in its lithiated and delithiated states. In addition, this stabilization significantly improved the charge and discharge performance of TiSi(2). The confirmation that the lithium-ion storage capacity of TiSi(2) is a result of its layered structure is expected to have major fundamental and practical implications.

Growth of p-type hematite by atomic layer deposition and its utilization for improved solar water splitting.

Mg-doped hematite (α-Fe(2)O(3)) was synthesized by atomic layer deposition (ALD). The resulting material was identified as p-type with a hole concentration of ca. 1.7 × 10(15) cm(-3). When grown on n-type hematite, the p-type layer was found to create a built-in field that could be used to assist photoelectrochemical water splitting reactions. A nominal 200 mV turn-on voltage shift toward the cathodic direction was measured, which is comparable to what has been measured using water oxidation catalysts. This result suggests that it is possible to achieve desired energetics for solar water splitting directly on metal oxides through advanced material preparations. Similar approaches may be used to mitigate problems caused by energy mismatch between water redox potentials and the band edges of hematite and many other low-cost metal oxides, enabling practical solar water splitting as a means for solar energy storage.