February 18, 2010

Silicon-coated Nanonets Could Build a Better Lithium-ion Battery

Frame (a) shows a schematic of the Nanonet, a lattice structure of Titanium disilicide (TiSi2), coated with silicon (Si) particles to form the active component for Lithium-ion storage. (b) A microscopic view of the silicon coating on the Nanonets. (c) Shows the crystallinity of the Nanonet core and the Si coating. (d) The crystallinity of TiSi2 and Si (highlighted by the dotted red line) is shown in this lattice-resolved image from transmission electron microscopy. (Source: Nano Letters)

A tiny scaffold-like titanium structure of Nanonets coated with silicon particles could pave the way for faster, lighter and longer-lasting Lithium-ion batteries, according to a team of Boston College chemists who developed the new anode material using nanotechnology.

The web-like Nanonets developed in the lab of Boston College Assistant Professor of Chemistry Dunwei Wang offer a unique structural strength, more surface area and greater conductivity, which produced a charge/re-charge rate five to 10 times greater than typical Lithium-ion anode material, a common component in batteries for a range of consumer electronics, according to findings published in the current online edition of the American Chemical Society journal Nano Letters.

The structure and conductivity of the Nanonets improved the ability to insert and extract Lithium ions from the particulate Silicon coating, the team reported. Running at a charge/discharge rate of 8,400 milliamps per gram (mA/g) – which is approximately five to 10 times greater than similar devices – the specific capacity of the material was greater than 1,000 milliamps-hour per gram (mA-h/g). Typically, laptop Lithium-ion batteries are rated anywhere between 4,000 and 12,000 mA/h, meaning it would only take between four and 12 grams of the Nanonet anode material to achieve similar capacity.

Wang said the capability to preserve the crystalline Titanium Silicon core during the charge/discharge process was the key to achieving the high performance of the Nanonet anode material. Additional research in his lab will examine the performance of the Nanonet as a cathode material.

Si/TiSi2 Heteronanostructures as High-Capacity Anode Material for Li Ion Batteries

We synthesized a unique heteronanostructure consisting of two-dimensional TiSi2 nanonets and particulate Si coating. The high conductivity and the structural integrity of the TiSi2 nanonet core were proven as great merits to permit reproducible Li+ insertion and extraction into and from the Si coating. This heteronanostructure was tested as the anode material for Li+ storage. At a charge/discharge rate of 8400 mA/g, we measured specific capacities >1000 mAh/g. Only an average of 0.1% capacity fade per cycle was observed between the 20th and the 100th cycles. The combined high capacity, long capacity life, and fast charge/discharge rate represent one of the best anode materials that have been reported. The remarkable performance was enabled by the capability to preserve the crystalline TiSi2 core during the charge/discharge process. This achievement demonstrates the potency of this novel heteronanostructure design as an electrode material for energy storage.

8 pages of supplemental material

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