|SEM images before and after the silicon deposition. Source: Chen et al.Click to enlarge.|
Researchers at the University of Maryland have used a nickel-coated, genetically modified Tobacco mosaic virus (TMV1cys) as a 3-D current collector, combined with electrodeposition (ED), to fabricate a porous silicon anode for lithium-ion batteries.
Preliminary data shows that the porous silicon anode has very strong cycleability, with more than 1,000 mAh g-1 capacity retained after 170 cycles in the voltage range of 0-1.5V. The researchers attribute this performance to the porous silicon structure and the 3-D current collector. In both structures, the team notes, there is enough space to accommodate the silicon volume expansion during lithium insertion.
The high electronic conductivity of the nickel layer allows electrochemical deposition of silicon onto the coated virus to form nickel silicon core-shell nano-wires. In addition, the highly conductive nickel cores, which are attached to the current collector, enable all porous silicon shells to contribute to the total capacity.
Although silicon is a promising high-capacity anode material for lithium-ion batteries (3572 mAh g-1 and low charge/discharge voltage at room temperature) a silicon anode experiences a large volume expansion during lithium-ion insertion and a consequent shrinkage during extraction. This large volume change leads to severe particle pulverization, resulting in a quick electrode structure failure. Accordingly, a numerous efforts are underway to devise a structure and a material resistant to those changes, which result in a rapid capacity fade with cycling.
The virus-based material is one of several types of porous silicon anode materials members of the University of Maryland team have developed, including ones using polymer scaffold binders and carbon fiber as a current collector.
Juchen Guo and Chunsheng Wang (2010) A polymer scaffold binder structure for high capacity silicon anode of lithium-ion battery. Chem. Commun., 46, 1428 doi: 10.1039/b918727h
Juchen Guo, Ann Sun and Chunsheng Wang (2010) A porous silicon–carbon anode with high overall capacity on carbon fiber current collector. Electrochemistry Communications Volume 12, Issue 7 Pages 981-984 doi: 10.1016/j.elecom.2010.05.006