|A new USC-developed process produces porous silicon nanoparticles for high-performance Li-ion anodes. Click to enlarge.|
Researchers at the University of Southern California (USC) have developed a new nanostructured silicon material for use as high performance lithium-ion battery anodes. The porous silicon nanoparticles, prepared using a novel two-step process combining controlled boron doping and facile electroless etching, have achieved capacities around 1,400 mA·h/g at a current rate of 1 A/g, and 1,000 mA·h/g at 2 A/g, with stable operation when combined with reduced graphene oxide and tested over up to 200 cycles.
In a paper published in the journal Nano Research, the team attributed the overall good performance to the combination of porous silicon that can accommodate large volume change during cycling and provide large surface area accessible to electrolyte, and reduced graphene oxide that can serve as an elastic and electrically conductive matrix for the porous silicon nanoparticles.
The design, currently under a provisional patent, could be commercially available within two to three years.
Silicon is one of the most promising anode candidates because of its high theoretical capacity of approximately 3,600 mA·h/g at room temperature. However, the drawbacks of silicon anodes are equally obvious. The large volume change during the insertion and extraction of lithium in silicon leads to severe pulverization and capacity fading, which has limited the use of silicon in real battery applications.
...Recently, we have reported [Ge et al. 2012] that a porous silicon nanowire anode can achieve a capacity of over 1,000 mA·h/g at a current rate of 4 A/g for 2,000 cycles when using commercially available alginate as the binder. We note that while porous silicon nanowires may find broad applications including in lithium-ion batteries, biomedical imaging, and thermoelectric devices, the preparation of porous silicon nanowires and similar nanostructures is usually achieved by wet etching of doped silicon wafers, and therefore is limited in quantity. A more scalable method is highly desirable for the preparation of porous silicon nanostructures.
Here, we introduce a new and simple synthetic route for the preparation of porous silicon nanoparticles. By doping and then etching of commercially available silicon nanoparticles, porous silicon nanoparticles can be synthesized in bulk quantities. Our approach represents a quantum leap from traditional porous silicon nanowires...—Ge et al.
In their process, they started with silicon nanoparticles with a size of <200nm. They first doped the silicon with boron, then etched the boron-doped silicon in an etchant containing silver nitrate (AgNO3) and hydrofluoric acid (HF) to obtain a porous structure.
Future research by the group will focus finding a new cathode material with a high capacity that will pair well with the porous silicon nanowires and/or porous silicon nanoparticles to create a completely redesigned battery.
The work was funded by the USC Viterbi School of Engineering.
Mingyuan Ge, Jiepeng Rong, Xin Fang, Anyi Zhang, Yunhao Lu, Chongwu Zhou (2013) Scalable preparation of porous silicon nanoparticles and their application for lithium-ion battery anodes. Nano Research doi: 10.1007/s12274-013-0293-y
Mingyuan Ge, Jiepeng Rong, Xin Fang, and Chongwu Zhou (2012) Porous Doped Silicon Nanowires for Lithium Ion Battery Anode with Long Cycle Life. Nano Lett. 12 (5), pp 2318–2323 doi: 10.1021/nl300206e