Better Lithium-Ion Electrodes
Silicon nanowires could increase the storage capacity of batteries.

Source: “High-performance lithium battery anodes using silicon nanowires”
Yi Cui et al.
Nature Nanotechnology 3: 31-35

Results: Researchers at Stanford University demonstrated that silicon nanowires used as anodes in lithium-ion batteries have five to eight times the energy-storage capacity of the graphite anodes normally used in the batteries. The researchers also showed that the nanowires can absorb and release lithium ions quickly over many cycles without breaking apart.

Why it matters: The advance could lead to greater storage capacity in lithium-ion batteries. Such batteries work by shuttling lithium ions between the cathode and the anode (the positive and negative electrodes) as the batteries are charged and discharged. Silicon has long been considered a promising electrode material because it can, in theory, hold 10 times as many lithium ions as graphite. But as silicon absorbs lithium ions, it swells to many times its original volume. Over several cycles, this normally causes silicon electrodes to break apart and stop functioning properly. The silicon nanowires, however, were able to swell to four times their original size and remain intact, demonstrating that silicon could be a practical material for battery electrodes.

Methods: The researchers distributed gold nanoparticles on a stainless-steel substrate. When they exposed the nanoparticles to silane, a gas containing silicon, the gold catalyzed the growth of silicon nanowires. The researchers then tested the nanowire electrodes. They also studied the composition and structure of the nanowires.

Next Steps: The researchers are developing other ways to make the silicon nanowires, with the goal of finding techniques that are less expensive and thus potentially more practical for commercial manufacturing. Better cathodes also need to be developed before the full benefits of the new anode materials can be realized.