Spongy Silicon Electrodes Promise Big Boost for Lithium-Ion Batteries

The key to making lithium-ion batteries cheaper and far more powerful could be a new anode material made of conductive hydrogel and silicon nanoparticles.

Materials researchers at Stanford University say the spongy composite they developed offers both high energy density and long cycle life. The team reported its results earlier today in the online journal Nature Communications.

In lab tests, an anode made of the material maintained more than 90% of its initial current density (6.0 Ag^-1) after 5,000 cycles, according to the scientists.

Battery researchers know that silicon offers 10 times the charge storage capacity of conventional carbon electrodes. But the material can expand and contract by a factor of four as it gains and sheds lithium ions. The effect causes silicon to crack, lose electrical contact and reduce the battery's storage capacity.

The Stanford developers say they overcame that problem with a three-dimensional structure of hydrogel, a water-based substance similar to the material used in soft contact lenses.

The team populated the sponge-like material with silicone nanospheres, then coated both hydrogel and spheres with a conductive polymer. Finally, they removed water from the hydrogel to guard against internal runaway discharges that could cause a fire.

The resulting composite simultaneously holds the silicon spheres and provides plenty of channels through which ions can move quickly during the charging and discharging processes.

The researchers say some technical hurdles remain. But they describe their fabrication process as compatible with existing lithium-ion batterymaking technology. They also note that the silicon and hydrogel materials required are plentiful and inexpensive.

The Stanford research was funded primarily by the university's Precourt Institute for Energy, the Natural Science Foundation of China, the U.S. National Science Foundation and the U.S. Dept. of Energy's SLAC Laboratory Directed Research and Development Program.