South Korea – A research team led by Jaephil Cho at Hanyang University has developed a 3-dimensional, porous silicon structure that can replace graphite as an anode in lithium-ion batteries. The result is a far more powerful solution that, according to Cho, could lead to a whole new generation of lithium-ion batteries.
Graphite is weak
Lithium-ion batteries operate by accumulating and moving lithium ions around. A cathode (positive terminal) made of materials like lithium cobalt oxide, sits on one end while an anode (negative terminal) made of graphite, sits on the other. When the battery is charged the lithium ions move toward the negative side, finding resting places near the multiple graphite layers. When the battery is giving off power, the ions move back toward the cathode.
While graphite is a weak material, meaning that it can only absorb a certain amount of ions, it can be repeatedly charged and discharged without significant issues. Silicon alternatives, on the other hand, tend to swell when charged – and shrink when discharged – resulting in stress fractures. These make traditional silicon alternatives impractical for use after several charge/drain cycles.
The new materials developed by Cho are much more porous than those previously used. In addition, a type of annealing process was applied whereby short chained hydrocarbon molecules are bonded to the silicon at 900 degrees Celsius in an argon atmosphere. Once bonded, a mass etching process is applied to remove the silicon dioxide particles, resulting in a three-dimensional, highly porous structure.
Because they are so porous, their surface area is extreme. In addition, when charged, the swelling which normally occurs in silicon, occurs in the pores itself resulting in very little overall swelling in size – just a decrease in the space between pores.
Researchers using this material have noted much faster charge times and much higher discharge rates. Even after 100 charge/drain cycles, they reported no noticeable changes in the materials or electrical properties of the battery.
While more work is needed to produce commercial products based on this technology, the reality seems to be that silicon is a multi-faceted achiever. Not only are our computers running at high speeds because of its semi-conductor traits, but we may soon also have a new form of battery which renders today’s 2-hr notebook use times a laughable thing of the past. All I can say is “bring it on!”