June 4, 2013
New Silicon Electrode Could Make Your Device’s Battery Last A Lot Longer
Brett Smith for redOrbit.com - Your Universe Online
Scientists led by a team at Stanford University have developed a new silicon-based electrode for lithium-ion batteries that could significantly improve the performance of the popular batteries, according to a new report in Nature Communications.In a lithium-ion battery, the electrode connects the lithium electrolyte, which is primarily responsible for power generation, with the rest of a circuit.
"Developing rechargeable lithium-ion batteries with high energy density and long cycle life is of critical importance to address the ever-increasing energy storage needs for portable electronics, electric vehicles and other technologies," said study co-author Zhenan Bao, a professor of chemical engineering at Stanford University.
"We've been trying to develop silicon-based electrodes for high-capacity lithium-ion batteries for several years," added co-author Yi Cui, an associate professor of materials science and engineering at Stanford. "Silicon has 10 times the charge storage capacity of carbon, the conventional material used in lithium-ion electrodes. The problem is that silicon expands and breaks."
Because silicon particles can expand up to 400 percent of their size when combined with lithium, the swollen particles can splinter and lose electrical contact when the battery is being charged or discharged. To overcome this problem, the Stanford team coated the electrode´s silicon nanoparticles with hydrogel, a spongy material similar to material used in contact lenses.
Tests of the electrode showed that the novel battery retained a high storage capacity through 5,000 cycles of charging and discharging.
"We attribute the exceptional electrochemical stability of the battery to the unique nanoscale architecture of the silicon-composite electrode," Bao said.
Using a scanning electron microscope, the scientists were able to determine that the porous hydrogel contains countless empty spaces that permit the silicon nanoparticles to inflate when lithium is inserted. The nanostructures also form a network that produces a conducting pathway during charging and discharging.
"It turns out that hydrogel has binding sites that latch onto silicon particles really well and at the same time provide channels for the fast transport of electrons and lithium ions," Cui said. "That makes a very powerful combination."
To optimize battery performance, the engineers created the hydrogel and silicon electrodes using a technique called in situ synthesis polymerization.
“With our technique, each silicon nanoparticle is encapsulated within a conductive polymer surface coating and is connected to the hydrogel framework,” Bao said. “That improves the battery's overall stability."
The hydrogel initially presented another obstacle because water within the substance can cause lithium-ion batteries to burst into flames.
"We utilized the three-dimensional network property of the hydrogel in the electrode, but in the final production phase, the water was removed," Bao said. "You don't want water inside a lithium-ion battery."
The Stanford scientists said they are optimistic about the new technique that they´ve used to create electrodes made of silicon and other materials.
"The electrode fabrication process used in the study is compatible with existing battery manufacturing technology," Cui said. "Silicon and hydrogel are also inexpensive and widely available. These factors could allow high-performance silicon-composite electrodes to be scaled up for manufacturing the next generation of lithium-ion batteries. It's a very simple approach that's led to a very powerful result."