SAN FRANCISCO -- Scientists from Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory have developed a method that makes silicon lithium-ion battery anodes a possibility. Such anodes could store 10 times more energy per charge than existing commercial anodes and make high-performance batteries smaller and lighter.
Silicon particles swell to three times its normal size during charging, then crack and shatter. They also react with the battery electrolyte to form a coating that saps their performance. To alleviate these issues, the Stanford-SLAC team wrapped each silicon anode particle in a custom-fit cage made of graphene.
Stanford/SLAC process for creating graphene cages. Source: Y. Li et al./Nature Energy
The three-step method was described in Nature Energy and on the SLAC website. The cages should be roomy enough to let the silicon particle expand as the battery charges, yet tight enough to hold all the pieces together when the particle falls apart, so it can continue to function at high capacity. The strong, flexible cages also block destructive chemical reactions with the electrolyte.
The microscopic cage method can also apply to other electrode materials, wrote research lead Yi Cui, an associate professor at Stanford. This makes energy-dense, low-cost battery materials a “realistic possibility,” he said.
“This new method allows us to use much larger silicon particles that are one to three microns, or millionths of a meter, in diameter, which are cheap and widely available,” Cui said in a release. “In fact, the particles we used are very similar to the waste created by milling silicon ingots to make semiconductor chips; they’re like bits of sawdust of all shapes and sizes. Particles this big have never performed well in battery anodes before, so this is a very exciting new achievement, and we think it offers a practical solution.”
To make the microscopic cages fit exactly, researchers coated silicon particles with nickel then grew layers of graphene on top of the nickel, which acts as a catalyst to promote graphene growth. As a last step, they etched the nickel away, leaving just enough space within the graphene cage for the silicon particle to expand.
“The form-fitting graphene cages are the first coating that maintains high efficiency, and the reactions can be carried out at relatively low temperatures,” said Stanford postdoctoral researcher Kai Yan.
The next step is in graphene cage research is fine-tuning the process, and producing caged silicon particles in large enough quantities to build commercial-scale batteries for testing.
— Jessica Lipsky, Associate Editor, EE Times