Scientists have made the first step towards a lithium-ion anode with has the potential to boost a battery’s performance.
A team from Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory have devised a graphene cage for the silicon anode.
The cage blocks chemical reactions with the electrolyte and prevents the swelling and cracking of the particles during charging, said researchers in a report published in science journal Nature Energy.
To do this, researchers coated every silicon anode particle with nickel and grew layers of graphene on top. They then etched the nickel away, leaving just enough space within the graphene cage for the silicon particle to expand.
The challenge was to ensure the cage had enough room to let the silicon particle expand as the battery charges, yet tight enough to hold all the pieces together when the particle fell apart, to allow it to continue functioning at high capacity.
Yi Cui, an associate professor at SLAC and Stanford who led the research, said: “This new method allows us to use much larger silicon particles that are one to three microns, or millionths of a metre, in diameter, which are cheap and widely available.
“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.
“In testing, the graphene cages actually enhanced the electrical conductivity of the particles and provided high charge capacity, chemical stability and efficiency.”
Yi said the method could be applied to other electrode materials, making energy-dense, low-cost battery materials a realistic possibility.
“Researchers have tried a number of other coatings for silicon anodes, but they all reduced the anode’s efficiency,” said Stanford postdoctoral researcher Kai Yan, who carried out the experiments with graduate student Yuzhang Li.
“The form-fitting graphene cages are the first coating that maintains high efficiency, and the reactions can be carried out at relatively low temperatures.”
The team will now fine-tune the process with the aim of building commercial-scale batteries for testing.
Other researchers contributing to the study were Stanford’s Hyun-Wook Lee, Zhenda Lu and Nian Liu.
The research was carried out by SIMES, the Stanford Institute for Materials and Energy Sciences at SLAC, and funded by the Battery Materials Research program of the DOE’s Vehicle Technologies Office.
Above: This time-lapse movie from an electron microscope shows the new battery material in action: a silicon particle expanding and cracking inside a graphene cage while being charged. The cage holds the pieces of the particle together and preserves its electrical conductivity and performance. (Hyun-Wook Lee/Stanford University)