AsianScientist (Sep. 13, 2017) – Scientists in Japan have devised a way to preserve the structure and improve the power of silicon anodes used in lithium ion batteries. They report their findings in the journal Advanced Science.
As the world shifts towards renewable energy, there is a fast-growing need for larger high-performance batteries. Lithium ion batteries power most of our portable electronics devices, but they are flammable and can even explode. To prevent such accidents, the current solution is to encapsulate the anode—which is the negative electrode of the battery—into a graphite frame, thus insulating the lithium ions.
Silicon offers great advantages over carbon graphite for lithium ion batteries in terms of capacity. Six atoms of carbon are required to bind a single atom of lithium, but one atom of silicon can bind four atoms of lithium at the same time, thus multiplying the battery capacity by more than 10-fold.
However, being able to capture that many lithium ions means that the volume of the anode swells by 300 to 400 percent, leading to fracturing and loss of structural integrity. To overcome this issue, researchers from the Okinawa Institute of Science and Technology (OIST) have designed an anode built from nanostructured layers of silicon—not unlike a multi-layered cake—to preserve the advantages of silicon while preventing physical collapse.
Layers of unstructured silicon films are deposited alternatively with tantalum metal nanoparticle scaffolds, resulting in the silicon being sandwiched in a tantalum frame.
“We used a technique called cluster beam deposition,” said Dr. Marta Haro Remon of OIST. “The required materials are directly deposited on the surface with great control. This is a purely physical method; there are no need for chemicals, catalysts or other binders.”
“It is a very open synthesis approach, with many parameters you can play around with. For example, we want to optimize the numbers of layers, their thickness, and replace tantalum metal with other materials,” she added.
The researchers also revealed that the silicon exhibits important porosity, with a grain-like structure in which lithium ions could travel at higher speeds compared to unstructured, amorphous silicon, thus explaining the increase in power of their battery. At the same time, the presence of silicon channels along the tantalum nanoparticle scaffolds allows the lithium ions to diffuse throughout the entire structure.
This design is currently only at the proof-of-concept stage, and the tantalum metal casing still limits the overall capacity of the battery. Nonetheless, an anode with higher power, restrained swelling and excellent cyclability (the number of cycles that a battery can be charged and discharged before losing efficiency) opens the door to the future of batteries with improved capacity and increased power.
The article can be found at: Haro et al. (2017) Nanoscale Heterogeneity of Multilayered Si Anodes with Embedded Nanoparticle Scaffolds for Li-Ion Batteries.
Source: Okinawa Institute of Science and Technology Graduate University.
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