Next-Generation Batteries Incorporate Cells with Silicon Anodes

Rice University, Houston, TX

Full lithium-ion batteries were built with silicon anodes and an alumina layer to protect cathodes from degrading. By limiting their energy density, the batteries promise excellent stability for transportation and grid storage use. (Image: Jeff Fitlow/Rice University)

Researchers have developed better rechargeable batteries by applying silicon to the batteries’ cathodes. A previously unknown mechanism by which lithium gets trapped in batteries limits the number of times it can be charged and discharged at full power. By not maxing out their storage capacity, a new approach could provide steady and stable cycling for applications that need it.

Conventional lithium-ion batteries utilize graphite-based anodes that have a capacity of less than 400 milliamp hours per gram (mAh/g) but silicon anodes have potentially 10 times that capacity; however, silicon expands as it alloys with lithium, stressing the anode. By making the silicon porous and limiting its capacity to 1,000 mAh/g, the test batteries provided stable cycling with excellent capacity.

The lithium-ion batteries with silicon anodes and an alumina layer to protect cathodes from degrading. (Image: Biswal Lab/Rice University)

The team tested the concept of pairing the porous, high-capacity silicon anodes (in place of graphite) with high-voltage nickel manganese cobalt oxide (NMC) cathodes. The full cell lithium-ion batteries demonstrated stable cyclability at 1,000 mAh/g over hundreds of cycles. Some cathodes had a 3-nanometer layer of alumina (applied via atomic layer deposition) and some did not. Those with the alumina coating protected the cathode from breaking down in the presence of hydrofluoric acid, which forms if even minute amounts of water invade the liquid electrolyte. The alumina also accelerated the battery’s charging speed, reducing the number of times it can be charged and discharged.

There appears to be extensive trapping as a result of the fast lithium transport through alumina. The researchers already knew of possible ways silicon anodes trap lithium, making it unavailable to power devices but this is the first report of the alumina itself absorbing lithium until saturated. At that point, the layer becomes a catalyst for fast transport to and from the cathode.

For more information, contact Mike Williams at This email address is being protected from spambots. You need JavaScript enabled to view it.; 713-348-6728.