APPLICATIONS OF TECHNOLOGY:
- Automotive industry: electric vehicles, hybrid electric vehicles
- High performance lithium ion battery manufacturers
- Aerospace industry, for lightweight power storage
- Much higher charge-discharge capacity than graphite anodes
- Reduces substantial silicon expansion-shrinkage during charge-discharge
- Simple, low cost, non-toxic and scalable manufacturing process
- Excellent conductivity of graphene components
- Direct deposition on copper current collector surface with no binder and carbon black required
A team of Berkeley Lab researchers led by Yuegang Zhang and Liwen Ji has taken a major step toward an improved lithium ion battery with the development of anodes coated with vanishingly thin, alternating layers of graphene and silicon. Tests have shown that Berkeley Lab’s graphene-silicon layers create anodes with a much higher charge capacity than those made of graphite. In addition, the multilayer nanostructure of this easy-to-fabricate design resists the rapid degradation that occurs during the continuous charge-discharge cycles of pure silicon anodes.
Berkeley Lab scientists developed a process that deposits a nanoscale crust made of alternating layers of graphene and silicon on an anode surface. Graphene is an extraordinarily strong and highly conductive material made of a honeycomb lattice of carbon atoms arrayed in sheets as thin as a single atom. The carbon layer is fabricated in a process that dissolves graphene exfoliated from graphite, uses ultrasound to prevent clumping, and deposits a thin layer of graphene sheets on a surface using vacuum filtration of the solvent. A silicon layer is subsequently laid upon each graphene layer through a plasma-enhanced chemical vapor deposition process commonly used in semiconductor chip manufacturing. No binding agents are required to bond the graphene-silicon to the anode surface. Binding agents frequently used in other anode fabrication techniques can reduce conductivity of an electrode surface.
Published experiments demonstrated that the Berkeley Lab anode made of a copper terminal coated by a succession of just five alternating graphene-silicon layers retained its superior charge capacity through 30 charge-discharge cycles. At 30 cycles, the graphene silicon anode retained 59 percent of its initial capacity, compared to 16 percent for pure silicon. Further studies are determining whether battery life can be extended to commercially viable lengths through the addition of more graphene-silicon layers and by reducing the thickness of the deposited silicon.
Silicon could be an ideal anode material for lithium ion batteries because it offers ten times the theoretical charge capacity of graphite, the material typically used for anode surfaces. But silicon anodes swell with lithium when a battery is charged and shrink during discharge. This creates stress that rapidly fractures the silicon structure and destroys battery performance. Until now, this shortcoming has effectively barred silicon’s use in lithium ion batteries, despite properties that otherwise would make it superior to any other anode material.
DEVELOPMENT STAGE: Proven principle.
STATUS: Patent pending. Available for licensing or collaborative research.
FOR MORE INFORMATION:
Ji, L., Zheng, H., Ismach, A., Tan, Z., Xun, S., Lin, E., Battaglia, V., Srinivasan, V., Zhang, Y., “Graphene/Si multilayer structure anodes for advanced half and full lithium-ion cells," Nano Energy, August 27, 2011.
Ji, L., Zhang, X., “Evaluation of Si/carbon composite nanofiber-based insertion anodes for new-generation rechargeable lithium-ion batteries,” Energy & Environmental Science, Vol. 3, pp. 124-129, 2010.
SEE THESE OTHER BERKELEY LAB TECHNOLOGIES IN THIS FIELD:
REFERENCE NUMBER: IB-2955