While lithium-ion has become the battery platform of choice for electric-based transportation, none of the different existing lithium-ion cathode/anode chemistry pairs can meet all four of the most important criteria for longer-term, broader application: performance, life, abuse tolerance and cost, said Tien Duong, Team Leader in the US Department of Energy’s (DOE) Vehicle Technology Program, in the opening talk at the 1st International Conference on Advanced Lithium Batteries for Automobile Applications (ALBAA), organized by Argonne National Laboratory.
Dr. G. Abbas Nazri from GM Research was a bit more blunt in his talk at ALBAA, saying “most of the current chemistry is not going to make it for plug-in and particularly for EV applications.” GM, said Dr. Abbas, is looking for about a three-fold increase in anode and cathode capacity over that provided by the conventional combination of carbonaceous anodes and layered oxide cathodes.
Two promising approaches GM Research is exploring on the anode side to reach this target are the use of silicon-coated carbon nanofiber; and the use of metal hydrides. On the cathode side, Abbas said that GM had developed a material with capacity close to the 3X target, but that he could not discuss that yet.
|Voltage profile of C-Si composite anode optimized for 1,000-1,500 mAh/g, and morphology of the composite anode plate. Click to enlarge.|
The Li-C-Si anode is produced by layering silicon atop a carbon nanofiber. The anode material is produced first by reacting natural gas over a catalyst to produce the carbon nanofibers, and then using silane (SiH4) to put the silicon on top. GM is also looking at using the excess heat from the first reaction to support the second, further improving the cost and energy profile of the process.
The charge capacity of the resulting material can range approximately between 1,000 - 1,500 mAh/g; GM is seeking to optimize the system at around 1,000 mAh/g.
GM is also exploring using the Si-C nanocomposite anode material to form a carbon fiber anode plate, then using only copper tabs attached to the plate as a means to get expensive copper current collectors out of the system.
The other approach outlined by Dr. Nazri is the use of metal hydrides to produce a new generation of anode. In its work, GM has used a magnesium hydride, although the conversion reaction can be extended to all metallic and intermetallic hydrides, he said. GM improved the reversible electrochemical reaction of metal hydrides in a lithium cell through the formation of nano-sized particles of a hydride-carbon composite.
Theoretical capacity of the MgH2 anode is 2,038 mAh/g. GM has reached 1,510 mAh/g in its work with MgH2 materials, and further optimization of the cycle life is in progress.
David J. Burton, Maryam Nazri, Gholam Abbas Nazri, Patrick Lake, Max Lake (2008) Advanced Anode for High Energy and High Power Lithium Batteries (214th ECS Meeting)
Yassine Oumellal, Aline Rougier, Jean-marie Tarascon, Gholam-abbas Nazri and Luc Aymard (2007) Reactivity of Metal Hydrides toward Lithium Storage—A Bridge between NiMeH and Li-ion Technologies. (MRS 2007 Fall Meeting)