November 30th, 2011
Econintersect: The picture may look like coral in a tropical sea, but what is displayed is a new type of Lithium battery structure. It is composed of a form of carbon called graphene used to form an anode with an open, porous structure that solves a problem experienced with solid form grapheme sheets where particles quickly clog the surface pores and reduce the battery efficiency. Lithium-air batteries are considered to have the potential to eventually provide power for electric cars with much better performance than conventional solid batteries. The development of the new anode material structure was accomplished at the Pacific Northwest National Laboratory (PNNL) with the collaboration of Princeton University. Click on picture for larger image.
From the R&D Magazine report:
could allow for the creation of long-range electric vehicles, able to travel up to 300 miles between charges. Comparatively lightweight, lithium-air batteries still suffer from limited practical capacity and poor cycle life issues. However, this study showed how to maximize the capacity of the batteries.
Wikipedia describes the lithium-air battery as one which oxidizes lithium and reduces oxygen (from the air) to produce a flow of electrons. There are aqueous and non-aqueous systems. Here is a summary from Wikipedia:
Lithium–air batteries have higher energy density than lithium-ion batteries because of the lighter cathode and the fact that oxygen is freely available in the environment and does not need to be stored in the battery. With oxygen as an unlimited cathode reactant, the capacity of the battery is limited the space available in the cathode to hold discharge product. The theoretical limit is therefore governed by the energy content of a solid slab of Li2O2. This can in practice not be achieved due the necessity for electrolyte and electron conductor in the cathode. On the battery level this capacity must be matched by the appropriate amount of Li in the anode. Lithium-air batteries are currently on the level of basic research and are not yet commercially available.
The new development is still in very early stages. There is still a lot to do as outlined by the PNNL report:
The researchers found that the black porous structures store more than 15,000 milliamp hours per gram of graphene, making it far denser in term of energy capacity than other materials.
"Many catalysts are studied now for this technology. In our process we chose not to use precious metal," said Dr. Ji-Guang Zhang, the group leader in PNNL's Li-air battery research. "This will greatly reduce production costs and increase the adoptability."
The battery is achieving the highest levels of energy capacity in an oxygen-only environment. When operated in ambient air, the capacity drops because the water in the air fouls the lithium metal in the batteries. The PNNL team is working to develop a membrane to block the water and still allow the necessary oxygen to flow
"We also want to make the battery rechargeable," said Zhang. "Right now, it is not. It is not fully rechargeable. We are working on a new electrolyte and a new catalyst so that the battery can be recharged multiple times, potentially for battery backup applications that require high energy densities."