The rechargeable battery is a promising technology for reversible electricity storage in electric vehicles. Current electric vehicles are powered by lead-acid, NiCd or nickelmetal hydride batteries, which are limited by their energy density and calendar lifetime. The existing Li-ion battery technology, which uses LiCoO2 as cathode, lithiated graphite (LiC6) as anode, and LiPF6-organic solvent as electrolyte, has been the most important power source for portable electronics. However, the high cost and low production volume due to the scarcity of Co are the major hurdles to their wide applications in light duty vehicles. The solution is to decrease the cost and maximize the performance. The electrolyte in general does not limit the Li-battery technology. We identify the following as the most important areas to improve: 1) Use alternative cheaper and higher energy density cathode materials to replace scarce Co oxides; 2) Replace the anode with higher energy density and cheaper materials; 3) Maximize the performance by optimizing battery device architecture. To realize electrochemical energy storage for electric vehicles, we are working on a nanowire battery architecture combined with selection of appropriate materials. We will explore the following advantages of using NWs: 1) NWs have a very large surface to volume ratio to contact with electrolyte. 2) NWs form continuous conducting pathways for electrons through the electrodes. 3) The NW geometry can promote facile strain relaxation during battery operation.
Spinel LiMn2O4 is a low-cost, environmentally friendly, and highly abundant material for Li ion battery cathodes. We have successfully carried out the hydrothermal synthesis of single-crystalline β-MnO2 nanorods and their chemical conversion into free-standing single-crystalline LiMn2O4 nanorods using a simple solid-state reaction (Fig. 4). The LiMn2O4 nanorods have an average diameter of 130 nm and length of 1.2 μm. Galvanostatic battery testing showed that LiMn2O4 nanorods have a high charge storage capacity at high power rates compared with commercially available powders. More than 85% of the initial charge storage capacity was maintained for over 100 cycles. The structural transformation studies showed that the Li ions intercalated into the cubic phase of the LiMn2O4 with a small change of lattice parameter, followed by the co-existence of two nearly identical cubic phases in the potential range of 3.5 to 4.3V
Reference : http://gcep.stanford.edu
Full report available at http://gcep.stanford.edu/pdfs/jXWqtY2wJ ... c_2011.pdf
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