Improved Electrode Materials in Lithium-Ion (Li-ion) Batteries: Innovation and Optimization

January 14, 2008 - 12:00pm
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The advent of Li-ion batteries has played a central role in the impressive development of portable digital and wireless technology. Such success has triggered further efforts to utilize them as key components in other applications with an even larger impact on society, which include electric vehicles and energy backup for renewable energy sources. However, several challenges need to be met before these expectations can be realized, as Li-ion batteries currently do not meet the power and energy density requirements of these devices. New and better materials for the electrodes are needed. The continuous exploration of new phases with new structures, going beyond the boundaries of oxide chemistry, can uncover exciting reactivities with promising results. This is the case of new compounds such as Li7MnN4 or Li7.9MnN3.2O1.6, which show good capacity values and rate performance. Furthermore, the properties as electrodes of the family of compounds with formula Sr2MnO2Cu2m-0.5Sm+1 (m=1-3) open the possibility of using layered perovskite-type structures as a way of improving the capacity retention when Cu extrusion reactions take place. Nevertheless, discovering new attractive compounds is not the only step towards better electrodes for Li-ion batteries. Only through a thorough understanding of the processes undergone by the compounds proposed to date can we engineer optimized materials with enhanced rate capabilities and/or higher storage capacity. For instance, the preparation of LiNi0.5Mn0.5O2, an alternative to LiCoO2 as a positive electrode, by ion exchanging Na for Li in NaNi0.5Mn0.5O2 avoids the Li/Ni crystallographic mixing that is known to hinder lithium diffusion in the structure and lead to a poor rate performance. As another option for the positive electrode, the use of layered-spinel nanocomposites, such as xLi2MnO3*(1-x)Li1+yMn2-yO4 (0<1, 0y0.33) or xLi[Mn1.5Ni0.5]O4*(1-x)Li[Li1/3-2y/3NiyMn2/3-y/3)O2, allows the combination of the higher storage capacity of the former with the higher rate capabilities of the latter. A discussion of the crystal-chemical phenomena, using, among others, both long range (X-ray and neutron diffraction) and short range (NMR) characterization techniques, that lead to all these electrochemical results will be presented. For more information about this seminar, please contact: Venkat Srinivasan2679

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