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Battery materials

All the batteries on earth can store only ten minutes of the world's energy needs. - Isidor Buchmann

If batteries could do better they would have tremendous impact on renewable energies, such as wind, wave, solar, geothermal, which all require energy storage due to transient availabilities. Likewise, the impact on all-electric vehicles would be significant. The 2013 Nissan Leaf, an all-electric vehicle, can only travel 100 miles on a single charge and needs 4 hours to recharge.

While the high volumetric and gravimetric energy density of Li-ion batteries have driven the portable electronics market over the last two decades, they lack the energy capacity to satisfy the needs of the transportation industry. Major research efforts have focused on improving every aspect of Li-ion battery design, from cathode and anode materials to electrolytes, current collectors, and separators. This demand for inherently safe, high capacity, high-rate capability energy storage has recently led to the investigation of a class of metallic and semi-metallic elements that form stable intermetallics with lithium, providing Li+ storage capacities of 3 to 10 times that of Li+ intercalation into graphite sheets, the anode material currently used in most Li-ion batteries. Unfortunately, such high capacity intermetallic anodes undergo large volume expansions upon intercalation, changing the anode's microstructure and local chemical environments which leads to reduced capacity.

Our goal is to seek a fundamental understanding of materials properties during dynamic changes that occur throughout the lithiation (charging) and de-lithiation (discharging) processes, commencing with Sn and other Sn-based anode materials. Previous work has shown that a range of lithium-tin intermetallics can be formed electrochemically as a function of applied potential; however, preliminary data suggests that these intermetallics may be amorphous in nature depending on the rate at which they are formed. The condition at which the material transforms from a crystalline to an amorphous phase has great implications on their rate capability and stability over time. Lithium and Tin solid-state NMR is an ideal technique to probe amorphous materials and understand how kinetically driven compositional changes affect the material microstructure and the local chemical environment. Our lab is using NMR to investigate the structural transformations of LixSny starting with ex-situ measurements of these air-sensitive samples as a function of lithiation. We also working on the development in-situ solid-state NMR and NMR imaging methodologies to probe the dynamics or chemical reactions in charge storage materials.

Prof. Anne Co (Ohio State University)