Energy Focus: Modified SMP allows high resolution mapping of lithium-ion diffusion
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rgy Focus Modified SMP allows high resolution mapping of lithium-ion diffusion
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ithium-ion batteries are one of the most ubiquitous power sources for portable electronics, but the design of new batteries is currently limited by a poor understanding of the nanoscale mechanisms of lithium ion transport and how such mechanisms are affected by microstructure and defects. In the August 29th online edition of Nature Materials (DOI: 10.1038/nnano.2010.174), N. Balke of Oak Ridge National Laboratory (ORNL), A.N. Morozovska of the National Academy of Science of Ukraine, D.W. Chung of Purdue University, and their colleagues report on a novel method of mapping ion diffusion in LiCoO2 battery electrodes. Using a modified scanning probe microscope (SPM) tip, the researchers applied a periodic electric field to induce the motion of lithium ions. The flux of ions into or out of the electrode is ac-
tron microscopy revealed that the precipitates were nanosheets composed of a mixture of SnO2 main phase and SnO additional phase. Brunauer– Emmett–Teller (BET) surface area measured from nitrogen isotherms revealed a value of 194 m2/g, more than double the highest value reported in previous studies whereas pore sizes were measured at 1–2 nm.
The nanocrystalline sheets with large specific surface area produced in this technique are expected to be better suited for use in sensors. The researchers believe that this new fabrication method provides additional benefits as an eco-friendly alternative with reduced production costs through lower energy consumption and CO2 emission. Kaushik Chatterjee
companied by local structural changes that are detected by the deflection of the same tip. A combination of high frequency imaging and low frequency spectroscopy allows mapping of local ionic dynamics with nanoscale precision. The researchers estimate that this method offers a strain detection limit 6–8 orders of magnitude better than classical electrochemical techniques. The team first applied a constant voltage to the SPM tip, causing a change in lithium ion concentration and an associated strain of the electrode. They observed changes in the electrode’s morphology after biasing, as well as diffusion of ions across (001) planes. They then applied a high-frequency periodic voltage, inducing changes in the resonance frequency resulting from cathode structure changes. The team mapped variations in Young’s modulus and related them to fluctuations in lithium diffusion and intercalation behavior. In their final experiment they varied both biasing pulse frequency and amplitude, allowing them to measure ion
diffusion across large time scales in battery-like conditions with
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