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3D Nanoscale Changes in Rechargeable Battery Material Tracked During Operation

Posted on: 04/03/2014
Brookhaven National Laboratory has made the first 3D observations of how the structure of a lithium-ion battery anode evolves at the nanoscale in a real battery cell as it discharges and recharges.

Scientists have long known that repeated charging/discharging introduces microstructural changes in the electrode material, particularly in some high-capacity silicon and tin-based anode materials. These microstructural changes reduce the battery's capacity—the energy the battery can store—and its cycle life. Understanding in detail how and when in the process the damage occurs could point to ways to avoid or minimize it.

To successfully conduct the study, the Brookhaven team built a fully functioning battery cell with all three battery components contained within a quartz capillary measuring one millimeter in diameter. By placing the cell in the path of high-intensity x-ray beams generated at beamline X8C of Brookhaven's National Synchrotron Light Source, the scientists produced more than 1400 two-dimensional x-ray images of the anode material with a resolution of approximately 30 nanometers. These 2D images were later reconstructed into 3D images with nanometer-scale clarity. Because the x-rays pass through the material without destroying it, the scientists were able to capture and reconstruct how the material changed over time as the cell discharged and recharged, cycle after cycle.

Using this method, the scientists found that, "severe microstructural changes occur during the first delithiation and subsequent second lithiation, after which the particles reach structural equilibrium with no further significant morphological changes."

While the current study looked specifically at a battery with tin as the anode, researchers note that the electrochemical cell and the x-ray nanotomography technique used can be applied to studies of other anode and cathode materials. The general methodology for monitoring structural changes in three dimensions as materials can also be used to monitor chemical states and phase transformations in catalysts, other types of materials for energy storage, and biological molecules.

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