Energy Focus: Novel method developed to investigate stiffness and mechanical stress in Li-ion batteries
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Energy Focus Novel method developed to investigate stiffness and mechanical stress in Li-ion batteries
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Normalized PotentialDependent Stiffness, K
esearchers typically gauge the safety and reliability of batteries by the amount of heat that they evolve and the number of cycles that they can sustain before degrading. In addition, in Li-ion batteries, the ion intercalation charge-discharge process used also induces mechanical stress and strain in the electrode materials. The resulting deformation and delamination may, over
Voltage, E (V vs. Li+/0)
Electrochemical stiffness changes during lithiation of a composite graphite electrode. As lithium ions intercalate into the graphite anode during a multistage process, they influence the mechanical properties of the electrode. The charging process generates unique stagedependent stress and strain in the graphitelithium intercalation compound. Credit: Hadi Tavassol, Elizabeth M.C. Jones, Nancy R. Sottos, and Andrew A. Gewirth.
film. Oxygen that is loosely bound to the surface of the oxide grains can be pulled away much easier and diffuse readily along the surface of the Co grains. However, diffusion would be somewhat slower into the core of the Co grains producing a slow transition from a metallic to insulating state with an accompanying change in the magnetic properties. When the field is reversed the oxygen on the surface of the Co grains can diffuse back to the oxide layer, but due to an electric screening effect, the oxygen in the core of the Co grains remains trapped. This remaining oxide acts as a secondary
magnetic phase and an irreversible change in the overall magnetic properties. Until now this effect has only been seen in ultrathin films; this new work points to its application in bulk materials. Using this reversible migration of ions as a way to control physical properties in materials holds enormous potential for improving the energy efficiency of countless types of devices. Gilbert envisions this process enabling “control over essentially every physical property of our material … this work is just the first step.” Ian McDonald
time, lead to device failure. Due to the complex, heterogeneous nature of the lithium-ion exchange and the structures of the composite electrode materials used, it has proven challenging to develop effective techniques for assessing the kinetic effects of stress and strain, and correlating them with device charging and discharging. Now Hadi Tavassol, Elizabeth M.C. Jones, Nancy R. Sottos, and Andrew A. Gewirth of the University of Illinois at Urbana-Champaign (UIUC) have developed a novel approach that assesses in situ electrochemical stiffness of graphite-lithium intercalation compounds during cycling. They combined in situ electrochemical and mechanical measurement techniques to measure the intercalation-induced stress and strain of a graphite anode. The researchers used galvanostatic cycling and cyclic voltammetry, respectively, to assess the effects of capacity and electrochemical potential fluctuations on lithiation. The res
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