Energy Focus: Influence of grain boundaries on Li-ion conductivity characterized at atomic scale
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Energy Focus
acting on the body can cause an asymmetry. This is called flexoelectricity, which is a coupling between a strain gradient in a body (flexure) and the amount of charge generated on the surface. As the name suggests, “flexure” leads to electricity. Tiny hairs in the inner ear, for example, have evolved to use this phenomenon for converting air waves to neural signals, thereby making flexoelectricity fundamentally important in auditory functioning. The researchers then set out to carefully flex natural bone and synthetic hydroxyapatite in the laboratory, measuring the bending-induced current using a lock-in amplifier. The flexure-induced current in synthetic hydroxyapatite and natural bone were remarkably similar, suggesting that flexoelectricity does indeed play a major role in generating electricity in bones. Moreover, because synthetic hydroxyapatite has no collagen, the quantitative similarity between the results rules out collagen piezoelectricity as a relevant contributor to the flexoelectricity of bone.
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To fully understand the extent that flexoelectricity plays in bone regeneration, the researchers calculated the flexoelectric potential at a micro-crack in a bone. They found that even a small stress can be magnified at the apex of a crack tip, generating very high flexoelectric potentials. These flexoelectric potentials were compared with the electric fields that biologists had previously established to be sufficient to “electrostimulate” the beginning of the process of healing. As the crack starts healing, the apex shifts thereby serving as a beacon in directing the flow of healing cells. Thus flexoelectricity allows a micro-crack to call for help without the need for collagen piezoelectricity or streaming ions. Brian Rodriguez at the University College Dublin, who is not connected to this research, says, “This work underscores the significance and ubiquity of flexoelectricity and clarifies several nagging and, until now, unresolved issues related to our understanding of bone remodeling.” Vineet Venugopal
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Influence of grain boundaries on Li-ion conductivity characterized at atomic scale
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research team led by M. Saiful Islam of the University of Bath, UK, has investigated how the grain boundaries of solid electrolytes in Li-ion batteries influence Li-ion conduction at the atomic scale. The researchers performed a set of large-scale molecular dynamics simulations that analyzed the Li-ion conductivity at stable grain boundaries of Li3OCl, a promising anti-perovskite solid electrolyte for Li-ion batteries. Their findings were published in a recent issue of the Journal of the American Chemical Society (doi: 10.1021/jacs.7b10593). Solid electrolytes such as Li3OCl enable the manufacture of all-solid-state batteries with improved duration and safety, mainly due to their nonvolatility and nonflammability. Since electrolytes shuttle Li ions during battery operation, their ion conductivities are of critical
(a) Schematic illustration of a grain boundary (GB) in Li3OCl. A grain boundary is the su
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