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REPORT OF THE BASIC RESEARCH NEEDS WORKSHOP IN SITU ANALYSIS OF BURIED ALKALI-METAL/SOLID ELECTROLYTE INTERFACES Electrode topography and current density maps have been obtained from a symmetric lithium-polymer- lithium cell.84 Charge was passed from the top electrode (not shown for clarity) through a solid block copolymer electrolyte toward the bottom lithium metal electrode. The topography of the electrode (top) was determined from the tomograms while the local current density was obtained from differences between tomograms at different time points using Faraday’s law. The average current density was controlled to be 0.18 mA/cm2 using a potentiostat. A small protrusion is evident at early times. The current density, as anticipated from elementary electro- physics, is maximal at the tip of the protrusion. In a liquid electrolyte, this inhomogeneity in current density would amplify deposition at the tip, resulting in unstable dendrite growth. In a solid, however, the maximum deformation is also located in the vicinity of the tip of the protrusion. This elastic deformation slows down growth at the tip. The current density maximum is in the form of a ring well removed from the tip of the protrusion. This results in flattening of the protrusion. Note that dendrites, the classical mode of failure in lithium metal electrodes, can be averted by the use of a solid electrolyte. Methodologies for elucidating the local events that cause failure of batteries are essential for understanding and preventing them. Local probes such as X-ray micro tomography and scanning probe microscopy are essential for finding the “needle in the haystack” that causes battery failure. Measurement of local current density complements measurement of local potential, as discussed elsewhere in this document. Local current density maps on a lithium metal electrode determined by time-resolved synchrotron X-ray microtomography. Image from K. J. Harry et al., Influence of electrolyte modulus on the local current density at a dendrite tip on a lithium metal electrode, J. Electrochem. Soc., 2016, 163, A2216-A2224. abcd 0.9 0.6 0.3 0.0 mA/cm2 50 μm 3.5.3 IMPACT Lithium-ion technology could be reaching its fundamental limits of performance and safety, thus restricting opportunities for further improvement. To keep pace with the ever-increasing demands for high performance energy storage, new approaches, cell chemistries, and cell configurations are necessary. In principle, solid-state batteries at the cell level can achieve high energy densities (> 1000 Wh/l) while using non-flammable electrolyte to improve safety. In addition, some solid-state electrolytes can be synthesized in air to reduce fabrication costs. For high energy/power applications such as electric vehicles, the intrinsic stability and substantially wider operation temperature, enabled by certain solid electrolytes, can reduce the mass, volume, cost, and complexity of the battery management system to further improve pack-level performance. 140 PANEL 5 REPORT 150 z (μm) 0 150 z (μm) 0 150 z (μm) 0 150 z (μm) 0 0 y (μm) 200 0 y (μm) 200 0 y (μm) 200 0 y (μm) 200 0 x (μm) 200 0 x (μm) 200 0 x (μm) 200 0 x (μm) 200PDF Image | Next Generation Electrical Energy Storage
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