DMSE Doctoral Thesis Defense - Richard Park
Wednesday, May 05, 2021 at 12:00pm to 1:00pmVirtual Event
Doctoral Thesis Defense
Mechanisms of metal penetration in solid electrolytes
Wednesday, May 5, 2021
12:00 – 1:00 PM EST
Contact email@example.com for the Zoom link.
An important unresolved topic in materials science is the mechanism by which metals infiltrate solid electrolytes during electrodeposition. A deep understanding of this phenomenon in Li+-conducting solid electrolytes could determine whether these materials can enable fast-charging (> 3 mA cm-2) solid state batteries that are safer and more energy-dense than the state of the art. At present, it is thought that intensified stresses are generated at the largest surface flaws on the electrolyte during electrodeposition, and at the critical current density these stresses drive brittle fracture within the bulk to create paths for metal advancement.
This thesis demonstrates that metal penetration depends on two additional factors. The first is whether electric field focusing is present between the stripping and plating electrode. We show that amplified electric fields, which correlate with increased local current densities, cause Li filled cracks to initiate and grow to penetration, overriding the presence of larger surface defects elsewhere. The second factor is the yield stress of the electrodeposited metal. We show that in Li+-, Na+-, and K+-conducting solid state systems, the critical current density scales inversely with the mechanical deformation resistance of the electrodeposited metal.
We then present two novel electrode architectures in which a liquid phase enables higher critical current densities via interfacial stress relief and current homogenization. First, biphasic (liquid-solid) Na-K alloys are shown to exhibit K+ critical current densities over 15 mA cm-2, in contrast to 2.5 mA cm-2 for pure K metal. Second, an interfacial film of Na-K liquid between Li metal and Li6.75La3Zr1.75Ta0.25O12 solid electrolyte doubles the critical current density compared to cells without the Na-K interlayer. These design approaches hold promise for overcoming mechanical stability issues that have heretofore limited the performance of solid state batteries.
Yet-Ming Chiang, Kyocera Professor, Materials Science and Engineering, Massachusetts Institute of Technology
W. Craig Carter, POSCO Professor, Materials Science and Engineering, Massachusetts Institute of Technology
Ju Li, Battelle Energy Alliance Professor, Nuclear Science and Engineering, Materials Science and Engineering, Massachusetts Institute of Technology
C. Cem Tasan, Thomas B. King Associate Professor, Materials Science and Engineering, Massachusetts Institute of Technology