Ionic Conductivity Measurements of Solid State Electrolytes with Coin Cells Enabled by Dry-Pressed Holey Graphene Current Collectors

Coby H Scrudder¹Lopamudra Das²Jin Ho Kang¹Vesselin I Yamakov²Ji Su¹Donald Dornbusch³Rocco P Viggiano³Yi Lin^1*

• ¹Langley Research Center, National Aeronautics and Space Administration, Hampton, United States
• ²Analytical Mechanics Associates Inc, Hampton, United States
• ³NASA Glenn Research Center, Cleveland, United States

Solid-state batteries (SSBs) are poised to become the batteries of the future with advantages such as higher energy density, versatile geometry, and greater safety due to their inherent nonflammability. The most important parameter of the solid-state electrolyte (SSE) used is its ionic conductivity typically calculated from measuring the bulk impedance of a SSE pellet sandwiched between two ion-blocking current collectors. One of the challenges in conducting this measurement is the poor interfacial contacts between the SSE pellet and the current collector surfaces. To overcome this interfacial issue, high stack pressure (>10 - 100 MPa) is often used. However, this is unrealistic for the operation of practical cells where low or minimal stack pressure (<5 MPa) is more desirable. Thus, ionic conductivity values obtained at high stack pressures may not accurately reflect the true conducting properties under operational conditions. Holey graphene (hG) is a carbon nanomaterial with high electrical conductivity and unique dry compressibility, which is unusual for carbon materials. In this work, it is demonstrated that a thin layer of dry-pressed holey graphene as the current collector for sulfide-based SSE impedance measurements significantly improves the interfacial contact. The ionic conductivity values obtained at low stack pressure conditions were sometimes an order of magnitude higher than the data measured for sulfide SSEs without the hG layers. The use of hG also allows for convenient measurements even using coin cells where a very low internal stack pressure is used. The measurements attained in this work confirm that sulfide SSE ionic conductivity could be at a high level despite the low stack pressure used. This work also calls for more standardized measurement procedures to reduce the discrepancies in reported ionic conductivity values.