Kinetics and Pore Formation of the Sodium Metal Anode on NASICON‐Type Na3.4Zr2Si2.4P0.6O12 for Sodium Solid‐State Batteries

• Published in: Advanced energy materials Vol. 13; no. 5
• Main Authors: Ortmann, Till, Burkhardt, Simon, Eckhardt, Janis Kevin, Fuchs, Till, Ding, Ziming, Sann, Joachim, Rohnke, Marcus, Ma, Qianli, Tietz, Frank, Fattakhova‐Rohlfing, Dina, Kübel, Christian, Guillon, Olivier, Heiliger, Christian, Janek, Jürgen
• Format: Journal Article
• Language: English
• Published: 03.02.2023
• Subjects: current constriction; impedance spectroscopy; interphase growth; NASICON electrolytes; SEI formation; sodium metal anodes
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.202202712

In recent years, many efforts have been made to introduce reversible alkali metal anodes using solid electrolytes in order to increase the energy density of next‐generation batteries. In this respect, Na3.4Zr2Si2.4P0.6O12 is a promising solid electrolyte for solid‐state sodium batteries, due to its high ionic conductivity and apparent stability versus sodium metal. The formation of a kinetically stable interphase in contact with sodium metal is revealed by time‐resolved impedance analysis, in situ X‐ray photoelectron spectroscopy, and transmission electron microscopy. Based on pressure‐ and temperature‐dependent impedance analyses, it is concluded that the Na|Na3.4Zr2Si2.4P0.6O12 interface kinetics is dominated by current constriction rather than by charge transfer. Cross‐sections of the interface after anodic dissolution at various mechanical loads visualize the formed pore structure due to the accumulation of vacancies near the interface. The temporal evolution of the pore morphology after anodic dissolution is monitored by time‐resolved impedance analysis. Equilibration of the interface is observed even under extremely low external mechanical load, which is attributed to fast vacancy diffusion in sodium metal, while equilibration is faster and mainly caused by creep at increased external load. The presented information provides useful insights into a more profound evaluation of the sodium metal anode in solid‐state batteries. The interfacial stability and the dissolution kinetics under external current load of a Na3.4Zr2Si2.4P0.6O12 solid electrolyte in contact with sodium metal are systematically studied. Beside the formation of a kinetically stabilized interphase, current constriction is identified as a dominating process at the interface. After anodic dissolution a pronounced equilibration of the formed interfacial morphology is observed at resting conditions.