Transport Number Gradients and Solid Electrolyte Degradation

Abstract

Ion conduction is considered through electrolytes containing an immobile gradient in the electronic/ionic transport number ratio. It is shown that internal deposition of the metal phase (reduced ions) can occur in such electrolytes during electrolysis. A "critical" applied voltage or current density can be formulated above which electrolyte fracture would be caused by the internally deposited material.Application of the analysis to the sodium-beta alumina type electrolytes leads to identification of factors that could contribute to electrolyte degradation.

Understanding metal propagation in solid electrolytes due to mixed ionic-electronic conduction

“…The dendrite growth in this mode requires the electronic conductivity of the SE to be high enough to transport electrons to pre-existing internal defects (such as vacancies, pores, and GBs). The two metal propagation modes may occur simultaneously in a real solid-state battery (SSB) system 4,5 making it difficult to study them separately.…”

“…1 However, metal penetration is frequently observed in SEs, including Li 2 S-P 2 S 5 (LPS), 2 Li 7 La 3 Zr 2 O 12 (LLZO), 3 and beta-alumina. 4,5 Extensive studies have been conducted to explain the unexpectedly low maximum charging rate (critical current density [CCD]) that an SE can withstand without metal penetration (less than 1mA=cm 2 Þ. [6][7][8] Different mechanisms for metal propagation in SEs have been proposed, including possible low diffusivity of mobile cations at grain boundaries (GBs), 9 low relative density of SEs, 7 pre-existing microstructural defects (such as cracks and pores) on the surface of and in bulk SEs, 10 inhomogeneous plating resulting from contact loss between metal anodes and SEs, 11 and enhanced electronic conductivity in SEs resulting from vacancy generation during cycling.…”

Thermochemical Stability of β‐ and β″‐Alumina Electrolytes in Na/S Cells: II . Assessment

“…Na20 "leaching" mechanism.--In this situation, the various possible reactions can be written as follows 3[Na~O] + C = Na2CO3 + 4Na T + 4e [1] 3[Na20] + S = Na2SO3 + 4Na § + 4e [2] 4[Na20] + S = Na~SO4 + 6Na + + 6e [3] [Na~O] + C = CO + 2Na + + 2e [4] 2[Na20] + S = SO2 + 4Na + + 4e [5] 2[Na20] = O2 + 4Na + + 4e [6] where [Na20] represents Na20 in the electrolyte at the prevailing activity. These two reaction schemes are considered in further detail in the following paragraphs.…”

“…Interestingly, DeJonghe et al (4,5) have attributed the coloration of the electrolytes in contact with Na to be due to the introduction of oxygen vacancies, compensated by electrons. Interestingly, DeJonghe et al (4,5) have attributed the coloration of the electrolytes in contact with Na to be due to the introduction of oxygen vacancies, compensated by electrons.…”

Fracture Toughness Anisotropy of Sodium β‐ Alumina

“…The layered crystals cleave easily along the 00.1 conduction planes and may show spontaneous fractures when left in ambient moist air. Grain boundaries with 00.1 habit planes are also known to be mechanically weak (8). Since 00.1 cleavage is most likely to be involved in the initial crack configuration and growth, it is necessary to determine the Kc anisotropy.…”