Visualizing the Chemical Incompatibility of Halide and Sulfide‐Based Electrolytes in Solid‐State Batteries

Abstract

Halide‐based solid electrolytes are currently growing in interest in solid‐state batteries due to their high electrochemical stability window compared to sulfide electrolytes. However, often a bilayer separator of a sulfide and a halide is used and it is unclear why such setup is necessary, besides the instability of the halides against lithium metal. It is shown that an electrolyte bilayer improves the capacity retention as it suppresses interfacial resistance growth monitored by impedance spectroscopy. By using in‐depth analytical characterization of buried interphases by time‐of‐flight secondary ion mass spectrometry and focused ion beam scanning electron microscopy analyses, an indium‐sulfide rich region is detected at the halide and sulfide contact area, visualizing the chemical incompatibility of these two electrolytes. The results highlight the need to consider more than just the electrochemical stability of electrolyte materials, showing that chemical compatibility of all components may be paramount when using halide‐based solid electrolytes in solid‐state batteries.

Li3–xZrx(Ho/Lu)1–xCl6 Solid Electrolytes Enable Ultrahigh-Loading Solid-State Batteries with a Prelithiated Si Anode

“…No increase in the interfacial resistance between Li 2.6 Zr 0.4 (Ho/Lu) 0.6 Cl 6 and Li 6 PS 5 Cl was noted, indicating their chemical compatibility. We note that other work suggests incompatibility between chloride and sulfide solid electrolytes, but this contradicts our results. , This suggests that the compatibility between chloride and sulfide solid electrolytes could be material dependent. The semicircles in the Nyquist plot are mainly attributed to Li ion transport in the cathode composite and to the NCM85–chloride solid electrolyte interphase, according to the model applied by Zhang et al The latter resistance clearly dominates the overall response, which corresponds to formation of a thicker Li ion blocking interphase at higher cutoff potentials that drives faster capacity fading.…”

Balancing Partial Ionic and Electronic Transport for Optimized Cathode Utilization of High‐Voltage LiMn2O4/Li3InCl6 Solid‐State Batteries

“…This bilayer setup helps with protection of the halide solid electrolyte from the anode and protection of the sulfide solid electrolyte from the high cathode potentials. Nevertheless, recent work suggests some underlying chemical instability [19,20,41] . Therefore, in this work, the Li 3 InCl 6 halide solid electrolyte is also inserted as protection layer between the Li 6 PS 5 Cl and cathode composite.…”

“…Nevertheless, recent work suggests some underlying chemical instability. [19,20,41] Therefore, in this work, the Li 3 InCl 6 halide solid electrolyte is also inserted as protection layer between the Li 6 PS 5 Cl and cathode composite.…”

Synthesis-Controlled Polymorphism and Anion Solubility in the Sodium-Ion Conductor Na3InCl6–xBrx(0 ≤x≤ 2)

“…19 Lithium-containing halides have wide electrochemical windows and excellent electrochemical compatibility toward oxide cathode materials, as well as good mechanical deformability and scale-up capability, which is why they are viewed as promising candidates for catholyte materials. 20,21 Nevertheless, recent instabilities against sulfide separators in their lithium counterparts 22 suggest that chemical stability may remain an issue in Na + -based halides as well.…”

“…However, their low oxidation stability and poor compatibility with sodium metal do not favor their practical application. , In contrast, scandium-substituted NASICON Na 3.4 Sc 0.4 Zr 1.6 (SiO 4 ) 2 (PO 4 ) exhibits an ionic conductivity of up to 4 × 10 –3 S·cm –1 , and the sodium solid-state battery employing it can be operated at a voltage up to 4.2 V against the cathode Na x CoO 2 , demonstrating its outstanding electrochemical stability; however, the high sintering temperatures (>1000 °C), undesirable mechanical properties, and significant grain boundary resistances are unfavorable for the practical application of oxide-based Na + conductors . Lithium-containing halides have wide electrochemical windows and excellent electrochemical compatibility toward oxide cathode materials, as well as good mechanical deformability and scale-up capability, which is why they are viewed as promising candidates for catholyte materials. , Nevertheless, recent instabilities against sulfide separators in their lithium counterparts suggest that chemical stability may remain an issue in Na + -based halides as well.…”