Understanding the Surface Regeneration and Reactivity of Garnet Solid-State Electrolytes

Abstract

Garnet solid-electrolyte-based Li-metal batteries can be used in energy storage devices with high energy densities and thermal stability. However, the tendency of garnets to form lithium hydroxide and carbonate on the surface in an ambient atmosphere poses significant processing challenges. In this work, the decomposition of surface layers under various gas environments is studied by using two surface-sensitive techniques, near-ambient-pressure X-ray photoelectron spectroscopy and grazing incidence X-ray diffraction. It is found that heating to 500 °C under an oxygen atmosphere (of 1 mbar and above) leads to a clean garnet surface, whereas low oxygen partial pressures (i.e., in argon or vacuum) lead to additional graphitic carbon deposits. The clean surface of garnets reacts directly with moisture and carbon dioxide below 400 and 500 °C, respectively. This suggests that additional CO2 concentration controls are needed for the handling of garnets. By heating under O2 along with avoiding H2O and CO2, symmetric cells with less than 10 Ωcm2 interface resistance are prepared without the use of any interlayers; plating currents of >1 mA cm–2 without dendrite initiation are demonstrated.

Removal and Reoccurrence of LLZTO Surface Contaminants under Glovebox Conditions

“…The minor remaining contamination may be mainly associated with grain boundaries . However, we avoided annealing at higher temperatures to prevent excessive vaporization of the lithium metal from the near-surface regions, as suggested in previous reports …”

“…LiOH is removed at temperatures up to 500 °C by reversing eq , while Li 2 CO 3 decomposes into Li 2 O and CO 2 mostly around and above 700 °C. ,, The precise annealing temperature required for the complete contamination removal depends on various LLZTO characteristics, for instance, doping elements and grain size, as well as on the annealing environment. Under ultrahigh vacuum (UHV) conditions, where materials volatilize at lower temperatures, annealing at 500–600 °C can almost completely remove the surface contaminants. ,, However, a significant drawback of the heat treatment lies in the potential evaporation of lithium that can trigger the formation of pyrochlores such as La 2 Zr 2 O 7 on the pellet surface, which possess a lower ionic conductivity. , An alternative to annealing is acid etching, particularly appealing due to its simplicity and efficiency. − A rapid immersion in a dilute aqueous acid solution such as HCl (aq) can successfully decompose Li 2 CO 3 according to normalL normali 2 normalC normalO 3 + 2 H C l → 2 L i C l + normalC normalO 2 + H 2 normalO …”

Regulating Grind‐Induced Lattice Distortion for Nickel‐Rich Cathodes by Annealing

“…Weight loss occurring below 400 °C is attributed to the evaporation of water and the decomposition of surface impurities, such as Li 2 CO 3 and LiOH, which may have accumulated during prolonged storage. [42] Furthermore, when annealing temperatures exceed 900 °C, a noticeable decomposition reaction is observed. Therefore, annealing temperatures of 600, 700, and 800 °C are selected for the annealing process.…”

Optimization strategies for key interfaces of LLZO-based solid-state lithium metal batteries

“…28 Grey et al heated air-exposed LLZO under oxygen at 500 °C, achieving complete regeneration of LLZO and low lithium metal/LLZO interfacial resistance (10 Ω cm 2 ). 48 Although Li 2 CO 3 can be removed by high-temperature calcination, more lithium volatilization happens concurrently, and additional contaminants are also produced. In addition, high-temperature calcination is generally energy-consuming and time-consuming.…”