Electrochemical Oxidation in Garnet-Type Solid Electrolyte by Formation of Point Defects

Journal Article · Thu Jul 31 00:00:00 EDT 2025 · Chemistry of Materials

DOI:https://doi.org/10.1021/acs.chemmater.5c01174· OSTI ID:2587336

Chandra, Subhash ^[1]; Saini, Shikha ^[1]; Fincher, Cole D. ^[1]; Wright, Joshua T. ^[2]; Waluyo, Iradwikanari ^[3]; Hunt, Adrian ^[3]; Segre, Carlo U. ^[2]; Chiang, Yet-Ming ^[1]; Yildiz, Bilge ^[1]

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1. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
2. Illinois Institute of Technology, Chicago, IL (United States)
3. Brookhaven National Laboratory (BNL), Upton, NY (United States). National Synchrotron Light Source II (NSLS-II)

All-solid-state batteries hold greater promise for improving safety and energy density over conventional battery technology employing organic liquid electrolytes. One of the required features of a Li⁺ conducting solid electrolyte is electrochemical stability, attained thermodynamically or kinetically, within the targeted operating voltage and temperature ranges. Therefore, understanding of the oxidative or reductive degradation mechanism is important to allow the design of stable solid electrolyte materials. This work contributes to building an understanding of the oxidative degradation mechanism in lithium solid electrolytes at cell operating conditions. Here, we have focused on resolving the oxidative decomposition mechanism of Al-doped lithium garnet Li_6.28Al_0.24La₃Zr₂O₁₂ (LLZO) as a state-of-the-art inorganic ceramic electrolyte. By combining experimental and computational analyses, we show that oxidation of LLZO occurs by simultaneous loss of oxygen and lithium from the structure, resulting in substoichiometric LLZO, at a moderate temperature (80 °C) and a high electrode potential (4.3 V vs Li/Li⁺). Based on X-ray absorption and diffraction analyses, we find that the zirconium coordination shells in LLZO contract while the crystal structure experiences positive chemical strain upon electrochemical oxidation. The results from ex situ structural characterization of both the local structure and crystal symmetry are supported by a substoichiometric LLZO with lithium and oxygen vacancies, modeled by density functional theory (DFT) calculations. These chemical and structural changes in LLZO suppress effective lithium-ion conductivity by an order of magnitude. Formation of lithium and oxygen vacancies in LLZO upon electrochemical oxidation is different from prior thermodynamic predictions of phase decomposition of LLZO. The difference here is that the experiments were conducted at near-room temperature, which can hinder the kinetics of phase separation, and thus, the resultant LLZO solid electrolyte is still single-phase but substoichiometric in Li and O. In conclusion, these findings contribute an important degradation mechanism of the electrolyte, relevant for practical operational conditions of solid-state batteries.

• Research Organization: Brookhaven National Laboratory (BNL), Upton, NY (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF)
• Grant/Contract Number: AC02-06CH11357; SC0012704; SC0023438
• OSTI ID: 2587336
• Report Number(s): BNL--228852-2025-JAAM
• Journal Information: Chemistry of Materials, Journal Name: Chemistry of Materials Journal Issue: 15 Vol. 37; ISSN 1520-5002; ISSN 0897-4756
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

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36 MATERIALS SCIENCE