# Sol–Gel-Derived Ge-Substituted LLZO Ceramic Coatings on Lithium-Rich Layered Oxide Cathodes for Improved Interfacial Stability

## TL;DR

A sol-gel method is used to coat lithium-rich cathode particles with a ceramic layer that improves battery performance and stability.

## Contribution

A citrate-assisted sol-gel process is introduced to create Ge-substituted LLZO coatings that enhance interfacial stability in lithium-rich oxide cathodes.

## Key findings

- Ge-LLZO coatings are successfully deposited on LMLO cathodes using a sol-gel method.
- Coated cathodes show improved electrochemical stability and slower capacity decay compared to uncoated ones.
- Structural analysis confirms preservation of the LMLO host structure after coating.

## Abstract

Gel-based routes, particularly sol–gel processes, offer a versatile pathway to generate uniform inorganic networks and gel-derived functional ceramics with controlled composition and interfacial coverage. In this study, we employ a citrate-assisted sol–gel coating strategy to form a precursor gel containing Li, La, Zr, and Ge species on lithium-rich manganese-based layered oxide (LMLO) cathode particles, followed by drying/thermal conversion to obtain a Ge-substituted garnet-type Li7La3Zr2O12 (Ge-LLZO) ceramic coating. Structural and surface analyses (FE-SEM/EDS, XPS, and FE-TEM) confirm the presence of surface-deposited coating-related species and coating-induced changes in surface chemistry, while bulk XRD is primarily used to verify that the layered LMLO host structure is preserved after the gel-to-ceramic treatment. Electrochemical testing indicates that the gel-derived Ge-LLZO coating can influence interfacial kinetics and resistance evolution, as reflected by differential capacity behavior, impedance responses, and rate capability trends, alongside microstructural observations suggesting reduced damage compared with bare LMLO after cycling. Overall, this work demonstrates that gelation-assisted deposition and gel-to-ceramic conversion enable Ge-LLZO surface coatings on LMLO cathodes that modulate interfacial kinetics and resistance evolution. Under the harsh 4.8–2.0 V/1C condition, the bare LMLO shows an abrupt capacity drop after ~60 cycles, while the coated LMLO exhibits a more gradual decay up to 100 cycles; further optimization is required for robust long-term stability.