Thermal effects on precursor-based garnet Li-La-Zr-O coatings for high-voltage Ni-rich cathodes

Abstract

High-voltage (>4.3 V vs. Li/Li⁺) Ni-rich cathodes, essential for high-energy-density lithium-ion batteries, suffer from electrolyte-induced surface degradation. Garnet-type Li-La-Zr-O coatings are promising, but their high crystallization temperature can trigger detrimental interfacial reactions. Amorphous coatings offer a potential solution, but require optimized synthesis and thermal treatment. This study investigates precursor-derived Li-La-Zr-Al-O (LLZAO) coatings on Li(Ni_0.5Co_0.2Mn_0.3)O₂ (NCM523) cathodes annealed at 300 °C, 500 °C, and 750 °C, correlating precursor thermal behavior with surface microstructural and interfacial chemical changes. To quantitatively analyze thermally induced changes at the cathode-coating interface, particularly the overlapping Ni 2p and La 3d core-level spectra in X-ray photoelectron spectroscopy (XPS), we developed a spectral deconvolution approach. Combined with X-ray fluorescence (XRF), this reveals how annealing affects coating homogeneity. A 500 °C anneal yields a sub-crystalline LLZAO coating with optimal homogeneity and minimal Ni/La migration, significantly enhancing cycling stability and rate capability at 4.55 V vs. Li/Li⁺. Coatings annealed at 300 °C remained amorphous with carbon residues, offering limited protection, while those at 750 °C exhibited secondary phase formation and interfacial degradation. This work highlights the critical role of thermal control in optimizing amorphous LLZAO coatings and provides a quantitative methodology for understanding and mitigating interfacial reactions in high-voltage lithium-ion batteries.