Exploring the impact of \({\varvec{\gamma}}\)-Al2O3 coating on reaction kinetics and lithium-ion diffusion in LiNi0.5Mn0.3Co0.2O2 cathode materials: a tale of two techniques

Abstract

The surface of LiNi_0.5Mn_0.3Co_0.2O₂ (NMC532) cathode material reacts easily with electrolytes in Li-ion batteries, causing capacity fade during cycling. In this research, ultrasonic-assisted and dry-mixed coating techniques are compared as coating methods of γ-Al₂O₃ nanoparticles on NMC532 to fix this issue. Microscopy techniques reveal the porous layer of Al₂O₃ with different uniformity. Cyclic voltammograms confirm less lithium-ion loss during the formation process and minimum electrode/electrolyte side reactions for coated samples. The discharge capacity retentions of pristine (PNMC), ultrasonic-assisted (UNMC), and dry-mixed (DNMC) NMC cathodes are 80.3, 91.9, and 78.7% after 100 cycles at 0.5C, and the coated samples experience superior rate performance. Electrochemical impedance spectroscopy evaluations depict that faster Li⁺ diffusion with decreased charge transfer resistance and increased interfacial stability are both made possible by the γ-Al₂O₃ uniform surface coating. Cycling also has a negative effect on diffusion coefficients for both pristine and coated electrodes. Finally, Li-ion diffusion coefficient is calculated from electrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic intermittent titration technique, and it shows that the diffusion coefficient of UNMC is higher than that of PNMC and DNMC, which establishes the fact that the ultrasonic-assisted coating layer can enhance lithium-ion diffusion during the extraction/insertion processes more effectively.