Synergistic interface design of Al2O3-coated NMC811 and graphitic-based pre-lithiated anodes for enhanced full-cell performance

Abstract

This work investigates aluminum oxide (Al2O3) surface coatings on lithium nickel manganese cobalt oxide (NMC811) cathodes using a wet-chemical process based on aluminum ethoxide (Al(OEt)3) dissolved in ethanol. Three coating concentrations, 1%, 2%, and 3% Al precursor relative to NMC811 mass, were synthesized and are referred to as NMC811@AlO-1, NMC811@AlO-2, and NMC811@AlO-3, respectively. The workflow involved structural and surface characterization of the coated samples, followed by electrochemical evaluation in both half-cell and full-cell configurations. FTIR confirmed the formation of Al–O bonds, while XRD and Raman spectroscopy verified that the NMC811 lattice structure remained unchanged after coating. Transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (TEM-EDX) confirmed the successful deposition of the Al2O3 layer. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis showed Al3+ ion diffusion into the grain interiors, suggesting a potential impact on the electrodes' electrochemical performance. Electrochemical tests showed that all coated samples improved stability, with NMC811@AlO-3 (3% coating) delivering the best capacity retention in half-cells. In the second phase, full cells were assembled using pre-lithiated graphite, graphene, and graphene oxide (GO) anodes, for which pre-lithiation conditions were optimized. Among all combinations, the NMC811@AlO-3/GO full cell exhibited the highest initial discharge capacity (183 mAh/g) and the best cycling retention (80.1% after 250 cycles at C/2). These results demonstrate that a 3% Al2O3 coating, combined with a GO anode, offers the most promising pathway toward high-performance full-cell systems.