Coating on cathode of NMC811 lithium ion batteries

Abstract

Nickel-rich NMC811 cathodes offer high energy density but degrade through surface reactions, cation mixing, and electrolyte instability during cycling. This thesis investigates three sol-gel coating routes for applying Al₂O₃ and mixed Al₂O₃-Ta₂O₅ layers onto commercial NMC811 to improve structural and electrochemical stability. The DI water and ethanol route produced uncontrolled gelation and agglomerated coatings, which resulted in poor capacity retention and were excluded from performance comparison. In contrast the toluene based routes yielded uniform amorphous surface layers that preserved the R3m crystal structure, SEM and EDS confirmed controlled deposition without particle collapse. Electrochemical testing showed that 1 wt% Al₂O₃, and mixed 0.5 wt% Al₂O₃ + 0.5 wt% Ta₂O₅, coatings improved capacity retention, voltage stability, and specific energy density relative to uncoated NMC811. The mixed-oxide coating showed the most stable behavior. The findings demonstrate that sol-gel coatings can enhance NMC811 performance when solvent and precursor conditions are tightly controlled, with toluene routes offering the most reliable results.