Atomic Layer Deposition of Ta2O5 on Composite Nickel-Rich Cathodes for High-Voltage Lithium-Ion Batteries

Abstract

Nickel-rich layered oxides, such as LiNi0.8Mn0.1Co0.1O2 (NMC811), are promising cathode materials for high-energy lithium-ion batteries but suffer from severe interfacial and structural degradation under high-voltage and high-temperature operation. Here, we demonstrate an electrode-level surface engineering strategy by depositing conformal Ta2O5 coatings onto entire composite NMC811 electrodes via atomic layer deposition (ALD). Unlike conventional particle-level coatings, the electrode-level Ta2O5 coating uniformly covers active materials, conductive additives, and polymer binders, preserving continuous electronic and ionic transport pathways without compromising capacity or rate capability. Among the samples investigated, the electrode coated with five ALD cycles of Ta2O5 exhibits the optimal balance between interfacial protection and electrochemical performance, delivering markedly improved cycling stability at both 30 and 50 °C under high-voltage operation (4.6 V vs Li/Li+). Electrochemical impedance spectroscopy and distribution of relaxation time analyses reveal significantly reduced contact, interfacial, and charge-transfer resistances for the coated electrodes and suppressed impedance growth during long-term cycling. Post-mortem surface analyses show that the Ta2O5 coating regulates cathode–electrolyte interphase chemistry by mitigating LiPF6 decomposition, reducing HF-induced degradation, and promoting the formation of a balanced, ionically conductive CEI. In addition, the coating effectively suppresses surface reconstruction from the layered structure to the rock-salt phase while remaining chemically stable upon cycling. This work highlights electrode-level ALD Ta2O5 coatings as a robust and scalable strategy for stabilizing Ni-rich cathodes under extreme operating conditions, offering important insights for the design of next-generation high-energy lithium-ion batteries.