High Voltage Cycling Stability of LiF-Coated NMC811 Electrode

The development of LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) as a cathode material for high-energy-density lithium-ion batteries (LIBs) intends to address the driving limitations of electric vehicles. However, the commercialization of this technology has been hindered by poor cycling stability at high cutoff voltages. The potential instability and drastic capacity fade stem from irreversible parasitic side reactions at the electrode-electrolyte interface. To address these issues, a stable nanoscale lithium fluoride (LiF) coating is deposited on the NMC811 electrode via atomic layer deposition. The nanoscale LiF coating diminishes the direct contact between NMC811 and the electrolyte, suppressing the detrimental parasitic reactions. LiF-NMC811 delivers cycling stability superior to uncoated NMC811 with high cutoff voltage for half-cell (3.0-4.6 V vs Li/Li⁺) and full-cell (2.8-4.5 V vs graphite) configurations. The structural, morphological, and chemical analyses of the electrodes after cycling show that capacity decline fundamentally arises from the electrode-electrolyte interface growth, irreversible phase transformation, transition metal dissolution and crossover, and particle cracking. Overall, this work demonstrates that LiF is an effective electrode coating for high-voltage cycling without compromising rate performance, even at high discharge rates. The findings of this work highlight the need to stabilize the electrode-electrolyte interface to fully utilize the high-capacity performance of NMC811.