High Voltage Cycling Stability of LiF-Coated NMC811 Electrode

Abstract

The development of LiNi 0.8 Mn 0.1 Co 0.1 O 2 (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.

Artificial Layer Construction via Cosolvent Enables Stable Ni-Rich Cathodes for Enhanced Lithium Storage

“…Ni-rich layered lithium metal oxide (LiNi x Mn y Co 1– x – y O 2 , x ≥ 0.6, NMC) material is one of the most commonly used cathode materials in lithium-ion batteries (ILBs) owing to its potential to gain high capacity and low cost. , The composition of NMC can be NMC111, NMC622, or NMC811, where the numbers represent the molar ratios of Ni, Mn, and Co, respectively. Increasing the Ni content increases the capacity because Ni is the main element that participates in redox reactions within a certain voltage range. , Although the redox reactions of oxygen in NMC can increase the capacity, they result in material instability and large capacity decay during cycling. , Co and Mn in NMC materials are essential because they provide structural stability that enables performance stability. , Ni-rich NMC material such as NMC811 has recently attracted attention because of its high capacity and low Co dependence, which is prohibited because of the child labor issues and health concerns. , …”