New Chemical Insights into the Beneficial Role of Al₂O₃ Cathode Coatings in Lithium-ion Cells

Abstract

Inorganic surface coatings such as Al 2 O 3 are commonly applied on positive electrode materials to improve the cycling stability and lifetime of lithium-ion cells. The beneficial effects are typically attributed to the chemical scavenging of corrosive HF and the physical blockage of electrolyte components from reaching the electrode surface. The present work combines published thermochemistry data with new density functional theory calculations to propose a new mechanism of action: the spontaneous reaction of the LiPF 6 electrolyte salt with Al 2 O 3 -based surface coatings. Using 19 F and 31 P solution nuclear magnetic resonance spectroscopy, it is demonstrated that the storage of LiPF 6 -containing electrolyte solution with Al 2 O 3 produces LiPO 2 F 2 , a well-known electrolyte additive. The production of LiPO 2 F 2 is also observed for electrolyte solutions that were stored for 14 days at 40 °C with Al 2 O 3 -coated LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) and LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) materials. Given the beneficial nature of this species for the lifetime and stability of lithium-ion cells, this reaction is here proposed to similarly benefit the performance of cells that use Al 2 O 3 -coated cathode materials.

Lithium Difluorophosphate as an Effective Additive for Improving the Initial Coulombic Efficiency of a Silicon Anode

“…[37,38] But for the Figure 7b, the another peaks at 84.6 and 86.5 ppm were considered the characteristic peaks from the additive of LiDFP, owing to these peaks are not presented in samples without this additive. [39] After charge-discharges process for Figure 7c, the position of both peaks did not changed, and the intensity is nearly same. Only after 5 cycles did the intensity of the peak slightly decrease in Figure 7d.…”

An Overview on the Advances of LiCoO2 Cathodes for Lithium‐Ion Batteries

“…In a commercial verification test at 4.6 V, LiAlO 2 ‐coated LiCoO 2 delivers a high reversible capacity of 200 mAh g −1 and retains high capacity after 50 cycles, confirming that the formation of LiAlO 2 or LiAl x Co 1− x O 2 solid solution during high temperature is important for Al 2 O 3 coating process. Recently, Dahn et al [ 117 ] predicted that Al 2 O 3 coating layer reacts with LiPF 6 in the electrolyte spontaneously to form a kind of electrolyte additive, LiPO 2 F 2 . Likewise, MgO coating layer shows the same function.…”

Surface/Interface Structure Degradation of Ni‐Rich Layered Oxide Cathodes toward Lithium‐Ion Batteries: Fundamental Mechanisms and Remedying Strategies

“…a) Normalized capacity and corresponding Δ V (40 °C) for the NCM523/graphite pouch cells cycled at C/3 between 3.0 and 4.3 V. Reproduced with permission . Copyright 2019, American Chemical Society.…”