Ab Initio Modeling of Electrolyte Molecule Ethylene Carbonate Decomposition Reaction on Li(Ni,Mn,Co)O₂ Cathode Surface

Abstract

Electrolyte decomposition reactions on Li-ion battery electrodes contribute to the formation of solid electrolyte interphase (SEI) layers. These SEI layers are one of the known causes for the loss in battery voltage and capacity over repeated charge/discharge cycles. In this work, density functional theory (DFT)-based ab-initio calculations are applied to study the initial steps of the decomposition of the organic electrolyte component ethylene carbonate (EC) on the (10 4) surface of a layered Li(Ni x ,Mn y ,Co 1-xy )O 2 (NMC) cathode crystal, which is commonly used in commercial Li-ion batteries. The effects on the EC reaction pathway due to dissolved Li + ions in the electrolyte solution and different NMC cathode surface terminations containing adsorbed hydroxyl -OH or fluorine -F species are explicitly considered. We predict a very fast chemical reaction consisting of an EC ring-opening process on the bare cathode surface, the rate of which is independent of the battery operation voltage. This EC ring-opening reaction is unavoidable once the cathode material contacts with the electrolyte because this process is purely chemical rather than electrochemical in nature. The -OH and -F adsorbed species display a passivation effect on the surface against the reaction with EC, but the 1 2 extent is limited except for the case of -OH bonded to a surface transition metal atom. Our work implies that the possible rate-limiting steps of the electrolyte molecule decomposition are the reactions on the decomposed organic products on the cathode surface rather than on the bare cathode surface.

Fading Mechanisms and Voltage Hysteresis in FeF2–NiF2 Solid Solution Cathodes for Lithium and Lithium‐Ion Batteries

“…The LNO was also detected in NiF 2 sample (Figure b,c). Note that LNO could result in degradation of electrolyte as was observed for similar metal oxide materials, and we will discuss it in more detail later in this paper.…”

“…The bulk crystal volume and atom positions were reoptimized with VASP 5.2.2 using the PBE+U functional, 520 eV cutoff, and a Methfessel–Paxton k ‐point mesh of 5 × 5 × 1 . The U parameter was set to 6.37 eV as reported by Xu et al In all calculations, a 0.2 eV first‐order Methfessel–Paxton broadening function was used and all structures were initialized in a ferromagnetic state with 3 µ B assigned to Ni and 0.6 µ B to everything else. Lithium was modeled with the “_sv” potential variant that considers the 1s electrons as valence; all other atoms used the standard set of potentials.…”

Computer Simulation of Cathode Materials for Lithium Ion and Lithium Batteries: A Review

“…[89] Electrolyte decomposition on the Li(Ni,Mn,Co)O 2 cathode surface has also been studied, which provides useful insights on the formation of solid electrolyte interphase (SEI) layers at the cathode surfaces. [90]…”

Revealing electrolyte oxidation via carbonate dehydrogenation on Ni-based oxides in Li-ion batteries by in situ Fourier transform infrared spectroscopy

“…Multiple reaction mechanisms on carbonate electrolyte oxidation have been proposed, including nucleophilic attack reactions between oxides and carbonate molecules, [31][32][33] electrophilic attack, 34,35 and dehydrogenation reactions, including EC dissociation by breaking C-H bond, 36,37 and dissociation with oxygen vacancy formation. 34 However, recent density functional theory (DFT) results 13 show that EC dissociation on layered Ni-rich oxides is more energetically favorable than the other processes reported.…”