Direct Operando Observation of Double Layer Charging and Early Solid Electrolyte Interphase Formation in Li-Ion Battery Electrolytes

Abstract

The solid electrolyte interphase (SEI) is the most critical yet least understood component to guarantee stable and safe operation of a Li-ion cell. Herein, the early stages of SEI formation in a typical LiPF 6 and organic carbonate-based Li-ion electrolyte are explored by operando surface-enhanced Raman spectroscopy, on-line electrochemical mass spectrometry, and electrochemical quartz crystal microbalance. The electric double layer is directly observed to charge as Li + solvated by ethylene carbonate (EC) progressively accumulates at the negatively charged electrode surface. Further negative polarization triggers SEI formation, as evidenced by H 2 evolution and electrode mass deposition. Electrolyte impurities, HF and H 2 O, are reduced early and contribute in a multistep (electro)chemical process to an inorganic SEI layer rich in LiF and Li 2 CO 3 . This study is a model example of how a combination of highly surface-sensitive operando characterization techniques offers a step forward to understand interfacial phenomena in Li-ion batteries.

Decomposition of Carbonate‐Based Electrolytes: Differences and Peculiarities for Liquids vs. Polymers Observed Using Operando Gas Analysis

“…[11] OH À can also attack polymer chains resulting in a metastable mono-substituted carboxyl group that can undergo further fragmentation and form CO 2 and an alcohol. The discrepancy between the observed onset of H 2 evolution in PTMC : LiTFSI (0.75 V vs. Li + /Li) compared to the onset observed for EC/DEC : LiTFSI (1.4 V) and the onset reported for EC/ DEC : LiTFSI and EC/DEC : LiPF 6 (1.6 and 1.8 V, respectively), [25,27] can be explained by the liquid electrolyte reaching contact with the stainless steel mesh beneath the kynol electrode, unlike the restricted solid diffusion of SPE which only allows contact to the kynol electrode and not the stainless steel. Metal surfaces have a higher electrocatalytic activity for hydrogen evolution reactions in comparison to carbon surfaces and can thus explain the observed difference in H 2 evolution onset.…”

Development, retainment, and assessment of the graphite-electrolyte interphase in Li-ion batteries regarding the functionality of SEI-forming additives

“…Such approaches could be used also for mechanistic studies. For instance, online electrochemical assessment along with mass spectrometry has been applied to monitor the initiation stage of the interphase formation process ( Mozhzhukhina et al., 2020 ). SIMS technique is capable to provide in-depth information about the content of solid surfaces and thin films.…”

Investigating oxidative stability of lithium-ion battery electrolytes using synthetic charge-discharge profile voltammetry

“…The motivation behind choosing these particular electrolytes was that they together span common lithium-ion battery electrolyte solvent functionalities. Furthermore, LP40 is a carbonate-based electrolyte that is the most commonly used for the Li-ion systems, [22][23][24] sulfolane:LiPF6 is often claimed to be more oxidatively stable, [25] while ether-based systems such as TEGDME:LiPF6 are is often described as oxidatively less stable and is therefore expected to display more rapid decomposition. [26] The mixture of LP40 and sulfolane:LiPF6 is employed primarily as a bench-marking system, and is expected to have intermediate properties of the two components.…”