In Situ Studies of Solid Electrolyte Interphase (SEI) Formation on Crystalline Carbon Surfaces by Neutron Reflectometry and Atomic Force Microscopy

Abstract

The solid electrolyte interphase (SEI) is a complex and fragile passivation layer with crucial importance for the functionality of lithium-ion batteries. Due to its fragility and reactivity, the use of in situ techniques is preferable for the determination of the SEI's true structure and morphology during its formation. In this study, we use in situ neutron reflectometry (NR) and in situ atomic force microscopy (AFM) to investigate the SEI formation on a carbon surface. It was found that a lithium-rich adsorption layer is already present at the open circuit voltage on the carbon sample surface and that the first decomposition products start to deposit close to this potential. During the negative potential sweep, the growth of the SEI can be observed in detail by AFM and NR. This allows precise monitoring of the morphology evolution and the resulting heterogeneities of individual SEI features. NR measurements show a maximum SEI thickness of 192 Å at the lower cutoff potential (0.02 V vs Li/Li), which slightly decreases during the positive potential scan. The scattering length density (SLD) obtained by NR provides additional information on the SEI's chemical nature and structural evolution.

Microgravimetric and Spectroscopic Analysis of Solid−Electrolyte Interphase Formation in Presence of Additives

“…As a consequence, the observed surface morphology will induce mainly a frequency decrease. In support of our analysis, morphological characterisation of SEI layers by means of neutron reflectometry and AFM revealed that the SEI formed in 1 M LiPF 6 , EC:DEC has a very low roughness reaching 10 nm . Under these circumstances the trapped liquid in the layer cavities moves in phase with the quartz crystal and therefore performs as a rigid mass .…”

“…These structural features are already confirmed by neutron refractometry and AFM studies. Steinhauer et al., for instance, demonstrate that SEI formed in reference electrolyte has a layer average roughness of only 10 nm . Contrary, the SEI formation in DPOP is characterized by a significant damping increase.…”

“…In support of our analysis, morphological characterisation of SEI layers by means of neutron reflectometry and AFM revealed that the SEI formed in 1 M LiPF 6 , EC:DEC has a very low roughness reaching 10 nm. [28] Under these circumstances the trapped liquid in the layer cavities moves in phase with the quartz crystal and therefore performs as a rigid mass. [39][40][41][42] At these conditions the SEI morphology does not affect the damping of the oscillating system.…”

Review on multi-scale models of solid-electrolyte interphase formation

“…Since 1979 a multitude of experimental SEI research has been performed [4,18], recent examples include battery storage at various state-of-charge (SoC) [12,13], differential capacity analysis during cycling [19], neutron reflectometry [20], atomic force microscopy [21], nuclear magnetic resonance [22], redox shuttles [23,24], fourier-transform infrared spectroscopy [25], and photo-electron spectroscopy [26]. As a consequence, there is a general understanding of SEI composition and morphology for few specific systems.…”

Deactivating Defects in Graphenes with Al2O3 Nanoclusters to Produce Long‐Life and High‐Rate Sodium‐Ion Batteries

“…Figure 3a shows the first two cycles of charge/discharge profiles for Al 2 O 3 /PGM-5 and PGM-T at a current density of 0.1 A g −1 between 0.005-3 V versus Na/Na + . [56][57][58][59] It is noted that the Al 2 O 3 /PGM-5 has a much lower peak intensity than PGM-T, indicating that the decomposition of NaOTf is suppressed. In the CV profiles in Figure 3b, there is an irreversible broad cathodic peak between 0.3 and 1.0 V during the first cycle, which is due to the continuous decomposition of aprotic solvent (diglyme) and conductive electrolyte sodium salt (NaCF 3 SO 3 ) to form a protective SEI.…”