Operando Observations of SEI Film Evolution by Mass‐Sensitive Scanning Transmission Electron Microscopy

Abstract

SEI films directly affect the dissolution and deposition of lithium during discharge and charge and thus are one of the key factors that determine the safety, power capability, morphology of lithium deposits, shelf life, and cycle life of LIBs. In particular, the breakdown of SEI can result in the nucleation and growth of lithium dendrites and cause the safety risk for the practical applications of LIBs in the electric vehicles and other high-energy-density electronic devices. [5,6] While, a stable and robust SEI film can effectively inhibit the lithium dendrite growth and thus prominently enhance the cycling performance and safety of the batteries. [1,7] Owing to directly growing on anode surfaces, the formation and stability of SEI films are greatly influenced by the volume variation of anodes during the charge-discharge cycling, especially at a high current density. [1,8] Although the importance of SEI has been widely recognized, the structure and kinetics of SEI are the less wellunderstood phenomena impacting battery technology. Various in situ techniques, for instances, in situ spectroscopic ellipsometry, [9] in situ nuclear magnetic resonance (NMR), [10] in situ X-ray diffraction, [11] in situ Fourier transform infrared (FTIR) spectroscopy, [12] and in situ electrochemical impedance spectroscopy, [13] have been employed to investigate the evolution of SEI films. Nevertheless, most of them are limited to the nonintuitive investigations. Several key questions on the SEI film formation, structure and failure are still elusive.Recently, in situ transmission electron microscopy (TEM) has been utilized as a power tool to explore the evolution of SEI films in LIBs. In particular, a liquid cell TEM technique can well mimic the chemical and electrochemical reactions in liquid media with controllable charge and discharge conditions of LIBs. Sacci et al. performed the first in situ TEM observations of SEI film formation on a gold electrode during cyclic voltammetry testing. [14] They found that SEI films form heterogeneously on the gold electrode and possess dendritic morphology. The formation and growth of SEI films on graphite/electrolyte interfaces were studied by Unocic et al. using in situ TEM. [15] By utilizing the liquid cell TEM, Zeng et al. monitored the structural evolution of SEI films in a cyclic voltammetry process and found that the growth of SEI films is limited by the electron transport and produces gaseous The solid electrolyte interphase (SEI) spontaneously formed on anode surfaces as a passivation layer plays a critical role in the lithium dissolution and deposition upon discharge/charge in lithium ion batteries and lithiummetal batteries. The formation kinetics and failure of the SEI films are the key factors determining the safety, power capability, and cycle life of lithium ion and lithium-metal batteries. Since SEI films evolve with the volumetric and interfacial changes of anodes, it is technically challenging in experimental study of SEI kinetics. Here operando observations are reported of SEI...

Lithium Metal Electrode with Increased Air Stability and Robust Solid Electrolyte Interphase Realized by Silane Coupling Agent Modification

“…[ 7 ] It has been observed by operando scanning transmission electron microscopy that the SEI layer is damaged during interfacial fluctuations and finally exfoliated, leaving an exposed electrode surface in the electrolyte. [ 8 ] The SEI layer exfoliation can be attributed to poor chemical adhesion between the SEI layer and the Li substrate. Obviously, a stable and robust SEI layer is the decisive factor for safe, dendrite‐free, and long‐lifespan Li metal based batteries.…”

Toward Critical Electrode/Electrolyte Interfaces in Rechargeable Batteries

“…[ 80 ] The causes for the preferential distribution of these organic/inorganic species are related to the initial decomposition sequence of electrolyte ingredients [ 82 ] and the subsequent evolution process of initial SEI. [ 83 ] The originally generated organic species might get further reduced to form more stable inorganic components near the surface of electrode, which play an essential role in achieving the electronic insulation of SEI. [ 84 ] Further, Cheng et al indicated that the layered model and mosaic model are not contradictory in essence, since the building blocks in each layer of layered model still distribute in a mosaic form.…”

Recent Progress on Advanced Imaging Techniques for Lithium‐Ion Batteries

“…e) The configuration of lithium ion microcell with three electrodes for electrochemical measurements Schematic picture of the closed cell and testing mechanism and the in situ HAADF‐STEM images of Au lithiation. [ 23 ] Reproduced with permission. [ 23 ] Copyright 2019, Wiley‐VCH.…”

“…Therefore, this technique was able to visualize the nanoscale chemical valence change, and reveal the lithiation mechanism. Similar in situ TEM cells were also used to study the lithiation process of Li‐alloying process, [ 22 ] SEI evolution, [ 23 ] and lithium dendrite growth. [ 24 ]…”