Advanced Transmission Electron Microscopy for Electrode and Solid‐Electrolyte Materials in Lithium‐Ion Batteries

Abstract

Understanding the reaction processes of electrode and electrolyte materials is important for achieving high‐performance lithium‐ion batteries (LIBs). Currently, transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) can readily characterize the structural and chemical features of these materials from the micrometer scale to the atomic scale. In situ (S)TEM can further monitor their non‐ or quasi‐equilibrated states in real time. Here, the recent progress in unraveling the crystal and electronic structures of the electrode and solid‐electrolyte materials using ex situ and in situ (S)TEM is reviewed. Three fundamental functions, including imaging, diffraction, and spectroscopy, are jointly used to decipher the configuration of the defects and ordering, the variations near the surfaces and across the interfaces, and the evolution of the coexisting phases. Novel and deep insights are proposed for the material growth, reaction, and capacity fading mechanisms. Advanced (S)TEM studies for LIB materials pose numerous challenges and perspectives, including the development and application of local diffraction analysis, large‐scale phase mapping techniques, 3D reconstruction, and cryoelectron microscopy, which are further discussed.

Lab‐Scale In Situ X‐Ray Diffraction Technique for Different Battery Systems: Designs, Applications, and Perspectives

“…Due to the complexity of phenomena occurring in cycling and the difficulty in detecting samples with low crystallinity, it is important to combine with various characterization techniques on multiple scales to provide more comprehensive information . In situ XRD technique provides information about structure evolutions and phase transitions, while electron microscopy techniques can further support the results with direct evidence of morphology . Meanwhile, optical techniques are helpful to reveal chemical composition of electrodes.…”

Recent Progress in Advanced Characterization Methods for Silicon‐Based Lithium‐Ion Batteries

“…Additionally, the composition of the SEI and binder components, such as organic species and Li compounds generated during cycling, can be determined. Based on how the chemical shift of characteristic peak is affected by specific local environments, 7 Li NMR spectra are often used to clarify the Li compounds and the anode alloy states present during lithiation/ delithiation. With magic-angle spinning (MAS) configurations, high-resolution NMR spectra can be obtained, and information of greater detail can be obtained by in situ NMR characterization than by other NMR methods.…”

“…Key et al [10,82,83] systematically studied the short-range structure of the amorphous phase in Si anodes. Their latest results [10] report the investigation of the first charge and second discharge cycles using ex situ 7 Li MAS NMR spectroscopy. NMR spectra of anode samples were collected after a voltage that is near total amorphization of the crystalline Si matrix following the discharge cutoff and subsequent charge.…”

“…This result indicated that during discharge (lithiation of the amorphous Si), small Si clusters could form first; then, these clusters broke to form isolated Si anions, explaining the discharge hysteresis observed in the electrochemical profiles. In addition, Ogata et al [84] reported a study on the second and subsequent cycles using in situ 7 Li NMR spectroscopy, where the lithiation behaviors of amorphous Si in Si nanowires (SiNWs) were clearly visualized: small Si clusters formed during the second cycle in the electrochemical profile, and these small Si clusters may act as nuclei for the transformation of crystalline Li x Si to amorphous Li x Si, highlighting the key role of amorphous phases in the observed electrochemical performance.…”

“…[3][4][5][6] In addition to the demand for large-scale energy storage, the ever-growing global market of electric vehicles and portable electronic devices has also urged the development of efficient rechargeable batteries. [7] Among the various rechargeable batteries, the lithiumion battery (LIB) is expected to meet these needs because of its high energy density. [8] In the case of LIBs, the anode capacity is of great significance in improving the battery energy density.…”