In Situ Observation of the Effect of Accelerating Voltage on Electron Beam Damage of Layered Cathode Materials for Lithium-Ion Batteries

Abstract

Electron beam damage from transmission electron microscopy of layered lithium transition-metal oxides is a threshold phenomenon that depends on the electron beam energy, which we demonstrate in this study by varying the accelerating voltage of a scanning transmission electron microscope. The electron beam irradiation experiment shows that Ni in LiNiO 2 has much lower threshold energy for displacement than Co in LiCoO 2 , which is supported by DFT calculations predicting that Ni has lower migration energy. The transition-metal ions are reduced from the oxidation state of +3 to +2 during migration from their original positions to the lithium sites, and Ni is more easily reduced than Co because of its electronic configuration. In addition, the high-energy electron beam induces oxygen release, which is another symptom of degradation of materials that occurs more strongly in Ni-containing materials with ion displacement.

Deep Learning‐Assisted Quantification of Atomic Dopants and Defects in 2D Materials

“…Continuous electron bombardment at high accelerating voltages usually induces structural modifications by elastic knock‐on collisions, breakage of ionic bonds by inelastic radiolysis reaction, or other phenomena such as heating and electrostatic interactions. [ 8 , 9 , 25 , 26 , 27 , 28 , 29 ] In 2D TMDs under a relatively low accelerating voltage, the radiolysis interaction between electrons of sample atoms and electron beam occurs dominantly, preferentially accompanying the sublimation of chalcogen ions. [ 3 , 25 ] This radiation‐induced change is known to appear as a threshold phenomenon depending on the total electron dose, and can be used as a means of point defect engineering and for fundamental studies of structural response under harsh irradiation environments.…”

“…Intriguingly, the content of V dopants under continuous electron beam irradiation remained almost constant (green graph in Figure 5c ), which suggests that anions are more susceptible to the radiolysis interaction with the electron beam than cations, which is in accordance with many studies on electron beam interactions. [ 3 , 9 , 21 , 27 , 30 ] This dynamics of defect generation behavior was first revealed from the massive image dataset with the help of deep learning‐assisted quantification, which does not require data sampling to reduce the load of interpretation at the cost of accuracy.…”

“…The tradeoff relationship between electron beam irradiation damage and signal‐to‐noise ratio (SNR) is another issue that needs to be considered. [ 7 , 8 , 9 ] The electron dose can be reduced by increasing the scanning rate of the electron probe to mitigate the radiation‐induced damage of the sample. However, ADF images acquired in low electron dose conditions are often too noisy to be analyzed for quantitative estimation of atomic defects.…”

Intrinsic Li Distribution in Layered Transition-Metal Oxides Using Low-Dose Scanning Transmission Electron Microscopy and Spectroscopy

“…Cation mixing or phase transformations caused by the electron beam are very similar to those resulting from charge−discharge cycling. 3,26 The high-energy electron beam induces oxygen release, which is another symptom of material degradation that occurs more strongly in Nicontaining materials with ion displacement. Since the degradation features caused by the electron beam are very similar to those by electrochemical cycling, TEM analysis should be performed with minimized beam exposure to obtain the intrinsic structural information of layered cathode materials.…”

“…Li is the lifeblood of the current battery technologyunderstanding where and how it distributes within the electrodes is crucial to the full understanding and knowledge of the energy storage system . The small atomic number of Li makes it highly susceptible to be displaced from its true intrinsic position by energy transfer from impinging high-energy irradiation, such as electron beams. − This makes it a difficult element to image in its intrinsic state at the atomic and nanoscale levels using transmission electron microscopy (TEM) methods. Reducing the dose of incoming electrons to the sample often leads to reduced damage. , Systematic studies at the atomic level of Li-ion battery materials that directly address the electron dose dependence on damage are limited and more work is needed to understand the benefits that can be obtained using low-dose scanning TEM (STEM) imaging and spectroscopy.…”