Atomic‐Scale Structure Evolution in a Quasi‐Equilibrated Electrochemical Process of Electrode Materials for Rechargeable Batteries

Abstract

Lithium-ion batteries have proven to be extremely attractive candidates for applications in portable electronics, electric vehicles, and smart grid in terms of energy density, power density, and service life. Further performance optimization to satisfy ever-increasing demands on energy storage of such applications is highly desired. In most of cases, the kinetics and stability of electrode materials are strongly correlated to the transport and storage behaviors of lithium ions in the lattice of the host. Therefore, information about structural evolution of electrode materials at an atomic scale is always helpful to explain the electrochemical performances of batteries at a macroscale. The annular-bright-field (ABF) imaging in aberration-corrected scanning transmission electron microscopy (STEM) allows simultaneous imaging of light and heavy elements, providing an unprecedented opportunity to probe the nearly equilibrated local structure of electrode materials after electrochemical cycling at atomic resolution. Recent progress toward unraveling the atomic-scale structure of selected electrode materials with different charge and/or discharge state to extend the current understanding of electrochemical reaction mechanism with the ABF and high angle annular dark field STEM imaging is presented here. Future research on the relationship between atomic-level structure evolution and microscopic reaction mechanisms of electrode materials for rechargeable batteries is envisaged.

Ni and Co Segregations on Selective Surface Facets and Rational Design of Layered Lithium Transition‐Metal Oxide Cathodes

“…[17][18][19][20][21][22] For example, a surface reconstruction layer (SRL) was frequently observed on cathode particle surface after battery cycling, which was believed to act as a barrier for Li-ion transport and thus contribute to battery' high polarization and poor rate capability. [17][18][19][20][21][23][24][25] Moreover, such SRL keeps growing from particle surface into inner bulk as battery cycling continues, which is believed to contribute to battery's capacity and voltage decay. The nature of the surface layer also infl uences the solid electrolyte interphase (SEI), [ 21,[26][27][28] particle corrosion [ 22,29,30 ] and side reactions with the electrolyte, [ 26,28,29 ] all of which are critical to LIB performance.…”

Review—Post-Mortem Analysis of Aged Lithium-Ion Batteries: Disassembly Methodology and Physico-Chemical Analysis Techniques

“…119,136,137 Therefore, TEM unveils sample characteristics in terms of particle morphology, crystallinity, stress or even magnetic domains. However, due to the higher energy, beam damage has to be taken into account for battery materials.…”

Atomic‐Scale Monitoring of Electrode Materials in Lithium‐Ion Batteries using In Situ Transmission Electron Microscopy

“…ABF-STEM, in which the contrast has a low scaling rate with the atomic number, allows simultaneous imaging of light and heavy elements. [5,59,60] Gong et al used a state-of-the-art chip-based in situ TEM holder and found that the pristine single crystal LiCoO 2 became a nanosized polycrystal connected via coherent twin boundaries (TBs) and antiphase domain boundaries after high voltage delithiation at the atomic scale, and this was different from the case of a typical liquid electrolyte cell. [25] Liu et al studied the electrochemical lithiation/delithiation and the mechanics of few-layer graphene nanoribbons (GNRs) and found that, unlike multiwalled carbon nanotubes, lithiated GNRs were mechanically robust because of their unconfined stacking of planar carbon layers.…”

“…Significant progress has been made with respect to atomic-scale observations of quasiequilibrium states using ex situ transmission electron microscopy (TEM). [4][5][6] However, nonequilibrium states can relax into quasiequilibrium, and in such a case, they are not observed during ex situ experiments, which merely provide information regarding the initial and final phases with respect to lithiation kinetics. The intermediate phases corresponding to nonequilibrium electrochemical processes can only be detected using in situ characterization methods.…”