Abstract
The investigation of chemical and structural dynamics in battery materials is essential to elucidation of structure-property relationships for rational design of advanced battery materials. Spatially resolved techniques, such as scanning/transmission electron microscopy (S/TEM), are widely applied to address this challenge. However, battery materials are susceptible to electron beam damage, complicating the data interpretation. In this study, we demonstrate that, under electron beam irradiation, the surface and bulk of battery materials undergo chemical and structural evolution equivalent to that observed during charge-discharge cycling. In a lithiated NiO nanosheet, a Li2CO3-containing surface reaction layer (SRL) was gradually decomposed during electron energy loss spectroscopy (EELS) acquisition. For cycled LiNi0.4Mn0.4Co0.18Ti0.02O2 particles, repeated electron beam irradiation induced a phase transition from an layered structure to an rock-salt structure, which is attributed to the stoichiometric lithium and oxygen removal from 3a and 6c sites, respectively. Nevertheless, it is still feasible to preserve pristine chemical environments by minimizing electron beam damage, for example, using fast electron imaging and spectroscopy. Finally, the present study provides examples of electron beam damage on lithium-ion battery materials and suggests that special attention is necessary to prevent misinterpretation of experimental results.
Highlights
Correspondence and requests for materials should be addressed to Chemical and Structural Stability of Lithium-Ion Battery Electrode Materials under Electron Beam
We showed that, in NiO nanosheets, the surface reaction layer (SRL) are primarily composed of Li2CO3 embedded in a complex organic matrix[6]
We showed that the combined knock-on, ionization, and thermal effects of the electron beam readily broke down the surface structure leading to the degradation of the SRL
Summary
The chemical environment at the particle surface determines the way an active electrode interacts with its surrounding electrolyte and impacts the resulting cycling behaviors. Surface modifications, such as artificial solidelectrode interphases, were reported to improve cycling performance[16,17]. Lithium-containing compounds (e.g., electrode materials, SRLs) are degraded under electron beams due to the knock-on effect (i.e., atomic displacements by electronnuclear collisions)[22] and thermal effects It is critical to distinguish these processes from those arising from the electrochemistry to ensure the correct interpretation of the experimental results
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