Quantitative Operando Visualization of Electrochemical Reactions and Li Ions in All-Solid-State Batteries by STEM-EELS with Hyperspectral Image Analyses

Abstract

All-solid-state lithium-ion batteries (LIBs) are one of the promising candidates to overcome some issues of conventional LIBs with liquid electrolytes. However, high interfacial resistance of Li-ion transfer at the electrode/solid electrolyte limits their performance. Thus, it is important to clarify interfacial phenomena in a nanometer scale. Here, we present a new method to dynamically observe the Li-ion distribution and Co-ion electronic states in a LiCoO cathode of the all-solid-state LIB during charge and discharge reactions using operando scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS). By applying a hyperspectral image analysis of non-negative matrix factorization (NMF) to the STEM-EELS, we succeeded in clearly observing the quantitative Li-ion distribution in the operando condition. We found from the operando observation with NMF that the Li ions did not uniformly extract/insert during the charge/discharge reactions, and the activity of the electrochemical reaction depended on the Li-ion concentration in a pristine state. An electrochemically inactive region was formed about 10-20 nm near the LiCoO/LiO-AlO-TiO-PO-based solid electrolyte interfaces. The STEM-EELS, electron diffraction, and Raman spectroscopy experimentally showed that the inactive region was a mixture of LiCoO and CoO, leading to the higher interfacial resistance of the Li-ion transfer because CoO does not have pathways of Li-ion diffusion in its crystal.

In-situ visualization of the space-charge-layer effect on interfacial lithium-ion transport in all-solid-state batteries

“…Therefore, there is no doubt that the electric field due to the MIP difference interferes with the DPC-STEM result (only from the SCL) at 0 V to some extent. The Li element mapping obtained by EELS can reflect the migration of Li ions after cathode/electrolyte contact 21,38,39 , so we further analyze the Li and Co elemental profiles from the EELS line scan ( Supplementary Fig. 8) under 0 V at the interface.…”

“…The Li element mapping obtained by EELS can reflect the migration of Li ions after cathode/electrolyte contact 21 , 38 , 39 , so we further analyze the Li and Co elemental profiles from the EELS line scan (Supplementary Fig. 8 ) under 0 V at the interface.…”

Ex-situ Analysis of Lithium Distribution in a Sulfide-based All-solid-state Lithium Battery by Particle-induced X-ray and Gamma-ray Emission Measurements

“…The available techniques for analyzing the light element lithium are mostly limited to scanning transmission electron microscopy combined with electron energy loss spectroscopy. 13,14 However, these techniques are not suitable for analyzing the composite at micrometer scales of the powders.…”

Direct Observation of Ion Concentration Distribution in All-Solid-State Rechargeable Battery Using <i>operando</i> X-ray Radiography and Silver-Ion Conductor

“…Direct observation is difficult owing to the lightness of the lithium ion, which is generally difficult to detect. Although heterogeneous reaction of LiCoO 2 thin films at the nanoscale has been observed by operando scanning transmission electron microscopy and electron energy-loss spectroscopy, 17 the macroscopic reaction distribution phenomena in all-solid-state batteries has not been understood thus far. Observation of the solid electrolyte and composite electrode over hundreds of micrometers is necessary to understand the characteristic behavior of all-solid-state rechargeable batteries.…”