Direct Observation of a Li‐Ionic Space‐Charge Layer Formed at an Electrode/Solid‐Electrolyte Interface

Abstract

When two different materials come into contact, mobile carriers redistribute at the interface according to their potential difference. Such a charge redistribution is also expected at the interface between electrodes and solid electrolytes. The redistributed ions significantly affect the ion conduction through the interface. Thus, it is essential to determine the actual distribution of the ionic carriers and their potential to improve ion conduction. We succeeded in visualizing the ionic and potential profiles in the charge redistribution layer, or space‐charge layer (SCL), formed at the interface between a Cu electrode and Li‐conductive solid electrolyte using phase‐shifting electron holography and spatially resolved electron energy‐loss spectroscopy. These electron microscopy techniques clearly showed the Li‐ionic SCL, which dropped by 1.3 V within a distance of 10 nm from the interface. These techniques could contribute to the development of next‐generation electrochemical devices.

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.…”

“…Unfortunately, inspiring solutions for the SCL issue still remain to be explored owing to the unclear action mechanism of the SCL on interfacial lithium-ion transport in ASSLIBs. Although previous studies have tried to visualize the ionic and potential profiles in the SCL via in situ electron-holography transmission electron microscopy (EH-TEM) 20 , spatially resolved electron energy-loss spectroscopy (SR-EELS) 21 , and Kelvin probe force microscopy (KPFM) 22 , the SCL effect on interfacial lithium-ion transport is still unclear due to the lack of direct experimental evidence of the interfacial charge distribution and accumulation 23 , 24 . Furthermore, it has been reported that the oxide/sulfide interface exhibits more severe SCL effects than the oxide/oxide interface 25 .…”

Enabling a Durable Electrochemical Interface via an Artificial Amorphous Cathode Electrolyte Interphase for Hybrid Solid/Liquid Lithium‐Metal Batteries

“…The Li + will spontaneously migrate from the solid polymer interface to the cathode interface (Figure c), when they contact together, driven by the enormous discrepancy of chemical potential . At the same time, a steep potential drop is formed at the interface (NCM622/PDXL), which sharply raises Li ions diffusion impedance, deteriorates interfacial dynamics. Differently, after the ionic conducting Li x BO y F z is introduced in situ, the chemical potentials can be effectively coordinated, accompanied by a weakened space charge separation (Figure d) .…”

“…[6b, 7] Besides, the aggregation of space charge still exists across the cathode/polymer or cathode/ ceramic interface, [3a, 8] which is liable to hinder ionic transportation. [9] A valid scenario is urgently required to ameliorate the above instability to extend the application of hybrid solid/liquid electrolytes.…”

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.…”