Space Charge Layer Evolution in All-Solid-State Batteries Probed via Operando Kelvin Probe Force Microscopy and...

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Ionics

Background:

• Space charge layers at solid-solid interfaces are critical but poorly understood in solid-state batteries (ASSBs).
• Existing controversies hinder the development of improved interfaces and overall ASSB performance.

Purpose of the Study:

• To investigate the role and characteristics of space charge layers in ASSBs.
• To quantitatively determine the interfacial resistance contribution of space charge layers.

Main Methods:

• Utilized operando heterodyne Kelvin probe force microscopy (KPFM) and operando nuclear reaction analysis (NRA).
• Studied a model thin-film ASSB: lithium (Li)|Li3PO4 (LPO)|LiCoO2 (LCO).
• Operated the battery within a voltage range of 3.0 to 4.3 V vs Li/Li+.

Main Results:

• Identified a space charge layer (<50 nm width) primarily at the LPO|LCO interface, caused by Li-ion redistribution.
• Quantitatively determined the interfacial space charge layer resistance, with a maximum of 18.4–19.1 Ω cm² at 4.3 V vs Li/Li+.
• Demonstrated that space charge layer resistance is significantly smaller than bulk solid electrolyte resistance in the studied ASSB.

Conclusions:

• Resolved controversies regarding the role of space charge layers in ASSBs.
• Advanced understanding of space charge layer evolution at solid electrolyte-electrode interfaces using KPFM and NRA.
• The findings suggest space charge layers have a limited impact on overall interfacial resistance in optimized ASSBs.