Measuring the buried interphase between solid electrolytes and lithium metal using neutrons

TL;DR

This study compares neutron depth profiling and neutron reflectometry to analyze buried interfaces in solid-state lithium batteries, revealing gradient interphases less than 30 nm thick and demonstrating complementary resolution capabilities.

Contribution

It introduces a combined neutron-based approach to non-destructively characterize buried solid electrolyte-electrode interfaces across multiple length scales.

Findings

NR detects gradient interphases less than 30 nm thick.

NDP resolves features in the 50 nm to 1 mm range.

Combined methods offer comprehensive interface insights.

Abstract

Interfaces are the key to next generation high energy batteries including solid state Li metal batteries. In solid state batteries, the buried nature of solid solid electrolyte electrode interfaces makes studying them difficult. Neutrons have significant potential to non destructively probe these buried solid solid interfaces. This work presents a comparative study using both neutron depth profiling (NDP) and neutron reflectometry (NR) to study a model lithium metal-lithium phosphorus oxynitride (LiPON) solid electrolyte system. In the NDP data, no distinct interphase is observed at the interface. NR shows a difference between electrodeposited, and vapor deposited LiPON -Li interfaces but finds both are gradient interphases that are less than 30 nm thick. Additional simulations of the LiPON-Li2O-Li system demonstrate that NDP has an excellent resolution in the 50 nm-1 mm regime while NR has an ideal resolution from 0.1 - 200 nm with different sample requirements. Together NDP and NR can provide a complementary understanding of interfaces between Li metal and solid electrolytes across relevant length scales.