# Tracking Interphase Growth at Alloy Anode Interfaces in Sulfide Solid-State Batteries

## TL;DR

This study examines how alloy anodes interact with a solid-state electrolyte, finding that they form thinner and more stable interphases compared to lithium metal.

## Contribution

The study introduces a detailed analysis of interphase growth on alloy anodes in sulfide solid-state batteries, revealing their potential for enhanced stability.

## Key findings

- Interphase thickness on alloy anodes is less than half that of pure Li metal after 400 h.
- Interphase growth rate depends on stack pressure and varies among alloy materials.
- Alloy anodes show thinner and more uniform interphase growth compared to Li metal.

## Abstract

The chemical stability
of solid-state electrolytes (SSEs)
in contact
with negative electrode materials is essential to enable high performance
and safety of solid-state batteries (SSBs). While interphase layers
are known to form between Li metal and various sulfide SSEs, there
is a lack of understanding of interphase growth in contact with other
promising anode materials, such as silicon and aluminum alloys. Here,
we track and quantify interphase growth rate, thickness, and composition
of various alloy anode thin films in contact with the widely used
argyrodite Li6PS5Cl SSE. Using coulometric titration
time analysis (CTTA), we find that the average interphase thickness
on four alloy anode materials (Ag, Al, Si, and Ge) is less than half
that of pure Li metal after 400 h of growth. Furthermore, the interphase
growth rate is strongly dependent on the applied stack pressure and
varies among the different alloy materials. The interfacial contact
area, which is governed by alloy mechanical properties and deformation
under stack pressure, is found to be a critical factor in determining
interphase growth rate. Time-of-flight secondary-ion mass spectrometry
further confirmed thinner and uniform interphase growth on alloy anodes
compared to Li metal. This study bolsters our understanding of interfacial
stability of various alloy anode materials married with Li6PS5Cl SSE, and it suggests that alloy anodes could exhibit
enhanced stability compared to Li in sulfide SSB applications.