# Linking Pressure to Electrochemical Evolution in Solid-State Conversion Cathode Composites

## TL;DR

This paper explores how pressure changes in solid-state batteries relate to electrochemical reactions in cathode materials like sulfur, FeS2, and FeF3.

## Contribution

The study introduces a method to link pressure evolution with electrochemical and structural changes in conversion cathode materials.

## Key findings

- Nonlinear stack pressure in cells is due to material-specific volume changes and reaction intermediates.
- Sulfur, FeS2, and FeF3 show distinct pressure evolution patterns linked to their unique reaction processes.
- Mesoscale modeling connects pressure measurements to particle-scale species evolution and intermediate phases.

## Abstract

Conversion-type cathodes, such as sulfur, FeS2, and
FeF3, offer high theoretical capacities in solid-state
lithium batteries but are hindered by substantial volume changes during
cycling, leading to interfacial contact loss, crack formation, and
microstructural degradation. Here, we investigate the relationships
between electrochemical, mechanical, and structural evolution in solid-state
electrode composites with these three active materials. Using real-time
stack-pressure monitoring, synchrotron X-ray absorption spectroscopy,
and electrokinetic modeling, we elucidate how stress evolution is
linked to reversible and irreversible redox reactions. Nonlinear stack
pressure evolution in cells with sulfur, FeS2, and FeF3 electrode composites is found to arise from material-specific
volume changes, the balance of volume change between the working and
counter electrode, and the formation of distinct reaction intermediates.
The three materials exhibit distinct stack pressure evolution, which
is closely related to the different reaction processes in the materials,
as demonstrated with X-ray absorption spectroscopy measurements. Through
mesoscale modeling, we relate the experimental measurements to species
evolution at the particle scale and track the dynamic coexistence
of intermediate phases. Our findings highlight the importance of designing
for volume changes of a given active material in solid-state battery
systems.