# Effect of Process Duration on Electrochemical Performance in Composite Cathodes for All-Solid-State Li-Ion Batteries Processed via Warm Isostatic Pressing

## TL;DR

This study shows how the duration of warm isostatic pressing affects the performance of composite cathodes in all-solid-state lithium-ion batteries.

## Contribution

The study identifies process duration as a critical factor in optimizing interfacial properties and electrochemical performance in composite cathodes.

## Key findings

- Shorter WIP treatments (1 s) resulted in lower specific capacities (80 mAh g–1) due to voids in solid electrolytes.
- Longer WIP treatments (60–1800 s) eliminated voids and improved specific capacities to around 125 mAh g–1.
- Lower-temperature WIP caused insufficient densification and additional degradation modes like cracks.

## Abstract

Isostatic pressing is frequently used to densify various
components
of all-solid-state batteries (ASSBs). Among these, warm isostatic
pressing (WIP) has proven to be a useful technique for ASSB production.
We conducted a parametric study of the performance of composite cathodes
treated with WIP to investigate the effect of the process duration
on the performance of ASSBs. Electrochemical impedance spectroscopy
(EIS) and charge–discharge performances of the test cells were
examined to determine the interfacial properties of the composite
cathodes. X-ray computed tomography (CT) using synchrotron radiation
was performed before and after WIP to correlate the interfacial properties
with the microstructures of the composite cathodes. Our findings showed
that the test cells had specific capacities of around 125 mAh g–1 when the composite cathodes were treated with WIP
for 60–1800 s. However, for shorter WIP treatments (1 s), it
remained around 80 mAh g–1, which is two-thirds
of those obtained from longer WIP. According to the X-ray CT analysis,
the cathodes treated with one s WIP contained a large number of small
voids in the solid electrolytes (SE). Such voids were eliminated during
longer WIP treatments. The change in the void ratio correlated well
with the EIS results, suggesting that the resistance related to charge
transfer was the dominant factor determining the performance of the
ASSBs. The lower-temperature WIP resulted in insufficient densification.
Additional degradation modes were enhanced in the low-temperature
regime, probably due to the formation of gaps and cracks. In conclusion,
process duration is a crucial factor in determining the performance
of composite cathodes and hence should be carefully controlled to
obtain suitable interfacial properties between the active materials
and SEs. The presented results give insights into the comprehension
of the interface issues in the ASSBs from both scientific and industrial
aspects. They contribute to further improvement of the electrochemical
performance of ASSBs.