Solid-State Electrolytes: X-ray CT Reveals Fast Degradation

Solid-state lithium batteries (SSLBs) are gathering a lot of attention as the next generation of batteries for high-performance technologies due to having a higher energy density and safety compared to conventional Li-ion batteries―thanks to their non-flammable electrolytes and high-capacity lithium metal anode. There’s a lot of interest in developing SSLBs for electric vehicles (EVs), but there still needs to be a better understanding of the degradation mechanisms of the solid-state electrolytes for them to become more commercially viable on a large scale. 

Barriers in Solid-State Commercialisation in EVs 

Several obstacles remain in the implementation of SSLBs on a large scale. This ranges from a low ionic conductivity of the electrolyte, challenges at the electrode-electrolyte interface, and the potential for short circuiting due to dendrite growth (where lithium fills in cracks within the solid electrolyte, leading to rapid deterioration once those initial cracks have formed). Because very minute cracks in the electrolyte can have drastic consequences, it means that mechanical forces inside the battery can also be a challenge due to the limited space to accommodate volumetric changes while cycling. 

Understanding the morphological evolution of the solid-state electrolyte is crucial for understanding the different degradation processes―such as mechanical cracking and propagation, lithium penetration into cracks, and interfacial degradation. However, directly observing these changes is difficult due to their close contact with the electrodes and the electrolyte being buried deep in the battery, meaning that many microscopy techniques are not suitable for imaging the degradation progression in situ and rely on the electrolyte being removed. Removal of the electrolyte from the battery leads to characterisation in non-realistic operational scenarios and can’t capture the dynamic changes during charge and discharge. So, to truly capture what is happening in the solid-state electrolyte, imaging methods that can provide real-time observations are required, and that is where X-ray computed tomography (CT) comes in. 

X-ray Computed Tomography (CT) Used to Track Solid State Electrolyte Degradation 

X-ray CT is a non-destructive way of detecting and 3D imaging the internal structures of SSLBs. In a recent study, researchers built on their previous work of using x-ray CT to study battery structures and used it to study the 3D morphological evolution of the Li3PS4 (LPS) solid electrolyte during cycling of the SSLB. The electrolyte was studied during the cycles until it short circuited due to excessive degradation. 

The process of measuring the degradation involved initiating cracks within the electrolyte. Cracks in the electrolyte were alternately generated using the two electrode-electrolyte interfaces and continued propagating the cracks until the battery shorted. 3D images of the degradation were reconstructed at every stage of the electrolyte cracking. 

The initial cracks were formed during the first cycle, and lithium dendrites filled the cracks. However, they had a low filling ratio after the first plating cycle, and this allowed the electrolyte to continue working until it became fully fractured with cracks. The filling of the cracks with lithium ions during each cycle added direct stress to the crack walls, causing them to grow in both length and width. The electrolyte was bent back and forth due to the lithium depositing into the partially filled cracks from two directions during charging and discharging. 

The researchers looked at how the mechanical force and electric potential fields are redistributed during cycling, investigating the speed of crack propagation, the changes in electrode thickness, and the filling ratio of lithium deposition in cracks. It was found that the two lithium electrodes became compressed within the first 5 cycles of the testing, leading to a 4-7 μm reduction in thickness, a fast crack propagation, and a high filling ratio occurred in the initial cycles. It was also found that the majority of the major electrode changes were confined to the initial cycling stages and that there was a fast degradation of the solid electrolyte. Another important aspect is that after the fast initial degradation, the partially filled cracks caused a lag in a short circuit because the strain energy in the cracks was largely released after each charge and discharge, so the battery worked with stable voltage curves for a while.  

After the initial large deposition, the lithium slowly filled the cracks, and this created an electrical connection between the cathode and the anode. In this study, this happened quickly in terms of overall battery life, with short circuiting occurring after only the 15th cycle. This led to the battery cell working for less than 7 hours after the solid electrolyte was penetrated, showing how quickly solid electrolytes can degrade if they experience mechanical and electrochemical degradation. 

Tackling Early Degradation to Enable the Future of Solid-State Batteries 

The findings from this study make it clear that the earliest stages of degradation in solid-state lithium batteries are the most critical. Once initial cracking occurs, the degradation process accelerates rapidly and can lead to catastrophic failure in a matter of hours. The research highlights how these cracks allow lithium to infiltrate and exert mechanical stress on the solid electrolyte, causing it to fracture further until the cell short circuits.

This understanding presents both a challenge and an opportunity. For solid-state batteries to become commercially viable—particularly in electric vehicles where reliability and safety are paramount—engineers must develop strategies to mitigate or entirely prevent the onset of these early-stage failures. Potential pathways could include materials engineering to improve the fracture toughness of solid electrolytes, design optimisations that allow for mechanical strain relief, or even self-healing materials that can arrest crack propagation before it becomes irreversible.

By identifying how and when degradation initiates, and using advanced imaging techniques like X-ray CT to visualise the failure mechanisms in real time, researchers now have powerful tools to guide the development of more robust SSLB systems. As innovation continues, these insights will be essential for bridging the gap between experimental success and large-scale deployment—bringing the promise of safer, higher-performance batteries closer to reality.

Reference: 

Hao S. et al, Fast Degradation of Solid Electrolyte in Initial Cycling Processes, Tracked in 3D by Synchrotron X-ray Computed Tomography, ACS Nano, 19(22), (2025), 20516–20525.