Researchers at the University of Oxford have conducted a study revealing the mechanisms that cause failures in lithium metal solid-state batteries (Li-SSBs). The findings offer a path to overcome these challenges and potentially lead to a transformative improvement in electric vehicle (EV) battery range, safety, and performance.

The team said their research could also have far-reaching implications for electric aviation, propelling the development of electrically powered aircraft.

Li-SSBs differ from conventional batteries by replacing the flammable liquid electrolyte with a solid electrolyte and utilizing lithium metal as the anode.

The use of solid electrolytes enhances safety, while the incorporation of lithium metal allows for greater energy storage capacity.

However, a critical hurdle Li-SSBs face is the occurrence of short circuits during the charging process caused by the formation of dendrites. The study finds that these filament-like structures composed of lithium metal penetrate the ceramic electrolyte, leading to performance degradation and safety concerns.

Analyzing the Li-SSB Failures

As part of a collaborative effort between the University of Oxford’s Departments of Materials, Chemistry, and Engineering Science, researchers utilized advanced imaging techniques, specifically X-ray computed tomography at Diamond Light Source, to visualize dendrite failure during charging.

The study reveals that dendrite cracks initiate and propagate through distinct underlying mechanisms. Cracks form due to lithium accumulation in sub-surface pores, and further charging increases the pressure until the cracks propagate.

The propagation occurs through a wedge-opening mechanism, with lithium partially filling the crack and driving it open from behind.

Implications for Future Li-SSB Development 

The researchers said the newfound understanding of dendrite behavior in Li-SSBs holds viable promise for overcoming technological challenges.

Dominic Melvin, co-lead author of the study, emphasized the importance of balancing pressure within the lithium anode. The study reveals that while pressure is necessary to avoid gaps at the interface with the solid electrolyte during discharge, excessive pressure can be detrimental, increasing the likelihood of dendrite propagation and short-circuiting during charging.

The insights open avenues for refining battery designs and optimizing operating conditions to mitigate dendrite formation and enhance battery performance.

Professor Sir Peter Bruce, a key researcher involved in the study, highlighted the significance of comprehending how a soft metal like lithium can penetrate a dense ceramic electrolyte and hopes that the insights will help the progress of solid-state battery research toward a practical device.

According to a recent report by the Faraday Institution, solid-state batteries have the potential to fulfill substantial portions of global battery demand.

By 2040, they are projected to meet 50% of battery demand in consumer electronics, 30% in transportation, and over 10% in aircraft applications.

Professor Pam Thomas, CEO of the Faraday Institution, emphasized the importance of research initiatives like these, which tackle the mechanistic understanding of solid-state battery failures, as these endeavors pave the way for strategies that cell manufacturers can adopt to avoid such failures and drive advancements in battery technology.

A recent study by the Karlsruhe Institute of Technology (KIT) found that the formation of the solid electrolyte interphase, which is crucial for the functioning of lithium-ion batteries, occurs through the aggregation of solutions rather than directly at the electrode. The findings offer insights into developing more efficient and long-lasting batteries in the future.

In April this year, Nanyang Technological University NTU Singapore partnered with Se-cure Waste Management (SWM), a Singapore-based battery recycling and processing firm, to recycle spent lithium-ion batteries using biomass.