Solid-state lithium batteries fail for the same reason over-bent paperclips snap – metal fatigue in the anode itself, according to a new study. The findings, which show that this fatigue follows well-documented mechanical behavior, provide a quantitative framework for predicting the cycle life of solid-state batteries, enabling new pathways for designing longer-lasting and safer energy storage systems. Solid-state lithium metal batteries (SSBs) promise both high energy and improved safety by combining a lithium metal anode with a solid, nonflammable electrolyte and a high-voltage cathode. However, their widespread use is hindered by early failure due to the growth of lithium dendrites—tiny, needle-like structures that can cause short circuits. Recent evidence suggests that mechanical factors play a more important role in failures than previously appreciated. The solid electrolyte, unlike liquid counterparts, struggles to absorb the stresses caused by lithium expansion and contraction during battery cycling. These stresses can lead to material fatigue, resulting in cracking, dendrite formation, and eventual failure, even when electrochemical conditions appear stable. However, lithium fatigue from the repeated stresses of battery cycling has been largely overlooked, leaving a gap in our understanding of long-term SSB reliability. Using scanning electron miscopy, phase-field simulations, and electrochemical analysis, Tengrui Wang and colleagues discovered that the failure of SSBs is closely linked to the cycle fatigue of the lithium metal anode, which leads to microcracks at the anode-electrolyte interface, driving degradation and dendrite growth – even at low current densities. Moreover, Wang et al. found that this fatigue follows well-established mechanical laws, namely the Coffin-Manson law, confirming it as an intrinsic and predictable property of the system. “The work of Wang et al. recognizes the importance of fatigue in the performance of lithium metal anodes in solid-state batteries,” write Jagjit Nanda and Sergiy Kalnaus in a related Perspective. “Further investigations should follow to describe the complex stress-strain state of lithium, including cycle rate, length scale, and temperature.”
