Battery flaw exposed: Why solid-state cells short-circuit under lithium dendrite stress

Researchers at the Max Planck Institute for Sustainable Materials have uncovered how lithium dendrites trigger fractures inside solid-state batteries, a finding that could help solve one of the biggest roadblocks facing next-generation energy storage. Solid-state batteries are widely seen as a future replacement for today’s lithium-ion cells because they can potentially store more energy, last longer, and improve safety. They replace the flammable liquid electrolyte used in conventional batteries with a solid ceramic electrolyte. But a major issue has slowed commercialization. During charging, tiny lithium structures known as dendrites can grow from the electrode, pierce the solid electrolyte, and create internal short circuits. The new study explains how that happens. Instead of electrons leaking ahead of the dendrite tip, researchers found that internal stress builds inside the lithium metal until it cracks the stiff ceramic barrier. Soft metal, hard break “Although the electrodes and the forming dendrites consist of lithium metal, which is soft like a gummy bear, the dendrites are able to penetrate the ceramic electrolyte and lead to a short circuit,” said Dr. Yuwei Zhang, first author of the study and head of the group “Chemo-Mechanics of Battery Materials” at MPI-SusMat. To investigate the failure process, the team prepared and analyzed battery samples under vacuum and cryogenic temperatures. This helped eliminate interference from oxygen, moisture, or microscope beam effects that could alter the results. The researchers examined lithium trapped inside cracks and found no evidence that lithium was accumulating ahead of the dendrite tip. That weakened one leading theory that electrons leaking along grain boundaries were causing new lithium growth inside the ceramic. Instead, the team concluded that hydrostatic pressure inside the dendrite creates enough tensile stress to fracture the electrolyte. “The soft lithium metal is able to penetrate the stiff ceramic el…