Cracking the Code on Lithium Battery Safety
New research reveals hidden risks in solid-state designs — and a path toward safer, longer-lasting batteries. They’re small, powerful, and packed with potential — but lithium batteries still have one explosive problem: dendrites. These tiny, needle-like metal structures can grow inside a battery, short-circuit it, and in the worst cases, cause fires or explosions. Until now, scientists believed they had a solution. Solid-state batteries, especially those using polymer-based electrolytes, were thought to be the ultimate fix — stable, solid, and far less flammable than liquid-based designs. But a team at the Technical University of Munich (TUM) has just discovered something that could change that narrative. Their research shows that dendrites can form not only at the electrodes — where they were expected — but also within the polymer electrolyte itself. That’s the very material meant to prevent these dangerous growths. “Our measurements show that dendrite growth can also occur directly inside the polymer electrolyte — in the very material designed to stop it,” says Fabian Apfelbeck, a physicist pursuing his doctorate at TUM and lead author of the study. This revelation could reshape how scientists approach solid-state battery design. To uncover this hidden process, the TUM team used a nanofocus X-ray technique at the German Electron Synchrotron (DESY) in Hamburg. With an X-ray beam just 350 nanometers wide — roughly 200 times thinner than a human hair — they watched structural changes unfold inside a working battery for the first time. The finding surprised even seasoned researchers. “We’ve long assumed dendrites only grow at the interface between electrode and electrolyte,” explains Prof. Peter Müller-Buschbaum, who leads TUM’s Chair of Functional Materials. “Seeing them form deeper inside the material challenges that assumption completely.” Understanding where dendrites form — and why — is a critical step toward creating safer, longer-lasting, and more efficient solid-state batteries. With this knowledge, researchers can now focus on developing electrolytes that stop internal crystallization before it starts. The study, “Local crystallization inside the polymer electrolyte for lithium metal batteries observed by operando nanofocus WAXS,” was published in Nature Communications in 2025.
