Lithium dendrites, i.e. tiny crystalline thorns that grow off of lithium-ion battery anodes during charging, have been a persistent challenge for the world's most widely used form of energy storage. "Dendrites can penetrate the battery's separator, causing catastrophic short circuits and safety hazards," said Qing Ai, a former research scientist at Rice University who is a first author on a new study published in Science that reports for the first time exactly how these tricky structures behave inside batteries. "Despite decades of study, the fundamental nanomechanical properties of lithium dendrites remained a mystery—until now."