Nature Materials, Published online: 16 January 2026; doi:10.1038/s41563-025-02465-7Short-circuiting during fast charging through lithium dendrite intrusion into electrolytes is a major challenge in solid-state batteries. Here, using thermally annealed 3-nm-thick Ag coatings, lithium penetration into brittle electrolyte Li6.6La3Zr1.6Ta0.4O12 is inhibited at local current densities of 250 mA cm−2 due to an increase in surface fracture toughness.