Solid-state batteries are often described as the future of energy storage.
They could allow phones to run for days without charging and give electric cars much longer driving ranges.
Compared with today’s lithium-ion batteries, they are also expected to be safer and longer-lasting. But one stubborn problem has slowed their progress: they can suddenly fail due to internal short circuits.
A new study from the Max Planck Institute for Sustainable Materials helps explain why this happens.
The research, published in Nature, focuses on tiny structures called dendrites—branch-like formations that grow inside batteries during charging.
In a typical lithium-ion battery, a liquid sits between two solid parts to help ions move. In solid-state batteries, that liquid is replaced with a solid material. This design sounds safer, but it introduces a new challenge.
As the battery charges, lithium metal can form thin, needle-like dendrites that grow from one side and push into the solid material. If they reach the other side, they create a shortcut for electricity, causing a short circuit.
What makes this puzzling is that lithium metal is very soft—almost like a gummy candy. The solid material it pushes through, often a ceramic, is much harder. So how can something so soft break something so stiff?
The researchers explored two main ideas. One possibility was that stress builds up inside the growing dendrites until they crack the material. Another idea was that tiny electrical leaks inside the solid material help new lithium deposits form, which then connect and create a pathway.
To find the answer, the team carried out highly controlled experiments. They studied the materials under vacuum and extremely cold conditions to avoid any outside interference. Using advanced imaging and analysis techniques, they observed what was happening at a very small scale.
Their results showed that the first explanation is the correct one. As dendrites grow, pressure builds up inside them. Even though the lithium itself is soft, this pressure becomes strong enough to crack the surrounding solid material. The researchers compared it to a high-pressure water jet cutting through rock. Over time, this pressure causes tiny fractures, allowing the dendrites to keep pushing forward until a short circuit forms.
Understanding this process is an important step forward, because it suggests ways to fix the problem. If scientists can make the solid material tougher, it may resist cracking for longer. Another idea is to design the material with tiny gaps that redirect the dendrites, preventing them from growing straight through. Protective layers on the lithium surface could also slow down dendrite formation.
These findings show that solving battery problems is not just about chemistry, but also about understanding how materials behave under stress. With better designs based on this knowledge, solid-state batteries could move closer to real-world use, bringing safer and more powerful energy storage to everyday devices.
