Scientists Finally Crack the Mystery of Why Lithium-Ion Batteries Die

Researchers have for the first time directly observed the mechanical behaviour of lithium dendrites, the needle-like metal structures that grow inside lithium-ion batteries during charging and are one of the leading causes of battery degradation and dangerous short circuits.

The study was conducted by teams from universities in the US and Singapore. Using high-resolution electron microscopy and specialized experimental platforms, the researchers isolated individual dendrites from operating battery cells and tested how they respond to stress.

The key finding overturns a long-standing assumption. Scientists had believed that because lithium metal is relatively soft and pliable, dendrites would behave the same way. Instead, the experiments showed the opposite: dendrites are stiff and brittle, snapping under pressure rather than bending.

Researchers have found that as dendrites develop, they get covered with a thin layer called the solid electrolyte interphase, or SEI for short. This coating gives the dendrites a stiffer, more needle-like shape. Because of this newfound rigidity, these structures can actually puncture battery separators and electrolytes, which raises the chances of internal short circuits.

The reason is a thin coating called the solid electrolyte interphase, or SEI, that forms around dendrites as they grow. This layer makes them rigid and capable of puncturing the internal separators that keep a battery’s positive and negative terminals apart.

When dendrites pierce a separator, they can create an internal short circuit, leading to battery failure or, in severe cases, thermal runaway. When they fracture instead, the broken fragments become electrically isolated “dead lithium” that accumulates inside the cell, gradually reducing its capacity. There is currently no practical method to clear dendrites from a working battery.

“To enable the quantitative study of lithium dendrites, we developed customized sample preparation and mechanical characterization platforms for such delicate work,” said Boyu Zhang, a Rice doctoral alum and co-lead author of the study.

The structures themselves are extraordinarily small, roughly 100 times thinner than a human hair, which is why observing them has been so difficult. Lithium is also highly reactive, meaning samples had to be handled in sealed environments to prevent contamination.

“Lithium dendrites are widely recognized as one of the biggest obstacles to the commercialization of lithium-metal batteries,” said Xing Liu, an assistant professor of mechanical and industrial engineering at New Jersey Institute of Technology.

For a long time, scientists thought that lithium dendrites were soft and flexible as lithium is generally pliable. But the experiments turned up some surprising results. Instead of being easily bendable, the dendrites acted more like brittle structures that could snap when put under stress.

The findings directly affect the development of lithium-metal batteries, which promise significantly higher energy density than current lithium-ion technology. However, they have long faced setbacks because of this exact problem. Researchers say these results could guide new strategies e.g., modifying anode materials, using lithium alloys to limit brittle fracture, and suppress dendrite growth.

You can read the complete research paper here.

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