Cause of pesky failure mode in solid state Li-ion batteries found Premium

Scientists discover mechanical laws behind solid-state battery failures, paving the way for longer lifetimes.

Scientists have reported in Science that the key to fixing solid-state battery (SSB) failures may lie in well-documented mechanical laws, paving the way for longer operational lifetimes.

A battery consists of an electrolyte sandwiched between the positive cathode and the negative anode. “In most batteries, including lithium-ion batteries in your cell phone, this electrolyte is a liquid solution, very similar to salt in water, that allows ions to move back and forth from the electrodes,” said Naga Phani B. Aetukuri, an associate professor at the Indian Institute of Science, Bengaluru, not involved in the new study. His team is among the top groups in India developing SSBs.

In a battery, ions move freely through the electrolyte while electrons flow from the cathode to the anode via an external circuit, charging the battery. In the reverse process, the electrons given up by the lithium (Li) anode travel to the cathode via the external circuit, powering it. Inside the battery, the corresponding lithium ions scurry to the cathode through the electrolyte during discharge.

In an SSB Li-ion battery, a ceramic block is the electrolyte. Solid electrolytes last longer, can store more energy, and are neither volatile nor flammable. Their solid structure separates the two electrodes well, reducing the need for bulky safety equipment and their weight. Currently, pacemakers and smartwatches use SSBs.

On the flip side, solids can crack, so solid electrolytes are inhospitable to volume changes or higher stress. This causes a persistent problem called dendrite growth. Li ions shuttle to the anode while charging and are deposited there, forming lithium filaments at the anode.

“Have you ever seen hairy roots growing from a central root? This occurs in plants to maximise their ability to receive nutrients,” Aetukuri said. Like a plant root, the anode tries to absorb as many ions as it can. “The dendritic growth of Li in SSBs maximises the anode’s ability to receive the most Li ions coming its way.” But like roots penetrate rocks, the dendrites pierce the electrolyte layer and reach the cathode, creating a short circuit.

Scientists don’t know the actual physical mechanism that causes such a failure. Now, researchers from Tongji University in Shanghai and other institutions have said the answer may lie in a known mechanical problem.