Mystery Solved: This Is Why Electric Car Batteries Destroy

An international research team has discovered the fundamental mechanism behind battery degradation and lifespan. Now they want others to use the knowledge to develop future batteries.
“Now that we understand what causes batteries to degrade, we can tell battery manufacturers what to improve in their designs,” says Professor Michael Toney.

Batteries lose their capacity over time. This is true for both those in mobile phones and those in electric cars. This phenomenon has never been properly explained before, but now an international research team from the University of Colorado Boulder has solved the mystery.

Lithium-ion batteries are the most common in the world, and they typically contain cobalt, a hazardous material for the environment. Battery engineers have tried replacing the material with nickel and magnesium, but it hasn’t worked very well and has reduced the amount of energy they can store.

The CBU research team chose to investigate the cause of lithium-ion battery self-discharge, and discovered that hydrogen molecules from the battery electrolyte had taken up places on the cathode where lithium ions would normally be. This meant that lithium ions had fewer places to bond to the cathode, weakening the electric current and reducing the battery capacity.

“We found that the more lithium you pull from the cathode during charging, the more hydrogen atoms accumulate on the surface,” says Zhang Wan, who is Author of the study on University of Colorado Boulder Home. This process leads to self-discharge and causes mechanical stress that can lead to cathode cracks and accelerate degradation.

The CBU researchers now hope their discovery will lead battery manufacturers to produce a new type of coating on the cathode of their batteries that blocks hydrogen molecules. Previously, scientists thought batteries self-discharged because not all of the lithium ions returned to the positive electrode when they were charged, reducing the number of charged ions available to create current and provide power.
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William Carlsson is a qualified journalist and has worked for Sveriges Radio and Sörmlands Nyheter, among others.