Breakthrough Study Uncover Key Cause of Battery
Using multiscale X-ray diffraction and high-resolution electron microscopy, researchers discovered that structural changes in the lattice of the cathode are responsible for its degradation after repeated charge-discharge cycles.
The cathode is a crucial component of batteries, with several potential materials offering the promise of significantly higher energy storage and extended driving ranges. However, the capacity, or the amount of current a battery can provide over a given time, tends to decrease rapidly with repeated charge-discharge cycles for reasons that have not been well understood.
Researchers at the U.S. Department of Energy’s (DOE) Argonne National Laboratory have uncovered the primary reason behind the degradation of one of the more promising cathode materials: lithium nickel manganese cobalt (NMC) oxide, which is rich in nickel and exists in the form of single nanosized crystals.
In single crystals, atoms are arranged in a highly ordered, uniform pattern. Typically, a nickel-rich NMC cathode is composed of multiple crystalline forms, or polycrystals, randomly oriented with respect to each other. During charge-discharge cycles, these polycrystalline clusters develop cracks at the boundaries between crystals, leading to a rapid decline in cathode capacity. In single crystals, the atoms are arranged in orderly rows and columns, known as lattices.
The research team developed an innovative method that combines multiscale X-ray diffraction and high-resolution electron microscopy to study the changes in the lattice structure of single-crystal cathodes during charging and discharging. They discovered that introducing a charge causes strain on the lattice, causing it to expand and rotate, disrupting the orderly arrangement of atoms. When the battery discharges, the lattice contracts back to its original state, but the rotation remains. With repeated charge-discharge cycles, this rotation becomes more pronounced, leading to significant structural changes in the cathode and a steep decline in performance.
“The team’s innovative method was crucial in uncovering why nickel-rich NMC cathodes with single crystals degrade so quickly,” said Khalil Amine, an Argonne Distinguished Fellow. “This new insight provides us with the tools to address this problem and pave the way for more affordable electric vehicles with extended driving ranges.”
