On the right the
cube represents the structure of lithium- and manganese- rich transition
metal oxides. The
models on the left show the structure from three different directions,
which correspond
to the STEM images of the cube.
(October 29, 2015) Berkeley
Lab scientists unravel structural ambiguities in lithium-rich transition metal
oxides.
Using complementary microscopy and spectroscopy techniques,
researchers at Lawrence Berkeley National Laboratory (Berkeley Lab) say they
have solved the structure of lithium- and manganese-rich transition metal
oxides, a potentially game-changing battery material and the subject of intense
debate in the decade since it was discovered.
Researchers have been divided into three schools of thought
on the material’s structure, but a team led by Alpesh Khushalchand Shukla and
Colin Ophus spent nearly four years analyzing the material and concluded that
the least popular theory is in fact the correct one. Their results were
published online in the journal Nature Communications in a paper titled,
“Unraveling structural ambiguities in lithium- and manganese- rich transition
metal oxides.” Other co-authors were Berkeley Lab scientists Guoying Chen and
Hugues Duncan and SuperSTEM scientists Quentin Ramasse and Fredrik Hage.
This material is important because the battery capacity can
potentially be doubled compared to the most commonly used Li-ion batteries
today due to the extra lithium in the structure. “However, it doesn’t come
without problems, such as voltage fade, capacity fade, and DC resistance rise,”
said Shukla. “It is immensely important that we clearly understand the bulk and
surface structure of the pristine material. We can’t solve the problem unless
we know the problem.”
Colin Ophus (left)
and Alpesh Khushalchand Shukla in front of the TEAM 0.5 microscope
at the Molecular
Foundry. (Photo by Roy Kaltschmidt/Berkeley Lab)
A viable battery with a marked increase in storage capacity
would not only shake up the cell phone and laptop markets, it would also
transform the market for electric vehicles (EVs). “The problem with the current
lithium-ion batteries found in laptops and EVs now is that they have been
pushed almost as far as they can go,” said Ophus. “If we’re going to ever
double capacity, we need new chemistries.”
Using state-of-the-art electron microscopy techniques at the
National Center for Electron Microscopy (NCEM) at Berkeley Lab’s Molecular
Foundry and at SuperSTEM in Daresbury, United Kingdom, the researchers imaged
the material at atomic resolution. Because previous studies have been ambiguous
about the structure, the researchers minimized ambiguity by looking at the
material from different directions, or zone axes. “Misinterpretations from
electron microscopy data are possible because individual two-dimensional
projections do not give you the three-dimensional information needed to solve a
structure,” Shukla said. “So you need to look at the sample in as many
directions as you can.”