A multi-national team of scientists have found a mixed sodium oxide, patented by vehicle OEM Renault, could be a promising sodium-ion cathode material.
A team made of researchers from Russia, France, the US, Switzerland, and Australia created and mixed a Na(Li1/3Mn2/3)O2 oxide they believe could one day complement, or replace, lithium-ion batteries.
The team found the compound showed promise as a cathode material with high energy density, no voltage fade over multiple charge cycles, and moisture stability.
To date, sodium technology has failed to match lithium-ion’s high energy density and cycling stability.
The paper, detailing their search for an optimal design for Na-based cathodes, was published in the journal Nature Materials.
The team investigated the crystal structure of Na(Li1/3Mn2/3)O2 using electron diffraction and directly visualised it with atomic resolution scanning transmission electron microscopy (TEM) techniques.
Additional studies of the material at various states of charge were observed using TEM, which allowed the researchers to trace the evolution of its crystal structure during cycling.
The team found the new compound possesses a reversible specific discharge capacity of 190 mAh/g. It also demonstrated a good capacity retention and moisture resistance. No significant voltage fade was observed during prolonged cycling —a key drawback of similar lithium-rich, layered cathode materials.
However, despite these promising results, Na (Li1/3Mn2/3)O2 exhibits a large voltage hysteresis during cycling, which leads to a decrease in the energy efficiency of the cathode material. That may create an obstacle in commercial implementation, according to the team.
Skoltech professor and director of the Center for Energy Science and Technology, Artem Abakumov, and PhD student Anatolii Morozov were part of an international team.
Morozov said: “We assume that the appearance of a large voltage hysteresis is associated with the migration of Mn within the structure. Thus, in the future it is necessary to develop a model for cation ordering and find a path to control it to overcome this issue.”