New Sodium Oxide Paves the Way for Advanced Sodium-Ion Batteries

Skoltech researchers and their collaborators from France, the US, Switzerland, and Australia were able to create and describe a mixed oxide Na(Li_1/3Mn_2/3)O₂ that holds promise as a cathode material for sodium-ion batteries, which can take one day complement or even replace lithium-ion batteries. The paper was published in the journal Nature Materials.

Lithium-ion batteries are powering the modern world of consumer devices and driving a revolution in electric transportation. But since lithium is rather rare and challenging to extract from an environmental standpoint, researchers and engineers have been looking for more sustainable and cost-effective alternatives for quite some time now.

One option is sodium-ion technology, as sodium is much more abundant than lithium. Na-ion batteries, however, still struggle to provide high energy density and cycling stability. Thus, the search for an optimal design for Na-based cathodes is underway in laboratories across the world.

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 that studied the compound Na(Li_1/3Mn_2/3)O₂, patented by Renault. This compound showed promise as a cathode material with high energy density, no voltage fade over multiple charge cycles, and moisture stability.

“We have performed all the transmission electron microscopy (TEM) studies using the equipment at Advanced Imaging Core Facility of Skoltech. We investigated the crystal structure of Na(Li_1/3Mn_2/3)O₂ by electron diffraction and directly visualized it with atomic resolution scanning transmission electron microscopy techniques. Furthermore, we investigated this material at various states of charge by TEM, which allowed us to trace the evolution of its crystal structure during the electrochemical cycling,” Morozov says.

Among other things, the team found that the new compound possesses a reversible specific discharge capacity of 190 mAh/g, which is a relatively high value for sodium-ion battery cathode materials. Morozov also demonstrates good capacity retention and moisture resistance, which is unusual for compounds of this kind. “Moreover, no significant voltage fade was observed during prolonged cycling of Na(Li_1/3Mn_2/3)O₂; it’s a key drawback of similar Li-rich layered cathode materials,” the Skoltech PhD student says.

However, despite these promising properties, Na(Li_1/3Mn_2/3)O₂ exhibits a large voltage hysteresis during charge and discharge, leading to a decrease in the energy efficiency of the cathode material can become an obstacle in commercial implementation. “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,” Anatolii Morozov notes.

“The team used Titan Themis Z electron microscope at our Advanced Imaging Core Facility (AICF), which allows to visualize single atoms in the crystal lattice of material and study its structure and how it relates to the properties of that material. But top-level equipment is necessary but not enough for impressive scientific results; we see our staff scientists and students' skills as crucial and invest a lot in the development of those skills. With Prof. Abakumov being a Research Advisor of AICF, close scientific collaboration between our team and Skoltech scientists becomes possible. This gives Skoltech a competitive advantage when it comes to the implementation of complex research projects or development of unique technologies.” notes Yaroslava Shakhova, Head of the Skoltech Advanced Imaging Core Facility.

Other organizations involved in this research include Chimie du Solide-Energie, Collège de France; Sorbonne Université; Renault Technocentre; Réseau sur le Stockage Electrochimique de l’Energie (RS2E); Université d’Orléans; Université de Pau et des Pays de l'Adour; Lawrence Berkeley National Laboratory; Paul Scherrer Institute; The University of Sydney; Australian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organisation; University of Illinois at Chicago; University of Montpellier.