Indian Scientists Develop Stable And High-Performance Cathode Materials For Sodium-ion Batteries

Indian scientists have developed a new cathode material that can produce high-performance, cost-effective, environment-friendly Sodium-ion (Na-ion) batteries as next-generation energy storage systems.

By addressing the air/water-instability and structural-cum-electrochemical instability of Sodium–transition-metal–oxide (Na-TM-Oxide) based cathode materials for Sodium-ion batteries, they have successfully developed new cathode materials that are both stable and high-performing.

The newly developed materials exhibit remarkable electrochemical cyclic stability and can withstand exposure to air and water.

This significant advancement paves the way for the development of cost-effective and sustainable energy storage systems for various applications such as consumer electronics, grid energy storage, renewable energy storage, and electric vehicles.

With the increasing importance of battery-driven electric vehicles in addressing climate and environmental concerns, it is crucial to develop a cost-effective, resource-friendly, safe, and sustainable alkali metal-ion battery system beyond the conventional Li-ion system.

In India, the abundance of sodium sources makes the upcoming Na-ion battery system particularly significant in the local context.

A Na-ion cell consists of cathode and anode active materials that enable the reversible insertion and removal of the charge carrier, sodium ions, during the cell's charge and discharge processes.

The performance of Na-ion batteries relies heavily on the structural and electrochemical stability of the electrodes, sodium-ion transport kinetics, and various dynamic resistances.

Despite the advantages of Sodium-ion batteries, the electrochemical behavior and stability of the 'layered' Na-TM-oxide-based cathode materials upon moisture exposure require substantial improvements to enable widespread usage of Na-ion battery systems.

The lack of stability not only poses challenges in handling and storing Na-TM-oxides but also negatively affects their electrochemical performance. Additionally, the water instability necessitates the use of toxic, hazardous, and expensive chemicals during electrode preparation.

To overcome these challenges, Professor Amartya Mukhopadhyay's group at IIT Bombay conducted research supported by the Science and Engineering Research Board (SERB) and the Department of Science and Technology (DST)'s Materials for Energy Storage scheme.

"They have evolved a universal design criterion, paving the way towards successful design and widespread development of environmentally stable and high-performance cathodes for the sustainable Na-ion battery system and beyond," the Ministry of Science and Technology said in a release on Tuesday (16 May).

The researchers proposed a change in the alternate slab layered structure of the Na-TM-oxide cathode material by introducing "interslab" spacing through tuning the TM-O bond covalency.

Their findings, published in the journal Chemical Communications, highlight the significance of adjusting the degree of covalency to modify the net/effective negative charge on the oxygen ions (O-ions).

This, in turn, affects the electrostatic attraction between sodium ions (Na-ions) and O-ions, as well as the repulsion between O-ions across the Na-layer.

By reducing the TM-O covalency and increasing the net negative charge on the O-ions, the electrostatic attraction between Na-ions and O-ions strengthens, resulting in a more stable and shorter Na-O bond.

This leads to a reduced "inter-slab" spacing and improved air/water stability, addressing the limitations of the cathode materials.

Moreover, this design enables the use of health/environment-friendly and cost-effective "aqueous" processing routes for the preparation of water-stable cathodes, as demonstrated in another publication in the Journal of Materials Chemistry A.

Conversely, increasing the TM-O bond covalency decreases the effective negative charge on the O-ions, resulting in a weaker and longer Na-O bond and an enlarged "inter-slab" spacing.

This modification facilitates faster Na-transport kinetics and enhances the rate capability of the cathode, ultimately promising significantly higher power density for Na-ion batteries.