Scandium doping and coating extend sodium-ion battery life

Researchers at Tokyo University of Science have investigated how scandium doping and surface coating can improve the durability and cycling performance of sodium-ion battery cathodes.

Sodium-ion batteries are being developed as a lower-cost alternative to lithium-ion technology and are already being commercialized for applications that include electric vehicles. Their broader use in EVs, however, will depend in part on improving cycle life and reducing capacity loss over repeated charging and discharging.

The research focused on O3-Na[Ni1/2Mn1/2]O2, a layered sodium nickel manganese oxide cathode material that offers relatively high reversible capacity but suffers from capacity fading caused by structural changes during cycling.

The team evaluated two approaches for incorporating scandium ions: bulk doping and surface coating. Both methods improved charging and discharging durability, but through different mechanisms.

After 100 cycles, capacity retention increased from 18.6% for the undoped material to 67.8% for the scandium-doped sample and 75.4% for the scandium-coated sample.

Full cells using the modified cathodes and hard-carbon anodes also showed improved long-term cycling. After 300 cycles, the scandium-doped cell retained 71.4% of its initial capacity, while the coated cell retained 91.2%.

The researchers found that scandium doping helped stabilize the bulk crystal structure by reducing large volume changes during cycling. The surface coating, meanwhile, suppressed side reactions and interfacial degradation.

“Sc ions can be incorporated either into the bulk structure or through an external coating. Both can improve the cycling performance, but the underlying mechanisms have not been elucidated,” said Shinichi Kumakura, associate professor at Tokyo University of Science.

The team noted that scandium itself may not be practical for large-scale battery manufacturing because of its cost and availability. The next step is to apply the same design principles using more abundant and lower-cost elements that could be more suitable for commercial sodium-ion batteries.

For EV applications, the work is relevant because longer-lasting sodium-ion cells could help expand the chemistry’s use in lower-cost electric vehicles, where durability and material cost are both important considerations.

This version keeps the science intact, adds the EV connection where it actually matters, and avoids making scandium sound like a near-term commercial EV solution.