Tokyo Scientists Unlock Copper-Based Solution for Long-Lasting Sodium-Ion Batteries

In a major breakthrough for next-generation battery technology, researchers from the Tokyo University of Science (TUS) have identified a new material design strategy that could pave the way for stable, high-performance sodium-ion batteries, offering a cost-effective alternative to lithium-ion systems.

Advertisment

The study, published on July 15 in Advanced Materials, reveals that copper (Cu) doping can eliminate long-standing structural defects known as stacking faults in β-phase sodium manganese oxide (β-NaMnO₂) electrodes. These defects have historically limited the material’s viability for energy storage, causing rapid performance degradation.

“Among various metal dopants, copper proved uniquely capable of stabilising the β-phase and suppressing stacking faults,” said Professor Shinichi Komaba, who led the research at the Department of Applied Chemistry, TUS. “This leads to much greater cycle stability and battery longevity.”

Sodium: The Affordable, Abundant Alternative

Advertisment

Sodium-ion (Na-ion) batteries are gaining attention as a more sustainable and economical alternative to lithium-ion batteries, due to sodium’s abundance and lower cost. However, the development of durable cathode materials remains a bottleneck. Layered NaMnO₂—particularly in its β-phase—has shown promise, but stacking faults created during high-temperature synthesis have hampered its practical application.

These faults, formed when crystal planes slip into misaligned sequences, not only degrade the battery’s performance but also obscure the material’s underlying chemistry. The result is poor cycling stability, rendering the technology unsuitable for long-term use—until now.

Cu Doping Eliminates Defects, Boosts Performance

Komaba and his team—including  Syuhei Sato, Yusuke Mira, and Dr. Shinichi Kumakura—synthesised a series of Cu-doped β-NaMnO₂ samples (NaMn₁₋ₓCuₓO₂) with varying copper levels. They found that increasing Cu content drastically reduced stacking faults—from 4.4% in lightly doped samples to just 0.3% in more heavily doped ones.

Electrochemical testing showed dramatic improvements in performance. Undoped electrodes lost capacity within 30 cycles, while Cu-doped variants—particularly NMCO-12 and NMCO-15—retained full capacity beyond 150 cycles, demonstrating their superior stability.

The researchers also used advanced X-ray diffraction and density functional theory modelling to uncover a previously hidden structural behaviour in the β-phase: a unique gliding motion of the MnO₂ layers during sodium insertion and extraction. This insight was previously impossible to observe due to the prevalence of stacking faults.

A Step Toward Affordable Energy Storage

“This work confirms that manganese-based oxides are a sustainable and scalable option for developing long-life Na-ion batteries,” said Komaba. “Given the global push for affordable energy solutions, this research could accelerate the deployment of sodium-ion technology in smartphones, electric vehicles, and grid storage.”

The study also has strategic significance, addressing supply chain concerns tied to critical battery materials like lithium. By offering an efficient alternative using abundant, low-cost elements, the findings align with UN Sustainable Development Goal 7: Affordable and Clean Energy.