Calcium Doping Could Help Solve Sodium-Ion Battery Stability Issues: Study

Researchers in Japan have found that adding small amounts of calcium to sodium-ion batteries (SIBs) can significantly improve their stability in air and water, addressing one of the key barriers to their commercial use as a low-cost alternative to lithium-ion batteries.

A team led by Professor Shinichi Komaba at the Tokyo University of Science (TUS) reported that calcium doping of the cathode material Na₂/₃[Fe₁/₂Mn₁/₂]O₂ prevents degradation and boosts performance. The study, published in the Journal of Materials Chemistry A on Aug. 29, 2025, shows that the modified cathode retained its full discharge capacity even after two days of air exposure, while the undoped version lost 35%.

Surface Analysis 

“Surface analyses suggest that calcium migration during air exposure forms a protective, calcium-enriched surface layer that suppresses degradation,” Komaba said. The team found that the doping also enhanced the material’s crystallinity and interlayer spacing, improving electrochemical performance.

The research, co-authored by Assistant Professors Zachary T. Gossage and Changhee Lee, Project Scientist Shinichi Kumakura, and doctoral student Monalisha Mahapatra, could pave the way for more sustainable, large-scale energy storage. Sodium-ion batteries are seen as a promising alternative to lithium-ion systems because sodium is abundant and cheaper to source.

Low-cost modification

Komaba said the work demonstrates how a simple and low-cost modification can make sodium-ion technology more viable for renewable energy storage and consumer electronics.

The study was partly funded by Japan’s Ministry of Education, Culture, Sports, Science and Technology (MEXT) and other government research programs.

Reference: “Enhanced air stability by calcium doping in Na₂/₃[Fe₁/₂Mn₁/₂]O₂ cathode material for Na-ion batteries,” Journal of Materials Chemistry A, DOI: 10.1039/D5TA04742K.