Sodium-ion batteries (SIBs) are increasingly becoming popular as alternatives to lithium-ion batteries. This is due to the much greater abundance of sodium (Na) in Earth’s crust compared to lithium, presenting an opportunity for lower costs. In addition, SIBs also offer better safety and low-temperature performance. Indeed, SIBs are already being commercialized for applications ranging from portable electronics to electric vehicles.
Among the various cathode materials under development, layered sodium nickel manganese oxides (Nax[Ni,Mn]O2) have emerged as particularly promising candidates. Specifically, the O3 polytype of Na[Ni1/2Mn1/2]O2 is particularly attractive as it contains stoichiometric Na+ in the pristine state and delivers a relatively large reversible capacity. However, it suffers from severe capacity fading due to large volume changes that occur during charging and discharging processes. To address this issue, previous studies have explored hetero-metal substitution. Among the available candidates, scandium ions (Sc3+) have shown great promise in improving cycling performance. Yet, the exact mechanisms behind these improvements remain underexplored.
Against this backdrop, a research team led by Professor Shinichi Komaba and Associate Professor Shinichi Kumakura from the Department of Applied Chemistry at Tokyo University of Science (TUS), Japan, investigated how the incorporation of Sc3+ into O3-Na[Ni1/2Mn1/2]O2 (NNMO) affects its crystal structure and electrode properties. The team also included Mr. Kodai Moriya and doctoral student Sho Toriumi from TUS, in collaboration with Professor Yoshitaka Tateyama and Assistant Professor Hoang Duc Luong. Their study was published in the journal Small on August 06, 2026. The researchers utilized two approaches to study the effects of incorporating Sc3+: doping and surface coating.
“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,” explains Dr. Kumakura. “In this study, we explored how scandium improves battery performance of SIBs through both doping and coating, clarifying their distinct mechanisms.”
The researchers synthesized Sc-doped samples of NNMO, termed NNMSOx, where ‘x’ denotes the percentage of Sc doping, through a bulk doping method. In particular, the study focused on NNMSO8 due to its superior cycling performance. In addition, the team also prepared samples with Sc coating, where NNMO particles underwent a wet process using scandium isopropoxide solution, followed by annealing at 800 °C, creating NNMO-SC800.
The team then evaluated the electrochemical properties of the synthesized samples using coin-type aprotic Na cells. The results showed that both doping and coating significantly improved charging/discharging durability of the cells, improving capacity retention after 100 cycles from 18.6% for undoped NNMO to 67.8% for NNMSO8 and 75.4% for NNMO-SC800. This improved performance was attributed to suppression of side reactions and bulk stabilization of structure due to Sc3+ doping. In the case of NNMSO8, the Sc3+-doped structure stabilized the bulk phase, while for NNMO-SC800, the Sc3+-coated phase acted as a protective layer that suppressed interfacial degradation.
In addition, NNMSO8 demonstrated a smoother charging/discharging curve compared to NNMO. The team found that this effect was due to the suppression of Na+/vacancy ordering due to Sc3+ substitution. In contrast, NNMO-SC800 did not show any noticeable change in charging/discharging curve shape, suggesting that Sc3+ is present mainly at the surface. Both modified materials also demonstrated improved rate capability.
The researchers further evaluated Na-ion full cells using NNMSO8 or NNMO-SC800 as cathodes and hard carbon as the anode. Both full cells exhibited substantially improved long-term cycling performance. After 300 cycles, the full cell employing NNMSO8 retained 71.4% of its initial capacity, while the cell using NNMO-SC800 retained 91.2%. While direct comparisons across different battery chemistries are complex, this level of durability enhancement represents a significant advancement over current leading Na-ion cathodes.
To understand the origin of these improvements, the team performed detailed structural and mechanistic analyses. They found that doping and coating improved cycling performance through distinct mechanisms. When incorporated into the crystal lattice, electrochemically inactive Sc3+ ions, whose ionic radius is comparable to those of the transition metals, immobilize a fraction of Na+ ions, which then act as pillars stabilizing the layered structure. This smooths charge/discharge profiles and mitigates large volume changes. In contrast, Sc3+ coating leads to the formation of an O3-NaScO2-like phase on the surface of NNMO particles, without any change in the bulk structure. The coating effectively suppresses side reactions, improving cycling performance.
Overall, coating enhances cycling stability but does not prevent loss of crystallinity during long-term cycling, while doping suppresses bulk degradation but does not fully mitigate capacity fading.
“Our findings show that a synergistic combination of bulk doping and surface coating is a promising strategy to improve performance of SIBs,” notes Prof. Komaba. “This will help extend the lifespan of SIBs and consequently widen their practical application.”
While Sc serves as an ideal model system to demonstrate these distinct structural mechanisms, its cost and availability mean that the team’s next crucial step will be applying these insights to more abundant, cost-effective elements suitable for commercial scaling.
This study offers valuable design principles for developing longer-lasting, high-performance SIBs.
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Reference
DOI: 10.1002/smll.75049
About The Tokyo University of Science
Tokyo University of Science (TUS) is a well-known and respected university, and the largest science-specialized private research university in Japan, with four campuses in central Tokyo and its suburbs and in Hokkaido. Established in 1881, the university has continually contributed to Japan's development in science through inculcating the love for science in researchers, technicians, and educators.
With a mission of “Creating science and technology for the harmonious development of nature, human beings, and society," TUS has undertaken a wide range of research from basic to applied science. TUS has embraced a multidisciplinary approach to research and undertaken intensive study in some of today's most vital fields. TUS is a meritocracy where the best in science is recognized and nurtured. It is the only private university in Japan that has produced a Nobel Prize winner and the only private university in Asia to produce Nobel Prize winners within the natural sciences field.
Website: https://www.tus.ac.jp/en/mediarelations/
About Professor Shinichi Komaba from Tokyo University of Science
Dr. Shinichi Komaba is currently a Professor in the Department of Applied Chemistry at Tokyo University of Science (TUS), Japan, having previously served as a JSPS Research Fellow, a Research Associate at Iwate University, and a researcher at CNRS-ICMCB in France. Concurrent with his professorship at TUS, he has also served as a Project Professor for the ESICB Project at Kyoto University. An internationally recognized pioneer in electrochemistry and functional energy materials, he has published hundreds of articles that have received over 52,000 citations to date. His research primarily focuses on advanced lithium-, sodium-, and potassium-ion batteries, as well as biofuel cells and ion sensors.
About Associate Professor Shinichi Kumakura from Tokyo University of Science
Dr. Shinichi Kumakura is currently an Associate Professor at the Research Institute for Science and Technology at Tokyo University of Science (TUS), Japan. Before joining TUS, he worked as a Senior Scientist at Umicore Japan K.K. He is the recipient of multiple awards, including Silver Poster Award of the 10th International Conference on Sodium Batteries (ICNaB) and Tokyo University of Science Biology and Chemistry Encouragement Award. He has published over 50 articles that have received over 3,100 citations to date. His research primarily focuses on sodium-ion batteries and solid-state batteries.
Funding information
This study was partially funded by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) Program: Data Creation and Utilization Type Materials Research (JPMXP1122712807); JST CREST (Grant No. JPMJCR21O6), ASPIRE (JPMJAP2313), and GteX (JPMJGX23S4); and JSPS KAKENHI (JP25H00905, JP24H00042, JP25K23611 and JP20H02849). Analytical measurement was partly carried out at National Institute for Materials Science (NIMS) Battery Research Platform under the JST Grant Number JPMJPF2016.
Small
Experimental study
Not applicable
Scandium doping and coating for improving O3-NaNi1/2Mn1/2O2 electrode in sodium battery
8-Aug-2026
The authors declare no conflict of interest.