Stacking faults are structural defects that occur in crystalline materials, including those used in batteries. These faults, where the regular stacking sequence of atomic layers is disrupted, can significantly impact battery performance by affecting ion diffusion and structural stability
Layered sodium manganese oxide (NaMnO2), especially its β-phase, has received considerable attention for use as cathodes in sodium-ion batteries. However, β-NaMnO2 exhibits stacking faults (SFs), which severely reduce its cycling stability.. This strategy can lead to the development of longer-lasting sodium-ion batteries, leading to more affordable energy-storage solutions.
Sodium (Na)-ion batteries have recently emerged as cost-effective and sustainable alternatives to lithium (Li)-ion batteries. Na, the sixth most abundant element on Earth, offers lower material costs and greater availability compared to Li-ion batteries. The design of cathode materials plays a key role in determining battery life and stability. Layered sodium manganese oxide (NaMnO2) has received increased attention from researchers for its use as a cathode material in Na-ion batteries.
NaMnO2 exists in two crystal forms: α-NaMnO2 and β-NaMnO2. Electrodes made from SF-containing β-NaMnO2 suffer from severe capacity reduction during charge/discharge cycles, limiting their practical applications. Moreover, SFs complicate the understanding of the material’s solid-state chemistry.
In a new study, a research team led by Professor Shinichi Komaba from the Department of Applied Chemistry at Tokyo University of Science (TUS), Japan, investigated how copper (Cu) doping can stabilise SFs in β-NaMnO2.
“In a previous study, we found that among the metal dopants, Cu is the only dopant that can successfully stabilise β-NaMnO2” said Professor Komaba. “In this study, we systematically explored how Cu doping can suppress SF and improve the electrochemical performance of β-NaMnO2 electrodes in Na-ion batteries.”
The team also included Mr. Syuhei Sato, Mr. Yusuke Mira, and Dr. Shinichi Kumakura from the Research Institute for Science and Technology, TUS. Their findings were published online in the journal Advanced Materials on July 15, 2025.
The team synthesised a series of highly crystalline, Cu-doped β-NaMnO2 samples (NaMn1xCuxO2) with varying amounts of Cu, corresponding to Cu doping levels from 0 percent to 15 percent. The NMCO-00 sample served as the undoped reference. Through X-ray diffraction (XRD) studies, the team found that among the Cu doped samples, NMCO-05 exhibited the highest SF concentration at 4.4 percent, while in NMCO-12, the SF concentration was only 0.3 percent, indicating a clear suppression of SFs with increased Cu doping.
“Our findings confirm that manganese-based oxides are a promising and sustainable solution for developing highly durable Na-ion batteries” added Professor Komaba. “Owing to the relatively low cost of manganese and Na, this research will lead to more affordable energy-storage solutions for a variety of applications, including smartphones and electric vehicles, ultimately leading to a more sustainable future.”
This study also demonstrates that stabilisation of SF using Cu doping could resolve the supply chain vulnerabilities that are commonly faced with metals like lithium. Moreover, the study has potential implications in grid storage, electric vehicles, and consumer electronics.
The study offers valuable insights for developing more stable and long-lasting Na-ion batteries, leading to wider renewable energy adoption, aligning with the United Nations Sustainable Development Goal 7: Affordable and Clean Energy.
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