Researchers from the Tokyo University of Science have identified how scandium (Sc) doping can significantly improve the cycling stability of sodium-ion batteries. Their findings provide a new design strategy for developing longer-lasting, high-capacity alternatives to lithium-ion systems
Sodium-ion batteries depend heavily on the choice of cathode material. Na₂/₃MnO₂ is considered a strong candidate thanks to its high initial capacity, but it suffers from rapid degradation during charge–discharge cycling. This fading is linked to changes in manganese oxidation states that trigger Jahn-Teller distortion, a repeated structural strain that leads to a loss of crystallinity and declining performance over time. Previous research has attempted to address this issue by substituting other metals at manganese sites.
In the new study, Professor Shinichi Komaba, Mr Kodai Moriya, and Dr Shinichi Kumakura investigated how scandium doping affects different structural variants, or polytypes, of Na₂/₃MnO₂. Komaba said, “Previously, we discovered that Sc doping in P’2 Na₂/₃[Mn₁₋ₓScₓ]O₂ electrodes can improve the battery performance and long-term stability. However, the exact mechanism for this improvement remains unresolved, and it was unclear whether this effect is generally applicable. In this study, we systematically studied P2 and P’2 polytypes of Na₂/₃[Mn₁₋ₓScₓ]O₂ to understand the role of Sc doping.”
The P2 and P’2 polytypes differ in how Jahn-Teller distortion occurs. P2 materials show localised distortions, while P’2 features cooperative distortions that align over long ranges. Tests on doped and undoped samples showed that Sc doping in P’2 electrodes produced smaller particles, altered crystal growth, and preserved both the cooperative distortion and overall superstructure. This enhanced structural stability, reduced side reactions with the electrolyte, and improved moisture resistance by forming a protective interface layer.
Electrochemical testing confirmed that Sc-doped P’2 electrodes offered far greater cycling stability than undoped samples, with 8% Sc content delivering the best performance. Unlike non-doped samples, the doped electrodes maintained crystallinity throughout cycling. Interestingly, Sc doping had little effect on P2 electrodes, and substituting other cations such as ytterbium or aluminium did not prevent capacity fading.
Building on these findings, the researchers fabricated coin-type full cells using the 8% Sc-doped P’2 electrodes, which achieved 60% capacity retention after 300 cycles.
Komaba said, “Since Sc is an expensive metal, our study demonstrates its feasibility in the development of batteries. Our findings can potentially lead to development of high-performance and long-life sodium-ion batteries. Moreover, beyond sodium-ion batteries, our study illustrates a new strategy to extend the structural stability of layered metal oxides involving the lattice distortion and improve the performance of batteries made using these materials.”
