<p>➀ Researchers at Tokyo University of Science discovered copper doping effectively eliminates stacking faults in β-NaMnO₂, addressing capacity degradation in sodium-ion batteries;</p><p>➁ Doping with 12% copper achieved negligible stacking faults and zero capacity loss over 150 charge cycles, demonstrating unprecedented stability;</p><p>➂ The study enabled deeper analysis of the material’s ion-insertion mechanics, confirming manganese oxides as a viable foundation for durable Na-ion battery development.</p>