NaFeO 2 : Possible Materials for Anode and Cathode of Na-Ion Batteries

High Resolution Image Download MS PowerPoint Slide The charge–discharge behaviors of α-NaFeO 2 and β-NaFeO 2 were evaluated for the first time as Na-ion battery anodes. We revealed that both phases showed reversible charge–discharge reactions based on the conversion reaction mechanism of Fe 2 O 3 because of the phase change from NaFeO 2 to Fe 2 O 3 in the first sodiation. The mechanical milling treatment for NaFeO 2 enhanced the discharge capacity, which is more significant for β-NaFeO 2: it attained an excellent cycling performance with the discharge capacity of 590 mA g –1 at the 100th cycle. As the cathode material, no charge–discharge reaction of β-NaFeO 2 was observed, whereas the α-NaFeO 2 electrode exhibited a reversible charge–discharge reaction based on the insertion reaction mechanism. We assembled a full cell using of α-NaFeO 2 anode and α-NaFeO 2 cathode, and succeeded to operate reversible charge–discharge with the discharge voltage of 0.8–1.8 V and the discharge capacity of 90 mA h g –1 . This is the first report that the full cell can operate using the same active material of NaFeO 2 for the anode and cathode. Interestingly, the anode and the cathode can operate according to different charge–discharge mechanisms of the conversion reaction and the insertion reaction, respectively.