Anode Properties of NaTi₂(PO₄)₃ Prepared by Adding Excess Na₂CO₃ for Aqueous Sodium-Ion Batteries

Aqueous Na-ion batteries (ASIBs) are being developed as one of the next-generation large-scale rechargeable battery types. In the development of ASIBs, the further improvement of the anode properties of one of them, NaTi2(PO4)3 (NTP), is important. Therefore, we tried to modify the NTP surface with a material having Na-ion conductivity, such as a solid electrolyte interphase layer. NTP was prepared with the addition of an excess amount of Na2CO3 and exhibited better cyclability and rate capability. In particular, this NTP showed good cycle stability even with the use of an aqueous electrolyte with a low salt concentration. The surfaces of the obtained NTPs were analyzed using S/TEM and electron energy loss spectroscopy measurements. The particle surface was modified by a Na-rich phase such as Na3Ti23+(PO4)3. In addition, the prepared NTPs had high crystallinity, which is thought to contribute to the good rate capability. We have found a simple method of adding excess Na2CO3 during NTP synthesis to improve the anode properties of NTPs.