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.