Newly developed γ-NaTiOPO4 by simple solid-state synthesis for anode material of Na-ion batteries in both nonaqueous and aqueous electrolytes

Sodium-ion batteries (SIBs) are a promising next-generation energy storage system in terms of cost due to the abundance of sodium. However, obtaining good anode materials for SIBs remains a challenge. NaTiOPO 4 has been investigated as an anode not only for SIBs but also for aqueous SIBs. Despite the various NaTiOPO 4 polymorphs, only the β-NaTiOPO 4 phase has been investigated as an anode for SIBs due to the limited synthesis process. In this study, we successfully stabilized γ-NaTiOPO 4 via our newly developed solid-state synthesis process. In addition, its electrochemical properties as an anode for SIBs were investigated in this study. The synthesized material demonstrates a high voltage of 1.7 and ∼1.5 V vs Na/Na + with 120 mAh/g and good capacity retention of 64% for up to 500 cycles at 0.5C in a nonaqueous electrolyte. In an aqueous electrolyte, Na 0 · 44 MnO 2 //γ-NaTiOPO 4 full cell achieves excellent stable capacity retention with a high Coulombic efficiency for 175 cycles. It shows high cycling stability with a three-dimensional framework despite the relatively high redox potential. Thus, it demonstrates that γ-NaTiOPO 4 is a promising anode material for both nonaqueous and aqueous rechargeable SIBs. • γ-NaTiOPO 4 is synthesized via new solid-state synthesis process for the first time. • γ-NaTiOPO 4 is a promising anode for both aqueous and nonaqueous Na-ion batteries. • γ-NaTiOPO 4 shows high cycling stability in Na-ion batteries.