Superior lithium storage performance of hierarchical N-doped carbon encapsulated NaTi2(PO4)3 microflower

Na-superionic conductor (NASICON) structured NaTi₂(PO₄)₃ (NTP) as anode shows broad prospect in aqueous lithium ion battery. However, inherent low electrical conductivity of NaTi₂(PO₄)₃ remains a pivotal issue to be resolved. Herein, we report N-doped carbon encapsulated NaTi₂(PO₄)₃ microflower (NTP-CN) as anode for aqueous lithium ion battery, which is prepared via solvothermal way. NTP-CN with unique structural feature displays superb electrochemical performances. It delivers the discharge capacities of 131.2, 110.1, and 84.3 mAh g⁻¹ at 0.2, 3.0, and 15 C, respectively, 38.8, 33.8, and 51.1 mAh g⁻¹ higher than these of pristine NTP. NTP-CN also shows remarkable cycling stability at 6 C after 1000 cycles (capacity retention: 88.8%), superior to NTP (70.7%). The outstanding properties of NTP-CN may be due to that microflower structure can increase touching area between electrolyte and electrode, and carbon coating for electrode improves stability in aqueous electrolyte and ameliorates electrical conductivity. Moreover, nitrogen doping can further enhance hydrophilicity and conductivity of the sample, and also form lots of defects on electrode surface, which is beneficial for the intercalation/deintercalation of Li ions. This work reveals that the combination of microflower structure and N-doped carbon layer offers a promising method to improve electrochemical performances of NaTi₂(PO₄)₃.