Simultaneous texturing and conductivity tailoring of mesoporous NaTi ₂ (PO ₄ ) ₃ nanocrystals by gadolinium doping for enhanced Na storage

Doping is an effective method to produce hybrid materials with desirable properties and functions. Herein, gadolinium ions (Gd ³⁺ )are introduced to substitute Ti in mesoporous NaTi ₂ (PO ₄ ) ₃ (MNTP)nanocrystals to tailor the texture and conductivity simultaneously to improve Na storage properties. Microstructure characterization and kinetics analysis reveal that the superior electrochemical characteristics arise from the expanded cell, optimized porous structure, enhanced intrinsic electron conductivity, and better Na ion mobility as a result of Gd ³⁺ introduction into the MNTP nanocrystals. In the half cells for sodium-ion battery, the MNTP nanocrystals with 5% Gd ³⁺ exhibit a large ICE beyond 97% at 1 C, superior rate capability of 47.5 mAhg ⁻¹ at 50 C, and long cycling life time (>75% capacity retention at 5 C after 2000 cycles). Furthermore, using the Gd ³⁺ doped MNTP nanocrystals as the anode and activated carbon as the cathode, the assembled sodium-ion hybrid capacitor shows a high energy density of 63 Whkg ⁻¹ at a power density of 46 Wkg ^-1 . Even at a large current rate of 5 Ag ⁻¹ , a stable capacity is maintained after 30,000 cycles without obvious degradation. Gadolinium ion doping provides a new technique to improve the electrochemical properties of NASICON-type anodes in sodium-based energy storage devices.