Self-Supported NaTi2(PO4)3 Nanorod Arrays: Balancing Na+ and Electron Kinetics via Optimized Carbon Coating for High-Power Sodium-Ion Capacitor.

The NaTi2(PO4)3 (NTP) anode materials exhibit high Na+ diffusion dynamics; carbon-based materials can effectively improve its limited electronic conductivity. However, the low Na+ diffusion of NTP/C composite materials from inhomogeneous carbon mixing or uncontrollable carbon coating cannot keep up with fast electron transfer, leading to undesirable electrochemical performances. Herein, a uniform and controllable carbon layer is designed on the self-supported-coated NTP nanorod arrays with binder-free (NTP@C NR) to improve Na+ and electron kinetics simultaneously. As a result, the NTP@C NR electrodes possess initial coulombic efficiency (ICE = 97%), good rate capabilities (89.1 mA h g-1 at 100 C), and stability with ≈78.4% of capacity retention rate at even 30 C over 1200 cycles. The sodium-ion capacitors with NTP@C NR as an anode and commercially activated carbon as a cathode exhibit ∼9180.0 W kg-1 of power density at 10 A g-1 and super high retention of ≈94.5% at 1 A g-1 over 7000 cycles. This work will help balance transport kinetics between the ion and electron for materials applied in storage devices.