Highly Stable Na3Fe2(PO4)3@Hard Carbon Sodium-Ion Full Cell for Low-Cost Energy Storage

Abundant flake-porous Na 3 Fe 2 (PO 4 ) 3 has been prepared via a simple spray drying method. As a cathode material in sodium-ion batteries (SIBs), the galvanostatic charge/discharge test results indicate that the initial reversible discharge specific capacity of the flake-porous Na 3 Fe 2 (PO 4 ) 3 electrode can reach to 100.8 mAh g –1 (about 93% of the theoretical capacity of 105 mAh g –1 ) under a current density of 10 mA g –1 (0.1 C) and the high rate capability at 500 mA g –1 (5 C) is up to 60 mAh g –1 after 1100 cycles. The in situ X-ray diffraction pattern and ex situ X-ray photoelectron spectroscopy results indicate that the charge/discharge processes of this cathode material go through a reversible electrochemical reaction of Na 3 Fe 2 (PO 4 ) 3 /Na 5 Fe 2 (PO 4 ) 3 . The outstanding electrochemical performance of Na 3 Fe 2 (PO 4 ) 3 is attributed to its [Fe 2 (PO 4 ) 3 ] “lantern unit”-stacked NASICON-type structure and two-dimensional (2D) porous-sheet morphology. The flake-porous Na 3 Fe 2 (PO 4 ) 3 cathode with a commercial hard carbon anode full cell shows an energy density of 76 Wh kg –1 and the maximum power density of up to 760 W kg –1 . The full cell also shows excellent low-temperature performance even at −20 °C (40 mAh g –1 at 100 mA g –1 ). The outstanding electrochemical and low-temperature performances prove that this full cell is an ideal device for large-scale electrical energy storage (EES).