Uniform and continuous carbon coated sodium vanadium phosphate cathode materials for sodium-ion battery

Sodium vanadium phosphate Na sub(3)V sub(2)(PO sub(4)) sub(3) coated with uniform and continuous carbon film is synthesized by heat treatment of the precursors under C sub(2)H sub(2)-pyrolysis reducing atmosphere, in which Na sub(3)V sub(2)(PO sub(4)) sub(3) is formed synchronously with carbon coating. As a cathode material for Na-ion batteries, Na sub(3)V sub(2)(PO sub(4)) sub(3)/C shows a flat charge plateau at about 3.39 V in the potential window of 2.5-4.0 V versus Na+/Na. The charge capacity of 83.7 mAh g super(-1) and discharge capacity of 82.1 mAh g super(-1) can be obtained at a current rate of 1C after 300 cycles and the coulombic efficiency averages 98% throughout. The enhanced electrochemical performance can be contributed to the uniform and continuous carbon layer, which greatly improves the electric conductivity of Na sub(3)V sub(2)(PO sub(4)) sub(3).