Two-step carbon modification of NaTi2(PO4)3 with improved sodium storage performance for Na-ion batteries

NASICON-type structured NaTi2(PO4)3 has been regarded as a promising anode material for non-aqueous and aqueous Na-ion batteries, whereas its sodium storage performance was greatly restricted by its inherent inferior electronic conductivity. In the present work, a two-step carbon modification method using prefabricated carbon spheres as support and phenolic resin as carbon source was proposed to prepare advanced NaTi2(PO4)3/C. The as-prepared composite with carbon spheres displayed a much higher reversible capacity (126.7 mA·h/g vs 106.7 mA·h/g at 0.5C) than the control sample without carbon spheres. Superior rate capability with discharge capacities of 115.1, 95.5, 80.8 mAh/g at 1C, 10C, 20C, respectively and long-term cycling stability with capacity retention of 92.4% after 1000 cycles at 5C were also observed. Owing to the designing of two-step carbon modification, although the as-prepared sample shows much smaller surface area, it possesses much better conductive network and more uniform particle distribution, resulting in higher electronic conductivity and faster ionic conductivity, thereby superior sodium storage ability at high rate.