Synergy of Black Phosphorus-Graphite-Polyaniline Based Ternary Composite for Stable High Reversible Capacity Na-ion Battery Anodes.

In recent times, few-layer black phosphorus (BP) has attracted tremendous attention as a promising anode material for sodium-ion batteries due to its particular two-dimensional structure, good electron conductivity and high theoretical capacity. The main disadvantages of BP based materials are the lower practical specific capacity of the BP based composite than expectation because of the low P atom utilization, and the structural fracture due to the large volume expansion that occurs during sodiation/desodiation cycles. In this work, we report a ternary composite comprising BP, graphite and polyaniline (BP-G/PANI) with a BP mass content of ~65 wt.%. The ternary composite provides an optimized ion pathway (electrolyte → PANI → BP-G → BP), which reduces the charge transfer resistance of the electrode. And further ex-situ X-ray absorption spectroscopy(XAS) measurements demonstrate the presence of graphite in the BP-G composite allows a deep sodiation of BP and also leads to a higher sodiation/desodiation reversibility. In addition, the uniformly coated PANI also restricts the huge volume expansion of BP electrode through discharge/charge processes, which promise stable cycling performance of BP-G/PANI. Thus, our composite shows a high reversible gravimetric capacity of 1530 mAh gcompo.-1 at 0.25 A g-1 and a capacity retention of 520 mAh gcompo.-1 after 1000 cycles at a high current density of 4 A g-1.