Black P can intercalate three Li ions in the fully discharged state (Li 3 P) and therefore possesses a high theoretical specific capacity of 2,596 mAh g -1 upon lithiation. This renders black P a potential anode material for Li-ion batteries with high gravimetric and volumetric energy density, the authors noted.

Researchers from Northeast Normal University, Changchun, China, report that black phosphorus (black P) anode materials for lithium-ion batteries exhibit high specific capacity and excellent cycling performance. A paper on their work is published in the ACS Journal of Physical Chemistry C .

Black phosphorus obtained from white phosphorus at 4 GPa and 400 °C exhibited the highest first discharge and charge capacities of 2,505 and 1,354 mAh g-1. Black phosphorus obtained from red phosphorus at 4.5 GPa and 800 °C exhibited the highest first discharge and charge capacities of 2,649 and 1,425 mAh g-1.

Here we synthesized black P by a high pressure and high temperature (HPHT) method using white and red P separately as starting materials. —Sun et al.

The team prepared orthorhombic black P using a HPHT method in a cubic anvil high-pressure apparatus under pressures of 2-5.0 GPa and temperatures of 200-800 °C for 15 min. For electrochemical measurements, they used CR2025-type coin cells with metallic lithium as the counter electrode and an electrolyte comprising 1 M LiPF 6 in a 1:1 volume fraction of ethylene carbonate (EC) and diethyl carbonate (DEC). Celgard 2400 was used as separator. The working electrode consisted of 80 wt % black P with acetylene black (5 wt %) and polyvinylidene fluoride (15 wt %) in N-methyl-2-pyrrolidone.

During testing, they found that the samples showed large irreversible capacities in the first discharge-charge cycle and initial low Coulombic efficiency. However, after the fifth cycle, the Coulombic efficiency is greater than 95%.

WBP [black P from white phosphorus] and RBP [black P from red phosphorus] samples all exhibited much higher electrochemical activity towards Li insertion than black P samples prepared by HEMM. Although the reaction conditions involved high pressure and temperature, the entire synthetic procedure is simple and rapid. The synthetic conditions can be accurately controlled by regulating the parameters of the high-pressure apparatus.

The highest initial charge capacity of RBP is approximately 3.8 times higher than the theoretical specific capacity of graphite. RBP retained a highly stable capacity of 703 mAh g-1 after 60 cycles, which makes it a promising anode material for high energy Li-ion batteries. These favorable results are attributed to the high crystallinity and purity of the as-prepared black P by HPHT, which may improve the dynamic mechanism of Li ion intercalation/ deintercalation.

Further investigations on black P to improve its overall electrochemical performance (capacity, cyclability, Coulombic efficiency, and voltage profile) will be carried out, including the electrode structure design, controlling cutoff potential, the electrolyte choice and the surface coating treatment etc. These results will be reported in a future publication. —Sun et al.

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