Phase Transformation Mechanism From Red Phosphorus To Black Phosphorus And Performance Of Fibrous Phosphorus,Hittorf's Phosphorus As Anode For LIBs

There are three allotropes of phosphorus,namely:red phosphorus?RP?,white phosphorus?WP?,and black phosphorus?BP?.In addition to amorphous red phosphorus,there are four different crystalline red phosphorus,which are classified into type II,type III,type IV and type V.Among them,fibrous phosphorus?FP?and Hittorf's phosphorus?HP?are assigned to type IV and type V,respectively.We focused on black phosphorus,fibrous phosphorus,Hittorf's phosphorus.Because of the complex temperature program,the synthesis mechanism of BP should be complicated and confusing in its preparation by means of CVD.Herein,radial orthorhombic BP crystals bunches were successfully synthesized by CVD and the phase transitions at every stage were explored systematically,which were usually confirmed via a series of interference experiments and supported by structure characterization.Additionally,the nucleation agents and nucleation sites were systematically investigated.Based on these exploration,we found that the synthesis of BP is a process of stage-by-stage phase-induction.At first,RP is transformed into to HP without the assistance of mineralizers.Subsequently,HP is transformed into BP at the cooling stage.Moreover,Sn₂₄P_19.3I₈ should work as the sole nucleation agent,and leads to BP crystal nucleation and growth to form large crystals in the subsequent heat preservation stage.Also,the nucleation site lies in the product region opposite the source region.In addition,the radial morphology of the BP crystal bunches under an RP/SnI₄/Sn?granule?system was revealed firstly,and taking the straps out from the BP bunches is convenient for exfoliating.Subsequently,we proposed a promising LIBs anode based on fibrous phosphorus and Hittorf's phosphorus.An Iodine-assisted CVD method was used to synthesize urchin-like fibrous phosphorus crystals and flower-like Hittorf's phosphorus crystals and the morphology of the twin phases was investigated systematically.Hittorf's Phosphorus exhibited an initial capacity of 2113.8 mA h g^-1 and a capacity of 558.0 mA h g^-1 after 40 cycles,whereas the fibrous phosphorus delivered a slightly lower initial discharge capacity of 1783.0 mA h g^-1 but a higher capacity of 817.0 mA h g^-11 after 40cycles.It is concluded that fibrous phosphorus exhibited a best performance comparing with other single phases such as commercial red phosphorus?irreversible?and black phosphorus(the capacity fades from 1800.0 mA h g^-1 to 200.0 mA h g^-1 after 30 cycles).The Li-ion storage mechanism of fibrous phosphorus was investigated deeply.The uniform rod-like morphology and high conductivity of fibrous phosphorus improved the performance.Besides,the presence of Li₃P and LiP phases contributed to the cyclability.The large specific capacity and cyclability comparing with other phases of phosphorus makes fibrous phosphorus a new alternative anode material for LIBs.This job comes to be the basis for building stable composite structures to obtain Phosphorus-based LIBs anode materials with better performance.