posted on 2019-08-14, 12:04authored byWei Xiao, Qian Sun, Mohammad Norouzi Banis, Biqiong Wang, Jianneng Liang, Andrew Lushington, Ruying Li, Xifei Li, Tsun-Kong Sham, Xueliang Sun
As
a competitive anode material for sodium-ion batteries (SIBs),
a commercially available red phosphorus, featured with a high theoretical
capacity (2596 mA h g–1) and a suitable operating
voltage plateau (0.1–0.6 V), has been confronted with a severe
structural instability and a rapid capacity degradation upon large
volumetric change. In particular, the fundamental determining factors
for phosphorus anode materials are yet poorly understood, and their
interfacial stability against ambient air has not been explored and
clarified. Herein, a high-performance phosphorus/carbon anode material
has been fabricated simply through ball-milling the carbon black
and red phosphorus, delivering a high reversible capacity of 1070
mA h g–1 at 400 mA g–1 after 200
cycles and a superior rate capability of 479 mA h g–1 at 3200 mA g–1. More importantly, we first reveal
the significance of inhibiting the exposure of phosphorus/carbon electrode
materials to air, even for a short period, for achieving a good electrochemical
performance, which would sharply decrease the reversible capacities.
With the assistance of synchrotron-based X-ray techniques, the formation
and accumulation of insulating phosphate compounds can be spectroscopically
identified, leading to the decay of electrochemical performance. At
the same time, these passivation layers on the surface of electrode
were found to occur via a self-oxidation process in ambient air. To
maintain the electrochemical advantages of phosphorus anodes, it is
necessary to inhibit their contact with air through a rational coating
or an optimal storage condition. Additionally, the employment of a
fluoroethylene carbonate (FEC) additive facilitates the decomposition
of the electrolyte and favors the formation of a robust solid electrolyte
interphase layer, which may suppress the side reactions between the
active Na–P compounds and the electrolyte. These findings could
help improve the surface protection and interfacial stability of phosphorus
anodes for high-performance SIBs.