Electrospinning has recently attracted considerable attention as a powerful and versatile technique to produce efficient, specifically tailored and high-added value anodes for lithium ion batteries (LIBs) and sodium ion ones (SIBs) [1]. Carbon electrospun nanofibers (CNFs), obtained via polymer electrospinning and subsequent carbonization, provide faster intercalation kinetics with respect to commonly employed powder material thanks to the high surface to volume ratio and to the shorter diffusion paths for ions and electrons transport. They offer a large number of ions insertion sites and the charge-transfer resistance at the electrolyte/active material interface is therefore reduced [2].

Recently, red phosphorus has been considered as one of the most promising anode materials for LIBs and SIBs alternative to the C-based ones [3] but its widespread and easy application has been prevented due to its low conductivity and large volume expansion during cycling, leading to low cyclability and poor rate performances. For this reason, red phosphorus cannot be used alone, but it must be combined with other anode materials able to accommodate its expansion and to increase its conductivity.

Here we suggest a simple double-step procedure to obtain high-capacity electrospun carbon nanofibers anodes and to enhance their electrochemical performances with the insertion of red phosphorus in the matrix. In particular, we propose a simple drop-casting method to confine micro- and nanosized amorphous red P within the carbon mat, thus obtaining an highly efficient, self-standing, binder- and collector-free anode. Red P insertion in the CNFs net has been demonstrated by SEM and TEM analysis and the resulting material has been used to manufacture anodes for LIBs and SIBs. The reversible specific capacity and the rate capability of the obtained composite anodes have been significantly improved with respect to the electrospun carbon mat alone. The outstanding electrochemical performances for both LIBs and SIBs can be accounted to the synergic action of high-capacity red P clusters with the fast transport properties of the carbon fiber mat, acting also as an accommodation-volume matrix for the significant phosphorus expansion during charging/discharging.

[1] Wang, H. G., Yuan, S., Ma, D. L., Zhang, X. B. & Yan, J. M. Electrospun materials for lithium and sodium rechargeable batteries: from structure evolution to electrochemical performance. Energy Environ. Sci. 8, 1660–1681 (2015)

[2] Kim, C. et al. Fabrication of electrospinning‐derived carbon nanofiber webs for the anode material of lithium‐ion secondary batteries. Adv. Funct. Mater. 16, 2393–2397 (2006)

[3] Qian, J., Wu, X., Cao, Y., Ai, X. & Yang, H. High capacity and rate capability of amorphous phosphorus for sodium ion batteries. Angew. Chemie 125, 4731–4734 (2013)