Repurposing Face Masks after Use: From Wastes to Anode Materials for Na-Ion Batteries

Nowadays, face masks play an essential role in limiting coronavirus diffusion. However, their disposable nature represents a relevant environmental issue. In this work, we propose the utilization of two types of disposed (waste) face masks to prepare hard carbons (biochar) by pyrolytic conversion in mild conditions. Moreover, we evaluated the application of the produced hard carbons as anode materials in Na-ion batteries. Pristine face masks were firstly analyzed through infrared spectroscopy and thermogravimetric analysis. The pyrolysis of both mask types resulted in highly disordered carbons, as revealed by field-emission scanning electron microscopy and Raman spectroscopy, with a very low specific surface area. Anodes prepared with these carbons were tested in laboratory-scale Na-metal cells through electrochemical impedance spectroscopy, cyclic voltammetry and galvanostatic cycling, displaying an acceptable specific capacity along a wide range of current regimes, with a good coulombic efficiency (>98% over at least 750 cycles). As a proof of concept, the anodes were also used to assemble a Na-ion cell in combination with a Na3V2(PO4)2F3 (NVPF) cathode and tested towards galvanostatic cycling, with an initial capacity of almost 120 mAhg−1 (decreasing at about 47 mAhg−1 after 50 cycles). Even though further optimization is required for a real application, the achieved electrochemical performances represent a preliminary confirmation of the possibility of repurposing disposable face masks into higher-value materials for Na-ion batteries.