Molten salt-assisted valorization of waste PET plastics into nanostructured SnO2@terephthalic acid with excellent Li-ion storage performance

Polyethylene terephthalate (PET) is one of the most widely used plastic materials, and therefore, its clean, efficient and low-cost valorization into high-value materials is of substantial economic and environmental interest. Here, for the first time, the utilization of molten salts for the facile, scalable and fast depolymerization of PET into terephthalic acid (C8H6O4) is reported. It is asserted that the simple heat-treatment of PET in molten KCl-LiCl containing SnCl2 in air leads to the green preparation of nanocrystalline terephthalic acid embedded with SnO2 nanocrystals, with an excellent performance as the anode of lithium ion batteries (LIBs). The structural, morphological, thermal, surface, electrical and electrochemical characteristics of plastic-derived nanocomposites are evaluated by various techniques. The sample prepared at 500 °C (PDN-500) contains 28.3 wt% SnO2, and exhibits an enhanced bulk electrical conductivity of 447.3 S m−1, and an excellent Li-ion storage capacity of 498 mAh g-1 after 500 cycles, corresponding to 1657 mAh per gram of SnO2. This performance is accompanied by an enhanced lithium ions diffusion coefficient of 8.51 × 10−10 cm2 s−1 recorded after 300 cycles, and a capacitive storage contribution of above 42 %. The sustainability of the presented molten salt approach is discussed from two complementary points of view, in terms of the clean conversion of waste plastics into high-performance anode materials for LIBs, as well as the facile and scalable depolymerization of PET, reducing the waste plastics in our environment. This article proposes an efficient and green strategy for the valorization of waste plastics into nanostructured SnO2@terephthalic acid for energy storage applications.