Boosting the Initial Coulombic Efficiency of Sustainable Hard Carbon Derived from Polyethylene Terephthalate with Cyclopentyl Methyl Ether As a Co-Solvent for Wide-Temperature Sodium-Ion Batteries

Abstract

Upcycling plastic waste into value-added products helps to generate cost-effective and sustainable resources towards a circular materials economy and safer ecosystem. The conversion of polyethylene terephthalate (PET) municipal waste via the carbonization process into hard carbon (HC) delivers a high-reversible capacity, low-cost, sustainable anode material for sodium-ion batteries (SIBs). However, the low initial Coulombic efficiency (ICE) is a significant challenge of the HC anode, which should be optimized by electrolyte and interfacial chemistry.1 In conventional carbonate esters-based electrolytes, ethylene carbonate (EC) forms an organic-rich thick SEI layer, soluble on cycling, limiting the cyclic stability. The low-temperature performance is also a significant concern in achieving high capacity, long cyclability, and ICE.2 Herein, HC derived via single-step carbonization at 1000℃ exhibits larger interlayer spacing of 0.379 nm, low surface area (~205 m2g-1), and unique slit-shaped pores with 84% mesoporosity in the structure. PET-HC exhibits a high reversible capacity of 337 mAh g-1 with ICE of just 66%, using EC-PC-based electrolyte. EC-free cyclopentyl methyl ether (CPME) was used due to its weakly solvating and wide temperature solvent.3 CPME-PC-based electrolytes significantly enhanced the ICE value to 74.5% and reversible capacity to 356 mAh g-1 with superior cycling of 91% after 100 cycles at 0.1C rate. The inorganic-rich SEI layer for CPME-PC-based electrolytes results in a thin SEI that improves the ICE and cyclic stability of the anode. The low-temperature performance (up to -20°C) for CPME-PC-based electrolytes showed ~30% added capacity compared to EC-PC-based electrolytes. This work provided an eco-friendly approach to developing hard carbons from plastic trash and offered an effective strategy to replace EC with CPME for low-temperature sodium storage applications. References Shen, L., Shi, S., Roy, S., Yin, X., Liu, W., Zhao, Y., Adv. Funct. Mater. 2021, 31, 2006066. Ramasamy, H. V., Kim, S., Adams, E. J., Rao, H. & Pol, V. G. Chem. Commun. 2022, 58, 5124–5127.Zhang, H., Zeng, Z., Ma, F., Wu, Q., Wang, X., Cheng, S., Xie, J., Angew. Chem. 2023, e202300771. Figure 1