Tuning Porous Carbon into Hard Carbon via an S _N 2 Reaction for Enhanced Sodium Storage

Porous carbon (PC) is widely used in energy storage devices such as supercapacitors due to its high surface area and abundant ion-accessible pores. However, its excessive open porosity in sodium-ion batteries (SIBs) leads to severe side reactions and low initial Coulombic efficiency. Regulating pore structures to transform PC into hard carbon (HC) with rich closed-pores is essential for improving sodium storage performance. Here, we report a direct microstructural conversion of PC into high-performance HC anodes for SIBs via the upcycling of polytetrafluoroethylene (PTFE) waste. Assisted by Brønsted-basic NH₃, the ultrastrong C-F bonds in PTFE are efficiently cleaved, inducing <i>in situ</i> carbon deposition that transforms open pores into a closed-pore structure with curved graphitic domains. The optimized YPT-1200 electrode achieves a high reversible capacity of 370.3 mAh g^-1 with satisfactory initial Coulombic efficiency of 78.0% as well as impressive cycling stability (83.4% capacity retention over 300 cycles at 0.5C).