Electrochemical Stabilization of Polytetrafluoroethylene (PTFE) via Electronic Band Engineering Enables Long-Life, High-Energy-Density Li-Ion Batteries

Abstract

The dry-coating process with polytetrafluoroethylene (PTFE) binder has emerged as a promising technology for fabricating thick electrodes toward high-energy-density lithium-ion batteries (LIBs). However, its practical application is limited by the poor electrochemical stability of PTFE at the anode. The intrinsically low lowest unoccupied molecular orbital (LUMO) energy of PTFE renders it highly susceptible to reduction-induced side reactions at the anode, leading to low initial Coulombic efficiency (ICE) and degradation of electrode microstructure during cycling. To overcome this limitation, the frontier orbital energy level of PTFE is rationally engineered by incorporating weakly electron-withdrawing oxygen- and nitrogen-containing functional groups via O2 plasma treatment and gas-phase nitridation. This molecular modification strategy induces an increase in LUMO energy, which enhances the electrochemical stability of PTFE under anodic environments. The dry-processed anode employing modified PTFE exhibits a high ICE of 92.8%, compared with 87.8% for the anode with pristine PTFE. Furthermore, full-cells exhibit outstanding long-term cycling stability with negligible electrode swelling with a practical areal capacity of 7 mAh cm−2 over 600 cycles. This finding highlight that the molecular engineering of the PTFE fiber network offers straightforward and effective strategy to suppress PTFE reduction, enabling practical high–energy–density LIBs with long-term cycling stability.