Non-Electroconductive Polymer Coating on Graphite Mitigating Electrochemical Degradation of PTFE for a Dry-Processed Lithium-Ion Battery Anode

Polytetrafluoroethylene (PTFE)-based dry process for lithium-ion batteries is gaining attention as a battery manufacturing scheme can be simplified with drastically reducing environmental damage. However, the electrochemical instability of PTFE in a reducing environment has hampered the realization of the high-performance dry-processed anode. In this study, we present a non-electroconductive and highly ionic-conductive polymer coating on graphite to mitigate the electrochemical degradation of the PTFE binder and minimize the coating resistance. Poly(ethylene oxide) (PEO) and poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) coatings on the anode material effectively inhibit the electron transfer from graphite to PTFE, thereby alleviating the PTFE breakdown. The graphite polymer coatings improved initial Coulombic efficiencies of full cells from 67.2% (bare) to 79.1% (PEO) and 77.8% (P(VDF-TrFE-CFE)) and increased initial discharge capacity from 157.7 mAh g_(NCM)^-1 (bare) to 185.1 mAh g_(NCM)^-1 (PEO) and 182.5 mAh g_(NCM)^-1 (P(VDF-TrFE-CFE)) in the full cells. These outcomes demonstrate that PTFE degradation in the anode can be surmounted by adjusting the electron transfer to the PTFE.