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

Abstract

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.

Effect of PVdF Distribution on Properties and Performance of Dry Spray-Coated Graphite Electrodes for Lithium-Ion Batteries for Electric Vehicle Applications

“…The high plasticity of PTFE allows forming fibers under shearing to connect electrode particles. However, there are challenges associated with PTFE in LIB anodes since it is known for its unstability at low potential, 16 contributing to capacity loss in the early stages of battery cycling. 14,17 PTFE production has also been singled out as having significant environmental impacts.…”

Dry Electrode Processing Technology and Binders

“…A full cell assembled with a commercial NCM electrode as the cathode was tested, and the results showed that the PEO and P(VDF-TrFE-CFE) layers increased the initial discharge capacity of the battery from 157.7 mAh/g (uncoated graphite anode) to 185.1 mAh/g and 182.5 mAh/g, respectively, and the ICE was improved from 67.2% (uncoated graphite anode) to 79.1% and 77.8%; this work provides a reliable idea for solving the instability problem of PTFE in anode. To solve this problem, a strategy was proposed and experimentally verified by Taegeun Lee et al [83] in 2024, in which the graphite particles were coated with a layer of PEO or poly(vinylidene-fluoride−trifluoroethylene−chlorofluoroethylene) (P(VDF-TrFE-CFE)) that does not conduct electrons but conducts ions to partially block the occurrence of side reactions of PTFE at the anode (Figure 17). A full cell assembled with a commercial NCM electrode as the cathode was tested, and the results showed that the PEO and P(VDF-TrFE-CFE) layers increased the initial discharge capacity of the battery from 157.7 mAh/g (uncoated graphite anode) to 185.1 mAh/g and 182.5 mAh/g, respectively, and the ICE was improved from 67.2% (uncoated graphite anode) to 79.1% and 77.8%; this work provides a reliable idea for solving the instability problem of PTFE in anode.…”

“…In the same year, Ziqi Wei et al [84] prepared a dry graphite anode using PEO-coated graphite with PTFE as the fibrillated binder, and compared the contents of the side reaction components between the uncoated graphite anode and PEO-coated graphite anode with an XPS test, which proved that the PEO-coated graphite anode had fewer side reactions; when the half-cell was assembled using a lithium foil as the counter electrode for the test, the PEO-coated graphite anode showed a much higher CE of 90.9% than that of the uncoated graphite anode (69.5%), which again verified the feasibility of this strategy (Figure 18). To solve this problem, a strategy was proposed and experimentally verified by Tae geun Lee et al [83] in 2024, in which the graphite particles were coated with a layer o PEO or poly(vinylidene-fluoride−trifluoroethylene−chlorofluoroethylene) (P(VDF-TrFE CFE)) that does not conduct electrons but conducts ions to partially block the occurrenc of side reactions of PTFE at the anode (Figure 17). A full cell assembled with a commercia NCM electrode as the cathode was tested, and the results showed that the PEO and P(VDF-TrFE-CFE) layers increased the initial discharge capacity of the battery from 157. mAh/g (uncoated graphite anode) to 185.1 mAh/g and 182.5 mAh/g, respectively, and th ICE was improved from 67.2% (uncoated graphite anode) to 79.1% and 77.8%; this work provides a reliable idea for solving the instability problem of PTFE in anode.…”