Investigation of PEO as an alternative non-fluorinated binder for P2-NFMO cathode material for SIBs

Poly(vinylidene fluoride) is a widely used binder for cathodes in lithium-ion and sodium-ion batteries. However, poly(vinylidene fluoride) is sensitive to base-induced decomposition via defluorination, which can negatively impact electrochemical performance. This issue is particularly pronounced in sodium-ion batteries due to the higher basicity of sodium, underscoring the need for alternative binder systems. In this work, poly(vinylidene fluoride) and poly(ethylene oxide) are investigated as binders for a P2-Na 2/3 Mn 2/3 Fe 1/3 O 2 cathode material, with poly(ethylene oxide) selected as a fluorine-free alternative to poly(vinylidene fluoride) due to its favorable ionic conductivity, mechanical properties, affordability, and environmental compatibility, thereby enabling a systematic comparison between fluorinated and fluorine-free binders. Fourier-Transform Infrared Spectroscopy revealed structural changes in poly(vinylidene fluoride) during slurry preparation, whereas poly(ethylene oxide) remained unaffected. X-ray Photoelectron Spectroscopy analysis confirmed the chemical and electrochemical stability of poly(ethylene oxide), while NaF formation provided clear evidence for poly(vinylidene fluoride) defluorination and its further degradation during cycling. Galvanostatic charge/discharge measurements showed an improvement in capacity retention of 5.8% after 100 cycles for poly(ethylene oxide) -based electrodes compared to poly(vinylidene fluoride), demonstrating the detrimental impact of poly(vinylidene fluoride) degradation on electrochemical performance. These findings highlight the importance of developing chemically stable binder systems for sodium-ion batteries.