Abstract: Rechargeable Aluminum Batteries (RABs) use a Lewis acidic Aluminum chloride (AlCl3) and 1-Ethyl-3-methylimidazolium chloride (EMImCl) ionic liquid electrolyte. Electrode fabrication often relies on procedures from Lithium-Ion Batteries (LIBs), including the use of Polyvinylidene fluoride (PVdF) as a binder. However, PVdF reacts with Al2Cl7- in the RAB electrolyte, making it unsuitable for new battery types. The literature lacks details on the products formed, changes in the ionic liquid electrolyte, and the implications for electrochemical performance. With potential European Chemical Agency (ECHA) restrictions on per- and polyfluoroalkyl substances (PFAS) by 2025, Polyvinylidene chloride (PVdC) is being explored as an alternative binder. In contact with AlCl3:EMImCl (1.50:1.00) electrolyte, both, PVdF and PVdC transform into amorphous carbon during dehydrofluorination (DHF) and dehydrochlorination (DHC), respectively, as confirmed by Raman spectroscopy. Furthermore, via 19F-NMR, it is shown that the reaction time between the soaked polymers and the ionic liquid has a significant influence on the newly formed aluminum chlorofluoride (ACF) complexes. Electrochemical tests of graphite-based electrodes indicate increasing specific capacity of PVdF compared to PVdC with a continuous number of cycles. Amorphous carbon can prevent the disintegration of graphite and enhance conductivity. Furthermore, newly formed AlF4- can run a co-intercalation and lead to increasing specific capacity.
TechnicalRemarks: Fourier-transform infrared (FT-IR) data of pristine PVdF and PVdC powders and soaked in AlCl3:EMImCl PVdF and PVdC.
Raman data of PVdF and PVdC powders. Furthermore, in AlCl3:EMImCl ionic liquid soaked PVdF and PVdC.
19F-NMR (nuclear magnetic resonance) data of ionic liquid electrolyte (black liquid) after soaking PVdF for 1 hour and electrolyte soaked for 12 hours.
Galvanostatic cycling with potential limitation (GCPL) data in the potential window of 0.30 V-2.30 V at a current density of 20 mA.g-1 of PVdF- and PVdC-based graphite positive electrodes at different cycle numbers. Corresponding cyclic voltammograms (CVs) data with a scan rate of 0.20 mV.s-1 at different cycles.
