Suppressing Self-Discharge in Aluminum-Graphite Batteries with a Triple-Function Polymer Electrolyte

Abstract Aluminum–graphite (Al–G) batteries suffer from severe self-discharge, with capacity losses of up to 26% within 12 h in conventional chloroaluminate ionic liquid electrolytes. In the Al–G system, self-discharge manifests as the spontaneous deintercalation of AlCl4– anions from the graphite cathode and is further accelerated by parasitic reactions involving the electrolyte, binder, separator, and current collector. Here, we demonstrate a PAN-based polymer electrolyte that simultaneously functions as ion conductor, separator, and cathode binder, thereby suppressing multiple self-discharge pathways at once. The dense polymer matrix kinetically hinders anion deintercalation while eliminating additional binders and porous separators that may promote parasitic reactions. As a result, the system retains 99.5% capacity after 24 h, 97.7% after 7 days, and 94.3% after 21 days under open-circuit conditions, corresponding to a capacity loss of only 0.27% per day. The suppression of self-discharge is primarily attributed to the polymer electrolyte binder, as confirmed by controlled comparisons using an identical current collector across different binder systems. These results were achieved using a commercially available conductive polyimide current collector instead of glassy carbon collectors, which are typically employed in low-self-discharge Al–G systems. This represents an additional advantage for large-scale manufacturability. The proposed multifunctional polymer approach therefore provides a practical route toward aluminum batteries with substantially improved storage stability and enhanced suitability for long-term stationary energy storage applications.