A Flexible Solid-State Ionic Polymer Electrolyte for Application in Aluminum Batteries

Rechargeable aluminum batteries are promising candidates for post-lithium energy storage systems. The electrolyte system of rechargeable aluminum batteries is an urgent research topic hindering the deployment in large-scale applications. To solve the critical problems of current ionic liquid electrolytes, such as leakage, corrosivity, and the need for using separators, we developed a freestanding ionic polymer electrolyte using the direct complexation of polyamide 6 (PA6) with aluminum chloride (AlCl3) and the organic salt triethylamine hydrochloride (Et3NHCl). This complexation allows a dissolution of up to 20 wt % of PA6 in the sample to achieve outstanding mechanical strength and stable electrode–electrolyte interfaces without loss of electrolyte properties. The mechanical and electrochemical properties of the polymer were studied and correlated to the complexation mechanism, which was investigated by FTIR spectroscopy. The ionic polymer electrolyte allows the elimination of unfavorable separators and achieves a high ionic conductivity up to 0.3 mS cm–1 and is capable of electrochemical stripping/plating of aluminum. An Al/graphite battery using this electrolyte provides excellent cycling performance. In addition, the nonflowing ionic polymer electrolyte eliminates the corrosion caused by electrolyte leakage in aluminum batteries and enables the use of conventional stainless steel housings. Our results indicate that this type of solid-state ionic polymer is a promising strategy for achieving stable and safe, yet flexible aluminum batteries.