High-performance aluminum-ion batteries based on AlCl₃/caprolactam electrolytes

Aluminum-ion batteries (AIBs) have become a promising energy storage system due to their excellent cycling performance and safety properties. However, many problems persist in the electrolyte system as well as high cost and harsh working environments. In this study, we prepared two novel electrolytes, namely, AlCl₃/caprolactam (CPL) and AlCl₃/urea/CPL for use in AIBs. The AlCl₃/CPL electrolyte exhibited a specific capacity of 136 mA h g^-1 at a current density of 5 A g^-1. The performance of AIBs was improved when an appropriate amount of urea was added. The AlCl₃/urea/CPL electrolyte achieved a high initial specific capacity of 151 mA h g^-1 at 5 A g^-1 and reached 132 mA h g^-1 with a high coulombic efficiency of ∼98% after 3000 cycles. The CPL electrolyte improved the cutoff voltage and initial discharge voltage of AIBs, and the capacity of AIBs was significantly improved when compared with that of the reported electrolyte. This work provides innovative insights into AIBs, and CPL will be a promising electrolyte for AIBs.