Composite cathode material for improved aluminum–polymer batteries

Abstract

Rechargeable aluminum batteries (RABs) are an emerging post-lithium technology for their large ore reserves and better safety properties. However, conventional cathode materials like graphite have limited storage capacity because the intercalation of AlCl₄⁻ occurs only in every third or fourth layer of graphite. On the other hand, organic compounds with a different working principle lack stability in the strongly Lewis acidic electrolytes due to rapid dissolution. Hence, this investigation presents a composite consisting of an organic compound 9,10-phenanthrenequinone (PQ) and graphite as a cathode material for improved RABs. For the melt diffusion synthesis, spherical graphite (SPG) was used at a ratio of 2 : 3 to PQ. A recently developed solid polymer based on aluminum chloride (AlCl₃), triethylamine hydrochloride (Et₃NHCl) and polyamide (PA6) was used as electrolyte. The combination of fabricated composite and solid polymer electrolyte (SPE) with an Al anode offered significant improvement in capacity and cyclability compared to pure SPG or pure PQ cathodes. The cyclic voltammetry analysis showed that both components contribute to the capacity, which was also confirmed by operando XRD, FT-IR, XPS, and EPR analysis. Therefore, both intercalation and coordination reactions take place synergetically. Additionally, SPG was exchanged with meso carbon micro-beads (MCMB) and graphite flakes (GF), which demonstrated no considerable impact of the graphite particle shape on the cathode performance.