Dense graphene papers: Toward stable and recoverable Al-ion battery cathodes with high volumetric and areal energy and power density

Since Al ion batteries (AIBs) are known to be a novel energy storage prototype of more safe and higher energy density, challenges are still in the currently explored carbon cathodes, specifically in balancing the rapid ion transport channels and volumetric/areal energy storage capability at a dense fashion. In this contribution, exceptional graphene nanosheet (GN) papers that are well stacked by conductive graphene nanosheets have been demonstrated as an electrochemically stable host for fast AlCl₄ ^- ion transport/storage along with high volumetric/areal energy storage at a dense state (1.6~1.8 g cm⁻³). Owing to the exclusive morphological and chemical advantages, the as-assembled AIBs with the binder-free GN paper cathode enables to deliver considerably high specific capacity 100 mA h g⁻¹ at the current density 50 mA g⁻¹ (approaching the theoretic value of carbon AIB cathodes), coupled with much enhanced volumetric capacity, areal energy density and power density compared to the reported carbon AIB cathodes. Particularly, the term of tortuosity has been employed to understand the fundamental relationship between volumetric energy performance and microscopic structures, which suggests a unique platform for developing advanced practical AIBs.