Electrostatic modification of expanded graphite cathode for high-performance aluminum-ion batteries

Abstract

Graphite and its derivatives, as cathode materials for aluminum-ion batteries (AIBs), have excellent cyclic properties, so they have garnered significant research interest over the years. Preliminary research has demonstrated that expanded graphite (EG) exhibits a dual aluminum storage mechanism, i.e., intercalation (1.5–2.5 V) and adsorption (0.5–2.5 V). In this study, for the adsorption mechanism, we propose positively charged EG as a cathode material for AIBs. Using electrostatic modification methods, we found that positive charge on the surface of EG can depress the surface barrier and lead to the adsorption of more anions through electrostatic forces during chemical reactions. Moreover, the improvement of adsorption capacity could play a synergistic coupling role to improve the intercalation kinetics of anions, in which has a high reversible capacity and excellent rate cycling property. Thus, positively charged EG with a large layer space (0.41 nm) demonstrates a high reversible capacity of 118.3 mAh/g at a current density of 1 A/g, along with a conspicuous rate performance of 74.8 mAh/g at 15 A/g. Additionally, as-prepared EG hybrids indicate superb cyclic stability with a retained capacity of 101.8 mAh/g over 10,000 cycles at 5 A/g. The electrostatic modification strategy and expansion of the layer space could facilitate the development of high property graphite cathode materials for AIBs.