Graphene-Stabilized δ-MnO2 Cathode for High-Capacity Aqueous Aluminum-Ion Batteries

Aluminum-ion batteries (AIBs) are emerging as promising alternatives to lithium-ion batteries due to their cost-effectiveness and resource abundance. However, their practical application is hindered by low capacity, poor cycle life, and limited rate capability. In this study, δ-MnO2 and δ-MnO2/Graphene composite cathodes are developed and tested in aqueous aluminum-ion batteries (AAIBs) using a mixture of 0.5 M Al2(SO4)3 and 0.4 M MnSO4 as the electrolyte. The electrochemical properties are evaluated alongside treated aluminum (TAl) and Zn–Al alloy anodes. Among the configurations tested, the δ-MnO2/Graphene|0.5 M Al2(SO4)3, 0.4 M MnSO4|Zn–Al system showed the best performance, achieving a high discharge voltage of 1.63 V, a specific capacity of 746 mAh g−1, and excellent cycling stability over 352 cycles. The stabilizing effect of graphene, due to increased oxygen vacancies and the formation of Mn–O–C bonds, enhances electron and ion transport, thereby improving cathode integrity and the overall performance of the AAIB. Additionally, the Zn–Al alloy anode extends the battery’s cycle life compared to the TAl anode. This work demonstrates the potential for low-cost, high-performance AAIBs, paving the way for more sustainable and scalable energy storage solutions.