Realizing rechargeable cathode-free aluminum-ion batteries via regulating solvation structure in aqueous-aprotic electrolytes

Abstract

Aqueous aluminum-ion batteries (AIBs) are promising candidates for large-scale energy storage due to the abundant resource reserve, high theoretical capacity, intrinsic safety, and low cost of Al. However, the development of aqueous AIBs is constrained by the inefficient Al plating, inevitable parasitic side reactions, and the collapse of the cathode materials. Herein, we propose a novel Al3+/Mn2+ hybrid electrolyte in a water-acetonitrile co-solvent system with a regulated solvation structure to realize cathode-free AIBs. The inclusion of acetonitrile as a co-solvent plays a crucial role in reducing the desolvation energy and suppressing side reactions. The introduction of Mn2+ can enable the reversible plating/stripping of Al-Mn alloy with reduced overpotentials on the anode and deposition/stripping of AlxMnO2 on the cathodic current collector to realize cathode-free AIBs. The architected AIB delivers a high discharge capacity of 397.9 mAh g−1, coupled with superior rate capability and stable cycling performance. Moreover, the cathode-free AIB shows superior low-temperature performance and can operate at −20 °C for over 120 cycles. This work provides new ideas for developing high-performance and low-cost aqueous AIBs.