Achieving long-cycling life rechargeable aluminum batteries with a Cu2Se cathode enabled by a carbon-functionalized separator

Transition metal selenides (TMSs) become one of the most promising cathode materials for rechargeable aluminum batteries (RABs) due to the advantages of high specific capacity, low cost, and simple preparation process. However, TMSs are soluble in the acidic chloroaluminate ionic liquid electrolyte during cycling, leading to undesirable electrochemical performance. Herein, rechargeable Al-Cu2Se batteries are fabricated with acetylene black modified separator (AB/GF/A) showing excellent electrochemical performance with capacity retention of 95 mAh g−1 after 5000 cycles at 0.5 A g−1 and 166.1 mAh g−1 at 1.0 A g−1. By combining electrochemical tests and ex situ spectroscopy and electronic microscope characterizations, it is revealed that the dissolved Cu and Se species adsorbed on the surface of AB/GF/A still remain electroactivity, which transforms the diffusion-controlled mechanism of Cu2Se to surface pseudocapacitance-controlled behavior, thus suppressing the shuttle effects and boosting the reaction kinetics. The in-depth understanding of the functionalized separator in energy storage mechanism of TMSs could provide reference for further progress of RABs in the future work.