Revealing the multiple cathodic and anodic involved charge storage mechanism in an FeSe2 cathode for aluminium-ion batteries by in situ magnetometry

Abstract

Rechargeable aluminium-ion batteries (AIBs) are considered to be promising alternatives to current lithium-ion batteries (LIBs), since they can have the advantages of low cost with high energy-to-price ratios. Unlike in LIBs, the charge storage mechanism in AIBs involving different ionic species is far more complicated and remains largely unexplored, which impedes further screening and optimization of cathode materials that can reversibly accommodate aluminium-based (complex) charge carriers with boosted cell performance. Here, we report a comprehensive study of the battery chemistry in metal selenide based cathodes in AIBs from an integrated chemical and physical point of view. Various in situ and ex situ characterization techniques and theoretical calculations reveal that both Cl⁻ and AlCl₄⁻ can act as charge carriers in FeSe₂ cathodes during the charge process, and the Al³⁺ can also be embedded into the host upon the discharge process. Furthermore, using in situ magnetometry, the spin-polarized surface capacitance is observed in AIBs for the first time, which proves that Al³⁺ can serve as a charge compensator in the formation of space charge zones with electrons. These innovative findings provide unprecedented insight into the charge storage mechanism of AIBs.