Evidence for dual anions co-insertion in a transition metal chalcogenide cathode material NiSe2 for high-performance rechargeable aluminum-ion batteries

Rechargeable aluminum-ion batteries (RAIBs) are the subject of great interest owing to their attractive features like natural abundance, trivalent character, ultrahigh theoretical volumetric energy density and inherent safety, which endow RAIBs great prospect for large-scale energy storage devices. Nevertheless, the application of transition metal chalcogenide compounds as energy-dense cathode materials for RAIBs is currently hindered by their poor cycling stability and inadequate understanding of energy storage mechanisms. Here, we report dramatically enhanced aluminum storage performance from well-designed three-dimensional (3D) NiSe2 sponges wrapped with graphene oxide nanosheets (3D NiSe2 sponges@carbon composite). Electrochemical studies confirm that high capacity, superior rate capability and extraordinary cycling stability can be achieved from the prepared 3D NiSe2 sponges@carbon composite, rendering it a competitive cathode material for RAIBs. Moreover, combining comprehensive experimental measurements with systematic theoretical calculations, we show that dual anions co-insertion of AlCl4- and Cl- involved charge storage mechanism can be uncovered for the first time in NiSe2 -based RAIBs. This new understanding of the aluminum storage mechanism provides chemical clues to further exploit the transition metal chalcogenide compounds electrode with substantial energy benefits.