Stable CoSe2/carbon nanodice@reduced graphene oxide composites for high-performance rechargeable aluminum-ion batteries

Abstract

Rechargeable aluminum-ion batteries (RAIBs) are regarded as the next generation of low-cost and high-capacity electrical energy storage systems. Compared to graphene-based cathodes, metal dichalcogenide cathodes can potentially provide RAIBs with higher capacities. However, metal dichalcogenides suffer from poor cycling performance, hindering the further development of high-capacity RAIBs. Thus, to further improve the performance of RAIBs, it is imperative to gain a deep understanding of the mechanisms behind the energy-storage and capacity-deterioration characteristics of these materials. In this work, we conducted detailed characterization to acquire a deep understanding of the energy storage mechanism of a CoSe₂-based cathode. The characterization results revealed that energy storage involved incorporation of Al³⁺ into CoSe₂ to generate Al_mCo_nSe₂ (i.e., partial substitution of Co²⁺ by Al³⁺) and elemental Co, while capacity deterioration resulted from the dissolution of active cobalt species into the electrolyte and the pulverization of the CoSe₂ phase. The understanding of the capacity-deterioration mechanism allowed us to design a two-step concept for a new type of RAIB composite cathode material. Thus, we employed a conductive wrapping layer of reduced graphene oxide (rGO) to protect CoSe₂/carbon nanodice composites from cobalt dissolution and CoSe₂ pulverization while also improving the conductivity of the materials. This novel design resulted in a CoSe₂/carbon nanodice@rGO composite material with an outstanding cycling performance (after 500 cycles) of 143 mA h g⁻¹ at 1000 mA g⁻¹, which is one of the best performances for a metal-based RAIB cathode material reported to date. These findings are of great significance for the further development of high-capacity RAIBs.