Stabilizing anionic redox processes in electrospun NiS₂–based cathode towards durable aluminum-ion batteries

Rechargeable aluminum-ion batteries (AIBs) are receiving considerable attention as a desirable device for large-scale energy storage owing to high theoretical capacity and abundance of aluminum. However, due to strong charge of Al³⁺, the state-of-the-art AIBs often show sluggish electrode reaction kinetics and rapid capacity fading and the available cathode materials always demonstrate poor structural stability, thereby greatly hindering their practical use. NiS₂ with anion redox species (S₂^2– dimers) and favorable electronic conductivity is a promising cathode to boost the performance of AIBs in terms of reversible capacity, rate capability and cycling stability. Here, we report a systematic investigation of the Al storage behavior and mechanism of NiS₂/S-doped carbon (NiS₂/SC) cathode based on a series of electrochemical tests and ex situ measurements. We further develop electrospun NiS₂/S-doped carbon@S-doped carbon nanofiber (NiS₂/SC@SCNF) structure as the cathode of AIBs. The as-fabricated AIB delivers an unprecedented Al³⁺ storage performance with a stable capacity of 76 mAh/g at 0.5 A/g CV 500 cycles and a superior cycling Coulombic efficiency of 97 %. This study reveals that NiS₂/SC@SCNF undergoes a reversible evolution of initial Al³⁺ insertion followed by anionic redox between S₂^2– and S^2–, paving the road for the futher development of NiS₂–based cathodes for AIBs.