A novel Na_(8)Fe_(5)(SO_(4))_(9)@rGO cathode material with high rate capability and ultra-long lifespan for low-cost sodium-ion batteries

Sodium-ion batteries(SIBs)are regarded as the most promising technology for large-scale energy storage systems.However,the practical application of SIBs is still hindered by the lack of applicable cathode materials.Herein,a novel phase-pure polyanionic Na_(8)Fe_(5)(SO_(4))_(9) is designed and employed as a cathode material for SIBs for the first time.The Na_(8)Fe_(5)(SO_(4))_(9) has an alluaudite-type sulfate framework and small Naþion diffusion barriers.As expected,the as-synthesized Na_(8)Fe_(5)(SO_(4))_(9)@rGO exhibits a high working potential of 3.8 V(versus Na/Naþ),a superior reversible capacity of 100.2 mAh g1 at 0.2 C,excellent rate performance(~80 mAh g1 at 10 C,~63 mAh g1 at 50 C),and an ultra-long cycling life(91.9%capacity retention after 10,000 cycles at 10 C,81%capacity retention after 20,000 cycles at 50 C).We use various techniques and computational methods to comprehensively investigate the electrochemical reaction mechanisms of Na_(8)Fe_(5)(SO_(4))_(9)@rGO.