Stabilizing Sulfur Cathode in Carbonate and Ether Electrolytes: Excluding Long-Chain Lithium Polysulfide Formation and Switching Lithiation/Delithiation Route

Due to the inevitable chemical reactions between the nucleophilic lithium polysulfides and electrophilic carbonate solvents, conventional S cathodes are incompatible in carbonate-based electrolytes. Alternative ether-based electrolytes are confronted with another concern of the dissolution of long-chain Li 2 S x (4 ≤ x ≤ 8) intermediates. Herein, originally designed strategy to stabilize S cathodes in these two electrolytes was proposed by introducing central Fe linkers to switch the lithiation/delithiation route from the formation of long-chain Li 2 S x intermediates to Li y FeS x intermediates. Based on this, amorphous FeS x /C (a-FeS x /C, x = 2, 4, 6) composites, synthesized by comelting ferrocene and sulfur, were demonstrated as effective cathodes for Li–S batteries. a-FeS 4 /C cathode delivers a remarkably high capacity of 931 mAh g –1 at 0.1 A g –1 and a stable cycling performance of over 500 cycles in a carbonate electrolyte without any compatibility problem. Good cyclability with high capacity is also demonstrated in a LiNO 3 -free ether electrolyte.