Preparation And Electrochemical Performance Of Sulfur/carbon Composite Cathode Materials For Li/S Batteries

Due to high theoretical specific energy of2567Wh/kg, natural abundance,extremely low cost and environment friendly, sulfur-containing cathode materialshave received considerable attention as prime candidates for high performance energystorage systems. However, they suffer from some significant drawbacks which inhibitthe commercialization of Li-S batteries. Poor charge transfer ability and limited rateperformance are derived from the insulating nature of sulfur and its reductionintermediates/products. Moreover, various soluble Li2Sn(3≤n≤8) intermediates giverise to shuttle effect and active mass loss, leading to fast capacity degradation.In order to address these challenges, a sulfur/carbon composite was prepared by asimple chemical deposition method. A feasible vacuum soaking step was introducedto absorb the sulfur source (Na2Sx) into the carbon micropores/mesopores. It isconfirmed that the S/C composite with vacuum soaking (78wt%sulfur) leads to moredispersion of sulfur into the carbon micropores/mesopores and displays betterelectrochemical features, especially cycling stability, compared to the S/C compositewithout vacuum soaking, the synthesized sulfur/carbon and pristine sulfur/carbonball-milled composite. The S/C cathode with vacuum soaking delivers an initialdischarge capacity of1116.1mAh/g (based on sulfur weight) and retains534.2mAh/gafter150cycles with a discharge/charge rate of0.35C. When the sulfur content islowered as59wt%, the S/C composite with vacuum soaking yields an initial dischargecapacity of1396.9mAh/g and retains683.3mAh/g after150cycles with adischarge/charge rate of0.35C. Moreover, The S/C electrode achieves429.7mAh/gafter120cycles at high-rate of2C.Furthermore, a novel sulfur/carbon composite enhanced by polyvinylpyrrolidone(PVP) was prepared via chemical deposition. The results show that the sulfur/carboncomposite enhanced by PVP could improve the stability of the electrode structure andcycling performance of Li-S battery by minimizing the size of elemental sulfur withinnanoscale and PVP partially serving as binder, which would suppress the shuttle effectand reduce the deposition of Li2S2/Li2S on the electrodes. The prepared S/C electrodedelivers an initial discharge specific capacity of1360.9mAh/g and retains868.6mAh/g (63.8%of the initial specific capacity) after120cycles at0.35C. It achieves aninitial discharge specific capacity of807.9mAh/g and retains435mAh/g after200 cycles even at high-rate of2C.The effect of different binders on the electrochemical performance of Li-S batterywas investigated. Gelatin improves the discharge specific capacity of the Li-S battery.The electrode with PVP binder has better cycling stability than that with other threebinders. The electrode with gelatin retains the specific capacity of354.1mAh/g andthe electrode with PVP achieves a discharge specific capacity of622mAh/g after80cycles at0.2C.