Regulating and Understanding Charge-Discharge Process for High-Performance Lithium-Sulfur Batteries
The charge-discharge process of lithium-sulfur battery is a 16-electron transfer process,which makes the specific capacity of the sulfur cathode up to 1675 mAh/g. However,the slow and complex kinetic process also results in shuttle effects and low availability of active substances for soluble polysulfides. In view of this,the use of cisplatin as a redox medium to regulate the charge-discharge process of lithium-sulfur batteries through the spontaneous redox reaction between polysulfide and cisplatin was reported. Meanwhile,cisplatin was used as a molecular probe to identify the redox reaction path of active substances in lithium-sulfur batteries. It was demonstrated that the introduction of cisplatin could accelerate charge transfer kinetics,regulate redox pathways and achieve deep transformation of Li2S2 to Li2S. The maximum specific capacity of the lithium-sulfur battery reached 1290 mAh/g,and the average capacity attenuation per cycle was only 0.017％after 1000 cycles,and the high energy density of 318.8 Wh/kg was achieved in the pouch cell with low electrolyte/sulfur ratio (2.5μL/mg) for practical application value. The mechanism of cisplatin was investigated by in-situ Raman spectroscopy,electrochemical quartz crystal microbalance,mass spectrometry and other characterization methods. The results showed that cisplatin could regulate the reaction path of lithium-sulfur batteries by generating redox active cisplatin/polysulfide complexes. The sluggish charge-discharge process was replaced by the more rapid redox process of Pt4+/Pt2+pairs. The results of this study provided a unique insight into the rational use of functionalized redox mediators to solve the key issues of lithium-sulfur batteries.
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