由于汽车工业的持续发展,对高能量密度二次电池的需求逐步增加,锂硫电池开始走进人们的视野.锂硫电池的理论比能量高达2600Wh/kg,而单质硫的理论比容量达1680mAh/g.同时,硫的储量丰富,廉价,并且环境友好.虽然可充电锂硫电池相比于传统锂离子电池有诸多优势,但目前其可实现的实际比容量远低于理论比容量,循环寿命也较短等弊端限制了其大规模应用.作者从Li-S电池正极的工作原理出发,对硫正极容量损失及衰减机理做了深刻的解析,并结合本实验室的工作归纳总结了导致硫正极容量衰减的主要因素.针对硫正极容量衰减因素,从碳导电结构、聚合物包覆以及纳米金属氧化物添加剂等方面,对近年来提高硫正极性能的主要研究方向及最新研究进展进行了综述,并对其中存在的问题进行分析,最后对提高Li-S电池的整体性能提出展望.%Because of automotive industry sustainable development, the demand for higher energy density rechargeable batteries make the lithium-sulfur (Li-S) batteries become one of the most attractive candidates. The Li-S systems have a theoretical specific energy of 2600 Wh/kg while the theoretical capacity of sulfur is 1680 mAh/g. Sulfur is abundant, low cost and environment friendly. Although the rechargeable Li-S batteries possess more advantages over the conventional lithium ion batteries, the practical use faces with a variety of problems such as low specific capacity and short cycle life. Based on the fundamental electrochemical process of the sulfur cathode, the capacity fading mechanism of the sulfur cathode is analyzed in details. Combining with the works of our research team, the factors leading to the cathode property fading mechanism are summarized. Firstly, the main issue is that sulfur is both ionically and electrically insulating. And the insoluble low-order lithium polysulfide discharge products are also expected to be electronic insulators. So the cathode structure must contain electronic conductors (carbon or metal powder) which will decrease the energy density. Secondly, researchers impute the capacity fading into the residual Li2S2 and Li2S in sulfur cathode even at 100% depth of charge. The formation of Li2S2 and Li2S increasing with cycling results in active material loss. And the deposition of irreversible Li2S or Li2S2 at cracked surfaces of carbon particles causes cathode structural failure. Thirdly, high ordered lithium polysulfide (Li2Sn, 3≤n≤8) is soluble in electrolyte, but low ordered lithium polysulfide (Li2S2 and Li2S) is insoluble. Thus chemical precipitation/dissolution reactions occur during the electrochemical process resulting in active material transition between liquid phase and solid phase. But it is difficult for the high ordered lithium polysulfide to transfer completely from liquid phase to solid phase at the end of cycles, so that will lead to the active material loss. Fourthly, another serious problem is the irreversible oxidation of cathode active material. The formation of LixSOy species increasing with cycling indicates an important capacity fading mechanism of Li-S battery. In this paper, the main research directions and the latest development to enhance the performance of sulfur cathode are reviewed from the aspects of carbon conductive structure, polymer coatings and metal oxides additives, and also the problems in each research directions are analyzed. Finally, the further development of Li-S battery is discussed.
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