锂硫电池用键合型一体化硫电极的构筑及其性能研究

Lithium sulfur batteries are becoming current research hotspot in the field of chemical power sources for their prominent advantage on energy density. However, such problems including the low utilization of active sulfur, poor cycling stability and damaged cathode framework by volume change during charge/discharge process seriously restricted the development of lithium sulfur batteries. In allusion to the problems mentioned above, commercial conductive carbon black were used in this project as matrix materials for sulfur loading to prepare sulfur/carbon composites. Then, polydopamine coated sulfur/carbon composites with core-shell structure, based on carbon-polymer synergy effect, were obtained by using in situ self-polymerization technology. Furthermore, the synthesis of bonding integrated sulfur cathode was innovatively carried out by grafting of both conductive additives and binders onto polymer coated materials via chemical bonding methods. The influence of the structure, morphology and structure-activity relationship of related composites and integrated sulfur cathode on electrochemical performances were systematically investigated by corresponding testing and characterization technologies, and the electrochemical performances were then compared with the sulfur cathode prepared by physical mixing processes. The design route of bonding integrated sulfur cathode, presented in this project, will provide important theoretical and experimental basis for further studies and applications of lithium-sulfur batteries.

锂硫电池在能量密度方面的显著优势使其成为当前化学电源领域研究的热点。但是，硫电极存在的活性物质利用率低、循环稳定性差以及充放电过程中体积变化对电极结构的破坏等问题严重制约了锂硫电池的发展。针对上述问题，本项目提出以商业化导电炭黑作为基体材料负载活性物质硫，制备不同硫含量的硫/碳复合材料；利用原位自聚技术，获得基于碳-聚合物协同作用的核壳结构聚多巴胺包覆硫/碳复合材料；在此基础上，创新性地将聚合物包覆材料通过化学键合的方式同时接枝导电添加剂和粘结剂，从而实现键合型一体化硫电极的构筑。利用相应的测试表征技术，系统研究所制备的相关复合材料和一体化硫电极的结构组成、微观形貌、构效关系对其电化学性能的影响规律，同时对采用物理混合方式制备的硫电极的电化学性能进行比较。本项目提出的键合型一体化硫电极的设计思路，将为锂硫电池的进一步研究和应用提供重要的理论和实验依据。

基于“轻质”、多电子氧化还原反应的锂硫电池，由于其高达2600 Wh/kg的理论能量密度，近年来受到广泛关注。锂硫电池理论比能量比传统锂离子电池高出一个数量级。锂硫电池尽管研究了数十年，但活性物质利用率低，容量快速衰减，倍率性能差等难题制约了其实际应用。本项目对锂硫电池体系中的正极、电解液和隔膜材料进行了认真的研究，取得了一定的进展，主要包括如下3个方面：.（1）将导电添加剂科琴碳黑与升华硫进行不同方法的复合，制备了硫含量相同的3种硫/碳复合材料。对比发现，采用两步高温热处理法制备的硫/碳复合材料电化学性能最佳。将复合材料在不同锂盐浓度的电解液中测试，发现在浓度高的电解液中电化学性能更优异。研究表明，硫/碳复合材料的制备方法及电解液中锂盐的浓度对硫电极的性能将产生重要影响。.（2）将商品化的导电碳黑BP2000作为活性硫的导电基体材料，通过高温热处理，制备了硫含量分别为50wt.%，60wt.%和72wt.%的3种S/BP2000复合材料。3种硫/碳复合材料在碳酸酯类电解液中进行电化学性能测试表明，硫含量为50wt.%的硫/碳复合材料具有最佳的电化学性能。在50 mA/g小电流密度下，首周放电容量能达到1624.5 mAh/g，接近理论放电比容量。即使在800 mA/g大电流密度下，首周放电容量也能达到1288.6 mAh/g，循环180周以后容量还能保持在522.8 mAh/g。表现出良好的循环性能和倍率性能。因此，廉价易得的商品化导电碳黑BP2000有望用于锂硫电池中硫电极的导电基体。.（3）采用两步浸渍法制备了亲水性聚多巴胺修饰隔膜，并将其应用于锂硫电池。研究发现采用亲水性聚多巴胺隔膜组装的锂硫电池比采用未修饰的疏水性隔膜组装的锂硫电池性能更为优越。采用亲水性隔膜组装的锂硫电池在0.2 C倍率放电下，首周放电容量达1271 mAh/g，循环30周以后容量能稳定在1020.3 mAh/g，比未修饰隔膜组装的锂硫电池容量提升77%。测试结果表明具有亲水性特性的隔膜能显著提高锂硫电池的电化学性能。