锂/硫电池用金属锂负极的表面修饰及电化学性能研究

To increase the energy density is the driving force for secondary batteries. In recent year, lithium-sulfur (Li-S) battery is one of the most potential candidates in the research and development of high energy secondary batteries. In particular, the metallic Li is the anode material with the highest specific capacity, which is a key issue to achieve high energy density and good cycle stability of Li-S battery. The key problems of the metallic Li anode in the application of Li-S battery based on the the electrochemical dissolution-deposition reaction are mainly related to the formation of serious cracks, pulverization and high reduction activity on Li anode. In this proposal, the surface modification will be mainly conducted for metallic Li anode, in order to restrict the formation of serious cracks on Li anode and shuttle reaction of soluble lithium polysulfides, and to reach the good stability during long cycles. Therefore, the in-situ surface modification with stable inorganic fluoride films and multi-composite surface modification on the metallic Li anode will be investigated with a focus on the interface manipulation mechanism of the metallic Li anode, as well as the effect of the surface modification on the electrochemical performance of the metallic Li anode. Some new insights into the control mechanism of restricting the dramatical structure change with serious cracks, and pulverization on lithium anode, as well as the shuttle reaction of lithium polysulfides to lithium anode should be provided in this proposal based on the surface modification of the metallic Li anode. Meanwhile, the long cycle stability of the metallic Li anode in Li-S battery should be realized as the target. The knowledge proposed in this study will be important for fabrication and development of secondary batteies with high energy density based on the metallic Li anode in future. This will beneficial to the theoretical research and potential application of anode materials and batteries.

提高能量密度一直是二次电池发展的驱动力。锂/硫电池是高能量密度二次电池领域中的研究重点之一。别特是，金属锂负极具有高比容量，是实现高能量密度和高稳定性锂/硫电池的关键。针对在基于电化学溶解-沉积反应的锂/硫电池中金属锂负极面临的裂化、粉化和高还原性等关键问题，本申请重点进行金属锂负极的表面修饰，以期抑制锂负极的严重裂化和可溶性锂多硫化物的穿梭反应，以实现金属锂负极的高稳定性。因此，本项目拟采用原位形成稳定性无机氟化物膜和对金属锂进行多重复合表面修饰的技术途径，重点研究在表面修饰对金属锂负极的界面作用机制和电化学行为的影响规律。本申请拟探讨建立基于表面修饰来抑制金属锂负极的验严重裂化、粉化和多硫化物穿梭反应的控制机制，以期实现在锂硫电池体系中金属锂的长期循环稳定性的目标。这也将可为未来基于金属锂负极的高能量密度二次电池体系的构筑与发展奠定可靠基础，具有重要的科学意义和潜在的应用前景。

提高能量密度一直是二次电池发展的驱动力。锂/硫电池是高能量密度二次电池领域中的研究重点之一。金属锂负极具有高比容量，是实现高能量密度和高稳定性锂/硫电池的关键。但是，基于电化学溶解-沉积反应的锂/硫电池中金属锂负极面临的裂化、粉化和高还原性等关键问题。.为解决以上关键问题，项目在锂负极表面修饰、凝胶电解质和锂合金化方面开展了探索研究。主要研究成果如下：.1）在表面修饰研究方面，探索研究了硝酸镧的原位表面修饰，形成硫化锂/硫化镧的钝化膜有助于降低金属锂的强还原性，稳定了在锂-硫电池环境中金属锂负极的形貌；2）在凝胶电解质抑制锂负极腐蚀方面，重点针对金属锂负极的高反应活性与不均匀沉积问题，引入亲锂性和对阴离子吸附性的凝胶电解质，即降低了电解液用量，也减缓了对金属锂负极的腐蚀，确保了金属锂在长期循环过程中的稳定性；3）在锂合金化稳定机制方面，引入非活性金属镁，结合导电网络骨架设计与表面SEI膜的支撑作用，探明了锂镁合金化作用机制和稳定锂负极的策略，实现了研究预期的设计思路。4）在基于硫正极性能提升同时改善锂负极稳定性方面，利用金属氧化物和金属纳米粒子对多硫化物的吸附和催化作用，减缓和抑制多硫化物多锂负极的副反应，进而改善了锂负极的稳定性。本工作研发的S/NiCo2O4复合材料体积比容量和重量比容量分别达到1867mAh/cm3和1125mAh/g(composite)，圆满完成了项目预期的研究目标。总之，本项目研究成果推进高比能锂硫电池的研发进程，具有重要的理论意义和潜在的应用前景。.项目研究成果申请中国发明专利6项，发表SCI收录论文11篇，其中包括Adv. Energy Mater. (2篇)和Adv. Funct. Mater. (2篇)。项目执行期间，培养博士研究生5名，硕士研究生3名。