电子器件的性能在不断提高，对电池能量密度的要求也随之增加。金属锂负极具有理论比容量高，氧化还原电势低的优点，被认为是最具潜力的负极材料之一。然而，金属锂电极在循环过程中还存在两大问题亟待解决，一方面是金属锂电极循环过程中会形成枝晶，刺穿隔膜，导致电池内部短路，致使电池发生起火、爆炸等一系列安全事故；另一个问题则是金属锂与电解液发生反应，在大量消耗电解液的同时，反应的产物会增加电池界面内阻，同时枝晶从金属锂电极表面脱落后形成“死锂”，会进一步增加内阻，影响电池循环性能。因此提高金属锂电池的安全性能和循环性能势在必行，本论文主要围绕功能复合隔膜的制备及其在金属锂电池中的应用开展了如下四个方面的工作：

1. 制备了锆钛酸铅（PZT）/聚丙烯（PP）复合隔膜，利用复合隔膜中涂层与金属锂之间的自发反应，使隔膜上的涂层原位转移至金属锂表面形成保护层，探讨了复合隔膜对金属锂负极保护的机理，并研究了复合隔膜的电池性能。研究发现，金属锂和PZT接触时，其中的铅离子被还原生成金属铅和氧化铅，氧化铅可被继续还原生成金属铅和氧化锂，其中金属铅与金属锂可以形成铅-锂合金，能够降低锂沉积时的成核过电位，促进锂的均匀沉积。该保护层可以在循环过程中持续保护金属锂电极不被继续腐蚀，减少电解液以及金属锂的消耗；同时保护层还可以起到匀化界面电场、降低锂成核过电位、促使锂均匀沉积、抑制枝晶形成的作用，从而提高锂-锂对称电池、铜-锂电池和磷酸铁锂-锂电池的循环性能以及安全性能。

2. 制备了氧化锡（SnO₂）/PP复合隔膜，进一步探究了原位转移隔膜涂层至金属锂表面形成保护层的反应机理。实验结果表明，SnO₂涂层材料组成更加简单，其与金属锂之间的反应更加充分，对金属锂沉积过程影响也更为有效，从而使得含有SnO₂涂层的锂-锂对称电池以及磷酸铁锂-锂电池循环寿命都得到成倍增长。此外，在SnO₂涂层作用下电镀形成的锂电极在磷酸铁锂-锂中可以稳定循环170圈以上，第170圈时容量保持率约为90%，若形成的锂电极表面含有SnO₂涂层，对应磷酸铁锂-锂电池循环寿命更可增加至400圈以上，第400圈时容量保持率约为84%，表现出良好的循环性能。

3. 开发了聚偏氟乙烯（PVDF）和SnO₂的水分散复合涂布浆料，制备了PVDF/SnO₂/PP有机/无机复合隔膜，并研究了复合隔膜的电池性能。实验结果表明，PVDF纳米颗粒与SnO₂无机颗粒按照不同比例混合均可以形成稳定的隔膜涂层浆料，且浆料在PP隔膜上形成的涂层中无机和有机两种组分分布均匀，没有出现聚集和相分离的现象。此外，PVDF/SnO₂复合涂层同时利用了PVDF与电解液的亲和力、PVDF与电极之间的粘合力以及SnO₂促进金属锂均匀沉积的作用，使得复合隔膜对应电池性能大幅提升，具有良好的循环稳定性以及安全性能。

With the continuous improvement of electronic devices, the requirements of high energy density batteries are also rapidly growing. Lithium (Li) metal electrode is considered to be one of the most promising potential anode materials due to its high theoretical specific capacity and low redox potential. However, there are still two problems to be solved in the Li metal battery. First, dendritic Li, resulted from nonuniform Li deposition, tends to penetrate porous separator and lead to an internal short circuit, which will cause temperature increase extremely and then fire or explosion. The second is the reaction of metallic Li with the liquid electrolyte, which will not only consume a great deal of liquid electrolyte but also increase the interfacial resistance. At the same time, the dendritic Li can easily fall off from Li metal anode and become so-called “dead” Li, which will deteriorate the battery performance. Therefore, it is imperative to improve the safety and cycle performance of Li metal batteries. This dissertation mainly focuses on the preparation of functional composite separator for Li metal battery. Following results have been obtained.

1. A lead zirconate titanate (PZT)/polypropylene (PP) composite separator had been prepared, and a protection layer had been in situ transferred from the composite separator to Li metal surface by the spontaneous reaction. The protection mechanism of composite separator on Li metal anode had been studied and the battery performances of the composite separator had also been investigated. The results indicate that when metallic Li contacts PZT, Pb element can be reduced to form metallic Pb and PbO, which can be further reduced to form metallic Pb and Li₂O. During this process, metallic Pb can form Pb/Li alloy, which can decrease the nucleation overpotential and promote uniform deposition of Li. The protective layer can continuously protect Li metal electrode away from continuous corrosion and reduce the consumption of electrolyte and metal lithium. At the same time, it can homogenize the interface electric field, reduce the nucleation potential of lithium, promote the uniform deposition of lithium, reduce the formation of dendrite, and improve the cycle performance of Li-Li symmetric battery, Cu-Li battery and LiFePO₄ (LFP)-Li battery.

2. A tin oxide (SnO₂)/PP composite separator had been prepared, and the reaction mechanism of the protective layer had been further studied, which forms on the Li metal anode surface by in situ transferring coating layer from the composite separator. The results show that the composition of SnO₂ coating layer is simpler, and the reaction between SnO₂ coating and Li metal is more sufficient. Both the Li-Li symmetric battery and LFP-Li battery with the composite separators exhibit significantly improved Coulombic efficiency and cycling life. In addition, the lithium electrode prepared by electroplating under the help of SnO₂ coating can stably cycle for more than 170 cycles in the LFP-Li battery with about 90% capacity retention. If the surface of the electroplated prepared Li electrode contains SnO₂ layer, the cycling life of the LFP-Li battery can be increased to more than 400 cycles with about 84% capacity retention.

3. A water based coating slurry containing both polyvinylidene fluoride (PVDF) and SnO₂ has been developed, which is used to prepare PVDF/SnO₂/PP composite separator. Battery performance of the composite separator has been investigated. The results show that the composite slurry containg PVDF nanoparticles and SnO₂ inorganic particles can form uniform coating layer on the PP separator. In addition, the PVDF/SnO₂ composite coating could improve affinity to electrolyte, and enhance the cycling life of the Li-Li battery.