锂离子电池作为当前重要的化学储能设备之一，已经广泛应用于我们的日常中。制备锂离子电池的主要材料包括正极、负极、电解液和隔膜。在这些材料中，隔膜材料对锂离子电池的循环稳定性和安全性能都有着重要的影响。因此，探究隔膜在电池组装和使用过程中出现的结构和性能等方面的变化规律，对改善和提高锂离子电池的性能有着重要的意义。在锂离子电池的组装过程中，注入电解液后隔膜会出现褶皱等现象，导致电池内极片与隔膜间的界面接触不均匀，从而影响电池的一致性和循环稳定性。此外，无论是采用碳材料还是锂金属做负极，在过充或低温充放电过程中，锂枝晶的形成不可避免。锂枝晶的不断生长，会刺穿隔膜引起电池内部短路，最终导致起火甚至爆炸，带来极大的安全隐患。同时，随着人们对高能量密度锂离子电池的追求，作为非活性物质的电池隔膜越用越薄，隔膜厚度与电池安全性能间的关系，也是本研究拟关注的重点。综上，本文围绕隔膜在锂电池加工和使用过程中呈现的问题开展以下三个方面的工作：

       1. 针对隔膜在锂离子电池制备过程中，注入电解液后隔膜出现褶皱这一实际问题，系统研究了不同种类、厚度和涂层的隔膜在电解液流动浸润过程中宏观褶皱产生的原因，探究了隔膜出现褶皱的微观机制。我们认为电解液浸润隔膜的微孔产生的毛细作用是引起隔膜褶皱的主要原因。利用热压把极片与隔膜粘合，有效地解决了流动浸润过程中毛细压导致的隔膜褶皱现象，并且在一定程度提高了电池的性能。

       2. 针对隔膜在锂金属电池使用过程中的安全性这一问题，建立和完善了隔膜内阻和短路时间的评价方法，系统研究了不同厚度和制备工艺隔膜的内阻和短路时间等性能间的相关性。研究表明随着隔膜厚度和内阻的增加，对应的短路时间呈线性增大。另外，提高隔膜厚度和内阻，可以改善电池在使用过程中的安全性。

As one of the most important chemical energy storage devices, lithium-ion batteries (LIBs) have been widely used in our daily life. The main materials for manufacturing LIBs include cathode, anode, electrolyte and separator. Among these materials, the separator material has an important influence on the cycle stability and safety performance of LIBs. Therefore, during the battery assembly and application, it is of great significance to improve the performance of LIBs by exploring the change rules of separator structure and performance. In the assembly process of LIBs, the separator will wrinkle after electrolyte filled, resulting in uneven interfacial contact between the inner electrode and the separator, which will affect the consistency and cycle stability of the batteries. Whether carbon material or lithium metal is used as an anode, the formation of lithium dendrites is inevitable in the process of overcharging or charging and discharging at low temperature. The continuous growth of lithium dendrites will cause short circuit inside the battery by penetrating the separator, which will eventually lead to fire or even explosion, resulting in great safety risks. At the same time, the relationship between the thickness of the separator and the safety performance of the battery is also worth studying, since the battery separator, as an inactive material, is getting thinner and thinner to pursue high energy density. In summary, this thesis focuses on the following studies based on the separator problems during manufacting and using lithium batteries.

1. Aiming at the practical problem that separator wrinkles after electrolyte is injected during manufacturing LIBs, separators of various types, thickness and coating materials were systematically studied to investigate the cause of separator wrinkle, and a microscopic mechanism of separator wrinkle is explored. It is proposed that the separator wrinkle is mainly originated from the capillary force of liquid electrolyte wetting the pores of separator. Binding electrode with separator by hot pressing is a way to countact capillary force in the process of flow infiltration, which can improve the performance of the battery to a certain extent.

2. In order to solve the safety problem of separators during using lithium metal batteries, the evaluation methods for internal resistance and short circuit time of separator were established and improved. The correlation between internal resistance and short circuit time of separator with different thickness and preparation methods was studied systematically. The correlation among thickness, internal resistance and short circuit time of battery separators was explored. It is concluded that the corresponding short circuit time increases linearly with the increase of separator thickness and internal resistance, indicating that the safety of battery can be improved by increasing separator thickness and internal resistance.

3. Aiming at the potential risk of short circuit time decline caused by decreasing separator thickness and internal resistance, the internal resistance and short circuit time of composite separators with various functional coating materials such as: alumina (Al₂O₃), polyvinylidene fluoride (PVDF), manganese oxide (MnO), titanium nitride (TiN) and tin oxide (SnO₂) were studied systematically. It is concluded that the functional coating layer, which can react with lithium, can greatly increase the short circuit time of the composite separators. Our strategy has provided a solution to reduce and eliminate the potential risk of battery caused by decreasing separator thickness.