基于磁控溅射技术制备陶瓷隔膜及其提高锂离子电池性能的机理

Safety has been the major bottleneck for the widespread application of high-capacity lithium ion battery, wherein the poor thermal stability of the polyolefin separator is the most important safety problems. At present, ceramic coated on the existing polyolefin membrane surface is one of the most effective solutions. Ceramic separator prepared by conventional mechanical coating method has some problems such as the poor binding between the film and the substrate, and the poor uniformity, especially in the late cycle. The project intends to prepare the ceramic separator using the improved plasma magnetron sputtering technique sputtered alumina ceramic layer as a single entity on one or both sides of the separator simultaneously, which possess the advantages of a uniform film thickness can be precisely controlled, high purity, good reproducibility, strong bonding force with the substrate, the industrialization, more anti-shrinkable without using the easy-to-swellable binder and the easy-to-agglomerate nanoscale Al2O3. The systematic study of new methods for preparing the ceramic layer, its effects on the physicochemical properties of the separator, and the influence of ceramic separator on the electrochemical performance, especially the safety of the battery will be conducted. By detecting the structure, microstructure, changes in oxidation resistance of the polyolefin separator, and the interfacial properties between the negative/electrolyte, reveal the scientific nature that the polyolefin separator affects the overall performance of the battery. This new approach is expected to further enhance the key performance of the battery, such as safety and cycle stability, than the commonly used mechanical coating method, and this is a creative and meaningful work.

安全性是锂离子电池规模应用的瓶颈，而聚烯烃隔膜的耐热性差是最重要的安全隐患。目前，在其表面引入陶瓷层是一种最有效的解决措施。常规机械涂布方法制备的陶瓷隔膜，膜层与基体结合力、均匀性都有待提高。本项目拟采用改进的等离子体磁控溅射技术，在隔膜单面或两面同时溅射自连为一体的陶瓷层，该方法具有膜层均匀、厚度可控、与基体结合力强、纯度高和重复性好等优点，且不使用循环中易溶胀的粘结剂和易团聚的纳米颗粒。将系统研究制备上述陶瓷层的新方法及其隔膜的物理化学性能；系统研究陶瓷层与基膜的界面行为，及其该陶瓷隔膜抗锂枝晶的特性；考察陶瓷隔膜制备电池的电化学性能，特别是安全性；通过检测该隔膜中聚烯烃的结构/微结构、抗氧化性和负极/电解液的界面性质，揭示这种隔膜影响电池综合性能的科学本质。这种新方法有望比现在普遍使用的机械涂布法进一步提高电池的安全、循环等关键性能，推进高比能动力电池的开发，是一项富有创意的工作.

锂离子电池的安全问题成为其规模应用的瓶颈，其中隔膜的耐热性差是最重要的安全隐患。聚烯烃隔膜表面陶瓷化是提高锂离子电池安全性的有效方法，但目前大规模生产过程采用的机械涂布方式，存在附着力和均匀性差等问题，在使用过程中有“掉粉”现象。.本项目采用高密度等离子体柔性连续卷对卷镀膜系统，以商业化聚丙烯（PP）隔膜作为基体，在其正反两面同时连续溅射了厚度为200nm左右的Al2O3陶瓷层。确定了陶瓷隔膜制备的最佳工艺参数：真空度为1×10-4 Pa左右、溅射气压为0.3Pa、溅射靶功率为1800W、靶基距为160mm，溅射时间为10min。.对溅射后的陶瓷隔膜的结构特性、热稳定性和离子电导率等进行了综合评价与表征。与商业PP膜相比，项目制备的陶瓷隔膜与电解液的润湿性，隔膜的吸液率、保液率、离子电导率和耐热性均有所提高。.考察了陶瓷隔膜对电池电化学性能的影响，与PP膜相比，项目制备的陶瓷隔膜具有较低的界面阻抗，降低了电池的极化，使电池的放电平台更高，电池的倍率和循环性能得到改善。.考察了陶瓷隔膜对电池安全性能的影响，与PP膜相比，项目制备的陶瓷隔膜具有更高的安全性，特别是循环后电池的安全性明显提高。陶瓷隔膜制备的18650石墨/三元正极材料体系锂离子电池，过充电、过放电、短路、挤压、针刺和加热项目都达到QC-743标准要求，即电池不爆炸，不起火。.采用SEM、XRD、EIS和LSV对循环前后的隔膜进行表征，结果表明，项目制备的陶瓷隔膜，电池阻抗较低，充放电循环中电池的放热量更小，温度更低，起到了抑制微孔闭合的效果；同时隔膜表面的Al2O3避免了其本体与正极的直接接触，从而提高了隔膜的抗氧化性，抑制了循环过程中隔膜本体结构和微结构的衰败，从而使电池的电化学性能提高。.这种新方法比现在普遍使用的机械涂布法进一步提高电池的安全和循环等关键性能，从而推动高比能锂离子电池的发展，是一项有意义的工作。