还原合成内嵌倒金字塔的高耐折金属薄膜及界面增强生长纳米线制备可折叠锂离子电池

There is an urgent need to develop foldable Li-ion batteries for their applications in the wearable electronic devices, which still face three key challenges: i) fabrication of highly foldable current collector; ii) enhancement of the interfacial bonding between active material and current collector; iii) increase of interfacial contact between active material and solid electrolyte. We have developed a simple and innovative strategy for synthesizing silver film with inverted-pyramid-structures that possesses high folding endurance. A less than 0.5% deviation from the initial resistance can be maintained over 35000 repetitive folds for the 9.2 um thick silver film when tested at the folding site. We found this growth mechanism is also suitable for the growing nickel film and may also be appropriate for synthetizing copper and aluminum film. The initial results show that a 5 um thick nickel film demonstrates less than 7.6% deviation from the initial resistance after 18000 folding cycles. After it was overlaid with in-situ grown LiCoO2 nanowires, the electrode can still be folded up to 1000 times. This project intends to deeply understand the growth mechanism and then developed a general method for controllable synthesis of highly foldable metal films. We will also investigate the in situ growth of LiCoO2 and Li4Ti5O12 nanowires on foldable metal films as the cathode and anode for LIBs. The inverted-pyramid-structures not only effectively increase the folding resistance of current collectors but also enhance the interfacial strength between nanowires and current collectors that would be beneficial for electron transport collection. In addition, we will investigate the growth kinetics mechanism of nanowires to regulate their vertical orientation and pore size distribution, allowing nanowires to fully contact with electrolyte, which will make Li-ions more accessible to the active materials and provide the abundant electrochemical active sites for lithium storage. This project will provide a new method and theory for the research of highly foldable metal films and Li-ion batteries.

可穿戴设备迫切需要开发柔性可折叠锂离子电池作为电源，但要解决的难题是：1)高耐折集流体的制备；2)活性材料与集流体的界面结合；3)活性材料与固态电解质的界面接触。申请人前期报道了内嵌倒金字塔的高耐折银膜，9.2 um厚银膜折叠3.5万次电阻变化小于0.5%。我们又发现该生长机理适用于合成镍膜，5 um厚镍膜折叠1.8万次电阻变化小于7.6%，并预期生长成本更低的铜膜和铝膜。初期实验镍膜上生长LiCoO2纳米线可折叠达1千次未脱落。本项目拟深入认识生长机理实现金属薄膜的可控合成及通用方法，并生长LiCoO2和Li4Ti5O12纳米线作为正负极。通过构筑倒金字塔结构既提高集流体的耐折性，又增强纳米线与金属薄膜的界面结合以提高电子收集；研究生长动力学调控纳米线垂直取向和孔径分布，增加与聚合物电解质界面接触以提高锂离子传输和储锂位点。本项目将为高耐折金属薄膜和可折叠锂离子电池研究提供新理论和方法。

便携电子产品、可穿戴设备，如可折叠智能眼镜、智能衣服、可折叠手机、电子纸等将形成巨大市场潜力的新兴高科技产业。这类器件必须承受相当次数的折叠，因此，迫切需要开发高耐折导电薄膜和可折叠锂离子电池。. 本项目提出以制绒硅片为模板，采用水热还原法通过成核-溶解-再结晶生长内嵌倒金字塔的高耐折金属薄膜。该方法制备的5μm厚镍膜电导率达125000 S/cm，经22000次完全外折和18000次完全内折后，折痕处电阻相对于初始值变化仅为0.19%和0.72%。高耐折镍膜上生长LiCoO2和Li4Ti5O12纳米线的电极可以对折1000次。在深入分析机理的基础上，我们采用结构诱导剂合成了高长径比并有介孔的LiCoO2和Li4Ti5O12纳米纤维。通过多层金字塔-倒金字塔互锁界面设计实现了高耐折厚膜电极。此外，制备的内嵌倒金字塔的聚合物电解质隔膜可以经受22000次对折。采用活性材料载量为14.9-19.4 mg/cm2的LiCoO2和Li4Ti5O12电极组装的可折叠锂离子电池完全对折15000次后可保持初始比容量的102%。无论是在活性材料载量还是折叠次数上，都达到了实用标准。我们还将可折叠锂离子电池集成在智能眼镜模型上，进行了9000次的边折叠、边工作的应用展示。我们对电极耐折机理的研究表明，倒金字塔和金字塔的锥面和棱边可以切向分散折叠时产生的应力；金字塔-倒金字塔互锁界面设计像拉链一样有效地增强活性材料内部及与集流体的界面结合，从而提高耐折性能和活性材料载量。我们通过电化学机理分析，建立了纳米线锂离子扩散和电子传输动力学模型，高长径比一维的一维纳米材料可有效提升电极中锂离子扩散和电子传输性能。. 本项目为其它可折叠导电薄膜、一维结构功能材料、功能器件界面设计的研究提供了新思路，对可穿戴设备的发展有重要的科学意义和实用价值。