金属锂电极表面非晶碳纳米多层膜的构建与循环稳定性改善的作用机理

On the basis of the requirements of high specific capacity and security of the anodes for new types of lithium secondary batteries such as Li-S cell, this project will design and controllably prepare thin amorphous carbon (a-C) nanomultilayers, which have high adhesion to lithium anode substrate, and can also adjust the change of stress and have structural stability during the charge-discharge process at high current densities. And then the electrochemical performances of the lithium anodes deposited with a-C nanomultilayers, as well as the transport properties of lithium ions across the interface of modified lithium anode, the process of lithium deposition- dissolution and the electrode reaction kinetics will be investigated under different electrochemical conditions. Furthermore, its mechanisms of a-C nanomultilayer on the improved stability of solid electrolyte interface (SEI) film and the inhibition of dendrite growth will be elucidated. Also, the relationship between the microstructure of a-C nanomultilayers and the electrochemical performance of lithium anode will be established..From this research, we can obtain a modified lithium anode which has high specific capacity, excellent cycling performance and can operate well at both high and low temperatures. Furthermore, this study can provide an important theoretical basis and experimental evidence to solve the problems of safety and cycling stability of high energy/power secondary batteries with lithium anode.

根据对Li-S等新型锂二次电池负极高比容量和高安全性的性能要求，本课题设计并在锂金属电极表面采用磁控溅射技术可控制备较薄厚度、良好机械性能并能适应大电流充放电过程电极应力变化而保持结构稳定性的非晶碳（a-C）纳米多层膜。研究表面镀覆a-C纳米多层膜金属锂电极的电化学行为以及在不同电化学条件下锂离子在镀覆a-C纳米多层膜金属锂电极界面的传输特性、锂沉积-溶解和电极反应动力学过程，阐明a-C纳米多层膜在电化学过程中稳定电极表面SEI（solid electrolyte interface）膜结构和抑制锂枝晶生长的作用机制，建立a-C纳米多层膜组织结构与锂电极电化学性能的相互关系。获得具有高比容量、优异高低温性能和良好循环性能的表面镀覆a-C薄膜的金属锂电极，为解决高能量和高功率密度锂二次电池的安全性和循环稳定性等问题提供重要的理论基础和实验依据。

本课题设计了由富sp2 C键含量的a-C层与富sp3 C键含量的a-C层相互交叉构成的纳米多层结构薄膜，研究了沉积工艺对a-C纳米多层膜调制周期、sp2/sp3 C键含量比、薄膜沉积速率以及薄膜与基体界面结合力的影响，实现金属锂表面a-C纳米多层膜的可控制备。在此基础上，本课题进一步研究了碳基纳米多层膜与金属锂复合负极材料的电化学性能，建立了碳基纳米多层膜的微观组织结构与电极电化学性能的相互关系。并通过共聚焦显微原位观察测试，观察了电化学过程中金属锂枝晶的生长过程，建立了对应的热力学模型，为金属锂电池中的枝晶生长问题提供了合理的解释。