金属锂由于其极高理论比容量和极低电极电势等优势，长期以来被认为是高比能电池首选的负极材料之一。但是，金属锂负极存在的枝晶生长、体积膨胀等一系列问题，严重阻碍了其实用化进程。通过基础电化学模型分析可知，在二维金属锂负极中引入三维骨架材料构筑复合锂负极可以有效降低负极的电流密度，调控电极表面的空间电场，从而促进金属锂均匀地沉积和脱出。但目前复合锂负极的理性设计还极度缺乏，现有研究仅侧重于将金属锂和三维骨架复合，而忽略了锂离子在复合锂负极复杂界面处的输运行为以及在内部限域空间中的沉积脱出行为。此外，前人研究主要局限于温和条件而忽略了实用化条件下金属锂软包电池的构筑。针对实用化条件下，金属锂沉积脱出行为不明确等问题，本文对软包电池中金属锂的沉积脱出规律进行研究，发现软包电池中金属锂负极的失效行为图分为极化区、过渡区和短路区，明确了电流密度和循环容量分别在金属锂脱出和沉积过程中发挥的关键作用，指出了实用化条件下复合锂负极是解决金属锂负极问题的有效途径。针对复合锂负极缺乏理性设计的问题，本文研究了锂离子在骨架/金属锂/电解质界面处的输运行为以及限域空间内锂沉积和脱出行为，总结了复合锂负极的设计原则和策略。本文通过金属锂和碳骨架材料的原位化学反应在骨架/金属锂界面处构筑了一层均匀亲锂的锂碳界面层，促进了锂离子的均匀传输。其次，本文利用骨架材料与不同溶剂分子作用力不同的特点，诱导了含氟溶剂分子在金属锂表面富集，形成了富含氟化锂的固态电解质层，稳定了金属锂/电解质界面。对于限域空间内的锂枝晶生长，本文提出自调节压力策略，通过限域空间内引入的弹性聚合物形变来实现对金属锂沉积脱出行为的有效控制。综上所述，本论文在深刻理解实用化条件下金属锂沉积脱出行为的基础上，通过骨架与金属锂及电解质之间的物理化学作用实现了对骨架/金属锂/电解质界面的调控，同时提出了利用自调节压力调控限域空间内金属锂沉积脱出行为的新方法。在此基础上，本文总结了实用化复合锂负极的设计原则，推动了金属锂电池的实用化进展。
Lithium (Li) metal is considered as one of the promising anode materials for high-energy-density rechargeable batteries due to its extremely high theoretical specific capacity and low reduction potential. However, the practical application of Li metal anode is still hindered by uncontrolled growth of Li dendrites and extreme volume expansion. Based on the fundamental electrochemical model, it is found that composite Li anodes with three-dimensional (3D) host materials can effectively reduce the current density of anodes and weaken the effect of space charge on the surface of anodes, and thus realize the uniform plating/stripping of Li metal. However, the rational design of composite Li anodes is extremely lacking. The 3D host and Li metal is simply compounded to fabricate the composite anodes, but the transport behavior of Li ion at the complex interface of composite Li anodes and the plating/stripping behaviors of Li metal in the inner confined space are ingored. In addition, previous publications were mainly limited in mild conditions and the importance of the construction of Li metal pouch cells under practical conditions is not recognized.In order to reveal the behaviors of Li plating/stripping under practical conditions, the regulation of Li plating/stripping in pouch cells is demonstrated. The electrochemical diagram of Li metal anodes is divided into three categories: polarization, transition, and short-circuit zones. The key roles of current density and cycle capacity during the process of Li plating/stripping are clarified. It is pointed out that the composite Li anode is an effective way to solve the problem of Li metal anodes. To solve the lack of rational design of composite Li anodes, the transport of Li ion at the interface of host/Li metal/electrolyte and behaviors of Li plating/stripping in confined space are investigated. The design principles and strategies of composite Li anodes are concluded. A uniform lithiophilic composite layer between carbon fibers and Li metal is formed to promote the uniform Li plating/stripping through the in-situ reaction of Li metal and carbon. In addition, fluorine (F)-containing solvent molecules are concentrated on the surface of Li metal by taking advantage of the different interactions between hosts and different solvent molecules, forming a LiF-riched solid electrolyte interphase. For the growth of Li dendrites in the confined space, a self-adaptable pressure, generated by the filled elastic polymer inside conductive hosts, is proposed to effectively control the behaviors of Li plating/stripping in the confined space of the composite Li anode.In summary, based on the understanding of behaviors of Li plating/stripping under practical conditions, the regulation of interface of electrolyte/host/Li metal in composite Li anodes is realized through the interaction between the host, Li metal and electrolyte. Meanwhile, a method of self-adaptable pressure is proposed to control the behaviors of Li plating/stripping in the confined space. Furthermore, the design principles of composite Li anode under practical conditions are summarized, which is helpful to promote the practical application of Li metal batteries.
