二维过渡金属碳/氮化物载体的构筑及其对金属锂负极电化学行为的调控

Lithium metal is a promising battery anode because of its extremely high specific capacity and low redox potential. However, dendrite growth and infinite volume change during cycling result in serious safety hazards and relative low energy density. The key to develop rechargeable lithium metal batteries with high energy density is to construct safe and stable lithium metal anode. Metallic Li host with suitable structure is supposed to effectively address the uncontrolled Li dendrite growth and significant dimensional change, so as to realize the superior long lifespan and high safety of rechargeable battery. In this work, we start from the viewpoint of structure design and aim to construct MXene-based Li host featured with self-supported, lightweight, and 3D structure based on 2D transition-metal carbide/nitrides (MXene). The work mainly investigates the science and technology of the controllable preparation of 3D MXene-based Li host, as well as the deposition mechanism and electrochemical behavior of lithium metal in MXene host. Further research is performed on the interface between liquid/solid-state electrolyte and MXene-based Li anode. These researches could help design novel metallic Li host, direct the construction of stable lithium metal batteries, as well as provide useful information for the design flexible solid-state battery with high rate capability and high safety.

金属锂，因比容量高、还原电位低，是非常有前景的电池负极材料。但其在电化学循环过程中会形成锂枝晶以及存在巨大的体积膨胀效应，导致严重的安全性问题和较低的能量密度。因此，开发高能量密度的金属锂二次电池的关键在于构筑安全、稳定的金属锂负极。构建合适结构的金属锂载体能够有效地解决金属锂枝晶生长和金属锂体积膨胀等问题，以实现电池的长循环性能和高安全性能。本项目从结构设计的角度出发，以二维过渡金属碳/氮化物（MXene）为原料，构筑一种三维质轻自支撑MXene基金属锂载体，研究MXene基金属锂载体的可控制备，考察金属锂在MXene基载体中的沉积机理和电化学行为，探究三维MXene基金属锂负极与液体电解质或聚合物固体电解质之间的界面稳定性问题。本项目的实施不仅为金属锂负极载体的设计及金属锂二次电池的构建提供了思路，而且为高倍率、高安全性的柔性固态聚合物电池的构建奠定了理论及实践基础。

本项目主要集中在构建复合的结构和设计界面来抑制锂枝晶生长，制备高安全复合锂负极。研究结果表明，载体的表面结构特性，如表面官能团含量、表面杂原子的种类、杂原子的分布及载体本身的结构特点都会影响金属锂的电化学沉积行为。比如，二维MXene与纤维素共筑的“互锁拓扑结构”可以实现金属锂的花瓣式沉积；尺寸小于3 μm的MXene空心球会导向金属锂的包覆式沉积；尺寸大于3 μm的MXene空心球会诱导金属锂呈现颗粒状形貌；包覆有纳米铝镀层的三维铜可以实现金属锂的球状沉积。高弹性、高韧性的聚合物界面层可以稳定动态的锂/电解质的界面。构造表面粗糙度和纳米效应可以实现熔融锂在基底表面的快速铺展。该项目的研究成果为实用化锂负极的构建提供了思路。