固态电池体系自修复金属锂负极基础研究

High energy density and high safety batteries has already become an urgent demand for rapid growth market. Since lithium metal have low electrode potential (-3.040 V versus standard hydrogen electrode) and high capacity (3,860 mAh g-1), it is thus considered as the most desired anode. Consequently, developing the solid-state lithium metal rechargeable batteries has become a hot-topic in the recent years, due to the requirement of higher energy density and more safety characterized. However, there are two issues will significantly restrict the performance of solid state lithium batteries. The first is limited electrochemical stability of the solid electrolyte is caused by the slow kinetics of the decomposition reactions. Second, lithium dissolved & deposited on the surface of anode is not uniformly with repeatedly, it will be causing the loss of electrical contact between the lithium anode and the electrolyte. As those reasons, this project will build a buffer layers with self-repairing function on the surface of lithium metal anode by in-situ reaction. We will study the polymer matrix and functional additives agents, the precursor solutions of preparation and various characterization test methods employment for the buffer layer construction, and then optimize the parameters of buffer layer according the test results. It is expected that the buffer layer can be effectively isolated the solid electrolyte and the metallic lithium layer, so it will to prevent side reactions. Meanwhile, the function of volume deformation with self-adaptive by buffer layer will avoid the electrical contact loss caused by lithium non-uniform dissolved & deposited. Finally, we will obtain a lithium metal anode with long-term stable output, and establish the model of lithium dendrite growth suppress mechanism and then explain it. We hope that this project will promote the commercial application process of metal lithium rechargeable state solid batteries.

随着市场对更高能量密度、更高安全性二次储能电池日益迫切的需求，开发金属锂负极的高比能固态二次电池已成为近年来化学电源领域的研究热点。但是，由于大部分的无机固态电解质对金属锂不稳定兼容以及锂的体积形变，严重的影响了固态电池的循环寿命。基于此，本项目拟开展在金属锂负极表面原位构建自修复功能缓冲层的研究工作，通过缓冲层聚合物骨架的合成、功能添加剂的筛选、前驱体溶液的研制以及多种理化性能测试表征手段来优化缓冲层的构建参数。期望构建的缓冲层能够实现有效隔离，防止固态电解质与金属锂的直接接触而发生副反应；同时，发挥缓冲层的体积形变自适应功能，防止锂反复不均匀溶解-沉积所导致的电接触损失；最后，建立长效抑制锂枝晶生长的自修复机制模型，获得长周期稳定输出的金属锂负极。希望通过本项目的实施，为推进金属锂二次固态电池的商业化进程提供理论基础和技术储备。

本项目针对金属锂负极在固态电池体系中应用所存在的化学稳定性及输出稳定性差的问题，开展固态电池体系自修复金属锂负极的基础研究工作。通过弹性聚合物、功能添加剂的设计和优化在金属锂表面原位构建功能缓冲层，获得对金属锂枝晶抑制的长效作用机制，从而提升金属锂负极在固态锂二次电池体系中的长周期稳定输出性能。基于此，首先设计和筛选缓冲层的主体聚合物，从四氢呋喃（THF），1,3-二氧环戊烷（DOL），1-乙烯基-3-丁基咪唑双三氟甲烷磺酰亚胺盐（VBImTFSI）三种溶剂组分中筛选出DOL作为聚合物骨架的初始溶剂分子。其次，筛选能够实现自修复功能的添加剂，从碘化合物（I2或PI3）以及NaPF6、Mg(PF6)2四种功能添加剂中筛选出I2作为调控金属锂均匀沉积的功能添加剂。因此，I2既可以作为氧化还原功能添加剂，同时也可用于溶剂分子自聚合的引发剂，不需要引入额外的催化剂。接着，将初步引发聚合的混合溶液涂覆到金属锂表面，待聚合物完全凝固后，I2组分会被聚合物分子均匀的包裹固定在功能缓冲层中。将修饰后的金属锂负极组装成固态金属锂对称电池以及固态金属锂全电池，测试其电化学性能，并进行工艺参数的进一步优化。然后，结合多种具有高分辨率的表征技术（XPS、FTIR、Raman、XRD以及SEM），获取缓冲层在电化学反应过程中功能组分的信号衍变规律，并对其进行相应的解析。最后，提出金属锂负极表面自修复机制的工作原理：在电池充电过程中，当持续生长的锂枝晶插入功能缓冲层并遇到I3-后，枝晶的活性位点会被钝化生成LiI，使得锂离子沉积的位点发生变化，从而调控金属锂的均匀沉积。而当电池放电时部分的I-（LiI）又会可逆的转化为I3-，这样又可以实现在上周期锂沉积期间功能缓冲层中所消耗的I3-的补充，因此这种氧化还原电对能够对金属锂负极的枝晶生长起到长效抑制的效果。通过本项目的实施，在金属锂表面原位构建的功能缓冲层，除了隔离固态电解质和金属锂负极之间的物理接触外，还能够调控金属锂的均匀溶解/沉积，实现金属锂负极在固态电池体系中长周期稳定输出，为推进金属锂二次固态电池的商业化进程提供一定的理论基础和技术储备。