有机碘在氧化环境下生长类SEI膜抑制锂氧气电池中穿梭效应的研究

This project aims to suppress the shuttle effect of redox mediators in secondary lithium-oxygen batteries, and thus improve the battery performance of electrical energy efficiency and cycleability. The ionic and covalent organic iodine with rich variety are proposed as redox mediators, which hopefully exhibit comparable lithium peroxide-oxidizing capability with inorganic iodide, meanwhile, release organic components to generate the solid electrolyte interphase (SEI)-like layer at the interface of Li metal/electrolyte to suppress the shuttle effect. The fundamental strategy is establishing the theory of reductive radical detaching of organic iodine at the surface of Li metal based on the density-functional theory calculation. At the same time, considering the special oxidative environment in lithium-oxygen batteries, the free radical would be oxidized by the oxidative intermediates like superoxide to grow the organic and inorganic composite, similar with SEI composition. The in situ generating SEI-like layer possesses both the Li-ion conductivity and electronic insulation, hence protecting Li metal from the reaction with the oxidizing state of RM, and facilitating the Li-ion transfer. This project will emphasize on the growth mechanism of the SEI-like layer, revealing the key factors SEI-like layer formation under the oxidative environment, and exploring the relationship between the SEI-like layer and its function on suppressing the shuttle effect. Finally, the optimized organic iodine system will be utilized to assemble the lithium-oxygen devices with high electrical energy efficiency and stability.

本项目针对抑制二次锂氧气电池中氧化还原中间体（RM）穿梭效应这一科学问题，围绕提高能量利用效率和循环稳定性的目标，提出用种类丰富的离子型和共价型有机碘作为氧化还原中间体，在分解过氧化锂的同时释放出有机组分在锂金属/电解液界面生长类SEI膜抑制穿梭效应。基本的策略是基于密度泛函理论框架下，建立有机碘在锂金属表面发生还原性脱离释放自由基的理论方法。同时将锂氧气电池特殊的氧化环境纳入考虑，通过有机自由基和超氧根离子等中间产物的氧化反应生成类似于SEI膜组分的有机/无机复合物。原位生长的类SEI膜既具备锂离子导电性，又具有电子绝缘性，既能够有效地阻断RM氧化态的还原反应，又利于锂离子的传输。本项目将重点研究类SEI膜的生长过程，揭示在氧化环境下形成具有离子导电性和电子绝缘性的类SEI膜的关键因素，深入探讨类SEI膜的结构对于抑制穿梭效应的调控原理，在此基础上实现高效、稳定的二次锂氧气电池原型器件。

针对抑制二次锂氧气电池中氧化还原中间体穿梭效应这一关键科学问题，我们首次设计并引入了三乙基碘代硫等有机碘类液相催化剂，通过还原性乙基脱离以及随后的氧化过程在锂金属表面原位生成SEI膜，显著提高了电池的能量利用效率；并通过将碘类氧化介体与固相催化剂复合，基于电解液的强溶剂化效应和正极吸附的协同作用，从源头处解决了液相催化剂与锂金属的副反应，为高效率的锂空气电池器件的可溶性催化剂的应用提供了一条可行的思路。其次，我们通过实验和理论计算，进一步筛选出碘代三甲基硅烷、碘氮杂环丁烷和溴代硝基甲烷等新型有机卤素类氧化还原中间体，系统研究了这类有机物对固态电解质保护层的组成和结构影响，以及其对锂氧气电池的穿梭效应的抑制机制。我们进一步开发出六甲基二硅氮氨烷，全氟三丁胺和甲基咪唑/四乙二醇二甲醚等添加剂及溶剂的新体系，在锂氧和锂空电池工作过程中全面研究了锂金属负极表面的原位形成保护层的过程。最后，我们将氧化还原中间体与多孔固态电解质框架组合构筑出一种新型安全性高的二次锂氧气电池原型器件。并基于固液协同催化机制，提出了单原子催化剂与碘基氧化还原介体协同的新体系。基于上述研究成果，我们最终组装的锂氧气电池器件在200次循环后可保持超过80%的能量利用效率。