纳米金胶体电解液锂氧电池的反应机制和循环性能研究

Improvement on the cycling performance of lithium-oxygen battery has attracted concurrent interest, where the control over the corrosion of lithium anode, the passivation of cathode and the decomposition of electrolyte solutions is the key point. Based on our previous work, the systematic study on the lithium-oxygen batteries with gold nanocolloid electrolytes is proposed for the first time，which makes use of the unique adsorption and catalytic properties of Au nanoparticles, to result in the co-deposition with the discharge product Li2O2. The electric conductivity of the cathode deposit can be improved, and the OER overpotential for the decomposition can be decreased, and the corrosion of lithium anode can be inhibited, leading to the improvement of the cycling performance of lithium-oxygen batteries. In the proposal, the ORR catalytic property of the Au nanoparticles on the composition, morphology and OER decomposition of the cathode deposits will be discussed, and the role of the Au nanoparticles dispersed in the electrolytes on the adsorption of soluble ORR products and subsequent reactions will also be investigated, by means of the comprehensive application of microscopic observation, in situ monitoring, electrochemical analysis and battery testing. The working mechanism of Au nanoparticles on the nucleation, crystal growth, chemical stability and OER decompositon of Li2O2 in LiClO4-DMSO electrolytes will be demonstrated in detail. Moreover, the cycling live of the lithium-oxygen batteries with Au nanocolloid electrolytes will be further improved, by using the home-made nanocomposite separator to reduce the consumption of Au nanoparticles in charge/discharge cycles, and by the optimization of charge/discharge parameters and the concentration of supporting electrolytes, which will offer important theoretical guidance on the practical utilization of lithium-oxygen batteries.

改善循环性能是当前锂氧电池研究的热点，其关键在于控制锂正极钝化、负极锂腐蚀和电解液分解。基于前期工作，本项目首次提出开展纳米Au胶体电解液锂氧电池的研究，利用Au纳米粒子独特的吸附和催化性能，实现与放电产物Li2O2共沉积，提高导电性，降低OER分解过电位，抑制锂负极腐蚀，提高锂氧电池的循环性能。拟通过显微分析、原位分析、电化学分析以及电池测试相结合的方法，讨论Au纳米粒子的ORR催化对正极放电产物成分、形貌及对OER分解过程的影响，分析电解液中悬浮的Au纳米粒子对可溶性ORR产物的吸附及其后续转化，进而揭示Au纳米粒子对LiClO4-DMSO体系中Li2O2成核与生长、成分稳定以及促进OER分解的作用规律。在此基础上，采用复合隔膜减少Au纳米粒子充放电消耗，优化充放电制度、支持电解质浓度等实验条件，进一步改善纳米Au胶体电解液锂氧电池的循环性能，为锂氧电池实用化开发提供重要的理论指导。

改善锂氧电池循环性能的关键在于控制锂正极钝化、负极锂腐蚀和电解液分解。本项目对纳米Au胶体电解液锂氧电池的研究表明，Au纳米粒子能优先吸附可溶性ORR中间体，进而与Li2O2在正极共沉积；在Li2O2充电分解时重新释放到电解液中。Au纳米粒子的引入提高了放电产物中Li2O2成分占比，并诱导Li2O2生成模式由溶液路径变为表面路径，形貌上由大晶粒变为非晶薄膜。纳米Au与Li2O2的共沉积提高了薄膜的导电性，强化了Li2O2分解过程动力学。纳米Au胶体电解质锂氧电池的失效机制是Au纳米粒子在电解液中团聚和长大，导致正极钝化。在此基础上，进行了纳米Au胶体电解液锂氧电池的综合优化，制备出了高性能原型电池。纳米金属Pd和Ag在锂氧电池过程中起到了与纳米Au相似的作用，能吸附可溶性ORR中间产物，并与Li2O2在正极共沉积，显著提高放电产物导电性。其中，Ag纳米粒子成本低，对ORR过程具有催化作用；Pd纳米粒子主要对OER过程具有催化作用。纳米Ag和Pd胶体电解质锂氧电池的失效机制是纳米粒子在电解液中团聚和长大，导致正极钝化。此外，介孔SiO2具有大比表面积，能够吸附ORR中间产物，在锂氧电池放电过程中可与Li2O2共沉积在正极，能够提供离子通路，有助于Li2O2的充电分解；另外，介孔SiO2与Li+具有交互作用，可以使Li均匀沉积/溶解，从而起到综合优化锂氧电池的效果。我们还探索了电化学预处理、制备人工SEI膜、单离子导体隔膜、高效低成本氧电催化剂、镓基液态金属修饰正极、封闭结构锂氧电池等多种方法，进一步提高锂氧电池的综合性能，均取得了创新性成果，为锂空气电池实用化提供重要的理论指导。