微量水参与的锂-氧气电池正极反应研究

The phenomenon of water-containing electrolyte greatly reducing discharge/charge overpotentials and improving cycling stability of Li-O2 batteries was successively found and reported by the applicant and Grey’s group in Cambridge University in Nat. Commun. and Science, respectively. However, the reaction mechanisms of oxygen reduction/oxygen evolution reaction at the electrode and the Li-O2 battery during discharge/charge are not clear and need urgent investigation. This proposal will employ rotating ring-disk/disk electrodes, cyclic voltammetry, electrochemical workstation-gas chromatography, XRD, XPS, Raman, FT-IR, SEM, TEM, etc. to analyze and characterize the intermediates in oxygen reduction/oxygen evolution reaction and during discharge/charge. Much attention will be paid to the reactions at cathodes, overpotential generation, and factors affecting cycling stability of Li-O2 batteries. This will enable the designing and controlling the valence, composition, structure, and morphology of the discharge products, and eventually adjustment of the overpotentials during discharge/charge. This will offer important insights into the construction of high efficiency, high performance Li-O2 batteries, and bridge the mechanisms of oxygen reduction/oxygen evolution reaction in two separate aqueous and nonaqueous electrolytes.

申请人和剑桥大学Grey小组相继在Nat. Commun.和Science上报道了含微量水的电解质能够极大降低锂-氧气电池放电/充电过电位和改善电池循环稳定性。然而，微量水参与的氧还原/氧析出反应中间产物和放电/充电过程中反应步骤仍然不明确，亟待进一步研究。本项目拟采用旋转环盘和圆盘电极、循环伏安法、电化学工作站气相色谱仪联用，XRD、XPS、Raman、FT-IR、SEM、TEM等技术对氧还原/氧析出反应中间产物和锂-氧气电池放电/充电中间态进行分析和表征。重点关注含微量水的锂-氧气电池放电/充电过程中的正极反应、过电位形成机制和影响电池循环稳定性的可能因素。实现设计与调控放电产物的价态、组成、结构和形貌以达到锂-氧气电池放电/充电过电位的可控，为构建高效、高性能锂-氧气电池提供理论基础和实验依据，同时也为目前独立的水系和有机体系氧还原与氧析出反应提供重要补充。

锂-氧气电池具有高的比能量密度，吸引了全世界科学家们的广泛关注，是当前化学电源热门的研究课题之一。锂-氧气电池面临的主要问题在于放电产物Li2O2在充电过程中分解困难、过电位高。即使在理想条件下，Li2O2的分解过电位仍高于0.44 V，即充电电压高于3.4 V，这与Li2O2的分解机制密切相关。本项目围绕锂-氧气电池面临的关键科学问题，研究了电解液中含有的少量水或K+对锂（钠）-氧气电池的充放电特性和电池的循环稳定性的影响，深入阐述了不同添加剂情况下的锂-氧气电池充放电反应机制，锂-氧气电池在可逆运行200周充放电容量仍保持在90%以上。同时，利用半导体氮化碳作为锂-氧气电池的光正极，成功将光引入到锂-氧气电池中，促进光生电子和空穴分离及氧还原和氧析出反应，揭示新的锂-氧气电池反应机理，使锂-氧气电池的放电电压提高到3.22 V和充电电压降低到3.38 V，使锂-氧气电池的库仑效率提高至95.3%。这将为锂-氧气电池的发展提供新思路和光在可充电池中的应用提供实验基础。