Liu Wei, Shen Yue, Yu Yao, Lu Xia, Zhang Wang, Huang Zhaoming, Meng Jintao, Huang Yunhui, Guo Zaiping
State Key Laboratory of Material Processing and Die & Mould Technology, School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, P. R. China.
Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Ministry-of-Education Key Laboratory for Synthesis and Applications of Organic Functional Molecules, College of Chemistry and Chemical Engineering, Hubei University, Wuhan, 430062, P. R. China.
Small. 2019 May;15(19):e1900154. doi: 10.1002/smll.201900154. Epub 2019 Apr 12.
Lithium-oxygen batteries have an ultrahigh theoretical energy density, almost ten times higher than lithium-ion batteries. The poor conductivity of the discharge product Li O , however, severely raises the charge overpotential and pulls down the cyclability. Here, a simple and effective strategy is presented for regular formation of lithium vacancies in the discharge product via tuning charge/discharge mode, and their effects on the charge transfer behavior. The effects of the discharge current density on the lithium vacancies, ionic conductivity, and electronic conductivity of the discharge product Li O are systematically investigated via electron spin resonance, spin-alignment echo nuclear magnetic resonance, and tungsten nanomanipulators, respectively. The study by density functional theory indicates that the lithium vacancies in Li O generated during the discharge process are highly dependent on the current density. High current can induce a high vacancy density, which enhances the electronic conductivity and reduces the overpotential. Meanwhile, with increasing discharge current, the morphology of the Li O changes from microtoroids to thin nanoplatelets, effectively shortening the charge transfer distance and improving the cycling performance. The Li O grown in fast discharge mode is more easily decomposed in the following charging process. The lithium-oxygen battery cycling in fast-discharge/slow-charge mode exhibits low overpotential and long cycle life.
锂氧电池具有超高的理论能量密度，几乎比锂离子电池高十倍。然而，放电产物Li₂O₂的导电性较差，严重提高了充电过电位并降低了循环稳定性。在此，提出了一种简单有效的策略，通过调整充放电模式在放电产物中定期形成锂空位，以及它们对电荷转移行为的影响。分别通过电子自旋共振、自旋排列回波核磁共振和钨纳米操纵器系统地研究了放电电流密度对放电产物Li₂O₂的锂空位、离子电导率和电子电导率的影响。密度泛函理论研究表明，放电过程中Li₂O₂中产生的锂空位高度依赖于电流密度。高电流可诱导高空位密度，增强电子导电性并降低过电位。同时，随着放电电流的增加，Li₂O₂的形态从微环变为薄纳米片，有效缩短了电荷转移距离并提高了循环性能。在快速放电模式下生长的Li₂O₂在随后的充电过程中更容易分解。以快速放电/缓慢充电模式循环的锂氧电池表现出低过电位和长循环寿命。
