State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences , Changchun 130022, P. R. China.
University of Chinese Academy of Sciences , Beijing 100039, P. R. China.
Nano Lett. 2015 Dec 9;15(12):8084-90. doi: 10.1021/acs.nanolett.5b03510. Epub 2015 Nov 9.
The aprotic Li-O2 battery has attracted a great deal of interest because, theoretically, it can store far more energy than today's batteries. Toward unlocking the energy capabilities of this neotype energy storage system, noble metal-catalyzed high surface area carbon materials have been widely used as the O2 cathodes, and some of them exhibit excellent electrochemical performances in terms of round-trip efficiency and cycle life. However, whether these outstanding electrochemical performances are backed by the reversible formation/decomposition of Li2O2, i.e., the desired Li-O2 electrochemistry, remains unclear due to a lack of quantitative assays for the Li-O2 cells. Here, noble metal (Ru and Pd)-catalyzed carbon nanotube (CNT) fabrics, prepared by magnetron sputtering, have been used as the O2 cathode in aprotic Li-O2 batteries. The catalyzed Li-O2 cells exhibited considerably high round-trip efficiency and prolonged cycle life, which could match or even surpass some of the best literature results. However, a combined analysis using differential electrochemical mass spectrometry and Fourier transform infrared spectroscopy, revealed that these catalyzed Li-O2 cells (particularly those based on Pd-CNT cathodes) did not work according to the desired Li-O2 electrochemistry. Instead the presence of noble metal catalysts impaired the cells' reversibility, as evidenced by the decreased O2 recovery efficiency (the ratio of the amount of O2 evolved during recharge/that consumed in the preceding discharge) coupled with increased CO2 evolution during charging. The results reported here provide new insights into the O2 electrochemistry in the aprotic Li-O2 batteries containing noble metal catalysts and exemplified the importance of the quantitative assays for the Li-O2 reactions in the course of pursuing truly rechargeable Li-O2 batteries.
非质子 Li-O2 电池因其理论上可以储存比现今电池更多的能量而备受关注。为了挖掘这种新型储能系统的能量存储能力，贵金属催化的高比表面积碳材料已被广泛用作 O2 阴极，其中一些在往返效率和循环寿命方面表现出优异的电化学性能。然而，由于缺乏对 Li-O2 电池的定量分析，这些出色的电化学性能是否归因于 Li2O2 的可逆形成/分解，即所需的 Li-O2 电化学，仍不清楚。在此，通过磁控溅射制备的贵金属（Ru 和 Pd）催化碳纳米管（CNT）织物被用作非质子 Li-O2 电池的 O2 阴极。催化的 Li-O2 电池表现出相当高的往返效率和延长的循环寿命，这可以与一些最佳文献结果相匹配，甚至超越。然而，使用差分电化学质谱和傅里叶变换红外光谱的综合分析表明，这些催化的 Li-O2 电池（特别是基于 Pd-CNT 阴极的电池）并没有按照预期的 Li-O2 电化学运行。相反，贵金属催化剂的存在会损害电池的可逆性，这一点可以从充电过程中 O2 回收率（充电过程中消耗的 O2 量与放电过程中消耗的 O2 量之比）的降低和 CO2 释放量的增加得到证明。这里报道的结果为含有贵金属催化剂的非质子 Li-O2 电池中的 O2 电化学提供了新的见解，并说明了在追求真正可充电 Li-O2 电池的过程中对 Li-O2 反应进行定量分析的重要性。
