Morimoto Kota, Kusumoto Takayoshi, Nishioka Kiho, Kamiya Kazuhide, Mukouyama Yoshiharu, Nakanishi Shuji
Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan.
Research Center for Solar Energy Chemistry, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan.
ACS Appl Mater Interfaces. 2020 Sep 23;12(38):42803-42810. doi: 10.1021/acsami.0c11382. Epub 2020 Sep 9.
Various electrolyte components have been investigated with the aim of improving the cycle life of lithium-oxygen (Li-O) batteries. A tetraglyme-based electrolyte containing dual anions of Br and NO is a promising electrolyte system in which the cell voltage during charging is reduced because of the redox-mediator function of the Br/Br and NO/NO couples, while the Li-metal anode is protected by LiO formed via the reaction between Li metal and NO. To maximize the potential of this system, the fundamental factors that limit the cycle life should be clarified. In the present work, we used nondestructive electrochemical impedance spectroscopy to analyze the temporal change of the charge transfer resistances during cycles of Li-O batteries with dual anions. The charge transfer resistance at the cathode was revealed to exhibit good correlation with the reduction of the discharge voltage. These results, combined with the results of electrode surface inspections, revealed that irreversible accumulation of insulating deposits such as LiO and LiCO on the cathode surface was a major cause of the short cycle life. Furthermore, the analyses of the time course of the solution resistance suggested that diminished reactivity between the redox mediators and LiO was a critical factor that led to the irreversible accumulation of the less-reactive LiO on the cathode and eventually to a shortened cycle life. These findings indicated that increasing the reactivity between Br and LiO is essentially important for improving the cycle stability of Li-O batteries and the reactivity can be nondestructively assessed by tracking the dynamic changes in the solution resistance.
为了提高锂氧（Li-O）电池的循环寿命，人们对各种电解质成分进行了研究。一种含有Br⁻和NO₃⁻双阴离子的四甘醇二甲醚基电解质是一种很有前景的电解质体系，在该体系中，由于Br⁻/Br₂和NO₃⁻/NO₂⁻电对的氧化还原介质功能，充电过程中的电池电压会降低，同时锂金属负极受到锂金属与NO₃⁻反应形成的LiNO₂的保护。为了最大限度地发挥该体系的潜力，应阐明限制循环寿命的基本因素。在本工作中，我们使用无损电化学阻抗谱来分析具有双阴离子的Li-O电池循环过程中电荷转移电阻的时间变化。结果表明，阴极处的电荷转移电阻与放电电压的降低具有良好的相关性。这些结果与电极表面检查结果相结合，表明阴极表面LiNO₂和Li₂CO₃等绝缘沉积物的不可逆积累是循环寿命短的主要原因。此外，对溶液电阻随时间变化过程的分析表明，氧化还原介质与LiNO₂之间反应性的降低是导致反应性较低的LiNO₂在阴极上不可逆积累并最终导致循环寿命缩短的关键因素。这些发现表明，提高Br⁻与LiNO₂之间的反应性对于提高Li-O电池循环稳定性至关重要，并且可以通过跟踪溶液电阻中的动态变化来无损评估这种反应性。
