Potential-Dependent Generation of O2– and LiO2 and Their Critical Roles in O2 Reduction to Li2O2 in Aprotic Li–O2 Batteries,The Journal of Physical Chemistry C

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Potential-Dependent Generation of O2– and LiO2 and Their Critical Roles in O2 Reduction to Li2O2 in Aprotic Li–O2 Batteries
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2016-02-12 00:00:00 , DOI: 10.1021/acs.jpcc.5b12338
Yelong Zhang _{1,

2} , Xinmin Zhang ₁ , Jiawei Wang ₁ , William C. McKee ₃ , Ye Xu ₃ , Zhangquan Peng ₁

Affiliation

Discharging of the aprotic Li–O₂ battery relies on the oxygen reduction reaction (ORR) producing Li₂O₂ in the positive electrode, which remains incompletely understood. Here, we report a mechanistic study of the Li-ORR on a model system, i.e., an Au electrode in a Li⁺ dimethyl sulfoxide (DMSO) electrolyte. By spectroscopic identification of the reaction intermediates coupled with density functional theory calculations, we conclude that the formation of O₂^– and LiO₂ in the Li-ORR critically depends on electrode potentials and determines the Li₂O₂ formation mechanism. At low overpotentials (> 2.0 V vs Li/Li⁺) O₂^– is identified to be the first surface intermediate, which diffuses into the bulk electrolyte and forms Li₂O₂ therein via a solution-mediated disproportionation mechanism. At high overpotentials (ca. 2.0–1.6 V vs Li/Li⁺) LiO₂ has been observed, which can rapidly transform to Li₂O₂ by further electro-reduction, suggesting a surface-mediated mechanism. The solution-mediated Li₂O₂ formation that can account for the widely observed toroid-shaped discharged Li₂O₂ particles has also been thoroughly examined. Thus, O₂^– formation controls the overall reaction onset potential, and LiO₂ formation demarcates the change from a solution- to surface-mediated reaction mechanism. The new findings and improved understandings of the Li-ORR in DMSO will contribute to the further development of aprotic Li–O₂ batteries.

中文翻译：

的O-潜在的依赖性产生₂^-和LIO ₂及其Ø关键作用₂减少到李₂ Ø ₂在非质子LIO ₂电池

非质子传递的Li–O ₂电池的放电依赖于氧还原反应（ORR）在正极中产生Li ₂ O ₂，这一点尚不完全清楚。在这里，我们报告了在模型系统（即Li ⁺二甲基亚砜（DMSO）电解质中的Au电极）上进行Li-ORR的机理研究。通过加上密度泛函理论计算的反应中间体的光谱鉴定，我们得出结论的O的形成₂^-和LIO ₂中的Li ORR关键取决于电极电位，并且确定李₂ ö ₂形成机制。在低电势下（> 2.0 V vs Li / Li ⁺）O ₂^–被确定为第一个表面中间体，它通过溶液介导的歧化机理扩散到本体电解质中并在其中形成Li ₂ O ₂。在高电势下（相对于Li / Li ⁺约为2.0–1.6 V ），观察到LiO ₂可以通过进一步的电还原迅速转变为Li ₂ O ₂，这表明是表面介导的机制。还已经彻底研究了溶液介导的Li ₂ O _2的形成，该形成可以解释广泛观察到的环形放电的Li ₂ O ₂颗粒。因此，O ₂^–LiO _2的形成控制着整个反应的开始电位，而LiO _2的形成则界定了从溶液到表面介导的反应机理的变化。在DMSO中对Li-ORR的新发现和改进的理解将有助于进一步发展非质子传递Li-O ₂电池。

更新日期：2016-02-12

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