A density functional theory based study of the electron transfer reaction at the cathode–electrolyte interface in lithium–air batteries†,Physical Chemistry Chemical Physics

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A density functional theory based study of the electron transfer reaction at the cathode–electrolyte interface in lithium–air batteries†
Physical Chemistry Chemical Physics ( IF 2.9 ) Pub Date : 2015-03-31 00:00:00 , DOI: 10.1039/c4cp06121g
Saeed Kazemiabnavi _{1,

2,

3,

4} , Prashanta Dutta _{1,

2,

3,

4} , Soumik Banerjee _{1,

2,

3,

4}

Affiliation

The unique properties of ionic liquids such as a relatively wide electrochemical stability window and very low vapor pressure have made them promising candidates as electrolytes for improving the cyclic performance of lithium–air batteries. The local current density, which is an important parameter in determining the performance of lithium–air batteries, is a function of the rate constant of the electron transfer reactions at the surface of the cathode. In this study, a novel method based on Marcus theory is presented to investigate the effect of varying the length of the alkyl side chain of model imidazolium based cations and the operating temperature on the rates of electron transfer reactions at the cathode. The necessary free energies of all the species involved in the multi-step reduction of oxygen into the peroxide ion were calculated using density functional theory (DFT). Our results indicate that the magnitude of the Gibbs free energy for the reduction of oxygen into the superoxide ion and also for the reduction of superoxide into the peroxide ion increases with an increase in the static dielectric constant of the ionic liquid. This trend in turn corresponds to the decrease in the length of the alkyl side chain of the ionic liquid cation. Furthermore, the change in Gibbs free energy decreases with increase in the operating temperature. The inner-sphere reorganization energies were evaluated using Nelsen's four point method. The total reorganization energies of all reduction reactions increase with decrease in the length of the alkyl side chain and increase in the operating temperature. Finally, the rate constants of the electron transfer reaction involved in the reduction of oxygen were calculated. The logarithm of the reaction rate constants decreases with increase in the static dielectric constant and increases with increase in the operating temperature. Our results provide fundamental insight into the kinetics and thermodynamics of the electron transfer reactions at the cathode that will help in the identification of appropriate electrolytes for enhanced performance of lithium–air batteries.

中文翻译：

基于密度泛函理论的锂-空气电池中阴极-电解质界面电子转移反应的研究†

离子液体的独特特性，例如相对较宽的电化学稳定性窗口和极低的蒸气压，使其成为有望改善锂空气电池循环性能的电解质的有希望的候选者。局部电流密度是决定锂空气电池性能的重要参数，它是阴极表面电子转移反应速率常数的函数。在这项研究中，提出了一种基于马库斯（Marcus）理论的新方法，以研究改变基于咪唑鎓型阳离子的烷基侧链长度和操作温度对阴极电子转移反应速率的影响。使用密度泛函理论（DFT）计算了将氧气多步还原为过氧化物离子所涉及的所有物质的必要自由能。我们的结果表明，随着离子液体静态介电常数的增加，用于将氧气还原成超氧化物离子以及将超氧化物还原成过氧化物离子的吉布斯自由能的大小也随之增加。该趋势又对应于离子液体阳离子的烷基侧链长度的减少。此外，吉布斯自由能的变化随着工作温度的升高而减小。使用Nelsen的四点法评估了内部球的重组能。所有还原反应的总重组能随烷基侧链长度的减少和操作温度的增加而增加。最后，计算了与氧的还原反应有关的电子转移反应的速率常数。反应速率常数的对数随着静态介电常数的增加而降低，并且随着工作温度的升高而增加。我们的结果提供了对阴极电子转移反应的动力学和热力学的基本认识，这将有助于鉴定适当的电解质以增强锂空气电池的性能。反应速率常数的对数随着静态介电常数的增加而降低，并且随着工作温度的升高而增加。我们的结果提供了对阴极电子转移反应的动力学和热力学的基本认识，这将有助于鉴定适当的电解质以增强锂空气电池的性能。反应速率常数的对数随着静态介电常数的增加而降低，并且随着工作温度的升高而增加。我们的结果提供了对阴极电子转移反应的动力学和热力学的基本认识，这将有助于鉴定适当的电解质以增强锂空气电池的性能。

更新日期：2015-03-31

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