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锂氧电池中电解质氧气传输特性对反应机制的影响

Effects of the oxygen transport properties of electrolytes on the reaction mechanisms in lithium‒oxygen batteries

  • 摘要: 锂氧电池因其极高的理论能量密度而备受关注,但其发展仍处于早期阶段。正如人们普遍认为的那样,溶液机制可提高放电容量,而表面机制可提高循环稳定性。因此,可以通过调整反应机制来提高电池性能。以往的研究主要集中在极薄或极平的电极,与此相反,本研究采用厚电极,强调传质的重要性。鉴于电解质溶剂是传质的主要场所,我们研究了两种典型溶剂对传质和电池性能的影响:低黏度、高氧气扩散率的二甲基亚砜和高氧气溶解度、高锂离子传输能力的四甘醇二甲醚。研究结果揭示了一种新的反应机制诱导途径,即反应机制随电极的空间位置而变化。随着电极空间分布的变化,出现了溶液机制产物、过渡态产物和表面机制产物的分层现象,这归因于传质阻力的增加。这项工作从一个独特的角度展示了溶剂影响反应机制的方式,并为调节反应机制提供了一种新方法。

     

    Abstract: Lithium–oxygen batteries attract considerable attention due to exceptionally high theoretical energy density, while the development remains in its early stage. As is widely suggested, the solution mechanism induces greater discharge capacity, while the surface mechanism induces greater cycle stability. Therefore, battery performance can be improved by adjusting the reaction mechanism. Previous studies predominantly focus on extremely thin or flat electrodes. In contrast, this work utilizes thick electrodes, emphasizing the importance of mass transport. Given that the electrolyte solvent is the main site of mass transport, the effects of two typical solvents on mass transport and battery performance are investigated: dimethyl sulfoxide with low viscosity and a high O2 diffusion rate and tetraethylene glycol dimethyl ether with high O2 solubility and high Li+ transport capability. The results reveal a novel pathway for reaction mechanism induction where the mechanism varies with the spatial position of the electrode. As the spatial distribution of the electrode progresses, a layered appearance of solution mechanism products, transition state products, and surface mechanism products emerges, which is attributed to the increase in the mass transfer resistance. This work presents a distinct perspective on the way solvents influence reaction pathways and offers a new approach to regulating reaction pathways.

     

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