用 Operando X 射线衍射了解 Li2O2 和 LiOH 的电化学形成和分解,Chemistry of Materials

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用 Operando X 射线衍射了解 Li2O2 和 LiOH 的电化学形成和分解
Chemistry of Materials ( IF 7.2 ) Pub Date : 2017-02-13 00:00:00 , DOI: 10.1021/acs.chemmater.6b04370
Zhaolong Li ₁ , Swapna Ganapathy ₂ , Yaolin Xu ₂ , Jouke R Heringa ₂ , Quanyao Zhu ₃ , Wen Chen ₃ , Marnix Wagemaker ₂

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锂空气或 Li-O ₂电池系统是一种很有前途的电化学储能系统，因为它具有非常高的理论比能量，符合汽车应用的要求。基础研究在减轻有害（电）化学过程方面取得了很大进展；然而，结晶 Li ₂ O ₂和 LiOH 放电产物的详细结构演变，至少部分负责有限的可逆性和较差的倍率性能，在实际电化学条件下很难测量操作数。本研究使用操作数的 Rietveld细化完整放电-充电循环期间的 X 射线衍射数据，分别揭示了 Li ₂ O ₂和 LiOH 微晶在 1,2-二甲氧基乙烷 (DME) 和 DME/LiI 电解质中的详细结构演变。_{各向异性加宽反射证实并量化了 Li 2} O ₂和 LiOH的片晶形状，并显示了在放电和充电期间平均微晶形状如何演变。Li ₂ O ₂显示通过成核和生长机制形成，而分解似乎从最小的 Li ₂ O _2开始微晶尺寸，因为它们的暴露表面较大。在 LiI 的存在下，片状 LiOH 微晶通过逐个粒子的成核和生长过程形成，在放电结束时，H ₂ O 耗尽被认为导致亚化学计量的 Li(OH) _{1- x}，出现充电时优先分解。操作X 射线衍射证明了在 LiI 存在下，LiOH 微晶在多个循环中的循环形成和分解，结构演变为理解和改进这些高度相关的电化学系统提供了关键信息。

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Understanding the Electrochemical Formation and Decomposition of Li2O2 and LiOH with Operando X-ray Diffraction

The lithium air, or Li–O₂, battery system is a promising electrochemical energy storage system because of its very high theoretical specific energy, as required by automotive applications. Fundamental research has resulted in much progress in mitigating detrimental (electro)chemical processes; however, the detailed structural evolution of the crystalline Li₂O₂ and LiOH discharge products, held at least partially responsible for the limited reversibility and poor rate performance, is hard to measure operando under realistic electrochemical conditions. This study uses Rietveld refinement of operando X-ray diffraction data during a complete discharge–charge cycle to reveal the detailed structural evolution of Li₂O₂ and LiOH crystallites in 1,2-dimethoxyethane (DME) and DME/LiI electrolytes, respectively. The anisotropic broadened reflections confirm and quantify the platelet crystallite shape of Li₂O₂ and LiOH and show how the average crystallite shape evolves during discharge and charge. Li₂O₂ is shown to form via a nucleation and growth mechanism, whereas the decomposition appears to start at the smallest Li₂O₂ crystallite sizes because of their larger exposed surface. In the presence of LiI, platelet LiOH crystallites are formed by a particle-by-particle nucleation and growth process, and at the end of discharge, H₂O depletion is suggested to result in substoichiometric Li(OH)_1–x, which appears to be preferentially decomposed during charging. Operando X-ray diffraction proves the cyclic formation and decomposition of the LiOH crystallites in the presence of LiI over multiple cycles, and the structural evolution provides key information for understanding and improving these highly relevant electrochemical systems.

更新日期：2017-02-13

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