Synthesis, Characterization, and Structural Modeling of High‐Capacity, Dual Functioning MnO2 Electrode/Electrocatalysts for Li‐O2 Cells
Synthesis, Characterization, and Structural Modeling of High‐Capacity, Dual Functioning MnO2 Electrode/Electrocatalysts for Li‐O2 Cells
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DOI：
10.1002/aenm.201200037
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发表时间：
2013
影响因子：
27.8
通讯作者：
L. Trahey;N. Karan;M. Chan;Jun Lu;Yang Ren;J. Greeley;M. Balasubramanian;A. Burrell;L. Curtiss-L.
中科院分区：
文献类型：
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作者：
L. Trahey;N. Karan;M. Chan;Jun Lu;Yang Ren;J. Greeley;M. Balasubramanian;A. Burrell;L. Curtiss-L.
很明显，在碳酸盐电解液中循环锂氧电池是不切实际的，因为由氧还原产物引发的电解液分解主导着电池化学。这项研究表明，使用α-MnO_2/Ramsdellite-MnO_2电极/电催化剂会在碳酸亚丙酯中形成类锂氧化物放电产物，据报道，这种产物极易分解。X射线光电子数据表明，在空气电极表面，特别是在MnO2表面，似乎形成并分解了可能的锂氧化物(Li2O2和Li2O)，同时也形成了Li2CO3。相比之下，没有α-MnO_2/Ramsdellite-MnO_2的电池在电化学循环中迅速失败，可能是由于放电产物的差异。使用未经优化的空气电极，可以获得相对较高的电极容量，最高可达5000 mAh/g(碳+电极/电催化剂)。用第一性原理密度泛函理论计算方法研究了锂、过氧化锂(Li2O)和氧化锂(Li2O)在α-MnO2隧道中的可逆插入反应，以及锂与卫星-MnO2的反应，为一些观测结果提供了可能的解释。推测具有Mn4+/3+性质的Li2O稳定且部分锂化的电极组分0.15Li2O·α-LixMnO2可能促进Li2O2/Li2O的放电/充电化学反应，提供双电极/电催化功能。
It has become clear that cycling lithium‐oxygen cells in carbonate electrolytes is impractical, as electrolyte decomposition, triggered by oxygen reduction products, dominates the cell chemistry. This research shows that employing an α‐MnO2/ramsdellite‐MnO2 electrode/electrocatalyst results in the formation of lithium‐oxide‐like discharge products in propylene carbonate, which has been reported to be extremely susceptible to decomposition. X‐ray photoelectron data have shown that what are likely lithium oxides (Li2O2 and Li2O) appear to form and decompose on the air electrode surface, particularly at the MnO2 surface, while Li2CO3 is also formed. By contrast, cells without α‐MnO2/ramsdellite‐MnO2 fail rapidly in electrochemical cycling, likely due to the differences in the discharge product. Relatively high electrode capacities, up to 5000 mAh/g (carbon + electrode/electrocatalyst), have been achieved with non‐optimized air electrodes. Insights into reversible insertion reactions of lithium, lithium peroxide (Li2O2) and lithium oxide (Li2O) in the tunnels of α‐MnO2, and the reaction of lithium with ramsdellite‐MnO2, as determined by first principles density functional theory calculations, are used to provide a possible explanation for some of the observed results. It is speculated that a Li2O‐stabilized and partially‐lithiated electrode component, 0.15Li2O·α‐LixMnO2, that has Mn4+/3+ character may facilitate the Li2O2/Li2O discharge/charge chemistries providing dual electrode/electrocatalyst functionality.