Unveiling performance evolution mechanisms of MnO2 polymorphs for durable aqueous zinc-ion batteries
Unveiling performance evolution mechanisms of MnO2 polymorphs for durable aqueous zinc-ion batteries
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揭示用于耐用水性锌离子电池的 MnO2 多晶型物的性能演化机制
DOI：
10.1016/j.ensm.2021.10.039
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发表时间：
2021-11-15
影响因子：
20.4
通讯作者：
Wang, Kuikui
中科院分区：
文献类型：
--
作者：
Liao, Yanxin;Chen, Hai-Chao;Wang, Kuikui
MnO 2基水溶液锌离子电池（ZIB）由于其安全性和可持续性，在大规模储能应用中具有巨大的应用前景。然而，在高放电深度下的快速容量衰减限制了MnO 2阴极的应用。同时，由于对MnO 2阴极的反应化学和降解过程还不能完全理解，导致其循环稳定性的改善缺乏稳健的方法。在此，ZIB性能的MnO 2多晶型物进行了研究，以揭示其详细的反应化学和降解机制。在不同循环下的非原位表征显示了活性物质（原始MnO 2-> Mn 2 +->水钠锰矿-> ZnMn 2 O 4/Mn 3 O 4）的演变以及共插入、溶解/沉积和化学转化机制的共存反应。来自这些中间产物和不同反应机理的变化贡献导致循环期间的波动性能。水钠锰矿的初始性能活化来自于其活性的增强，而降解则是由于其转化为电化学惰性的ZnMn 2 O 4和Mn 3 O 4而引起的。通过优化隧道结构，发现R-MnO 2具有低的锰溶解，其反应主要通过Zn 2 +/H+的嵌入/提取实现，理论计算验证了其在放电状态下的低Jahn-Teller畸变。这种特性避免了R-MnO 2转化为亚稳态水钠锰矿，从而在高放电深度下产生稳定的容量。
MnO2-based aqueous Zn-ion batteries (ZIBs) hold great promising for large-scale energy storage applications owing to their safe and sustainable nature. However, rapid capacity decay under high depth of discharge limits the applications of MnO2 cathodes. In the meantime, the reaction chemistry and degradation process of MnO2 cathodes cannot be fully understood, leading to improvement of their cycling stability lacks of robust methods. Herein, ZIB performances of MnO2 polymorphs are investigated to disclose their detailed reaction chemistry and degradation mechanisms. Ex situ characterizations at different cycles exhibit evolution of active materials (original MnO2 -> Mn2+-> birnessite -> ZnMn2O4/Mn3O4) and coexisted reactions from co-insertion, dissolution/deposition and chemical conversion mechanisms. Variational contributions from these intermediate products and different reaction mechanisms cause fluctuated performance during cycling. Initial performance activation is from enhanced activity of birnessite, while the degradation is caused by its conversion to electrochemically inactive ZnMn2O4 and Mn3O4. By optimizing tunnel structures, it is found that R-MnO2 shows low manganese dissolution with its reaction mainly achieved by intercalation/extraction of Zn2+/H+, and theoretical calculations verify its low Jahn-Teller distortion at discharged state. This specific property circumvents conversion of R-MnO2 to metastable birnessite, giving rise to a stable capacity under high depth of discharge.