Origin of unusual spinel-to-layered phase transformation by crystal water,Chemical Science

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Origin of unusual spinel-to-layered phase transformation by crystal water
Chemical Science ( IF 7.6 ) Pub Date : 2017-10-24 00:00:00 , DOI: 10.1039/c7sc04114d
Eunjeong Yang _{1,

2,

3,

4} , Heejin Kim _{4,

5,

6,

7} , Sangryun Kim _{8,

9,

10,

11} , In Kim _{1,

2,

3,

4} , Jaehoon Kim _{1,

2,

3,

4} , Hyunjun Ji _{1,

2,

3,

4} , Jang Wook Choi _{1,

2,

3,

4,

12} , Yousung Jung _{1,

2,

3,

4}

Affiliation

It is well known that many layered transition metal oxides can transform into a spinel structure upon repeated battery cycling, but a phase transition in the opposite direction is rare. Recently, the transformation from spinel Mn₃O₄ to layered MnO₂ was observed during the operation of a Mg battery in aqueous conditions, resulting in high performance Mg batteries. We hereby use ab initio calculations to unveil the mechanism by which crystal water plays a critical role in this unique transformation. Once inserted into the spinel form, a water molecule donates an electron, offering a key structural and thermodynamic driving force to initiate the transformation process. These crystal water molecules then get favorably clustered into a planar form in the layered structure and act as a stabilizing agent for birnessite. Kinetically, the inserted crystal water dramatically promotes the necessary rearrangement of Mn during the transition by lowering the activation barrier by >2 eV. The present structural, thermodynamic and kinetic understanding of the crystal water-driven phase transition provides novel insights to further the design of related low dimensional hydrated materials for multi-valent cathodes.

中文翻译：

结晶水异常的尖晶石-层状相变的起源

众所周知，许多层状过渡金属氧化物可在重复的电池循环中转变成尖晶石结构，但是在相反方向上的相变很少见。最近，在Mg电池在水性条件下的操作期间观察到从尖晶石Mn ₃ O ₄到层状MnO ₂的转变，从而产生高性能的Mg电池。我们特此使用从头开始通过计算揭示了结晶水在这种独特转化中起关键作用的机理。一旦插入尖晶石形式，水分子就会提供电子，从而提供关键的结构和热力学驱动力来引发转化过程。然后，这些结晶水分子在层状结构中有利地聚集成平面形式，并用作水钠锰矿的稳定剂。从动力学上讲，通过将活化势垒降低> 2 eV，插入的结晶水可显着促进过渡过程中Mn的必要重排。对晶体水驱动的相变的当前结构，热力学和动力学理解为进一步设计用于多价阴极的相关低维水合材料提供了新的见识。

更新日期：2017-11-08

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