Probing Electrochemical Mg-Ion Activity in MgCr2–xVxO4 Spinel Oxides,Chemistry of Materials

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Probing Electrochemical Mg-Ion Activity in MgCr2–xVxO4 Spinel Oxides
Chemistry of Materials ( IF 7.2 ) Pub Date : 2020-01-17 , DOI: 10.1021/acs.chemmater.9b04206
Bob Jin Kwon _{1,

2} , Ka-Cheong Lau _{1,

2} , Haesun Park _{2,

3} , Yimin A. Wu _{2,

4} , Krista L. Hawthorne _{1,

2} , Haifeng Li ₅ , Soojeong Kim _{1,

2} , Igor L. Bolotin ₅ , Timothy T. Fister _{1,

2} , Peter Zapol _{2,

3} , Robert F. Klie _{2,

4} , Jordi Cabana _{2,

5} , Chen Liao _{1,

2} , Saul H. Lapidus _{2,

6} , Baris Key _{1,

2} , John T. Vaughey _{1,

2}

Affiliation

Mg migration in oxide spinels is impeded by strong affinity between divalent Mg and oxygen, suggesting a necessity of exploring new chemistry of solid lattices for functional Mg-ion electrode materials. Cationic mobility with a suitable activation energy in Cr spinels is evidenced by theoretical and experimental results, while redox potentials of V are appropriate to operate with currently limited candidates of nonaqueous electrolytes. By controlling the structure, composition, and complexity, a largely solid-solution MgCrVO₄ spinel was synthesized, which, unlike nanocomposites, can bring together the advantages of each transition metal in the lattice. The spinel was successfully synthesized by a simple solid-state reaction with minor inactive Cr- or V-rich components, which was confirmed via ²⁵Mg MAS NMR and high-resolution X-ray diffraction analyses. A thermally and anodically stable Mg(TPFA)₂/triglyme electrolyte was utilized for high-temperature electrochemistry and lowering kinetic barriers at and across interfaces so as to observe intercalation behavior of Mg in the designed lattice. Multimodal characterization confirmed an apparent bulk demagnesiation from MgCrVO₄ with partial reversibility by probing evolution of the local and long-range structure as well as vanadium and chromium electronic states within the lattice. Characterization experiments also provided a direct evidence for (de)intercalation reactions that occurred without any major competitive conversion reactions or insertion of protons into the lattice, except for the formation of a surface rock salt phase upon charge. These findings in Mg-ion activity expand opportunities to design Mg spinel oxide materials while highlighting the need to identify the origins of reversibility challenges due to, but not limited to, phase stability, particularly for the charged states, barriers at the interface, electrolyte stabilities, and desolvation phenomena, collectively hindering practical use as cathode materials.

中文翻译：

在MgCr _{2– x} V _x O ₄尖晶石氧化物中探测电化学Mg离子活性

Mg在氧尖晶石中的迁移受到二价Mg与氧之间的强亲和力的阻碍，这表明有必要探索功能性Mg离子电极材料的新型固体晶格化学。理论和实验结果证明了具有合适活化能的Cr尖晶石中的阳离子迁移率，而V的氧化还原电势适合与目前有限的非水电解质候选物一起使用。通过控制结构，组成和复杂性，合成了固溶体很大的MgCrVO ₄尖晶石，与纳米复合材料不同，它可以将晶格中每种过渡金属的优点结合在一起。尖晶石通过简单的固态反应与少量不活泼的富含Cr或V的成分成功合成，通过²⁵镁MAS NMR和高分辨率X射线衍射分析。利用热和阳极稳定的Mg（TPFA）₂ /三甘醇_二甲醚电解质进行高温电化学，并降低界面处和界面之间的动力学势垒，从而观察Mg在设计晶格中的嵌入行为。多峰表征证实了从MgCrVO ₄明显的整体脱镁通过探究晶格内局部和远程结构以及钒和铬电子态的演化，从而实现部分可逆性。表征实验还提供了发生（脱）插层反应的直接证据，该反应没有任何主要的竞争性转化反应或质子插入晶格中，只是在充电时形成了表面岩盐相。Mg离子活性的这些发现为设计Mg尖晶石氧化物材料提供了更多的机会，同时强调了由于（但不限于）相稳定性（特别是对于带电状态，界面的势垒，电解质的稳定性）而需要确定可逆性挑战的根源的必要性。以及去溶剂化现象，共同阻碍了作为阴极材料的实际应用。

更新日期：2020-01-17

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