Ariyoshi Kingo
Department of Applied Chemistry and Bioengineering, Graduate School of Engineering, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan.
Phys Chem Chem Phys. 2022 Jun 1;24(21):12984-12992. doi: 10.1039/d2cp00383j.
The transition-metal ions in a solid matrix are oxidised and reduced a solid-state redox reaction during the charge/discharge process of lithium insertion materials, which are commonly used as positive and negative electrodes in lithium-ion batteries. Therefore, the electrode potentials of lithium insertion materials should be different from the redox potentials of transition-metal ions in aqueous solution (, the standard electrode potential). In this study, the solid-state redox potentials of the transition-metal ions in polyanionic materials with three distinct structures (, olivine, NASICON-type, and MOXO-type structures, where M = 3d transition-metal ion, and X = P or S) were surveyed to understand the electrode potentials of lithium insertion materials. The redox potentials of the transition-metal ions in polyanionic materials were very similar to those in aqueous solution despite the differences between the environments of these ions in the MO octahedron in polyanionic materials and the aqua complexes of [M(HO)] in aqueous solutions. The high coefficient of determination ( ≈ 0.990) of these two potentials indicated that the solid-state redox potential for the lithium insertion reaction in polyanionic materials can be estimated using the standard electrode potential of the corresponding transition-metal ion in aqueous solution. Finally, the similarity between the redox potentials of the transition-metal ions in polyanionic materials and those in aqua complexes is discussed from the thermodynamic perspective. The present findings on the similarity of the redox potentials of transition-metal ions in different media could provide useful insights into the design of novel insertion materials for rechargeable batteries based on lithium, sodium, potassium, and magnesium, among other metals.
在锂离子电池中常用作正负极的锂嵌入材料的充放电过程中，固体基质中的过渡金属离子会发生氧化还原反应，即固态氧化还原反应。因此，锂嵌入材料的电极电位应与过渡金属离子在水溶液中的氧化还原电位（即标准电极电位）不同。在本研究中，对具有三种不同结构（橄榄石型、NASICON型和MOXO型结构，其中M = 3d过渡金属离子，X = P或S）的聚阴离子材料中过渡金属离子的固态氧化还原电位进行了研究，以了解锂嵌入材料的电极电位。尽管聚阴离子材料中MO八面体中这些离子的环境与水溶液中[M(H₂O)₆]的水合配合物之间存在差异，但聚阴离子材料中过渡金属离子的氧化还原电位与水溶液中的非常相似。这两种电位的高决定系数（≈0.990）表明，聚阴离子材料中锂嵌入反应的固态氧化还原电位可以使用相应过渡金属离子在水溶液中的标准电极电位来估算。最后，从热力学角度讨论了聚阴离子材料中过渡金属离子的氧化还原电位与水合配合物中氧化还原电位之间的相似性。目前关于不同介质中过渡金属离子氧化还原电位相似性的研究结果，可为基于锂、钠、钾和镁等金属的新型可充电电池嵌入材料的设计提供有用的见解。
