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Ab Initio Study of Sodium Insertion in the λ-Mn2O4 and Dis/Ordered λ-Mn1.5Ni0.5O4 Spinels.
Chemistry of Materials ( IF 7.2 ) Pub Date : 2018-09-13 , DOI: 10.1021/acs.chemmater.8b01634 Alexandros Vasileiadis 1 , Brian Carlsen 1 , Niek J J de Klerk 1 , Marnix Wagemaker 1
Chemistry of Materials ( IF 7.2 ) Pub Date : 2018-09-13 , DOI: 10.1021/acs.chemmater.8b01634 Alexandros Vasileiadis 1 , Brian Carlsen 1 , Niek J J de Klerk 1 , Marnix Wagemaker 1
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The main challenge of sodium-ion batteries is cycling stability, which is usually compromised due to strain induced by sodium insertion. Reliable high-voltage cathode materials are needed to compensate the generally lower operating voltages of Na-ion batteries compared to Li-ion ones. Herein, density functional theory (DFT) computations were used to evaluate the thermodynamic, structural, and kinetic properties of the high voltage λ-Mn2O4 and λ-Mn1.5Ni0.5O4 spinel structures as cathode materials for sodium-ion batteries. Determination of the enthalpies of formation reveal the reaction mechanisms (phase separation vs solid solution) during sodiation, while structural analysis underlines the importance of minimizing strain to retain the metastable sodiated phases. For the λ-Mn1.5Ni0.5O4 spinel, a thorough examination of the Mn/Ni cation distribution (dis/ordered variants) was performed. The exact sodiation mechanism was found to be dependent on the transition metal ordering in a similar fashion to the insertion behavior observed in the Li-ion system. The preferred reaction mechanism for the perfectly ordered spinel is phase separation throughout the sodiation range, while in the disordered spinel, the phase separation terminates in the 0.625 < x < 0.875 concentration range and is followed by a solid solution insertion reaction. Na-ion diffusion in the spinel lattice was studied using DFT as well. Energy barriers of 0.3-0.4 eV were predicted for the pure spinel, comparing extremely well with the ones for the Li-ion and being significantly better than the barriers reported for multivalent ions. Additionally, Na-ion macroscopic diffusion through the 8a-16c-8a 3D network was demonstrated via molecular dynamics (MD) simulations. For the λ-Mn1.5Ni0.5O4, MD simulations at 600 K bring forward a normal to inverse spinel half-transformation, common for spinels at high temperatures, showing the contrast in Na-ion diffusion between the normal and inverse lattice. The observed Ni migration to the tetrahedral sites at room temperature MD simulations explains the kinetic limitations experienced experimentally. Therefore, this work provides a detailed understanding of the (de)sodiation mechanisms of high voltage λ-Mn2O4 and λ-Mn1.5Ni0.5O4 spinel structures, which are of potential interest as cathode materials for sodium-ion batteries.
中文翻译：
钠在 λ-Mn2O4 和无序/有序 λ-Mn1.5Ni0.5O4 尖晶石中插入的从头算研究。
钠离子电池的主要挑战是循环稳定性，这通常会因钠插入引起的应变而受到损害。与锂离子电池相比，钠离子电池通常较低的工作电压，需要可靠的高压正极材料来补偿。在此，使用密度泛函理论（DFT）计算来评估高电压λ-Mn2O4和λ-Mn1.5Ni0.5O4尖晶石结构作为钠离子电池正极材料的热力学、结构和动力学性质。形成焓的测定揭示了钠化过程中的反应机制（相分离与固溶体），而结构分析强调了最小化应变以保留亚稳态钠化相的重要性。对于 λ-Mn1.5Ni0.5O4 尖晶石，对 Mn/Ni 阳离子分布（无序/有序变体）进行了彻底检查。研究发现，确切的钠化机制取决于过渡金属的排序，其方式与在锂离子系统中观察到的插入行为类似。完美有序尖晶石的优选反应机制是在整个钠化范围内发生相分离，而在无序尖晶石中，相分离在 0.625 < x < 0.875 浓度范围内终止，然后进行固溶插入反应。还使用 DFT 研究了尖晶石晶格中的钠离子扩散。预测纯尖晶石的能垒为 0.3-0.4 eV，与锂离子的能垒相比非常好，并且明显优于报道的多价离子的能垒。此外，通过分子动力学 (MD) 模拟证明了 Na 离子通过 8a-16c-8a 3D 网络的宏观扩散。对于 λ-Mn1.5Ni0.5O4，600 K 下的 MD 模拟提出了高温下尖晶石常见的正向反尖晶石半转变，显示了正向晶格和反向晶格之间 Na 离子扩散的对比。室温 MD 模拟中观察到的 Ni 迁移到四面体位点解释了实验中遇到的动力学限制。因此，这项工作提供了对高电压 λ-Mn2O4 和 λ-Mn1.5Ni0.5O4 尖晶石结构的（脱）钠机制的详细了解，这些结构作为钠离子电池的正极材料具有潜在的意义。
更新日期：2018-09-13
中文翻译：
钠在 λ-Mn2O4 和无序/有序 λ-Mn1.5Ni0.5O4 尖晶石中插入的从头算研究。
钠离子电池的主要挑战是循环稳定性，这通常会因钠插入引起的应变而受到损害。与锂离子电池相比，钠离子电池通常较低的工作电压，需要可靠的高压正极材料来补偿。在此，使用密度泛函理论（DFT）计算来评估高电压λ-Mn2O4和λ-Mn1.5Ni0.5O4尖晶石结构作为钠离子电池正极材料的热力学、结构和动力学性质。形成焓的测定揭示了钠化过程中的反应机制（相分离与固溶体），而结构分析强调了最小化应变以保留亚稳态钠化相的重要性。对于 λ-Mn1.5Ni0.5O4 尖晶石，对 Mn/Ni 阳离子分布（无序/有序变体）进行了彻底检查。研究发现，确切的钠化机制取决于过渡金属的排序，其方式与在锂离子系统中观察到的插入行为类似。完美有序尖晶石的优选反应机制是在整个钠化范围内发生相分离，而在无序尖晶石中，相分离在 0.625 < x < 0.875 浓度范围内终止，然后进行固溶插入反应。还使用 DFT 研究了尖晶石晶格中的钠离子扩散。预测纯尖晶石的能垒为 0.3-0.4 eV，与锂离子的能垒相比非常好，并且明显优于报道的多价离子的能垒。此外，通过分子动力学 (MD) 模拟证明了 Na 离子通过 8a-16c-8a 3D 网络的宏观扩散。对于 λ-Mn1.5Ni0.5O4，600 K 下的 MD 模拟提出了高温下尖晶石常见的正向反尖晶石半转变，显示了正向晶格和反向晶格之间 Na 离子扩散的对比。室温 MD 模拟中观察到的 Ni 迁移到四面体位点解释了实验中遇到的动力学限制。因此，这项工作提供了对高电压 λ-Mn2O4 和 λ-Mn1.5Ni0.5O4 尖晶石结构的（脱）钠机制的详细了解，这些结构作为钠离子电池的正极材料具有潜在的意义。
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