Hydrogen titanium oxide (HTO) is a promising material in extracting lithium ions from dilute sources such as geothermal or oil/gas brines. However, experiments show limited Li adsorption in HTO compared to its theoretical maximum capacity, where all H atoms in HTO are replaced by Li that forms lithium titanium oxide (LTO). Here, molecular dynamics (AIMD) simulations show clear evidence of phase transitions at specific Li adsorption in pure or doped HTO/LTO, which directly predict their experimental maximum capacity. Analysis of thermodynamic properties as well as layered crystal structures show distinct Li-poor to Li-rich phase transitions in the pure, Mo-doped, and Fe-doped HTO/LTO. In addition, it is observed a second phase transition in the Fe-doped HTO/LTO in the Li-poor phases that further constrains Li adsorption. To the best of my knowledge, this is the first study that accurately predict the experimental capacities in ion sieves from first principle. More importantly, this study puts spotlights on phase transitions as an important consideration in molecular engineering developments of functional separation materials, such as the high-performance lithium-ion sieves presented herein.

中文翻译：

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相变限制了钛基离子筛中的锂吸附


氢钛氧化物 (HTO) 是一种很有前景的从地热或油气盐水等稀源中提取锂离子的材料。然而，实验表明，与理论最大容量相比，HTO 中的 Li 吸附有限，其中 HTO 中的所有 H 原子都被 Li 取代，形成锂钛氧化物 (LTO)。在这里，分子动力学 (AIMD) 模拟显示了纯或掺杂 HTO/LTO 中特定 Li 吸附时发生相变的明显证据，这直接预测了它们的实验最大容量。热力学性质以及层状晶体结构的分析表明，纯 HTO/LTO、Mo 掺杂和 Fe 掺杂 HTO/LTO 中存在明显的贫锂到富锂相变。此外，还观察到贫锂相中 Fe 掺杂的 HTO/LTO 发生第二相变，这进一步限制了 Li 的吸附。据我所知，这是第一项根据第一原理准确预测离子筛实验能力的研究。更重要的是，这项研究将相变作为功能分离材料（例如本文介绍的高性能锂离子筛）分子工程开发中的一个重要考虑因素。