Henan Key Laboratory of Materials on Deep-Earth Engineering, School of Materials Science and Engineering, Henan Polytechnic University, Jiaozuo 454003, China.
Phys Chem Chem Phys. 2023 Mar 29;25(13):9428-9436. doi: 10.1039/d3cp00012e.
Along with Li-ion extraction/intercalation during charge and discharge processes, structural phase transitions often occur in the electrode materials of Li-ion batteries (LIBs). By determining atomic positions before and after Li adsorptions, structural phase transitions of two-dimensional MXenes were investigated systematically using first-principles density functional calculations. The lithiation-induced phase transitions of ten MC MXenes with oxygen groups can be divided into three types. No phase transitions occur for Ti-type MXenes including TiCO, ZrCO and HfCO. The oxygens in Ta-type MXenes (ScCO, YCO, NbCO and TaCO) move from one type of octahedral void to another type of octahedral void. However, for Mo-type MXenes including VCO, CrCO and MoCO, the oxygens move from octahedral voids to tetrahedral voids. The mechanisms whether phase transitions happen or not are dependent on the sizes of M ions. Furthermore, all the predicted phase transitions were confirmed by molecular dynamics simulations. The calculated results of electron localization functions and Bader charge illustrate that there exist strong Coulomb interactions (ionic bonds) between Li and MXene surfaces. The band structure, diffusion energy barrier, open circuit voltage and storage capacity were calculated to evaluate the lithium storage properties of different MXenes, which reveals that VCO and CrCO should be optimal candidates as electrode materials for LIBs.
伴随着锂离子在充放电过程中的嵌入/脱出，锂离子电池（LIB）的电极材料通常会发生结构相变。通过在锂离子吸附前后确定原子位置，利用第一性原理密度泛函计算系统地研究了二维 MXenes 的结构相变。含氧基的十种 MC MXenes 的锂化诱导相变可分为三种类型。对于 Ti 型 MXenes（包括 TiCO、ZrCO 和 HfCO），不会发生相变。Ta 型 MXenes（ScCO、YCO、NbCO 和 TaCO）中的氧从一种八面体空穴迁移到另一种八面体空穴。然而，对于 Mo 型 MXenes 包括 VCO、CrCO 和 MoCO，氧从八面体空穴迁移到四面体空穴。是否发生相变取决于 M 离子的大小。此外，所有预测的相变都通过分子动力学模拟得到了证实。电子局域函数和 Bader 电荷的计算结果表明，Li 和 MXene 表面之间存在强烈的库仑相互作用（离子键）。计算了不同 MXenes 的能带结构、扩散能垒、开路电压和存储容量，以评估其锂离子存储性能，结果表明 VCO 和 CrCO 应是 LIB 电极材料的最佳候选材料。
