二维“双面神”MXene的物性及其储能机理研究

As one novel two-dimensional material, MXene has been widely studied. It is a promising energy storage material in secondary batteries, but its experimental capacity is far from the theoretical capacity. The root cause is the surface passivation that cannot be removed during the preparation process. The passivation affects the interaction between lithium (sodium, potassium) and MXene, so it is important to study the intrinsic effect of the passivation on the energy storage mechanism. Property is often determined by geometric structure. Most of the previous researches are relative to symmetric passivation, and the asymmetry of the "Janus" structure is rarely investigated. The dipole moment induced by the Janus structure may increase the interaction of lithium (sodium, potassium) with the electrode material, resulting to increase of the storage capacity. Hence, this project is aimed at the key problem that how surface passivation seriously affects MXene’s energy storage properties. Taking the Janus structure of MXene and its passivation as the starting point, we utilize the high-throughput method mixed by density functional theory to screen out the Janus structure with a large dipole moment, afterward we explored the physical properties of the Janus structures that pass the screen. Finally, we plan to reveal the positive influence of the dipole moment on lithium intercalation (sodium and potassium) and furthermore the energy storage mechanism. The implementation of the project will provide reliable basic research data and valuable mechanistic explanations for the experimental study, eventually achieving high-capacity electrode material for lithium (sodium, potassium) ion batteries.

MXene作为一种非常有潜力的二次电池储能材料已被广泛研究，但其实际容量与理论容量相去甚远，根本原因在于制备过程中难以避免表面钝化。钝化物会影响锂（钠、钾）与MXene之间的相互作用，因此研究钝化物对储能机理的本质影响意义重大。性能往往由结构决定，以往的研究绝大部分都是关于对称性钝化物，而不对称性的“双面神”（Janus）结构研究甚少。Janus结构诱发的偶极矩，有可能会增加锂（钠、钾）与电极材料的相互作用而提高储存容量，因此，本项目针对钝化物严重影响MXene储能性质的关键问题，以MXene及其钝化物的Janus结构为出发点，通过密度泛函理论结合高通量分析方法筛选出具有大偶极矩的Janus结构，探索该类结构的物理特性，阐明结构中偶极矩对嵌锂（钠、钾）的积极影响，揭示其储能机制。项目的实施将为实验研究提供可靠的基础研究数据和有价值的机理解释，以获得高容量的锂（钠、钾）离子电池电极材料。

二维层状材料作为二次电池的电极材料的研究已成为一个重要领域。本项目采用密度泛函理论方法对不同类型的二维层状材料的储能行为及机理进行了系统研究。我们的研究表明二维层状材料在储锂、储钠、或储钾等的能力上各有优势，在引入掺杂或异质结构后可提高存储性能。具体来说，我们预测了二维h-B2O、T-Graphene、MnN和VSi2N4等层状材料的储锂、储钠或储钾性能，最高的理论容量可达2232 mAh/g；研究了反阻挡层异质结构增强钠离子存储动力学，发现反阻挡层异质结构有利于电子传输、降低扩散能垒、提升扩散动力学，表现出优异的高倍率和循环性能；研究了带有硫空位的 Mo-S-Co 异质结用于锂硫电池，硫空位的引入提高了锂硫电池的容量、倍率性能和循环性能；开发了一种具有共形亲锂锌涂层（CF@Zn）的三维导电碳膜，以引导均匀的锂镀层/剥离，并容纳大量的金属锂；提出了一种新的金属有机膦框架（MOPFs）衍生策略，并研究了所合成铜掺杂炭长方体的储钠性能。同时，我们报告了一种高度可逆的锌化学反应，其中典型的硫酸锌电解液中添加了磷酸，确保了（002）纹理的锌箔上长期（>1500 小时，1500 次）的外延生长。这些研究工作对今后电极材料的设计与应用提供了指导。