摘要：近年来，充电能源市场主要依靠锂离子电池，随着电子、交通等领域的迅速发展，对锂离子电池的依赖也逐渐加剧，锂资源将面临短缺问题。这意味着，需要研制出能替代锂离子电池的新型电池，来满足日益增长的消费需求。由于电化学性能相似，钠离子电池已被提议作为锂离子电池的替代品，研究表示，与锂离子电池相比，钠离子电池具有三个明显的优势：（1）钠资源丰富且价格低廉，广泛分布于地壳沉积和海水中，天然钠储量比锂多1000倍。（2）钠离子电池具有较高的半电池电势，因此电解质的可选范围更为宽广。（3）钠离子电池的电化学性能更稳定，使用起来安全性更高。
钠离子电池技术的关键之处在于电极材料的选取，其中，硅基材料的比容量较高，是目前钠离子电池负极材料的研究热点。但是，钠离子比锂离子半径大且重，导致钠离子迁移动力学缓慢，无法完成快速充放电的过程。此外，最近的实验表明，晶体硅不适用于钠原子，因为形成NaSi在能量上是不可行的，并且当钠离子进入硅后，会使硅发生巨大的体积形变，这将缩短电池的使用寿命，并影响电池的安全性。因此，对于钠离子电池技术，研究钠在硅电极中的运动特性是十分必要的。在本文中，我们使用QM/MM空间多尺度计算方法，该方法耦合了第一性原理（DFT）和分子动力学（MD），成功模拟了钠在硅中的稳定构型和扩散特性。
本文的主要内容：
（1）利用DFT和多尺度计算方法模拟钠在硅中的稳定构型，计算表明钠在硅中的稳定位置在硅的四面体结构的中心位置（��）处。
（2）计算钠在硅中��位点的结合能，并对比纯DFT的计算结果，验证本文使
用的多尺度方法的准确性。
（3）模拟钠在硅中的扩散路径。
（4）计算钠在硅中的扩散势垒值，并与DFT计算结果和实验数据作对比。绘制能量变化曲线，并与锂相比较。
关键词：钠离子电池；硅电极；钠的运动；DFT；多尺度计算方法
Abstract
In recent years, the charging energy markets mostly rely on lithiumion battery, with the development of the areas such as electronics, transportation etc, the reliance on lithiumion batteries are also gradually increasing, limited lithium resources will face shortages. It means that, we need to develop a new batterie to replace the lithiumion batterie to meet the growing consumer demand. Due to the electrochemical properties similarities, the sodiumion batteries have been proposed as an alternative to the lithiumion batteries,study says, compared with lithiumion batteries, sodiumion
batteries have three distinct advantages（: 1）Sodium is available in great abundance and at low cost,natural sodium is over 1000 times more abundant than lithium, and can be sourced from both deposits in the earth’s crust and salt water. （2）The half cell potential of sodiumion batteries is higher,so electrolyte selection is wider.（3）Electrochemical properties of sodiumion batteries are more stable and use more secure.
The key of the sodiumion batteries is the selection of electrode materials, among them, the siliconbased materials is the hot spot in sodiumion batteries anode material because of it’s high capacity. However, the sodium ion is larger and heavier than the lithium ion radius, resulting in slow migration of sodium ions, can not complete the process of rapid charge and discharge. Besides, recent experiments indicate that diamond Si does not work for Na, since the formation of NaSi is energetically unfeasible,otherwise, the Silicon will have a large volume deformation when the sodium ions insertion into Silicon, this will shorten the life of the battery and affect the battery safety. Therefore, for sodium ion battery technology, the study of sodium movement characteristics in the silicon electrode is very necessary. We used the QM / MM space multiscale calculation method, which coupled the first principle (DFT) and molecular dynamics (MD), and successfully simulated the stable configuration and diffusion characteristics of sodium in silicon.The main contents of this paper: Lammps钠在硅电极中的运动特性研究:http://www.youerw.com/wuli/lunwen_203522.html