利用分子動力學探討外加電場對鋰金屬電池中溶劑層 和固態電解質界面的影響

Abstract

電池是目前生活中一個重要的儲能工具，而現今所應用的電池以鋰離子電池為大宗，為了追求未來更大電容量和續航力，需要找尋能夠替代鋰離子電池的新型電池。鋰金屬因具備高容量（3860mAh/g）及低電化學電位（-3.04Vvs. SHE），被視為下一代高能量密度電池的關鍵負極材料，然而，其商業化的目標受枝晶生長問題制約。枝晶不僅會降低電池循環壽命，更可能穿透隔膜引發短路甚至爆炸風險。此問題的核心在於電解液分解所形成的固態電解質界面（SEI）——其結構不均勻性與機械性能不足，導致鋰沉積不均且無法有效抑制枝晶的生長。外加電場能夠影響化學反應，其主要透過改變分子間的運動與相互作用，這些機制使得外加電場能夠調控反應速率與反應選擇性，影響反應產物的種類與比例。因此，外加電場作為一種外部調控手段，在提升反應效率與精確控制反應路徑方面具有重要潛力。近年來，許多分子動力學結合電場的研究，有助於從微觀層面理解這些效應與反應機制。因此，本研究希望透過分子動力學作為模擬方法在電解液系統中外加電場對離鋰子溶劑殼的影響做討論，再生成鋰金屬電池之SEI層，並且添加不同大小的電場，來觀察SEI的厚度以及測試其機械性質，希望能夠更了解外加電場和SEI之間的關係，對如何生成更加穩定的SEI有新的見解。

Batteries are essential energy storage devices in modern life, with lithium-ion batteries (LIBs) currently dominating commercial applications. However, to meet the growing demand for higher energy density and longer cycle life, next-generation battery systems are being actively explored. Lithium metal, owing to its exceptionally high theoretical specific capacity (3860 mAh/g) and low electrochemical potential (–3.04 V vs. SHE), is considered a promising anode material for high-energy-density batteries. Nevertheless, its commercialization is hindered by the issue of lithium dendrite growth, which not only reduces cycling stability but also poses serious safety risks due to potential short-circuiting through the separator and even thermal runaway. At the core of this problem lies the solid electrolyte interphase (SEI), a passivation layer formed by the decomposition of electrolyte components. The inhomogeneous structure and poor mechanical integrity of the SEI often lead to uneven lithium deposition and insufficient suppression of dendrites. External electric fields have the ability to influence chemical reactions by altering molecular motion and intermolecular interactions, thereby affecting reaction rates and selectivity, as well as the distribution of products. As a result, the application of external electric fields presents a promising strategy for modulating interfacial reactions and controlling reaction pathways with greater precision. In recent years, molecular dynamics (MD) simulations combined with electric fields have provided valuable microscopic insights into these mechanisms. In this study, we employ MD simulations to investigate the influence of externally applied electric fields on the Li⁺ solvation shell in the electrolyte system. Subsequently, the formation of the SEI layer at the lithium–electrolyte interface is simulated under varying electric field strengths, with a focus on analyzing its thickness and evaluating its mechanical properties. The goal is to gain a deeper understanding of the relationship between electric field conditions and SEIcharacteristics, thereby contributing to the development of more stable and robust SEI layers for future lithium metal batteries.