安全電池実現のための適切添加剤を用いた先端的非引火性電解液の理論的設計

本研究的主要目的是为实用安全的锂离子电池设计一种先进的不可燃电解液。为此，我们重点研究了基于不可燃的磷酸三甲酯(TMP)溶剂的高盐浓(HC)电解液的稀释。首先，我们研究了HC TMP基电解液中固体电解质界面层(SEI)形成的微观机制。用红月亮方法发现，在HC电解液中，大量的盐负离子定位在SEI表面，促进了SEI盐衍生物种的致密无机层的网络形成。下一步，我们的目标是“稀释”这种基于HC TMP的电解液，以解决其低离子电导率和高粘度的问题。为此，人们设计了高氟化度的新型氢氟醚(HFES)。MD和QM计算表明，与其他常用的HFe稀释剂相比，双(1，1，2，2-四氟乙基)醚(B2E)和双(五氟乙基)醚(BPE)稀释可以显著提高Li+的自扩散常数和离子电导率。此外，HFES具有在HC-TMP溶液中形成局部浓缩电解质的能力，这使得人们对形成稳定而致密的无机SEI膜抱有很高的期望。最后，通过微观分析SEI的组成对其力学性能的影响，研究了SEI层的弹性。评价了SEI的延展性以及各电解液化合物对SEI稳定性的影响。

The main goal of this study is to design computationally an advanced non-flammable electrolyte for a practical safe Li-ion batteries. For that, we focused on the dilution the highly salt-concentrated (HC) electrolyte based on non-flammable trimethyl-phosphate (TMP) solvent. First, we aimed to investigate the microscopic mechanism of the solid electrolyte interphase (SEI) layer formation in HC TMP-based electrolyte. Using Red Moon methodology, it was revealed that a large amount of salt anions is localized on the SEI surface in HC electrolyte, enhancing the network formation of a dense inorganic layer with SEI salt-derived species. Next, we aimed to “dilute” such HC TMP-based electrolyte in order to address its low ionic conductivity and high viscosity. For that, new hydrofluoroethers (HFEs) were designed with high degree of fluorination. Using MD and QM calculations, self-diffusion constant of Li+ and the ionic conductivity should be significantly improved by dilution with bis(1,1,2,2-tetrafluoro ethyl) ether (B2E) and bis(pentafluoro ethyl) ether (BPE) compared to other common HFE diluents. In addition, HFEs have high ability to form a localized-concentrated electrolyte in HC TMP-based solution, leading to high expectation for the formation of a stable and a compact inorganic SEI film. Finally, the elasticity of the SEI layer was investigated through the microscopic analysis of the composition effect of the SEI on its mechanical properties. The ductility of the SEI were evaluated as well as the role of each electrolyte compound on the SEI stability.