锂离子电池EC/EMC/FEC电解质中的低温输运：分子动力学与机器学习模拟
Low-Temperature Transport in Li-Ion Battery EC/EMC/FEC Electrolytes: Molecular Dynamics and Machine-Learning Modeling
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中文总结 AI 辅助
本研究结合分子动力学与机器学习，探究含不同比例FEC的EC/EMC基LiPF₆电解质的低温输运，揭示温度、溶剂组成及FEC含量对电导率的影响规律。
中文摘要 AI 辅助
低温运行对电池电解质中的锂离子输运造成严重限制，但低温范围内溶剂组成与氟化添加剂的耦合效应仍未得到充分解析。本研究结合经典分子动力学（MD）与机器学习（ML），探究含1 M LiPF₆的电解质，其溶剂包含碳酸乙烯酯（EC）、碳酸甲乙酯（EMC）及EC/EMC（体积比3:7），并添加0-10 mol%碳酸氟乙烯酯（FEC），研究温度范围为298 K至233 K。MD模拟量化了Li⁺自扩散、能斯特-爱因斯坦（NE）电导率与格林-久保（GK）电导率及局部配位情况，而高斯过程替代模型则模拟了电导率随组成与温度的变化关系。降温会显著加剧输运衰减，尤其在含EMC的电解质中，其GK电导率在233 K时下降超过98%，而富EC体系的该值约为90%。含EMC体系的Li⁺自扩散活化能为0.49-0.54 eV，富EC体系则为0.27-0.29 eV。在EC体系中，添加0-2 mol% FEC可提供相当的低温输运性能，而添加5-10 mol% FEC在模拟的最低温度下电导率保持率更低。分析显示配位通道仍以溶剂主导，且本研究的径向分布函数（RDF）未检测到直接的Li⁺-FEC配位。高斯过程替代模型在组成不相交的交叉验证中，NE与GK电导率的均方根误差（RMSE）分别为0.56 mS·cm⁻¹与0.57 mS·cm⁻¹。在模拟的液态轨迹中，温度与主体溶剂组成主导体相输运响应，FEC仅起次要调节作用。
英文摘要
Low-temperature operation imposes severe limitations on lithium-ion transport in battery electrolytes, yet the coupled effects of solvent composition and fluorinated additives in the cold-temperature regime remain insufficiently resolved. Here, we combine classical molecular dynamics (MD) and machine learning (ML) to investigate 1 M LiPF$_6$ electrolytes containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and EC/EMC (3:7), with 0-10 mol% fluoroethylene carbonate (FEC), from 298 to 233 K. MD simulations quantify Li$^+$ self-diffusion, Nernst-Einstein (NE) and Green-Kubo (GK) conductivities and local coordination, while Gaussian-process surrogates model conductivity across composition and temperature. Cooling produces a pronounced transport penalty, particularly in EMC-containing electrolytes, whose GK conductivity decreases by more than 98% at 233 K, compared with approximately 90% in EC-rich systems. Li$^+$ self-diffusion activation energies are 0.49-0.54 eV for EMC-containing systems and 0.27-0.29 eV for EC-based systems. Within the EC family, 0-2 mol% FEC gives comparable cold-temperature transport, whereas 5-10 mol% FEC shows lower conductivity retention at the coldest simulated temperature. The analyzed coordination channels remain solvent dominated, while direct Li$^+$-FEC coordination is not quantified in the present RDF set.The Gaussian-process surrogates achieve composition-disjoint cross-validated RMSE values of 0.56 and 0.57 mS cm$^{-1}$ for NE and GK conductivity. Within the simulated liquid-state trajectories, temperature and host-solvent composition dominate the bulk-transport response, with FEC acting as a secondary modifier.
