AI 中文总结
本研究通过机器学习生成硬碳结构并进行分子动力学模拟，揭示了碳密度对钠离子存储和传输的影响，表明微观结构是决定离子持续渗透的关键因素。
AI 中文摘要
硬碳是钠离子储能领域有前景的负极材料，但其异质微观结构与钠离子传输之间的关系仍知之甚少。本文结合机器学习生成的硬碳结构与显式1 M NaPF6在碳酸乙烯酯/碳酸二甲酯电解液中的分子动力学模拟，研究了密度在0.5至2.0 g cm-3范围内的碳结构中钠的存储与传输。碳密度的增加导致可接近的孔隙网络减少，石墨化局部有序度增加，从而可以系统地考察微观结构对电化学响应和Na+传输的影响。钠的摄取量随施加电位的增加而增加，但随碳密度的增加而显著减少，而即使在最致密的结构中，电极充电仍然持续，尽管Na+摄取量非常小。配位分析显示，在施加电位下，与碳框架的相互作用增强，而Na+保持部分溶剂化环境。三维轨迹分析揭示了异质的、以曲折为主的传输路径，其中更开放的HC-C1结构支持更广泛的渗透和更大的持续位移。最大渗透深度和保留位移并不等同：离子可以瞬态到达更致密碳结构的深层区域，然后返回电解质界面。平均力势分析进一步表明，深层渗透发生在一定的投影自由能变化范围内，不能由单一的能量标准来描述。这些结果表明，Na+的存储和传输受静电力驱动力、电解质溶剂化、孔隙可及性和限域效应的共同作用，突出了碳微观结构作为持续离子渗透的关键决定因素。
英文摘要
Hard carbons are promising anodes for sodium-ion energy storage, yet the relationship between their heterogeneous microstructure and sodium transport remains poorly understood. Here, we combine machine-learning-generated hard-carbon structures with molecular dynamics simulations of explicit 1 M NaPF6 in ethylene carbonate/dimethyl carbonate electrolyte to investigate sodium storage and transport across carbon structures with densities from 0.5 to 2.0 g cm-3. Increasing carbon density produces less accessible pore networks and greater graphitic local ordering, allowing the influence of microstructure on electrochemical response and Na+ transport to be examined systematically. Sodium uptake increases with applied potential but decreases strongly with carbon density, while electrode charging persists even in the densest structure, where Na+ uptake remains very small. Coordination analysis shows increasing interaction with the carbon framework under applied potential, while Na+ retains a partially solvated environment. Three-dimensional trajectory analysis reveals heterogeneous, predominantly tortuous transport pathways, with the more open HC-C1 structure supporting broader penetration and greater sustained displacement. Maximum penetration depth and retained displacement are not equivalent: ions can transiently reach deep regions of denser carbon structures before returning towards the electrolyte interface. Potential-of-mean-force analysis further shows that deep penetration occurs across a range of projected free-energy changes and cannot be described by a single energetic criterion. These results show that Na+ storage and transport are governed by the interplay between electrostatic driving force, electrolyte solvation, pore accessibility and confinement, highlighting carbon microstructure as a key determinant of sustained ionic penetration.
