微孔离子溶剂化膜减薄机制及煤基炭电容性能研究

Abstract: Thinning the ion-solvation shell can significantly improve the electrical capacity of the micropores electrode material, which subverts the traditional understanding of the low contribution rate of micropores to electrical capacity. At present, the relationship between the micropore size of and the thickness of the ion-solvation shell is researched in-depth, but the mechanism of the influence of the surface functional groups on the structure and the thickness thinning of the film is unclear. The infrared spectra and Raman spectra of the ion-solvation shell in the electrolyte are calculated based on first-principles principle at the electronic level. Those characteristic peaks are determined by contrasting the spectral analysis from the experimental analysis, and then the structure and thickness of the ion-solvation shell are explored. The effect of the interaction between the functional groups in the micropores and the pore diameter on the structure and thickness of the ion-solvation shell is studied by Monte Carlo and molecular dynamics methods at the atomic level. The changes of structure and the degree of thinning for the ion-solvation shell are analyzed. By testing the capacitance performance of coal-based microporous carbon, the trend of electrical capacity per unit area for microporous obtained by experiment and calculation is comparatively analyzed, and the rationality of theoretical calculation is verified. The mechanism of the thickness thinning of ion-solvation shell and its effect on capacitance performance are obtained by comprehensive analysis. The research results will be helpful to enrich the theoretical system of ion salvation for microporous carbon and helpful to establish the preparation method of high performance coal-based microporous carbon. It is of great significance to the high value-added utilization of coal.

离子溶剂化膜减薄能够显著提高微孔电极材料电容量的发现，颠覆了微孔对电容量贡献率低的传统认识。目前，微孔孔径与离子溶剂化膜厚度的关系研究较为深入，但微孔表面官能团对离子溶剂化膜结构和厚度减薄的影响机制尚不清楚。项目采用第一性原理从电子层次计算电解液中离子溶剂化膜的红外光谱和拉曼光谱，并与实验分析的光谱对比确定特征峰归属，研究离子溶剂化膜结构和厚度。采用蒙特卡罗和分子动力学方法从原子层次计算微孔内官能团及其与孔径相互作用对离子溶剂化膜结构和厚度的影响，分析离子溶剂化膜结构变化和减薄程度；通过测试煤基微孔炭的电容性能，对比分析实验和计算获得的单位表面积微孔电容量变化趋势，验证理论计算合理性。综合分析研究获得微孔内离子溶剂化膜厚度减薄机制及其对电容性能的影响。研究成果有助于丰富微孔炭离子溶剂化理论体系，有助于建立高性能煤基微孔炭的制备方法，对煤炭高附加值利用具有重要意义。

离子溶剂化膜减薄能够显著提高微孔电极材料电容量，项目从理论计算与实验角度重点研究了微孔孔径与官能团对离子溶剂化膜结构、厚度和电容的影响，确定了溶剂化离子精确去溶剂化的微孔孔径，建立了离子溶剂化膜去溶剂化的尺寸关系。.项目采用本征双层石墨烯（BG）和少层石墨烯模型分别模拟碳微孔中的基面平板孔、端面孔、混合孔，以及官能团（羟基、环氧基、羧基）修饰的平板孔，利用第一性原理计算方法研究微孔孔径与表面官能团对电解液离子溶剂化膜的结构与厚度的影响机理。AA、AB堆垛的本征平板孔内溶剂化Li+、Na+、K+的完全去溶剂化层间距分别约为4.80 Å、4.70 Å，4.40 Å、4.70 Å，4.40 Å、4.40 Å。[Li(H2O)n]+在不断脱去水分子发生去溶剂化时产生的相对电容最大，达到了2.5倍。只有在外孔孔径为3.61 Å左右、内孔孔径为7.40 Å左右的“缩颈瓶”式孔结构才可以容纳更多的Li+。在官能团修饰的平板孔中，只有[K(H2O)]+在环氧基化平板孔中的去溶剂化效果最好。.在实验方面，通过使用酚醛树脂对煤基炭材料进行液相沉积调孔，制备出了平均孔径在5Å左右的煤基多孔碳材料。碳基电容器的比电容与微孔对应的比表面积具有一定的关系，其中<0.504nm的微孔有助于提升K+比电容，0.5-0.65nm的微孔有助于提升Na+比电容，微孔与Li+比电容关系不明显。高通量拟合分析发现，K+的优势孔径集中在<0.504nm的微孔中，Na+的优势孔径集中在0.55-0.72nm的微孔中，这与实验研究结果相互匹配。.另外还探索了氮、磷掺杂基面平板孔对电解液离子溶剂化膜的结构与厚度的影响。AA、AB堆垛时氮掺杂平板孔内[Li(H2O)n]+、[Na(H2O)n]+、[K(H2O)n]+的完全去溶剂化层间距尺寸分别约为5.00 Å、4.90 Å，4.21 Å、4.57 Å，均小于4 Å。相比于氮掺杂，磷掺杂后效果更好，其中BGP-x@[Li(H2O)n]+结构的相对电容提高最大可达到3.0倍。.本研究从理论计算角度揭示了微孔孔径与官能团对离子溶剂化膜结构和厚度的影响机制，从实验角度获得了微孔内离子溶剂化膜厚度减薄机制及其对电容性能的影响，并建立了高性能煤基微孔炭电极的制备方法，有助于丰富微孔炭离子溶剂化理论体系，对煤炭高附加值利用具有重要意义。