Lv Xiaojun, Han Zexun, Guan Chaohong, Jiang Liangxing, Wu Shangyuan
School of Metallurgy and Environment, Central South University, No. 932, South Road Lushan, Changsha 410083, Hunan, China.
Phys Chem Chem Phys. 2019 Aug 14;21(30):16573-16582. doi: 10.1039/c9cp02811k. Epub 2019 Jul 17.
Nowadays, low-temperature aluminium electrolytes are reported to have good prospects for application in the industrial process of aluminium production. In this paper, low-temperature electrolytes containing potassium cryolite and sodium cryolite with a cryolite ratio of 1.3 were investigated by using first-principles molecular dynamics simulation. This calculation reproduces the ionic structure of low-temperature 1.3(KF + NaF)-AlF electrolytes, indicating that [AlF], [AlF] and [AlF] are the fundamental aluminum-fluoro clusters and [AlF] is the predominant species. The calculated results for the ionic structure indicate that molten 1.3(KF + NaF)-AlF electrolytes have a high ionic polymerization degree, which is unfavorable for the transport properties of low-temperature 1.3(KF + NaF)-AlF electrolytes. Fortunately, increasing the mass fraction of NaF can effectively reduce the polymerization degree of ionic structure and thus improve the ionic conductivity of low-temperature 1.3(KF + NaF)-AlF electrolytes, which is an important guiding factor for the component selection of low-temperature electrolytes in future. Also, DFT calculations were adopted to further analyse the small aluminum-fluoro complexes. The calculated Raman spectrum of the aluminum-fluoro complexes is excellently consistent with literature results. Our calculated ionic conductivity falls in between the estimated value of the empirical equation of different literature studies, demonstrating that our results may be more precise than the literature results. This further proves the practicability of our modified N-E equation.
如今，据报道低温铝电解质在铝生产工业过程中具有良好的应用前景。本文采用第一性原理分子动力学模拟研究了冰晶石比为1.3的含钾冰晶石和钠冰晶石的低温电解质。该计算再现了低温1.3（KF + NaF）-AlF电解质的离子结构，表明[AlF]、[AlF]和[AlF]是基本的铝氟簇，[AlF]是主要物种。离子结构的计算结果表明，熔融的1.3（KF + NaF）-AlF电解质具有较高的离子聚合度，这对低温1.3（KF + NaF）-AlF电解质的传输性能不利。幸运的是，增加NaF的质量分数可以有效降低离子结构的聚合度，从而提高低温1.3（KF + NaF）-AlF电解质的离子电导率，这是未来低温电解质成分选择的重要指导因素。此外，采用密度泛函理论（DFT）计算进一步分析了小铝氟络合物。铝氟络合物的计算拉曼光谱与文献结果非常一致。我们计算的离子电导率落在不同文献研究经验方程估计值之间，表明我们的结果可能比文献结果更精确。这进一步证明了我们修正的N-E方程的实用性。
