School of Metallurgy and Environment, Central South University, No. 932, South Road Lushan, Changsha, Hunan 410083, China.
Phys Chem Chem Phys. 2019 Apr 3;21(14):7474-7482. doi: 10.1039/c9cp00377k.
We used the first-principles molecular dynamics simulations combined with the interatomic potential molecular dynamics to study the ionic structure and transport properties of KF-NaF-AlF3 fused salt. Simulation results show that the ionic structure of KF-NaF-AlF3 fused salt is principally dominated by the distorted five-coordinated [AlF5]2- and six-coordinated [AlF6]3- groups. When melting to a liquid, a part of the six-coordinated [AlF6]3- group dissociated into the four-coordinated [AlF4]- and five-coordinated [AlF5]2- groups. Four, five and six-coordinated aluminum-fluoro complexes coexist in KF-NaF-AlF3 fused salt, while the tetrahedral [AlF4]- groups are relatively rare. The content of the bridging fluorine atom is relatively small, about 5-11%, which indicates that the polymerization degree of the ionic structure of the KF-NaF-AlF3 fused salt system is lower. The KF-NaF-AlF3 fused salt has better liquidity and ionic conductivity due to the high self-diffusion coefficients of all particles in the fused salt system. KF can effectively break the F atom bridges, which reduces the polymerization degree of the ionic structure of the fused salt system and increases its ionic conductivity.
我们使用第一性原理分子动力学模拟结合原子间势分子动力学研究了 KF-NaF-AlF3 熔盐的离子结构和输运性质。模拟结果表明，KF-NaF-AlF3 熔盐的离子结构主要由畸变的五配位[AlF5]2-和六配位[AlF6]3-基团控制。当熔化为液体时，一部分六配位[AlF6]3-基团解离成四配位[AlF4]-和五配位[AlF5]2-基团。四、五、六配位的铝氟络合物在 KF-NaF-AlF3 熔盐中同时存在，而四面体[AlF4]-基团相对较少。桥接氟原子的含量相对较小，约为 5-11%，这表明 KF-NaF-AlF3 熔盐体系的离子结构聚合度较低。由于熔盐体系中所有粒子的自扩散系数较高，KF-NaF-AlF3 熔盐具有较好的流动性和离子电导率。KF 可以有效地破坏 F 原子桥，降低熔盐体系离子结构的聚合度，提高其离子电导率。
