Huang Bowen, Zhang Junbo, Shi Yutao, Lu Xiaodong, Zhang Jingjing, Chen Bingbing, Zhou Jianqiu, Cai Rui
Department of Mechanical and Power Engineering, Nanjing Tech University, Nanjing, 210009, Jiangsu Province, China.
Department of Energy Science and Engineering, Nanjing Tech University, Nanjing, 210000, Jiangsu Province, China.
Phys Chem Chem Phys. 2020 Sep 16;22(35):19816-19822. doi: 10.1039/d0cp03487h.
The mechanical strength and ionic conductivity of sulfide solid electrolytes have received widespread attention for their application in solid sodium batteries. Herein, first-principles calculations are used to determine the properties, including the electronic, mechanical and ionic transport properties, of Na3PS4 sulfide solid electrolytes doped with low and high Ca ion concentrations. Our theoretical results demonstrate that low Ca ion concentrations can be easily doped in tetragonal and cubic phases (t-Na3PS4 and c-Na3PS4) and create a suitable number of Na vacancies based on the formation energy analysis. Furthermore, the calculated density of states and charge density differences indicate that the surrounding electronic environment is changed, and Ca-S ionic bonds are formed in Na3PS4 with Ca-doping. In addition, the improved ductility and mechanical strength of c-Na3PS4 and t-Na3PS4 achieved by low-concentration Ca doping may help suppress dendritic growth and electrode deformation. Finally, sodium ion migration in Ca-doped Na3PS4 is described with the aid of the CI-NEB method, and it is found that the migration energy barriers are less than those of pure Na3PS4, which suggests that the sodium ion conductivity can be effectively improved by doping with low Ca2+ concentrations. The present work improves the understanding of the influence of doping on the performance of solid electrolytes and provides a feasible framework for the future design of high-performance solid electrodes.
硫化物固体电解质的机械强度和离子电导率因其在固体钠电池中的应用而受到广泛关注。在此，采用第一性原理计算来确定掺杂低浓度和高浓度钙离子的Na3PS4硫化物固体电解质的性质，包括电子、机械和离子传输性质。我们的理论结果表明，基于形成能分析，低浓度钙离子可以很容易地掺杂到四方相和立方相（t-Na3PS4和c-Na3PS4）中，并产生合适数量的钠空位。此外，计算得到的态密度和电荷密度差表明，周围的电子环境发生了变化，并且在Ca掺杂的Na3PS4中形成了Ca-S离子键。另外，低浓度Ca掺杂实现的c-Na3PS4和t-Na3PS4的延展性和机械强度的提高可能有助于抑制枝晶生长和电极变形。最后，借助CI-NEB方法描述了Ca掺杂的Na3PS4中钠离子的迁移，发现迁移能垒小于纯Na3PS4的迁移能垒，这表明通过低浓度Ca2+掺杂可以有效提高钠离子电导率。本工作增进了对掺杂对固体电解质性能影响的理解，并为未来高性能固体电极的设计提供了一个可行的框架。
