Savoie Brett M, Webb Michael A, Miller Thomas F
Division of Chemistry and Chemical Engineering, California Institute of Technology Pasadena , California 91125, United States.
J Phys Chem Lett. 2017 Feb 2;8(3):641-646. doi: 10.1021/acs.jpclett.6b02662. Epub 2017 Jan 23.
Solid polymer electrolytes (SPEs) have the potential to increase both the energy density and stability of lithium-based batteries, but low Li conductivity remains a barrier to technological viability. SPEs are designed to maximize Li diffusivity relative to the anion while maintaining sufficient salt solubility. It is thus remarkable that poly(ethylene oxide) (PEO), the most widely used SPE, exhibits Li diffusivity that is an order of magnitude smaller than that of typical counterions at moderate salt concentrations. We show that Lewis-basic polymers like PEO favor slow cation and rapid anion diffusion, while this relationship can be reversed in Lewis-acidic polymers. Using molecular dynamics, polyboranes are identified that achieve up to 10-fold increases in Li diffusivities and significant decreases in anion diffusivities, relative to PEO in the dilute-ion regime. These results illustrate a general principle for increasing Li diffusivity and transference number with chemistries that exhibit weaker cation and stronger anion coordination.
固态聚合物电解质（SPEs）有潜力提高锂基电池的能量密度和稳定性，但低锂离子电导率仍然是其技术可行性的障碍。SPEs的设计旨在使锂相对于阴离子的扩散率最大化，同时保持足够的盐溶解度。因此，值得注意的是，最广泛使用的SPE聚环氧乙烷（PEO）在中等盐浓度下，其锂扩散率比典型抗衡离子的扩散率小一个数量级。我们表明，像PEO这样的路易斯碱性聚合物有利于阳离子缓慢扩散和阴离子快速扩散，而在路易斯酸性聚合物中这种关系可以逆转。通过分子动力学，我们发现相对于稀离子体系中的PEO，聚硼烷可使锂扩散率提高多达10倍，并显著降低阴离子扩散率。这些结果说明了一个通用原则，即通过表现出较弱阳离子配位和较强阴离子配位的化学组成来提高锂扩散率和迁移数。
