Pang Mei-Chin, Marinescu Monica, Wang Huizhi, Offer Gregory
Electrochemical Science & Engineering, Department of Mechanical Engineering, Imperial College London, SW7 2BP London, UK.
Phys Chem Chem Phys. 2021 Dec 15;23(48):27159-27170. doi: 10.1039/d1cp00909e.
Inorganic solid-state lithium-metal batteries could be the next-generation batteries owing to their non-flammability and higher specific energy density. Many research efforts have been devoted to improving the ionic conductivity of inorganic solid electrolytes. For a wide range of electrolytes including liquid and solid polymer electrolytes, an independent measurement or calculation of both electrolyte conductivity and diffusion coefficient is often time-consuming and challenging. As a result, Nernst-Einstein's relation has been used to relate the ionic conductivity to ionic diffusivity after the determination of either parameter. Although Nernst-Einstein's relation has been used for different electrolytes, we demonstrate in this perspective that this relation is not directly transferable to describe the ionic mobility for many inorganic solid electrolytes. The fundamental physics of Nernst-Einstein's relation shows that the relationship between the diffusion coefficient and electrolyte conductivity is derived for ionic mobility in a viscous or a gaseous medium. This postulation contradicts state-of-the-art experimental studies measuring the mechanical behaviour of inorganic solid electrolytes, which show that inorganic solid electrolytes are usually brittle rather than viscoelastic at ambient room temperature. The measurement of loss tangent is required to justify the use of Nernst-Einstein's relation. The outcome of such measurement has two implications. First, if the loss tangent of inorganic solid electrolytes is less than unity in the range of batteries operating temperatures, the impacts of using Nernst-Einstein's relation in modelling the ionic mobility should be quantified. Secondly, if the measured loss tangent is comparable to that of solid polymers and lithium metal, inorganic solid electrolytes may behave in a viscoelastic manner as opposed to the brittle behaviour usually suggested.
无机固态锂金属电池因其不可燃性和更高的比能量密度，有望成为下一代电池。许多研究致力于提高无机固体电解质的离子电导率。对于包括液体和固体聚合物电解质在内的多种电解质，独立测量或计算电解质电导率和扩散系数通常既耗时又具有挑战性。因此，在确定其中一个参数后，能斯特 - 爱因斯坦关系被用于将离子电导率与离子扩散率联系起来。尽管能斯特 - 爱因斯坦关系已被用于不同的电解质，但我们在本文中表明，这种关系不能直接用于描述许多无机固体电解质的离子迁移率。能斯特 - 爱因斯坦关系的基本物理学原理表明，扩散系数与电解质电导率之间的关系是针对粘性或气态介质中的离子迁移率推导出来的。这一假设与测量无机固体电解质力学行为的最新实验研究相矛盾，这些研究表明，在室温环境下，无机固体电解质通常是脆性的，而非粘弹性的。需要测量损耗角正切来证明能斯特 - 爱因斯坦关系的适用性。这种测量结果有两个含义。第一，如果在电池工作温度范围内无机固体电解质的损耗角正切小于1，则应量化在模拟离子迁移率时使用能斯特 - 爱因斯坦关系的影响。第二，如果测得的损耗角正切与固体聚合物和锂金属的相当，则无机固体电解质可能表现出粘弹性行为，而非通常认为的脆性行为。
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