Culver Sean P, Squires Alexander G, Minafra Nicolò, Armstrong Callum W F, Krauskopf Thorben, Böcher Felix, Li Cheng, Morgan Benjamin J, Zeier Wolfgang G
Institute of Physical Chemistry, Justus-Liebig-University Giessen, Heinrich-Buff-Ring 17, D-35392 Giessen, Germany.
Center for Materials Research (LaMa), Justus-Liebig-University Giessen, Heinrich-Buff-Ring 16, D-35392 Giessen, Germany.
J Am Chem Soc. 2020 Dec 16;142(50):21210-21219. doi: 10.1021/jacs.0c10735. Epub 2020 Dec 7.
Strategies to enhance ionic conductivities in solid electrolytes typically focus on the effects of modifying their crystal structures or of tuning mobile-ion stoichiometries. A less-explored approach is to modulate the chemical bonding interactions within a material to promote fast lithium-ion diffusion. Recently, the idea of a solid-electrolyte inductive effect has been proposed, whereby changes in bonding within the solid-electrolyte host framework modify the potential energy landscape for the mobile ions, resulting in an enhanced ionic conductivity. Direct evidence for a solid-electrolyte inductive effect, however, is lacking-in part because of the challenge of quantifying changes in local bonding interactions within a solid-electrolyte host framework. Here, we consider the evidence for a solid-electrolyte inductive effect in the archetypal superionic lithium-ion conductor LiGeSnPS. Substituting Ge for Sn weakens the {Ge,Sn}-S bonding interactions and increases the charge density associated with the S ions. This charge redistribution modifies the Li substructure causing Li ions to bind more strongly to the host framework S anions, which in turn modulates the Li ion potential energy surface, increasing local barriers for Li ion diffusion. Each of these effects is consistent with the predictions of the solid-electrolyte inductive effect model. Density functional theory calculations predict that this inductive effect occurs even in the absence of changes to the host framework geometry due to Ge → Sn substitution. These results provide direct evidence in support of a measurable solid-electrolyte inductive effect and demonstrate its application as a practical strategy for tuning ionic conductivities in superionic lithium-ion conductors.
提高固体电解质离子电导率的策略通常集中在改变其晶体结构或调整可移动离子化学计量比的影响上。一种较少被探索的方法是调节材料内部的化学键相互作用，以促进锂离子的快速扩散。最近，有人提出了固体电解质诱导效应的概念，即固体电解质主体框架内的键合变化会改变可移动离子的势能分布，从而提高离子电导率。然而，缺乏固体电解质诱导效应的直接证据——部分原因是难以量化固体电解质主体框架内局部键合相互作用的变化。在这里，我们考虑了典型的超离子锂离子导体LiGeSnPS中固体电解质诱导效应的证据。用Ge取代Sn会削弱{Ge,Sn}-S键合相互作用，并增加与S离子相关的电荷密度。这种电荷重新分布改变了Li子结构，导致Li离子与主体框架S阴离子的结合更强，进而调节Li离子势能面，增加Li离子扩散的局部势垒。这些效应中的每一个都与固体电解质诱导效应模型的预测一致。密度泛函理论计算预测，即使由于Ge→Sn取代而主体框架几何结构没有变化，这种诱导效应也会发生。这些结果提供了直接证据，支持了可测量的固体电解质诱导效应，并证明了其作为调节超离子锂离子导体离子电导率的实用策略的应用。
