Progress of Lithium-Ion Transport Mechanism in Solid-State Electrolytes
- 2021年第27卷 
固态电解质在室温下表现出非凡的离子导电性,使其有潜力应用于全固态锂离子电池。开发新的高性能固态电解质需要对锂离子传输机理及其规律进行深入研究。本文论述了近期研究中锂离子传输机理方面的研究进展,包括离子传输理论基础的概述;总结Li10GeP2S12、Li7La3Zr2O12和Li1+xAlxTi2-x(PO4)3固态电解质材料中晶体结构、离子传输和研究进展;阐述锂离子传输中结构特征、传输机理（单离子跳跃传输和多离子协同传输）以及构效关系;总结（反）Meyer-Neldel规则的关键问题和相关电解质材料。最后,展望了给出电解质材料的设计策略和未来机理研究的重点,为无机固态电解质材料的探索提供新的思路和方向。Inorganic crystalline solid electrolytes exhibit exceptional room-temperature ionic conductivities, giving them the potential to enable all-solid-state lithium (Li) - ion batteries. Developing new high-performance electrolytes is one of the most critical challenges to realize solid-state batteries, which requires understanding how chemistry facilitates fast ionic conduction and what the Li-ion migration mechanism is in inorganic solid electrolytes. In this review, we aim to summarize recent fundamental research progress in Li-ion transport, including crystal structure, behavior of ion migration (i.e., single-ion jump and multi-ions cooperative migration), and the relationship between ion migration and microstructure. Generally, ion transport in crystalline structure can be categorized into vacancy and non-vacancy mechanism. For Li-ion conduction, the migration can be achieved through single-ion hopping and collective diffusion mechanism. For single-ion hopping mechanism, the diffusivity is determined by the depth of potential well (activation energy) and lattice dynamics; whereas in the later mechanism Li-ion moving from high potential to low potential could partially offset the energy required for Li-ion moving from low potential to high potential. By studying the collective diffusion from the perspective of local structures, it is believed that collective diffusion in fast ion conductor originates from the local “dual Li-S/O” structure units, which can be characterized by the “nearest Li-Li distance”. Next, the paradigm of ion transport in solids is summarized. It is pointed out that most ion conductors follow Meyer-Neldel rule, where the activation energy and pre-exponential factor are mutual compensating. As a result, a balance should be adapted between these two values to achieve high Li-ion conductivity. However, for some fast ion conductors, the relationship does not follow the Meyer-Neldel rule (i.e., anti-Meyer-Neldel rule). Therefore, the physical significance of anti-Meyer-Neldel rule should be understood to develop next-generation lithium ion conductors. In the end, future perspectives and open questions are proposed to design and develop high-performance inorganic solid electrolytes.