Gautam Ajay, Al-Kutubi Hanan, Famprikis Theodosios, Ganapathy Swapna, Wagemaker Marnix
Storage of Electrochemical Energy, Department of Radiation Science and Technology, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands.
Chem Mater. 2023 Sep 18;35(19):8081-8091. doi: 10.1021/acs.chemmater.3c01525. eCollection 2023 Oct 10.
Lithium argyrodite superionic conductors have recently gained significant attention as potential solid electrolytes for all-solid-state batteries because of their high ionic conductivity and ease of processing. Promising aspects of these materials are the ability to introduce halides (LiPSHal, Hal = Cl and Br) into the crystal structure, which can greatly impact the lithium distribution over the wide range of accessible sites and the structural disorder between the S and Hal anion on the Wyckoff 4 site, both of which strongly influence the ionic conductivity. However, the complex relationship among halide substitution, structural disorder, and lithium distribution is not fully understood, impeding optimal material design. In this study, we investigate the effect of bromide substitution on lithium argyrodite (LiPSBr, in the range 0.0 ≤ ≤ 0.5) and engineer structural disorder by changing the synthesis protocol. We reveal the correlation between the lithium substructure and ionic transport using neutron diffraction, solid-state nuclear magnetic resonance (NMR) spectroscopy, and electrochemical impedance spectroscopy. We find that a higher ionic conductivity is correlated with a lower average negative charge on the 4 site, located in the center of the Li "cage", as a result of the partial replacement of S by Br. This leads to weaker interactions within the Li "cage", promoting Li-ion diffusivity across the unit cell. We also identify an additional T4 Li site, which enables an alternative jump route (T5-T4-T5) with a lower migration energy barrier. The resulting expansion of the Li cages and increased connections between cages lead to a maximum ionic conductivity of 8.55 mS/cm for quenched LiPSBr having the highest degree of structural disorder, an 11-fold improvement compared to slow-cooled LiPSBr having the lowest degree of structural disorder. Thereby, this work advances the understanding of the structure-transport correlations in lithium argyrodites, specifically how structural disorder and halide substitution impact the lithium substructure and transport properties and how this can be realized effectively through the synthesis method and tuning of the composition.
锂硫银锗矿型超离子导体因其高离子电导率和易于加工，最近作为全固态电池的潜在固体电解质受到了广泛关注。这些材料的一个有前景的方面是能够将卤化物（LiPSHal，Hal = Cl和Br）引入晶体结构，这会极大地影响锂在广泛可及位点上的分布以及Wyckoff 4位点上S和Hal阴离子之间的结构无序，这两者都会强烈影响离子电导率。然而，卤化物取代、结构无序和锂分布之间的复杂关系尚未完全理解，这阻碍了优化材料设计。在本研究中，我们研究了溴化物取代对锂硫银锗矿（LiPSBr，0.0 ≤ ≤ 0.5范围内）的影响，并通过改变合成方案来调控结构无序。我们利用中子衍射、固态核磁共振（NMR）光谱和电化学阻抗谱揭示了锂子结构与离子传输之间的相关性。我们发现，由于Br部分取代了S，位于锂“笼”中心的4位点上较低的平均负电荷与较高的离子电导率相关。这导致锂“笼”内的相互作用减弱，促进了锂离子在晶胞中的扩散。我们还确定了一个额外的T4锂位点，它能够提供一条迁移能垒较低的替代跳跃路径（T5 - T4 - T5）。由此导致的锂笼膨胀以及笼之间连接增加，使得具有最高结构无序度的淬火LiPSBr的最大离子电导率达到8.55 mS/cm，相较于具有最低结构无序度的慢冷LiPSBr提高了11倍。因此，这项工作推进了对锂硫银锗矿中结构 - 传输相关性的理解，特别是结构无序和卤化物取代如何影响锂子结构和传输性能，以及如何通过合成方法和成分调控有效地实现这一点。
