Structural and Compositional Factors That Control the Li-Ion Conductivity in LiPON Electrolytes
Structural and Compositional Factors That Control the Li-Ion Conductivity in LiPON Electrolytes
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DOI：
10.1021/acs.chemmater.8b02812
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发表时间：
2018-10-23
影响因子：
8.6
通讯作者：
Ceder, Gerbrand
中科院分区：
文献类型：
--
作者：
Lacivita, Valentina;Artrith, Nongnuch;Ceder, Gerbrand
非晶态锂离子导体是重要的固态电解质。然而，Li在这些系统中的传输比晶体材料少得多。我们通过从头算分子动力学研究无定形LiPON电解质，为Li+迁移率的机制提供原子水平的见解。我们发现，后者是强烈影响的化学和连接的磷酸盐聚阴离子附近的Li+。非晶化在Li（O，N）（4）和P（O，N）（4）之间产生边缘共享多面体连接，并产生配位不足和过配位的Li位点，这使Li+不稳定并增强其流动性。N取代O以两种方式有利于导电性：（1）伴随1（N）：1（O）取代的过量Li引入额外的载流子;（2）能量上有利的N-桥接取代使磷酸盐单元缩合并使结构致密化，这与直觉相反，对应于更高的Li+迁移率。最后，桥接N不仅电负性比O小，而且与P形成强共价键，这削弱了与邻近Li+的相互作用，为它们的迁移铺平了道路。当PO 4多面体的缩合导致孤立的O阴离子的形成时，Li+的迁移率降低，突出了合成过程中氧分压控制的重要性。这种对影响Li+迁移率的结构机制的详细理解是优化LiPON和其他非晶Li离子导体导电性的关键。
Amorphous Li-ion conductors are important solid-state electrolytes. However, Li transport in these systems is much less understood than for crystalline materials. We investigate amorphous LiPON electrolytes via ab initio molecular dynamics, providing atomistic-level insight into the mechanisms underlying the Li+ mobility. We find that the latter is strongly influenced by the chemistry and connectivity of phosphate polyanions near Li+. Amorphization generates edge-sharing polyhedral connections between Li(O,N)(4) and P(O,N)(4), and creates under- and overcoordinated Li sites, which destabilizes the Li+ and enhances their mobility. N substitution for O favors conductivity in two ways: (1) excess Li accompanying 1(N):1(O) substitutions introduces extra carriers; (2) energetically favored N-bridging substitutions condense phosphate units and densify the structure, which, counterintuitively, corresponds to higher Li+ mobility. Finally, bridging N is not only less electronegative than O but also engaged in strong covalent bonds with P. This weakens interactions with neighboring Li+ smoothing the way for their migration. When condensation of PO4 polyhedra leads to the formation of isolated O anions, the Li+ mobility is reduced, highlighting the importance of oxygen partial pressure control during synthesis. This detailed understanding of the structural mechanisms affecting Li+ mobility is the key for optimizing the conductivity of LiPON and other amorphous Li-ion conductors.