Structural and Compositional Factors That Control the Li-Ion Conductivity in LiPON Electrolytes,Chemistry of Materials

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Structural and Compositional Factors That Control the Li-Ion Conductivity in LiPON Electrolytes
Chemistry of Materials ( IF 7.2 ) Pub Date : 2018-09-15 00:00:00 , DOI: 10.1021/acs.chemmater.8b02812
Valentina Lacivita ₁ , Nongnuch Artrith ₂ , Gerbrand Ceder _{1,

2}

Affiliation

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.

中文翻译：

控制LiPON电解质中锂离子电导率的结构和组成因素

非晶态锂离子导体是重要的固态电解质。但是，与结晶材料相比，人们对这些系统中的Li传输知之甚少。我们通过从头算分子动力学研究无定形LiPON电解质，提供有关Li ⁺迁移率潜在机制的原子级见解。我们发现后者受到Li ⁺附近磷酸根聚阴离子的化学性质和连通性的强烈影响。非晶化会在Li（O，N）₄和P（O，N）₄之间生成边缘共享的多面体连接，并会形成Li位过低和过高的Li位，这会破坏Li ^+的稳定性并增强他们的机动性。O的N取代以两种方式促进电导率：（1）伴随1（N）：1（O）取代的过量Li引入了额外的载流子；（2）大力支持的N桥取代可缩合磷酸酯单元并致密化结构，这与直觉相反，对应于较高的Li ⁺迁移率。最后，桥接N不仅比O具有负电性，而且还与P形成强共价键。这削弱了与相邻Li ^+的相互作用，为它们的迁移铺平了道路。当PO ₄多面体的缩合导致形成孤立的O阴离子时，Li ⁺迁移率降低，突出了合成过程中控制氧分压的重要性。对影响Li ⁺迁移率的结构机理的详细了解是优化LiPON和其他非晶态锂离子导体导电性的关键。

更新日期：2018-09-15

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