npj：阴离子电荷越少—锂离子扩散越……

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将商业化锂离子电池中的液态电解质替换为固态电解质，并搭配锂金属负极组成全固态锂离子电池系统，有望从根本上解决锂离子电池系统的安全性问题并大幅提高能量密度。锂离子固态电解质材料需具备可与液态电解质比拟的室温电导率、良好的化学、电化学稳定性以及机械性能，拥有与电极材料优良的接触性和兼容性。传统认识认为，晶体中较小的阴离子电荷也往往被认为有利于锂离子的快速传输，即负一价阴离子比负二价阴离子更有利于阳离子扩散。

来自上海交通大学的朱虹研究团队，通过构建阴离子亚晶格模型结合密度泛函理论计算研究了阴离子电荷和晶格体积对其中锂离子占据稳定性和锂离子迁移的影响，发现只有综合调控阴离子电荷与锂离子配位数才能够有效降低锂离子迁移活化能垒。较多的阴离子电荷和较大的晶格体积都会提高锂-阴离子四面体的相对稳定性，使锂离子更偏向于占据四面体位点。对于锂离子从一个四面体中心通过八面体过渡态迁移到相邻的四面体中心，即Tet-Oct-Tet路径，阴离子负电荷越少，锂离子迁移活化势垒就越低。对于锂离子从一个八面体中心通过四面体过渡态迁移到相邻的八面体中心，即Oct-Tet-Oct路径，阴离子负电荷越多，锂离子的迁移活化势垒就越低。该研究团队基于此发现提出了利用阴离子亚晶格模型开发和优化超离子导体的新设计指导原则，即通过调节相同晶体结构内的非锂元素以获得阴离子元素和非锂阳离子元素之间合适的电负性差异，从而实现低锂离子迁移活化势垒。为高效地高通量计算筛选新型锂离子超导体和优化已有锂离子超导体提供一定的理论指导。

该文近期发表于npj Computational Materials 6: 47 (2020)，英文标题与摘要如下，点击左下角“阅读原文”可以自由获取论文PDF。

Anion charge and lattice volume dependent lithium ion migration in compounds with fcc anion sublattices 

Zhenming Xu, Xin Chen, Ronghan Chen, Xin Li & Hong Zhu 

Proper design principles are essential for the efficient development of superionic conductors. However, the existing design principles are mainly proposed from the perspective of crystal structures. In this work, the face-centered cubic (fcc) anion sublattices were creatively constructed to study the effects of anion charge and lattice volume on the stability of lithium ion occupation and lithium ion migration by the density functional theory calculations. Both the large negative anion charges and large lattice volumes would increase the relative stabilities of lithium-anion tetrahedron, making lithium ions prefer to occupy the tetrahedral sites. For a tetrahedral lithium ion migration to its adjacent tetrahedral site through an octahedral transition state, the smaller the negative anion charge is, the lower the lithium ion migration barrier will be. While for an octahedral lithium ion migration to its adjacent octahedral site through a tetrahedral transition state, the more negative anion charge is, the lower the lithium ion migration barrier will be. New design principles for developing and optimizing superionic conductors with the fcc anion sublattice were proposed. Low lithium ion migration barriers would be achieved by adjusting the non-lithium elements within the same crystal structure to obtain the desired electronegativity difference between the anion element and the non-lithium cation element.

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