將商業化鋰離子電池中的液態電解質替換為固態電解質，并搭配鋰金屬負極組成全固態鋰離子電池系統，有望從根本上解決鋰離子電池系統的安全性問題并大幅提高能量密度。鋰離子固態電解質材料需具備可與液態電解質比擬的室溫電導率、良好的化學、電化學穩定性以及機械性能，擁有與電極材料優良的接觸性和兼容性。傳統認識認為，晶體中較小的陰離子電荷也往往被認為有利于鋰離子的快速傳輸，即負一價陰離子比負二價陰離子更有利于陽離子擴散。

來自上海交通大學的朱虹研究團隊，通過構建陰離子亞晶格模型結合密度泛函理論計算研究了陰離子電荷和晶格體積對其中鋰離子占據穩定性和鋰離子遷移的影響，發現只有綜合調控陰離子電荷與鋰離子配位數才能夠有效降低鋰離子遷移活化能壘。較多的陰離子電荷和較大的晶格體積都會提高鋰-陰離子四面體的相對穩定性，使鋰離子更偏向于占據四面體位點。對于鋰離子從一個四面體中心通過八面體過渡態遷移到相鄰的四面體中心，即Tet-Oct-Tet路徑，陰離子負電荷越少，鋰離子遷移活化勢壘就越低。對于鋰離子從一個八面體中心通過四面體過渡態遷移到相鄰的八面體中心，即Oct-Tet-Oct路徑，陰離子負電荷越多，鋰離子的遷移活化勢壘就越低。該研究團隊基于此發現提出了利用陰離子亞晶格模型開發和優化超離子導體的新設計指導原則，即通過調節相同晶體結構內的非鋰元素以獲得陰離子元素和非鋰陽離子元素之間合適的電負性差異，從而實現低鋰離子遷移活化勢壘。為高效地高通量計算篩選新型鋰離子超導體和優化已有鋰離子超導體提供一定的理論指導。

該文近期發表于npj Computational Materials 6： 47 （2020）。

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.

責任編輯:pj