將商業(yè)化鋰離子電池中的液態(tài)電解質(zhì)替換為固態(tài)電解質(zhì)，并搭配鋰金屬負(fù)極組成全固態(tài)鋰離子電池系統(tǒng)，有望從根本上解決鋰離子電池系統(tǒng)的安全性問題并大幅提高能量密度。鋰離子固態(tài)電解質(zhì)材料需具備可與液態(tài)電解質(zhì)比擬的室溫電導(dǎo)率、良好的化學(xué)、電化學(xué)穩(wěn)定性以及機(jī)械性能，擁有與電極材料優(yōu)良的接觸性和兼容性。傳統(tǒng)認(rèn)識(shí)認(rèn)為，晶體中較小的陰離子電荷也往往被認(rèn)為有利于鋰離子的快速傳輸，即負(fù)一價(jià)陰離子比負(fù)二價(jià)陰離子更有利于陽(yáng)離子擴(kuò)散。

來自上海交通大學(xué)的朱虹研究團(tuán)隊(duì)，通過構(gòu)建陰離子亞晶格模型結(jié)合密度泛函理論計(jì)算研究了陰離子電荷和晶格體積對(duì)其中鋰離子占據(jù)穩(wěn)定性和鋰離子遷移的影響，發(fā)現(xiàn)只有綜合調(diào)控陰離子電荷與鋰離子配位數(shù)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(huì)提高鋰-陰離子四面體的相對(duì)穩(wěn)定性，使鋰離子更偏向于占據(jù)四面體位點(diǎn)。對(duì)于鋰離子從一個(gè)四面體中心通過八面體過渡態(tài)遷移到相鄰的四面體中心，即Tet-Oct-Tet路徑，陰離子負(fù)電荷越少，鋰離子遷移活化勢(shì)壘就越低。對(duì)于鋰離子從一個(gè)八面體中心通過四面體過渡態(tài)遷移到相鄰的八面體中心，即Oct-Tet-Oct路徑，陰離子負(fù)電荷越多，鋰離子的遷移活化勢(shì)壘就越低。該研究團(tuán)隊(duì)基于此發(fā)現(xiàn)提出了利用陰離子亞晶格模型開發(fā)和優(yōu)化超離子導(dǎo)體的新設(shè)計(jì)指導(dǎo)原則，即通過調(diào)節(jié)相同晶體結(jié)構(gòu)內(nèi)的非鋰元素以獲得陰離子元素和非鋰陽(yáng)離子元素之間合適的電負(fù)性差異，從而實(shí)現(xiàn)低鋰離子遷移活化勢(shì)壘。為高效地高通量計(jì)算篩選新型鋰離子超導(dǎo)體和優(yōu)化已有鋰離子超導(dǎo)體提供一定的理論指導(dǎo)。

該文近期發(fā)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.

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