Interfacial strain effects on lithium diffusion pathways in the spinel solid electrolyte Li-doped MgAl 2 O 4
Interfacial strain effects on lithium diffusion pathways in the spinel solid electrolyte Li-doped MgAl 2 O 4
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DOI：
10.1103/physrevmaterials.2.045403
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发表时间：
2017-12
影响因子：
3.4
通讯作者：
C. O’Rourke;B. Morgan
中科院分区：
文献类型：
--
作者：
C. O’Rourke;B. Morgan
（Li,Al）共掺杂镁尖晶石$({\mathrm{Li}}_{x}{\mathrm{Mg}}_{1\ensuremath{-}2x}{\mathrm{Al}}_{2+x}{\mathrm{O}}_{4})$是一种固体锂离子电解质，在全固态锂离子电池中具有潜在的应用前景。尖晶石结构意味着与尖晶石电极的界面，如${\mathrm{Li}}_{y}}{\mathrm{Mn}}_{2}{\mathrm{O}}_{4}$和${\mathrm{Li}}}{4+3z}{\mathrm{Ti}}_{5}{\mathrm{O}}_{12}$，可能是晶格匹配的，具有潜在的低界面电阻。在晶格匹配界面上，微小的晶格参数差异是不可避免的，这会导致残余的外延应变。这种应变可能会改变锂在电解质-电极界面附近的扩散，从而导致界面电阻。本文采用密度泛函理论研究了在${x}_{\ mathm {Li}}=0.25$和${x}_{\ mathm {Li}}=0.5$时（Li,Al）共掺杂镁尖晶石中应变对锂扩散路径的影响。不牵强附会的材料我们计算扩散概要文件,以及各向同性和双轴拉伸菌株6%美元,对应于美元\左\{100 \ \}外延接口与美元{\ mathrm{李}}_ {y} {\ mathrm {Mn}} _ {2} {\ mathrm {O}} _{4} $和$ {\ mathrm{李}}_ {4 + 3 z} {\ mathrm {Ti}} _ {5} {\ mathrm {O}} _{12} $。我们发现，各向同性拉伸应变使锂扩散势垒降低了$0.32\phantom{\rule{0.28em}{0ex}}\ mathm {eV}$，典型势垒降低了$\ensuremath{\sim}0.1$ eV。这种效应与过渡八面体位置的体积增加有关，并且广泛地遵循局部静电电位的定性变化。对于更接近于晶格匹配的电解质-电极界面应变的双轴（外延）应变，八面体位体体积和锂扩散势垒的变化要比各向同性应变小得多。典型障碍仅减少$\ensuremath{\sim}0.05$ eV。然而，个体效应取决于所考虑的途径和相对应变方向。这些结果预测，各向同性应变强烈影响（Li,Al）共掺杂镁尖晶石电解质中的离子电导率，并且拉伸应变是增强锂输运的潜在途径。然而，对于具有候选尖晶石结构电极的晶格匹配界面，外延应变对锂扩散势垒的影响很小，但很复杂。
The (Li,Al)-codoped magnesium spinel $({\mathrm{Li}}_{x}{\mathrm{Mg}}_{1\ensuremath{-}2x}{\mathrm{Al}}_{2+x}{\mathrm{O}}_{4})$ is a solid lithium-ion electrolyte with potential use in all-solid-state lithium-ion batteries. The spinel structure means that interfaces with spinel electrodes, such as ${\mathrm{Li}}_{y}{\mathrm{Mn}}_{2}{\mathrm{O}}_{4}$ and ${\mathrm{Li}}_{4+3z}{\mathrm{Ti}}_{5}{\mathrm{O}}_{12}$, may be lattice matched, with potentially low interfacial resistances. Small lattice parameter differences across a lattice-matched interface are unavoidable, causing residual epitaxial strain. This strain potentially modifies lithium diffusion near the electrolyte-electrode interface, contributing to interfacial resistance. Here, we report a density functional theory study of strain effects on lithium diffusion pathways for (Li,Al)-codoped magnesium spinel, for ${x}_{\mathrm{Li}}=0.25$ and ${x}_{\mathrm{Li}}=0.5$. We have calculated diffusion profiles for the unstrained materials, and for isotropic and biaxial tensile strains of up to $6%$, corresponding to $\left\{100\right\}$ epitaxial interfaces with ${\mathrm{Li}}_{y}{\mathrm{Mn}}_{2}{\mathrm{O}}_{4}$ and ${\mathrm{Li}}_{4+3z}{\mathrm{Ti}}_{5}{\mathrm{O}}_{12}$. We find that isotropic tensile strain reduces lithium diffusion barriers by as much as $0.32\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$, with typical barriers reduced by $\ensuremath{\sim}0.1$ eV. This effect is associated with increased volumes of transitional octahedral sites, and broadly follows qualitative changes in local electrostatic potentials. For biaxial (epitaxial) strain, which more closely approximates strain at a lattice-matched electrolyte-electrode interface, changes in octahedral site volumes and in lithium diffusion barriers are much smaller than under isotropic strain. Typical barriers are reduced by only $\ensuremath{\sim}0.05$ eV. Individual effects, however, depend on the pathway considered and the relative strain orientation. These results predict that isotropic strain strongly affects ionic conductivities in (Li,Al)-codoped magnesium spinel electrolytes, and that tensile strain is a potential route to enhanced lithium transport. For a lattice-matched interface with candidate spinel-structured electrodes, however, epitaxial strain has a small, but complex, effect on lithium diffusion barriers.