Grain Boundaries and Their Impact on Li Kinetics in Layered-Oxide Cathodes for Li-Ion Batteries
Grain Boundaries and Their Impact on Li Kinetics in Layered-Oxide Cathodes for Li-Ion Batteries
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DOI：
10.1021/acs.jpcc.1c02400
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发表时间：
2021-05-10
影响因子：
3.7
通讯作者：
Zhao, Kejie
中科院分区：
文献类型：
--
作者：
He, Xiaomei;Sun, Hong;Zhao, Kejie
缺陷在多个长度尺度的电化学系统中是普遍存在的。缺陷化学性质与本体行为有很大不同，并且通常决定电池材料的倍率性能。然而，材料缺陷对Li动力学的影响仍然难以捉摸，因为它们的复杂性和反应动力学对局部原子环境的敏感性。在这里，我们专注于层状氧化物阴极中的晶界（GB），并使用第一性原理理论方法解决它们在Li输运中的作用。我们构造了Sigma 2（1（1）over bar 0（4）over bar）、Sigma 3（（1）over bar 10（2）over bar）、Sigma 5（1（1）over bar 0（1）over bar）和Sigma 9（1）over bar 10（4）over bar）GBs的重合位格。绘制了Li迁移穿过和沿着晶粒平面的能量分布图。我们详细讨论了如何与各种晶粒结构，如局部结构扭曲和电荷重新分配的原子特征决定锂输运动力学。具体地，相干的西格玛2GB促进Li迁移，其中扩散率比体扩散增加1-2个数量级，不对称的西格玛3GB显著地阻碍Li扩散，并且局部无序的西格玛5和西格玛9 GB在中间扩散距离（类似于15 A）处引起稍微增加的Li扩散率。我们进一步评估的整体锂扩散率和导电性的层状氧化物晶格中的锂运输的区别，在散装，跨越GB，和沿着晶粒平面。基本的理解揭示了最先进的阴极中普遍存在的缺陷及其对Li动力学的潜在优化。
Defects are pervasive in electrochemical systems across multiple length scales. The defect chemistry largely differs from the bulk behavior and often dictates the rate performance for battery materials. However, the impact of material defects on Li kinetics remains elusive because of their complex nature and the sensitivity of the reaction kinetics on the local atomic environment. Here we focus on the grain boundaries (GBs) in layered-oxide cathodes and address their role in Li transport using the firstprinciples theoretical approach. We construct the coincidence site lattices of Sigma 2(1 (1) over bar0 (4) over bar), Sigma 3((1) over bar 10 (2) over bar), Sigma 5(1 (1) over bar0 (1) over bar), and Sigma 9((1) over bar 10 (4) over bar) GBs. The energy profiles for Li migration across and along the grain planes are plotted. We discuss in detail how the atomistic features associated with various grain structures such as the local structural distortion and charge redistribution determine the Li transport kinetics. Specifically, the coherent Sigma 2 GBs facilitate Li migration with 1-2 orders of magnitude increased diffusivity than the bulk diffusion, the asymmetric Sigma 3 GBs significantly impede Li diffusion, and the locally disordered Sigma 5 and Sigma 9 GBs cause slightly increased Li diffusivity at the intermediate diffusion distance (similar to 15 A). We further evaluate the overall Li diffusivity and conductivity in the layered-oxide lattice by a distinction of Li transport in the bulk, across the GBs, and along the grain planes. The fundamental understanding sheds insight on a prevalent defect in the state-of-the-art cathode and its potential optimization of Li kinetics.