Department of Engineering Science, University of Oxford, Parks Road, Oxford, OX1 3PJ, UK.
Phys Chem Chem Phys. 2019 Sep 18;21(36):20354-20359. doi: 10.1039/c9cp03884a.
Solid-state lithium batteries cannot achieve reasonable power densities because of dendrites, whose formation mechanisms remain uncertain. This paper applies principles of chemomechanics to investigate the critical current above which dendrites form in lithium-conductive ceramics. Applied voltage induces stress in solid electrolytes; dendrites appear to nucleate in the exemplary garnet-oxide material Li7La3Zr2O12 (LLZO) when the interfacial pressure exceeds a particular value. The critical pressure of polycrystalline LLZO correlates well with the surface-energy changes incurred by lithium plating in its grain boundaries. A derived formula, validated by experiments, predicts quantitatively how critical current varies with properties including interfacial impedance, bulk permittivity, and grain size. As well as suggesting novel strategies to create more resilient ion-conductive ceramics, the proposed mechanism rationalizes experimental observations of bulk lithium plating and explains how LLZO exhibits an electrically activated transition from stable low-current cyclability to high-current dendrite nucleation.
固态锂电池由于枝晶的形成而无法实现合理的功率密度，其形成机制仍不确定。本文应用化学力学原理来研究在锂导体陶瓷中形成枝晶的临界电流。外加电压会在固体电解质中产生应力；当界面压力超过特定值时，枝晶似乎会在典型的石榴石氧化物材料 Li7La3Zr2O12（LLZO）中形核。多晶 LLZO 的临界压力与锂在其晶界上电镀引起的表面能变化很好地相关。通过实验验证的导出公式定量预测了临界电流如何随界面阻抗、体介电常数和晶粒尺寸等特性变化。所提出的机制不仅为创造更具弹性的离子导电陶瓷提供了新的策略，还解释了为什么 LLZO 表现出从稳定的低电流循环到高电流枝晶成核的电激活转变，以及解释了为什么 LLZO 表现出从稳定的低电流循环到高电流枝晶成核的电激活转变。
