Lanthanum lithium titanate is one of the promising electrolytes for solid-state lithium-ion batteries due to its high bulk ionic conductivity up to ∼10 S/cm. However, the practical application of this material has been bottlenecked by high grain boundary (GB) resistance, while the underlying mechanism is still under debate. Here we report a comprehensive study with direct evidence to reveal the origin of high GB resistance in LaLiTiO (LLTO). Atomic-scale observations via advanced scanning transmission electron microscopy show that the GBs are uniformly subject to subsurface segregation of La atoms to compensate for the excess surface charges. The La segregation leads to an abrupt decrease of charge carrier concentration neighboring GBs and hence is supposed to have deleterious effect on GB conductivity. The findings suggest a novel mechanism of space-charge-induced cation segregation, which shed lights on the intrinsic origin of low GB ionic conductivity in LLTO.

中文翻译：

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固体电解质钛酸镧锂高晶界电阻的原子成因

钛酸镧锂由于其体积离子电导率高达~10 S/cm，是最有前途的固态锂离子电池电解质之一。然而，这种材料的实际应用一直受到高晶界（GB）电阻的瓶颈，而其潜在机制仍存在争议。在这里，我们报告了一项综合研究，并提供了直接证据来揭示 LaLiTiO (LLTO) 中高 GB 电阻的起源。通过先进的扫描透射电子显微镜进行的原子尺度观察表明，晶界均匀地受到La原子的亚表面偏析，以补偿多余的表面电荷。La偏析导致邻近晶界的载流子浓度突然降低，因此被认为对晶界电导率产生有害影响。研究结果提出了一种空间电荷引起的阳离子偏析的新机制，这揭示了 LLTO 中低 GB 离子电导率的内在起源。