Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99352, USA.
Energy and Environment Directorate, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99352, USA.
Nat Commun. 2017 Jan 16;8:14101. doi: 10.1038/ncomms14101.
LiNiMnCoO-layered cathode is often fabricated in the form of secondary particles, consisting of densely packed primary particles. This offers advantages for high energy density and alleviation of cathode side reactions/corrosions, but introduces drawbacks such as intergranular cracking. Here, we report unexpected observations on the nucleation and growth of intragranular cracks in a commercial LiNiMnCoO cathode by using advanced scanning transmission electron microscopy. We find the formation of the intragranular cracks is directly associated with high-voltage cycling, an electrochemically driven and diffusion-controlled process. The intragranular cracks are noticed to be characteristically initiated from the grain interior, a consequence of a dislocation-based crack incubation mechanism. This observation is in sharp contrast with general theoretical models, predicting the initiation of intragranular cracks from grain boundaries or particle surfaces. Our study emphasizes that maintaining structural stability is the key step towards high-voltage operation of layered-cathode materials.
层状 LiNiMnCoO 阴极通常以二次颗粒的形式制备，由紧密堆积的一次颗粒组成。这为高能量密度和缓解阴极副反应/腐蚀提供了优势，但也引入了诸如颗粒间开裂等缺陷。在这里，我们通过使用先进的扫描透射电子显微镜报告了在商业 LiNiMnCoO 阴极中观察到的意想不到的颗粒内裂纹成核和生长的现象。我们发现，颗粒内裂纹的形成与高压循环直接相关，这是一个电化学驱动和扩散控制的过程。颗粒内裂纹的形成是从晶粒内部开始的，这是基于位错的裂纹萌生机制的结果。这一观察结果与一般的理论模型形成鲜明对比，后者预测颗粒内裂纹是从晶界或颗粒表面开始萌生的。我们的研究强调，保持结构稳定性是实现层状阴极材料高压运行的关键步骤。
