Estandarte Ana Katrina C, Diao Jiecheng, Llewellyn Alice V, Jnawali Anmol, Heenan Thomas M M, Daemi Sohrab R, Bailey Josh J, Cipiccia Silvia, Batey Darren, Shi Xiaowen, Rau Christoph, Brett Dan J L, Jervis Rhodri, Robinson Ian K, Shearing Paul R
Electrochemical Innovation Lab, Department of Chemical Engineering, University College London, Torrington Place, London WC1E 7JE, United Kingdom.
Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom.
ACS Nano. 2021 Jan 26;15(1):1321-1330. doi: 10.1021/acsnano.0c08575. Epub 2020 Dec 23.
Due to complex degradation mechanisms, disparities between the theoretical and practical capacities of lithium-ion battery cathode materials persist. Specifically, Ni-rich chemistries such as LiNiMnCoO (or NMC811) are one of the most promising choices for automotive applications; however, they continue to suffer severe degradation during operation that is poorly understood, thus challenging to mitigate. Here we use Bragg coherent diffraction imaging for 4D analysis of these mechanisms by inspecting the individual crystals within primary particles at various states of charge (SoC). Although some crystals were relatively homogeneous, we consistently observed non-uniform distributions of inter- and intracrystal strain at all measured SoC. Pristine structures may already possess heterogeneities capable of triggering crystal splitting and subsequently particle cracking. During low-voltage charging (2.7-3.5 V), crystal splitting may still occur even during minimal bulk deintercalation activity; and during discharging, rotational effects within parallel domains appear to be the precursor for the nucleation of screw dislocations at the crystal core. Ultimately, this discovery of the central role of crystal grain splitting in the charge/discharge dynamics may have ramifications across length scales that affect macroscopic performance loss during real-world battery operation.
由于复杂的降解机制，锂离子电池正极材料的理论容量与实际容量之间仍然存在差异。具体而言，富镍化学组成，如LiNiMnCoO（或NMC811）是汽车应用中最有前景的选择之一；然而，它们在运行过程中继续遭受严重降解，而人们对这种降解了解甚少，因此难以缓解。在这里，我们通过检查处于不同充电状态（SoC）的一次颗粒内的单个晶体，使用布拉格相干衍射成像对这些机制进行4D分析。尽管一些晶体相对均匀，但我们在所有测量的SoC下始终观察到晶间和晶内应变的不均匀分布。原始结构可能已经具有能够引发晶体分裂并随后导致颗粒破裂的不均匀性。在低电压充电（2.7 - 3.5 V）期间，即使在最小的体脱嵌活性期间晶体分裂仍可能发生；而在放电期间，平行畴内的旋转效应似乎是晶体核心处螺型位错成核的前兆。最终，这一关于晶粒分裂在充/放电动力学中核心作用的发现可能会在不同长度尺度上产生影响，从而影响实际电池运行期间的宏观性能损失。
