China State Key Laboratory for Turbulence and Complex Systems, College of Engineering , Peking University , Beijing 100871 , China.
ACS Appl Mater Interfaces. 2018 Dec 19;10(50):43623-43630. doi: 10.1021/acsami.8b15260. Epub 2018 Dec 7.
Lithium-ion batteries (LIBs) with high energy efficiency are urgently needed in various fields. For the LIBs electrodes, defects would be generated during the manufacturing processes and mechanical degradation and significantly impact the stability and performance of the LIBs. However, the effects of electrode defects on the electrochemical processes are still not clear. Herein, an in situ optical observation system is developed for monitoring the Li diffusion around the preintroduced defects in the commercial graphite electrodes. The experiments show that the gas-filled defects vertical to the direction of the Li diffusion would obviously decelerate the Li diffusion, whereas the electrolyte-filled defects parallel to the direction of the Li diffusion would accelerate the Li diffusion. In addition, finite element analysis (FEA) suggests, consistent with the experiments, a nonuniform distribution of local Li concentration around the defect. The equivalent diffusivity obtained by the FEA is also dependent on the configuration of the defects. The diffusivities of the electrolyte-filled parallel defect and gas-filled vertical defect are 12.6 and 11.0%, respectively. For the gas-filled defects, the size-effect calculation manifests that the equivalent diffusivity would decrease with the enlarged defect size, and the shape of the defects would substantially impact the decrease rate. The results directly reveal the mechanisms of the defect-induced diffusion behavior change in the electrodes by the new equivalent two-dimensional experiments, and the equivalent diffusivity would be useful for optimizing the electrode designs in LIBs.
锂离子电池（LIBs）在各个领域都急需具有高效率的电池。对于 LIBs 电极，在制造过程中会产生缺陷，并且机械退化也会显著影响 LIBs 的稳定性和性能。然而，电极缺陷对电化学过程的影响尚不清楚。在此，开发了一种原位光学观察系统，用于监测商业石墨电极中预先引入的缺陷周围的 Li 扩散。实验表明，垂直于 Li 扩散方向的充有气体的缺陷会明显减缓 Li 的扩散，而平行于 Li 扩散方向的充有电解质的缺陷会加速 Li 的扩散。此外，有限元分析（FEA）表明，与实验一致，缺陷周围局部 Li 浓度的分布不均匀。通过 FEA 获得的等效扩散系数也取决于缺陷的配置。充有电解质的平行缺陷和充有气体的垂直缺陷的扩散系数分别为 12.6%和 11.0%。对于充有气体的缺陷，尺寸效应计算表明，等效扩散系数随缺陷尺寸的增大而减小，并且缺陷的形状会极大地影响减小速率。这些结果通过新的等效二维实验直接揭示了电极中缺陷诱导扩散行为变化的机制，等效扩散系数对于优化 LIBs 中的电极设计将是有用的。
